Getting my head wrapped around subs

[bilgirami]

Hey guys,

I am trying to get my head wrapped around some subwoofer questions. I am sure someone will be able to help me out here...

When I am using a powered subwoofer with its own amp, I am sending pre-amp signal from my AVR to my sub, correct? Now this signal, does it only carry the frequencies (in the form of current) or information about the "volume" as well. What I am trying to say is that with the subwoofer volume at a certain level, how does it decide that the explsions are supposed to be louder than lets say a person falling on a wooden floor. What information does a pre-amp LFE signal carry to the amp of a power subwoofer.
Thanks

 

[snappy_snoopy]

Yes the signal which gets sent to your powered sub woofer is a energy signal not a power signal, the signal being sent does go through the amplifier in the av receiver but bypasses the power stage at the end used to drive the low impedance sources, in this case the speakers. If the sub woofer LFE channel did not go through the amplifier, the magnitude of signals sent to the other speakers would be different to that of the sub woofer and all sorts of havok would happen, ie the bass would either be really loud and dominating or too weak for a given audio track.

Hope that helps

 

[PeterWhite]

Hey guys,

I am trying to get my head wrapped around some subwoofer questions. I am sure someone will be able to help me out here...

When I am using a powered subwoofer with its own amp, I am sending pre-amp signal from my AVR to my sub, correct? Now this signal, does it only carry the frequencies (in the form of current) or information about the "volume" as well. What I am trying to say is that with the subwoofer volume at a certain level, how does it decide that the explsions are supposed to be louder than lets say a person falling on a wooden floor. What information does a pre-amp LFE signal carry to the amp of a power subwoofer.
Thanks

The LFE output on your receiver is at pre-amp out level, just as any other pre out would be for say the front main speakers to go to a power amp. Your powered subwoofer has a power amp and a level control just before the amplifier stage.

So volume to the subwoofer is controlled both by the pre-amp in your receiver and the level control on the sub.

The reason the sub has a level control is because it also has its own power amp, and that amp can have different gain than the power amp in your receiver. Also, different positions of the sub and your listening position can effect its level relative to the output of the other speakers.

To set the subwoofer level, you need a source of sound that has the same level at all frequencies, so you can use the level control to balance the sub's output relative to the other speakers. Your receiver may have a test tone that you can use, or you can get test tone CDs. I use software for my MAC that generates tones at any frequency, making it fairly easy to adjust levels.

If you can get the sound level from the sub consistent with the sound level from your other speakers with a constant input, then, when you're playing a movie or music, the levels will automatically be correct. The explosion should be just as loud as the filmmaker intended. Of course it's simply not possible to get the system to have perfectly flat response, but the closer you get the system to flat response, the more closely the sound from your system will represent what the audio engineer had in mind, or at least what he or she put on the disc.

 

[bilgirami]

PeterWhite, I think you may have hit the nail on the head. This is what I am having a bit of challenge with. I am using a Yamaha RX-V663 which has a test tone to calibrate the system. It also has YPAO auto calibration thing. I just feel that my sub does not blend in with the rest of my speakers. In some situations it seems that it is playing louder than my other speakers and in others, at same placement and gain, it seems it is underpowered. I have to find a better way to balance it, just not sure how.

 

[Warpdrv]

Even with YPAO self calibration, I like to use a SPL Meter from radio shack and check the level of each speaker as well as the sub... When you are in the calibration/setup screen, you should have the ability to use the on-board test tones to check each individual speaker channel and the subwoofer, to double check that each are putting out the same db level by using the SPL meter to get an exact db level reading, some people like to run the sub a little hot, some like it the same as the speakers. There will be plenty of times where the sub will explode with sound and be very subtle in other places in movies, that is how the dynamics of movies can and will at times scare the CR@P out of ya.... Thats what makes this hobby so fun...

Do you have an SPL Meter?
Like this one..

I have yet to have the automatic calibration work perfectly in any of my receivers I have owned, I rarely trust what they set it at, and find myself tweeking each channel a touch from the meters response...