Aperiodic vented box for sub, any good?

[TEK]

Hello

Just curious to hear if any of you have heard or tested the use of Aperiodic vented boxes for subs.

Stuff before edit, just ignore:

Not sure if "acoustic vented sub box" is the correct english term, so let me try to explain.

It's a opening in the cabinet that is damped or filled so that it only allows some air to pass trough.
In a closed cabinet this is supposed to give you a lower Q without affecting the resonance frequencey.

Should possibly works as a alternative to damping the box.

So, what do you folks think?
Is it any good?
Do you know about simulation tools that calculates the effect of this? Anyone tested it and found it good or not so good?

Edit: Changed title and use of terms based on first feedback.

[Landroval]

Not sure if "acoustic vented sub box" is the correct english term, so let me try to explain.

Aperiodic vent/box is the word you're looking for.

[Feyz]

Is this what you are asking: what happens if I use a ported box, but stuff the port with something like fiberglass to restrict air flow?

If that is the question, you can model it with something like WinISD Pro, by decreasing the value of Qp (port's Q). It can be accessed from Box tab->Advanced-> part of WinISD. Default comes with Qp = 100, which means port loss is low by default, little resistance to air flow inside port. By decreasing this you are adding resistance in the port. If too much resistance is added be decreasing Qp to a very low value, it will turn into a closed box. Decreasing Qp has these effects from what I have tried: Excursion at box tuning is increased, F3 is increased, the first impedance peak is decreased, group delay is lowered. In other terms as you increase the port resistance, the box gradually transforms from a ported box into a closed box. Doesn't seem to me a good thing to do.

I have some ready SPICe models if you want to play around more, not as user friendly as WinISD though. You can access them from here:

http://www.geocities.com/pirimoglu/SpeakerSPICEModels.html

The PortedBox2.asc file models a ported box. In there, the circuit model has a Map_ inductor element, which represents the port acoustic mass. If you right click on it and add some "series resistance" like 10K, it will do the same trick as decreasing Qp in WinISD. In there if you decrease the port length to like 0.01meter, and keep the series resistance of Map_ high, you get a aperiodically damped closed box. Advantage over a regular closed box seems to be a lower impedance peak value, if it is an advantage. It will drive more current because of reduced impedance peak. You can model the same thing in WinISD by chosing a high box tuning that gives you a small port length and keeping Qp value very low.

One big problem in all these simulations is I have no idea what a real variovent's acoustic resistance value or a port's that is stuffed with fiberglass acoustic resistance value in reality is. Or what is a realictic Qp value for a stuffed port is, which is the same problem. It could be tried, tested and learned but I don't have neither the means nor the desire at the moment

In case you may ask what is a variovent, it is what Dynaudio used to call, make and sell as a flow resistor device: a circular vent that has a layer of fiberglass trapped in it. Such a device is still made by Scan-Speak, and avaiable from Scan-Speak distributors like Madisound:

http://www.tymphany.com/scanspeak/accf.php

[David R.]

Im familar with AP membrane enclosures.. Its basically a Infinite baffle with a "membrane" over one side of the speaker.

this type of enclosure is quite popular in the Sound Quality car audio Competition scene.

A example of a in car AP setup:
ruff IB work:

http://www.mts.net/~dreddy/AP%20sub/APsub.jpg

AP mat construction:

http://www.mts.net/~dreddy/AP%20sub/Apmat.jpg

AP mat installed:

http://www.mts.net/~dreddy/AP%20sub/finap.jpg

The idea for it is to have a low-q system, using drivers that dont have the suspension for IB, so the membrane helps control the cones movement at (or around) FS during high volume levels.

I dont really see this for a home situation though..