# How Do I Measure Mains+Sub?



## Lumen (May 17, 2014)

Hey, I'm only going to say this once... :foottap:

Just kidding! Hope that got your attention. :R

Please let me know if any of this doesn't ring true. :nerd:



I'd like to clear up some confusion I've come across in several threads the past few weeks. It concerns using REW to measure speaker/room response. Seems like some of us think you only need to measure L+sub and R+sub. Others of us seem to think L+R+sub works just fine. In reality, both are right. In general: 
Measure all your subs as one group

Measure each speaker individually

Measure only each speaker combined with the subs

Measure both speakers combined with subs




The following paraphrased info from pages 93 & 94 of Getting Started with REW: A Step-by-Step Guide should help clarify the reasoning behind those speaker/sub measurement combinations:

 _Measure Left, Right, Center, and any/all other channels separately. The reason you want to do this is to see exactly how your speakers, individually, interact with the room so you can ensure the best placement for each speaker and choose the best listening position._



_Subs should first be measured separately from the L/C/R/etc. speakers, but as a group. The reason we want to see the subs separately from the mains "first" is to ensure we have found the best placement for our sub or group of subs relative to our listening position(s) and only by measuring them separately from our (assuming bass managed/small with crossover) mains first can we find the best placement for them (to obtain the smoothest response) without possible interactions from the mains which could create or even hide problems with phase/interaction. Basically, by doing this measurement first, we'll later know how our speakers interact with our subs and whether it's positive or negative and where to look to solve the problems._



_If when you measure Speaker+Subs your response in the crossover range deteriorates from your sub(s) only measurements you then know you have poor phase interaction and you need to either raise the crossover, change the distance/phase settings on the sub(s) and/or your AVR, and possibly a combination of both. Without separate measurements first of your individual speakers and sub or sub "group" you won't know if including your speakers have made this response better or worse._



_Once you're satisfied with your per channel + sub(s) response you can then combine L+R+Sub(s) and show the combined response BELOW 300Hz unsmoothed. This is the ONLY measurement you "need" to show with the L+R combined with the sub(s). The reason for this is that most bass is summed/mono and you want to make sure your "combined" response is smoothest since this is what you'll actually be listening to most of the time as far as bass goes._


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

Note that with mains and subs measured together, the information in the quote is talking about a primary interest in response below 300 Hz. For full range measurements, graphs can show a reduction in the high frequencies (some, not wholesale) if both speakers are measured together. This is caused by cancellation due to the mic not being perfectly centered between the two speakers. Naturally this is more of an issue (not having the mic perfectly between the two speakers) the closer the measurement mic is to the speakers. 

Not to say that measuring both speakers together is not without its uses, though. If you were going to manually equalize them, you want to use matching filters above 300 Hz or so, so a reduction in the highs that might occur would be ignored, as you’re looking to deal with any peaks and valleys in the response, not address an overall level issue.

Regards, 
Wayne


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## ceh383 (Jan 26, 2013)

Lumen said:


> [*]Measure both speakers combined with subs


So, to the title of this thread...With REW connected via HDMI, how do you measure both speakers + your subs?


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## Lumen (May 17, 2014)

ceh383 said:


> So, to the title of this thread...With REW connected via HDMI, how do you measure both speakers + your subs?


REW has no capability to activate three simultaneous channels, so set your AVR to output stereo with bass management. You may need to refer to your owner's manual for details on suitable mode names.


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