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Old 5th October 2012, 04:00 PM   #1
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Default Need to make a simple balance control

I am planning to have 2 center speakers for my home theater setup, one above and one below the screen. I know about the phase issues but it would be present in my ideal listening position. Others sitting off ideal are not people that will care nor hear it.

I intend to connect a y-splitter to the center output from the preamp to create 2 channels of mono going into 2 channel power amp.

Rather than use a passive balance pot (difficult to find, expensive, lower quality and introduces loss in both channels), Is it possible to use just a mono volume pot on one of the channels to attentuate one channel while the other is just interconnect straight into power amp. Or would doing this just attenuate both channels regardless since they both originate from the same y-splitter?

I am doing this so I can adjust the percieved height of the center channel sound to the height of the LR front speakers. Due to mounting constraints if I run both center channels without attenuating one, the sound will come from mid point of the 2 center speakers and will be at 3/4 height of screen or about 3-4 feet above the front LR speakers.

Thanks for any input/advice
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Old 8th October 2012, 03:26 AM   #2
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Quote:
Originally Posted by pzull View Post
I am planning to have 2 center speakers for my home theater setup, one above and one below the screen. I know about the phase issues but it would be present in my ideal listening position. Others sitting off ideal are not people that will care nor hear it.

I intend to connect a y-splitter to the center output from the preamp to create 2 channels of mono going into 2 channel power amp.

Rather than use a passive balance pot (difficult to find, expensive, lower quality and introduces loss in both channels), Is it possible to use just a mono volume pot on one of the channels to attentuate one channel while the other is just interconnect straight into power amp. Or would doing this just attenuate both channels regardless since they both originate from the same y-splitter?

I am doing this so I can adjust the percieved height of the center channel sound to the height of the LR front speakers. Due to mounting constraints if I run both center channels without attenuating one, the sound will come from mid point of the 2 center speakers and will be at 3/4 height of screen or about 3-4 feet above the front LR speakers.

Thanks for any input/advice
Above about 1.5kHZ, and up to about 7kHZ, we detect image location primarily by amplitude comparison. Below about 900HZ, we detect image location primarily by timing comparisons.

To get a perception of balance in the lower midrange make sure the distance from the two speakers to the listeners ears is pretty close to the same (pick a target height). This will only matter when you're laying on a couch and your head is turned sideways to some extent. With the half wavelength of 900 HZ being close to 7 inches., being off by several inches could make an audible difference.

In the upper midrange, I might put a resistor in series with the speaker that sounds louder, knowing that the resistor will usually throw off the crossover a bit. It can shift the crossover frequencies, since most crossovers are designed assuming a zero ohm source impedance (output impedance of the poweramp). The good news is that the shift will often be in the same direction in frequency, in both the high-pass section and the low pass section. If the crossover is of simple design, the problem should be very small. With a complicated crossover that has notch filters to tame resonance of a metal cone driver, for example, I'd worry a bit more.

Last edited by Bob Richards; 8th October 2012 at 03:28 AM.
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Old 8th October 2012, 06:19 AM   #3
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Thanks for the reply. My center speakers will be exactly equi-distant from the main listening position measured from my ear sitting on a couch of known height.
So I just add a resistor to the louder speaker without any shunt to ground?
My speakers are 6ohm impedance. If I wanted one speaker to be say about 3/4 as loud as the other I can just add a 2ohm resistor? So one channel is 8 ohms vs the other at 6 ohms?
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