Room Equalization with Multiple Subwoofers

I've read in some of your answers that subwoofers should be placed at the same distance from the seating area, after which a y-cable can be used to split the signal to them. I have a unique situation where I have 2 identical subwoofers (PSB Subseries 6i) and a receiver with MultEQ XT (Denon AVR-989). The issue I have is that I am unable to put them in symmetrical positions along the front wall. It's close, but one subwoofer will be directly next to my television unit, and one will be approximately 2 feet away from the television unit, on the other side. Will using MultEQ XT with a y-splitter be advisable in my case, or should I be looking at eventually purchasing something that can apply independent correction on both subwoofers, such as an SVS AS-EQ1? Thank you very much in advance for your time!
Bobby

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13 Comments

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    Chris Kyriakakis

    The best solution is to have the ability to control level and delay individually in each sub. The AS-EQ1 does that and will give the best results. In fact, the delay and level adjustments are applied first and then MultEQ pings the two subs as "one". This gives the best performance. While you decide on whether to get that unit, you should do as you propose above. Combine the two subs and let MultEQ ping them as one. Although they won't be time aligned, the effects of their misalignment will try to be corrected by the filter. It's the best you can do given the setup you have.

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    Michael Dowhopoluk

    Is the implementation of MultEqXT in the AS-EQ1 different than that in the 9.2/9.3 receivers with multiple sub outs?  ie.  Can any of the current receivers do independent delay and level adjustments on 2 subs, and then combine them for the MultEQ adjustments?

     

    thanks,

    Mike.

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    Chris Kyriakakis

    Yes, the implementation in the AS-EQ1 is different.  In that product, MultEQ XT first pings each sub separately and finds the relative differences in level and delay.  Then it applies compensation to level and time align the subs to each other.  After that it pings them together as "one" and we found that this produces the best results.  This is not something that has been implemented in AVRs.  The ones that currently allow individual control of each sub give MultEQ the ability to produce individual delays, levels, and room correction filters, but not the ability to measure the subs after the time and level delays have been applied.

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    Michael Dowhopoluk

    So, with the AS-EQ1 you essentially combine the 2 subs, letting their room modes interact, and then create a filter to correct the resultant.

    With a AVR with dual sub outs, a filter is created for each sub, and then the resultant is added together.

    Not that I doubt you, I am just wondering why the first approach gives better results.  The first method adds two nonlinear functions (room modes) together and then applies a nonlinear smoothing, while the second applies the smoothing first and adds the functions second.  While I wouldn't expect the output to be the same from the two, I can't see why one would be repeatedly better than the other. 

    Just curious.

     

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    Chris Kyriakakis

    It's not a linear problem, so the order matters!  Summing two subs that are not time aligned can produce deep nulls due to phase issues between them.  Our research showed that minimizing these effects first (through time alignment) makes it "easier" for the filters to correct the combined response.

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    Michael Dowhopoluk

    Ah, I didn't read your posting carefully enough - in the AS-EQ1 the subs are time aligned to one another, whereas in the case of an AVR with dual sub outs, only the delay to the main listening point is corrected.  Not that I'm sure what the difference between the two is....

    Is there any difference between the AS-EQ1 and the Audyssey Sub Equalizer? 

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    Chris Kyriakakis

    The AS-EQ1 and Sub Equalizer are identical in performance.  The Sub Equalizer is for the installer market and requires the Audyssey Installer Kit for calibration.  It also allows you to place the 2nd subwoofer in a separate room (zone).

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    Bill Sokoloski

    I have Pro already installed on my 9.9 and I now want to do the Sub EQ. The Pro was done by an installer and I have since gotten my own Installer Kit but have never gone in and updated or reset the Pro myself. Now that I want to install the Sub Eq, I have a question - on page 9 & 19, do I click the Sub EQ Assist to on or off? Or, do I have to completely reset the 9.9 back to factory specs and start all over again, like installing the Sub EQ for 2 subs first and then installing the Pro in the 9.9? Or, can I just install the Sub EQ without reinstalling the Pro software on the 9.9? I'm new to Audyssey and it feels like Greek to me.

     

    Thanx, Bill

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    Gior

    So Chris, just to clarify - with something like the Integra DHC-80.1 which has a dual Sub-output, each sub channel is independently level matched and delayed (distance setting) and Audyssey applies filters to these channels independently. However, their combined response is not addressed by the preamp at all and potential phase cancellation and summation issues still exist.  What I understand you are saying is this is where something like the Audyssey Sub Equalizer or SVS AS-EQ1 comes to the rescue. However, the connection option for that to work with dual subs would then be for you to output just one of the sub channels to the Sub A input of those Equalizers and connect the subs out to both of outputs. That would make the .2 sub outputs on these receivers kind of superfluous then wouldn't it? Also, with the 80.1, Audyssey pro does tune each sub channel to about 75db. Wouldn't two independent sub channels at this level result in a higher level of bass than intended?

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    Bill Sokoloski

    I have the Audyssey Sub EQ with 2 subs. In the Pro software in the Sub EQ there is a place where you equalize the 2 subs with the mains. The equalizer section takes care of the dual sub output when youi equalize the mains and two subs togther. The subs together will be at 75 db as well as the mains.

    Bill

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    Chris Kyriakakis

    Gior,

    Your understanding is correct.  If you do use a Sub Equalizer of AS-EQ1 you don't need the second subwoofer output of the DHC 80.1.  But, if you do decide to use the two independently corrected sub outputs of the 80.1, the levels will be correctly calculated by MultEQ so that the two subs will combine to produce proper reference level as Bill pointed out.

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    Gior

    Hi Chris,

    Bill was however using the Audyssey Sub Equalizer which I understand has a mains + sub level checking function. On the Audyssey Pro on the 80.1, it only seems to check each channel independently (like the Integra 9.9) and seems to set everything including BOTH sub channels to 75dB which does result in a significant amount of bass (not that I mind too much :)). It's just that I've been wondering if it is possibly TOO much bass or if the Integra has software in it to compensate for the two subs when actually operating with source material rather than the test tones.

    I don't suppose you guys are going to put out a balanced version of the Sub Equalizer for users who want to keep with XLR connections all the way through their audio chain in the near future? I am thinking it would be preferable to avoid the cancellation issue I am getting when running the two subs independently with the 80.1 as there does not seem to be any way with that unit to independently level match and delay but correct as a whole.

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    Chris Kyriakakis

    Gior,

    Yes, Integra deals with the two sub level correctly.  No current plans for a balanced Sub Equalizer, but we will keep you posted if that changes.

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