Sub/Main Integration

[Nordo]

Has anyone done a Primer/Help thread on integration of the sub with the mains using REW?

[brucek]

No, what do you need to know?

[Wayne A. Pflughaupt]

IMO, it’s a bit difficult to use REW for this, and it really isn’t REW’s intended purpose. The usual methods for blending subs and mains – Avia, Video Essentials, or simply using receiver-generated test tones w/ SPL meter - all work fine.

Regards,
Wayne

[Nordo]

brucek wrote:

No, what do you need to know?

When I finish EQing my sub, ending with a 24dB/octave roll-off, how do I check that against my mains?

I assume I have to run REW through my receiver, making sure the receiver is set up to only output to sub and mains. I'm not too sure how to do that, but I can find out on the forum for my Onkyo 805 receiver. Also should I included the centre with the L & R? I assume so.

Is there anything special I need to know to set up the graphs for full range responses?

[Nordo]

Wayne A. Pflughaupt wrote:

IMO, it’s a bit difficult to use REW for this, and it really isn’t REW’s intended purpose. The usual methods for blending subs and mains – Avia, Video Essentials, or simply using receiver-generated test tones w/ SPL meter - all work fine.

Regards,
Wayne

I've got Video Essentials, but I've always found it difficult to use, with confusing menus. But I'm willing to persist

I think using a SPL meter isn't a good idea, because you've just set up the sub with a variable response (sloping target based on your ear , not your SPL meter). Using a meter or VE, you would have to guess how much higher the sub would have to be set against the mains using pink noise.

BUT, checking the sub against the mains using REW, you should be able to see how smooth the Xover is - shouldn't you?

[Nordo]

Another reason for wanting to check the sub and mains together, is that my Onkyo has Audyssey, which is an automatic equaliser incorporating filters, phase adjustment, and levelling. It would be interesting to check the full range before and after running Audyssey.

[imbeaujp]

REW was useful to me to verify the cross point between my subs and my mains. Make a mesurment with your subs, then add the mains. You will then see if the mains interfers with the subs, sometimes they are not in phase and they cancell or boost each other. In my case, I adjust the sub distance (delay) by one feet increments and look at the graphs. Just one feet delay could add or remove some dips. Here are some examples :

[brucek]

When I finish EQing my sub, ending with a 24dB/octave roll-off, how do I check that against my mains?

Same way as you tested the sub only, except turn on the mains.

I assume I have to run REW through my receiver, making sure the receiver is set up to only output to sub and mains. I'm not too sure how to do that

Hopefully you checked the sub itself by running REW through the receiver with the receiver in stereo mode and crossover engaged and the mains disconnected. There is no change to that procedure when you test the sub + mains. Just re-connect the mains cables (with power off, of course).

Also should I included the centre with the L & R? I assume so.

Certainly not. REW produces a mono analog signal. There is no way it can support digital sound field steering. The receiver is always in stereo mode when using REW and for sub and mains only (stereo of course automatically shuts off all speakers except the mains and sub. To turn off the mains, unplug the speaker wires with the power off).

Is there anything special I need to know to set up the graphs for full range responses?

Turn on the mains with the sub and measure to 200Hz just as you did with the sub only except now you want to look at the crossover area to ensure it's as flat as possible and at the same level as the sub.

The diagram below shows the target for a sub and for a set of mains using a 80Hz crossover (in a perfect world). The goal is to end up with that red line occuring as a result of the sub and mains adding together.. REW is quite useful in accomplishing this. You'll need to adjust level and phase of the sub in this case.



If you want to measure out to 20KHz full range, you would need a microphone that supported that bandwidth. The RS meter does not.

brucek

[Nordo]

Thanks Guys. You've answered a lot of questions.

When I tested my subs (I've got 2), I connected the output of my sound card direct to the input of my sub's amps.

So to keep things uniform, I'll redo my sub readings going via my receiver.

Also I should read my receiver's manual. I didn't realise that in stereo mode, the sub is active. (I do know that there is some modes where the sub is not active).

Thanks Heaps.

[atledreier]

if you switch it off it's inactive in all modes....

[brucek]

I didn't realise that in stereo mode, the sub is active. (I do know that there is some modes where the sub is not active).

A lot of receivers shut off the sub if the mains are set to large. This is why you want the crossover engaged (mains to small)...

brucek

[Nordo]

brucek wrote:

A lot of receivers shut off the sub if the mains are set to large. This is why you want the crossover engaged (mains to small)...

brucek

The Onkyo keeps the sub on when the mains are set to large (I've always had them set to small). I've never bothered to understand much about the Onkyo's 2 channel modes, that's why I was a bit confused which modes have the sub active. I'm sure now that the stereo mode has the sub active. But I think it's the "pure" mode that does not have the sub active (and maybe "mono" as well).

Anyway, none of that should concern me. So long as the sub is active in stereo mode (which it is), that's all I need to know.


Another point that may be a problem for me. I don't have phase adjustment on my subs. I can swap the leads (ie 180deg), but that's about all I can do manually. HOWEVER, the Onkyo has Audyssey. And Audyssey will alter phase if I let it run automatically, but I can't manually alter it's phase settings. It also does bass management, and I CAN alter it's Xover settings.

What I plan to do is find the best Xover settings using REW and without Audyssey engaged. Then run Audyssey. Let it set everything up, then compare it's Xover area with mine - again using REW. As I said before, one of the few Audyssey settings I can alter (without upsetting any of it's other settings), is it's Xover settings.
So, if I like my Xover point better, I can alter it in Audyssey whilst keeping all of it's other settings (phase alignment, etc).

Jean-Pierre's graphs really hi-light what I am hoping to achieve. Great stuff Jean-Pierre.

[brucek]

I don't have phase adjustment on my subs.

The time distance adjustment for the sub (in the receiver) is a very close proxy. Use that.

brucek

[clubfoot]

I'll just toss in my 2 cents on sub center integration and say that if you're using your system primarily as a 5.1/7.1 system, the center and sub integration is very very important.
All you need to do is connect the center to the left or right channel and check its integration with the sub and use delay to fine tune so that it matches the left and right.

[atledreier]

Or you could use the new system delay function in REW 4.11. It's awesome. I've time-aligned my entire system now, and it really works. I'm at 26ms +-0.2ms for all my speakers right now, and it really helps. Especially front/rear imaging is much more solid and correct.

[Nordo]

brucek wrote:

The time distance adjustment for the sub (in the receiver) is a very close proxy. Use that.

brucek

Good thinking 99.
Maybe that's what Jean-Pierre did.

[Nordo]

clubfoot wrote:

I'll just toss in my 2 cents on sub center integration and say that if you're using your system primarily as a 5.1/7.1 system, the center and sub integration is very very important.
All you need to do is connect the center to the left or right channel and check its integration with the sub and use delay to fine tune so that it matches the left and right.

Thanks, I give it a try. It should only need minor adjustment as the mains and centre are equi-distant from the main listening area (although the centre is a little bit closer to the sub).

[Nordo]

atledreier wrote:

Or you could use the new system delay function in REW 4.11. It's awesome. I've time-aligned my entire system now, and it really works. I'm at 26ms +-0.2ms for all my speakers right now, and it really helps. Especially front/rear imaging is much more solid and correct.

I haven't looked, or even realised that 4.11 can time align (more information to read and learn).
How do you transfer what you achieve in REW into your system?

Quick Wayne/brucek, write a sticky on how to use the system delay function.

[brucek]

how to use the system delay function

I guess you forgot to read this post part way down....

[Nordo]

brucek wrote:

I guess you forgot to read this post part way down....

Thanks brucek
And of course a very big thanks to John M

[clubfoot]

brucek wrote:

I guess you forgot to read this post part way down....

Thanks brucek, I'm also guilty of not reading up on this. Next week I'll find some time to play with the sub and new REW.

[DrWho]

Wayne A. Pflughaupt wrote:

IMO, it’s a bit difficult to use REW for this, and it really isn’t REW’s intended purpose. The usual methods for blending subs and mains – Avia, Video Essentials, or simply using receiver-generated test tones w/ SPL meter - all work fine.

REW is a perfect tool for this purpose - in fact, light years beyond what any test tones w/ SPL meter might provide.

If you wanted to be hardcore, you could use the impulse response measurements to determine the exact phase rotation and time delay required to properly sum the acoustical wavefronts from your subs and mains. I've got an article here somewhere for anyone interested in digging through the numbers...

The easier approach is to simply watch the frequency response until everything flattens out. I have found that a lot of people have their subs cranked up way too high, which in turn makes it difficult to see the acoustic interference.

The ideal way to align the signals with the frequency response is to first measure each speaker independently from each other. Overlay the plots and then adjust the subwoofer gain until the sub plot and the mains plot intersect at -6dB. This will likely be at a slightly different frequency than the actual crossover frequency set in your receiver.

Once you have the individual passbands intersecting correctly, then you want to measure the combined system. If you have a dip at the frequency where they intersect, then you have destructive interference. Sometimes flipping the polarity of the sub will fix this. If flipping the polarity of the sub introduces a new small dip above the crossover frequency, then the signals aren't time-aligned...the fix for that would be to adjust the delay of the subwoofer (rather than its phase or polarity). The steeper your crossover slopes, the harder it is to tell if the system is time-aligned. You can definitely get in the ballpark though by simply measuring the distances of all your speakers.

You know you're done when you measure +6dB at the frequency where your signals intersect. +6dB from -6dB results in a perfectly flat crossover transition.

I would wager that most people that dial in their system this way will think the bass sounds a bit lean (especially if you don't have a house curve). I would encourage you to force yourself to listen to it this way a bit and see if it actually doesn't sound more accurate after a while. Sometimes our ears need a little recalibration. If you still want more bass, then go ahead and crank it up...proper acoustical summation through the crossover region really doesn't matter anymore with the sub cranked...

One of these days I'll get around to posting steps with pictures. I use the exact same approach when using REW to dial in LF/MF and MF/HF crossovers too. It's a bit more complicated since the acoustical centers of horns move around quite a bit, but I'm looking forward to playing with the new version that will actually measure that.

[Wayne A. Pflughaupt]

Hee hee - Mike, I think you’ve managed to successfully show that it is indeed difficult to use REW for this!

Regards.
Wayne

[DrWho]

lol, this is one of the methods your typical professional loudspeaker engineer might be employing. I think it's great fun that we can do it for free and exactly the same way with REW...and get results within about +-0.2dB.

Let me post some pics - it really is quite simple.

[Nordo]

Mike
I've got a couple of queries.

DrWho wrote:

The ideal way to align the signals with the frequency response is to first measure each speaker independently from each other.

Do you equalise their spl first, including the sub e.g. 75dB?

DrWho wrote:

You know you're done when you measure +6dB at the frequency where your signals intersect. +6dB from -6dB results in a perfectly flat crossover transition.

That doesn't make sense to me.

DrWho wrote:

One of these days I'll get around to posting steps with pictures.

That would be great.