2 sub placement

[norpus]

Here's some more ideas on 2 sub placement

http://www.audioholics.com/techtips/...acementP17.php

[Sir Terrence]

norpus wrote:

I agree, corner placement can get you more output
I guess my goals are not the same as those you mention. Like Ayreonaut, I am not chasing output as we have enough of that, including ELF.
The way I read the Harman paper was the more subs, the less LF support - agreed. But, the things that I am chasing are a flat response to 20Hz (or below) and smoothing of room nodes in multiple listening positions, not just one sweet listening position.

This is where spatial averaging plays a roll. Midwall placements do not avoid exciting room nodes, it just doesn't excite CERTAIN room nodes

I do not agree that 'EQ can smooth out the modes that are excited by corner placement' or placement at other places. The whole idea of the Harmanising process is to reduce the room nodes as much as possible, using the most practical number and position of subs. Then EQ can be applied to bandaid up the smaller problems and preferably they'll be not so sharp now. We'll see when I get the measurements done following my second IB sub commissioning

You may not agree that EQ can smooth out modes, but Dr Toole's research proves that it does indeed. My experience also shows that EQ does exactly that. Subwoofer driver placement in a null located at or near "1/4" (or 3/4) of the distance between opposing walls can be used to reduce excitation of second-order front-wall-to-back-wall and second-order side-wall-to-side-wall axial room modes, assuming those room modes would otherwise cause a bass peak at your listening position. Everything really depends on where your ears are placed. You can place a sub in the corner and sit in a null position and possibly not hear a single mode. That is why I say your listening position might be as important as the sub placement itself. Lots of bass traps and/or parametric EQ are more effective in reducing bass peaks heard at the listening position, but subwoofer placement can help with a few of the five or six axial room modes under 80Hz. in the typical home listening room. The only way to avoid modes and nodes altogether is to place the sub in the center of the room, suspended halfway between the floor and the ceiling, and lay on it.

You can see by my original graph above that I had a couple of room node issues in my room at that microphone position where I often sit. With high levels of EQ around those nulls, they could appear to be tamed. But move the microphone 12" away and the EQ is then incorrect. This is what I believe the multiple subs can assist with, and hence my committment to the experimentation in this area

This is why one never should measure from one position. There is such a process called frequency averaging. This means taking measurement from several different positions (always recommended) and equalize the measurements averages. A second sub in a opposite corner helps smooth the frequency response in the front row in multiple seating arraingments, but is not as helpful as you move to the rear of the room. There are advantages to dual subs in none modal setups if you are not looking for LF support or lower distortion from your sub.

Unusually then my flat response below 40Hz to 20Hz and below (without EQ boost in this area) using my mid front wall position must be a freak. I'm happy to accept that. (And yes I have a couple of large drivers but were not using much power or distortion at all to produce this result)

Have you ever measured the distortion from your sub when played back you your loudest listening level? As my point stated, you can get away with this position with large drivers and a powerful amp, but you are not really avoiding room modes and nodes with this position.

[Ayreonaut]

I did not get better results from EQ and corner placement, though they were arguably "smoother." Surely the merits of corner placement and alternative placements vary from room to room.

Here is what happened in my room. (These are some old graphs generated from test tones played through my old B&W ASW600. I manually measured four listening locations and EQed for the average. It was a pain before I got my REQ sweeps figured out!)

Note: These were not generated at the same playback volume.

Here is the result of CORNER loading the sub, and EQing for the "average."


Here is the result of locating at a QUARTER point, and EQing for the "average."


The corner loading did gain 3 or 4 dB and the seat-to-seat response was similar and smooth through parts of the spectrum, but there was a huge difference in the responses around 40 Hz. By contrast the quater point location yielded somewhat rougher responses, but without the very large differences at 40 Hz.

By inspection you could argue either way. But my conclusions are based on extended listening. I find the quarter point location to generate less reverberation and it simply sounds better to me in all of the listening positions.

I would like to someday experiment with multiple subs, which was the original topic, come to think of it...

[norpus]

Sir Terrence wrote:

This is where spatial averaging plays a roll. Midwall placements do not avoid exciting room nodes, it just doesn't excite CERTAIN room nodes

Thanks for your good reply
Agreed, placement to avoid overlapping of the ubiquitous room nodes is my aim. And yes every room may be different - which is why experimentation by ear and measurement is good first.

[norpus]

Sir Terrence wrote:

This is why one never should measure from one position. There is such a process called frequency averaging. This means taking measurement from several different positions (always recommended) and equalize the measurements averages. A second sub in a opposite corner helps smooth the frequency response in the front row in multiple seating arraingments, but is not as helpful as you move to the rear of the room. There are advantages to dual subs in none modal setups if you are not looking for LF support or lower distortion from your sub.

Agreed, the multiple listening positions will be tested with one sub and then two to see what the effect of the second is. Will report back findings when done (I have to wait for a mate to bring his measuring equipment over again)

[norpus]

Sir Terrence wrote:

Have you ever measured the distortion from your sub when played back you your loudest listening level?

No I have not measured it as I do not have equipment (apart from my ears). Have you and what did you use?
My ears tell me at high volumes that the sub sound is still sweet - but (at 30dB down) the 75-80dB where I listen to 2ch I am sure distortion is negligible with the IB, as designed.

Edit: Oops, thought these 3 replies would layer on top into one like yours did ST - seems the board is a little different to somes others I visit. Tip from anyone please?