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post #811 of 817 Old 03-26-2013, 08:57 PM
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Originally Posted by BeeMan458 View Post

I have a big hump that goes into a big null and although I can get a great +/-3 dB graph, well, except for that hump and null that's killing me. tongue.gif

(no smoothing applied)



In my opinion, the only thing that will cure that glaring anomaly, will be a third sub.

I'm looking to possibly fill that hole with a PC13-Ultra.

-

Truly tone sucking at 80. Correct me if I'm wrong but a big hump right before a big dip is The Allison Effect right? I had a very similar situation...but mine was at 60hz. I found that by raising my crossover to 120 helped alot, but I didn't like it that high because of localization....and with the third sub and some acoustic treatment I was able to go back to 80 or 70.
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post #812 of 817 Old 03-26-2013, 11:00 PM
 
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Originally Posted by luketo View Post

Truly tone sucking at 80. Correct me if I'm wrong but a big hump right before a big dip is The Allison Effect right? I had a very similar situation...but mine was at 60hz. I found that by raising my crossover to 120 helped alot, but I didn't like it that high because of localization....and with the third sub and some acoustic treatment I was able to go back to 80 or 70.

No idea but all of my efforts have had fail written all over them. I'll put some effort into learning about "The Allison Effect" and see if the new found information will help with my dealing with this suckout.

"The Allison Effect."

Audyssey has our crossovers set low, mains, center, surrounds; 40/40/60Hz. They're very efficient Klipsch, horn speakers. Raising the crossovers messes with the frequency response graph so I leave the crossover where Audyssey recommends.

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I did not realize my room needed that third sub. the bass is so smooth now and it's coming from everywhere.

How did you place the third sub in relationship to the first two subs? Did you place the third sub on a wall opposite to the first two subs or do you have all three subs on the same wall? In our case, due to WAF and aesthetics, I would want to place the third sub on the same wall as the first two subs as opposed to placing it out in the open, on the opposite was of the first two subs (low WAF), where it should be placed.

Here's to a successful outcome and thanks for the heads-up suggestion regarding "The Allison Effect."

.....biggrin.gif

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post #813 of 817 Old 03-27-2013, 06:37 AM
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Quote:
Originally Posted by luketo View Post

Truly tone sucking at 80. Correct me if I'm wrong but a big hump right before a big dip is The Allison Effect right? .
Possibly. Allison Effect is where the reflection off the wall behind the speaker is 180 degrees out of phase with the front wave, caused by the radiating plane (baffle) being 1/4 wavelength from the wall. At 80Hz that would be 3.5 feet. Allison Effect is easily identified, as it will be relatively uniform throughout the room, no matter where the mic is placed. If the dip shifts dramatically with the mic position then the dip is probably sourced from one of the other room boundaries. But a dip at 80Hz should set off an alarm if the crossover is 80Hz, probably indicating a polarity issue between the sub and mains.
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I found that by raising my crossover to 120 helped alot, but I didn't like it that high because of localization
If raising the crossover helped it wasn't Allison Effect. You can only fix that by moving the sub. Your issue was polarity.

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The Laws of Physics aren't swayed by opinion.
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post #814 of 817 Old 03-27-2013, 10:49 AM
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Originally Posted by Bill Fitzmaurice View Post

Possibly. Allison Effect is where the reflection off the wall behind the speaker is 180 degrees out of phase with the front wave, caused by the radiating plane (baffle) being 1/4 wavelength from the wall. At 80Hz that would be 3.5 feet. Allison Effect is easily identified, as it will be relatively uniform throughout the room, no matter where the mic is placed. If the dip shifts dramatically with the mic position then the dip is probably sourced from one of the other room boundaries. But a dip at 80Hz should set off an alarm if the crossover is 80Hz, probably indicating a polarity issue between the sub and mains.
If raising the crossover helped it wasn't Allison Effect. You can only fix that by moving the sub. Your issue was polarity.

Thanks Bill...One of the first thing I check when I got the subs was polarity. I didn't want to open them up so I put them together and level match both one at a time and them played them together and got a 6db gain....so I assumed they are correctly wired internally. If there is a polarity issue... it will have to be with my subs XLR to RCA cable that I made. I wanted good cables so I got some Mogami Cables and Canare connectors to make them. This is how I wired it http://www.mediacollege.com/audio/connection/xlr-rca-1.htm. Is this right?

Thanks again Master,

Luke


@BeeMan....... I have one sub in the front right corner, one sub on the left side wall 1/3 from the rear wall and the third sub on the rear wall...2ft from the wall and 1/3 from the right side wall. Thanks Luke
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post #815 of 817 Old 03-27-2013, 11:04 AM
 
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Originally Posted by luketo View Post

@BeeMan....... I have one sub in the front right corner, one sub on the left side wall 1/3 from the rear wall and the third sub on the rear wall...2ft from the wall and 1/3 from the right side wall. Thanks Luke

Thanks for sharing your layout. I have read much regarding the benefits of asymmetrical subwoofer placement.
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post #816 of 817 Old 03-27-2013, 01:57 PM
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Quote:
Originally Posted by BeeMan458 View Post

I have a big hump that goes into a big null and although I can get a great +/-3 dB graph, well, except for that hump and null that's killing me. tongue.gif

(no smoothing applied)



In my opinion, the only thing that will cure the above glaring anomaly, will be a third sub.

I'm looking to possibly fill that hole with a PC13-Ultra.

-
What crossover are you using?

Craig

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Perfection is not attainable, but if we chase perfection we can catch excellence."

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post #817 of 817 Old 11-26-2013, 11:49 AM
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