Updates:
22 May 2005: I just measured a pair of these woofers that I bought a
few years back but never used. They came out at about Fs=116Hz,
Qts 1.05, which is significantly different from what my original pair
measured. This will have a definite effect on the sound under 100Hz,
so I don't recommend building this design.
Design Goals
These started out as a version of Adire's Pop. Well, I built them,
and to be honest, thought they sounded like crap. There was no bass,
no coherence between the drivers - in short the sounded like a $40 speaker
from Best Buy. Actually, there are better $40 speakers for sale at Best Buy.
So, a year after I gave up on it, I set out to redesign it. I needed a small, shielded speaker to use with my computer. So, here we go...
So, a year after I gave up on it, I set out to redesign it. I needed a small, shielded speaker to use with my computer. So, here we go...
Drivers
Not much to say. They're the 55-1840 carbon-fiber woofer from
MCM and the Vifa
D19SD-05-08. Same as the Pop.
By the way, the 55-1840 is an mediocre woofer (due to its size) but would make a helluva midrange for the price!
By the way, the 55-1840 is an mediocre woofer (due to its size) but would make a helluva midrange for the price!
The Box
I built the box different from what's on Adire's web site. Since I wanted
to keep the front of the box as small as possible, I put the port on the rear.
The box is 9.125"x5.5"x10.5" (HxWxD, external). The front and back are
3/4" thick, while all other sides are 1/2" thick. The edges are rounded
1/4" for aesthetic purposes. You can use 1/2" or 3/4" MDF all the way around, just be sure to adjust
the dimensions of the box to maintain the same volume.
The port is 1" diameter by 1.75" long. It was made by adding two 1/2" thick pieces of scrap about 2" square on the inside of the rear of the speaker and drilling through. This is different than the port shown on Adire's site, because that site is wrong (their length is correct for a 1.5" diameter port, not the 1" port they show on the site.)
The drivers are both centered on the baffle. The tweeter's center is 7" from the bottom. The woofer's center is 2.75" from the bottom. (The box below is still using the old too-long Adire port.)
The port is 1" diameter by 1.75" long. It was made by adding two 1/2" thick pieces of scrap about 2" square on the inside of the rear of the speaker and drilling through. This is different than the port shown on Adire's site, because that site is wrong (their length is correct for a 1.5" diameter port, not the 1" port they show on the site.)
The drivers are both centered on the baffle. The tweeter's center is 7" from the bottom. The woofer's center is 2.75" from the bottom. (The box below is still using the old too-long Adire port.)
The Crossover
Nothing exciting. Looks like Adire's, but all the values are different.
I think Adire didn't add any baffle step compensation, which, combined with the typo
in the port specifications, explains the absence of bass. Note polarity
reveral on the lowpass.
Lowpass...
Highpass...
If you use the 18 gauge red wire coils and Dayton caps from Parts Express, you should be able to get the drivers and XO for $85 + shipping and handling. Total cost to build shouldn't be more than $100/pair.
Again, this compares favorably with the Pop, which is supposed to cost less than $100. But they used odd component values, which means you'll have to combine multiple caps and coils to get the right values. Even with cheap parts, the Pop costs about $125/pair.
Lowpass...
Highpass...
If you use the 18 gauge red wire coils and Dayton caps from Parts Express, you should be able to get the drivers and XO for $85 + shipping and handling. Total cost to build shouldn't be more than $100/pair.
Again, this compares favorably with the Pop, which is supposed to cost less than $100. But they used odd component values, which means you'll have to combine multiple caps and coils to get the right values. Even with cheap parts, the Pop costs about $125/pair.
Conclusions
They are still a bit bass-shy, but I think this is because of the rear
port combined with relatively high port frequency. Flip them around and
there's bass galore.
If you use them with a subwoofer (a real one, not some computer sub) and an old stereo receiver or amplifier, you will have computer speakers that will smash your friends' little plastic boxes, no matter how much they paid for them.
Here is the measured impedance. The low is 5.5 Ohm at 4700Hz. The phase swings a bit bit it should be no trouble for any solid state amp.
If you use them with a subwoofer (a real one, not some computer sub) and an old stereo receiver or amplifier, you will have computer speakers that will smash your friends' little plastic boxes, no matter how much they paid for them.
Here is the measured impedance. The low is 5.5 Ohm at 4700Hz. The phase swings a bit bit it should be no trouble for any solid state amp.