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[Lee Buckalew]

Also, if the stage area has parallel side walls that do not extend out into the room then you may experience some phase problems that may decrease bass output or if the backwall of the stage and the back wall of the house are parallel then the same could happen between those surfaces depending on the distances involved.  

In any case, moving the subs a bit is a very good start.  Also try having them not be exactly mirror images in the room.  Having some assymetry to them may help avaoid reflection/comb filtering issues.

Lee Buckalew
Pro Sound Advice, Inc.

[Brad Weber]

Could it simply have been the location on stage?  If the stage traps some frequencies it would most likely resonate at others, was that happening?  What was the stage construction involved?  Knowing a bit more about the situation might let someone be able to address what was actually happening in that application and how that might relate to this application.

You are right that it should be fairly easy to test, but based on Doug's picture of the setup I would be hesitant to move the subs down on the floor by the front of the stage.  That would most likely not resolve any 'power alley' problems and they almost seem to be using the subs as part of the stage monitor system.  You would also lose the rear wall loading and you'd be putting the subs very close to the people in the front row but cause a much larger differential in level to other listeners.

[Evan Foster]

Brad Weber wrote on Fri, 05 December 2008 17:01

Could it simply have been the location on stage?  If the stage traps some frequencies it would most likely resonate at others, was that happening?  What was the stage construction involved?  Knowing a bit more about the situation might let someone be able to address what was actually happening in that application and how that might relate to this application. You are right that it should be fairly easy to test, but based on Doug's picture of the setup I would be hesitant to move the subs down on the floor by the front of the stage.  That would most likely not resolve any 'power alley' problems and they almost seem to be using the subs as part of the stage monitor system.  You would also lose the rear wall loading and you'd be putting the subs very close to the people in the front row but cause a much larger differential in level to other listeners.

They were both on the front edge of the stage as well as back against the wall on the back of the stage. The Stage was made of 2x6s and plywood that was carpeted. But it doesn't matter we found our solution. As you said the stage could be resonating at other frequencies which could also be some of the problem. Sometimes its good to have things resonate with your subs, other times its not.

The second part of your reply. I agree completely. If you moved the subs and found out that there was some cancellation on stage you could put them back and play with processing. Im sure the drummer appreciates the sub closest to him as a monitor whether its on purpose or not. The point is if the stage is adding or taking away from the subs you could find out very quickly and easily, then if it is or isn't at least you know. Its just an option.

[Doug Bishop]

Evan Foster wrote on Fri, 05 December 2008 17:35

Brad Weber wrote on Fri, 05 December 2008 17:01 Could it simply have been the location on stage?  If the stage traps some frequencies it would most likely resonate at others, was that happening?  What was the stage construction involved?  Knowing a bit more about the situation might let someone be able to address what was actually happening in that application and how that might relate to this application. You are right that it should be fairly easy to test, but based on Doug's picture of the setup I would be hesitant to move the subs down on the floor by the front of the stage.  That would most likely not resolve any 'power alley' problems and they almost seem to be using the subs as part of the stage monitor system.  You would also lose the rear wall loading and you'd be putting the subs very close to the people in the front row but cause a much larger differential in level to other listeners. They were both on the front edge of the stage as well as back against the wall on the back of the stage. The Stage was made of 2x6s and plywood that was carpeted. But it doesn't matter we found our solution. As you said the stage could be resonating at other frequencies which could also be some of the problem. Sometimes its good to have things resonate with your subs, other times its not. The second part of your reply. I agree completely. If you moved the subs and found out that there was some cancellation on stage you could put them back and play with processing. Im sure the drummer appreciates the sub closest to him as a monitor whether its on purpose or not. The point is if the stage is adding or taking away from the subs you could find out very quickly and easily, then if it is or isn't at least you know. Its just an option.

The setup in the photo is current.  Our original position was on the floor outboard of the stage alcove by about 4' which spread them about 50'+ apart.  Version 2 brought them into the notch of the stage extensions (made from 3/4" plywood 4'X 8' sections).  Version 3 brought them inboard again (still on the floor) next to the forward most section of stage extensions which are a pair of 4'x6' putting the subs approx 16' apart.

We then experimented with the on stage setup and found much better bass coverage in the room.  And as you mentioned; yes the drummer likes it but all of our bass players love it more.

Our problems seemed to be much improved with going through the system setup but we probably are expecting far too much from these speakers in a room of this size.  We now appear to have another one that is having issues that sound like there may be damage to the speaker.

Several posters have been critical of the Yamaha SW118's.  A question I posed further down the thread is basically, could we purchase better quality speakers as replacements in these cabinets?

Also there doesn't seem to be any consensus of opinion here as to whether we should maintain the bridge mono setup or split the outputs to dual mono from the amp.

[Evan Foster]

[/quote]

Our problems seemed to be much improved with going through the system setup but we probably are expecting far too much from these speakers in a room of this size.

[/quote]

That could be the problem right there, which would also explain the drivers failing.

Least its not the stage, it was just a possibility, some may say its unlikely or stupid but Ive had it happen more than once.

I would probably keep it in a bridge mono. How lacking are you of bass?  replacement cabs could be an option but possibly expensive. If you can get the two Yamahas to sound good before the straining point, then get two more of those and another xs1200 bridge the amps, one for the left subs one for the right subs.

[Tim Padrick]

If a subwoofer is more than 2' and less than 8' from any room boundary (floor, wall, ceiling), there will be a notch in the frequency response in the range that we are asking the sub to produce.  Having the subs on stage usually qualifies.  The notch frequency is directly related to the distance.  This is called Boundary Cancellation ( http://www.peavey.com/support/technotes/soundsystems/boundar ycancellation.cfm ).  For instance:

2 feet will notch at ~140Hz
2.5' at ~112Hz
3' at ~95 Hz
3.5' at ~ 80Hz
4' at ~ 70Hz
5' at ~ 57Hz
6' at ~ 47Hz
7' at ~ 40Hz
8' at ~ 35Hz


Having the subwoofers split L/R will usually cause uneven response (sometimes horribly uneven response) throughout the room - heavy down the center aisle, passable in some places, and dead as a doornail in others.  This is called the Power Alley ( http://www.prosoundweb.com/live/articles/jbrusi/pa.php ).

See http://www.padrick.net/LiveSound/SubwooferInfo.htm for a couple of additional links.  

[Karen Furno]

Doug Bishop wrote on Tue, 02 December 2008 22:31

Since we are pretty much at the end of the warranty period on the speakers I was wondering what the possibility would be of replacing the spekers in the cabinets with a better speaker with a higher power rating.  I noticed when we opened up the cabinet on the first one that went bad (checking for a possible broken wire) that the speakers are manufactured by Celestion.  I had looked up the model and found a couple with higher power handling specs.  Would a better replacement speaker be an option?   Any suggestions?

This sub, like many others, has an enclosure with a tuned duct or port, giving it a smoother and more extended low frequency response (a so-called bass reflex cabinet design).  The response depends critically on the dimensions of the cabinet and its port, and upon precise mechanical characteristics of the driver, such as its mass and how stiff its cone suspension is.  If a different driver is substituted, it will likely throw off the tuning of the enclosure, especially its resonant frequency.

A bass reflex enclosure provides back pressure on the speaker cone as it vibrates, helping keep it from over-extension.  But this back pressure disappears once the frequency of the tone goes below the tuning frequency of the enclosure.  The driver is said to become unloaded, and applying power to an unloaded driver will either cause the voice coil to bottom out, or slam the spider out to its limit.  I think Yamaha specs this sub down to something like 31Hz, but if you check the response curve, 31Hz is already 10dB or more down from tones just an octave higher.  If you sweep a sub down with a sine wave, you can hear it unload the driver as the tone abruptly disappears.  I would raise your dbx260 highpass setting on the sub up from 20Hz to 30 or 35Hz.  And keep the filter slope at 48 dB/octave.  This will sharply reduce the amplitude of frequencies below the cutoff, and help keep the driver from becoming unloaded.

[ProSoundWeb Community]