I like my Spendor S3/5 speakers except for the cabinet, which rings like a bell. I've tried some simple tweaks like placing a bag of lead shot on top. I would like to try a more dramatic tweak, and I was wondering if anyone has ever tried something similar.

Basically I want to construct an enclosure around the speaker, turning it into a double walled enclosure, and fill the space between with lead shot. I have some ideas about how to do this simply. The front baffle would be extended but would maintain a simple plane (no steps/edges added to it).

Any ideas? Any opinions on what this might do to the sound?

Mike

If you’re going to go through all that effort, why not just build all new cabinets? The only three things that you need to do are ensure that the baffle is the same shape (HxW), the box volume is the same, and the port length and diameter are the same. The trick will be removing the drivers and particularly the crossover without destroying the cabinet.

If you try and sheath the outside of the cabinet as you propose you will have to make the baffle taller and wider, which may affect the frequency response.

Instead of lead shot…try searching for constrained layer damping materials. You might be able to apply a thin layer of material between two layers of MDF and achieve much better damping than with shot.

Just my .02

Mike

Hi, thanks for the information.

Perhaps you are right. Do you have any good sources for damping materials, particularly constrained layer?

One problem in maintaining W and H is that the cabinet is barely wider than the bass driver. A double-walled cabinet is not really possible if it will result in thicker walls.

This would destroy the existing cabinet but I could also use metal as the constraining layer and attach the damping material directly to the outside of the cabinet; then it wouldn't change the baffle shape much.

thanks,
Mike

I read the review in Stereophile…it looks like the largest resonance is on the rear panel. Instead of destroying the nice exterior of the speaker try just addressing that panel. You could use the blue-tak between the speaker and the stands. Then cover the rear panel with damping material. There are several varieties of constrained layer damping material out there that are primarily intended for use inside the speaker to damp rear wave reflections. I think they would work just as well on the exterior of the cabinet. Try covering the rear panel with some blackhole 5 or whispermat and see if you can detect the difference. It would be a easy way to see if you are hearing that resonance.

The constrained layer damping works best between two layers of stiff material. The constrained layer absorbs the energy as it tries to pass between the two stiff surfaces. The stuff like BH5 and Wispermat do this by sandwiching a layer of foam like material between the wall of the speaker and the outer layer of vinyl like material. The energy has to pass through the foam and resonate the vinyl.

You should really try and determine if you are hearing the panel resonance or just some artifact of you room acoustics or an inherent property of the drivers. If it has something to do with the room placement or a breakup mode in the driver…a completely inert cabinet will not help.

For some really interesting reading on cabinet design try this article: http://stereophile.com/floorloudspeakers/904rockport/

mike

Thanks for the info. The reason I think it is a cabinet vibration is that I put my ear against the speaker and I could hear two pitches clearly where the cabinet rings like a bell (some chamber music for solo strings demonstrates the exact pitches quite nicely). Then in normal listening I can hear the same pitches ringing.. it is those pitches that bother me. Does that sound like a cabinet vibrational resonance? Or could it be the standing waves in the cabinet? I think the frequencies are about 125 and 500 Hz. The former could not be a standing wave as it corresponds to a wavelength of 8 feet. The latter might be the top-to-bottom mode of the cabinet (cabinet is about 12 inches high so wavelength would be 2 feet), although I hear a clear ringing (a sense of a note being held about a second after it ends because it is still ringing) that does not sound like a standing wave to me.

You have some good ideas. Thanks, Mike

I think you are correct…that sounds like a panel resonance. Even if it’s a standing wave at 500hz you would primarily hear it out the port or the driver opening. Ditto if it was a driver resonance.

You could rebuild the enclosure with the same wall thickness and just add a several internal braces to stiffen the walls. You just make it a tad deeper to offset for the volume of the new braces.

BTW there are a lot of great TM DIY designs out there from this website as well as HT Guide forum. Not to knock your speaker, but you can get a lot higher quality driver and crossover components for your money if you are willing to build the cabinets.

Have fun.

Mike