Sub locations...

**Sonnie** · **06-30-06, 11:19 PM**

I decided tonight I would do a little experimenting with sub locations on my two SVS PB12-Plus/2's.

I took a couple dozen or so measurements leaving one sub in the front right corner and moving the other sub around. I measured one sub and both subs on various tests. All of these below are with both subs since I will ultimately be using both subs.

First I took a normal "as they were" measurement which proved to be what I'd been getting unfiltered on a regular basis. Nothing unusual...

M1...

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Next I tried moving them around... changing the way they were sitting... mostly minor changes and kept getting pretty much the same response as above. Then I moved the left one 1/4 out from the corner of the room and got the response below. Below is the test with both subs running... I forgot to save the one with the one sub... but basically there was very little difference below 60hz, except the output was down 3-4db. Above 60hz there were some more noticeable differences.

M2...

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I moved the left sub up the wall a couple feet at a time... taking several measurements at 0, 45, 90, 135, 180 degrees phase. None of them were impressive at all. I changed the crossover levels on one or both... various combinations but couldn't get anything to look right. Finally I moved the sub to the rear of the room... can't get it in a corner because there is really no back corner with the 45 degree wall on each side. Below is the measurement at 180 degree phase.... I'm thinkin' rear of the room... that what it needs to be. The area from 20-25hz really suffered but I did notice the 40hz area got a little better.

M3...

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Next I tried 90 degrees phase... ugly. Then I said okay... let me just see what 0 degrees will look like for the heck of it. Surprisingly it looked pretty good. Got rid of the 40hz problem... minor nip of a dip at 29hz but it dropped like a cliff at 60hz.

M4...

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So I thought... hmmm... why not try moving that crossover to 60hz and lets see if it's a cancellation issue that we might can eliminate by eliminating that response somewhat in that area. So I set it at 60hz on the rear sub and left the front as is at 80hz. No doubt the best non-filtered response I've seen in my room thus far.

M5...

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All of these above were measured with both subs tuned to 16hz. So I thought... okay let me try 20hz and 25hz and see what happens. I tried both and then one... nope... for some reason none of those looked good no matter what I did. Here's the 20hz tuned on just the rear sub... front sub still at 16hz.

M6...

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So I went back to my best unfiltered response and chunked a few filters in there to smooth it out with a small house curve and remeasured.... I listened to a few DVDs and I'm pretty impressed. I don't know if it's my imagination and/or just knowing that the one sub is back there or maybe some localization (even though it's crossed over back there at 60hz) or what... but the bass just kind of envelops me in a way that I like. It's really sounds good.

M7...

I'm about to watch the Chronicles of Riddick in HD-DVD and really test them.

**Jack Gilvey** · **07-01-06, 06:47 AM**

Very nice! Moving subs around a room and measuring for a few hours is worth years of reading about placement, eh?

**brucek** · **07-01-06, 06:59 AM**

Of course that exercise before REW would have taken about a month...... thank goodness for REW..

You have the ability to cross your subwoofers at different points? I'm able to cross at different points for mains, center, surrounds and backs....... but subs?

**Sonnie** · **07-01-06, 07:39 AM**

Seems like I have been reading a lot about placement here lately and that is what really triggered me to do this.

And most definitely... no way I could have done what I did without REW... lol... yeah... at least a month. Just makes me sick to even think about having to do that manually with tones, pen, paper... walking back and forth to the computer... YUCKKKKK! HUSH ALREADY!!!!! (where's the puke emoticon?)

You mean that expensive Bryston pre-pro don't allow for dual crossover points on your subs? You gotta trade that thing in and get a real pre-pro... heeheehe

I'm using the x-over on the sub itself for the rear located sub. I did try crossing them both over at 60hz on the receiver but that created other problems. There was definitely some wierd interactions between crossover points and phase going on with some of the stuff I was trying. I never even imagined how phase and x-over could effect response like I was seeing yesterday. I would take a measurement and my face wourld turn sour lookin' and I'd be scratchin' my head.

Is the phase 0 degrees working out okay because of the equal distance of the two subs to the listening position? I was worried that it wasn't gonna sound right once I started listening but it sounds good to me.

**brucek** · **07-01-06, 09:07 AM**

Quote:

I'm using the x-over on the sub itself for the rear located sub. I did try crossing them both over at 60hz on the receiver but that created other problems

OK, so you used an 80hz crossover on the processor and then dialed back the rear subs internal crossover to around 60Hz. Strange, but the proof is in the final results. The same for phase..doesn't matter where it's set if the final result is a smooth response at the listening area.

How are you going to accomplish that 60Hz crossover on an IB in the rear location - it has no internal crossover - unless you use something like an X-30 after the BFD channel or perhaps use the BFD to affect a quasi cross......

brucek

**Sonnie** · **07-01-06, 11:13 AM**

My thinkin' is to use the BFD. I'll split up the channels, one front and one back and on the back one insert those steep filters at 60hz and above. That might create more of a challenge to eq both though.

Hopefully if I can get a similar response after they are actually installed I want need but a few filters to level it out and can copy the same filters to both engines... then add the 60hz and above filters for the rear manifold.

If that don't work then yeah... X-30 will have to do the job.

**brucek** · **07-01-06, 02:34 PM**

I would think that in most parts of Canada there would be a temperature swings from ~-20F in the winter up to +120F in the summer in an attic. I can't imagine that would be too good for a driver. In the beautiful state of Alabama, I doubt the lows are too bad, but certainly the attic must reach 120F.

Wouldn't a wall (in a basement HT) or a floor (in a main floor IB) be a better place to mount an IB.......

**Sonnie** · **07-01-06, 03:16 PM**

Well yeah... it would be... but I don't got no choice. The drivers I'm considering are the SoundSplinters and they are more popular for cars (trunks). I'd say it gets just as hot and cold in those as it does our attic. And yes... 120F is probably on the low side in the dead heat of the summer.

I've given some thought to building them inside the room in a baffle type enclosure... 2 drivers front left and 2 drivers front right and then 4 drivers in the rear across that back wall. The box would take up about the same footprint as the SVS but it would be a lot taller because I'd have to have some serious cubic footage. I could probably get close to 12 cubic feet per driver I think. It would no doubt clutter up my room, but who cares, it's an HT room. The location then would help keep the back waves in the room.

EDIT: Nope... scratch the thought of building a box and locating the IB's inside the room. You need about 10X the Vas of the driver, which on the SS drivers is 5+.... 50 cubic feet per driver.

You can get by with less and it still sound pretty good, but if you want true IB, 10X sounds like the magic number.

**Jack Gilvey** · **07-02-06, 09:05 AM**

Quote:

EDIT: Nope... scratch the thought of building a box and locating the IB's inside the room. You need about 10X the Vas of the driver, which on the SS drivers is 5+.... 50 cubic feet per driver. You can get by with less and it still sound pretty good, but if you want true IB, 10X sounds like the magic number.

I think the "technical" definition (Dickason?) is 4x Vas. That's already so big, you see incremental changes after that. It's also tough to make that huge a traditional box be non-resonant, so IB's lack of such starts to be a real advantage.

**bobgenie** · **07-14-06, 04:18 PM**

Hi Sonnie,
That's a nice curve you've got there

How do you get the sub to roll off so gently? I've got the same 2 PB12+s and they roll off really steep at 80 hz. Both tuned to 17 hz with port plug in. I've got them in close to the corners and I have really strong bass below 20 hz but seems to roll off so quick. What do you have the crossovers set to?
Cheers,
Bob.

**Sonnie** · **07-14-06, 04:56 PM**

Hi Bob,

Thanks... I now have moved one of the subs from its original front corner position and to the rear, but the roll off below 20hz as pretty much been the same in any location... it doesn't start to dive until about 15hz or so and then it's not straight down, but a good sliding board.

It may be my room... only 1800 cubic feet and sealed up pretty tight. Mine are tuned to 16hz.

The receiver crosses over at 80hz and I cross over the rear sub further with its own crossover at 60hz. This eliminated the obvious standing waves I was getting at about 75-80hz.

**Chrisbee** · **07-16-06, 02:51 AM**

Unless I have misunderstood your post you can't just set a crossover point on your receiver and then dial in another roll-off point on one or both of your subs.

Well you can of course, but the roll-offs become much steeper and no longer represent the nominal figures you are reading on your setting dials. (in Hz or dBs/octave)

You can use both crossovers to your heart's content provided you understand that the crossover slopes are now unique to your system.

The SVS crossover roll-off is 12 dB/octave I believe. This would have to be added to the receiver's own slope. Which means the sub with the crossover point set on the plate amp probably rolls off lower than you think and with a much steeper slope.

Another other way of doing things would be to set your receiver crossover point as high you can and then just use the sub's own crossovers. That is if you want a particular crossover point. It's all swings and roundabouts in AV.

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