Big Brother Has Arrived – The Sonorous 12S Subwoofer Build

Posted on November 2, 2022 by Dan

Earlier this year I built the Sonorous 10S subwoofer and have absolutely loved this subwoofer. So when the opportunity presented itself to build a second bigger version of this sub, I knew I had to do it. And so I introduce the Sonorous 12S Subwoofer! This sub is identical to its littler brother with the exception of the use of a Reference Series 12″ Dayton Audio RSS315HF-4 subwoofer driver and an enclosure that is 10 liters bigger. This sub uses the same Dayton Audio SPA300-D subwoofer plate amplifier which pushes a solid 300 watts. If the 10″ version was an awesome little subwoofer, the 12″ version thing takes it to the next level. Even when driven with the same mount of power, the Sonorous 12S has a touch more extension and just about 2 dB more output than the 10S subwoofer. But for the most part these two subs are nearly identical. This post won’t got into nearly as much detail as my previous post since the amplifier is the same, and most of that post was about the amp, but I will talk through some of the differences as compared to the little 10S version.

First let’s get straight to the technical brochure for the Sonorous 12S Subwoofer:

Dayton Audio RSS315HF-4 12″ Reference Series Subwoofer
Dayton Audio SPA300-D 300W Plate Amplifier with Selectable Bass Boost
RCA Inputs, Auto On/Off, 10 mV detect threshold, 30 minute on-time, Adjustable Gain (volume)
Adjustable Low-pass Filter 45 Hz to 150 Hz (24 dB/octave)
0/180 Phase Shift Switch
Switchable +5 dB bass Boost, Q 1.5, at 30 Hz
20 Hz Subsonic Filter (-6 dB at 20 Hz) 12 dB/Octave
Sealed Design, 35L Enclosure (1.48 cuft.)
System Qtc = 0.707 (critically damped, perfectly damped)
f3 = ~44 Hz (Bass Boost OFF)
f3 = ~26 Hz (Bass Boost ON, +5 dB at 30 Hz)
Max SPL = ?????? (measurements to come….) mathematical limit at 300W is 111 dB
15″ x 15″ x 16.25″ (H x W x D)
3/4″ + 1/4″ MDF Construction
Internal Cross Bracing + Corner Cleats
Fiberglass Insulation Damping, Walls Lined, 2″ thick
Semi-gloss Brushed White Finish
1/2″ Radius Cosmetic Roundovers (running front to back)
(4) Large Rubber Feet
5 Year Warranty on amplifier and driver (from Dayton Audio)

If you read the datasheet for the 10S subwoofer, you’ll notice that both subs share a favorable amount of details. Mainly because the amplifier is same across both subs. Honestly this was a decision I struggled with though. I kept tossing around amplifier ideas that pushed more power, I really wanted at least 500W. The Yung SD500-6 was an obvious contender as it had the raw power to push the sub to its limits and the 25 Hz bass boost to keep the response flatter in this tiny 35L box. In fact the 25 Hz boost modeled a bit better than the 30 Hz boost, but in the end I couldn’t justify the $100 price increase for an extra 200W of power at the expense of a solid 5-year warranty, a defeatable bass boost, no turn on/off thump and just good old fashioned Dayton Audio quality. Nothing against Yung, but with plate amps, this thing becomes a part of the sub, and if down the road I did have to replace it, it would mean having to figure out how to cut a new hole or fill this hole to make a new amp fit. I figured this way I’m covered for 5 years no matter what. The only other option that was tempting was the SPA500DSP amp which also offers a solid 500W and offers a complete DSP solution so tailoring the bass response would be right at my fingertips. In the end this option was also ruled out simply due to cost. This option adds significant cost to what otherwise is a pretty affordable subwoofer. Money-no-object scenario though, that would be the amplifier to get with this subwoofer in my opinion. External amplification can also work just fine, especially if you can do some DSP.

Up until now I had been using the 12″ RSS315HF-4 subwoofer for Garage Theater duties in a 95L ported enclosure with a 450W amp and that combo was awesome. I ended up swapping out that sub for an older TC Sounds dB-500 sub that was in my daughter’s car that she is no longer using. So after playing a little bit of musical subs, that landed me this 12″ bad boy to play around with. Since I really liked the way the 10S version sounded in my living room paired with my DM-4 mains, and since that sub was moved to my bedroom, I thought it would be really cool to have a dedicated sub for that system. That way for those times when I really wanted to crank up some tunes with bass, there’d be plenty of bump to go around. Plus I really liked the look of that small, sealed, white enclosure with that single black aluminum cone driver emanating on it its front baffle. I knew I could make a bigger version and have it sound at least as good, while still not taking up a ton of real estate, with the RSS315HF-4 12″ driver.

So with the the driver and amp in mind, I designed up the enclosure. In a similar fashion to the Sonorous 10S, I wanted this sub as small as possible, so naturally a sealed option made sense. And with the +6 dB bass boost of the SPA300-D, I could buy back some extension that’s always lost using a compact sealed design like this. But even without the boost, this sub models/sims great. Being a bit of a perfectionist, I went for a perfectly critically damped Q of dead on 0.707 and was able to design the box to be exactly 34.7 liters. This offers an ideal response that is neither underdamped nor overdamped. Though actually turning on the bass boost does mess with the total system Q overall, this is a great starting point to be at as far as volume goes. F3 is around 44 Hz without the boost and about 27 Hz with the boost enabled. The roll-off below 27 Hz is quite steep, due to the high-pass filter in the SPA300-D. It’s roughly -6 dB down at 20 Hz with a 12 dB/octave filter. Combine that with the natural 12 dB/octave roll-off of the sealed enclosure and the response is rolling off at a combined 24 dB/octave. This is apparent in the excursion plots where you can see that at no time is the subwoofer at fear of over-excursion, no matter the source frequency. So that’s kinda nice as I’m always afraid of blowing my subs from too much power.

The enclosure design is pretty basic but has some unique qualities. It’s made from 3/4″ MDF and finished in 1/4″ MDF for a total panel thickness of 1.0″. Four 3/4″ x 3/4″ corner cleats run front to back to strengthen these joints. Additional panel bracing was added to all four panels in the form of 3/4″ x 1.5″ ribbing pieces. This ribbing is then cross-braced to opposing panels using 3/4″ x 2″ MDF braces that are interlocking in 4 locations. All of this bracing does take up some additional volume but was calculated into the initial design from the start. The overall enclosure sits at 15″x15″x16.25″ (LxWxD). This size looks absolutely sweet with that massive 12.4″ subwoofer on its face. This was absolutely deliberate leaving a mere 1.3″ from the edge of the driver to the edge of the cabinet. The driver is also perfectly centered too to provide a pleasing aesthetic. The top and bottom edges are rounded over at 1/2″ front to back while all other edges are simply sanded down lightly to take off the sharp corner. This is opposite to many of the Dayton Audio cabinets which round-over the front and back edges, top-to-bottom. I just think this way looks better but is up for personal taste. Rounding over the edges is purely cosmetic and provides no other sonic benefits given that the upper frequency of this sub will likely never exceed 100 Hz. Making the box slightly deeper than its width/height is also somewhat cosmetic as I think it looks better, but is also to allow the box volume to increase just to under 35 liters.

Continue reading →

Posted in DIY Audio | Tagged , , , , , , , , , , , , , , , , , , , , , , , , , , | Leave a comment

Simulating Subsonic Filters and Subwoofer Response-Excursion Effects

Posted on July 8, 2022 by Dan

So this is going to be a Part II to my original post from 14 years ago where I first discussed the topic of proper subsonic filter design in conjunction with subwoofer enclosure modeling. It’s been a while, but I recently got around to actually doing what I said I was going to do all those years ago. While my specific example incorporates this super-old (and no longer available) EV XEQ-2 crossover, the methods employed herein are practical for anyone looking into subsonic filter design, how it works, and the best way to incorporate it into you next sub project without sucking the life out of your bass. And more recently since the availability of online, web-based simulation tools, such as National Instruments MultismLive, taking the guesswork out of active filter design is a thing of the past. So let’s get into it!

I’ll do a quick re-cap of my previous post on this topic, but the main idea behind this post is to show how to design subsonic filters and then how to model them into a subwoofer design before you even buy or build anything. The two main tools for achieving this are NI’s MultismLive and Unibox 4.08. Unibox is a bit dated for speaker enclosure design and runs in Excel, which not everyone uses, but is my favorite box simulation software of choice. I took a stab at using WinISD to do this, but it doesn’t provide the option to import .frd files to create custom filters. You can create simple filters using the built-in filter tool, but is limited to certain prescribed filter types. Plus it’s not obvious how to go from the simulation to a real-world active filter, unless you’re building a system with DSP. Unibox 4.08 on the other hand will let you import .frd files which can have any shape, slope, Q, response, etc. you can come up with.

So with that let’s start out with this simple example, which is based on a sub I built several years ago, so we can see how it all plays out. First we’ll start with a simple simulation of the driver and enclosure. In this case I’ve got a Dayton Audio RSS315HF-4 in a 95-liter enclosure tuned to 22 Hz. This looks pretty good in the simulation, has a decent f3, a nice and flat in-band response, without any peaking or drooping, but if you look at the excursion below 19 Hz, you can see that Xmax is widely exceeded, as is the assumed Xmech. Regardless of the driver and enclosure, this is a pretty common behavior that will occur with any vented design. Passive radiator designs are bit better and sealed designs are even better yet, but they too can benefit from a properly designed subsonic filter to accompany them. So even though this sub is already tuned pretty low, if you didn’t want to implement a subsonic filter, you could argue three points: 1. there is little source material that is actually going to push the sub to those levels below 20 Hz and 2. most if not all amplifiers are not even flat 20 Hz, meaning below 20 Hz the amp is starting to roll-off anyway, thus limiting the actual excursion at the driver and lastly 3: eh, it’s just modeled data, who really cares? All valid, but flawed points on their own. A subsonic filter should be implemented to keep the driver under control below tuning to prevent possible driver damage, lower distortion, and keep the amplifier happy (i.e., possibly going into protect mode during playback and interrupting your movie/music).

The biggest problem with subsonic filters is by design, they limit excursion, and in doing so if not set to the correct frequency, will limit the output at and above tuning, which we do not want. Steeper slopes can help, but also make the filter more complex. In this case I am using a fairly simple 12 dB/octave active filter that requires only one op-amp to implement. So how do we determine where to set the corner frequency of this subsonic filter? Well, that’s where MultismLive comes into play. I built a model of the exact crossover that makes up the EV XEQ-2 and ran an AC simulation which lets you see the exact response of the filter. I show that circuit here, which is made up of an input buffer stage, which can be set just about any gain with no EQ, there’s an 18 dB/octave low-pass filter which can be set to any frequency desired, and then there’s the 12 dB/octave high-pass filter (the subsonic filter) which also can be set to any frequency and any Q desired. The input stage is unity gain, and provides a good buffer stage to the source, the LPF stage is set to about 90 Hz, but can be adjusted as shown with three resistors and last stage is the subsonic stage which is set by only two resistors. Depending on the values selected, you can actually create a bass boost circuit, which can be used to model bass boost circuits of common plate amps to see how they will sum with your enclosure, which is what I did with my Sonorous 10S subwoofer. But for this vented sub box, we want zero boost, in fact the ideal roll-off is where the Q=0.7 which can be achieved by changing R9 and R11 at a ratio of 1:2.

So I played around with a bunch of resistor values for gain, LPF and HPF and ran an AC simulation for each one to get an idea of different frequency responses that can be achieved. You can click on this link here and play around with the simulation and model some filter cutoff frequencies of your own. But we’re not done yet. MultismLive lets you export the data into a .csv file which this is where the whole design gets interesting. With that exported file, we can now import that into the Frequency Response Active Filter section of Unibox and actually see how the HPF affects the box response and how it affects the driver excursion. I created about 10 different filters, and imported each of them into Unibox and then compared them all see which one looked the best. And by looked the best, basically what I was shooting for is best control over excursion below tuning, but with minimal impact to frequency response above tuning. Go too low, and excursion is still too high, but FR is minimally impacted, go too high and excursion looks great, but FR suffers. The balance is basically somewhere in the middle. By plotting all of the options, we can better choose where we want this subsonic filter to sit. But even Unibox has limitations, one being you can’t compare more than 6 responses, and you can only compare FR plots and nothing else. So I exported the raw data from Unibox into my own worksheet in Excel where I plotted several configurations and overlay excursion and FR plots on the same graph. I’ve shown that here for this example design. Notice that a filter corner (-3 dB) of 20 Hz does the best at keeping excursion in check, but also has the most impact on FR. The 12 Hz corner is better than no filter at all, but still allows over-excursion. The sweet spot is probably right around 15 Hz or 17 Hz. So that’s the optimum subsonic filter corner for this subwoofer. And that’s the design. Short and sweet.

Continue reading →

Posted in DIY Audio | Tagged , , , , , , , , , , , , , , , , , , , , , , , , , , | Leave a comment

Detailed Measurements and Technical Review of the Crest Audio Vs900 Power Amp

Posted on July 2, 2022 by Dan

I have to admit, I’ve got the bug once again. After building and listening to my little Sonorous 10S Subwoofer over the last couple of weeks, I’ve suddenly got this need for more, more bass, more low-end bump, more rattling, more shaking, more chest-thumping boom. So I’ve started hatching a plan to build a bigger, better, more HT-centric subwoofer, where the size of the enclosure has no limits, no bounds. But before I get into that part of this project (saving that for another post), we’re going to check out the new/old amplifier I just picked up which will power this monster subwoofer. So per my usual browsing on the web, I tend to check out my local Craigslist (aka CL) at least a couple of times a week to see what kind of audio gear people trying to unload. I connected with a guy who was selling a bunch of pro-style amps from Carver, Peavey and Crest Audio that he had collected over the years. None of them really seemed all that interesting for a subwoofer build, though his pricing was reasonable.

But after digging a little deeper, I ended up looking up the datasheets on each of his amps and was surprised to find the Crest Audio Vs900 amp he was selling had some decent specs: class A/B architecture, 2-ohm stable per channel, bridgeable, 1100W max rated power into 4-ohms bridged (at 1 kHz, 1% THD), claimed frequency response down to 10 Hz (none of this 30 Hz high-pass filter nonsense some pro amps have) plus just a nice clean front panel with nothing but a couple of status LEDs. So with a subwoofer from Parts Express already in mind, I thought this amp would make a great pairing (can you guess what sub I’ve got in mind?). He said he’d let it go for $100 and I said sure, let’s do it. If this thing can do its rated power, we’re talking about 9 cents per watt here. So let’s see if this 20-year old, 46-pound boat anchor can actually deliver.

So I fired up REW and pulled out my 400-watt load box, which is just a bank of four 100 watt, 4-ohm load resistors wired in a parallel/series configuration. I picked them up for Amazon for about $10. I’ve got a 45:1 resistive divider network that effectively will take 40 Vrms down to 0.9 Vrms which is just about right for driving the input to my Presonus Firestudio Mobile with some headroom (which can take up to +10 dBu or 2.4 Vrms). Obviously this setup cannot measure the rated power of this amp in bridged mode or into to 2 ohms, so all of my measurements will be limited to one channel driven into 4 ohms. The measurements I was able to collect are as follows:

Maximum power (RMS) into 4 ohms (one channel driven) at 1 kHz
Maximum power (RMS) into 4 ohms (one channel driven) at 40 Hz
THD (total harmonic distortion) from 1W up to rated power
Frequency Response from 5 Hz to 20 kHz (overall flatness from 20-20 kHz)
Channel Imbalance

First things first, anything you buy off CL may not work at all, let alone meet any kind of performance parameters it once had 20 years ago. The guy said he tested it and it worked fine, so I was really hoping it didn’t go straight into protect mode the second I turned it on. At power-up, lights came up, fan spun up and the protect circuit kicked out after a couple of seconds as normal. This was a good start! I played some music through it to a small speaker, just to see that it made sound and that the volume/gain knobs worked okay. Then it was off to the test bench to really check it out. I tested CH B first and ran a quick frequency response plot at about 1 watt. Holy cow this thing was flat! I’d tested some smaller Class D amps recently and was expecting the typical low-cut/high-cut sort of thing, but was impressed to find the response down only -0.3 dB at 20 Hz and -0.4 dB at 20 kHz. I couldn’t even see the -3 dB point since my sweep started at 5 Hz and at 5 Hz the response was down only -2.3 dB. CH A was a touch better at -2.0 dB at 5 Hz. CH B also had a little wobble in the response that was not present in CH A. I suspect it’s due to some possible aging of a 100uF electrolytic cap in the pre-amp stage that makes up the high-pass circuit for this amp. I could replace it, but the effect is small enough that I probably am not going to worry about it. I ran some additional frequency response plots at higher power levels up to 50 watts. The plots shown here are at 50 watts.

With the frequency response plots you can also grab distortion over frequency using REW. Though it’s not as accurate as using the RTA at a single frequency, if you increase the measurement length from the standard to either 512k or 1M, you get some better fidelity on the distortion side of things, but still not as good as RTA. But this does provide a general idea of the overall distortion over frequency and can identify problems or other areas the amp may have at frequencies that you may not notice otherwise when just using RTA. In this case Ch A is slightly better below 20 Hz than Ch B but nothing too crazy. Again, points to possible aging of the inline electrolytic cap (this would be C202 in the schematic) in this channel. I did not run full sweeps up to full power since the protect circuit did kick in when running the sweep starts at 5 Hz. I could have upped the start frequency, but went ahead with RTA measurements instead.

So I ran tests from 1W up to 450W at 40 Hz and 1 kHz on both channels (separately) at about 50W increments and grabbed screenshots from REW RTA with the noise floor set at 130 dBc. This is about the limit of my setup with 128k FFT Length and 4 averages. This kept each measurement to about 6 seconds which helped prevent build-up of heat in the amp or my load resistors during testing. At least once I got above 100W or so. Tests were run about 1 minute apart, give or take the amount of time it took me to grab the screenshot and adjust the gain for the next measurement. I’ll probably only upload a few of them, since basically between 5W and 350W there isn’t much going on. Things only start to get interesting around the 400W mark. At 1 kHz into 4 ohms, one channel driven, I measured exactly 450 watts RMS at 0.097% THD on CH B. This was excellent! And an order of magnitude lower distortion than the spec! Of coursse, this was one channel driven not both as the spec stated, but still, this was impressive. I pushed the amp another 10W to 0.2% THD and the red clip light came on indicating it was time to turn it down. So I’d say max power for CH B was easily 450 watts with the clip light coming on at just around 460 watts.

Continue reading →

Posted in DIY Audio | Tagged , , , , , , , , , , , , , , , , , , | Leave a comment

The Complete Design and Build of The Sonorous 10S Subwoofer – Hits 26 Hz!

Posted on June 18, 2022 by Dan

This subwoofer project was 6 months in making but after a couple of weekends of really focusing on it, I’m happy to say that it is finally done! This will be the complete (and exhaustive) detailed design and build review of The Sonorous 10S Subwoofer. This subwoofer has changed my perspective of how much deep bass can be achieved in small packages. And you don’t need to spend a fortune to get good, detailed, deep bass for your home theater or stereo system. So read on to find out more about this sweet little subwoofer project and maybe it will fit the bill for a similar project you’re working on.

Here’s what would be the marketing brochure for The Sonorous 10S Subwoofer:

Dayton Audio RSS265Hf-4 10″ Reference Series Subwoofer
Dayton Audio SPA300-D 300W Plate Amplifier with Selectable Bass Boost
RCA Inputs, Auto On/Off, 10 mV detect threshold, 30 minute on-time, Adjustable Gain (volume)
Adjustable Low-pass Filter 45 Hz to 150 Hz (24 dB/octave)
0/180 Phase Shift Switch
Switchable +5 dB bass Boost, Q 1.5, at 30 Hz
20 Hz Subsonic Filter (-6 dB at 20 Hz) 12 dB/Octave
Sealed Design, 25L Enclosure (0.88 cuft.)
System Qtc = 0.785 (slightly under-damped)
f3 = ~40 Hz (Bass Boost OFF)
f3 = ~26 Hz (Bass Boost ON, +5 dB at 30 Hz)
Max SPL = ?????? (measurements to come….) mathematical/physical limit is 109 dB
13.5″ x 13.5″ x 14.5″ (H x W x D)
3/4″ + 1/4″ MDF Construction
Internal Cross Bracing + Corner Cleats
Fiberglass Insulation Damping, Walls Lined, 2″ thick
Semi-gloss Brushed White Finish
1/2″ Radius Cosmetic Roundovers (running front to back)
(4) Large Rubber Feet
5 Year Warranty on amplifier and driver (from Dayton Audio)

I don’t normally give my speakers names, but I decided to try something new with this one. Sonorous means “capable of producing a deep or ringing sound.” I thought it fitting for this sub project. Now on to the real fun!

Enclosure Design – My Thought Process

First and foremost, my main reason for selecting a 10″ driver was two parts: size and cost. First a 10″ driver doesn’t require a huge enclosure so a small footprint can be easily be achieved. In most cases this will come at a compromise in terms of total output and low-end extension, but depending on your needs, that may be acceptable trade to make. Although with this sub you’ll see that we hardly give up that much and still are able to deliver a very compelling bass experience. And second, this driver as of this writing costs about $209 with free shipping from Parts Express. Compared to larger comparable drivers, this is definitely cheaper than most options and very reasonably priced for what you get. And since this is only a 10″ driver, the amplifier needs are reasonable as well. You can get away with a simple 300-watt plate amp and you’ll be able to push this driver to its limits. The SPA300-D amp is brand new from Dayton Audio and runs $149 and is the cheapest of the bunch that PE offer in the 300W range. Other options you might consider would be the SPA250, Bash 300S, SPA250DSP, or the Yung SD300 which will run you from $180 – $225. I’ll go ahead and recommend the SPA300-D as it measures well, has the bass boost which can be turned on and off, plus all the other features you’d expect from a basic plate amp. In my opinion it’s the better value of these 5 units, unless you want the DSP options for additional in-room tailoring.

Since we’re going for a cute little sub here, I’m going to rule out a ported design from the start. Not that the RSS265HF-4 doesn’t model great in a port box, because it absolutely does, it just requires more than twice the volume to get there. So I modeled up 6 different sealed enclosure volumes, that were based on going from an 11″ cube and working my way up to a 15″ cube in 1″ increments to see if there was sort of a sweet spot between output, extension, excursion and size. Ultimately what you see in the plots is that all of these enclosure volumes can work. The smallest sub sacrifices some low-end extension, but excursion is best kept in check. The largest box does produce the lowest f3, but excursion limits will be exceeded at max power, so you gotta be careful with the volume knob. Somewhere in the middle you get what I would call the Goldilocks sealed design: acceptable f3, Qtc < 0.8 and driver excursion is no more than 15% above the specified Xmax.

With Xmax being the physical design constraint and all other parameters being design nice-to-haves, if we fix the input power at 300 watts (based on the amplifier selection) and we target 14.1 mm excursion (12.3 + 1.8) we end up with a volume of 23 liters. After playing around with some physical box dimensions, this ends up being an odd 13.25″ inch cube. What I ended up settling on was the dimensions shown above which result in a total enclosure volume of 25 liters, give or take. In this case we are at about +20% of xmax instead of the general rule of +15% but since PE doesn’t spec Xmech, the 15% is only a rule of thumb. Plus, as you will see, once we model the excursion taking into consideration the high-pass cutoff of the SPA300-D, our peak excursion drops to 14.4mm at 300W which reduced the excursion to only +17% of xmax which is even better. Fundamentally you can play around in this region of about 20 to 30 liters pretty safely with this driver without a high-pass filter, but with the inclusion of a high-pass filter around 20 Hz (-6 dB), you can get away with a slightly larger volume, which results in a slightly better f3 and lower Qtc.

So with the enclosure size decided upon and the basic dimensions roughed out, I drew up an cut-sheet and hopped on over to Home Depot some 3/4″ MDF. Man oh man has the cost of lumber gone up! I paid over $60 for a 4×8 sheet of 3/4″ MDF. I’ve never paid that much for MDF in my life. I’m hoping costs comes down because with lumber costs this high, it really starts to eat into the savings that make DIY speaker building so appealing. I bought a 2×4 foot piece of 1/4″ MDF as well as some other odds for projects around the house (gotta make the trip worthwhile since gas prices are also insane). I had one of the employees cut the board into three ~32″x49″ pieces so I could fit them into the back of my Durango. I’m hoping to actually get either another subwoofer out of this sheet or a pair of bookshelf speakers. The cut-sheet requires only one ~32″x49″ piece and even with that, there is some scrap for the bracing and corner cleats. You can download the basic plans by clicking on the pics and download the cut-sheet here.

I won’t go into details on building the enclosure as it’s pretty much just a basic box. I made all the cuts on my table saw and with some Gorilla Glue and my nail gun I just popped the thing together. You can use screws or clamps or whatever your joinery method of choice. After getting 5 of 6 sides together, I stopped to add the 3/4″ x 3/4″ cleats that run front to back in each of the corners. My intent here was to further secure the butt joints and because I really wanted to create a larger round-over on the edges and if I can get my hands on a larger bit, then one day I am going to cut those corners down in which case most of the butt joint will be cut away. I will need the corner cleats to really secure the enclosure. For now I just did a 1/2″ round-over so the cleats just help to strengthen the fairly week butt joints as they are. I added a center beam brace going front to back on all four sides and added the cross bracing which connects the beams to the sides and the top and bottom. Given how small this enclosure is, the interior panels are only about 1 square foot, this feels like just enough bracing without being too much and taking up precious internal volume. We’ve cut the panels in half and then cross braced them basically about 7″ back (not totally centered). The only other thing to do may have been to run a another set of beam supports around the inside of the box, thus cutting the panels in half again. But this seemed fine to me so I left it at that.

Continue reading →

Posted in DIY Audio | Tagged , , , , , , , , , , , , , , , | Leave a comment

3 Simple Modifications that Make the Jamo Concert Series 93 II Speakers Really Shine

Posted on January 27, 2022 by Dan

Here are 3 simple modifications I made to a pair of Jamo Concert Series 93 II bookshelf speakers that give them a much more balanced and more neutral sound with better bass extension and better vocal response. I’ll do a complete teardown of the speakers, sketch out the schematic for the crossover and go through each of the modifications one by and show how each modification produces a measurable improvement in the sound. If you’re up to the task, feel free to take on this project with your own Jamos, or if you’re just curious about what’s inside these little speakers, then read on!

So I picked up my Jamo C 93 IIs on sale from Crutchfield as a open box deal and did no-rush shipping so I think I only paid a little over $220 for the pair. I’m not sure what prompted the purchase, they aren’t one of the more popular speakers on the market but for the most part people who have bought them do like them. I thought they looked really cool and also thought just maybe they would lend themselves to some simple upgrades to make them sound better. Plus, coming from someone who’s spent most of his life designing and building speakers, there is something super intriguing to me about buying commercial speakers and figuring our what makes them work. The immediacy of the process is amazing too, to go from the day of purchase to fully-built speakers on my doorstep in 4 days is something I could get used to. I mean I love spending hot weekends in my garage, breathing MDF dust just as much as the next guy, but this takes the simplicity of purchasing/owning speakers to a whole new level.

Which is why I couldn’t leave well enough alone and within the first week of getting these speakers, decided to do a complete teardown and started working out what modifications might be possible. My initial intention wasn’t really to change anything, but to just inspect what we were working with and see if there was some performance left on the table, so to speak, due to the commercial drive to mass-produce cheap speakers. Some sound elements of a speaker are design choices, not technically limited by cost, but perhaps driven by the need to give a speaker that showroom sound, a little extra bass, a touch more treble, anything to give it the edge and make the consumer say, yeah this one sounds better. But once you get it home, the added bass and treble end up being too much for day to day listening, and without the A/B comparison to any other speaker, the speaker ends up becoming is own worst enemy always trying to out-do itself. Let’s see if we can fix that.

First Modification – The Crossover

The first thing I started to dive into was the crossover. See here a complete schematic of what we are working with. I was overall impressed with the complexity of the crossover. It contains a total of 11 elements comprising iron and air-core inductors, electrolytic and poly caps and sandcast resistors. I would say the quality of the components is just acceptable at this price-point and none of my modifications made any attempt to improve the quality of the parts. That of course is still an option down the road, though it comes at significant additional cost. But if you want to purchase better parts of the same values, like resistors, the cost is minimal, move up to better caps, that will cost a little more, and better inductors would cost even more. Initially I am just going to adjust the crossover a touch without swapping out any of the major parts.

The low-pass section is a quite nice, it’s a just simple 2nd order filter but it has some decent baffle loss compensation built into it. It’s got a big 1.3 mH inductor and large shunt 33 uF electrolytic cap. Shelving starts at about 200 Hz and with the inductor alone would be about 3 dB down at 400 Hz and 6 dB down at 800 Hz. Introducing the 33 uF cap brings up the response at 800 Hz by about 3 dB and adds a corner to the response at about 1300 Hz, which then transitions to the overall filter to a 12 dB/octave slope at this point. The series RLC notch filter (8.2 ohms + 1.2 mH + 22 uF) is centered at about 1000 Hz and provides a 4 dB notch that’s just a few hundred Hz wide. This cleans up some peaking in the driver response and also helps out with the final baffle step compensation network. This puts the crossover frequency to the tweeter at right around 1.9 kHz, which is a good spot for most woofers, considering it’s about 6″ in diameter and the tweeter is a full 1″ soft dome. Pushing the crossover lower can put stresses on the tweeter and can make vocals sound nasally while pushing it higher can lead to poor directivity and more interference from cone break-up modes. Jamo does not provide a specified crossover frequency in their cutsheet nor do they mention the filter slopes.

I played around a little bit with just the low-pass section, adjusting the notch filter and changing the shunt cap value, but after all my fiddling I decided that there wasn’t anything drastically wrong with where the response was sitting and decided just to leave it alone. I think Jamo did a decent job here getting the baffle step right, setting the crossover point just low enough, the notch filter prevents some peaking around 1 kHz and enables the woofer to blends nicely to the tweeter without any massive suckouts. The final response ends up being more 3rd order acoustic once you add in the natural roll-off of the driver. So I was happy with not changing anything here. Maybe a future upgrade might be swap the 22 uF and 33 uF electrolytics for some poly caps just because they’re pretty cheap and make for a better-looking crossover and you never know, maybe to some people it will even sound better. You could also swap the iron-core inductor for a lower-gauge air core.

So let’s break down the tweeter section: we’ve got a single 1.5 ohm series sandcast resistor feeding a 7.5 uF poly cap and 0.18 mH air core inductor creating a nice 2nd order filter. This is almost textbook, but with a smaller inductor value which increases the Q and creates a sharper roll-off with a tighter corner at the cut-off frequency. Pretty standard adjustment that I tend to do as well. So the only red flag I see at this point with the tweeter is that itty, bitty, teeny, weeny 1.5 ohm resistor. You know that soft dome tweeter is more efficient that the woofer, we know the woofer has nearly 4 dB of baffle step compensation, so there’s no way a single 1.5 ohm resistor is going to provide enough attenuation to level match the woofer and the tweeter. That tweeter is going to be bright! And that is clearly by design, because it’s so easy to make that resistor anything the designer wants at zero cost. Maybe the guy hand-tuning the final design at Jamo was in a heavily damped room, maybe the speakers were tuned off-axis, maybe they really wanted to compete in the showroom by giving that upper end some sparkle. I mean when you’re up against the likes of Klipsch and B&W at Best Buy, seriously, these won’t win an A/B standoff with your average listener if the treble is deadlocked with the mids and bass. Even if that’s where it should be. Or maybe that’s just the Jamo signature. As you can see here I adjusted everything from 0 ohms to 8 ohms which provides a 15 dB spread in tweeter level and eventually settled on 3.3 ohms as the ideal spot from both a measurement perspective and from my own listening even though the treble is still just above flat. I like a touch more brightness over flat if I can choose it. So let’s double the 1.5 ohm series attenuating resistor to 3.3 ohms and move onto the last crossover tweak.

Continue reading →

Posted in DIY Audio | Tagged , , , , , , , , , , , , | 14 Comments

Sealed 15″ Ultimax + MiniDSP + Crown XLS 1002 + Remote Trigger = Killer Subwoofer Project!

Posted on August 17, 2020 by Dan

About a year and a half ago the wife and I decided to retire our old entertainment center and completely make over our family room. We bought a new TV, a huge couch/sectional, a new area rug, a new leather ottoman (thanks Costco for basically furnishing my house), installed a bunch of ship-lap on the wall (thank you Fixer Upper for putting ideas into my wife’s head) and we bought a new media console (thank you HomeGoods, I really didn’t want to build another entertainment center). Of course after all this I took the opportunity to re-build an old pair pair of 2-way speakers and build a new center channel for the home theater to complement the new family room (thank you Parts Express). And that’s about where everything sat for over a year. It had everything we could have wanted but it lacked one vital thing…a subwoofer. So this past month I decided it was time to break out the power tools and start making some saw dust and built a killer new subwoofer for our family room theater. Now that it’s done I can finally say the room is officially complete! Man I can’t believe I went so long without having crazy bumping bass. Movies, games and music all sound so much better now, the bass is massive, it absolutely rattles the entire house. But before we get into that, let’s get down to the design, the build process, show off some pics, talk about my cool miniDSP enclosure, how I setup the miniDSP as well as how I made a neat little relay box to remote trigger the Crown amp to turn on and off with my receiver. So hunker down and read on below!

So the gist of the setup is this: a single Dayton Audio Ultimax UM15-22 subwoofer in a sealed 2.82 cu.ft. (80 liter) enclosure powered by a Crown XLS 1002 power amp and PEQ’d with a miniDSP 2×4 in a custom aluminum enclosure. Also I built a relay trigger for the Crown amp so that it goes into standby mode anytime the system is not use. This is a great setup for a small family room theater without being too over-the-top. Though it might pale in comparison to what some people have in their theaters, especially when it comes to the Ultimax series of subwoofers, for my modest little setup, it is just right. And quite frankly puts out way more rumble than should be possible for what is basically just a thousand watt 19.5″ cube. I’ll go through each of these parts of this project, explain some of the design choices I made, show a bunch of pics, and hopefully you find some of this useful if you want to build something like this for your home/family room theater.

The start of this project begins with probably one of the most important things – designing the subwoofer and picking out the drivers. I probably tossed around a hundred different ideas over the past year before really starting to commit to something I was going to follow through with. But at one point nothing was off the table, from doing a massive IB in the attic, to just a simple 8″ sub, to multiple sealed subs or just one massive ported sub to a smaller sub with passive radiators. Parts Express has such a great selection that it’s really hard to narrow down what you really want vs. what you really need vs. what you can really afford. Not to mention deciding how much time you want to spend building and integrating this thing into your home theater. All factors which can be very different for everybody, which is why to me there is no one-size-fits-all solution when it comes to subwoofer solutions. Which quite frankly is true for a lot of speakers or just audio gear in general. Here’s ultimately why I landed on the design that you see here today. And it’s based a lot on compromise, trading one design goal for another, putting a bit more emphasis on one factor than another, thus tipping the design in one direction when someone else might go another way. As you read on you will see that for me the major trade off was giving up some low-end SPL for a simple, small, compact enclosure.

I opened up my copy of Unibox 4.08 enclosure modeling software and entered in the T/S parameters for the last few Ultimax and Reference Series drivers that I was missing. Now I was able to compare everything from a single 8″ Ultimax to quad 18″ Reference Series drivers and everything in between. I realize that PE carries other subs and other websites carry other drivers, but truth be told, and let’s be honest, I am a Parts Express fan to the core. So I didn’t do a lot of shopping around on this front. And Dayton Audio make for such a great value proposition, you really can’t go wrong. Anyway, I swear I can spend hours playing around with driver combinations in Unibox, just comparing frequency response graphs of different size enclosures and comparing sealed to ported to PR designs. Seeing which ones have the best low-frequency extension, which designs exceed Xmax too soon, which ones need huge ports to maintain low air speed, which ones aren’t flat or need huge boxes, etc., etc. Everyone has their technique, and I look at a lot of factors when it comes to any notional design at this stage. Cost is always a concern as well, something Unibox can’t predict. I mean sure, I can simulate four 18″ Ultimaxes in 20 cubic foot enclosures all day long and then ooh and ahh at the crazy 14 Hz tune and an SPL approaching 130 dB at 15 Hz. But then I start to look at what that physically might look like in our family room and how much that type of setup might actually cost and I have to ask myself, is it really worth it? Well, duh, of course it would be worth it! But we’re going to choose to go another way with the objective of this build to keeping the cost to something fairly reasonable and that the sub be as inconspicuous as possible, something that fits the room and doesn’t take up a ton of space but can still hit 20-30 Hz with enough energy to shake and rattle the house.

What is a little more nuanced with the Daytons is differentiating between the Reference Series and Ultimax series drivers. They sort of each have their niche and they model completely differently. Ultimax tends to favor larger ported enclosures and needs a lot of power, but ultimately can hit louder and lower than the Reference Series without exceeding Xmax. Reference on the other hand is more efficient, it can do more with the power you do provide, doesn’t require nearly the same volume enclosure to still have great extension, but Xmax can easily be exceeded since they just don’t have quite the same excursion that Ultimax does. It can be a toss-up though and you really have to just look at the frequency response plots, the excursion plots and the box volumes for each and see if it’s something you want to do. Comparing difference designs is pretty easy especially across just two different driver families, if you just stick with one box type, but once you start comparing sealed to ported, to PR designs across different driver series, it can be a little tough to decide. Is it worth making the box just a little bit bigger to gain another 1-2 dB at 20 Hz? The excursion sims are starting to look a little scary, what if I am really easy on the volume knob, hey more power never hurt anyone as long as I am careful it should be fine, right? Whatever you have to tell yourself so that you can get to a design that you’re comfortable and happy with. But most importantly, it should be a design that you’re excited about building. A design so awesome that you can’t sleep the night before you start it because you’re just that excited to work on it. If building a plain-Jane ported 12″ box doesn’t seem like fun, even if the simulations say it will sound great, then don’t build it.

So for me to narrow down the process, I made the executive decision to just go sealed, because everything I modeled ported required a box that was just way bigger than what I wanted to do for this room. And if you really pay attention to port air speed to minimize port chuffing, port area need to be pretty big, which means the ports need to be long for proper tuning, which means the box needs to be that much bigger to account for the added port volume. Passive radiators do fix this problem (at a cost) and I almost bit the bullet on a single 12″ Reference driver with a matching pair of 12″ PRs. It basically checked all the boxes for my design, the box size was reasonable, the low-end extension was good and the cost was right on budget. I had everything in my cart, ready to check out and then at the last minute I backed out. I don’t recall my exact reasons, it would have been a perfectly fine subwoofer, but I think I was just a little bummed that I had settled on just a single 12″ driver. It just didn’t feel big enough. And for the same cost or even less, I realized I could go with a bigger driver in the same size box if I just committed to a sealed design. (Probably spending too much time on AVSForum didn’t help matters). That’s when I turned to Ultimax and realized that these drivers model fantastic in small sealed boxes. Extension rolls off as any 2nd order sealed driver would but you can still hit a decent f3 in enclosures that are not huge. And if you’re willing to compromise a bit on the system Qtc, then you can make the box even smaller, keeping Xmax even more in check without giving up too much on low-end extension. Not to mention the rugged glass fiber woven cone seemed like it would be a bit more durable than the softer aluminum cone of the RS series. Plus, I really think these drivers look awesome. That massively fat high-roll rubber surround, the omission of any sort of dust cap and that sweet-looking woven cone, a cast basket, leads stitched into the spider, plus the dual 2-ohm coils means more flexibility with amplifier options. So this was it, we were going Ultimax. And since I wasn’t too keen on just the 12″ it was really deciding between the 15″ and the 18″.

After modeling the UM15-22 and UM18-22 in various enclosures sizes, I ended up deciding to go with the 15″ as it didn’t require quite as big a box as the 18″ and with the money I saved I put towards a miniDSP. I figured if you had a $300 budget for just the driver, then the 15″ and a miniDSP would be more flexible and could possibly sound better than an 18″ without any DSP. And I realize the volume requirements are not that much different between the two subs, arguably I was splitting hairs a wee bit. The 18″ models fine in only 4 cubes but the 15″ works in a little as 3 cubes (it’s roughly the difference between an 18″ cube and a 20″ cube after bracing with 3/4″ MDF) if you’re willing to put up with a Qtc in the high 0.8’s. I ended up making my box only a 19.5″ cube which is 2.82 cu. ft. after bracing, driver, a double-thick front baffle and 1/4″ MDF finish) for a final Qtc of 0.88 (walls lined). Most people would probably just buy the 18″ and call it day, make the box as big as needed, and then end up buying the miniDSP (or equivalent) anyway. But I was really trying to keep the box under a 20″ cube and the budget wasn’t something I wanted to stretch any more (at least any more than I already had). However that 18″ can do another +2.5 dB over the 15″ at 20 Hz for only an extra 28 liters and at 5 cu. ft it will do +3.5 dB, which isn’t insignificant. But I can say that I am more than happy with just the 15″ so far. It absolutely bumps and shakes my whole house like nobody’s business. I don’t think you can go wrong with either driver. Also the 15″ on paper was a better match for the Crown XLS 1002 that would be driving it. I think the 18″ would have wanted more power. But going back to why I abandoned the 12″ PR design, I figured that the 15″ Ultimax also gave me a better upgrade path to either dual sealed 15’s or just building a 12 cu.ft. ported box down the road for just the cost of a couple sheets of MDF (which by comparison would be +10 dB at 20 Hz compared to the sealed enclosure that is one fourth that size, definitely not insignificant). So into the cart went the UM15-22 along with a miniDSP kit, a pair of terminal cups and some rubber feet. Done, let’s move on…

Continue reading →

Posted in DIY Audio | Tagged , , , , , , , , , , , , , | 1 Comment