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Author Topic: Wedges & Transfer Function Measurement: Meas. Mic Position?  (Read 17697 times)

Steve Anderson

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Re: Transfer Function Measurement: Meas. Mic Position?
« Reply #30 on: November 16, 2012, 10:07:52 am »

There's a slow and clean formula, its called the Kirchoff-Helmholtz integral :)
I felt smarter just knowing that!

But then I googled it, and now I don't  :-[

I will attempt to partly absorb it when I am more awake, but not at 2am (Syd, Aust)
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Ivan Beaver

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Re: Transfer Function Measurement: Meas. Mic Position?
« Reply #31 on: November 16, 2012, 08:22:43 pm »

Here is another example of a horn that has a "spec", but yet the actual data is not even close to it.  Yes it is a real product-not a simulation.

The spec is accurate for the 8Kz response, but look at some of the lower freq-they are WAY WAY off.

How would you array this speaker?  As if you were using the 8KHz coverage or the 4Kz coverage.  I would argue that both are to high for "normal intelligibility".  So if you tried to array "per spec" you would be way off.  My guess is that around 6Khz the pattern is pretty much omni.

The numbers under the freq are the coverage of the outer band-so the actual coverage is twice where the band is shown.

It is a bit hard to see-but the scale changes on the different graphs-so it is actually WORSE than it appears (as if the scale was the same)

You REALLY need to look a bit closer to get the real "picture" of what is happening.
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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!

Charlie Hughes

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Re: Transfer Function Measurement: Meas. Mic Position?
« Reply #32 on: November 17, 2012, 10:18:18 am »

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Ivan Beaver

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Re: Transfer Function Measurement: Meas. Mic Position?
« Reply #33 on: November 17, 2012, 12:39:37 pm »

This might be of interest, http://www.excelsior-audio.com/Publications/Understanding_Horn_Directivity.pdf.
Nice paper!

And it "should" be readily apparent that you CANNOT simply have a rotatable horn-that has different coverage patterns-yet the dimensions are the same.

The end result is NOT going to be what the user "thinks" it is.

However that does not stop manufacturers from making them and users from buying them-and then "spouting of that you can "rotate the horn on XYZ speaker" to get the coverage pattern you (think) you need to "array" them.

Oh how blindly people follow along------without actually verifying to testing to see if the product actually comes close to doing what the specs say.

Manufacturers wouldn't lie now would they??????????????????????????????????????
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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!

Tim McCulloch

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Re: Transfer Function Measurement: Meas. Mic Position?
« Reply #34 on: November 17, 2012, 03:49:45 pm »


Manufacturers wouldn't lie now would they??????????????????????????????????????

That reminds me of the saying "all fishermen are liars except me and you... and I'm a little concerned about you."   ;)
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"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut

Phil Graham

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Re: Transfer Function Measurement: Meas. Mic Position?
« Reply #35 on: November 19, 2012, 11:58:19 am »


And it "should" be readily apparent that you CANNOT simply have a rotatable horn-that has different coverage patterns-yet the dimensions are the same.


Ivan's excellent point about rotatable horns is worthy of a +1
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Phil Graham

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Re: Transfer Function Measurement: Meas. Mic Position?
« Reply #36 on: November 19, 2012, 11:59:35 am »

This might be of interest, http://www.excelsior-audio.com/Publications/Understanding_Horn_Directivity.pdf.

FWIW,

Also visible in charlie's papers' directivity balloons are the first order diffraction lobes off the main coverage axis.
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Douglas R. Allen

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Re: Wedges & Transfer Function Measurement: Meas. Mic Position?
« Reply #37 on: December 08, 2012, 05:20:24 pm »

Just started reading this thread after I did some measurements of some of my wedges today  :(.

I'm interested in if the phase response shown here is a result of incorrect measurements taken or if they are "ok" for what they are.
3 speakers were measured.

EV SxA250
Peavey PV 15pm
Yamaha MS400

Not a lot of filters were needed to keep them in a +/- 3db range.
Looking at them the Yamaha looks like the horn is not in correct polarity to the woofer but there is no major drop in response at the crossover point. There was an acoustic adjustment device used to raise the front up so I wonder if that is part of the dips in phase and response in the woofer range?
The peavey phase seems to be about what I'd expect to see.
The EV I'm unsure of as to if this is normal for this speaker?
Both the Peavey and EV have a peak around 200hz. I took this to floor / mic placement issue although I didn't see it in coh.
Coh was fine for this measurement and I was in a good sized room. I used the setup like in the Mic/speaker picture.
Thanks for any input on these. Sorry for the cell phone pictures..
Douglas R. Allen
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Art Welter

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Re: Wedges & Transfer Function Measurement: Meas. Mic Position?
« Reply #38 on: January 07, 2013, 02:59:10 pm »

Just started reading this thread after I did some measurements of some of my wedges today  :(.

I'm interested in if the phase response shown here is a result of incorrect measurements taken or if they are "ok" for what they are.
3 speakers were measured.

EV SxA250
Peavey PV 15pm
Yamaha MS400

Not a lot of filters were needed to keep them in a +/- 3db range.
Looking at them the Yamaha looks like the horn is not in correct polarity to the woofer but there is no major drop in response at the crossover point. There was an acoustic adjustment device used to raise the front up so I wonder if that is part of the dips in phase and response in the woofer range?
The peavey phase seems to be about what I'd expect to see.
The EV I'm unsure of as to if this is normal for this speaker?
Both the Peavey and EV have a peak around 200hz. I took this to floor / mic placement issue although I didn't see it in coh.
Coh was fine for this measurement and I was in a good sized room. I used the setup like in the Mic/speaker picture.
Thanks for any input on these. Sorry for the cell phone pictures..
Douglas R. Allen
Douglas,

There really are no "incorrect measurements",  but interpretation of measurements can be difficult.
The proximity of the monitor's baffle to the floor will affect FR and phase response somewhat, "audio logs" , "acoustic adjustment devices" or Angular Discrepancy Adjustment Modules (ADAM) all will get the HF pointing towards your ears, but change response due to differences in diffraction and woofer wrap/bounce.

The PV 15pm has the least phase wrap of the three monitors you tested, about 130 degree from 250 Hz up, the Yamaha MS 400 a bit more at around 145 degree, the EV the most at around 270 degrees.
Considering they all use active electronics, none of the phase responses look great, but none look "incorrect".

Below is a screen shot of three speakers with flatter phase response, a Mackie 1502HD, an active 2 way using Gunness focusing, and a DSL SH100, a passive 8" coaxial two way, and a Welter Systems 8H, a passive 8"& horn floor monitor.
The 1502HD and the SH100 were measured on a 6 foot pole, the WS8H, measured as in your picture.

I'd bet if you took another set of measurements with the PV, Yamaha & EV you could not reproduce the phase charts. Each of these monitors is designed with the HF horn placed horizontally adjacent to the LF driver and will have a different response depending on what is chosen as "on axis", and the response off axis to the left will be different than to the right.
The 1502HD, SH100 and WS8H are all quite consistent in response from left to right.

The Yamaha MS 400 manual claims a 30 dB per octave crossover at 1600 Hz, the phase looks consistent in that range, what makes you think the "horn" is not in correct polarity to the woofer?

Art
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Paul Tucci

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Re: Wedges & Transfer Function Measurement: Meas. Mic Position?
« Reply #39 on: January 07, 2013, 06:30:54 pm »

Douglas,

Using the arrow key to move the phase trace to center of the display will give you a better look at the phase trace.

 Instead of having to think through the confusion of the wraps, moving the trace to a spot where there are no wraps lets you do more accurate math.

PT
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Re: Wedges & Transfer Function Measurement: Meas. Mic Position?
« Reply #39 on: January 07, 2013, 06:30:54 pm »


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