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Old 7th January 2007, 10:28 PM   #1
Geoff H is offline Geoff H  Australia
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Default Aperiodic enclosures

Hi all. I have a question on aperiodic enclosures.

How much audible energy would you expect from the port?

I vented a system yesterday, still doing listening tests. Have done the classic boing, bonk, click test. Damping is very close to optimum with a sharp click on open circuit.

But I have deep mellow sounds radiating from the port. I thought the idea was to absorb it. So the real question is more to do with a heavily damped BR versus aperiodic.

I am very satisfied with the sound. I don't want to change it just to fit the criteria of a design.

Regards,

Geoff.
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Old 7th January 2007, 10:43 PM   #2
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Not sure,

I have made a couple of aperiodic enclosures and I love the sound quality. On one I just used the Scan Speak aperiodic vent so I did no tuning. To me this vent looks like a 3/4 inch thick piece of fiberglass insulation smashed flat into a 1/8 - 1/4 inch thickness between two pieces of mesh.

The other one was a home made aperiodic vent. I just varied the material until I got the optimum sound. But the trick is that it needs a thin but uniform amount of resistance for the vent.

If you are stuffing a port it is easy to put too much stuffing in there and the box essentially performs like a closed box. If you have access to inside the speaker box it works best if you disgard the tuning port if there is one and glue or staple a piece of aluminum or nylon screen door material over the hole from the inside. Then you need to make a removable cover for the outside with lots of holes in it. Kind of like a speaker cover or some mesh. A tweeter cover works well for this.

Then loose stuff some polyester or cut a round piece of fiberglass insulation to go in there. The stuffing should not be very dense as it needs to breath rather well.

The outer cover of course needs to be removable so that you can vary the stuffing. If you use polyfill it is easy to put too much in there and have the vent be too resistive but it is easy to experiment with.

Also, I think it's best if the psuedo port is not tuned anywere near a low frequency because it may try to act too much like a hemholtz resonator at low frequencies. It should just be a hole in the cabinet with no tube.

The aperiodic vent is not really supposed to absorb any sound coming from the port as much as it is meant to be a variable acoustic resistance so the speaker cabinet acts kind of like a combination of infinite baffle and closed box. It's like the shock absorber on a spring more or less.
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Old 7th January 2007, 10:50 PM   #3
Zen Mod is offline Zen Mod  Serbia
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Scan Speak /Dyunaudio Variovent?
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Old 7th January 2007, 11:56 PM   #4
Geoff H is offline Geoff H  Australia
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Hi Zen, those and Dynaco A25 and 35 etc.

These are actually my modified Wharfedales. The ones modded to use in lieu of 511s on my 811s. Even with the short 8 ohm vc they still go deep. And loud and clean. And true full range. Did my 24/7 thing last knight. Went for the volume control at 6 this morning, then the coffee.
No listening fatigue.

Cheers,

Geoff.
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Old 8th January 2007, 12:31 AM   #5
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Hi,

On this topic, does anyone have any good resources for Aperiodic enclosures?

Does the loudspeaker design cookbook have much info on Aperiodic?


I found this tid-bit:

Aperiodic Enclosure - an otherwise sealed enclosure design, but with a vent that is stuffed with damping material, which flattens out the impedance curve of the design. The area of this resistive vent should be about 10 sq. in. per cubic ft. of enclosure volume. This design might take some experimentation with the vent stuffing, testing the impedance curve several times with different amounts of damping material until the flattest impedance curve is found. The aperiodic resistive vent damps the driver in much the same way as fully stuffing a sealed enclosure with damping material (100% fill). In this way, an optimum design may be made up to 20% (or more) smaller due to the extra damping of the resistive vent. Enthusiasts of this design often compare the performance with transmission line enclosures, advocating that the design avoids the "ringing" effects of ported enclosures while alleviating the "pressure effect" of the sealed box. Dynaudio sells a DIY insertable resistive vent called the Variovent.
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Old 8th January 2007, 12:43 AM   #6
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However,

If you look at the amount of material in a Variovent and compare it to a stuffed port you will find a big difference. Since Vance Dickison doesn't seem to have much experience with these designs. Hence the little amount of information, I chose to assume that Dynaudio had done a lot more empirical testing.

And in the end I assume that it is the level of resistance and amount of flow that matters. What really takes the cake though is instead of making an aperiodic enclosure really small is to make it as big as you can and combined with the vent it mimicks an infinite baffle or critically damped design. Fast transient response and quite neutral.
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Old 8th January 2007, 01:15 AM   #7
holdent is offline holdent  Canada
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Although I haven't tried it, Martin King's MathCad worksheets allow you to simulate an aperiodic vent or stuffed port. It would probably be a great starting point to get anyone "into the ballpark" when building. You'd just have to spend a little time fine tuning it in the end.
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Old 8th January 2007, 01:29 AM   #8
Geoff H is offline Geoff H  Australia
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Hi GG, it seems to be a black hole. One we may have to paint!

My first encounter with aperiodic was when I was a kid. We had a pair of Wharfedales in large cabinets, about 4 or 5 cub feet. The rear panel had a series of slots almost the width of the cabinet, about 1/2" wide, and 1" apart, and lined with felt.

That's a huge cabinet compared to an A25. Your reference to port size would be in line with those cabinets.

I figured a 2" diameter port would tune my 1 cub ft cabs to 38Hz. (driver res) Rather than a 2" hole, I went to 16 1/2" holes to provide a distributed which has a wider bandwidth. The cabinet is lined with fibrefill, 30 mm at 200 GSM. The plan was to add extra material over the port, and when the correct amount obtained, place it inside.

There's a pic here: http://www.diyaudio.com/forums/showt...43#post1100043

I did find a couple of references to aperiodic. Ted Jenson designed a cabinet for the Goodmans Axiom. Called the Axiom cabinet. And it's paternted to Goodmans. Another reference points to Dynaudio, which quotes a patent, but doesn't say who owns it, using SEAS 10" drivers.

We were using aperiodic enclosures on the back of 5 and 8" Philips drivers to get rid of resonances, but never listened to what actually came out of the vent. But they produced better midrange than the sealed back units offered by Philips and Peerless at the time. (79-80)

I'll run an z sweep soon, that will tell us something.

Cheers,
Geoff.
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Old 8th January 2007, 01:36 AM   #9
Geoff H is offline Geoff H  Australia
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Hey Zen, if you are confused, when I said 811 I meant 411.
Too many numbers.

Geoff.
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Old 8th January 2007, 01:46 AM   #10
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by Geoff H
Hey Zen, if you are confused, when I said 811 I meant 411.
Too many numbers.

Geoff.

still confused

http://www.northcreekmusic.com

http://www.northcreekmusic.com/Vision/VisionCabinet.PDF

edit
on attached pic you can see pair of old ITT boxes (layin' on top of biggies) ; they're in fact OEM from Scan Speak, inside them are 21W38 and D3804 ,both Alnicos ; box have somewhere in the middle horizontally placed baffle,with rectangular hole,covered with sorta tiny felt .....this is certainly sort of inside aperiodic jobbie; x-over....naturally series one
touch of the Genius, Scaaning-who else ........(confirmed from his son )

after recappin' and repairing slightly damaged cone and surround on one woof, I made sorta DIY variovent on back of each cab ; that improved further bass from cabs.
but-comparing to biggies on pic,little boxes still have too much boxiness......meaning on medium freq. range........
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