Hi guys:) What is this......

[cole]

<A HREF="http://www.partsexpress.com/pe/pshow...TOKEN=43876155">http://www.partsexpress.com/pe/pshow...TOKEN=43876155</A>

I saw this in the new cat. Ive read the description but still cant seem to grasp the concept of the Aperiodic Vent. As far as I thought, sealed box and the word vent never fell into the same sentence.
I love the sealed box design. I would love to try out a new gizmo that may improve a sealed design but how exactly does this thing work?
Has anyone utilized one yet?
Thank you for the help.

cole

[Pete Schumacher ®]

>
> <A HREF="http://www.partsexpress.com/pe/pshow...TOKEN=43876155">http://www.partsexpress.com/pe/pshow...TOKEN=43876155</A>
> I saw this in the new cat. Ive read the
> description but still cant seem to grasp the
> concept of the Aperiodic Vent. As far as I
> thought, sealed box and the word vent never
> fell into the same sentence.
> I love the sealed box design. I would love
> to try out a new gizmo that may improve a
> sealed design but how exactly does this
> thing work?
> Has anyone utilized one yet?
> Thank you for the help.

> cole

It's basically a hole in the box with resistance. it's the same as Dynaudio's old Variovent. You get a sealed box response but it makes the box appear a bit larger and helps reduce the impedance resonance I believe.

[Jethro]

>
> <A HREF="http://www.partsexpress.com/pe/pshow...TOKEN=43876155">http://www.partsexpress.com/pe/pshow...TOKEN=43876155</A>
> I saw this in the new cat. Ive read the
> description but still cant seem to grasp the
> concept of the Aperiodic Vent. As far as I
> thought, sealed box and the word vent never
> fell into the same sentence.
> I love the sealed box design. I would love
> to try out a new gizmo that may improve a
> sealed design but how exactly does this
> thing work?
> Has anyone utilized one yet?
> Thank you for the help.

> cole

These things have been around for years. On its own, it can be used as a way of reducing the impedance peak at Fs. The result is a closed box system with a much lower Qtc than the box size would indicate (see the images on the PE page for this item). I found it much more effective than polyfill, but the vent did make some noise under high excursion conditions.

They can also be used in an actual aperiodic setup, where the driver(s) is mounted in a small enclosure, and connected to a larger enclosure via the aperiodic vent (ala North Creek Music Systems). Here are a few links to North Creek's white papers / spec sheets...

<A HREF="http://www.northcreekmusic.com/MAPD1.htm">http://www.northcreekmusic.com/MAPD1.htm</A>
<A HREF="http://www.northcreekmusic.com/Vision/VisionCabinet.PDF">http://www.northcreekmusic.com/Vision/VisionCabinet.PDF</A>

[cole]

The forest is clearing. Still a few trees in the way but I dont think Ill be building here anyway. To noisy.
Thank you, Pete and Jethro

[curt_c]

But it is useful in certain situations.

If we take a sealed speaker and add an aperiodic vent the following things happen:

Qtc goes down

f3 goes up -the varioment does not emulate a larger enclosure in this regard

The acoustical low impedance at fc will better control the cone around fc providing lower distortion/better resolution in the compliance controlled region. This can be quite audible and preferable to its sealed counterpart, in spite of the slightly higher f3.

C

[cole]

for the higher f3 but how audible do you think the chauffing from the vent would be? Also, if you happen to know, how much smaller do you think I could build an enclosure utilizing the vent as opposed to not using the vent?
Thanks for jumping in here, Curt. Mind pulling a few trees?

cole

[Paul K.]

make the rolloff more like 3rd-order instead of the 2nd-order as sealed? Someone told me that once, and I'm pretty sure it was Lynn Olson of "Ariel" fame.
Paul

> But it is useful in certain situations.

> If we take a sealed speaker and add an
> aperiodic vent the following things happen:

> Qtc goes down

> f3 goes up -the varioment does not emulate a
> larger enclosure in this regard

> The acoustical low impedance at fc will
> better control the cone around fc providing
> lower distortion/better resolution in the
> compliance controlled region. This can be
> quite audible and preferable to its sealed
> counterpart, in spite of the slightly higher
> f3.

> C

[curt_c]

> Thanks for jumping in here, Curt. Mind
> pulling a few trees?

More like you are making me jog a few brain cells...

That’s where the variovent shines, -utilizing an otherwise too small enclosure and still obtaining acceptable bass performance without the boom…

It of course depends on the enclosure, the resistivity of the vent, and the max SPL required. Long ago, I used one on an EPI 100 speaker, in which the woofer ideally required twice the provided enclosure volume. (Some of you may remember the later Genesis I, which was essentially the same speaker in a larger enclosure.) With the modified EPI 100, I noted no detriments due to the change at normal listening levels. No audible chuffing, but much better bass definition. The SS vents do easily disassemble, so you can add or remove material to change the resistance to suit your requirements.

C

[curt_c]

> make the rolloff more like 3rd-order instead
> of the 2nd-order as sealed? Someone told me
As a real world example, look at the Von Schweikert speakers, some of which are aperiodically damped. Here’s a link to a review of the Von Schweikert VR-1, (with its ‘pressure release cabinet’) as measured by the National Research Council of Canada. The measured response appears to be 12 dB / octave. Also note that this speaker doesn’t use a variovent by name, but simply a small hole in the back of the enclosure, which provides much the same function.

<A HREF="http://www.soundstage.com/revequip/v...eikert_vr1.htm">http://www.soundstage.com/revequip/v...eikert_vr1.htm</A>

<A HREF="http://www.soundstagemagazine.com/me...chweikert_vr1/">http://www.soundstagemagazine.com/me...chweikert_vr1/</A>

C

[Deward Hastings]

in the Dyna A-25 . . .

[Jeff B.]

> As a real world example, look at the Von
> Schweikert speakers, some of which are
> aperiodically damped. Here’s a link to a
> review of the Von Schweikert VR-1, (with its
> ‘pressure release cabinet’) as measured by
> the National Research Council of Canada. The
> measured response appears to be 12 dB /
> octave. Also note that this speaker doesn’t
> use a variovent by name, but simply a small
> hole in the back of the enclosure, which
> provides much the same function.

>
> <A HREF="http://www.soundstage.com/revequip/v...eikert_vr1.htm">http://www.soundstage.com/revequip/v...eikert_vr1.htm</A>
>
> <A HREF="http://www.soundstagemagazine.com/me...chweikert_vr1/">http://www.soundstagemagazine.com/me...chweikert_vr1/</A>
> C

Drivers in boxes roll-off at 12 dB/oct and ports roll-off at 12 dB/oct as well. In a ported box the over all 24 dB/oct roll-off is due to the phase relationship between the two. When you consider what the mechanism is for a 4th order roll-off in a vented box, an "aperiodic" box (one with no periodic or fundamental resonance, or a highly damped one, anyway) is just a lossy box and should only roll-off at 12 dB/oct.

Jeff B.

[bobraus]

I picked up a pair of Polk bookshelf speakers at a thrift store for $5.00 (they worked perfectly- but purchased them for the cabinets with protoyping my own designs in mind). It uses the same hole in the cabinet approach. The design sounded terrible even though everything was fully functional with the speakers- it just does not sound musical. I have dropped various drivers into the cabinet (it uses a 6 1/2 driver)and worked with my own crossover and alternate tweeters and found to date that the sound of the woofer is preferable with the hole- that is less than the size of a quarter prefereable to the that when sealing the cabinet. Now I understand what principle was at work with this. Thank you...

Also note that this speaker doesn’t
> use a variovent by name, but simply a small
> hole in the back of the enclosure, which
> provides much the same function.

>
> <A HREF="http://www.soundstage.com/revequip/v...eikert_vr1.htm">http://www.soundstage.com/revequip/v...eikert_vr1.htm</A>
>
> <A HREF="http://www.soundstagemagazine.com/me...chweikert_vr1/">http://www.soundstagemagazine.com/me...chweikert_vr1/</A>
> C

[Paul K.]

You and Curt are correct, of course, as I just refreshed my memory by reading the appropriate section in Vance's Cookbook. Still I remember with complete confidence that Lynn Olson told me about the 3rd-order effect when we were talking about using an aperiodic vent for a midrange enclosure in a 3-way (quite a few years ago).
Paul

> Drivers in boxes roll-off at 12 dB/oct and
> ports roll-off at 12 dB/oct as well. In a
> ported box the over all 24 dB/oct roll-off
> is due to the phase relationship between the
> two. When you consider what the mechanism is
> for a 4th order roll-off in a vented box, an
> "aperiodic" box (one with no
> periodic or fundamental resonance, or a
> highly damped one, anyway) is just a lossy
> box and should only roll-off at 12 dB/oct.

> Jeff B.

[bill]

> in the Dyna A-25 . . .

The vents in the A-25 were huge compared to the SS. IIRC, they were the width of the cabinet and about 2" high, solidly stuffed with fiberglass.

Best regards,
Bill