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Discussion Starter #1
Hi,


I wanted to know if I wanted to test to see if my subwoofer is in correct phase, what is the best method. I don't have access to measurement software. I've heard people use music to test, but I don't know if that is the best method or not.


My subwoofer has a variable phase control. The idea is that if the phase is correct the sound should be louder and if it not in phase the levels should be reduced. Would using a test tone CD be a good idea to check phase?


I'm using an 80 Hz crossover. If I used a 80 Hz single tone, and then vary the phase control, is that a good idea or stupid idea?
 

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Quote:
Originally Posted by OllieS  /t/1466670/best-method-for-testing-phase#post_23162823


Hi,


I wanted to know if I wanted to test to see if my subwoofer is in correct phase, what is the best method. I don't have access to measurement software. I've heard people use music to test, but I don't know if that is the best method or not.


My subwoofer has a variable phase control. The idea is that if the phase is correct the sound should be louder and if it not in phase the levels should be reduced. Would using a test tone CD be a good idea to check phase?


I'm using an 80 Hz crossover. If I used a 80 Hz single tone, and then vary the phase control, is that a good idea or stupid idea?

The reason why subwoofer phase or timing is important is to avoid cancellation or nulls in response at or near the crossover frequency. Ordinarily slowly rotating the phase control and listening for a maximum while listening to music with a consistent source of bass in it is sufficient.


Steady pure tones are generally not used for acoustic testing because they can be affected by standing waves in the room and other acoustic effects in ways that are not helpful to the test being performed.


I think the following download might be an ideal test tone to use for the purpose you desire. It is a slow sweep from 30 Hz to 120 Hz.

https://www.dropbox.com/s/6ooxl089gugils4/30-120%20sweep.wav


Let me know how it works.
 

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Discussion Starter #3

Quote:
Originally Posted by arnyk 

Steady pure tones are generally not used for acoustic testing because they can be affected by standing waves in the room and other acoustic effects in ways that are not helpful to the test being performed.

I don't understand about the standing wave part. If I run a pure tone like 70 Hz, for example and my crossover is 70 Hz, why would that not be a good idea? If you could please explain why its a bad idea, and elaborate more on the standing wave thing.


Why is a sweep better than a single tone for setting phase? Thanks for your assistance!
 

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Quote:
Originally Posted by OllieS  /t/1466670/best-method-for-testing-phase#post_23162958

Quote:
Originally Posted by arnyk 

Steady pure tones are generally not used for acoustic testing because they can be affected by standing waves in the room and other acoustic effects in ways that are not helpful to the test being performed.

I don't understand about the standing wave part. If I run a pure tone like 70 Hz, for example and my crossover is 70 Hz, why would that not be a good idea?

What if your room has a standing wave at exactly 70 Hz? It might create a deep null at your listening location which won't go away no matter how you adjust your audio system since it is due to the room, not the audio system.


Standing waves often take a little while to come in when excited by sounds. Normal music that is constantly changing might not excite them like a pure tone can.
Quote:
Why is a sweep better than a single tone for setting phase? Thanks for your assistance!

As I mentioned above, a null due to a phase mismatch with your subwoofer might occur at your crossover frequency or at a frequency near to the crossover frequency.


A pure tone only tests what happens at exactly one frequency. A swept tone is constantly changing (more like music) and covers a more useful range of frequencies.
 

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Discussion Starter #5
Correct me if I'm wrong, but if I use a 70 Hz crossover and I test to see if 70 Hz goes louder or softer using the phase control using a pure tone is it also not possible that 70 Hz is NOT the correct number to look for as there might be a phase shift involved?
 

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Quote:
Originally Posted by OllieS  /t/1466670/best-method-for-testing-phase#post_23163008


Correct me if I'm wrong, but if I use a 70 Hz crossover and I test to see if 70 Hz goes louder or softer using the phase control using a pure tone is it also not possible that 70 Hz is NOT the correct number to look for as there might be a phase shift involved?

If you are saying that a nominally 70 Hz crossover might not be exactly a 70 Hz crossover, that can be true as well.


Also, crossovers aren't brick walls, but rather their effects are spread over a range of frequencies and you want to check them all. Hence my sweep from 30 Hz to 120 Hz for testing an 80 Hz crossover.
 

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Discussion Starter #7

Quote:
Originally Posted by arnyk 

If you are saying that a nominally 70 Hz crossover might not be exactly a 70 Hz crossover, that can be true as well.

Why is that exactly? I was shooting in the dark, but if I was a right, then I glad.
 

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Discussion Starter #9
Tried the swept tone. It worked. Phase left at 0. If I changed it to 180 I could notice a drop in volume as the sweep progressed. I had someone help me change the phase.


Thanks Arny!
 

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Quote:
Originally Posted by OllieS  /t/1466670/best-method-for-testing-phase#post_23163076


Tried the swept tone. It worked. Phase left at 0. If I changed it to 180 I could notice a drop in volume as the sweep progressed. I had someone help me change the phase.


Thanks Arny!

That is what I expected - glad it helped!
 

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Discussion Starter #11
Still have a question that is bugging me though. About the single sine wave testing, even if you weren't in a null ... you mentioned that the nominal frequency may not be the actual frequency? Is that due to phase shifts .. or something else?


Sorry, I just want to understand this better otherwise it's going to drive me up the wall.
 

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Quote:
Originally Posted by OllieS  /t/1466670/best-method-for-testing-phase#post_23163095


Still have a question that is bugging me though. About the single sine wave testing, even if you weren't in a null ... you mentioned that the nominal frequency may not be the actual frequency? Is that due to phase shifts .. or something else?


Sorry, I just want to understand this better otherwise it's going to drive me up the wall.

Something else - just normal variations in electronic equipment and acoustical environments.
 

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interesting topic, I am currently testing out the subwoofer(s) response in my home theater room. Tagging for reference!

thanks,

Todd


Oh, ideally I could burn this to CD and play through my system? I don't have my pc connected to my AVR....


thanks,
 

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Quote:
Originally Posted by toddbigeasy  /t/1466670/best-method-for-testing-phase#post_23163255


interesting topic, I am currently testing out the subwoofer(s) response in my home theater room. Tagging for reference!

thanks,

Todd


Oh, ideally I could burn this to CD and play through my system? I don't have my pc connected to my AVR....

When I tested the track, I burned the same track to an audio CD about 20 times so that it would play and play while I was working with my subwoofer.


If you can't make CD burning work on your PC, try Infrarecorder (freeware).
 

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Discussion Starter #16

Quote:
Originally Posted by arnyk 

When I tested the track, I burned the same track to an audio CD about 20 times so that it would play and play while I was working with my subwoofer.

What subwoofer do you have, if you don't mind me asking?
 

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Quote:
Originally Posted by OllieS  /t/1466670/best-method-for-testing-phase#post_23164125

Quote:
Originally Posted by arnyk 

When I tested the track, I burned the same track to an audio CD about 20 times so that it would play and play while I was working with my subwoofer.

What subwoofer do you have, if you don't mind me asking?

Paradigm PS 1200
 

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Quote:
Originally Posted by OllieS  /t/1466670/best-method-for-testing-phase#post_23164763

Quote:
Originally Posted by arnyk 

Paradigm PS 1200

Nice sub.

I would say that it is OK, but not exceptional.


I have a number of friends who have very large subwoofers composed of 4 or more long-stroke 13-18" drivers with literally kilowatts of power backing them up. Those subwoofers are what it takes to really get the most out of the more extreme of modern high-impact recordings.


When the going gets tough, the little Paradigm sort of whimps out. And, this is in just a 2.1 system with modest bookshelf speakers and a low end AVR driving them. IME unlike digital players, amplfiers and other speakers, you have to go pretty far to get into diminishing returns with subwoofers.
 
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