# Huge -20db dip at 40Hz, Audyssey can compensate?



## mc_lover (Aug 25, 2012)

A few days back I REW(ed) by SVS Pb-13ultra. Only Subwoofer was measured.
The subwoofer response shocked me. I didn't realize that there has been a big dip like this in my HT
My question is that Audyssey is capable of fixing this dip? 
or if the response curve steeper than -3dB (as pointed somewhere in the forum), 
Audyssey will not XT32-compensate 



Another question.
So far, I have used REW to measure only one speaker at a time without a connection to AVR
Laptop --> Preamp-- > Power amp--> Speaker

If I want to measure all 7.1 speaker AVR......
Laptop --> Preamp --> what AVR input to connect ?
Thank you


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## sdurani (Oct 28, 2010)

Audyssey can't fix a 20dB dip. Likely no equalizer can without blowing the subwoofer amp. 

Do you have a room dimension that is around 4 to 4.5m?


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## mc_lover (Aug 25, 2012)

it's 3.5 by 5.5 meter
wow. Audyssey cannot fix this dip..this much... I got it.
I have to do a new placement.. keep changing until it's less dip?
or my room size cannot accommodate the sub?


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## sdurani (Oct 28, 2010)

Yup, keep moving the sub around until the frequency response improves. Try the midpoint of your front or back wall, or right behind your seating if possible (when all else fails try nearfield bass).


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## Owen Bartley (Oct 18, 2006)

Yeah, unfortunately 20dB is a big change. Let's see how bad my calculating skills are...

an increase of 3dB requires doubling the power (?) so assuming you're using 100 watts, you're looking at:
3dB increase = 200w (power x 2)
6dB increase = 400w (power x 2)
9dB increase = 800w (power x 2)
12dB increase = 1600w (power x 2)
15dB increase = 3200w (power x 2)
18dB increase = 6400w (power x 2)

That seems absurd... I must have fudged that theory somehow, but in any case, you are right, relocation is your best option by far. Follow Sanjay's advice and move the sub around until you find the sweet spot. This might mean that your main listening position sounds great, and the other seats are awful, or you might get lucky and have a location that works fairly well across the board.


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## mc_lover (Aug 25, 2012)

My system has two subs. SVS PB-13ultra and another Velodyne CHT12000.. it worked together with Audyssey XT32. and SUB EqHT.










The above Frequency Response is for SVS. it's located in the front. I experimented with sub placement total 5 positions in the front. but the shown FR is the best.. FR did't get any better while sub was relocated to the left and right most position. It turned out the front center is "THE BEST" position available to me.










The above FR is Velodyne sub located the center back of the room. It looks a little better to me. 

--> I plan to swap subwoofer positions Velodyne to SVS. 
Don't know how to fix a big DIP yet. 
I only tested a single sub at a time with REW, is it necessary to test two sub simultaneously using Y-cable to check the FR?


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## sdurani (Oct 28, 2010)

mc_lover said:


> The above Frequency Response is for SVS. it's located in the front. I experimented with sub placement total 5 positions in the front. but the shown FR is the best.. FR did't get any better while sub was relocated to the left and right most position. It turned out the front center is "THE BEST" position available to me.


Appears to be a modal problem, since your dip around 40Hz sorta repeats around 80Hz and 120Hz.


mc_lover said:


> The above FR is Velodyne sub located the center back of the room. It looks a little better to me.


Looks much better, especially if you cross over to your main speakers around 60Hz (below where the subwoofer response becomes problematic). Audyssey should be able to pull down the peaks at 30Hz, 60Hz and 90Hz (another modal problem).


mc_lover said:


> I only tested a single sub at a time with REW, is it necessary to test two sub simultaneously using Y-cable to check the FR?


If you plan on listening to both subs together, then you should be measuring them together.


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