how to use REW to measure available sub headroom? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 7 Old 10-23-2018, 05:33 PM - Thread Starter
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how to use REW to measure available sub headroom?

I am just getting comfortable with REW. Is there a simple way to use my mic and REW to measure how loud i can run my subs without clipping or distortion? subs are marty cubes with si18s and a crown 2502 amp
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post #2 of 7 Old 10-23-2018, 05:45 PM
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Originally Posted by sotwell View Post
I am just getting comfortable with REW. Is there a simple way to use my mic and REW to measure how loud i can run my subs without clipping or distortion? subs are marty cubes with si18s and a crown 2502 amp

If you have gain structure problems, you could be clipping prematurely, or even have not enough voltage drive to get full output of the amplifier.



Depending on the microphone, you may have enough spl to drive it into non-linear operation. The room can also contribute to measured distortion spectra in REW, if you have rattles and other noises.



So in short, it's a bit hard to figure out what you have if you have any of those other issues.

Ask your doctor if DIY is right for you. Side effects of DIY may include anxiety, elevated blood pressure, lightheadedness, rapid heartbeat, skeletal muscle flaccidity, euphoria, psychological dependence, insomnia, confusion, blurred vision, impulsivity, uncontrolled or repeated movements.
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post #3 of 7 Old 10-23-2018, 05:48 PM - Thread Starter
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Quote:
Originally Posted by michael hurd View Post
If you have gain structure problems, you could be clipping prematurely, or even have not enough voltage drive to get full output of the amplifier.



Depending on the microphone, you may have enough spl to drive it into non-linear operation. The room can also contribute to measured distortion spectra in REW, if you have rattles and other noises.



So in short, it's a bit hard to figure out what you have if you have any of those other issues.

sorry, maybe i was not clear. I do not believe that i am clipping, but how do i know if i am? after eq, i run my subs about 8db hot, is there a way to tell that i could clip at this level
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post #4 of 7 Old 10-23-2018, 06:13 PM
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The clipping LED on your amp will tell you if you're clipping.

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post #5 of 7 Old 10-23-2018, 06:16 PM
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Quote:
Originally Posted by sotwell View Post
sorry, maybe i was not clear. I do not believe that i am clipping, but how do i know if i am? after eq, i run my subs about 8db hot, is there a way to tell that i could clip at this level

You could be clipping the output of the AVR, or clipping the amplifier. If you have redirected bass, you are asking the subwoofers to reproduce >121 dB of bass, if you drive the system to reference volume level during a movie, and every gain stage is correct. If 8 dB hot, now the subwoofers will need to reproduce close to ~ 130 dB at reference.



Room gain is not factored in, a large lossy main floor room that is open to the rest of the house will behave far differently than a basement room that has two concrete walls and concrete floor.



If you know your maximum spl, then you can calculate back to figure out what you need at your subwoofers.
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Ask your doctor if DIY is right for you. Side effects of DIY may include anxiety, elevated blood pressure, lightheadedness, rapid heartbeat, skeletal muscle flaccidity, euphoria, psychological dependence, insomnia, confusion, blurred vision, impulsivity, uncontrolled or repeated movements.
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post #6 of 7 Old 10-23-2018, 07:06 PM
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The UMIK-1 maxes out at 130db peak from my experience with it.
It starts distorting around 120db continuous power / sinewave etc.

You have to modify the UMIK-1 to even reach +115db.

How to do that, can be seen in my thread on the topic:
https://www.avsforum.com/forum/155-d...-umik-1-a.html

If you truly want a no-limit SPL meter, then you'll have to buy an SPL Lab or Term Lab, solid-state sensor.

https://shop.termpro.com/products/te...-sensor-system
http://spllabusa.com/us/products/bas...ass-meter.html

Those max-out north of 180db.

Quote:
Originally Posted by michael hurd View Post
If you have gain structure problems, you could be clipping prematurely, or even have not enough voltage drive to get full output of the amplifier.
Quote:
Originally Posted by michael hurd View Post
You could be clipping the output of the AVR
True.

For the first one, just disconnect the driver. You should be able to clip the amp, ensuring you have sufficient voltage drive, then just back down the MV a notch and consider that your max-safe loudness.

You can only detect AVR clipping with an oscope (or voltage divider and a soundcard).
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post #7 of 7 Old 10-25-2018, 03:10 AM
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