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Couple of AV15 sub design questions...


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#1 of 6 Rob Formica

Rob Formica

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Posted May 01 2003 - 03:39 AM

Seeing that it is a little slow around here... I thought I'd verify a couple of design questions with you. For reference, I've decided to build a AV15 based subwoofer (already on pre-order) powered by a JBL MPC200 amp in mono. I do a lot of music listening, so I decided on a 6ft3 enclosure ported to around 21Hz.

Dimensions: Does anyone have the exact dimensions of the driver for the cut out? As well as the actual volume of it (to add to my internal volume)?

Grille: I would like to fabricate a grille to cover my driver.... yes I know some are thinking "show it off" but you have to admit big round shiny things have limited WAF. How far would the tissue have to be from the mounting flange to avoid contact with the driver? I figured it should be about an inch from the surface the driver will be mounted on. Correct me if I'm wrong, but the logic behind this is; in it's fully extended position the woofer surround is fully stretched and the edge cone is what will touch the fabric, the AV15 has a 23mm Xmax , the cone edge sits about even with the back of the mounting flange in its resting position. Am I safe?

Box construction: I had originally considered going sonotube, but seeing the time I have before getting the components, I think a box would look nice. My intention is to match my old Birch Plywood Klipsch.... but my question here is that I often see the two most "accepted" construction materials being MDF and void free marine plywood. Obviously the box's resonant frequency would be quite different in plywood vs MDF but will it hurt the sound? I have access to 5'x5' x ¾" sheets of the birch marine plywood and it would be a relatively close match to my mains. Is it better doubling the box with MDF, or just KISS?

Ports: to flare or not flare? I'd like a single 6" port... which I don't have access to flares for, but will my velocity be low enough not to hear port noise?

Thanks ahead for any help...
Rob.
*Shedding light by means of the combustion of snake oil* PC-ABX

#2 of 6 RichardHOS

RichardHOS

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Posted May 01 2003 - 05:54 AM

The cutout diameter is 14 1/16"

The countersink diameter is 15 5/8".

15 3/4" countersink dia. will allow plenty of room to for the rubber gasket.

8" from the back plate to the backside of the mounting flange.


All information from Stryke.



About birch vs. MDF - high grade plywood laminate has a higher elastic modulus than MDF, which will result in a higher resonant frequency for a given panel size and thickness. That is a good thing for a sub enclosure. Posted Image The glue binders in MDF act as natural hysteresis damping, which will help tame any "ringing" from impulse inputs, so it might be a good idea to use a bit of damping material on the inside of the plywood enclosure (rubber mat or dedicated acoustical damping mat... or something similar).

#3 of 6 DustinDT

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Posted May 01 2003 - 05:57 AM

I'm doing almost the exact same thing, with the exact same components, wondering the exact same things....

Anyone wanna offer any info?

#4 of 6 Rob Formica

Rob Formica

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Posted May 02 2003 - 05:50 PM

Does anyone want to dip the woofer into a bucket of water and see what amount of liquid it displaces? Posted Image Just kidding... I looked around on the Stryke site, and apart from some basic physical dimensions... no actual driver volume. I figure it should be around 350in3 but i'm guessing.

I also noticed most people using two 4" ports, so one 6" would be safe seeing it has a larger area?

later...
Rob
*Shedding light by means of the combustion of snake oil* PC-ABX

#5 of 6 Bob Huskison

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Posted May 03 2003 - 04:20 AM

My estimate, based upon the difference in the volume of two cones, was about 790in^3. Seems pretty big now.

#6 of 6 Frank Carter

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Posted May 03 2003 - 05:01 PM

Hey Rob,

My brother had a conversation with J. Janowitz and he said he likes to be conservative with his numbers. JJ said it's closer more like 28mm.

JJ also mentioned at the Stryke forum that the AV woofers are very similar to the SVS Plus series woofer(db12), the SVS db12 has an xmax of 28mm so that sounds about right.

What you need to look at is the Xsus(excursion limit due to the driver's suspension.) which for the AV woofers is 30mm.