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Discussion Starter · #1 ·
Just wondering in light of some of the questions I've had about how to determine the acoustic length around a corner.


Is anyone aware of a way to introduce a sound at the horn mouth and measure the delay of its return to determine the true acoustic length of the horn?
 

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Maybe an impulse burst. Put a speaker at the mouth and measure. Then remove the speaker and measure the horn without moving the mic or horn. The difference in time will be the difference between impulses. Which can be converted to distance.
 

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Quote:
Originally Posted by GlibHarbinger /forum/post/20808849


Just wondering in light of some of the questions I've had about how to determine the acoustic length around a corner.

You determine its true acoustic length with an impedance sweep. Use that result to adjust the simulation until they agree, then you can see what the sim gives for path length.
 

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You could try REW's loopback function.....and compare a driver in a sealed enclosure to one in the horn, the difference between the two values would be the horn length. It would only would work for a front loaded horn, though...



JSS
 

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Couldn't you just run MCACC / Audyssey full auto, see what distance setting it comes up with, and then subtract the physical distance from the measurement position to the mouth?
 

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Discussion Starter · #6 ·
There are some automotive retro fit ultrasonic products for measuring distance: Car Park Sensor


Wonder if you could rig an adapater to fit the ultrasonic transducer in the driver cutout and then mic the mouth. You might be able to measure the distance of everything but L12 with that. Although I bet the acoustic distance varies somewhat with frequency, and 40KHz is pretty far from the passband for a bass horn



How do you measure impedance (acoustic impedance?) Bill?
 

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Discussion Starter · #7 ·

Quote:
Originally Posted by Brad Horstkotte /forum/post/20811743


Couldn't you just run MCACC / Audyssey full auto, see what distance setting it comes up with, and then subtract the physical distance from the measurement position to the mouth?

That's a good point! I guess the Audyssey is taking a sounding, at least from the driver position. How accurate is it? Ideally it would be accurate to a cm if you wanted to compare it to a HornResp model.
 

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Quote:
Originally Posted by GlibHarbinger /forum/post/20811839



How do you measure impedance (acoustic impedance?) Bill?

You don't. You measure the electrical impedance, with a resistor bridge/generator/DMM or WT3.
 

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Quote:
Originally Posted by GlibHarbinger /forum/post/20811839


There are some automotive retro fit ultrasonic products for measuring distance: Car Park Sensor


Wonder if you could rig an adapater to fit the ultrasonic transducer in the driver cutout and then mic the mouth. You might be able to measure the distance of everything but L12 with that. Although I bet the acoustic distance varies somewhat with frequency, and 40KHz is pretty far from the passband for a bass horn



How do you measure impedance (acoustic impedance?) Bill?

Electrical impedance.


How-to here: http://www.avsforum.com/avs-vb/showthread.php?t=1340740
 

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Quote:
Originally Posted by GlibHarbinger /forum/post/20811894


How accurate is it?

Good question - I wonder if it would need to average the direct and reflected sounds and base the distance on that - versus the direct sound only. I've actually never run it and then measured to see how close it is - since most of the time, you only care about whether the arrival time is in synch with mains (and I've heard some reports that that can be off by a few ms / feet). Would be interesting for someone to test with a sealed sub (actually I'm sure a Google search would find someone who has done so) - but not terribly germaine to your original question.
 
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