96 Tears

Yep, you are going to cry, cry, cry, cry 96 tears because of all the tweeters used in this project. But, somehow, I got through it, in spite of all the crying, and yes, it was worth it. The picture below is the test setup without the back on for one side.

This is a replacement for Mom’s garden table, which was written up in the Projects section. That table never got put into service because the “cabinet” wasn’t strong enough for those rectangular glass woofers, and it sounded like it was going to tear apart at the volume levels that my wife prefers. In order to rise above the exhaust fan noise in her greenhouse, she needed a lot more output. This is a roughly 16 foot square greenhouse attached to our house, so there is a lot of volume in that space.

I had purchased a couple of boxes of clearance-priced 3″ drivers a while back, and I figure that a line array with 20 of them per side would be enough bass and midrange. I had also purchased over 200 of the 1/2″ “full range” drivers that PE had on clearance for about 40 cents each. 96 little bags to open. 96 times two leads to dress, 96 drivers to hot glue into place into 96 5/8″ holes per side. And then 96 and some extra solder connections before you can listen to it. Hence the name of these speakers: 96 tears. I had made a small line array with 9 of those tweeters a while back and thought they showed a lot of promise, so I wanted to use them for this project.

I had considered making another 20-channel line array with electronic curvature and shading with these drivers, but I decided to keep this project simple, because I really wasn’t sure that those 1/2″ “full range” drivers would be worth the effort. Those 20-channel amps are expensive and difficult to wire up, and these drivers were “too experimental” to risk all the cost and labor. So, this speaker has no shading or electronic curvature. I bought a box of 2″ Peerless drivers and will use AMT drivers for the 20-channel version.

This project uses the “updated” stereo 3-way design referenced in the previous post. This will be a “streamer” amp that uses the Wiim Mini as the source, with an optical interface to an ADAU1466 DSP for the crossover and EQ, with a digital (I2S) interface to a pair of Wondom TAS5756 amps. The DSP board also has an analog output for a subwoofer that I will use if I can’t get enough bass from the EQ’ed 3″ drivers. The DSP board schematic is shown in this link, and the completed CPU/DSP/Amp board is shown below. The CPU is the ESP32C3, which has enough memory to allow both a Bluetooth BLE and MQTT interface for controlling the volume, crossover and EQ. It’s a nice amp/DSP board, with a fully digital path from the Wiim streamer to the amps.

The Wondom TAS5756 amps are on the lower layer:

These amps are a generation beyond the TPA3116 series, with much improved specifications, and they sound great. The I2S interface for the TAS5756 connects directly to the digital ports of the ADAU1466 DSP. With the optical connection to the Wiim Mini, there is a completely digital path from the source through the DSP to the amplifier input. They are dead silent when nothing is being played and with 20 mid/bass and 96 tweeter motors, these 30W amps are plenty powerful.

I still need to finish the other side, but at least I know it will be worth the additional effort. Those 1/2″ full range drivers actually make fairly decent tweeters when you have 96 of them in a row. The high end is clear and articulate based on casual listening so far. The 20 3″ drivers combined have about the same surface area as a 10″ woofer, so once these get EQ’ed, I think they will have enough low end to make the greenhouse shake a bit.

Update, 5/23: Both channels are mounted on the wall, and the initial listening is impressive. Very clear and dynamic, and they fill up the space like only a line array can. Those 30W amps (4 total) are plenty, given the high efficiency due to the large number of motors. I still need to take some measurements to tweak the DSP, but it is clear that these are going to work out very well. This is a big month for Garden Club work, so please excuse the mess on the table.