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post #1 of 19 Old 02-16-2013, 10:15 AM - Thread Starter
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He, I'm building a sub for a PA. I just wanted to check with others that have done this more than once before I start. Its a dual 18" box, 3 ft long, 2 ft high, and 2 ft deep, but here is the weird part. I want to get the most db's out of this I can. I've read about designing the speakers to face each other will get more db's. the way I've designed it so far is that at 2 ft deep the cuts of wood with the speakers in them would come inward at a angle until 6 inches from the back where they would attach to a board in the middle. Ill post a link to a pic of a sub close to what I'm talking about. what do you guys think. i will also post a link to the subs I'm looking at.

speakers:
http://www.parts-express.com/pe/showdetl.cfm?partnumber=290-521

A speaker box that will be close to mine
http://www.musiciansfriend.com/pro-audio/nady-psw-152-dual-15-subwoofer
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post #2 of 19 Old 02-16-2013, 11:11 AM
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I've read about designing the speakers to face each other will get more db's.
Reference this please?
Honestly ( coming from working in "Pro Sound" since the 60's ) I would keep it simple and build 2 single 18 cabs. Lighter, more transportable, positioning flexibility. And would allow for a simple 2 element sub array ( w additional delay ) .

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post #3 of 19 Old 02-16-2013, 11:37 AM - Thread Starter
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I searched and could not find the page again. It went through many kinds of speaker boxes, listed pros/cons, and said a sub box like the one I posted a link to at the start of this thread would give a 3 - 10 db increase in spl depending on specifications. Would you know anything about this? I'll think about building 2 boxes, it would be easier. I just want to get the most out of the speakers in anyway I can volume wise, so we can adjust the power up or down in larger or smaller venues.
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post #4 of 19 Old 02-16-2013, 11:41 AM
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Well, welcome to AVS.

It's not weird to want to get the most dBSPL of of a sub. You state PA use, is this primarily for live music, DJ'ing, can you be a bit more specific. The community here is strong, you've come to the right place, but a bit more info could really help.

Are you designing a vented sub? Are you familiar with such tuned designs? Have you considered other types of designs, horn loaded, tapped horn, etc?

Do you already have the amplification you'll be using?

The design you're describing does nothing I'm aware of that raises the SPL of the output. The wavelengths inherent to subwoofer's range aren't affected by the positioning of the drivers, ie, angling them inward like your example showed. Perhaps one can save some space by doing so, maybe a full blown face to face design like the old EV manifold stuff can possess benefits. But acoustically, I'm not sure anything is to gain by angling them in the manner in which you're stating.

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post #5 of 19 Old 02-16-2013, 11:48 AM
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Quote:
Originally Posted by berr View Post

I searched and could not find the page again. It went through many kinds of speaker boxes, listed pros/cons, and said a sub box like the one I posted a link to at the start of this thread would give a 3 - 10 db increase in spl depending on specifications. Would you know anything about this? I'll think about building 2 boxes, it would be easier. I just want to get the most out of the speakers in anyway I can volume wise, so we can adjust the power up or down in larger or smaller venues.

A 3-10dB increase? ... sorry, that's not happening.

The manner in which acoustics increases work dictates a 3dB increase, is equal to doubling the power, ... and a 10dB increase equals a 10x increase in power! That's huge!

Everyone wants what you want. We all want as much out of our subs as possible. But the physics involved cannot be cheated.

I think if you posted a budget, and how many boxes you want, the group here will design something perfectly ideal, and it'll be the best possible quality, highest possible output for the money.

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post #6 of 19 Old 02-16-2013, 11:54 AM
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Originally Posted by FOH View Post


The design you're describing does nothing I'm aware of that raises the SPL of the output.
+1. It won't add any SPL, while it will reduce extension, as the interior volume is less than if the baffle was flat.
Quote:
Its a dual 18" box, 3 ft long, 2 ft high, and 2 ft deep,
How did you arrive at those dimensions? Did you use software to model the driver/enclosure?

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post #7 of 19 Old 02-16-2013, 11:57 AM
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Here's an interesting website, and it's a brief explanation of bass/subwoofer myths that are so prevalent. Also, after you've read those, look around a bit. That is the best subwoofer/driver testing website I'm aware of. The individual that started up the Data-Bass site, is also an avid AVS forum contributor.

Best of luck

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------------------------------------
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(3)Seaton Cat12C up front, (4)QSC K8 sides/rears
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post #8 of 19 Old 02-16-2013, 11:57 AM
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Quote:
Originally Posted by FOH View Post

The manner in which acoustics increases work dictates a 3dB increase, is equal to doubling the power, ... and a 10dB increase equals a 10x increase in power! That's huge!

Technically, wouldn't a 10db increase be a 6x increase in power (more or less)? Not that it has any relevancy to anything.

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post #9 of 19 Old 02-16-2013, 12:03 PM - Thread Starter
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WOW! That is pretty crazy. Thanks for the reply. I'm looking at around $500 for the box and speakers. The speakers I picked out are $150 each. I would like to just have one box, but I am up for what is best. The application used would be for a rock band . Punchy kicks, some bass guitar, and most importantly bass drops (Usually 70 hz- 20 hz range). In small rooms with the sub we have now (Mackie SRM1801 18in 1000W) gets the job done, but in slightly larger rooms is not enough. I have read about vented subs, horn subs, and sever other designs. This is my first time building a unit like this, so like I said I am open to anything from people that have done this many times. The little I've read has me interested in building this sub and more various enclosures to come. Is this enough info? I hope so. Thank you again for welcoming me to the forum and helping me out!
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post #10 of 19 Old 02-16-2013, 12:20 PM - Thread Starter
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I just drew up a design that was close to what I had see subs like this look like. I've had some carpentry experience (The drummers father is a carpenter ), so i have been trying to draw some stuff up so he can just look at it and see the end product
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post #11 of 19 Old 02-16-2013, 12:24 PM
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Quote:
Originally Posted by bass addict View Post

Technically, wouldn't a 10db increase be a 6x increase in power (more or less)? Not that it has any relevancy to anything.


Nope, sorry ... 10x = 10dB

10 dB more SPL, equals a 10x increase in amplifier power.


When working with power, 3dB means 2x, and 10dB = 10x


edit; to clarify further, a 6x increase you mentioned above, would equate to 7.8dB

For example, using 100 watts as the reference;

200w = 3dB
300w = 4.8dB
400w = 6dB
500w = 7dB
600w = 7.8dB
1000w = 10dB


P(dBW) = 10 · log10( P(W) / 1W )
The power in dBW is equal to the base 10 logarithm of the power in watts
The example is one thing, but I had to go find that formula redface.gif

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------------------------------------
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(3)Seaton Cat12C up front, (4)QSC K8 sides/rears
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post #12 of 19 Old 02-16-2013, 12:25 PM
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Originally Posted by berr View Post

Bill
I just drew up a design that was close to what I had see subs like this look like.
You need to spend a few days or even weeks here before even thinking about designing your own speaker:
http://techtalk.parts-express.com/showthread.php?219617-The-Speaker-Building-Bible

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post #13 of 19 Old 02-16-2013, 12:33 PM
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"I want to get the most db's out of this I can. I've read about designing the speakers to face each other will get more db's."

very minor increase, perhaps 1db of bass. the principal advantage seems to be in the low pass cutoff effect.

here is the spec sheet for a cab that employs this approach. at around 100db 1w1m for the bass end, it isn't much of an increase. there is a little increase up near 200hz before the rolloff, but i'm guessing that isn't what you are after.

http://www.rcf.it/c/document_library/get_file?p_l_id=251923&folderId=22487&name=DLFE-7309.pdf

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post #14 of 19 Old 02-16-2013, 12:57 PM - Thread Starter
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Thanks for the link I've been reading and will continue. I am not planning on building too soon, as I want advice on what to do, and to learn.
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post #15 of 19 Old 02-16-2013, 01:38 PM
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Originally Posted by LTD02 View Post


here is the spec sheet for a cab that employs this approach. at around 100db 1w1m for the bass end, it isn't much of an increase. there is a little increase up near 200hz before the rolloff, but i'm guessing that isn't what you are after.

http://www.rcf.it/c/document_library/get_file?p_l_id=251923&folderId=22487&name=DLFE-7309.pdf
That's a bit different. The drivers are at a tight enough angle that a true front chamber is created, making the cab a bandpass. It's not a very well done bandpass, it doesn't go low enough on the one hand and goes too high on the other, but that's what it is. The driver angle on the Nady is too shallow to accomplish anything useful, but Nady isn't exactly known for their speaker design expertise.

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post #16 of 19 Old 02-16-2013, 02:19 PM
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Originally Posted by berr View Post

..and most importantly bass drops (Usually 70 hz- 20 hz range). ...
This will give you a reasonably realistic expectation of what that driver is capable of in cabs of various sizes
www.eminence.com/pdf/Delta_Pro_18C_cab.pdf

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post #17 of 19 Old 02-16-2013, 02:25 PM
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I'd like to read some good measured work on the subject.

I'd suspect the EAW subs, similar to the ubiquitous SB1000 type subs (found everywhere over the past twenty years) wouldn't possess much bandpass effect at all within the subwoofer range. I enjoy the all the wonderful benefits of a quad 18 manifold outlet quad 18 IB, without any apparent/measurable bandpass effects, negative or otherwise. It's akin to a big ol' quad entrant compression driver.

Myself, contemplating the physics, I've never considered any such design as anything but a means to tighter packing of the LF sources. I always thought the idea was tighter packing, and all the benefits associated therein.

Then, other "knock off" mfrs styled their stuff similarly ... many of which don't even enjoy the benefits of tighter spacing, they angle them slightly, like the Nady, for mere aesthetic reasons.

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------------------------------------
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post #18 of 19 Old 02-16-2013, 02:42 PM
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Quote:
Originally Posted by FOH View Post

I'd like to read some good measured work on the subject.

I'd suspect the EAW subs, similar to the ubiquitous SB1000 type subs (found everywhere over the past twenty years) wouldn't possess much bandpass effect at all within the subwoofer range.
The SB1000 is pretty much the same as the RCF. A more extreme example would be the old EV MTL manifold subs, with the drivers directly facing each other, albeit reverse mounted. The dead giveaway that it's a bandpass is the steep rolloff in the midbass.

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post #19 of 19 Old 02-17-2013, 12:04 PM
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Berr, any update on your plans?

Good luck in what you choose

Quote:
Originally Posted by Bill Fitzmaurice View Post

The SB1000 is pretty much the same as the RCF. A more extreme example would be the old EV MTL manifold subs, with the drivers directly facing each other, albeit reverse mounted. The dead giveaway that it's a bandpass is the steep rolloff in the midbass.

You're right, that's why I mentioned them in my first post in this thread. Now that's tightly packed sources! In the early/mid 90's, I encountered these a handful of times. But I believe I've only mixed FOH with them one occasion. I remember discussion of them being limited wrt top end extension, but you're right 200hz is about it. But realistically, I wouldn't want the big excursions of the bass energy interacting much higher than 200 anyway.

From a both a theoretical and practical perspective regarding cooling, I thought having the motor structure being exposed was a great idea.

I don't know how much success EV enjoyed with the MTL stuff, but their current X line, is phenomenal. Sure, every major mfrs. line array stuff is superb these days, but I'd not been exposed to many EV rigs in a long time. I was blown away by their capability. I encountered them associated with a mammoth, multi-act country stadium tour. I spent a few days enjoying the capability, all at the floor FOH mix position. I wasn't mixing, I was working for the house. But my point is EV hasn't been left behind, as was my previous perception, in the quest for state of the art pro audio.


Thanks

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