Better bass in SACD 2 channel vs 5.1 - AVS Forum
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post #1 of 10 Old 01-09-2014, 11:27 AM - Thread Starter
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I was listening to Allman Brothers: Eat a Peach - SACD the other nite in 5.1 and was getting annoyed with the cymbal action on the surrounds so I switched the Oppo from multi-channel to 2 channel output for SACD's.

I couldn't believe the increase in bass output from going to multi-channel to stereo, despite losing the sub.

I guess my question is; is this normal or is there something wrong with my setup or settings? I use the Oppo's 8 analog outs and ext. in on the AVR.

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post #2 of 10 Old 01-09-2014, 11:34 AM
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Two different masters. Strange that they would be that different.
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post #3 of 10 Old 01-09-2014, 12:07 PM
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Quote:
Originally Posted by FMW View Post

Two different masters. Strange that they would be that different.

I would agree this is the very mostlikely explanation, by a long shot.

THere is, perhaps, a possibility of a phase mismatch between mains and sub (either, I suppose in the recording or in a particular system) that causes the mains plus sub te really be more like mains minus sub in the low end . . . . Perhaps worth investigating, but without owning that SACD, I'd guess the mix is just that different in multichannel for whatever reason, because one would expect to hear the phase-based bass suckout on all content, should it actually exist in a given system
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post #4 of 10 Old 01-10-2014, 08:29 AM
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The reason is almost certainly that the subwoofer is cancelling the bass from the main speakers. Software programs tend to get this wrong, so my advice is to totally defeat/shut off any room correction software and use your ears.

One reason this often happens is that the subwoofer filter knob (or software) is set so that the subwoofer is operating at frequencies above 50 Hz, which should NEVER be the case.

Make sure that your subwoofer is ONLY operating at frequencies below 40-50 Hz. The lower your main speakers can go, the lower the f should be set on the subwoofer filter knob. Otherwise, they will certainly interfere with each other. The subwoofer must only operate below the cutoff frequency of the main speakers.

The other issues are-

1) Subwoofer location

2) Subwoofer phase control setting.

It may take a LOT of time to find the optimum phase control setting and physical location for the subwoofer, since only experimentation will get you there.
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post #5 of 10 Old 01-10-2014, 08:48 AM
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I don't understand. Why shouldn't a subwoofer operate above 50 hz? I thought the idea was to let your sub work 120 hz and below if possible?

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post #6 of 10 Old 01-10-2014, 09:07 AM
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The subwoofer and main speakers cannot operate in a synchronized manner within the same frequency range. Frequency "overlap" between the subwoofer and mains is always detrimental to the sound.

The drivers are located at different physical locations and have different physical responses, because they are not identical.

This makes it impossible to prevent them from operating out-of-phase with each other, and some cancellation of their outputs always results, which ruins both the impact and clarity of the system bass.

If you have main speakers that go down to 50 hz, for example, you must make sure that the subwoofer only operates below 50 hz.

You can TRY to minimize cancellation by using the phase control of the subwoofer and moving the sub to different locations, but eliminating the frequency overlap completely is the most effective answer to the fundamental problem. Even a small amount of phase difference "smears' the bass and you get "muddy" unclear bass as a result.

IF you have Teensy main speakers that only go down to 120 hz, then the only solution is to run the subwoofer up that high, but that sucks. That means your bass is monaural up to 120 hz, which emasculates the music.

You want front speakers that go down to 60 hz or lower for nice sound quality, and a subwoofer that fills in the frequencies below.

That is WHY it is CALLED a SUBwoofer! Its ONLY legitimate purpose is to fill in the f region BELOW the LF cutoff point of the main speakers.

Trying to use it any differently causes problems.
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post #7 of 10 Old 01-10-2014, 09:36 AM
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Yes there can be some phase cancellation. When that occurs it is on the high side of subtle. In my system, I can't hear any difference in sound at all when I switch the subwoofer phase. You're listening to two different masters.
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post #8 of 10 Old 01-10-2014, 10:19 AM
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Quote:
Originally Posted by commsysman View Post

The subwoofer and main speakers cannot operate in a synchronized manner within the same frequency range. Frequency "overlap" between the subwoofer and mains is always detrimental to the sound.

The drivers are located at different physical locations and have different physical responses, because they are not identical.

This makes it impossible to prevent them from operating out-of-phase with each other, and some cancellation of their outputs always results, which ruins both the impact and clarity of the system bass.....

...but they MUST operate together at the same time and both will be playing at the same rolling off -6dB level at the crossover point.

Also to the OP: You may have your surrounds out of phase. You likely wouldn't notice this watching movies but would be apparent with multi-channel music.


EDIT: I found a chart of subwoofer and mains crossover:


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post #9 of 10 Old 01-10-2014, 05:14 PM
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Sounds like a classic case of low LFE when playing MC SACD.

http://www.avsforum.com/t/748147/lfe-subwoofers-and-interconnects-explained
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post #10 of 10 Old 01-13-2014, 12:49 PM - Thread Starter
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Thanks for all the kind responses.

I think it may have been a combo platter of things.

The def tec speakers are a fairly recent addition and I realized I hadn't recalibrated the sub. I ended up moving the sub a little bit, turned down the gain and turned up the sub output on the AVR. With those changes I'm getting better bass response from the sub and the difference between the 5.1 and 2.0 mixes, while still different on the above referenced disk, aren't quite as startling as before.

Also, as others have stated there just appears to be a difference in the mix. I sampled several other discs and couldn't recreate the difference in bass output between the 5.1 and 2.0 mixes.

Thanks again.

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