The Russell

Hmmm…what drivers lurk behind that cheap metal grill? And why is the name singular?

One of my goals in these retirement years is to use up or dispose of or somehow repurpose a large stash of boards or electronic equipment that I have accumulated during many years of this speaker-building hobby. I’ve got a lot of DSP boards with different CPU’s and software, and I’ve got lots of drivers and lots of cabinets with drivers in various build stages. One set of drivers that was particularly interesting was a SEAS Excel Millennium tweeter and a 7″ Excel W17EX-001 magnesium cone woofer. My friend Russ had given me these when I was his co-worker, along with a passive radiator that I had already used in a subwoofer project. These drivers were too good to just leave on the shelf, and they were too expensive to buy another set for making a stereo pair. So, what could I do with these?

I had already made a large “Hi-Fi” Bluetooth speaker for a friend’s gathering, by adding a Qualcomm Bluetooth module to a 12″ PA speaker that had been modified with a nice Galaxy Audio midrange and Audax horn tweeter. It had a 200W amp and a ready-made 3-way crossover. The crossover had not been optimized for those drivers, yet it still sounded quite good, and made an easy source of audio that could fill the room nicely. Since this formula seemed to work well, I decided to use the same approach to use these fine SEAS drivers. I also had an Icepower 500ASP amp already mounted in a chassis, so I would have plenty of “oomph” to power this speaker.

Since I am trying to use up parts rather than buy new stuff, a design goal was to keep the remaining components I needed on a tight budget. Also, this speaker is not addressing any new technical challenges, so I tried to keep the design and build time to a minimum.

The Excel magnesium cone woofers require a high-order crossover to suppress the resonances, but I found a nice design at the Troels Gravesen site for these exact same drivers. It uses a whopping 20 components, but I had a large stash of crossover components that I wanted to use up, and this was a worthy cause. I had to unwind a number of coils that I had to get the right values, but it turned out that I only needed to order a few extra resistors and capacitors that came to less than $10 for the lot. I got one of the bare 3-way boards from Parts Express and decided to go all-out ugly with cramming all those parts on the board. I think I nailed the “ugly” pretty good.

PE had some clearance 10″ drivers that were used in some of their subwoofers, and it turned out the 10″ was almost ideal for a smallish (1.7cuft) sealed cabinet. I added a few more crossover parts to make the Troels design a 3-way.

I didn’t want to spent much time making a nice cabinet, so I bought a DJ/PA cabinet with a 12″ woofer from Newark that was on sale for $51. The cabinet is made from low density fiberboard (LDF), which is only several steps up from cardboard in terms of strength and rigidity. But with some generous cross-bracing, I was able to get the cabinet satisfyingly sturdy. I had to fill in the 12″ driver opening with plywood and reinforce the entire front panel with a sheet of plywood but that turned out OK. After cutting out the new 10″ opening, there was plenty of front baffle space for the two Excel drivers. The W17 driver was installed in a 6″ PVC cap stuffed with absorbing material, which worked fine for the 2-pole 250Hz crossover frequency.

I toyed with using a simple QCC3008 Bluetooth module as the primary source but decided to go with a WiFi streamer instead. I had some old WFA28 streamers laying around, but found that Linkplay is selling refurbished Wiim Minis on eBay for $59, so I was able to discard the WFA28’s. I’ve got too many speakers on the 2.4GHz band already, and the Mini can use the 5GHz band, where there are a lot more channels available.

I was thinking about giving this speaker to a neighbor, but after I put on some James Taylor for my wife, she made it clear that we are going to keep this speaker. The Excel drivers are shockingly clear and articulate, and they can absorb that 500W amp without complaining. That 10″ woofer is surprisingly good in this cabinet, and it off-loads the 6.5″ W17 driver so that it can “specialize” in midrange, where it is an amazing speaker.

This is a nice speaker to have for a party or event where you don’t need stereo but want lots of clear high-quality audio. The handles make it easy to move around, and having a potent amp and streamer make it “fun”. Obviously, I failed miserably at clearing out my driver/electronics storage space, as I now have a large party speaker sitting in the same area. But if someone wants to hold a party, we are ready to provide the music.

Update: made a deal with the wife that this will go in her greenhouse, although right now it is in her kitchen area. Since it is not going back in my storage area, it’s more of a success than I thought previously.

Active speakers with built-in test signals

Sometimes it’s nice to have a tone or sweep generator or even some white noise to test your speakers. SigmaStudio has a good selection of “sources,” even for the ADAU1701, that don’t require a lot of instructions. I’ve never used them before, but I’m finding them very useful for this next round of active speakers that are starting to take shape. This post describes how those built-in test tools are implemented.

The ADAU1466/SSM3582 boards from the ElectrACC Store at AliExpress have quite a few inputs, but I’m only interested in the Bluetooth, SPDIF and analog sources. Once I got all that basic switching straightened out, I added a “Test” button and a new screen to control the sources:

This feature requires some new SigmaStudio “code” for the sources, along with the code that controls the switching. Here is the new section of SigmaStudio code:

The Mute is just an extra white noise generator that is turned off, and the VCO uses the potentiometer on the ADAU1466/SSM3582 board to control the oscillator frequency.

The ESP32C3 code to control the new blocks is fairly easy to write, as it only requires 3 new commands that reuse a lot of existing code. The new commands are: ADAU1466_Source, ADAU1466_Sine, and ADAU1466_Sweep. The VCO and white noise sources don’t require any software control, so they only need to be selected, without any other CPU control. I’m still working on the Sweep code to get a good combination of range, step size and sweep speed, but it’s coming along. These built-in test sources will be a nice feature to incorporate in all future active speaker designs.

On another topic, I had made a throw-away desktop speaker for testing the dipole compensation, using some cheap $1.29 drivers from MPJA. I’ve had to replace all the drivers because those SSM3582 amps have enough power to completely fry the voice coils when the volume is accidently turned up too high. Even though those amps aren’t rated for high output at 8 ohms, I think they will do fine for desktop speakers or the very efficient Martha speakers.

Overall, I’m still impressed with those ADAU1466/SSM3582 boards. For $120 shipped you get a nice ADAU1452/ADAU1466 DSP, plus Bluetooth and analog input that uses a “decent” PCM1808 ADC chip. You also get SPDIF I/O and 8 very high-quality power amps that can provide moderate power at 4 Ohms. With 2 Ohm loads and a 16V supply, they are rated at 50W each. If you can figure out what to do with all of those amps, these boards can be a lot of fun. These boards are an excellent “deal” for the price.