MunkeyQ
04-16-2009, 10:00 AM
A while ago on the way home, I found an old (early 90's) Altec computer speaker subwoofer put out for the bins, and brought it back to cannibalise for parts. The taxi driver was very confused. I thought it would be like most computer subs - cheap driver with a small magnet/motor, Chinese EI core transformer and minimal amplification.
However, I was surprised to see it used a 6.5" Altec branded dual voice coil driver with a vented pole piece and had a nice big toroidal transformer. For amplification, it's got a 22wpc amplifier module with each channel driving one voice coil and a dedicted IC for dynamic range compression. Nice. Obviously this was made after Altec was bought out in the 80's, but it's good to see they still made their stuff well.
No computer speakers I've seen nowadays have such a chunky driver and power supply. Seeing as my little Celestions with their 4" woofers could do with some help down low, I decided to make something of this, junking the tiny (albeit very solid) plastic cabinet. I can't justify setting aside beer money to buy/build a proper sub, hence this impulse project.
I plugged the driver into my trusty USB woofer tester to get the Thiele-Small parameters, and then used Bassbox 6 Pro to calculate cabinet size and port length given the tuning frequency. Surprisingly, the Fs was just under 50hz...rather good for such a tiny cone. The medium Q gave itself to either a big sealed box or a small ported box. Unfortunately I can't afford/can't be arsed to build a big box, so I opted for the smaller ported box. Which is handy as I had a rather solid orphan Technics speaker in the corner...once gutted it had an internal volume close enough to what Bassbox predicted.
The amp runs hotter than the Holocaust when pushed hard so it wouldn't be happy inside that box. So I just bolted it to the top with a little fan glued to it, along with the toroid. Oh, and I added a 10,000uF cap to the power supply to improve peak power demands. An empty tangerine box makes a rather good cage...don't want stray feet damaging it.
Sooo...it went from this:
http://i43.tinypic.com/24yo6ip.jpg
http://i44.tinypic.com/2dkfvas.jpg
to this:
http://i41.tinypic.com/2dlkbp3.jpg
http://i39.tinypic.com/2645qw7.jpg
in about an hour of furious ghetto productivity. Sound: obviously, not a whole lot of bass from a cone smaller than a dwarf's penis, but by ear it seems to be flat-ish to 40-45hz - about the tuning frequency of the box, as expected. However, it sounds quite a lot better than most computer subs...much more accurate and less boomy.
This isn't in my usual style of making speakers that look nice, but it was quick, dirty, cheap and sounds relatively decent. Like a low-rent prostitute, apart from the last bit. Thought I'd share it with DIY as thing have been a little slow recently.
Edit: And I can find my bloody measurement mic's cable, I'll post a quick-n-dirty response graph (with a buttload of room gain) for those few here who like pretty lines and numbers.
However, I was surprised to see it used a 6.5" Altec branded dual voice coil driver with a vented pole piece and had a nice big toroidal transformer. For amplification, it's got a 22wpc amplifier module with each channel driving one voice coil and a dedicted IC for dynamic range compression. Nice. Obviously this was made after Altec was bought out in the 80's, but it's good to see they still made their stuff well.
No computer speakers I've seen nowadays have such a chunky driver and power supply. Seeing as my little Celestions with their 4" woofers could do with some help down low, I decided to make something of this, junking the tiny (albeit very solid) plastic cabinet. I can't justify setting aside beer money to buy/build a proper sub, hence this impulse project.
I plugged the driver into my trusty USB woofer tester to get the Thiele-Small parameters, and then used Bassbox 6 Pro to calculate cabinet size and port length given the tuning frequency. Surprisingly, the Fs was just under 50hz...rather good for such a tiny cone. The medium Q gave itself to either a big sealed box or a small ported box. Unfortunately I can't afford/can't be arsed to build a big box, so I opted for the smaller ported box. Which is handy as I had a rather solid orphan Technics speaker in the corner...once gutted it had an internal volume close enough to what Bassbox predicted.
The amp runs hotter than the Holocaust when pushed hard so it wouldn't be happy inside that box. So I just bolted it to the top with a little fan glued to it, along with the toroid. Oh, and I added a 10,000uF cap to the power supply to improve peak power demands. An empty tangerine box makes a rather good cage...don't want stray feet damaging it.
Sooo...it went from this:
http://i43.tinypic.com/24yo6ip.jpg
http://i44.tinypic.com/2dkfvas.jpg
to this:
http://i41.tinypic.com/2dlkbp3.jpg
http://i39.tinypic.com/2645qw7.jpg
in about an hour of furious ghetto productivity. Sound: obviously, not a whole lot of bass from a cone smaller than a dwarf's penis, but by ear it seems to be flat-ish to 40-45hz - about the tuning frequency of the box, as expected. However, it sounds quite a lot better than most computer subs...much more accurate and less boomy.
This isn't in my usual style of making speakers that look nice, but it was quick, dirty, cheap and sounds relatively decent. Like a low-rent prostitute, apart from the last bit. Thought I'd share it with DIY as thing have been a little slow recently.
Edit: And I can find my bloody measurement mic's cable, I'll post a quick-n-dirty response graph (with a buttload of room gain) for those few here who like pretty lines and numbers.