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post #1 of 93 Old 07-01-2019, 08:07 AM - Thread Starter
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Dual B&C 21DS115-4 Build

Hi guys, in the next few weeks I will begin my dual sub build using the B&C 21's, to replace my current 18's. I have designed these boxes, measuring 80x80x60cm (UK build) to give 11.65cuft total volume. I've attached my sketchup model and the info I put into WINISD. These will be going in my 1000cuft home cinema room and will be powered by the inuke 6000dsp, can anyone also tell me the best fans that will keep the inuke safe when running at high volumes under the 4ohm loads of these drivers. I figured if I build the box to the exact dimensions and calcs from WINISD the tune should come in slightly lower? Can someone double check my calculations, and any suggestions are much appreciated! Cheers
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post #2 of 93 Old 07-01-2019, 08:31 AM
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Why not go sealed in a 1000cu room?

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post #3 of 93 Old 07-01-2019, 08:33 AM - Thread Starter
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Also, question about the bracing, if I sack off the window bracing and using cross bracing instead from left over mdf, I can save a whole sheet. Is there any advantage to window bracing over cross? I built some boxes a while back with cross bracing that resonated pretty badly, was this a case of not enough bracing? My current boxes use window braces and are dead silent!
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post #4 of 93 Old 07-01-2019, 08:39 AM
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Originally Posted by monty6400 View Post
I built some boxes a while back with cross bracing that resonated pretty badly, was this a case of not enough bracing?

That was a case of MDF. Don't use pressed trash (it's literally the trash of the wood shops).


But on the bracing differences.. Window bracing adds mass and stiffness to the panels, from which resonances move both up and down and thus free up a frequency band for your sub, which won't resonate (as much). Cross bracing can add more stability, but dampens the resonances less than window bracing, as it's less mass and stiffness added to each individual panel.

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post #5 of 93 Old 07-01-2019, 12:22 PM - Thread Starter
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Originally Posted by Mike Butny View Post
Why not go sealed in a 1000cu room?
I modeled the B&C sealed and it only crosses lines with the ported model around 13hz, which I'm not really bothered about anyway, above that is basically +6db for the ported version! Being in the UK I don't have great access to the high excursion drivers like the SI's for the sealed boxes. I can get these B&C's for around £800 a pair!
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post #6 of 93 Old 07-01-2019, 12:24 PM - Thread Starter
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Originally Posted by peniku8 View Post
That was a case of MDF. Don't use pressed trash (it's literally the trash of the wood shops).


But on the bracing differences.. Window bracing adds mass and stiffness to the panels, from which resonances move both up and down and thus free up a frequency band for your sub, which won't resonate (as much). Cross bracing can add more stability, but dampens the resonances less than window bracing, as it's less mass and stiffness added to each individual panel.
Thanks for this, I'll stick with the window bracing then! Much easier to cut anyway!
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post #7 of 93 Old 07-03-2019, 11:26 AM - Thread Starter
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Should I order the 8 or 4ohm versions, will be running off 1 channel of an inuke 6000dsp each?
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post #8 of 93 Old 07-03-2019, 11:49 AM
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"1000cuft home cinema room" if you can get a better deal on 8 Ohm vs 4 Ohm you might as well. Two either way are going to be insane in that space

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You can always turn it down, but you can only turn it up so much (before you run out of power, excursion or structural integrity).
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post #9 of 93 Old 07-03-2019, 11:52 AM - Thread Starter
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Originally Posted by Red Five View Post
"1000cuft home cinema room" if you can get a better deal on 8 Ohm vs 4 Ohm you might as well. Two either way are going to be insane in that space
Both are exactly the same price, just wondering if either one is more preferable for the inuke? Cheers
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@Purenv has been doing more reading on this subject, I believe he mentioned the power supply can dump about the same amount of power into either dual 8 Ohm loads or dual 4 Ohm load on a 6000. If you have two 3000s that do not share a common power supply you would have better sustained output on the 4 Ohm version of the sub.

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post #11 of 93 Old 07-03-2019, 12:00 PM - Thread Starter
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Originally Posted by Red Five View Post
@Purenv has been doing more reading on this subject, I believe he mentioned the power supply can dump about the same amount of power into either dual 8 Ohm loads or dual 4 Ohm load on a 6000. If you have two 3000s that do not share a common power supply you would have better sustained output on the 4 Ohm version of the sub.
Doubtful I'll ever run them hard enough to shut down the inuke, may aswell get the 4ohm methinks.
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post #12 of 93 Old 07-03-2019, 12:30 PM
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Originally Posted by monty6400 View Post
Should I order the 8 or 4ohm versions, will be running off 1 channel of an inuke 6000dsp each?
4 ohm. You can't bridge the Inuke 6k, so wiring them in parallel to drop the impedance doesn't work unless you are using just 1 channel of the Inuke. So unless you are planning on adding 2 more at some point, and running 2 each channel, 4 ohm is the way to go.
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post #13 of 93 Old 07-03-2019, 12:42 PM - Thread Starter
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Redesigned the box slightly larger, now 12.4cuft after port and driver displacement, tuned slightly lower at 18.3hz, does the bracing look good?
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post #14 of 93 Old 07-03-2019, 12:50 PM
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Originally Posted by monty6400 View Post
Redesigned the box slightly larger, now 12.4cuft after port and driver displacement, tuned slightly lower at 18.3hz, does the bracing look good?

I think it looks good Is there anymore space to find? I have bad ideas.

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post #15 of 93 Old 07-03-2019, 12:53 PM - Thread Starter
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I think it looks good Is there anymore space to find? I have bad ideas.
They've got to fit in between a htm 12 if you follow, this is the absolute max size, have to bear in mind how I will get them into the room also!

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Never mind, I think you would need a little bit more space for playing around with a band pass sub.

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You can always turn it down, but you can only turn it up so much (before you run out of power, excursion or structural integrity).
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post #17 of 93 Old 07-03-2019, 12:56 PM - Thread Starter
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Never mind, I think you would need a little bit more space for playing around with a band pass sub.
Are you talking about a storm beaker variant? That would be insane!!!! Hopefully 2 of these in a room my size should be 'enough'

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Are you talking about a storm beaker variant? That would be insane!!!! Hopefully 2 of these in a room my size should be 'enough'

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Stormbreaker is 11 cuft 18Hz tune, so you are already there with this box! This is the next evolution of that, not quite two 21DS115 worth of bass in vented enclosures, but it is getting close. https://www.avsforum.com/forum/155-d...enclosure.html

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post #19 of 93 Old 07-03-2019, 01:01 PM - Thread Starter
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Ah right, I'm getting names confused, I did mean that one, MDF is cheap in the UK so let's see where I'm at after this build. Hopefully not deaf.

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Ah right, I'm getting names confused, I did mean that one, MDF is cheap in the UK so let's see where I'm at after this build. Hopefully not deaf.

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No worries. I was not brave enough to design it in 18mm, it took me long enough using 3/4inch to do all the math.

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How do you like your HTMs in that cubby you've made? I'm moving to a house in about a month and one of my setup options would be to take off all the doors for the closet in one of the bedrooms and do something like that (including the Rockwool). Of course, I also need to build some speakers, too, but I'm considering HTM-10s. Maybe 12's. We'll see.
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post #22 of 93 Old 07-03-2019, 02:42 PM
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Doubtful I'll ever run them hard enough to shut down the inuke, may aswell get the 4ohm methinks.


If you are not listening to dub step or something similar at high volume levels you should be fine with the 4ohm models. But keep in mind that the 21DS 4 ohm model has a nasty dip in impedance and its Re is very low for a rated 4ohm sub.

Remember that the Behringer 6000 is already internally bridged.

Excerpt from Data-bass.com:
The 21DS115-4 driver has a rated DCR of 2.2 ohms which is quite low for an amplifier rated into a 4ohm bridged load. This is likely what caused the amplifier to protect when dumping full power into the impedance minimums. This behavior would likely diminish or disappear with a driver having a bit higher DCR closer to 3 or 4 ohms. An application of a light amount of limiter to keep the amplifier from clipping and keep the long term power applied down just a hair, would likely go a long way for safety and cleaning up the sound at the limit. It would probably eliminate the issues with the amp going into protect when heavily clipped into the 21DS115-4’s minimum impedances as well.

But like I said if you are not going to push it then you will be fine.
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Originally Posted by Purenv View Post
If you are not listening to dub step or something similar at high volume levels you should be fine with the 4ohm models. But keep in mind that the 21DS 4 ohm model has a nasty dip in impedance and its Re is very low for a rated 4ohm sub.

Remember that the Behringer 6000 is already internally bridged.

Excerpt from Data-bass.com:
The 21DS115-4 driver has a rated DCR of 2.2 ohms which is quite low for an amplifier rated into a 4ohm bridged load. This is likely what caused the amplifier to protect when dumping full power into the impedance minimums. This behavior would likely diminish or disappear with a driver having a bit higher DCR closer to 3 or 4 ohms. An application of a light amount of limiter to keep the amplifier from clipping and keep the long term power applied down just a hair, would likely go a long way for safety and cleaning up the sound at the limit. It would probably eliminate the issues with the amp going into protect when heavily clipped into the 21DS115-4’s minimum impedances as well.

But like I said if you are not going to push it then you will be fine.
I may occasionally want to blast it for demo purposes, the thing I am most worried about is the fan mod on the inuke. I plan on using the noctua fans, but dont want this to put the amp in even more danger, would a limiter around 1500w be sensible to avoid the amp running into trouble? Many thanks

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post #24 of 93 Old 07-03-2019, 03:10 PM - Thread Starter
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Originally Posted by CrusherW9 View Post
How do you like your HTMs in that cubby you've made? I'm moving to a house in about a month and one of my setup options would be to take off all the doors for the closet in one of the bedrooms and do something like that (including the Rockwool). Of course, I also need to build some speakers, too, but I'm considering HTM-10s. Maybe 12's. We'll see.
At first with them being in corners I was worried they may sound 'boomy' for lack of a better word, hence the rock wool, but ever since I have got them I have literally not even considered an upgrade, for the money (even after shipping to the uk) they are well worth it. I never tried them without the rockwool so cant comment on that, but I assume youd use something similar anyway. At the time it was between the 10's and the 12's, even though the 10's would have still been overkill, I fancied just getting the largest I could fit and also to try the seos 15, which does a great job!

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I may occasionally want to blast it for demo purposes, the thing I am most worried about is the fan mod on the inuke. I plan on using the noctua fans, but dont want this to put the amp in even more danger, would a limiter around 1500w be sensible to avoid the amp running into trouble? Many thanks

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then if you haven't ordered your B&Cs i would highly suggest 8ohm versions as they will be easier for your amplifier to drive at higher volumes for longer periods with less strain and power draw from the wall outlet. the amp with 8ohm loads can sustain 1100+ watts forever... 4ohm loads with shut down the amp over time depending on music type and bass durations... the wattage difference is going to be less than 1.5dB which your ears at that volume will not be able to tell the difference.... so why stress your equipement?

if you have already ordered the 4ohm, definately set a limiter! maybe try .5dB down from max voltage to start and if it shuts down, back it off another .5dB....
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then if you haven't ordered your B&Cs i would highly suggest 8ohm versions as they will be easier for your amplifier to drive at higher volumes for longer periods with less strain and power draw from the wall outlet. the amp with 8ohm loads can sustain 1100+ watts forever... 4ohm loads with shut down the amp over time depending on music type and bass durations... the wattage difference is going to be less than 1.5dB which your ears at that volume will not be able to tell the difference.... so why stress your equipement?



if you have already ordered the 4ohm, definately set a limiter! maybe try .5dB down from max voltage to start and if it shuts down, back it off another .5dB....
Thanks a lot for this, do the 8ohms experience a similar impedance dip to the 4ohms, ie is it likely that the amplifier will be seeing 6ohms hence be able to give more voltage?

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Thanks a lot for this, do the 8ohms experience a similar impedance dip to the 4ohms, ie is it likely that the amplifier will be seeing 6ohms hence be able to give more voltage?

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i believe the voltage dip drops to 5.1ohms at it's lowest point. But it really doesn't matter as voltage fluctuates constantly with the music. it's not like a sine wave which draws a constant voltage. if you ran a sine wave using the 4ohm versions you would definately shut down the amp within seconds... with the 8 ohm versions the amp will drive them at full volume for a long time....
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post #28 of 93 Old 07-04-2019, 02:17 AM - Thread Starter
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i believe the voltage dip drops to 5.1ohms at it's lowest point. But it really doesn't matter as voltage fluctuates constantly with the music. it's not like a sine wave which draws a constant voltage. if you ran a sine wave using the 4ohm versions you would definately shut down the amp within seconds... with the 8 ohm versions the amp will drive them at full volume for a long time....
Only thing I'm thinking is that my current subs are 8ohms and I've managed to get all 3 lights on the inuke front to come on with no limiter, so unless the sensitivity of the new subs is greater downlow I will have to model and compare. My goal is 125db peaks across the spectrum.

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post #29 of 93 Old 07-04-2019, 04:03 AM
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Dual B&C 21DS115-4 Build

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Originally Posted by monty6400 View Post
Only thing I'm thinking is that my current subs are 8ohms and I've managed to get all 3 lights on the inuke front to come on with no limiter, so unless the sensitivity of the new subs is greater downlow I will have to model and compare. My goal is 125db peaks across the spectrum.

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Are you replacing or adding to your 2 Faital Pro subs?

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post #30 of 93 Old 07-04-2019, 05:16 AM
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The 21DS115 is good for 117 to 120db on the left corner depending on what is giving it power. 117db + 6db for a second sub that has its own supply of power for 123db. Room gain should be in the neighborhood of 3 to 6db under 30Hz where output is harder to make, so worse case scenario for room gain is 126db peak on the left corner. With a 1000cuft room gain should be better. It will be close using two ported 21DS115s, the room can mess with all of this though.
monty6400 likes this.

Stormbreaker (For Sale) | Wisconsin Home Theater Meet Thread
You can always turn it down, but you can only turn it up so much (before you run out of power, excursion or structural integrity).
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