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post #1 of 20 Old 10-01-2013, 06:37 AM - Thread Starter
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Hello,

I'm not sure were I should post this but figured here would be a good choice.

I just got finished rearraging my home theater setup and I had to move my subs. They are now on the right and left side of my projection screen about 4 feet form each side of the wall. Before I had them both located in one corner. I am going to be running Audyssey again and I am not sure how to calibrate the subs.

This is my setup...
Onkyo Tx-NR709
Tapco Juice 1400 amp
2 x Rli 12 inch Sound Splinter subs
I have the amp bridged at 4ohms

What is the best way to calibrate them since they are no longer located in the same area? Should I co-locate them again and then move one after?

Thank you
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post #2 of 20 Old 10-01-2013, 07:28 AM
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You'll get more authoritative answers in the Audyssey thread, but...

My understanding is that you'll get a good calibration if the distances from both subs to the main listening position are the same, so that Audyssey detects the same over-all volume levels and distances for them both. Receivers which include Audyssey's Sub EQ XT can calibrate subwoofers which are at different distances.

Of course, those might not be the best locations in terms of actual low frequency response in your room.

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post #3 of 20 Old 10-01-2013, 09:10 AM
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Your Onkyo can only calibrate one sub and your amp does not have any type of EQ/DSP functionality so you have limited options.

1. Get an external DSP like the MiniDSP. This will allow you to set phase, distance and EQ.
2. Place the subs equidistant from the MLP and opposite walls. You can play with reversing the wires and see if that helps. This is the poor man's version of the phase switch.

Either method you choose, you will want to run Audyssey wherever the subs will be placed. Do not run Audyssey then move the subs afterwards. This will invalidate the Audyssey sub calibration. Getting a microphone and downloading REW will go a LONG way towards making all these measurements easier and faster.
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post #4 of 20 Old 10-01-2013, 09:52 AM
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Quote:
Originally Posted by splatee View Post

They are now on the right and left side of my projection screen about 4 feet form each side of the wall.
How wide is your room?

Sanjay
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post #5 of 20 Old 10-01-2013, 12:10 PM - Thread Starter
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The room is roughly 13 feet wide. I have the subs about 3 feet from each side of the wall. I am Audyessey and they sound good to my ears. I did have a switch set wrong on my sub amp. It some how got switched to "mono" instead of "bridged". The subs sounded a bit weak but after correcring it they sound good. My onkyo has Audyessey XT so it has eq for the subs. Do I really need to get a mini dsp or feedback destroyer? Will it make that much of an improvement? I was trying not to mess with all that and REW.

Thank you
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post #6 of 20 Old 10-01-2013, 12:24 PM
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No, you probably have no need for any additional sub EQing, especially if it sounds good.

If you want to know for sure, though, you do need to consider measuring your room's audio with a spectrum analyzer like REW or OmniMic. Help with REW is available in the thread http://www.avsforum.com/t/1449924/simplified-rew-setup-and-use-usb-mic-hdmi-connection-including-measurement-techniques-and-how-to-interpret-graphs

OmniMic is significantly easier to use than REW.

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post #7 of 20 Old 10-01-2013, 01:09 PM
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Quote:
Originally Posted by splatee View Post

They are now on the right and left side of my projection screen about 4 feet form each side of the wall.
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Originally Posted by splatee View Post

The room is roughly 13 feet wide. I have the subs about 3 feet from each side of the wall.
Can you move the subs so that their woofers are centered at 1/4 of room width from the side walls? Seems your subs are a few inches from those locations already (between 3-4 feet). Don't forget to re-calibrate with Audyssey. Should make the bass smoother across the seating area by minimizing the largest standing waves (resonances) across your room.
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Do I really need to get a mini dsp or feedback destroyer? Will it make that much of an improvement? I was trying not to mess with all that and REW.
The only way to know if any of those things will make an improvement is to measure, and you seem reluctant to "mess with all that". If your system sounds good to you, then continue to enjoy it.

Sanjay
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post #8 of 20 Old 10-01-2013, 06:52 PM
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Quote:
Originally Posted by sdurani View Post


Can you move the subs so that their woofers are centered at 1/4 of room width from the side walls? Seems your subs are a few inches from those locations already (between 3-4 feet). Don't forget to re-calibrate with Audyssey. Should make the bass smoother across the seating area by minimizing the largest standing waves (resonances) across your room.
The only way to know if any of those things will make an improvement is to measure, and you seem reluctant to "mess with all that". If your system sounds good to you, then continue to enjoy it.

Can you explain more with regards to the 1/4 wavelength room placement? How do you know what the 1/4 wavelength is?
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post #9 of 20 Old 10-01-2013, 07:01 PM
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I think he's talking about the placement. Place them both at 1/4 the total width of the room from the side wall. So place them both 3.25' from opposite sides of the room
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post #10 of 20 Old 10-01-2013, 09:08 PM
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Quote:
Originally Posted by Martycool007 View Post

Quote:
Originally Posted by sdurani View Post

Can you move the subs so that their woofers are centered at 1/4 of room width from the side walls?
Can you explain more with regards to the 1/4 wavelength room placement? How do you know what the 1/4 wavelength is?
1/4 room width, not 1/4 wavelength. See likelinus' reply to your post. The idea being use placement for mode cancelling by putting the subwoofers at locations of nulls. I thought it was worth suggesting, especially since the current locations of the OP's subs were already close to those spots.

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post #11 of 20 Old 10-02-2013, 04:50 AM
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How do you know where the nulls are without measuring? Is the 1/4 room-width placement the optimal placement in every room? I had always just done the sub crawl around my room until I found the best location, then use EQ to maximize the response.
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post #12 of 20 Old 10-02-2013, 05:23 AM
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The dimensions of the room determine the wavelengths (audio frequencies) which produce standing waves. In a perfectly rectangular room, the nulls will always be at the same relative positions. Many rooms are not rectangular. In those cases a "sub crawl" is very useful.

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post #13 of 20 Old 10-02-2013, 07:06 AM
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Quote:
Originally Posted by Selden Ball View Post

The dimensions of the room determine the wavelengths (audio frequencies) which produce standing waves. In a perfectly rectangular room, the nulls will always be at the same relative positions. Many rooms are not rectangular. In those cases a "sub crawl" is very useful.

So how can I predict the rooms wavelength and where the standing waves will be located at based on my rooms dimensions?
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post #14 of 20 Old 10-02-2013, 07:16 AM
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Ok, breaking it down step by step;

The principle at play is Selective Mode Cancelation

1.) A room's resonant modal behavior dominates the frequency response and the sound we experience in the low frequency range.

2.) There are 3 primary types of room modes, Axial, Tangential and Oblique. For our purposes here, the dominant resonances are axial (only involving two surfaces or boundaries).

3.) The distances between a room's boundaries (front-to-back, side-to-side, floor-to-ceiling) determine the resonant behavior in that axis.

4.) A subwoofer placed up against a boundary is located at a pressure maximum, thus maximum coupling or excitation to all modes in that axis.

5.) Leave that sub there, and place a second sub on the opposite wall boundary and you've canceled the odd order modes along that axis of the room due to acoustic polarity.

6.) Now, if we move each of these subs off their respective boundary, and to approx. the 1/4 points in that axis, we address the remaining problematic mode.

7.) By bringing those two subs into the 1/4 point, we're placing them at the pressure minimum, thus that mode is not energized.


We can utilize this approach to address a room's most problematic issues. If the front to back consistency is what one is most concerned with, easily it can be addressed. Side to side across a wide seating area, etc., any room axis, or even all three axis if need be (four subs placed at 1/4 points). Until one measures, you really don't know for sure. There's significance variance in boundary stiffness, and this can throw things off, so again measurements trump all. Soft, slightly moveable walls/boundaries are more ideal, stiff concrete like walls heighten problematic issues sharpening modal Q.

A careful multi-sub approach, is a fantastic first step toward great bass. Multiples combined with as much bass trapping as one can aesthetically handle, can easily yield superior results. Global EQ for the sub system can knock down any remaining issues, and if need be individual time delay of as many subs as possible can further smooth the complex summation of the sources.


Hope this is helpful, certainly don't want to muddy the waters so I'd be glad to clarify specific points.

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post #15 of 20 Old 10-02-2013, 07:23 AM
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Quote:
Originally Posted by Martycool007 View Post

So how can I predict the rooms wavelength and where the standing waves will be located at based on my rooms dimensions?

Sure, there are many room modal calculators.

However, even the finest computational tools availed to the pros can only approximate all the infinite variables in your room (boundary impedance, etc.). Because all the infinitely complex variables are included, even modest measuring gear can quickly illustrate what's going on in reality, by measuring the actual room itself.

Trust, but verify. smile.gif

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post #16 of 20 Old 10-02-2013, 10:08 AM
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Quote:
Originally Posted by Martycool007 View Post

Quote:
Originally Posted by Selden Ball View Post

The dimensions of the room determine the wavelengths (audio frequencies) which produce standing waves. In a perfectly rectangular room, the nulls will always be at the same relative positions. Many rooms are not rectangular. In those cases a "sub crawl" is very useful.

So how can I predict the rooms wavelength and where the standing waves will be located at based on my rooms dimensions?

If your room is rectangular, the Room Mode Calculator provided by Harman can be helpful: http://www.harman.com/EN-US/OurCompany/Innovation/Pages/Calculators.aspx

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post #17 of 20 Old 10-03-2013, 02:43 AM
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Quote:
Originally Posted by Martycool007 View Post

How do you know where the nulls are without measuring?
Modal behavior is reasonably (though not perfectly) predictable between parallel walls. The diagram below shows what the first 4 modes would look like:


Quote:
Originally Posted by Martycool007 View Post

Is the 1/4 room-width placement the optimal placement in every room?
Between parallel walls, a pair of subs placed at the 1/4 points of room width can cancel (or minimize) the first 3 modes (higher modes are typically out of the subwoofer range).

Here is Floyd Toole's explanation from an old white paper:


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post #18 of 20 Old 10-03-2013, 06:47 AM
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Thanks for the explanation guys! I have always kept my subs in the front two corners of my theater, as they get a nice amount of boundry gain that way. I wonder if I might get better bass if I moved them into the 1/4 width positions? I am almost done with my two Marty Subs, and I am planning on putting each of those in the front two corners, and each of my Dayton UM-15's in the rear two corners.
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post #19 of 20 Old 10-03-2013, 07:01 AM
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Remember that it'll be more accurate bass, not louder bass. Accurate bass often seems a little anemic to people who've gotten used to the "bloated" bass resulting from listening in a location at the one of the standing wave peaks.

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post #20 of 20 Old 10-03-2013, 11:06 AM
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Quote:
Originally Posted by Martycool007 View Post

I have always kept my subs in the front two corners of my theater, as they get a nice amount of boundry gain that way.
That's fine, since it will cancel all the odd width modes and boost the bass level.
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I wonder if I might get better bass if I moved them into the 1/4 width positions?
It will cancel the 2nd width mode (in addition to the odd-order modes already being cancelled). If you look at the diagram in my previous post, you'll see the 2nd width mode peaks in the middle of the room and nulls at the quarter points of room width. If these locations happen to coincide with the seats on your couch, the listeners are going to be hearing very different bass response. So it will help to address this resonance. Keep in mind that placing your subs in nulls will require turning up their levels to get them to the same volume as they were in the corners.
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I am almost done with my two Marty Subs, and I am planning on putting each of those in the front two corners, and each of my Dayton UM-15's in the rear two corners.
That will cancel all your odd length and width modes, not to mention maximizing output.

Sanjay
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