What is the ideal sealed qtc? Anyone have luck with an aperiodic setup?

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What is the best all around in car qtc? I know subs for automotive applications work best with a higher qtc then home apps...but I dont know how much. Around .7-.8 or so? I dont want it boomy, I prefer SQ over SPL. But at the same time want to preserve as much trunk real estate as I dont have very much to begin with (about 10cuft.)

Also, to shrink my enclosure further, I was considering making or buying an aperiodic vent. Any tips or advice on this subject would be greatly appreciated.

I have a beautiful linear power dps350, and a pair of 'so so' ID10's that have been sitting around for years that I want to reinstate into duty.
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GuyPanico said:
Also, to shrink my enclosure further, I was considering making or buying an aperiodic vent. Any tips or advice on this subject would be greatly appreciated.

I've built a few aperiodic boxes with good end results (all for the home thou).... th ereceipe is pretty simple. I use the plastic gutter mesh & squash fiberglass insulation between two pieces in a slot. This idea is borrowed directly from the Dynaco boxes.



the better sounding setups I've heard had a sytem qtc. of .7 or lower.....if you're a really close listener .8 or higher may be a little boomy but not offensively so....the smaller box you'll need for a lower qtc. will improve you're power handing a small amount...
aperiodic set ups are cool....if you don't want to build one you can buy them from madisound or speaker city
focal makes them and so does scan speak if i'm not mistaken
a single 10 inch sub may require 2...dynaudio used to make them too...they called them variovents
they work great but the smaller your box with the aperiodic set up will yeild a lower sensitivity a small amount as well
Thanks guys. I think what I'll do is shoot for .7 or so WITHOUT taking into account the aperiodic membrane. Then i'll play with the membrane to find the most pleaseant sound. If it increases the percieved volume by 25%, that will bring the .7 down to .65. Not terribly much difference.

Image Dynamics recommends a volume of .7cuft. Which comes out to .8qtc. I wasn't at all happy when I built a box that volume. It was boomy and didn't seem to extend low, or very smoothly.
Hi ya,

not sure if you are still planning this, but a few pointers:

For AP, you really want a sub with a QTC of below .45 (other units can work, but for a safe bet)

With AP the front and rear air space should be independent to avoid acoustic short circuit.

AP (if you didn't know), will smooth response at the expense of low end extension.

The enslosure should be as small as is absolutely possible.

As a rough guide the membrane should be at least 1/2 the cone area.

The membrane can be mounted on either side of the sub.

HTH, let me kknow if I can help any more :)
Hi Guys,

An Aperiodic vent will reduce system Qtc slightly.

So, if you design for a sealed box system Qtc of 0.9, and add an Aperiodic vent to the enclosure, system QTc should drop to about 0.7.

If you wanted a system Qtc of 0.9, design a sealed box for Qtc = 1.1, and add an Aperiodic vent to lower Qtc to 0.9.

Isn't that a bit general? Vent area, permeability, and the actual volume of the enclosure should make it very difficult to calculate the resultant QTC. At least I would believe so with that many variables.

Matt: Yup, i'm still thinking about going with an aperiodic setup. I'm hoping to finish up a project i'm on very soon, and then start on this one. The only thing I hate about the AP setup is having to seperate the vent from the listening area. How do dynaco speakers get away with having the membrane in front with the driver? This is what confuses me the most about AP setups. I see home speakers using them, and I also read how it's necessary to seperate vent to prevent interactions with the driver.
It is very general... You cant guess the Qtc that easily

Here's some ideas of mine...

Try out the aperiodic with the "vent" open to the same space as the driver. I doubt you'd notice a difference between that and it not being in the same space.

If you really want a low Qtc and dont want to occupy your entire trunk with a speakerbox then you can simply use the entire trunk as the enclosure and mount the speaker between the trunk and cabin. (aka IB or freeair, although I really doubt its an ideal IB if your trunk is only 10cubes and free air to me says open baffle)
I'm still confused as to how Dynacos and other speakers have no issues with the driver and membrane radiating into the same space, but everywhere I read it says they must be seperated. Seperating them makes sense to me, but at the same time I see successfull designs doing otherwise. Must be a simple answer, I just dont see it :whazzat: Please educate me! :)
I have never quite got my head round this, I think it's mainly to do with air pressure - in a car most people use AP mat's for subs, where obviously there are much greater air pressures at play. The small variovents etc produced by SS and Dyne seem to be for midbass/mid duties, where the air pressure is much less, and perhaps any accoustic short circuit effect is minimal.

Mind, it might just be becuase, as they say - 'there are no rules in car audio, the strangest things work'.

N.b. I'm not sure who the 'they' in 'as they say' actually are :D
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