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Old 6th October 2010, 01:20 PM   #1
IG81 is offline IG81  Canada
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Default Need advice on the execution of an aperiodic vent

Hi,

I am building aperiodic enclosures for a pair of Philips AD7060 6" fullrange drivers I have.

The initial sealed box, unstuffed, should yield a Qtc of 0.84. I expect that with stuffing, this figure should be down to around 0.8. My goal is to get it down between 0.65-0.7 with an aperiodic vent. I would like to execute this in a well-controlled, tuneable and/or progressive manner in order to adjust response until I'm satisfied and am juggling between a few options.

First, I thought of drilling ~" holes progressively and inserting punched open-cell foam cylinder in them. As a progressive procedure, that would work great and have well-controlled resistive material density, but I am questioning the suitability of open-cell foam, as it seems a biit too loose, what do you think?

Second, I could go the gutter-mesh + fiberglass sandwich way, but how to make it tuneable? Somehow change the exposed surface area or change thickness of sandwiched material for a same area?

Thanks,

IG
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Old 6th October 2010, 02:14 PM   #2
Henkjan is offline Henkjan  Netherlands
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I have once made a vent from a small, shortened bass reflex port and stuffed it with wool. easy to adjust by just adding or removing wool
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Old 6th October 2010, 06:00 PM   #3
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While more work than the other techniques (i've tried them all), the foam behind the array of holes works best for me. You do have to have the right kind of foam (i fortunately have lots -- a specific part of the paking from Apple service boxes). I've been spreading it around by using as packing material on outgoing shipments.

dave
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Old 6th October 2010, 06:31 PM   #4
IG81 is offline IG81  Canada
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Quote:
Originally Posted by planet10 View Post
While more work than the other techniques (i've tried them all), the foam behind the array of holes works best for me. You do have to have the right kind of foam (i fortunately have lots -- a specific part of the paking from Apple service boxes). I've been spreading it around by using as packing material on outgoing shipments.

dave
I too am collecting packaging foam, from a pharmacy in the same building that I work in. They are blocks of ~10"x6"x4" (iirc) of rather dense, grey, open-cell foam. Lots of cool things to do with those.

After giving it some thought I've settled on a circular fiberglass + gutter mesh sandwich, adjustable from the exterior. I can see how I can make it to be either too little or too much, so I should have the whole usable range in between to work with. Part of the reason I settled on that is that I bought a 20$ 4" DeWalt hole saw, and I'll be damned if I'm not gonna be usin' it!

IG
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Old 6th October 2010, 08:19 PM   #5
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Quote:
Originally Posted by IG81 View Post
I too am collecting packaging foam, from a pharmacy in the same building that I work in. They are blocks of ~10"x6"x4" (iirc) of rather dense, grey, open-cell foam. Lots of cool things to do with those.
Sounds similar. Mine are ~3" x 1.25" x long

Quote:
After giving it some thought I've settled on a circular fiberglass + gutter mesh sandwich, adjustable from the exterior. I can see how I can make it to be either too little or too much, so I should have the whole usable range in between to work with.
I have found that long & skinny (ie a slot) works much better with the gutter mesh. It is not stiff enuff to adequatly squish the fiberglass in the middle of the circle.

dave
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Old 6th October 2010, 08:54 PM   #6
TerryO is offline TerryO  United States
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Another thing that you could try is the method developed/promoted by the late John Wyckoff using Mr. Coffee filters in layers. Add to or remove to suit your taste.

Foam or filter, they both work.

Best Regards,
TerryO
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Old 7th October 2010, 12:50 PM   #7
IG81 is offline IG81  Canada
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Quote:
Originally Posted by planet10 View Post
Sounds similar. Mine are ~3" x 1.25" x long



I have found that long & skinny (ie a slot) works much better with the gutter mesh. It is not stiff enuff to adequatly squish the fiberglass in the middle of the circle.

dave
At the moment, I plan on a 4" diameter hole through the back baffle, directly behind the driver, with a square piece of 3/8 ply glued inside the baffle in which will be the actual vent hole of 3" diameter. I will install the 4" diam guttermesh - fiberglass - guttermesh sandwich recessed into the baffle, held on by a 4" OD - 3" ID 3/8 ply ring. This is not a really big area, ~7in^2, but my design is not too compromised to start with, so I thought I could still get by with it. I can make a test sandwich before drilling into the baffle to see how it works at this diameter, compression-wise. Then I'll make me a turkey sandwich cause all this talke made me hungry!

I should be able to get some work done tonight, I'll post some pics.

IG
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Old 7th October 2010, 01:59 PM   #8
oublie is offline oublie  United Kingdom
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Quote:
Originally Posted by IG81 View Post
Hi,

I am building aperiodic enclosures for a pair of Philips AD7060 6" fullrange drivers I have.

The initial sealed box, unstuffed, should yield a Qtc of 0.84. I expect that with stuffing, this figure should be down to around 0.8. My goal is to get it down between 0.65-0.7 with an aperiodic vent. I would like to execute this in a well-controlled, tuneable and/or progressive manner in order to adjust response until I'm satisfied and am juggling between a few options.

First, I thought of drilling ~" holes progressively and inserting punched open-cell foam cylinder in them. As a progressive procedure, that would work great and have well-controlled resistive material density, but I am questioning the suitability of open-cell foam, as it seems a biit too loose, what do you think?

Second, I could go the gutter-mesh + fiberglass sandwich way, but how to make it tuneable? Somehow change the exposed surface area or change thickness of sandwiched material for a same area?

Thanks,

IG
I'll be following this with interest, I have a set of ad8080's - the 8 inch version of your speakers - how did you work out what size box to use - have your found the t/s parameters somewhere or did you measure the speaker?
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Old 7th October 2010, 03:12 PM   #9
IG81 is offline IG81  Canada
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Quote:
Originally Posted by oublie View Post
I'll be following this with interest, I have a set of ad8080's - the 8 inch version of your speakers - how did you work out what size box to use - have your found the t/s parameters somewhere or did you measure the speaker?
I measured the T/S parameters myself. I found few useful references to this driver online, which would have been for interest mainly, as it is recommended to measure parameters of a specific driver, especially old ones, for better accuracy.

I use WinISD for simulation. I simply modeled a sealed enclosure with a higher Qtc than what I want, in order to have a smaller box, details in the first post of this thread. The aperiodic part of the design can be modeled with the leakage factor "Ql" I believe, but I do not really know how much of this metric to input. I will design it by trial and, quite possibly, error. I guess when my design is complete, I could compare with the WinISD sim to see how much Ql is needed to represent my actual aperiodic vent.

The same technique I use to measure T/S parameters will be used to measure the whole system's Fc and Qtc with varying amounts of fiberglass until I am satisfied.

For Dave: I found a section on one of your pages about different Philips FR's a while ago, but cannot re-locate it. It seems you have a bunch of these pages I discover through a link once in a while, that are not obviously accessible through the main website page. Not complaining here; I find it makes it kinda interesting!

IG

Last edited by IG81; 7th October 2010 at 03:15 PM.
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Old 7th October 2010, 03:39 PM   #10
oublie is offline oublie  United Kingdom
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Welcome to www.oudio.nl !

You may have seen this already but i thought id post it in case you were interested.

Click on brochures and then educational. The ones of interest are the loudspeaker brochures which contain box building plans and measurement graphs.


I'm having a lot of difficulty finding t/s data for my 8080/m8's so i'll probably end up measuring as well.
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