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