Open Baffle loudspeaker
This is the channel I've finished (so far), of my OB speakers.
This is a very frugal project, designed to live permanently out in the country (under cover). I'm running it from a battery powered amplifier, so I wanted a system with decent efficiency. I also wanted something I can easily hang, and I wanted something big and cheap - because it could be stolen or suffer catastrophe.
Almost all of it is made with scraps and freebies:
The drivers are all old salvage / hard rubbish finds.
The timber is scrap from old projects, and floorboards from a demolition.
The panel and frame are held together by a patchwork of scraps, including the discs that I cut out to mount the drivers.
This is a very frugal project, designed to live permanently out in the country (under cover). I'm running it from a battery powered amplifier, so I wanted a system with decent efficiency. I also wanted something I can easily hang, and I wanted something big and cheap - because it could be stolen or suffer catastrophe.
Almost all of it is made with scraps and freebies:
The drivers are all old salvage / hard rubbish finds.
The timber is scrap from old projects, and floorboards from a demolition.
The panel and frame are held together by a patchwork of scraps, including the discs that I cut out to mount the drivers.
Drivers
In the centre is a 30cm "full range" driver. I pulled these from an open backed electric piano that had been left out in hard rubbish. They appear to be manufactured to a tight budget - tiny magnet, light basket. It is fairly dull sounding, the treble is lacking.
I added the tweeters from a 3-way speaker that I broke up for parts years ago. They had 2.2uF capacitors wired to them already, so that's what I started with.
The bass driver is probably too good for this project: these are nice Plessey / Foster units, again from a salvaged speaker box. They look to be well made, and would probably work very well in a conventional 2-way system. A .56MH inductor is in series, so this woofer is helping right up into the mids. A bigger coil might make for a better sound, but I'm keeping the it small because I want cost low and efficiency (battery life) to stay high.
Plessey used to make guitar drivers, according to the Melbourne Music Centre website, "Plessey was the company who in turn took over the ROLA plant. (Rola-Celestion is the original manufacturer of the Greenback and other vintage speakers which were also tied in with JENSEN speakers in the USA)"
I added the tweeters from a 3-way speaker that I broke up for parts years ago. They had 2.2uF capacitors wired to them already, so that's what I started with.
The bass driver is probably too good for this project: these are nice Plessey / Foster units, again from a salvaged speaker box. They look to be well made, and would probably work very well in a conventional 2-way system. A .56MH inductor is in series, so this woofer is helping right up into the mids. A bigger coil might make for a better sound, but I'm keeping the it small because I want cost low and efficiency (battery life) to stay high.
Plessey used to make guitar drivers, according to the Melbourne Music Centre website, "Plessey was the company who in turn took over the ROLA plant. (Rola-Celestion is the original manufacturer of the Greenback and other vintage speakers which were also tied in with JENSEN speakers in the USA)"
Sound quality and tweaks
During setup, in my garage, these sounded pretty good, in a laid-back way: Vocals were nice, but sometimes a little too full. I guessed (partly from listening, partly from the type of drivers used) that the bass and mids were OK, but treble was a bit recessed with a broad dip around 10 kHz. I quickly measured some warble tones to test the low end:
120Hz 0dB (reference)
80Hz -2.5dB
60Hz -10dB
40Hz -20dB
Plotting individual test tones, the bass below 200 Hz was ragged (wall bounce etc?) and fell to <10 dB under 70 Hz.
Subjectively, there's enough bass there that bass guitar sounds fine, and rock music seems full bodied.
When I ran / plotted some more test tones, from a single microphone position, it looked very ragged, with deviations of nearly 10dB.
Taking further measurements with different microphone positions, I found that the peaks were all placement dependent. It averages to pretty flat from 160 Hz to 5 kHz.
There's a dip (lower than I had expected), and then the tweeter comes in from 8-12 kHz. It measured well at any position (from 0 to 30 degrees off axis), about 2dB lower than the mid band. The 16 and 20 kHz tones gave close to nothing, to both my ear or the meter, as might be expected from an old paper cone tweeter.
This was pretty decent, and better than I'd hoped for. Any more measurement was beyond my patience and also beyond my ability to improve (particularly on a zero budget). The only voicing tweak I did was to add a 1.5uF cap to the tweeter for 3.7 uF total, to try to fill in the 5-8 kHz hole.
120Hz 0dB (reference)
80Hz -2.5dB
60Hz -10dB
40Hz -20dB
Plotting individual test tones, the bass below 200 Hz was ragged (wall bounce etc?) and fell to <10 dB under 70 Hz.
Subjectively, there's enough bass there that bass guitar sounds fine, and rock music seems full bodied.
When I ran / plotted some more test tones, from a single microphone position, it looked very ragged, with deviations of nearly 10dB.
Taking further measurements with different microphone positions, I found that the peaks were all placement dependent. It averages to pretty flat from 160 Hz to 5 kHz.
There's a dip (lower than I had expected), and then the tweeter comes in from 8-12 kHz. It measured well at any position (from 0 to 30 degrees off axis), about 2dB lower than the mid band. The 16 and 20 kHz tones gave close to nothing, to both my ear or the meter, as might be expected from an old paper cone tweeter.
This was pretty decent, and better than I'd hoped for. Any more measurement was beyond my patience and also beyond my ability to improve (particularly on a zero budget). The only voicing tweak I did was to add a 1.5uF cap to the tweeter for 3.7 uF total, to try to fill in the 5-8 kHz hole.
This is a side view of the shack / tools ted the speakers back onto. The back wave is pretty free to scatter to infinity.
When set up in the country they sound shockingly good. Best listening position seems to be about 5 metres away. Bass is surprisingly meaty. They sounded particularly good with Massive Attack and Filistine - not coincidentally these are performers with strong links to / origins in outdoor festivals.
I'm looking forward to getting the second one set up. I will position them very closely, to effectively double baffle width and bring the bass up slightly.
What have I learned? Nothing really, I've just had common wisdom confirmed: a big OB with suitable drivers can sound quite good and enjoyable for very little money, without being the ultimate in low end and slam.
Sources: Sony Walkman (mp3 player), Dayton amp. Running the Walkman at full and amp at 12:00, the sound was too loud for easy conversation within a few metres. Most play was done with the Walkman at 2/3 output and amp at 12:00, probably putting <2 watts into the speaker.
When set up in the country they sound shockingly good. Best listening position seems to be about 5 metres away. Bass is surprisingly meaty. They sounded particularly good with Massive Attack and Filistine - not coincidentally these are performers with strong links to / origins in outdoor festivals.
I'm looking forward to getting the second one set up. I will position them very closely, to effectively double baffle width and bring the bass up slightly.
What have I learned? Nothing really, I've just had common wisdom confirmed: a big OB with suitable drivers can sound quite good and enjoyable for very little money, without being the ultimate in low end and slam.
Sources: Sony Walkman (mp3 player), Dayton amp. Running the Walkman at full and amp at 12:00, the sound was too loud for easy conversation within a few metres. Most play was done with the Walkman at 2/3 output and amp at 12:00, probably putting <2 watts into the speaker.