Sub EQ for Stereo vs. Surrond setup

I have done lots of reading here. The information here is terrific. Obviously there is a knowledgable group of peple here.

After reading a bit, I installed REW and did some measurements. I also ran some sweeps with my SMS-1 setup. I looked at how my Sub responded by itself, how my mains reponded by themsleves, and how the mains and rears reacted when played together.

I set up my system for Stereo crossing the mains at 80hz. I was able to make a nice flat response.

So then I switched on all 5 channels (by turning on PLIIx), and the response was lumpy again. To get the repsonse flat, I had to re-EQ the Sub.

Do some/many of you keep differnt Sub settings for 2CH and 5.1 listening?

Thanks,
Darrell

[brucek]

Well, I think some, if not many people use two BFD programs. One for two channel and one for movies. The difference being that the two channel utilizes no house curve and the one for movies does.

The equalization filtering is generally carried out with the sub by itself and then the mains are added to tweak up the crossover area. I never felt the crossover area would be that affected by the center or surrounds, but I suppose it might in some systems...

brucek

Bruce,

Getting the sub flat by itself sounds like the easiest way and with previous tools, probably the most common method. But when you add in 2 (stereo) or 5 other speakers that provide bass response I don't know if getting the sub flat (1 of 6) is enough. With today's tools we should be able get more than just the sub flat.

In my room (and on other charts I have seen posted here), there are 75db tones coming from the mains at 30hz. If you add in a flat sub, then you end up with a peak (or maybe a dip).

The Outlaw SMS-1 manual has you EQ the system with the mains engaged in your normal Stereo configuration. This makes sense to me.

It makes sense that we should also send test tones out to the full 5.1 setup and make that flat. I did this by sending the test tones in the 2ch analog input, then turned on PLIIx. I am guessing this is not perfect, but closer than just making the mains and sub flat.

So, Is this newbie crazy talk?

Regards,
Darrell

[brucek]

But when you add in 2 (stereo) or 5 other speakers that provide bass response I don't know if getting the sub flat (1 of 6) is enough.

But why are the other 5 speakers adding bass response? They are all set to small and so don't share any bass frequencies other than at the crossover. The sub drops off at the crossover at a 4th order rate and the mains drop at a 2nd order plus their natural ~2nd order, so the shared area with any common power to produce peaks and dips would be quite narrow.

Unless of course your mains, center and surrounds are set to large for some reason, then you've got lots of work to do.

brucek

[Wayne A. Pflughaupt]

Like brucek said, first make sure your mains are all set to small.

So then I switched on all 5 channels (by turning on PLIIx), and the response was lumpy again.

It’s normal to get some roughness an octave or so above and below the crossover point. Some of this is from physical time alignment situations (i.e., the sound from the mains and the sub reaching your ears at different times, due to them not being the same exact distance from your ears). Some of it is also due to phase characteristics of the crossover itself, although this is typically minimized with the 24-dB/octave filters common these days.

Elaborating on the first point, it makes perfect since that when you introduce all the main speakers that you’d get additional response-altering problems, unless all the speakers are electronically time-aligned. Most receivers today have this feature.

Nevertheless, this is why we typically only concern ourselves with optimizing response between the sub and the left and right main speakers, not the entire 5- or 7-speaker set up. After all, accuracy is more important with music than with movies.

It makes sense that we should also send test tones out to the full 5.1 setup and make that flat. I did this by sending the test tones in the 2ch analog input, then turned on PLIIx. I am guessing this is not perfect, but closer than just making the mains and sub flat.

This may be the source of your problem. The rear signal for Dolby Pro Logic is out of phase with the front speakers. That could really mess up measurements.

Typically if you concern yourself with getting the sub to sound good with the left and right mains, you’ll be satisfied with the way everything sounds with the other speakers engaged.

Regards,
Wayne

Bruce and Wayne,

Thanks for entertaining my toughts and newbie theories. Between you, you have explained everything I am seeing.

So, I have a nice flat response when I send sweeps to the Mains and sub. I will use this same setting for 5.1 sources also. My reciever does have the distance/time setting in place so I should be good in that regard.

I do have a direct mode on my Denon that does sound cleaner than the stereo mode, but because of a bug, it runs the mains as large, even when you set them to small. I have made a seperate sub EQ for this. The mains a very cabable and the sub just needs to fill a dip in the 55hz range. testing will prove out wheather this is worthwhile or not.

And, I have made a sub EQ setting for PLIIx. I do listen to some 2CH sources with this. I will try this and the stereo setting to see if I can hear a difference. So far, I can.

Three setting is all fine and good until I move a speaker or a piece of furniture and have to reset 3 EQs instead of just one, right?

Thanks for all your help.
Darrell

[RollsRoyce]

Wayne A. Pflughaupt wrote:

Like brucek said, first make sure your mains are all set to small.

It’s normal to get some roughness an octave or so above and below the crossover point. Some of this is from physical time alignment situations (i.e., the sound from the mains and the sub reaching your ears at different times, due to them not being the same exact distance from your ears). Some of it is also due to phase characteristics of the crossover itself, although this is typically minimized with the 24-dB/octave filters common these days.

Elaborating on the first point, it makes perfect since that when you introduce all the main speakers that you’d get additional response-altering problems, unless all the speakers are electronically time-aligned. Most receivers today have this feature.

Nevertheless, this is why we typically only concern ourselves with optimizing response between the sub and the left and right main speakers, not the entire 5- or 7-speaker set up. After all, accuracy is more important with music than with movies.


This may be the source of your problem. The rear signal for Dolby Pro Logic is out of phase with the front speakers. That could really mess up measurements.

Typically if you concern yourself with getting the sub to sound good with the left and right mains, you’ll be satisfied with the way everything sounds with the other speakers engaged.

Regards,
Wayne

I agree with Wayne that getting the sub/mains blend right will make multichannel sound good, too.

Another possible reason for the lumpy sub response you saw in multichannel mode is the fact that the sub was then receiving the bass information for all channels instead of just two. Although I've never gone back and remeasured my system in multichannel mode after making changes with REW, I have noticed an increase in sub output (it's right behind our couch) when going from stereo to multichannel while listening to the same program. Still sounds great, though...

Well, I took the advise here, and got the Mains and Sub blending nicely. With a couple more acoustic panels and moving the sub around, the multi-channel blends well with the same EQ settings.

Currently I have all my sources feeding my prepro with digital inputs, so the the prepro does the bass management. My DVD player seems to have beeter DACs so I would like to use the Analog outs for that. It I do this, the Bass Management will be done in the DVD player.

I can set the DVD player to use the same crossover points, but I don't know if the fall-off is the same. How would I go about measuring the blending of the subs and mains when doing BM in the DVD player?

BTW, I am using the SMS-1 for the sub EQ, and I have an Avia disk. I also have REW setup on a laptop.

Thanks,
Darrell

[Wayne A. Pflughaupt]

I can set the DVD player to use the same crossover points, but I don't know if the fall-off is the same. How would I go about measuring the blending of the subs and mains when doing BM in the DVD player?

Well, REW plugs directly into the system, which would bypass the DVD player. I guess you’re left with the old method – sine waves from a disc played on the player, and response plotted manually.

Regards,
Wayne

Yeah, or I can become content with the DACs in the prepro. I don't want to the the plotting thing.

Thanks for the info Wayne.

Wayne A. Pflughaupt wrote:

Well, REW plugs directly into the system, which would bypass the DVD player. I guess you’re left with the old method – sine waves from a disc played on the player, and response plotted manually.

Regards,
Wayne