Bass reflex cabinet tweaks - stuff or line

[nfafan]

Quick question please; have read that for bass reflex, you want to line the inside cabinet walls with sound deadening foam to reduce reflections, vs. poly-fill fluff stuffing the entire cabinet..

Any truth to this?

And if lined - on all the interior surfaces, or; just the tops, bottoms, sides, and back wall directly across from the back of the drivers?

Thanks!

[Feanor]

Quick question please; have read that for bass reflex, you want to line the inside cabinet walls with sound deadening foam to reduce reflections, vs. poly-fill fluff stuffing the entire cabinet..

Any truth to this?

And if lined - on all the interior surfaces, or; just the tops, bottoms, sides, and back wall directly across from the back of the drivers?

Thanks!

Based on advice from my BassBox Pro program, a reflex box ought to have the sound-absorption only on the walls so the air may move freely to the vent. Sealed-box is fine with a full "fluff" filling.

Both wall lining and full-filling have effect of making the box acoustically bigger than it actually is, the more more liner/fill the greater the effect. The usual advice if using wall lining is that it ought at least to behind the driver(s) on the rear wall plus one side and either top or bottom. Or some variation of that: maybe band of lining all the way around nearest the driver, plus top or bottom.

[nfafan]

Thanks! That pretty much matches what I thought for sure that I read in the past. And explains the paucity of foam that comes with "kit" bass reflex speakers such as from Parts Express...

[Dual-500]

To add a bit more. As posted above, damping materials makes the enclosure acoustically larger. To hit optimum damping is a balancing act between enclosure size, tuning and the Vas of the woofer. Vas is Volume Air Space or the compliance of the driver - the suspension, coupled against the moving mass = the same volume of air.

If the enclosure is optimum volume to correctly match up with the Vas and enclosure volume/tuning then lining is good. As enclosure size is reduced relative to the Vas, then the damping must be increased via damping materials. The trade off is overall efficiency. More damping = less efficiency.

There are other things that change as well when increasing damping in overall tone or character of the sound when taken to extremes.

This is why the loudspeaker enclosures of today are much smaller in size than those of yesteryear. Today we have monster amplifiers and drivers with much higher power handling capacity.

Woodstock probably had less than 1000W on the mains. Today there are stage monitors capable of handling 1kw. A touring system at a show like that today would have in excess of 100KW on the mains.

[nfafan]

Thanks guys! Have some experimenting to do soon!

[Dual-500]

My post above was somewhat abbreviated - hope it reads ok.

There are many good books out there that explain tuning of a reflex enclosure. You can download applications that will turn your computer sound card into a signal generator. A small amplifier is all it takes to drive a test setup. A voltmeter and an 8 ohm resistor, a few alligator clip leads for the setup.

The process is quite simple, however the final adjustments (tuning parameters) are where expertise and experience come in to play. That being said, go for it and have some fun. I've gone full circle with it. From DIY systems years ago, to commercially available stuff for years and finally back to customized stuff. The subwoofers in my den are JBL professional drivers in a JBL factory enclosure for now. To finish the build up, I will make custom enclosures with different dimensions, with same volume and tuning as the JBL for the subs and maybe tweak the low mid enclosures, and horns for top end.

That's another area that I found really interesting is horns.

Building it yourself is just a lot of fun for some.