Two subs fighting each other? - Home Theater Forum and Systems -

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post #1 of 7 Old 09-05-13, 10:22 PM Thread Starter
Join Date: Aug 2013
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Two subs fighting each other?

I've updated my basement TV room with a pair of subs that are located pretty much as tight into the front corners of the room as possible (Big WAF pushback on any other position.) Previously I only had one sub in one corner. The new subs are identical in build.

I set about to dink with REW tonight only to realize that my long mic cable is nowhere to be found, so instead I have just been noodling around (with the mic in the far left seat, instead of MLP) seeing how the DSP setup on my new NU3000DSP works.

Anyway, have a look at the graph here.

Two subs fighting each other?-subs-fighting.jpg

The purple trace is the room without any PEQ adjustments in the 65hz region. The green trace represents the best I could do with making adjustments equally to both subs, basically blasting the depression with boost (+12dB in a very focused range.) Although I have the headroom to do this (we don't tend to listen very loudly) I was interested to know what would happen if I only boosted one of the two subs. Low and behold, the mustard colored trace is the result of only boosting one of the two subs. As you can see from the DSP screenshots, the mustard only has +6dB of boost to one channel in a much broader region and shows a much flatter progression.

I have a decent understanding of modes and room interaction, but is this a normal way of dealing with them, or am I missing something?

Green Graph
Two subs fighting each other?-same-eq.jpg

Mustard Graph
Two subs fighting each other?-different-eq.jpg


Last edited by Suntan; 09-05-13 at 10:37 PM.
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post #2 of 7 Old 09-06-13, 03:39 PM
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Re: Two subs fighting each other?

Are the subs the same distance from the listening position? Worth measuring each sub individually to see what contribution it is making, ideally with a timing loopback connection so any differences in arrival time can be taken into account.
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post #3 of 7 Old 09-06-13, 05:46 PM Thread Starter
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Re: Two subs fighting each other?

In this instance, no, as the measurements were taken from the far left chair.

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post #4 of 7 Old 09-07-13, 06:34 AM
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Re: Two subs fighting each other?

What John said.

Boy it makes me feel good when I read a post and am about to respond and read below that John has responded with virtually the same idea. Of course, that almost never happens. John is a pretty smart guy.

What does it do at the center listening position?

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post #5 of 7 Old 09-07-13, 03:29 PM
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Re: Two subs fighting each other?

Placing the subs in the front corners of the room usually means the 1st and 3rd width mode are minimized. This leaves the 2nd width mode, which will peak at the middle of room width and dip at the quarter points of room width.

IF your room is around 17 feet wide (give or take) AND your far left chair you measured from is at/near the quarter point of room width, then the 65Hz dip might be your second width mode.

I know you said you have big WAF pushback to taking your subs out of their corner locations, but are you willing to move them briefly for the sake of measuring? If so, then move them temporarily to the quarter points of room width and re-measure from all three seats in your main row.

Worth finding out if you can get rid of that dip without EQ.

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post #6 of 7 Old 09-08-13, 10:14 AM
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Re: Two subs fighting each other?

Tuning by eye. Even with a fabulous tool like REW revealing various parameters of sound in your room, the final set-up is a matter of judgment by ear because there are many factors that matter.

I bet a 12dB boost at 62 Hz is pretty audible and particularly undesirable while an 8dB cut (possibly or partly an artifact of measurement) certainly is not audible.

The unboosted original curve (what averaging?) looks pretty good to me. Tune by ear from that point since getting a flat measurement typically doesn't sound quite right.

BTW, I'm with Sanjay in favouring experimenting with locations for most other people (your original curve really does look great). My belief (today) is having as much heterogeneity in subs and locations as possible (which is what the research seems to say too). I think of it the same way stock market investors think about diversity.


Last edited by bentoronto; 09-08-13 at 10:20 AM.
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post #7 of 7 Old 09-09-13, 11:13 PM Thread Starter
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Re: Two subs fighting each other?


I scrounged up a longer cable and took some measurements from the center, front seat.

I'm still getting a bit of mismatched results from side to side, even though the room and speaker setups are fairly symmetrical. However, this time it is with the mains. A few graphs.

This is a trace for just the two subs together:
Two subs fighting each other?-subs-only.jpg

And this graph shows two traces. One trace is the left main with both subs while the other trace is the right main with both subs.
Two subs fighting each other?-subs-plus-left-right.jpg

Both the mains and subs are equidistant from the MLP to within inches.

Is it normal to have such divergent performance from left to right?

Now when all is added together (both subs and both mains) I'm getting a fair bit of a drop at 75hz which is noticeable when listening to frequency sweeps (the blue trace.)
Two subs fighting each other?-left-right-plus-all-speakers.jpg

Finally, when I add a bit of delay to the subs (about 1' distance worth) it helps flatten out that 75hz dip (Green trace) compared to the subs with no delay (blue trace - which is the same trace as in the previous graph.)
Two subs fighting each other?-sub-1-foot-back.jpg

Next step is to have a good listening session on one of the nights ahead to listen to the real world differences of the changes I've made, however I'd be interested to hear if I'm going down the wrong path (making delay tweaks to the subs to address the 75hz dip) prior to wasting an evening.

Any thoughts?

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