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Author Topic: Wedges & Transfer Function Measurement: Meas. Mic Position?  (Read 15569 times)

Mac Kerr

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Re: Transfer Function Measurement: Meas. Mic Position?
« Reply #20 on: November 11, 2012, 02:32:13 pm »

Take look at the attachment.  This is the manufacturers data on the SAME loudspeaker.  Notice how the coverage is very different between 630=1800 &  8Kz.

What IS the correct spec this cabinet should have?   It depends on what freq you look at-but most all the others are very different.

Ivan, since the graphs are too low res to read, what do they represent? It is a nice illustration that in some way, something is changing vs frequency, but what are we looking at?

Are those polar plots of vertical coverage? Horizontal coverage? An illustration of pattern shape looking down the throat of the horn? For someone who rightly rails for clarity of information, this is sadly lacking.

Mac
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Jim McKeveny

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Re: Transfer Function Measurement: Meas. Mic Position?
« Reply #21 on: November 11, 2012, 03:51:50 pm »

Ivan-

Regarding 12" giving pattern control down to 2khz: What multiple/submultiple of frequency length can we use as a target range for horn pattern control? 1/4 wavelength is the baseline assumption for horn loading.Yes?
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Ivan Beaver

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Re: Transfer Function Measurement: Meas. Mic Position?
« Reply #22 on: November 11, 2012, 04:23:53 pm »

Ivan, since the graphs are too low res to read, what do they represent? It is a nice illustration that in some way, something is changing vs frequency, but what are we looking at?

Are those polar plots of vertical coverage? Horizontal coverage? An illustration of pattern shape looking down the throat of the horn? For someone who rightly rails for clarity of information, this is sadly lacking.

Mac
Yes it is a little fuzzy.  I tried to get all the graphs on the same page. Sorry.

The angles are in 10 increments with the outer edge being 80.

The "view" is looking out the front of the cabinet-not the horn per say-but could kinda be thought of that way..  So the coverage pattern that the "cabinet would project".  So horizontal and vertical at the same time.

This was gotten from their EASE data.
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Ivan Beaver
Danley Sound Labs

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Ivan Beaver

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Re: Transfer Function Measurement: Meas. Mic Position?
« Reply #23 on: November 11, 2012, 04:44:54 pm »

Ivan-

Regarding 12" giving pattern control down to 2khz: What multiple/submultiple of frequency length can we use as a target range for horn pattern control? 1/4 wavelength is the baseline assumption for horn loading.Yes?
The "target" should be as low as possible.  But if only the HF has a horn, then the horn should be at least large enough to provide pattern control down to (or preferably below- by 1/2 octave or so)  the ACOUSTICAL crossover of the horn.  The electrical crossover is often a good bit higher than the acoustical crossover (for a HF device and some midrange devices) 

Horn loading and horn pattern control are very different things.

Horn loading is limited on the upper end by the size of the opening that the driver is "entering" the horn at.  So the larger the driver exit -the less horn loading will be happening up high.

The horn pattern control extends all the way up (assuming the driver itself has a wide enough pattern at the exit to "fill" the horn).  The limit is the low end-which is a combination of physical size and pattern.  If one number stays the same-and the other number gets larger-then the freq to which it exhibits pattern control will go lower.  And if either gets smaller-then the freq will go higher.

A "quick and dirty" formula to remember for horn pattern control is 1,000,000/ (pattern coverage angle x Horn size in inches for the intended vertical or horizontal pattern of interest). Who says you can't multiply apples and walnuts?

I'm not sure where your 1/4 wavelength comes into play in the question.  There are lots of areas that 1/4 wavelength is of interest, but pattern control and horn loading are generally included in that.

Generally 1/4 wavelength is considered a good goal for distance between drivers to couple.  That would be within a single horn or seperate cabinets-doesn't matter.  Be it HF devices or subs.  The problem on the HF side is as you go higher and higher, that 1/4 wavelength gets very small.
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Ivan Beaver
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Jim McKeveny

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Re: Transfer Function Measurement: Meas. Mic Position?
« Reply #24 on: November 12, 2012, 08:33:09 am »

[quote.

A "quick and dirty" formula to remember for horn pattern control is 1,000,000/ (pattern coverage angle x Horn size in inches for the intended vertical or horizontal pattern of interest). [/quote]

I found the source of my confusion! When I hear "horn size" I think "path length". Whey you say "horn size" you are talking about "mouth area".

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Ivan Beaver

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Re: Transfer Function Measurement: Meas. Mic Position?
« Reply #25 on: November 12, 2012, 06:46:51 pm »

A "quick and dirty" formula to remember for horn pattern control is 1,000,000/ (pattern coverage angle x Horn size in inches for the intended vertical or horizontal pattern of interest).

I found the source of my confusion! When I hear "horn size" I think "path length". Whey you say "horn size" you are talking about "mouth area".

The path length will vary depending on the pattern of the horn.

As the pattern gets narrower-the path gets longer (to have the same freq of pattern control)-as the size of the mouth also gets larger.
« Last Edit: November 12, 2012, 07:21:33 pm by Mac Kerr »
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Ivan Beaver
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Steve Anderson

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Re: Transfer Function Measurement: Meas. Mic Position?
« Reply #26 on: November 15, 2012, 08:06:24 am »

A "quick and dirty" formula [...]

Just out of interest, what is the slow and clean formula?

Or is it just very rule-of-thumbish, and is really one of the questions that "is easily answered by a simple-easy to understand WRONG answer!"
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Shane Ervin

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Re: Wedges & Transfer Function Measurement: Meas. Mic Position?
« Reply #27 on: November 15, 2012, 10:37:37 am »

Shane- Keep us posted.

Weather was nice a couple of days ago, and I was able to get these traces.
  • Left Wedge - Overall + overlaid horn trace
  • Right Wedge - Overall + overlaid horn trace

Unplugged at the DUT end (same amp, X-Over channel, etc., in use).

High-pass at 100 Hz in MiniDrive preset.
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Shane

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Ivan Beaver

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Re: Transfer Function Measurement: Meas. Mic Position?
« Reply #28 on: November 15, 2012, 01:12:40 pm »

Just out of interest, what is the slow and clean formula?

Or is it just very rule-of-thumbish, and is really one of the questions that "is easily answered by a simple-easy to understand WRONG answer!"
The "correct" way is to MEASURE the product and then examine the results.

The formula that I gave is Don Keele's and gives a rought idea of the pattern control freq.
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A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

Phil Graham

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Re: Transfer Function Measurement: Meas. Mic Position?
« Reply #29 on: November 16, 2012, 09:16:07 am »

Just out of interest, what is the slow and clean formula?

Or is it just very rule-of-thumbish, and is really one of the questions that "is easily answered by a simple-easy to understand WRONG answer!"

Steve,

There's a slow and clean formula, its called the Kirchoff-Helmholtz integral :)

Keele's original CD horn paper "What's so sacred about the exponential horn" is a useful place to start on this topic.

Also, Keele's followup paper "Optimum horn mouth size" is an interesting read, even if makes the incorrect assumption of plane wave propagation.

The narrowing and subsequent expansion of the coverage pattern of a horn near the low cutoff ultimately results from diffraction effects.
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