Damping materials for speaker cabinets?

[planet10]

This is a transmission line right? Stuffing the line makes the line "longer" - retuning it, so I assume you tune that by measurement to the intended frequency. Stuffing = tuning in a t-line.

The latest research shows that this is not true -- that stuffing a line slows down the speed of sound is starting to look like a classical design myth. Stuffing the line does not move the fundemental resonance, it damps the ripple.

dave

 

[planet10]

Re: Damping in sealed vs ported

But you also asked about polyfill - isn't this stuffing (rather than damping?)

As determined from the sample you sent me polyfill = BAF wadding

It impedes airflow - slowing down the air and changing the resonant frequency of the air mass inside the cab while absorbing energy.

This is probably a somewhat inaccurate way of saying it. The damping material converts acoustic energy into heat, and thus makes the box behave as if it were a somewhat larger unfilled box. I doubt that it slows the air down at all -- just reduces its energy.

dave

 

[TheoM]

Design Myth: I buy it

I recently read an authorative sounding article that claimed this but I buy its a design myth. If the stuffing were denser sound would travel faster, not slower, right? Its right up there with Thermal momentum.
🙂

 

[planet10]

Re: Design Myth: I buy it

If the stuffing were denser sound would travel faster, not slower, right?

No, stuffing in the line has close to negligible effect on the speed of sound. Geometry thou can have a profound effect on the resonance footprint of a line.

dave

 

[7V]

Re: stuffing or padding?

Sealed: Stuff it. Kill the backwave. Actually, I'd add a low end damper to the walls like that roofing felt (stuffing does not do well with low end), hanging loosely along the walls, AND stuffing. I've seen high end sealed cabs stuffed to the gills - packed tight. Some people advocate for moderate stuffing which I read as 1/2 full - but I'd fill it up without packing it in, so to speak.

I don't think so Theo. "Kill the backwave" and you kill the speaker.
This is an extremely high end speaker using the best full-range units that money can buy (in my opinion). They're "open back" (conventional) cone drivers which go all the way to over 20kHz. I'm not sure exactly why but experience with my original speaker taught me that too much stuffing deadened the sound.

I'm amazed at how good the new cabinet sounds without any stuffing or padding at all. I will test them using measurement and ears for over stuffing, no stuffing and in between. Ditto with padding. I was just interested to hear other people's formulae for reaching the optimum amount of stuffing and padding (assuming that the cabinet walls are already damped so they don't vibrate significantly and, therefore, bracing is not an issue).

Steve