Dual 8", In-Wall Ported Box

14845 Views 57 Replies 10 Participants Last post by hddummy, Sep 21, 2009

hddummy

Discussion Starter · Apr 29, 2009

If you saw my other thread on this topic (link) you would know that I'm trying to help my parents install a 5.1 system since they are renovating their house. I was having trouble with sub design/placement options because they are very picky customers. I was inspired by joorge's post in my thread about the parts express "boogieman" sub. I came up with something that I think will work decently well. It won't shake the house down by any stretch, but they are not audiophiles and they have hardly given much to work with.

We settled on a small space in a wall that is centrally located in the large open room. This space is about 10" wide, 11" deep and 36" tall. I plan to build a ported box to take advantage of every cubic inch they will give me. The whole thing will be flushed in the wall and finished with a cloth grill. This is not a large space, so my choices are very limited. I have selected a tang band 8" (link) from PE. I'll use two of them and a 30" folded slot port to give me a box tune of about 29Hz. This driver has great power handling, Xmax and a small VAS, which was key to this design. I'll top it off with a 500 watt BASH plate amp, but it will be running only 250W because the drivers will be wired in series for an 8ohm load.

Look for box design pictures later today.

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hddummy

Discussion Starter · #21 · Apr 30, 2009

so you didn't have a real reason behind the values you chose other than it was one notch lower in the boost tables.

Mike P.

· #22 · Apr 30, 2009

The cone excursion of the default values dictated that a lower HPF could be used. The next lower HPF was 24.3 hz.

hddummy

Discussion Starter · #23 · Apr 30, 2009

Gotcha. Anything lower and you driver it past Xmax at these power levels. By the way, what subwoofer design software is that?

Mike P.

· #24 · Apr 30, 2009

WinISD Pro (version 0.50a7)

hddummy

Discussion Starter · #25 · May 1, 2009 (Edited)

Small problem. If I extend the port the additional length to get 27Hz tune, the end gets too close to the center brace. I would have to keep 29, which isn't bad or extend the port to about 39 inches total length so that it ends at the brace. That is getting too long and port resonance could come into play. I could also reduce the port cross section, which would reduce the length requirement for a given tune. The question is, what are the dimensional limits on a slotted port. It is currently 8.5 x 1.5, if I go down to 1.25, my port length goes down to 31.25" and my port air speed is about 13m/s. I think I'd be good and I get the added benefit of some extra effective volume. I just don't know if that is too thin for the slot. Any help?

Mike P.

· #26 · May 1, 2009

With a 29 hz tuning a 8.5 x 1.5 slot port is 32.5 inches long. With a HPF at 24.3 hz and the boost that goes with it and 500 watts input power the port air speed is 32 m/s at 29 hz, definitely at the limits. I'm not sure how you're coming up with 13m/s.

hddummy

Discussion Starter · #27 · May 1, 2009 (Edited)

2

I'm using Unibox right now, but I'll download WinISD and double check. I'm modeling with two drivers at 250W total input power. This is what I get. Of course this doesn't account for frequency response of the amp itself.

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Mike P.

· #28 · May 1, 2009

I modeled peak air speed with 500 watts input power.

hddummy

Discussion Starter · #29 · May 1, 2009

yeah...the amp is 500....until you wire two 4ohm drivers in series, which of course drops it to 250, giving 125 to each driver.

Mike P.

· #30 · May 1, 2009

Forgot about that ohm thing. :whistling:

hddummy

Discussion Starter · #31 · May 1, 2009

so, what do you show for port air speed at 250w? I guess that means the excursions you were showing was based on 500W as well...i can probably boost the low end a little more.

Mike P.

· #32 · May 1, 2009

Green is with 250 watts input, HPF at 21.6 hz and 2 db of boost from 25 - 30 hz. Maximum air speed is 25 m/s at 28 hz. Pink is the wrong modeling of 500 watts.

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hddummy

Discussion Starter · #33 · May 2, 2009

4

I've been messing around with WinISD and several different combinations of Port Tune and Amp Boost/HPF settings. I think I have settled on a good solution. Thanks for your help and encouragement.

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hddummy

Discussion Starter · #34 · May 5, 2009

I guess nothing is settled until it's built....right? In an effort to reduce port air speed, I've tweaked it more. Box volume 31l, tune to 28Hz, port dims: 1.375 x 8.5. Response changes marginally, port is a few inches longer, air speed drops to 20.5m/s.

Mike P.

· #35 · May 5, 2009

Sounds good. Don't forget your camera when you start building. :yes:

hddummy

Discussion Starter · #36 · May 5, 2009

You bet! I hope to start making dust next week.

hddummy

Discussion Starter · #37 · May 20, 2009

4

OK..... I've made some progress, so here are some pics.

All the parts cut out:

The eventual home:

Dry fit check:

Port up close:

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Mark Holmes

· #38 · May 21, 2009

Really nice round over cuts on the corners. You must have a really nice bit. :bigsmile:

DragonArt

· #39 · May 28, 2009

Very professional-looking work so far! :clap: I also like the design although I would have built a [email protected] rear loaded horn with those drivers

hsd: :dumbcrazy

, but I guess that would be kind of a overkill.

hddummy

Discussion Starter · #40 · May 28, 2009

Thanks! Yeah, it is a 1 1/4 round over bit, but I only cut it to 1 1/8 depth. I wanted to keep that slight edge on the face instead of driving the radius down flush with the front face. I was out of town this past weekend, so I hadn't made much progress. Also, I only glue and clamp one piece on at a time. A lot of guys will just throw it all together and tack it with nails or screws to hold it while it dries. I should get finished pictures up this weekend.

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