Aperiodic Vents

[stevev]

How do these vents affect the performance of a sealed enclosure? Do they somehow improve the sound or deepen the low end response of a sealed driver?
It is advertised that using the vent would enable a smaller enclosure volume, compared to the original sealed enclosure. Any comments?

[Jeff B.]

Re: Aperiodic Vents

How do these vents affect the performance of a sealed enclosure? Do they somehow improve the sound or deepen the low end response of a sealed driver?
It is advertised that using the vent would enable a smaller enclosure volume, compared to the original sealed enclosure. Any comments?

They provide a leak to the sealed box, thus lowering the box Q. This will help to reduce a peak in a higher Qtc box. However, the other affect will be to raise F3. They do not "deepen the response" of sealed driver; they do the opposite. They do improve transient response though.

[Hearing Specialist]

Re: Aperiodic Vents

which vendor are you checkin out for the vents?

[stevev]

Re: Aperiodic Vents

I saw these vents advertised at the Parts Express site. Just how much will they affect F3 of a sealed enclosure? Let's just say that the F3 in my sealed box is 48Hz, so what F3 would I expect to get with using the aperiodic vent? Just wondering if I would trade F3 response for transient response.

[Jeff B.]

Re: Aperiodic Vents

I saw these vents advertised at the Parts Express site. Just how much will they affect F3 of a sealed enclosure? Let's just say that the F3 in my sealed box is 48Hz, so what F3 would I expect to get with using the aperiodic vent? Just wondering if I would trade F3 response for transient response.

If the box modeling software you are using has the ability to enter the box leakage Q (Ql), then a number around 2-3 for this parameter and the result will be a pretty accurate approximation of the aperiodic vent.

Jeff

[ErinH]

Re: Aperiodic Vents

In order to tune the vent, I HIGHLY recommend a woofer tester or the like to do impedance sweeps. Doing this with a DMM and tones is a major pita.

[stevev]

Re: Aperiodic Vents

I will have to see if my software can give any results for leakage. I am using Bass box 6 Pro, and don't think there is an option for that. Anyway, was just curious as to what affect the vent would have, and from what you say, cleaner transients would be a plus, but without having any way to predict what amount of F3 would be lost, I will probably just keep the enclosure sealed without the vent. I just don't want to cut a 4" hole into my planned white ash cabinet just for testing the aperiodic vent. I don't see any speaker designs using them so it can't be a big improvement for a sealed enclosure or there would be many designs using them. Thanks for the comments.

[Jeff B.]

Re: Aperiodic Vents

I will have to see if my software can give any results for leakage. I am using Bass box 6 Pro, and don't think there is an option for that. Anyway, was just curious as to what affect the vent would have, and from what you say, cleaner transients would be a plus, but without having any way to predict what amount of F3 would be lost, I will probably just keep the enclosure sealed without the vent. I just don't want to cut a 4" hole into my planned white ash cabinet just for testing the aperiodic vent. I don't see any speaker designs using them so it can't be a big improvement for a sealed enclosure or there would be many designs using them. Thanks for the comments.

Any software worth using...Unibox, WinIsd, mine, etc..... has a Ql entry. Double check BassBox Pro. I would be surprised if it didn't.

Jeff

[Jeff B.]

Re: Aperiodic Vents

In order to tune the vent, I HIGHLY recommend a woofer tester or the like to do impedance sweeps. Doing this with a DMM and tones is a major pita.

You don't tune an aperiodic vent. That's a contradiction in terms. If it can be tuned then it's not aperiodic. An aperiodic vent is a leak without a tuning frequency by definition.

[OlderMongrel]

Re: Aperiodic Vents

You don't tune an aperiodic vent. That's a contradiction in terms. If it can be tuned then it's not aperiodic. An aperiodic vent is a leak without a tuning frequency by definition.

Right, Jeff, this is not a helmholtz resonator, but you can "tune" the system in a manner of speaking. The one I'm using now has a partition with a damped vent in it, between the two sides (like the old Dynaco A-50). You can try various materials in the vent, stuffed in with various densities, and read the changes with a WT3 or similar. You will also see Q and Fs changes from varying the stuffing in either side. You can see this with stuffing changes in a plain sealed enclosure, too, but the aperiodic has more variables. I think it's fairly common to use the word "tune" for going thru this process, but aperiodic is not all that popular, so it's not like there is a standard vernacular.

I don't see much use in fixed aperiodic vents like the old Dynaudio Variovents. It's like buying a port tube with the idea that you have to use it "as is" and can't change the length. You need to be able to change the type and density of stuffing in the vent, measure, and tweak to get the desired outcome. You might even need to change the vent area or depth.

John

[Taterworks]

Re: Aperiodic Vents

I have heard aperiodic systems exhibit some very desirable transient response characteristics -- immediacy in drum reproduction the likes of which I have never heard in any other type of enclosure, for example.

An aperiodic vent attempts to approximate a purely resistive element, so it essentially works like an acoustic 'brake'. Its negative effect on the bottom end response of a sealed speaker comes from increasing the acoustic damping on the back surface of the driver cone, which has the same effect as additional mechanical or electrical damping (hence an aperiodic vent is usually applied when one is trying to use drivers with very low damping of its own, which manifests as a high Qts, somewhere above 0.8), but these vents can also be applied with lower-Qts drivers for an even more damped sound.

The aperiodic vent also radiates some amount of out-of-phase energy into the listening space, which is attenuated with respect to the driver's front wave but can still cause a significant amount of cancellation if there is too much radiation from the vent. These vents are usually placed on the rear of the box, which helps the box retain some sort of 'dipole moment'. What I'd really like to see done one of these days (or experiment with, myself) is use an aperiodic vent directly behind the active cone driver, with the damping varied such that there would be phase cancellation behind the enclosure but summation in front of the enclosure, to achieve a "cardioid" radiation pattern in the bass range. This technique would reduce the effect of the room on the quality of the bass reproduction from the speaker because radiation toward the front wall (and nearby corners) would be reduced.

Happy experimenting. I think aperiodic vents are much less well understood than they deserve to be, and they could be a very useful tool in the designer's toolbox.

[Jeff B.]

Re: Aperiodic Vents

Right, Jeff, this is not a helmholtz resonator, but you can "tune" the system in a manner of speaking. The one I'm using now has a partition with a damped vent in it, between the two sides (like the old Dynaco A-50). You can try various materials in the vent, stuffed in with various densities, and read the changes with a WT3 or similar. You will also see Q and Fs changes from varying the stuffing in either side. You can see this with stuffing changes in a plain sealed enclosure, too, but the aperiodic has more variables. I think it's fairly common to use the word "tune" for going thru this process, but aperiodic is not all that popular, so it's not like there is a standard vernacular.

I don't see much use in fixed aperiodic vents like the old Dynaudio Variovents. It's like buying a port tube with the idea that you have to use it "as is" and can't change the length. You need to be able to change the type and density of stuffing in the vent, measure, and tweak to get the desired outcome. You might even need to change the vent area or depth.

John

I agree. In the end you are tuning the system Qtc by using Qa (Absorption) and Ql (leakage) as adjustable parameters. This is fine, and if it arrives at the target results, it's even better. Your approach can be very useful with higher Qts drivers.

[squib]

Re: Aperiodic Vents

If I remember correctly, there were a number of people over at DIYaudio using PC fan guards to create aperiodic vents. One guard was placed on the interior side of the opening in the cabinet followed by damping material. The second guard is mounted to the exterior of the cab. The density and materials can be swapped easily to adjust the Ql. Cheap way to experiment with the designs and the guards come in a variety of diameters.

[ErinH]

Re: Aperiodic Vents

You don't tune an aperiodic vent. That's a contradiction in terms. If it can be tuned then it's not aperiodic. An aperiodic vent is a leak without a tuning frequency by definition.

I disagree, but it may be semantics. As John said above, the term 'tune' is what is commonly referred to as part of finding the balance between material density/thickness and response. You certainly tune the enclosure via the membrane. I've done it many times myself with varying goals. IOW, you shouldn't just slap a mat of x material with x thickness in the vent and call it a day. You use a bit at a time and take measurements until you achieve desired response. Put material at the vent, sweep, add/remove material, sweep, try diffent material, rinse, wash, repeat until desired goal is met.
Not only does the membrane thickness affect the q and Fs, but so does the material used. Ive used everything from gortex to wool to fiberglass, all with varying effects. I had the results saved at one point but deleted them off my photo bucket account recently. :(

Think of it as changing the design... It's not an active tune (ie: on the fly). It is part of the design process... Or at least it should be.

[Jeff B.]

Re: Aperiodic Vents

I disagree, but it may be semantics. As John said above, the term 'tune' is what is commonly referred to as part of finding the balance between material density/thickness and response. You certainly tune the enclosure via the membrane. I've done it many times myself with varying goals. IOW, you shouldn't just slap a mat of x material with x thickness in the vent and call it a day. You use a bit at a time and take measurements until you achieve desired response. Put material at the vent, sweep, add/remove material, sweep, try diffent material, rinse, wash, repeat until desired goal is met.
Not only does the membrane thickness affect the q and Fs, but so does the material used. Ive used everything from gortex to wool to fiberglass, all with varying effects. I had the results saved at one point but deleted them off my photo bucket account recently. :(

Think of it as changing the design... It's not an active tune (ie: on the fly). It is part of the design process... Or at least it should be.

Your original comment of tuning with an impedance measurement made me think of tuning a port's Fb. However, I see you meant it in a different way, and I agree with you.