How about the sealed box with "variovent"?

[7V]

I just read a posting in another place about the sealed box with variovent bass loading (stuffed port with the lower port resonance completely eliminated by the stuffing).

This is said to be less reactive than a closed box, has the same 12 db/octave rolloff but has a lower resonance and lower box Q for the same volume.

Of course, if the port was completely stuffed it would be a closed box design but I wonder what treats lie in the region between ported designs and closed boxes?

Comments anyone?

Steve

[Pete Mazz]

My understanding is you'll wind up with ~3rd order rolloff, and as you said, being able to use a smaller than optimal box size for a woof.

Pete

[SY]

They work best if you've got drivers with a highish Q that you want to control- like Dynaudio's 17W75 series.

Dynaudio also used them as resistive structures in the interior of asymmetric isobaric enclosures. One of the best speakers I ever built used a 30W54 on the outside, 21W54 on the inside at right angles to the 30W, with the 21W firing through a Variovent. Astonishingly clean bass.

[planet10]

Steve,

This is called Aperiodic loading... not a lot of quantitative work available on the subject.

Ted Jordan published the 1st paper (i believe) in Wireless World, February 1956, "A Cabinet of Reduced Size With Better Low-frequency Performance", and the 1st commercial products were the Goodmans ARUs (Acoustical resistance Units). The Dynaco A25 & A10 are probably the 2 most successful aperiodic designs (plans now available on my website). Bill Perkins of PEARL did a lot of research on aperiodic loading during the development of his PR-2. Besides lowering the Q wrt a sealed box of the same size, its biggest benefit is a flattening of the impedance curve, including a flattening of the 1st derivative of the impedance curve. This produces a less reactive loudspeaker which most amps will find easier to drive.

I have had good success with aperiodic designs for drivers that would otherwise have had to have been fitted to impractically large boxes.

dave

[kelticwizard]

Steve, (7V):

Post #11 by Navin is of special interest.
Subwoofer Qtc and 'tightness'

Navin made other posts about aperiodic boxes. I will try to dig them up.

[Nappylady]

I remember seeing some things in the Madisound that looked like air filters, but were sold under the premise that they would increase the leakage of the box (or something like that) and reduce box size by up to 50% or somesuch, without the danger of port noise.

Sounds like a grand idea to me. If I hadn't just been converted to the gospel of Dipoles, I'd jump on that bandwagon.

[kelticwizard]

I understand you can use more than one in a box as well. There were two big companies that made them. Dynaudio, I believe, called them variovent. They aren't made anymore, I don't think. The other company still makes them.

Edit: I guess that other company was ScanSpeak. Here's the Parts Express page. I have seen European dealers sell them also at about the same price:
http://www.partsexpress.com/pe/pshow...number=296-546

[Hybrid fourdoor]

Parts Express use to sell these things....think they were peerless units maybe....they were like <$8 each....don't know if they still sell them....but they can be made very easy. Even PVC with some foam or insulation would do effectively the same thing.

In "How to build great sounding stereo speakers" or whatever by David Weems, he explained that not alot of poeple used the design but it was effective in having the same properties as a sealed enclosure...ie, tight and not boomy, but did alleviate the impedence rise at the Fs or whetever. The graphs showed it to be pretty effective, made more of a rounded bump than the steep curve.

[Hybrid fourdoor]

Here we go I found it...its a scan speak unit @ $7ea...not bad, considereing it look alot more professional looking.

SCAN SPEAK 29001 FLOW RESISTANCE VENT

[planet10]

Take 2 pieces of plastic gutter mesh and sandwhich a piece of fiberglass between them. One variovent.

dave