subwoofer gain knob - AVS Forum
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post #1 of 3 Old 08-03-2012, 11:21 AM - Thread Starter
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I am testing my room with REW and when I disconnect /connect speaker/subwoofers in differnet scenarios, I have to increase/decrease the volume though it is recommended to freeze fist time at 75db.

I have paradigm sub 15. I have couple of questions.

1. What is the relationship between increasing volume from receiver vs subwoofer? How do you determine where should be subwoofer volume?

2. If the cross over for sub is set to 120hz and if you send 0-20khz to subwoofer with disconnecting all other speakers, does signal sent with complete spectrum 20khz or just 120hz by the receiver. I have Anthem mrx 700.

3 What is typical phase value? Does it depend on whether subwoofer is pointing to side or to the back etc?


Thanks for your help.
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post #2 of 3 Old 08-03-2012, 11:35 AM
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Once you have things balanced so that test tones are equally loud for each speaker, most folks around here suggest making personal preference adjustments at the receiver. There's no real sonic difference, but the receiver makes the offset knowable and repeatable in a way that turning knobs on the back of the sub may not be. set the sub's volume control so that the resulting calibration to keep it equal with the other speakers is generally around the center of the adjustment range, especially if you want to tinker.

I don't know the MRXs in detail. AFAIK all receivers leave the low pass for the sub (from the crossover settings) in line whenever you divert sound from the non-subs, so any such sound would get rolled off. If you had an LFE channel signal with content up to 20 KHz, what happens depends on the receiver. Check whether the MRX has a low pass for the LFE channel. Many do. Some make it adjustable, some don't. Normally, there isn't "supposed" to be content above 120 Hz in the LFE channel (at least for movies).

Leave phase at 0 to start. Once you've calibrated, you could play content or test tones in the frequency range of your crossover, and see how the blend works. It's that "splice" that you need to get right. What the phase differences between the various speakers will be depends on the phase behavior of the speakers and their distances from the listening position so there's no "perfect" or even tyipcal for all. Many adjust the phase relationship using the receiver's distance setting for the sub. It accomplishes the same thing (delaying the signal through the sub to a greater or lesser degree until everything mateches up for max levels at the listening position at the crossover frequency). It is again more repeatable, and frankly simpler to make the incremental adjustments with a device that has a remote and a visible readout as to how far you've changed things.
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post #3 of 3 Old 08-03-2012, 04:06 PM - Thread Starter
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Quote:
Originally Posted by JHAz View Post

Once you have things balanced so that test tones are equally loud for each speaker, most folks around here suggest making personal preference adjustments at the receiver. There's no real sonic difference, but the receiver makes the offset knowable and repeatable in a way that turning knobs on the back of the sub may not be. set the sub's volume control so that the resulting calibration to keep it equal with the other speakers is generally around the center of the adjustment range, especially if you want to tinker.
I don't know the MRXs in detail. AFAIK all receivers leave the low pass for the sub (from the crossover settings) in line whenever you divert sound from the non-subs, so any such sound would get rolled off. If you had an LFE channel signal with content up to 20 KHz, what happens depends on the receiver. Check whether the MRX has a low pass for the LFE channel. Many do. Some make it adjustable, some don't. Normally, there isn't "supposed" to be content above 120 Hz in the LFE channel (at least for movies).
Leave phase at 0 to start. Once you've calibrated, you could play content or test tones in the frequency range of your crossover, and see how the blend works. It's that "splice" that you need to get right. What the phase differences between the various speakers will be depends on the phase behavior of the speakers and their distances from the listening position so there's no "perfect" or even tyipcal for all. Many adjust the phase relationship using the receiver's distance setting for the sub. It accomplishes the same thing (delaying the signal through the sub to a greater or lesser degree until everything mateches up for max levels at the listening position at the crossover frequency). It is again more repeatable, and frankly simpler to make the incremental adjustments with a device that has a remote and a visible readout as to how far you've changed things.

Thanks for detailed explanation.
I run Anthem correction, at that time it set as +10 for subwoofer and +1 for front left etc. I guess at that time I need to reduce sub knob to get it to close to +1 or +2 to match other speakers. I guess after that there is no use of the knob. I still have question that if receiver is increasing level of sub out with volume button, how can it be called pre amp out, Also, why should any body spend so much for subwoofer with powerful amplifier. I guess I missing something.
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