Double Bandpass Enclosure Design - Critique! - AVS Forum
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post #1 of 31 Old 04-28-2012, 08:40 AM - Thread Starter
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Hey everybody - I thought of a subwoofer enclosure design in which there are two drivers sharing the same rear cabinet (Vf) volume of a bandpass design. I made a quick thing in SketchUp to show you:
Attachment 244903
another view to show interior ports (typical of bandpass design) Attachment 244904
The dimensions aren't worked out, but the idea is that the three different volumes of the cabinet will have three different frequencies, making for a more even band. Let me know what you think!
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post #2 of 31 Old 04-28-2012, 09:11 AM
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i don't get anything when i click on your links.

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post #3 of 31 Old 04-28-2012, 10:32 AM - Thread Starter
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Hm, that's strange. They work for me. Also, it seems that I can't post other links because I'm new to the forum and they want to make sure I'm not a spammer. I need at least 3 posts.
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post #4 of 31 Old 04-28-2012, 10:32 AM - Thread Starter
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Here's my third post...
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post #5 of 31 Old 04-28-2012, 10:33 AM - Thread Starter
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And here are the links:



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post #6 of 31 Old 04-28-2012, 11:13 AM
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i can see them now.

each side of your enclosure kind of looks like one of these:

http://www.the12volt.com/caraudio/boxes6.asp

i have no idea what your box will do, but i will take a stab in the dark. one thing to keep in mind is that with two ports into one enclosure, there isn't as much of a 'smoothing' effect as an 'averaging' effect, so my best guess would be that you won't get smoothing across a wide frequency range as it will just all average out to some sort of single frequency tuning.

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post #7 of 31 Old 04-28-2012, 11:29 AM - Thread Starter
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Oh, that's funny. They must have been unavailable for the same reason I couldn't post any other links until I made 3 posts.

Hm. So how do regular bandpass designs specialize in two different frequencies then? Shouldn't they be "averaged" as well?
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post #8 of 31 Old 04-28-2012, 10:16 PM
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"Hm. So how do regular bandpass designs specialize in two different frequencies then? Shouldn't they be "averaged" as well?"

...by walling-off the enclosure behind the driver from the enclosure in front of the driver.

the bose bass module is one of the more complex designs going and combines all the chambers. as implemented, most folks consider it a dud. i suspect that the design choice was chosen to stack resonances on top of resonances in order to get the most spl out of the lowest cost driver possible in the smallest cabinet possible, and it made amar a billionaire, so i suppose it was a success? panem et circenses...

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post #9 of 31 Old 04-28-2012, 10:53 PM
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Ahoy Captain Clams!

if you can provide links to driver specifications, and a few details about the box dimensions I will be happy to simulate the system so you can see what it would do.

Regards,
Eric
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post #10 of 31 Old 04-28-2012, 11:56 PM - Thread Starter
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"...by walling-off the enclosure behind the driver from the enclosure in front of the driver."

But that wall is ported in most bandpass designs I've looked at. Why would having two ports cause an "averaging" effect, while one port does not?


And thank you, Fred. Here are the numbers:

http://www.parts-express.com/pe/show...number=290-109

These are the drivers I have currently. I'm not terribly sure of their quality, however. If you happen to know one way or another about them, let me know. I don't want to build this box for some cheap driver.

As for the scale of the enclosure, I think 20inx20in faces would be a good size. Now, I don't know how your calculations work and I don't want to be too demanding, but if the three enclosure areas could be tuned to 25Hz, 40Hz, and 60Hz or roundabouts, I would be very happy.
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post #11 of 31 Old 04-29-2012, 12:15 AM
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"But that wall is ported in most bandpass designs I've looked at."

take another look at them. not so.

most bandpass are the 4th order, sealed rear cab, ported front cab.

very rare are 6th order, where the rear cab is vented.

combining all the resonances as in the bose bass modules is very rare and like i said, most folks have found them to be not worth building.

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post #12 of 31 Old 04-29-2012, 12:27 AM
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Hello Captain,

I was just looking at the diagrams closer, and realize you have the rear chamber vented to a front chamber. I didn't catch that initially... Such a design is a bit over my head for simulation, however, I can try to come up with a bandpass box design for these drivers if you are interested. Some drivers can produce pretty decent results in 6th order boxes. Your cabinet "shape" could be used to accomplish this, but there would be a vent coming from the rear chamber into the open, and a vent from both front chambers to the open.

I would say that the drivers you have there are, IMO, not worth wasting a very complicated build on. They just don't have the sort of displacement capabilities that would make the trouble worth it...

What useful passband are you after?

Regards,
Eric
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post #13 of 31 Old 04-29-2012, 04:39 PM - Thread Starter
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If the interior ports complicate the design, then it's fine to remove them. And about the drivers I have, I didn't think they were worth the build either. Let's assume we use these for the drivers (as I am on an unfortunate budget).

As for what frequency ranges I'm looking to get out of it, I'd like to see a solid 18Hz to 70Hz range, which could be achieved by the three cabinet volumes attenuating 18, 40, and 70Hz if I'm thinking of my box correctly.
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post #14 of 31 Old 04-29-2012, 05:41 PM
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Quote:
Originally Posted by Captain_Clams View Post

If the interior ports complicate the design, then it's fine to remove them. And about the drivers I have, I didn't think they were worth the build either. Let's assume we use these for the drivers (as I am on an unfortunate budget).

As for what frequency ranges I'm looking to get out of it, I'd like to see a solid 18Hz to 70Hz range, which could be achieved by the three cabinet volumes attenuating 18, 40, and 70Hz if I'm thinking of my box correctly.

That driver is far to small to be useful as a sub IMO unless you're looking for a very small box. By no means will the following design be amazing, and it might be bigger then you want, but it will do OK for cheap. Check the attachments.

Goldwood GW-12PC-4
Dayton SA70
LL
LL
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post #15 of 31 Old 04-29-2012, 06:15 PM
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Just an FYI, you can basically achieve the same results with a standard ported cab outside of the built in bandpass filter of the high frequencies.
LL
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post #16 of 31 Old 04-29-2012, 06:37 PM - Thread Starter
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Thanks, friend, for the driver recommendation. I got my links mixed up and posted the wrong thing, but yours is more cost effective anyhow. Oh, and that enclosure volume is about exactly what I was hoping for. Now it's time for the drafts. If the subwoofers turn out as planned, I have this behemoth in mind for the midrange and tweeters to make it a full thing.

"Just an FYI, you can basically achieve the same results with a standard ported cab outside of the built in bandpass filter of the high frequencies."

You are certainly right. For this build, I'm more interested in making something unique than making something optimum though, honestly. To me, the fun in speaker building lies in the creative aspect equivalently as it does in the quest for optimization.
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post #17 of 31 Old 04-29-2012, 07:45 PM
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Cool! That certainly looks unique. Just be aware that the SPL chart I posted would be the limit of output, and xmax is slightly exceeded with 70 watts.
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post #18 of 31 Old 04-29-2012, 08:06 PM
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Having had a night to sleep on the idea, I realised why there is a reason no common simulation software would let you even bother with this...

If you have 2 drivers, sharing a rear chamber, but each with different front chambers, then you are creating a situation like having 2 drivers with different characteristics sharing a common chamber. It's usually a bad idea.

I would not consider that goldwood 12" or the dayton 10" options considered to be much of an improvement over the current pyramid drivers. I don't think I would waste money on either for a functioning 18-70hz sub.

If a bandpass box is not producing useful box gain over a traditional vented or sealed box, then it's being implemented poorly. Properly designed bandpass is a way to achieve greater box gain within a desired bandwidth than possible with simpler box alignments. 6th has a better chance of producing useful gain and wider bandwidth than 4th order. That said, with the ability these days to freely simulate various horn loaded, tapped horn, line and tapped line options, often the bandpass box options are passed up. There are cases where within box size restrictions, a bandpass can still offer the greatest box gain with an acceptable response even over more sophisticated box designs... It's all about finding the level of box sophistication that fits the driver and box size limits set.

How much amplification will you have for this?

Regards,
Eric
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post #19 of 31 Old 04-29-2012, 08:58 PM
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The 18-70hz requirement is really what cut the bandpass advantage, at least for those Goldwoods.

(vs ported full 6db increase)
LL
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post #20 of 31 Old 04-29-2012, 09:12 PM - Thread Starter
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"How much amplification will you have for this?"

I was planning on using this for amplification. It's inexpensive; seems like a responsible buy, as I don't normally play music very loud in my house.


"The 18-70hz requirement is really what cut the bandpass advantage"

What would be a more reasonable requirement that I could use to justify my desire to build the bandpass enclosure?
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post #21 of 31 Old 04-29-2012, 09:34 PM
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What I attached in post #19 would be ideal for the Goldwoods low end. There seems to be a 20hz range that maximizes output, so you could move that up to 40-60 (and gain even more output) or higher.

Other woofers may have a wider range, I just looked for something around $60 that would maximize SPL for cheap. This is all with only that $50 70 watt amp.
LL
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post #22 of 31 Old 04-29-2012, 09:57 PM - Thread Starter
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I think that seems like a sensible curve.

Now, I can't get these results you're getting on my computer (the beta of WinISD doesn't do 6th order bandpass). Could you shoot me another screenshot with port diameters, port lengths and other necessary box parameters?
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post #23 of 31 Old 04-29-2012, 10:11 PM
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Not sure which one you liked. First one's 30-50hz second 40-60hz. Here's the newest winisd

https://www.facebook.com/WinISD

you have to have facebook...
LL
LL
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post #24 of 31 Old 04-30-2012, 05:19 AM - Thread Starter
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Oh, yes I forgot to clarify that. I was looking at the 30-50 curve.

This is what happens when I try to run a 6th order bandpass in WinISD 7.0 (attachment)
LL
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post #25 of 31 Old 04-30-2012, 10:32 AM
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The goldwoods do not have enough of an advantage over the current pyramid drivers to warrant an exchange of money IMO.

Consider, a DCS450.

Regards,
Eric
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post #26 of 31 Old 04-30-2012, 10:43 AM
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Quote:
Originally Posted by Captain_Clams View Post

Oh, yes I forgot to clarify that. I was looking at the 30-50 curve.

This is what happens when I try to run a 6th order bandpass in WinISD 7.0 (attachment)

Just hit next. Winisd cant predict an alignment for bandpass.

Quote:
Originally Posted by mdocod View Post

The goldwoods do not have enough of an advantage over the current pyramid drivers to warrant an exchange of money IMO.

Consider, a DCS450.

Regards,
Eric

Hopefully OP can model all this himself now, but check the VAS on the drivers in question.
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post #27 of 31 Old 04-30-2012, 06:26 PM - Thread Starter
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Actually I'm having a hell of a time getting a flat transfer function in WinISD. What's your secret?
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post #28 of 31 Old 04-30-2012, 07:30 PM
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No secret, just have to find the proper volume and tune for each chamber.
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post #29 of 31 Old 05-01-2012, 12:59 AM
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for a good starting point, try tuning the front and the rear chamber to about the same frequency.

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post #30 of 31 Old 05-01-2012, 04:51 AM
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Quote:
Originally Posted by LTD02 View Post

for a good starting point, try tuning the front and the rear chamber to about the same frequency.

That would be a very bad starting point.

For a good starting point, try setting the front chamber to about 1/4 the volume of the rear chamber, and tuning them about 2 octaves apart; with the larger {rear} chamber tuned lower.
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