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Old 2nd October 2012, 09:24 PM   #1
col is offline col  Australia
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Default multi high tuned cabs for a better LF

I pulled the bit of text below out of the Bass My Soldier thread. I'm interested if anyone can expand on what Sreten has stated about using multiple small (100lt) cabs to achieve a low frequency response with the SPL limits of the combined cabs?

I'm approaching 6 x 121ltr BR boxes with 18" Peavey low riders tuned to 38hz and would like to tune the subs using my DSP to get a -3db at 35hz response, flat out to 100hz where I cross into 4 kick-bins. I'm using a couple of MiniDSP 2x4 balanced with the 4way mono crossover plugin. The PEQ has low-shelf, high-shelf filters with variable Q. Also, I can model the max SPL in WinISD. Is there anything I need to watch out for?


>All about specs. Response is almost irrelevant. For PA you can always EQ
>it. What you need to know is the maximum SPL profile of the cabinet.

>Instead of the 2 x18's per side suggested in this thread, if you went for
>4x18's per side but still low tuned but only say 100L per driver, so the
>bass response is restricted, with enough power and EQ you end up with
>a set-up that is simply better, SPL wise, for any response. However this
>thread is simply refusing to discuss the assumptions its making, YMMV.

>As I said miles earlier in the thread bass response is about driver maximum
>SPL at any frequency and having enough juice to achieve that SPL. Within
>the SPL limits you can actively EQ the bass to any response you want.

>rgds, sreten.
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Old 2nd October 2012, 10:23 PM   #2
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Quote:
Originally Posted by col View Post
I pulled the bit of text below out of the Bass My Soldier thread. I'm interested if anyone can expand on what Sreten has stated about using multiple small (100lt) cabs to achieve a low frequency response with the SPL limits of the combined cabs?

I'm approaching 6 x 121ltr BR boxes with 18" Peavey low riders tuned to 38hz and would like to tune the subs using my DSP to get a -3db at 35hz response, flat out to 100hz where I cross into 4 kick-bins. I'm using a couple of MiniDSP 2x4 balanced with the 4way mono crossover plugin. The PEQ has low-shelf, high-shelf filters with variable Q. Also, I can model the max SPL in WinISD. Is there anything I need to watch out for?
A usual, the two things to look out for is too much average power, which can cook voice coils in cabinets that restrict excursion, and too much excursion which occurs below Fb and about 1/3 octave above Fb.

Too much excursion can physically rip the cone, spyder or surround, and distortion increases dramatically above Xmax.

Excursion is easy to see and measure with a light colored dot on the cone, too much heat results in a "burnt glue" smell when the cones are new, but after a while that smell goes away, and the next step is "Fahrenheit 451", the smell of burnt paper.

As far as using EQ to achieve a response, if the cabinet design is 10 dB down at a frequency and SPL level that you want it to be flat to, the speaker would require 10 times the power to achieve that response compared to the upper spectrum. When you consider power compression from voice coil heating can easily amount to 3 dB or more at high average power levels, the 10dB difference becomes 100 watts compared to 2000 watts (1/20) rather than a 1/10 ratio.

That said, if the program material has 10 dB less average response down at 35 Hz, no worries, but if you are playing dubstep, hip-hop, or electronica type music that requires an equal output level down low compared to at 80-100Hz, LF boosts of more than 3 dB are a good way to start an expensive barbecue.

Although from a sound quality standpoint I do prefer more smaller, tighter sounding cabinets using some EQ to flatten out LF compared to fewer, big, floppier sounding cabinets that achieve the same SPL with a fraction of the amplifier and transducer expense , there are as many compromises to consider as there are musical genres.

Art Welter
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Old 3rd October 2012, 01:07 AM   #3
col is offline col  Australia
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Hi Art,

Thanks for your response as always good sense. I will play in software abit and post some screen grabs before I go out into the yard and start sticking them with watts
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Old 3rd October 2012, 02:53 AM   #4
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OK, if I pretend in WinISD that my 6 drivers are in one box tuned to 38hz this is what the max SPL profile looks like. note. WinISD max SPL doesn't include the high pass filter that I have set LR24db at 35hz:

Click the image to open in full size.

So looking at that profile I need to reduce everything from 35hz by 10db?

Click the image to open in full size.

I'm using 2 banks of 3 speakers each with a separate miniDSP channel so Iv'e implemented a -5db 35hz high-shelf with a 1.3Q

The crossover low pass is set at LR24db 100hz

Art, is this kind of setting the same as the boost that amounts to 2000W that you mentioned in the previous post?

cheers,
col.
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Old 3rd October 2012, 12:52 PM   #5
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Quote:
Originally Posted by col View Post
Is there anything I need to watch out for?
Hi Which T/S are you using?

b
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Old 3rd October 2012, 01:10 PM   #6
bjorno is offline bjorno  Sweden
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FYI:Adding filters

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Old 3rd October 2012, 02:51 PM   #7
dstmbgh is offline dstmbgh  United States
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Bjorno, please check your mailbox. I sent you a PM yesterday. Thanks if you're able to help. (OT for this thread)

David
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Old 3rd October 2012, 03:41 PM   #8
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Originally Posted by col View Post
So looking at that profile I need to reduce everything from 35hz by 10db?

Art, is this kind of setting the same as the boost that amounts to 2000W that you mentioned in the previous post?

cheers,
col.
Well, I mentioned 10 dB down with power compression requires the difference between 100 and 2000 watts, your plot looks about that bad.

Even if you do one (huge) cabinet for 3 speakers, I'd suggest separate chambers.

Look at the Peavey Cabinets in Bjorno's post above, if you want LF response, somewhere between 9 cubic foot with an Fb of 30 and 6.75 C.F. at 34 Hz looks good.

Art
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Old 3rd October 2012, 09:12 PM   #9
col is offline col  Australia
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I already have the cabs. I want to keep them small and modular. In WinISD I was combining the volume just for an example.

the TS used:

Click the image to open in full size.
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Old 3rd October 2012, 10:07 PM   #10
col is offline col  Australia
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I guess what I am getting at is can I shave off the top part of the MAX SPL and get an overall lower SPL (132db) but with a wider, lower frequency band (35-100hz)? I'm not trying to boost the LF up to where the boxes are most efficient. I thought that was clear in the initial post.

Edit: going back and reading the first post, actually it wasn't that clear. Overall I think I have a better understanding of what I need to do. Mainly just keep an eye on xmax when i set the limiter.

Bjorno, Art thanks for your input.

col.
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Last edited by col; 3rd October 2012 at 10:19 PM.
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