Some help with 10" sub design...?

[arcturus]

Hello all

Currently, I'm building a pair of 2-way bookshelf speakers with Vifa's TC-line drivers. The bass/midbass is only 5,5" (TC14WG49), so I'm thinking of building later somekind of a sub-woofer to play the lowest frequencies of music.

I planned about buying an 8" Peerless SLS woofer, but then I got this almost unused Focus Acustics 10" woofer from a friend for a cheap price. She didn't have its T/S parameters, so I decided to test it with Speaker workshop:

Qts: 0,735
Qes: 0,826
Qms: 6,658
Fs: 36,50 Hz
Vas: 21,16 liters

Nominal impedance: 4 ohm, single voice coil


The parameters look somewhat strange, is it recommended to mount such a high-Qts woofer into a bass-reflex box? I thought about 50L box tuned to 24 Hz, that combination would make the -3dB point @ 22-24 Hz... I gave also a thought for aperiodic and sealed designs (with similar 50L box), as they would reduce the group delay considerably. What do you think? Perhaps bass-reflex for movies, aperiodic & sealed for music?

Even though you don't actually listen to the _look_ of a woofer, at least for me, it looks very stable and "capable" unit. It has really fat foam surround and quite nicely of Xmax, cast basket and a big magnet. It weighs about 6,6 kilograms. I attached a pic of it...

[johninCR]

If it's not shielded and has a big magnet, then you should double check those T/S parameters, because a large magnet indicates better cone control at resonance which is the opposite of what a high Qts like .735 indicates.

[454Casull]

Originally posted by johninCR
If it's not shielded and has a big magnet, then you should because a large magnet indicates better cone control at resonance

Not necessarily.

[johninCR]

Originally posted by 454Casull

Not necessarily.

If I've learned something wrong, please provide some examples.

[BillFitzmaurice]

I also would be very surprised to see a Qts of more than .3 on a driver with that large a magnet structure and that low of a Qms. The 4ohm impedance could mean it's an autosound driver meant for an IB, but then the Qms should be a lot higher. I'd research those specs or measure them yourself before proceeding.

[Vigier]

Hey,

the woofer on the picture really looks like a Raveland AXX-1010 woofer, about 55 Euros (say $70)....

Grtz, Joris

P.S. Focus Acustics 10" doesn't ring a bell here... is that sold in europe?

[arcturus]

Well, I don't know where my friend got this woofer, but it is most propably automotive subwoofer. She asked 35 euros for it and then it was mine

Perhaps I should test its parameters again, when I've got some time (and a concentrated mind). I don't know where it's sold, nor know it's published parameters (there aren't any?)... I can't even find the manufacturer's website!

The Raveland model looks quite different, in my opinion...

[arcturus]

Even though it doesn't show in the picture, the woofer's dust cap was pretty much "smashed". So I just carefully removed it and replaced the broken dustcap with a cap from dead JBL GT2 12" woofer. I glued it in place with 2-component super epoxy glue, to ensure it stays in place. Then I painted it with black spray paint.

I did this fix because the broken dustcap made a sound, even in lower sound levels... of course, if it was a 300 euros Scan-Speak woofer, I wouldn't dare to attempt!

However, the cone's mass seem to increased a bit, here are the new parameters from Speaker Workshop:

Fs: 29,8 Hz
Vas: 42,144 L
Qts: 0,617
Qms: 3,617
Qes: 0,743


I did the testing two times, and got almost precisely same results. So, my previous results were wrong, maybe because of wrong added mass during the calculation of Vas.