Fighting cabinet resonace

[andy2]

I've just finished building a pair of semi-dipole speaker. There seems to be resonance that materialize itself as a midbass hum that makes male or female voice sound a little heavy or nasal though just a little.

The dimension of the internal size is 360 x 540 x 254 mm. The cabinet is made of 1 3/16 mdf thick so I don't think the problem is from cabinet flex.

I put some extra stuffings right behind the driver and it helps a little but make the bass weaker.

Here are a few pictures of the speaker:

http://www.geocities.com/hai_vu1/AcapellaCab.JPG

http://www.geocities.com/hai_vu1/CabinetRear.jpg

http://www.geocities.com/hai_vu1/RearNoStuffings.jpg

[GrahamT]

Wow, nice speakers.

Cant help with the resonance problem. I'm experimenting with cement on MDF right now but havent heard it yet.

[ThomasW]

How about providing some specifics regarding the crossover?

[Dennis H]

If that's an Acapella clone, you probably should have stuck with Troels' cabinet design. He put a lot of work into eliminating such resonances in both the dipole and ported sections using non-parallel walls, etc.

http://www.troelsgravesen.dk/diy_loudspeaker/The%20Acapella%20SE.pdf

That said, if the resonance is coming from the lower bass section, stuffing should help. It will do more good on the box walls (right, left, top, bottom, front, back) than right behind the driver. Leave a clear path between the driver and the port.

If it's coming from the dipole mid section, you'll probably need to make the wings smaller. Those are pretty deep for a midrange and I'd expect a cavity resonance that can't really be damped without losing the dipole behavior.

[andy2]

Dennis,

It is indeed the Acapella SE from Troels' design.

I don't think the resonance come from the side panels because when I disconnect the bass, I couldn't hear any. Although it's possible that the side panels vibrate because of the bass unit.

[andy2]

How about providing some specifics regarding the crossover?

Please check Troels website for the xover design or you could follow one of the link in the above post.