REW Measurement - left and right main speakers still have output when measuring for sub SPL

[STucker]

Hello - I am working to measure my two FVX15 subs using REW. Per recommendations from YT videos and other sources, I set the crossover on my Denon X-4400H to 250HZ for all speakers. With this crossover setting I didn't expect to hear any output from the left and right mains when I set the REW Generator to Sub Cal (30 to 80 HZ), but the main speakers had sound output. I disconnected one of the speaker wires to eliminate sound from the mains when doing the sub measurements.

Anyone have an idea why the main speakers are still outputing sound with a 250HZ crossover? Secondly, would this cause an issue with the sub measurements? For example, if the output to the mains should be going to the sub, am I loosing SPL on the sub when doing the REW measurement?

I have a related question. I used the REW SPL Meter, my Umik-1 and the Denon speaker test tone to measure the output of my 5 bedlayer and 4 Atmos speakers so they all measured 75DB at the MLP. When I set REW to measure the sub SPL, the volume on the left main, as referenced above, was far higher than the 75DB I had just calibrated. Any insights on what is causing this problem?

Steve T

 

[JStewart]

Anyone have an idea why the main speakers are still outputing sound with a 250HZ crossover?

It’s because a crossover is not a brick wall filter. Your Denon will have a high pass filter for the mains of 12dB per octave. So if you have 75dB at 250Hz then it will be 63dB at 125Hz and audible. Disconnecting the main as you did is necessary for a sub measurement.
The reason for setting the XO that high in the first place is to be able to measure the sub to as high a frequency as possible without interference of the low pass filter. This is 24dB per octave on a Denon.

Secondly, would this cause an issue with the sub measurements?

Yes

I have a related question. I used the REW SPL Meter, my Umik-1 and the Denon speaker test tone to measure the output of my 5 bedlayer and 4 Atmos speakers so they all measured 75DB at the MLP. When I set REW to measure the sub SPL, the volume on the left main, as referenced above, was far higher than the 75DB I had just calibrated. Any insights on what is causing this problem?

Missing info to know for sure, but usually test tones for calibrating an AVR to 75dB are attenuated 30dB to allow for 105dB peaks (reference volume). REW sine sweep measurement signals are set to 12dB attenuation by default and are easily changed if needed.

 

[STucker]

It’s because a crossover is not a brick wall filter. Your Denon will have a high pass filter for the mains of 12dB per octave. So if you have 75dB at 250Hz then it will be 63dB at 125Hz and audible. Disconnecting the main as you did is necessary for a sub measurement.
The reason for setting the XO that high in the first place is to be able to measure the sub to as high a frequency as possible without interference of the low pass filter. This is 24dB per octave on a Denon.



Yes



Missing info to know for sure, but usually test tones for calibrating an AVR to 75dB are attenuated 30dB to allow for 105dB peaks (reference volume). REW sine sweep measurement signals are set to 12dB attenuation by default and are easily changed if needed.

JStewart - I appreciate the responses to my questions...THANKS!

Is there a better way to calibrate my speakers to 75bB at the MLP or does the way I did it as described in my previous question suffice? Secondly, should I change the 12dB attenuation for the REW sine sweep signals to match the 30dB of the Denon? If not, is there anything I need to do differently when doing the sub measurements?

STucker

 

[JStewart]

Is there a better way to calibrate my speakers to 75bB at the MLP or does the way I did it as described in my previous question suffice?

Probably fine. If you’re striving for perfection for some reason then you would want to volume match with a THX recommended signal which is 500Hz to 2000Hz pink noise. This may have been what you used.

Secondly, should I change the 12dB attenuation for the REW sine sweep signals to match the 30dB of the Denon?

No reason when you are looking at relative levels between speakers or a sub and speakers. When measuring, it’s recommended to keep the volume a little above conversion volume and never at an uncomfortable level, however.

If not, is there anything I need to do differently when doing the sub measurements?

Nope.
However, when it comes time to set the relative level of the sub(s) to the mains or center, you will want to have the XO at the setting you’ll actually be using.
Use the higher XO setting as you have done to manually EQ from before setting the XO to the setting you’ll be using.

 

[STucker]

Probably fine. If you’re striving for perfection for some reason then you would want to volume match with a THX recommended signal which is 500Hz to 2000Hz pink noise. This may have been what you used.

No reason when you are looking at relative levels between speakers or a sub and speakers. When measuring, it’s recommended to keep the volume a little above conversion volume and never at an uncomfortable level, however.

Nope.
However, when it comes time to set the relative level of the sub(s) to the mains or center, you will want to have the XO at the setting you’ll actually be using.
Use the higher XO setting as you have done to manually EQ from before setting the XO to the setting you’ll be using.

JStewart - thanks again for the response. I appreciate the assistance and coaching.