Need help with cabinet design for 18" - AVS Forum
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post #1 of 10 Old 07-16-2012, 06:18 PM - Thread Starter
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Hello, DIY and design pro's. Well, to get straight down, I need some help (a lot) with cabinet design. I think to make it clearer, I was hoping someone could possibly draw up some cut plans, as I have no skill whatsoever with modeling/cad/what have you. I have a Peavy Black Widow 18" subwoofer that was previously inside of a car, but I would like to re-purpose it for home use. Problem is, I need a cabinet frown.gif As far as what I would like, it could be ported or sealed. I don't know the specifics of sub design, so whatever cabinet can get me the lowest possible Hz would be great. Power supply is not an issue, I've got a couple Behringer EP4000's and some other amps lying around. Thanks in advance for anyone's time to post!

Quick Edit: I should have also mentioned, I'd like to build the cabinet myself, thereby saving money. Preferably going with a cheaper wood option, like 3/4 MDF.

If one is going to make a simplistic assessment of the value of different alignments, it would be that sealed/IB goes the lowest, at the highest cost per dB; horns have the lowest cost per dB at the expense of size, and vented box characteristics lie in between the other two. None is inherently superior across the board, neither is any inherently inferior across the board. The one to use is the one that fits your response and output needs, available space and bank account. -BFM
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post #2 of 10 Old 07-16-2012, 06:20 PM
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one sec...

well, that appears to be a tough one to work with.

it wants a VERY large cab. with its low xmax, definitely go ported.

how big can you go? how low do you want?

Listen. It's All Good.
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post #3 of 10 Old 07-16-2012, 06:56 PM
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That's not a very good sub driver... Considering the EP4000 being used, you're going to have to be very careful with anything you do. A very large ported box tuned to about 30hz would probably be best, you can make use of the amps 30hz filter, and that driver really wont be able to handle playing lower then that with any kind of power. Here's a build you can copy:

http://www.avsforum.com/t/920648/project-quick-easy-cheap-ixl18-4-llt/30#post_11968394
(Instead of the 34" long ports, you will use 4.5" long ports)

If that's to much to handle, you should just go with a slightly undersized sealed box for protecting the driver, even if the low end is sacrificed.

http://www.avsforum.com/t/1051665/my-sealed-maelstrom-x-build

Both of these builds would be capable of significantly exceeding xmax by about the same amount, but you shouldn't be able to damage the woofer using a single channel (not bridged) unless you melt the voice coil with to much power.

Edit: what other amps do you have? That could change your options, but that driver still wont get you a great sub.


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post #4 of 10 Old 07-16-2012, 09:03 PM - Thread Starter
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1) Size isn't much of a concern for me.
2) I'll get back to you soon about the other amps. (Put them away, have to dig them out)

Hmm, well, I knew the woofer in question was rather cheap and not exactly up to par for this kind of thing, so I suppose I will pose another question. What would be a decent driver that would be 18" and $400 or less? I'm hoping to keep wood cost to $300 or less. (Ideally, less.)

If one is going to make a simplistic assessment of the value of different alignments, it would be that sealed/IB goes the lowest, at the highest cost per dB; horns have the lowest cost per dB at the expense of size, and vented box characteristics lie in between the other two. None is inherently superior across the board, neither is any inherently inferior across the board. The one to use is the one that fits your response and output needs, available space and bank account. -BFM
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post #5 of 10 Old 07-17-2012, 07:27 AM
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You definitely have substantial options with a $400 budget, the selection of good 18" woofers is still limited. Any reason you aren't considering 15" woofers? What are your goals for low frequency extension, and output?


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post #6 of 10 Old 07-17-2012, 07:32 AM - Thread Starter
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Well, no reason I guess. 15" could be fine. Goals would be at least 100 - 105 dB flat to 20Hz. I know the "best" 18's are way out of the price range (ie, the XXX, LMS Ultra, etc). But I just don't have 1K to drop on a woofer smile.gif Maybe some good 15's in that price range, or close to it? Other amps are: QSC GX3

If one is going to make a simplistic assessment of the value of different alignments, it would be that sealed/IB goes the lowest, at the highest cost per dB; horns have the lowest cost per dB at the expense of size, and vented box characteristics lie in between the other two. None is inherently superior across the board, neither is any inherently inferior across the board. The one to use is the one that fits your response and output needs, available space and bank account. -BFM
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post #7 of 10 Old 07-17-2012, 06:10 PM
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Since you have a 2 channel amp, I think a pair of ported 15"s would be a good option. Take this build for the box plan

http://www.avsforum.com/t/1414620/epik-15-diy-slot-ported-subwoofer

5 ft3 20 hz box. Take a pair of these sub drivers at $170 each

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=295-469

They will work great in that enclosure with 600 watts each. You will need to add a high pass filter to any ported sub you build though... Here's what the driver will do in the above enclosure with 600watts.

283


You could just start out with one sub, and the linked minidsp, with the option to add a second one later. Considering how much you set aside for wood in your budget you should be good either way.


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post #8 of 10 Old 07-23-2012, 12:29 AM
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If given the right box, I have no doubt you could achieve your bandwidth and SPL goals with the Peavey driver. The problem IMO, is that I doubt the published T/S parameters are very accurate. Peavey isn't well known for dead nuts specifications. Assuming the published specifications are accurate enough, we would still need to know more specifically which black widow you have. I'm aware of potentially as many as 3 18" woofers from peavey under the black widow name. A 4 ohm woofer, an 8 ohm woofer, and a "low rider" variant with a longer voice coil often sold as a "subwoofer" class driver.

Considering the amplification available, alternative driver options may be more appealing because you could achieve your SPL and bandwidth goals through driver displacement and amplification, rather than through box volume and box related gain. Trust me, the black widow you have can play over 100dB @20hz in the right box, the issue comes down to whether it's worth having a monstrous and complicated box to build, especially with thousands of watts of amplification available that could be used to overcome the inefficiencies of small box high driver displacement designs instead.

Regards,
Eric
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post #9 of 10 Old 07-23-2012, 07:25 AM
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There are several variations of the Black Widow driver, what is the model number?

 

Originally Posted by Bill Fitzmaurice:
It's also the very sort of Voodoo Engineering that should never be done.

 

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post #10 of 10 Old 07-24-2012, 07:36 AM
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I couldn't yet find any specific plans for that driver.

However you could build this bandpass design:

http://www.speakerplans.com/index.php?id=184sub

Pics of users who built the enclosure:
http://www.speakerplans.com/index.php?id=ian184
http://www.speakerplans.com/index.php?id=bob184

It goes down to 32hz and max spl is 130db.

And the Emience Omega Pro 18 driver/s suitablde for that plan are easily available worldwide at a moderately affordable price.
Other drivers listed suitable for that plan are much more expensive and less available worldwide.
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