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Old 13th March 2005, 02:21 PM   #1
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Default integrating subwoofers with ported main speakers

Hi!
I plan to add stereo subwoofers to my actively biamped Canton RC-L's. The Cantons are ported designs. How do I best integrate the subs in case they start above the portfrequencie of the Cantons? Should I close off the ports? What would that do to the frequenciecurve?
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Old 13th March 2005, 06:06 PM   #2
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Closing off the port is what I do if I can get the Q to be .7 and F3 in the range of 80 to 100Hz. But, this only works right if the lowpass in the crossover is 4th order, the highpass 2nd order and you can set the frequency to F3.

Unfortunately, crossovers with a 4th low and 2nd high are not generally available. You could use a full 4th order LR crossover and tap off in between the cascaded highpass sections but that may be more effort than you care to expend.

The option is to not close off the vent and use a full 4th order in the 100 to 120Hz range.

If you are using a plate amp for the sub you are stuck with the slopes they give you so all you can do is hope for the best although you could try it with ports closed and not closed to find out which you prefer.
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Old 13th March 2005, 08:21 PM   #3
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I have actually got a Behringer cx3400, a 3-way 4th order LR crossover. I also already have a stereo poweramp. I have absolutely no idea what the Q of the Cantons is right now, and I have no idea what ik may become when I close the ports.
The Canton has two 8 inch woofers, and already goes pretty deep. There's sufficient output at 40 hertz, and even some usable output at 30 hertz. I don't know what the F3 is. I neither know what the portfrequencie is.
Let's guess this is around 40 hertz. Say I use the crossover to let the subs start at 60 hertz. Then the port wouldn't do much anymore, right?
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Old 13th March 2005, 08:39 PM   #4
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Given this new information, I would then leave the Cantons unmodified and start the crossover at 120Hz. See how you like it.

You will definitely want to keep the woofers at the same listening distance as the Cantons.
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Old 13th March 2005, 08:59 PM   #5
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Bill,
My speaker originally had a 3way passive crossover, crossing @ 300 hertz & 3500 Hertz. The behringer now takes care of the cross between bass and mid/high. This means the two 8" woofers are working from 300 hz down. Since they already go quite deep, wouldn't it be a waste to cut them at 120 hertz?
Say I do cross at 120 hertz, why would it not make sense to close the port?
Martin
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Old 13th March 2005, 09:28 PM   #6
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Hi Martin,

You don't really want your low bass coming from more than one source. Too hard to integrate it. It's better to cut off the small woofers and have the big one do all the lows. It may be that you will want to lower the frequency a bit, down to say 80 Hz or so and let the woofer do the rest. Plugging the ports is probably an OK thing to do.

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Old 14th March 2005, 02:44 AM   #7
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I'm inclined to start over by asking exactly why you want to add subs and if you do, where will you locate them with respect to the positioning of the Cantons?
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Old 14th March 2005, 10:04 AM   #8
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I want to add subs, to get even deeper bass. Point is that I already have an amp, and a crossover. I also already have 2 Visaton W 300 s woofers (8ohm version). All I have to do is build a box.
I intend to place the subs next to the main speakers, and between them. Would it matter a lot if the subdrivers would be about 12 inches further away from me then the baffle of the Cantons?
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Old 14th March 2005, 07:36 PM   #9
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I'll concede that I'm no expert in vented box design but I've modeled your woofer in WinISD and have come to the conclusion that they will not reach any deeper than what I imagine your Cantons will do.

The compromises that will have to be made in mid-bass sound quality will overshadow any real or imagined gain in low bass performance, IMO.

Were I in your shoes, I would place the woofer so it is at the same distance from the listener as your Cantons (not 12" back as you would like). I would then cross it at 300Hz. I would then reduce the drive to the Canton woofers by 6db and adjust the the level of the Visiton so it was the same as the Canton woofers. You now have all 3 woofers effectively in parallel reproducing approximately the same frequency band at the proper level. You wind up with a system pretty much like you already have in terms of response and the sound quality should be pretty much unaffected. With each woofer now having an easier time of it in terms of excursion, I would then apply some low frequency equalization to both bass systems. Theoretically you could add a 6db boost at 30Hz.

I know this seems unconventional and some readers may yell and scream at me for such a weird idea but . .

I am curious as to what you gained by bi-amping the Cantons at 300Hz.
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Old 15th March 2005, 10:53 AM   #10
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Hi Bill,
I have also ran the woofer through (very basic) program, and I could manage a F3 round 35 hertz with a ported design. Considering its Qts, I think ported should be the way to go.
My Cantons reach pretty deep, as I mentioned before. Maybe an inroom response that gives a F3 even a bit lower than 40 hertz. But that estimate was based on inroom response.
Wouldn't you think the actual F3 anechoic would be a bit higher? Than it would still make sense to use the Visatons below that, right?
I thought the benefit of biamping wouldn't be very big. The greatest advantage I think is that you can remove the passive components from the chain.
The difference is clearly audible. Bass is more controlled, and seems more dynamic. The midband is clearer and sounds even less colored. Instuments are more clearly seperated. I don't think the extra amp amounts in less audible amp distortion, as the distortion from one amp is already below audible level. The Cantons were previously driven with one 120 Watt amp. I always thought this was enough, but by adding a 135 watt amp (for the bass) I now have nearly 500 Watts effectively for each speaker! It now sounds much more relaxed, at even reasonably high volumes.
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