A good way to loose bass

[Shashi Kumar]

Though trivial, thought I should share this information.

When everybody tells you that the set up can make or mar your sytem you tend to be a little fussy about everything. Couple that with incomplete awareness, and you have a potent combination.

Encouraged by the manual, and having read about the sub-sat system, I had the typical sub-sat connection set-up. This was-connect the left & right main speaker terminals of the receiver to the speaker level input terminals of the subwoofer. Connect the main left & right speakers to the speaker level output of the sub.

Typically, the TV screen, the left & right main speakers, and the centre speaker are approximately, in the same vertical plane.Due to the pecularities of the room set up, the right speaker, was behind this plane (further away from the listener position) by about three feet and slightly more towards the right.

Well! I thought no problem. In the receiver set up, for speaker distances, The right speaker distance was input as about 4 ft more than the left speaker.

Bass almost dissapeared from life.

After many days, I wanted a more conventional set up. The right speaker was brought back into the plane. The situation did not improve.

After a few more days, while reviewing the receiver set-up, I saw the different distances input for the left & right speakers while playing music, and corrected the blunder.

Bass immediately improved.

Mr. Holmes! The obvious, simple, non technical, explanation?

 

[MDS]

Sound travels approximately 1.1 feet per millisecond. A distance difference of 4 feet results in the sound from that speaker being delayed over 4 ms. So the sound from the two front speakers arrive at your ears at different times (not including reflections) and a difference of 4 ms is audible, at least for a complex waveform like music. For pure tones, maybe not so much - in general the ears can't distinguish between two pure tones unless they are at least 6 ms apart. [As with anything else, people are different and that is just a general rule of thumb].

 

[Davemcc]

I've got a way of looking at this that I'd like some comment on. It'll be easier to follow if I cut and paste your quote.

I had the typical sub-sat connection set-up. This was-connect the left & right main speaker terminals of the receiver to the speaker level input terminals of the subwoofer. Connect the main left & right speakers to the speaker level output of the sub.

I think it's important to note your setup, as above, because this plays into my theory.

Typically, the TV screen, the left & right main speakers, and the centre speaker are approximately, in the same vertical plane.Due to the pecularities of the room set up, the right speaker, was behind this plane (further away from the listener position) by about three feet and slightly more towards the right.

The location of a typical satellite speaker should not affect your bass output, as that comes from the sub.

Well! I thought no problem. In the receiver set up, for speaker distances, The right speaker distance was input as about 4 ft more than the left speaker.

Bass almost dissapeared from life.

Note the travel time of sound from MDS's post. In your setup, the receiver is sending two signals (L/R) to the sub, one 4ms after the other, each with similar bass information. In this case, the subwoofer would produce the sound from the first signal, then 4ms later, similar info from the second signal. I speculate (i.e. guess) that when your sub produces these near identical signals 4ms apart, the difference is enough that it is affected by room modes that cancel out your bass frequencies.

After many days, I wanted a more conventional set up. The right speaker was brought back into the plane. The situation did not improve.

I would not expect it to. That speaker doesn't produce bass. The sub does.

After a few more days, while reviewing the receiver set-up, I saw the different distances input for the left & right speakers while playing music, and corrected the blunder.

Bass immediately improved.

Again, I speculate that once both speakers were sending their signals to the subwoofer speaker inputs at identical times, the subwoofer was only producing one signal, instead of two signals 4ms apart, thus eliminating the second source of bass frequencies and eliminating the room mode that caused the cancellation.

Comments on this theory are welcome.

 

[Shashi Kumar]

I think Dave's theory is right in principle.

The two signals are 4 ms apart, this implies that they are out of phase with respect to each other. Out of phase signals can cancel each other, under right conditions. But where does this happen, at the subwoofer input, or after the signal has been converted to audio( as suggested by Davemcc), is something the experts will have to answer.