I have been reworking my shop lately. A large part of it was just cleaning out crap that was no longer used. Part of that crap was the sound system. It was an old FM tuner, record and cassette player someone had thrown out years ago. Quite frankly, it wasn’t much good and I wasn’t sorry to see it go.
Then, earlier this summer, I found myself working in the shop and realized that I had missed a show on NPR that I wanted to listen to. As I thought about it, I realized that I missed music in the shop, too. It was time to add a sound system to the shop.
First the speakers. I had picked up a set of Baby Advent II’s at a garaqge sale for $5. These are bookshelf speakers that were fairly high-end in their day (mid-1980’s, $200 a pair). But playing these speakers on my main stereo revealed a few problems. They had a broad, neutral tone balance but the midrange sounded muffled and the high end lacked the clarity and “sparkle” I have come to expect from modern tweeters. If the bass response went down to 100 Hz it wasn’t evident listening to them. One of the speakers had a problem common with 30-year old speakers:
The foam surround on the woofer had deteriorated and torn – the woofers were basically shot. I could have reconed the woofers but the sound quality just wasn’t there. I liked the speaker boxes, however, so I decided a driver upgrade was in order.
I started with a speaker system design from the Web – the PeeDei design by Lonesaguaro. This speaker was designed for a sealed enclosure close to the volume available in the Baby Advents and the drivers were still available. Here is a comparison between the original drivers and the new drivers (new drivers on the right):
Obviously some mods to the box are necessary to fit the new drivers. The existing tweeter hole was too large so I filled it for later drilling to the proper size and the woofer hole was too small so I enlarged it.
And did I say “sealed enclosure”? Not any more! The previous owner had drilled holes in the backs to hang them on the wall. I drilled them to a larger size and filled them with dowels to seal the enclosures.
After mounting the crossover networks and drivers, here is the final result:
On to the amplifier… I have been toying with class D audio amplfiers based on the TriPath chipset. The Sure board-only design at $35-$40 offers amazing bang for the buck. Coupled with a 24V, 6A power supply they will supply 50W per channel to 8 ohm loads.
So I started by mounting the board and power supply to a base:
Times have changed since they made the old system I threw out. The last thing I wanted in a new system was the need to run across the shop to change volume or change out tapes or CDs. Hell, I don’t even own any CDs anymore – everything is streamed from computer disk or memory. Bluetooth audio receiver modules are available now for less than $20. The one I bought is a bare board intended to run from 5V provided by a USB connector and provides audio out on a 3.5 mm headphone jack. The Sure amplifier module has a 5V supply for the chipset and screw terminals for audio input so I cut the connectors off of the cables supplied with the Bluetooth module to wire directly to the amplifier:
Here is everything wired up for testing on my workbench:
It sounded fabulous! So it was time to finish up the case:
This is working very well in the shop. As soon as I turn on the amplifier the Bluetooth module automatically syncs up to my phone. The phone itself acts as a remote control and allows me to control volume, play from music playlists, stream radio from the Internet, listen to podcasts or whatever!
Here is a picture of the completed system running on my assembly table:
What do you think?
-- "Find out what you cannot do and then go do it!"