# Subwoofer Positioning choise



## neo_2009 (Nov 13, 2009)

I've bought a new Subwoofer, a SVS PB1000, and this time, i want to use REW in order to select the best positioning for the Sub.

As i will use an Antimode-Cinema to calibrate it, and according to the Antimode manual, i should select the place where i would get the less NULLS, as the Antimode takes care of the PEAKS.

So, i've used REW to generate the SPL charts for three positions:
- Left corner (A), Right Corner (C), and Center (B).

First, a photo of the place (with the previous sub):
NOTE: Position C isn't accurate marked, although it cant be seen, the real position is 5cm away from the right wall.



The graphs of the measures of the three positions:
- Green is the Left Corner (Position A)
- Red is the Center (Position B)
- Blue is the Right Corner (Position C).



The graphs of the Left VS Right Corners:



The Waterfall for the Right Corner:




The Waterfall for the Left Corner:


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## neo_2009 (Nov 13, 2009)

Based on those measures, and considering i will be using an Antimode, what is the best position to place the sub?

- Right Corner?
or
- Left Corner ?


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## neo_2009 (Nov 13, 2009)

If needed, my REW file can be downloaded here : https://cloudpt.pt/link/dd41f2af-e4e2-4ebc-a436-a4149f0d9b1f/Full_Measures.mdat


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## JohnM (Apr 11, 2006)

Looking at the waterfalls in that measurement you have a very lively room with very little damping. The AntiMode is making a valiant attempt with the RC positioning, but not really managing to fully address the dramatic resonances it has to deal with (the smoothing in the plots you posted hides a bit too much). The left position looks a better starting point, but the room would benefit from something to damp it down, even if it is just rugs and well stuffed sofas!


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## neo_2009 (Nov 13, 2009)

That's totally correct, the room indeed has numerous resonances, at certain frequencies, the roof vibrates immensely. I suppose its probably because its a roof, with plasterboard ceiling walls, and also due to the emptiness of the room: 


I've tried the antimode on the right corner (for simplicity reasons), and although it helps reducing the vibrations, it still vibrates on certain frequencies. 

I will re-locate the sub to the left corner, apply the antimode, and re-measure with REW. 
As its a better starting point, i'm hopping it will provide a better final response.

In the future, its already planned some furniture additions to the empty zone, namely a table, a carpet, and 4 "leather sitting pillows" (i don't know the correct term in English ). 
For once, this hobby and my wife are in total agreement 

Thank you very much for your answer, as soon as i have the left corner measures (with Antimode ON/OFF) i will post them.


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## neo_2009 (Nov 13, 2009)

Well, this weekend i finally had the time to make the last measures and adjustments.
I played with the speaker positions, delays, phase, antimode filters, etc, in order to achieve the flattest response, and also the best mains and sub integration.

The final results were achieved with these settings:
- Speaker ports open;
- Crossover at 130Hz;
- Phase at 90º.

This is the final result, and i think the results are pretty good:



Unfortunately, as i have wooden floors and almost no furniture, the room is extremely lively, the waterfall chart shows the long ringing and decay times 



This long decay/ringing measures explains why in some specific movie scenes, the roof vibrates a lot.

In order to provide more information, the rest of the measures obtained with REW (note: all the charts are for SUB+mains)

Distortion


Impulse


Filtered IR


GD


RT60


Decay


Spectogram



Now, i have to say that the sound is excellent. The antimode and the tweaking with the help of REW really brought the sound to a level i'm almost satisfied.
Unfortunately, the long decay/ringing times lead to the annoying roof vibrations, and more annoying, the fact that the remote must be at hand to lower the volume when this happens.
I suppose that the subwoofer/hard wooden floor interaction, leads to the bass waves being reflected everywhere, and finally hitting the roof.
As the roof is made of paperboard, it vibrates a lot.

So, i understand that this problem can only be addressed with the help of room treatments.
As the AV roof is placed in the loft, i have some aesthetic freedom. Even so, i can only use materials that i could aesthetically integrate in the loft.

As such, i would like to ask your opinions, regarding this specific panels : http://www.amazon.co.uk/GIK-Acousti...&qid=1375053212&sr=1-3&keywords=gik+acoustics

They are reasonable cheap, and i could apply two of them (maybe four if two aren't enough), in the side walls of the loft.

Something like this :

Left Corner


Right corner



What do you think? Any other suggestions ?

Thank's in advance for your time and help :TT


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## neo_2009 (Nov 13, 2009)

The REW file can be downloaded here : https://cloudpt.pt/link/beb08d58-73c9-4344-bddf-300c51c22c7e/Full_Measures.zip


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## Wayne A. Pflughaupt (Apr 13, 2006)

I don’t agree that the roof vibration problem is because the room needs dampening treatments. If the roof exhibits sympathetic vibration at certain frequencies, then reducing the decay time of the signal is not going to help that. Basically, the roof needs to be “beefed up” or stiffened somehow.

Regards, 
Wayne


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## neo_2009 (Nov 13, 2009)

Even if my conclusion was wrong, the ringing times are too long. 
- What should i do to lower them? 
- Would two of those panels have any significant impact on reducing ringing and decay times?


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## Wayne A. Pflughaupt (Apr 13, 2006)

Why do you say the ring times are too long? Is it because a waterfall graph says it’s bad, or because it actually _sounds_ bad to you? (Aside from the vibrating roof.)

One “problem” is that you took the measurement at such a high SPL. That will automatically make a waterfall graph look worse than one taken at a more reasonable level like <80 dB. More reading on that here.

That said, the only way to reduce ringing in the lower frequencies is bass traps. _Lots_ of them.

Regards, 
Wayne


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## neo_2009 (Nov 13, 2009)

The measures were taking at 80db level.

Well, i'm still new to REW, so i stated long long times due to the waterfall graph and the room vibrations.
To be honest, i still cant fully explain what i see in the waterfall graph, but lokking at it it seems that all the frequencies from 20Hz to 200Hz have a decay time of 300ms.

Thank you for the link you posted, was very informative.

You say on your post : "... absorption is required to improve low-frequency decay times – a.k.a. “ringing.” Typically this means bass traps or something similar ..."

Can you please clarify me ? :
- Would the GIK accoustic 244/Monster panels provide the required absorption?
- Are this kind of room treatments effective on the < 100Hz range ?


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## Wayne A. Pflughaupt (Apr 13, 2006)

neo_2009 said:


> ... but lokking at it it seems that all the frequencies from 20Hz to 200Hz have a decay time of 300ms.


The decay times in your waterfalls are actually much longer than that. If the decay time were really only 300 ms, the signal at the 300 ms mark would be down to the room’s ambient noise floor, which is probably in the 35-40 dB range – below the 45 dB lower limit you used. You can change the settings in REW to extend the window out to 600 or even 1000 ms, to see how long it really takes the signal to fully decay.



> Can you please clarify me ? :
> - Would the GIK accoustic 244/Monster panels provide the required absorption?
> - Are this kind of room treatments effective on the < 100Hz range ?


 That’s a question best posed to GIK. However, I can tell you that it will take way more than two panels to make a measurable difference in the low frequencies.

Regards, 
Wayne


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## ilok (Jul 20, 2013)

Try an Audyssey receiver and see if it can do a better job?


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