Unexpected Goodwill Find – You Won’t Believe What I Turned it Into

A little over 2 years ago I was checking out my local Goodwill for any miscellaneous stereo/electronics/speakers (as one does on a Saturday morning) when I came across a pretty interesting find – 8 small carboard boxes with a familiar logo printed on the side – it said Dayton Audio. A closer look revealed 2 pairs of Dayton Audio Signature Series DA175 7″ aluminum cone woofers and 2 pairs of ND90 aluminum dish cone full-range midwoofers. I couldn’t believe what I was seeing. The boxes were opened but the drivers appeared to be brand new. And they were priced at only $6.99 and $3.99 each respectively. I immediately grabbed a cart and added the 8 boxes to it and headed to the checkout absolutely giddy with my find. For a total of $44 I basically had in my possession over $200 worth of brand new Dayton Audio drivers, for which at the time had no idea what I might do with them, but wasn’t about to pass up the opportunity to potentially make something great and do it for insanely cheap.

Fast forward 2 years and I have officially completed the Goodwill-inspired 4-way tower speakers that now adorn my small garage home theater. For nearly 2 years I tossed around almost every possible speaker combination I could come up with using these 8 drivers. Initially I was thinking of building two sperate types of speakers, like a Bluetooth speaker with the ND90s and maybe Zaph’s Bargain Aluminum MTM with the DA175s. Years ago I built a pair of speakers for my friend’s home theater using the DA175s and they were great speakers. But the more I thought about what do build with them, I just never could get over the fact these speakers need a pretty decent size box if you go the ported route. Going to a sealed box to remedy the size issue only brings about a major excursion issue above about 7 watts. So building a nice smaller 2-way or MTM just didn’t get me all that jazzed. And as far as the ND90s, I’m not too big on Bluetooth-based portable speaker systems in general. Parts Express sells some decent BT amp kits but I’ve got so many BT speakers lying around that just don’t really get used at all, so again I wasn’t super excited about that option either. So the speakers sat, month after month, with no plans in sight to every build them into the sweet speakers they deserved to be.

That’s when it sort of hit me one day to combine both sets of drivers into just one speaker design. It was an odd combo, the 7″ DA175 woofers and the 3.5″ ND90 full-range drivers, I thought there’s nothing I could possibly throw together where these two speakers would sound good together. Right? But I drafted up some concepts, taking into consideration the bass limitations of the DA175s and the lower efficiency of the ND90s and the upper frequency limitations (despite claiming to be full-range), I modeled up an WMTMW setup with a soft dome tweeter that I thought looked pretty good. I figured the ND90s would play great in just the midrange section and I could cross those to a nice soft dome in a 3-way setup. Add a sub and these could play great Left/Right duty in a home theater, with the receiver set to SMALL for the fronts. A potential design was coming together here, but it was still missing something.

Slowly that idea morphed into me deciding I really wanted a full-range tower speaker, something I could use in a 2-channel stereo setup without a sub. That’s when I added a pair of 8″ woofers to the design, making it effectively a 4-way speaker in a SSWMTMW (sub, sub, woofer, mid, tweeter, mid, woofer) configuration. After modeling up a bunch of different 8″ drivers from Parts Express, I settled on the DSA215-8 aluminum cone Designer Series woofers to act as the “sub” woofer in this 4-way monster. I liked that they matched the look of the DA175 speakers, they were offered in just a standard 8-ohm version so I could wire them in parallel for a final 4-ohm load (more power, easier crossover), they weren’t expensive, keeping in line with this being a budget speaker build, and they modeled great in a tower-sized cabinet that was exactly about the size I was shooting for. I drafted up some of the artwork you see here which helped give me an idea of exactly what this concoction of a speaker would look like. And you know what? I thought it looked awesome! You don’t see many commercial speakers in a configuration like this, but I knew it had the potential to sound amazing. For the tweeter I picked out the ND20FB-4 Rear-Mount 3/4″ Soft Dome Neodymium Tweeter. This ended up being an amazing tweeter for these speakers and was also pretty inexpensive. In the end, I think spent more on new crossover parts than anything else in this build. I was getting low on all my resistor/cap/inductor values from my last few passive speaker projects, so I stocked up on just about every value I thought I might need to build the massive crossovers for this 4-way speaker.

With the basic speaker configuration finally settled on, I played around in Passive Crossover Designer 8.0 (using the stock .frd and .zma files) to get an idea of what in the world the crossover for this thing would look like. Starting with 2nd order filters for all drivers, I came away with some candidate crossover frequencies that appeared to work. All the speakers would need is some attenuation to match the levels of the 8″ woofers after baffle step losses. So at least on paper, I knew I could get the response essentially flat from ~35 Hz to 20 kHz and I wouldn’t need any exotic notch filtering or any other overly complicated filter networks. Each driver was operating in what I would call its “sweet spot”, well below the cone break-up region but also above the bass region where the smaller drivers didn’t play as well either. The ND90s operate happily up to 10 kHz so cutting them off at a couple of kHz allowed the tweeter to pick up this critical region alone. And cutting off the DA175’s below 200 Hz prevented them from ever experiencing any over excursion. Also, limiting them to about 900 Hz, since they are in an MWTWM configuration and are over a foot apart from either, helped to minimize comb filtering effects, allowing the vertical off axis response of this speaker to be quite good despite the WMTMW configuration. Keeping the ND90s as close to together as possible and with a reasonably low crossover point also helps with improving the vertical off-axis response. Once I got the cabinets built I spent a good deal of time measuring all the drivers and ultimately designing the crossover real-time with REW, though PCD at least got me started in the right direction, especially when it came to picking a reasonable selection of part values from Parts Express. Inductors are not cheap, so I only bought what I thought I might use, and even then, I ended up purchasing iron-core inductors just to keep the cost down. Also purchased simple electrolytic caps for anything above about 20 uF. At 20 uF and below, they are all Dayton Poly caps.

Speaking of measuring and designing the crossover, I’m getting a little ahead of myself on this writeup. DIY speaker building has so many fun phases to it and I honestly enjoy each one so much, as each part of the design and build process carries its own challenges and rewards. Starting of with the concept phase (one of my favorites) just picking drivers, drawing up some pictures, pricing out options, I spend hours on Parts Express’s website downloading datasheets, running enclosure response simulations, trying ported, sealed, passive radiators, with EQ, without EQ, I mean I can do this for weeks, months, even years when I’m designing a new speaker. And it never gets old. It’s kind of funny because I go through my DIY Speaker folder on my computer and there’s at least 20 unfinished, un-built, half-baked speaker ideas that just never made it for every one speaker project that actually sees the light of day. If I had endless resources, money and time, I could easily build a new speaker every month and I would never tire of it. For now, I’m basically limited to about one speaker project every year, or if I’m lucky, I might squeak in two in a year, or more if it’s just simple “upgrade” project, like I’ve done a few of recently. Then there’s building the cabinet, cutting the wood, gluing it up, sanding it down, using every tool I own and spending weeks in the garage just making these bare wooden boxes. I’ve gotten more creative with some of my speakers and have been adding some real-wood veneers, or rather, plywood veneers like Birch. Wrapping plain MDF in some real wood suddenly makes the hobby go from what I did in High School to something a little more meaningful. Getting to use my flush trim bit on the router to get a perfect seam between the real wood and the MDF just feels so good. I spend a lot of time sanding and routering once I get the boxes built in preparation for my least favorite part of every speaker I’ve ever built – painting and staining. I settled on a process that works for me, which is spray painting the painted parts with a regular flat spray paint and then finishing the speaker with a Satin or semi-gloss polyacrylic. This water-based clear coat is the most forgiving of imperfections and leaves very few lines, but still has to be done right, or it can look really bad. I’ve gotten better over the years, but am by no means an expert. This goes well over an oil-based stain which is what I usually do if I’ve added a real-wood plywood to the sides. The stain goes on fine and is usually pretty forgiving of bad technique as long as you don’t put on too much, wipe the excess after each coat and do 3-4 coats until the desired darkness is reached. I’ve also found that using a pre-stain treatment on the wood before staining it works wonders for getting that even, clean, professional, stained look. It prevents that botchy look you can get with softer woods if not treated beforehand.

Which brings me to another favorite and basically the final part of the speaker building process, measuring and listening, and designing the crossovers. This also is one of the more frustrating parts of the design, because it’s so tedious. The endless tweaking of crossover values, pushing the response up and down, listening to music, gauging if it sounds better now with a 4.7 uF cap on the tweeter and a 4 ohm resistor or if it sounded better with the 5.6 uF cap and a 5.1 ohm resistor. But that’s just the start, with a 4-way speaker such as this, I had to decide where each speaker sounded best in terms of crossover point, summing with its neighbor, overall volume of each driver, figuring out which phase/polarity sounded best, especially when I started to venture into 18 dB/octave (3rd order) slopes, it was like, I can’t keep everything straight! Keeping good notes of every adjustment is key and of course, using REW with every measurement so that you an actually see how each crossover adjustment affects the response. I rely almost entirely on REW to get the response of each driver flat, and summing properly, before I start to listen to anything as part of the listening tests. I like to have the crossover basically where I want it visually before listening to anything. And then the listening part of things just allows me to dial in my own personal preferences such as the overall tonality of the speaker, which is influenced a lot by just how loud I allow each driver to play. Oddly enough with these speakers, those little ND90s were just screaming, despite them being the least efficient drivers of the group, I have a pretty decent sized resistor on them (3.3 ohms) just to keep them balanced between the tweeter and the DA175s. Anyway, last but not least in this magical DIY journey is the day the speakers are officially done and you get just sit back and put on some of your favorite music or watch a familiar scene in your favorite movie and just get to enjoy the creation that you and your little hands have put together. The months of design work, and then weekends in the garage cutting, gluing, painting and staining, to weeks behind a laptop screen staring at REW plots all day, to finally come out on the other side with something you can be truly proud of. And in some cases, something that is really one of a kind. And something you will enjoy for years, even decades to come, as I recently just turned the corner on 25 years of owning my Swans M3s, which I consider some of the nicest speakers I’ve ever built. I’m hoping that I get to enjoy these speakers for at least that long.

Continue reading

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

DIY Swans M3 Tower Speakers Get an Upgrade for 2024!

I’ve had a pair of Swans M3 speakers since around the year 2000 – that was 24 years ago as of this writing – they were one of the first pair of really nice speakers I had ever built at that time and were also some of the first speakers to adorn my budding web page called Audio Innovation. I have enjoyed these speakers over the years and they have truly served me well. Whether they were set up for dedicated two-channel listening or as part of a home theater, they have always sounded great. Until a few months ago I started to notice some buzzing from one of the speakers. Upon further inspection I noticed that one of the woofer’s voice coil was rubbing and creating sort of a scratching sound. It was not super obvious, so I didn’t bother with it too much. A while later I noticed that a second woofer was also starting to rub. Okay, so that makes two. Not to mention this also happened in a different pair of speakers I had built around the same time with the W6 woofers. Which I rebuilt with a pair of Dayton Audio RS180s.

I started to consider what it might take to replace the four W6 woofers with something more modern, something newer, something better. As I was researching woofers, I thought I would go ahead and disassemble the speakers and check everything else, make sure there wasn’t something else I needed to replace. I ran a few FR sweeps in REW and that’s when I realized that both of the F5 midrange’s surrounds had broken away and completely separated from the frame! At least 1/3 of the entire surround was completely floating and not connected to anything. Okay, so that has to be fixed. That’s when I turned my focus to the RT1C-A ribbon tweeter. I could see something weird inside the grill on one of them, so I pulled it apart and to my surprise found that the long rectangular magnets on both the frontside and backside had completely disintegrated, turned to basically magnetic dust. Upon disassembly of the other tweeter, the same fate had fallen it, although not quite to the same degree. So if you want to know how long a pair of Swans M3 speakers last, it’s basically less than 24 years. The woofers were toast, the midranges had fallen apart and the tweeters had returned to their natural magnetic form. Dang, this project this got a lot more complicated, but also, a lot more interesting.

So how do you rebuild a pair of Swans M3 speakers in 2024? As it turns out, quite easily actually. HiVi still manufactures and sells both the F5 midrange and the RT1C-A ribbon tweeter. Sadly the W6 woofer is no longer in production. But this is a great start as 1/2 of the drivers are still available, they can be replaced outright without changing anything with the cabinets or the crossover. I had drawn up some different options with other midranges and other tweeters, but felt it changed the classic Swans M3 look that was just so classic of the time back in 2000. If I really wanted to use completely new drivers, I should just go ahead and build a whole new pair of speakers. I wanted to fix these speakers while still maintaining that great look that I’ve grown so accustomed to over the last 24 years. The trick was going to be finding a good woofer that matched the old woofers, but also matched the look and feel of the speakers overall. I tossed around the idea of theDayton Audio RS180s, which I have already in at least 2 other pairs of speakers, so I was sort of tired of building speakers with those drivers again. The newer Signature Series with the flat aluminum dish cones looked like great alternates, but they only offer them in 4 ohm versions. Which would have meant wiring them in series, for an overall less efficient speaker, meaning a completely new crossover and not just for the woofers, but for the mids and tweeters as well. I wasn’t in the mood to completely redesign this thing, so I narrowed my search to only 8-ohm drivers, just like the W6s, so I could wire them in parallel for a 4-ohm load and at least keep most of the crossover in tact (though I would later end up tweaking the crossover anyway, while keeping most of it unchanged).

I wasn’t dead set on maintaining all HiVi drivers initially, until I narrowed my search again to just HiVi drivers and that’s how I landed on the M6N-B 6″ black aluminum/magnesium woofers. These things looked pretty awesome! A quick simulation in Unibox showed they were a perfect fit for a 47 liter boxed tuned to 42 Hz. I wasn’t a huge fan of the stamped steal basket, but otherwise it checked all the boxes. Not to mention they are actually one of the less expensive woofers in the 6-7″ variety. I mocked up a drawing of them paired with the F5 and the RT1C-A and they looked great together, one of the best combinations I had drawn. So with that, I made the decision to buy (4) M6N-B woofers and a new pair of RT1C-A tweeters. I elected not to buy new F5 midranges, but instead bought a small bottle of rubber-infused CA glue and repaired the ones I already had. I bought some rubber feet to clean up the bottom of the cabinets and a few crossover parts so I could tweak the crossover a bit as needed. Since now 24 years later I actually have the ability to measure these speakers and can make changes to the stock crossovers that were originally designed for these speakers.

About this time, I had removed all of the drivers and all of the crossover parts from the cabinet, I decided to refinish the cabinets to make them match some my other speakers I had built recently, like my center channel. This meant sanding down the entire cabinet and refinishing and re-staining them. I ended up going with a darker sort of Walnut look, and repainted the front/top/back in all black. I finished up everything with a few coats of a satin polyacrylic to give the speakers that nice and soft sheen that looks great on any speaker, since it’s not too flashy, but isn’t too dull. It’s sort of the Goldilocks of sheens, it’s just right. With the cabinets all cleaned up, I dropped in the drivers with the crossovers outside of the cabinet and that’s where the fun really began.

Continue reading

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

Cerwin Vega L-7 Bookshelf Speaker Crossover-Enclosure-Tweeter Upgrade!

Last month I was at my parents house when my dad says, “Hey do you want a pair of speakers?” I thought heck yeah, I’m not one to turn down a free pair of speakers. So he shows me a near perfect-condition pair of vintage Cerwin Vega L-7 bookshelf speakers just sitting on the floor of his bedroom. He said he hasn’t used them in years, they weren’t even connected to anything, and were just sitting around collecting dust. So I absolutely said I would give them a new home and took them off his hands. Almost 30 years ago I had borrowed these same speakers my sophomore year of college and seeing these speakers again instantly brought back memories of blasting Cake and Depeche Mode for all my neighbors to hear. These were decent speakers, even though they don’t have the traditional Cerwin Vega look. Without the badge on the grill, you’d never know who made them. But I always thought they were a good speaker. And now we get a chance to see what this speaker is made of and, of course, see what modifications we can perform to improve their sound and make them even better.

Speaker Breakdown

An external visual of the speaker reveals a 7″ paper cone woofer with rubber surround and a 1/2″ mylar dome tweeter. The cabinet is ported in the rear with a spring-loaded terminal cup. The cabinet is wrapped in a black wood grain veneer, typical of just about any inexpensive speaker available today. The L-7 is fairly lightweight and tapping on the cabinet sides and top reveal a very hollow “knock” indicating little to no internal bracing or damping. Opening up the speaker is quite easy (there are no decorative rings trying to dress up the stamped steal basket of the woofer) which reveals a hollow box with no bracing and basically zero actual acoustic damping, except for a single piece of what looks like a 3/8″ wool fiber pad that had completely dried out and was as stiff as cardboard. At this point we can see that the enclosure is made from 5/8″ particle board and not the more traditional MDF. The crossover is as bare as they come with only 4 components – a single 0.5 mH iron core inductor on the woofer (1st order), a 2.2 uF cap and inductor on the tweeter (2nd order) and a protection device to prevent damage to the tweeter in case of overload. This is extremely bare bones and definitely designed to hit a low price point.

An inspection of the woofer reveals a pretty decent design, although nothing fancy, it appears solid, beefy size magnet, it’s got a cheap stamped steel frame, but the paper cone, spider and surround all look really good. I read somewhere that the drivers were actually made in Germany and not by Cerwin Vega. There is certainly potential here. But the tweeters on the other hand are pretty much garbage. They were very common in cheap speakers back in the day and you can still buy a version of this 1/2″ mylar dome tweeter from Parts Express for about $4. Overall it’s not a great tweeter and will probably be the first thing to go in the upgrade. I measured the speaker with my ECM8000 mic and REW on axis at 0.5m in my room to get an idea of the speaker’s overall tonality and the plots below give you an idea of what we are working with. Cone break-up modes dominate the midrange region right around the crossover point. The sorry tweeter just can’t play low enough to push the crossover point any lower which results in a crossover point of about 5.3 kHz. The tweeter response also can’t keep up with the volume output of the woofer, so it rolls off leaving the midrange to sound even more forward. Overall just not great and clearly designed to be inexpensive and not designed to sound as good as it could. When I was looking up this speaker online I did find that there are two versions of the L-7 with the other version using what’s look like a much better tweeter. Probably a good choice, since besides the hollow particle board box, the tweeter is definitely a major limiting factor to making this a great speaker.

Continue reading

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

Converting this $6 Goodwill Vizio Subwoofer into a Bumping Beast!

Last weekend I stopped by my local Goodwill hoping to find some audio-related goodies I could play around with. Lately it’s been slim pickins in the used stereo department with mostly junky old Blu-ray players and bits of pieces of all-in-one home theater systems (and those were never any good when they were new). This time I noticed a pretty nice Vizio subwoofer that looked like it had potential. It was at least in good shape. The woofer was hidden behind a grill cover that at the time I couldn’t tell if it was going to be easy to remove. But the nice flared port on the front and the compact size, and decent heft, made me think this just might be a worthwhile buy. It was listed for $12.99, but since it had a blue tag, it just so happened to be a blue tag weekend, which meant it was 50% off. So for a whopping $6.50, I decided it’d be worth taking a shot. If nothing else, the enclosure alone was worth at least that much and I could buy a new driver and amp if I absolutely had to.

Once I got this little subwoofer home I found a model number and looked it up. Turns out it is a Vizio S4251W-B4 Subwoofer that was part of a Vizio S3851W-D4 Soundbar Surround Sound combo back in 2014. I found the old Amazon listing for it and it got surprisingly good reviews. There were no specifications for the sub itself, other that a completely needless output rating of 100 dB. Thanks for that Vizio! So after tearing this little subwoofer down we find a pretty hefty 6″ paper cone subwoofer with a decently fat foam surround. A stamped steal basket and a good-sized magnet make up the motor structure with a label indicating a 4 ohm rating and a 90W power capability. Pressing on the cone revealed it moved just fine with no voice coil rubbing, so at least it didn’t appear to be blown. But man that spider and surround sound were stiff, like this sub has zero compliance. I should have set up REW to measure the T/S parameters (I may still do this later when I measure the amp) but for now I was just checking things out and so far it was looking pretty good.

The enclosure looked decent, made from just 1/2″ MDF, but I really like the long flared port that fired out the front of the cabinet. It reminded me of the old Bose Acoustimass subs from back in the day. Of course this sub just has a regular side-firing driver in a basic 4th-order vented design, but size-wise and visually looked comparable. The amplifier module is mounted in its own smaller enclosure, since they made no attempt to seal off this part of the box, so the subwoofer is in its own enclosure which was really handy for providing options for how we were going to power this thing. So being that it’s part of a soundbar, even though it has an internal amplifier, it doesn’t have any way to connect to it with a regular RCA cable. It’s supposed to connect to the soundbar which most likely uses some kind of proprietary connection. I tried to see if the sub would show up as a Bluetooth device on my phone by using the PAIRING button on the back but to no avail. It wouldn’t show up. Doesn’t really matter, I couldn’t have used it as a Bluetooth device anyway, it just wouldn’t have worked. I needed a direct connection via an RCA to be driven with a regular line-level signal like a normal subwoofer.

I thought there might be a way to bypass the wireless connection portion and get straight to the amp. After poking around this sub actually contains two small chip amps, as the sub was supposed to provide power to a pair of surround sound speakers too. I was able to make out the part number to be a TSA5713 which is a 25W stereo class D chip amp from TI. So let’s take a look at the datasheet and see what we have to work with here. Since there are two amps on this board, one is clearly used in stereo mode (BTL) to drive 25W to each surround sound speaker (assuming they were 4 ohm speakers), which would be connected to the sub via the RCA jacks on the back. The second chip to probably was wired in mono mode (PBTL) to drive the single 4 ohm sub to an unspecified power level. The graph that shows this configuration stops at 40W, just before the amp distortion curve spikes. I’m guessing it can provide around 50W which is respectable, but honestly not great. These little amps are typical of what you find in cheap sound bars and/or TVs and aren’t really anything to write home about. So with that I figured I wouldn’t waste any more time trying to figure out how to tap into a line-level signal and decided just to replace the amp entirely.

Continue reading

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

Building a Notch Filter for the Beyerdynamic DT 770 Pro Headphones with Measurements

In this article I’ll go over how I designed, built and tested a passive notch filter for the Beyerdynamic DT 770 Pro 250-ohm closed-back headphones and include measurements using REW of the different filters responses. I bought these headphones over Black Friday weekend last year from Beyerdynamic’s website where they were doing a deal where you got a free pair of black Velour EDT 770 VB ear pads, a $40 value, plus the headphones were another $10 off their usual price of $169 and they did free shipping. I was in the market for some new headphones to replace my trusty old Audio-Technica ATH-M30’s that I’ve had for several years and I thought these would do quite nicely. That same weekend my son and I had stopped by Guitar Center and they had about 8 pairs of headphones on display that you could listen to with sample music of varying styles. We checked each of them out and after a quick listen it was pretty obvious the Beyerdynamic DT 770’s were the clear standout. Good bass, nice treble, clean and clear midrange, not to mention they were the most comfortable of the bunch. Before this I hadn’t even considered these headphones, and up until this point I had already picked up a pair of Sennheisers that were also on sale over Black Friday. Though I wasn’t able to A/B these two headphones directly, I decided to return the Sennheisers and picked up the Beyerdynamic DT 770 Pros instead. A decision that would later send me down this rabbit hole of researching filtering and EQ options in order to make these headphones actually listenable for the long term.

While these headphones do sound great overall, they suffer from one major flaw that could be a deal-breaker for most – they are extremely bright! Doing a direct comparison to some of my other headphones, these suckers have got some highs that seriously sparkle, and it’s not subtle. People say that this is just that classic Beyerdynamic sound and I will say that for some tracks, this does sound fantastic and, in short durations, is manageable. But in general, most songs sounds bright and harsh, making long listening expeditions not that enjoyable at all. In all other regards however these headphones sound amazing and they are super comfortable (even while wearing glasses, like I do) so after giving the DT 770s a fair shot straight up, I decided I had to figure out how to EQ these things into submission. Fortunately there’s a ton of info for these headphones on the internet, and I quickly realized I wasn’t alone in my perception of these headphones. And while there are plenty of reviews that will talk about how these headphones sound, I found three major sources to be the most valuable in providing raw measured data that enabled me to tackle this treble problem a little more scientifically.

Naturally my first stop was Rtings.com. Without question, one of the greatest resources for objective reviews of headphones and TVs. They give the DT 770’s an overall Neutral Sound score of 8.3 which is quite high and favorable. Raw frequency response measurements confirm what everyone can hear, that these headphones are extremely neutral (in terms of matching the Harmon target response) from 20 Hz up to almost 6 kHz and therefore have excellent lower-bass response and mid-bass response up through the midrange, but above 6 kHz is where things get a little wonky. The treble climbs well above the target by over 10 dB and peaks at around 8.2 kHz. Even though they provide frequency responses for all their headphones, they don’t offer filter or EQ suggestions on how to improve them. So you’re kind of on your own to figure out how to fix anything that looks amiss. But this is a good start.

That’s when I ran across another incredibly valuable resource for headphones, plus a second set of measurements for the DT 770s, and that was from oratory1990 over on Reddit. oratory1990 has measured response plots for the DT 770s including EQ options to bring them into alignment with the Harmon target. This is where for the first time I downloaded and played around with Equalizer APO and got my first taste of the possibilities for active EQ in Windows. I entered in the EQ settings he recommended and WOW, what a difference! For the first time these headphones sounded absolutely amazing all the way through, that overly bright treble, the sibilance, the shrill, was all gone. I couldn’t believe it was that easy and with that I had figured I had my solution. While I wasn’t a super fan of having to use a software-based EQ, it was powerful enough, and seamless enough, so, why not?

Well, I quickly learned why not, at least for me, that this solution was not a long-term fix. I planned on using these headphones in my mini-budget home recording studio and I quickly realized that Equalizer APO does not work with ASIO drivers and it does not work with live line-in sources, like a piano, microphone or guitar. Basically it doesn’t work with Reaper (my go-to DAW), as it does not EQ anything recorded in it or played through it or anything live via the line in. The EQ only applies only to pre-recorded music played directly in Windows, like with Spotify or YouTube. I thought I could build a similar filter in Reaper using ReaEQ, but quickly learned how much of pain that was as well. Not mention, the biggest gripe about using a software-based EQ was having to turn it off any time I switched to using speakers. So with the Equalizer APO not working for most of my intended applications, I ended up searching for another solution. Now if your setup is more dedicated to just playing back music, or you don’t have speakers, then Equalizer APO is fantastic and I found it to be super useful.

So then last but not least, I came across DIY-Audio-Heaven and as the name suggests, I was in heaven! I have to give mad props to Solderdude who basically inspired this entire project by being the first person (as far as I could tell) to offer a fully passive solution to fixing the Beyerdynamic treble peak. And it’s so simple! I don’t know why I didn’t think of this before. As someone who has designed and built so many freaking speakers, with crossovers, and filters, even notch filters, I don’t know why the idea to passively correct the DT 770s didn’t come to me sooner. But Solderdude absolutely nailed it with his notch filter design, and not to jump ahead too much, this one fix literally solved the treble peak issue with these headphones and has made them sound just incredible. Amazingly enough, he provides passive filter recommendations for hundreds of headphones, not to mention provides measurements and reviews of hundreds of headphones, for your reading pleasure. As it turns out, a lot of headphones that are bright, or sound bad for a myriad of other reasons, can be improved significantly with a single passive in-line filter. And he’s got options for how to fix a lot of them. Not only does he provide this as a service, where you can buy them from him, he basically gives you the design, so if you’re a little more into DIY, then you can tackle this project on your own pretty easily. This was all I needed to start down this path of how to passively EQ the DT 770 Pros to make them sound better.

Continue reading

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

Measurement & Review of the AIMIYA A07 Power Amplifier

A few months ago I purchased the AIMIYA A07 Power Amplifier from Amazon for a whopping $60 during Prime Day. I’ve had the unit hooked up to my simple studio setup and have been very impressed with it so far. The performance-to-cost ratio is pretty remarkable. It’s worked flawlessly over the past months and I have been very happy with it. I currently have it hooked up to my modded Jamo’s and it sounds absolutely amazing. It has plenty of volume and never seems to run out of power. So today I finally decided to pull out my measurement gear and so I could get some real data on its performance, to see just what this amp is capable of. I know there are plenty of other reviews out there for this amp, part of the reason I purchased it in the first place, so I don’t think I’ll be sharing anything earth shatteringly new. But I enjoyed putting this thing on the bench and getting some data of my own just the same. So read on to see how she performs!

The heart of the AIMIYA A07 is a TI TPA3255 High-power Class D chip amplifier. The datasheet for this part can be found here https://www.ti.com/product/TPA3255. This is a very popular chip amp and has made its way into many small home audio amplifiers from a variety of manufacturers. However, worth noting is implementation of this chip is still up to the designer and AIMIYA is no slouch in this realm touting a long line of amplifier options to suit almost anyone’s need. Overall output power is dictated mostly by how much raw DC power you can provide. AIMIYA supplies a very respectable 32V/5A power supply with the unit which for most people will be plenty, as I’ll show here. But note that that amplifier has more to give, if you’re willing to spend a little more for a larger, more powerful DC power supply. And based on the measurements I took with the stock power supply, I believe more power available in the TPA3255.

So a quick re-cap of my measurement setup (which take it for what it’s worth) is based on a simple loop-back measurement using REW, a PreSonous Firestudio audio interface and a custom balanced amp-level to line-level converter/load box that I designed and built for this exact purpose. I’ve played with this setup quite a bit and have basically got it dialed in as best as I can to take as accurate as possible frequency response and distortion measurements of amps that range from 10W to 400W watts. The Firestudio interface is calibrated (via soundcard cal) and is able to provide an overall THD of only 0.00074% and a THD+N of about 0.0063%. While probably not great for measuring high-performance DACs or headphone amps, this setup is fine for measuring most power amplifiers, or at least most of the amplifiers that I’ve come across, as their distortion levels are almost always much worse that this. I’ve included plots of the baseline loopback measurement of just my setup so you can get an idea of where the noise limitations exist. From this you can see that all of the amplifier measurements are higher than the baseline and are therefore going to be fairly representative of truth for this amp. Not to mention nothing I measured drastically contradicts anything already out there already showing what this amp can do.

So first let’s just look at the frequency response of the A07. One of the easiest things to measure, since REW was basically designed to measure frequency response of just about anything. I limited my measurement to 5-22,000 Hz which shows a very nice and flat response from 20-20,000 Hz where the response is down only -0.3 dB at 20 Hz and down -0.8 dB at 20 kHz. This was measured into a 4 ohm load. I did not do any measurements into an 8 ohm load, as I figured most speakers people are going to use with this amp are going to fall into the 4 ohm territory. Including the Jamo’s that I am current using with it. Basically you can assume the total available power will be lower, and the frequency response will peak slightly before cutoff, but it should be minimal. Overall this frequency response is excellent for a Class D amp and represents a decent filter design by the folks at AIYIMA. Take note that the response does start to roll off at around 5 kHz which when combined with a speaker that if normally sounds a bit bright, this roll-off will mellow it out just a bit, but not much, and will likely go unnoticed. The roll-off in the bass response when combined with the type of speakers that most people will use with this amp (ie, small bookshelf speakers) should also go basically unnoticed. That being said, I’d say this amp is about as neutral as you’d expect and should sound great with a majority of speakers.

Continue reading

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