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Re: But its not an open standard

Posted by tomservo (M) on January 27, 2006 at 09:37:19

In Reply to: But its not an open standard posted by EGeddes on January 27, 2006 at 06:15:49:

Hi Earl

I should explain the reason for having those measurements taken and CLF format is to have a common format to share among the room acoustics programs.
They generally require 5 degree measurement points over the sphere, smoothed to 1/3 rd octave. The CLF viewer is a handy way to look at the data before importing / converting it into EASE or whatever files.
The point is, this is a tool which helps consultants figure out how to best use the speakers in bad rooms.
I probably can get the raw data but I have no idea what form its in, other than being a large number of data points.

I have seen the “polar map” before, It does show frequency / intensity / angle, I think it only does so in one plane per graph right?.
One could rotate the speaker and repeat each 5 degrees and compile a 3d radiation view to encompass the entire radiation (sort like the spectrum of “Q” vs frequency), maybe that’s what your is..
The closest one can get with the CLF viewer is a response curve at any angle X,Y you choose and one has to interpret the level vs frequency differences point by point.
What you can see is that as soon as your out of the pattern angle, the level falls a great deal and is pretty uniform. For in example in X and Y, 25 degrees outside the pattern, the level above 500Hz is –10 to –15 dB down, 90 degrees off axis its –20 to –30dB down off axis.
I think one could take regular polar measurements from the TEF and also display them as a spectrogram vs angle.
I have some stored measurements of other speakers, I will see if I can do that . I can do a Horizontal polar on the 50 when its nicer out and send you those files. I normally have to include the rear radiation but I’m not sure if that is used in the map view.

One thing, which is visible on the SH50 CLF model, at this resolution, it does not have any trace of lobes or nulls associated with the transition from one range to another, the seven drivers couple into one acoustic source with no visible crossover interaction in response, time or directivity. (the time part being evident in the more or less broad band square wave response spanning all 3 ranges).
These combining points are roughly at 315 Hz and 1250Hz, if there was a problem with “not coherently combining” or producing lobes /nulls, it would be in these regions.
These nulls and lobes are plainly visible, even at “this” resolution in one plane or another and in the spherical view with a normal multi-way speaker fwiw.

Above a few KHz, the directivity behavior is a bit rougher, the reason is partly the transition to the desired “square” radiation pattern at higher frequencies.
If you view the balloon “on end” you can see the pattern shifts to one that is more square, which is needed to mate with an adjoining cabinet / fill the 50X50 degree coverage angle.

I am not saying these are “perfect”, just that this horn approach is a way to combine different frequency ranges / drivers in a way that that ends acting to a great degree like one much more powerful source in one horn.
If I were able to take these full spherical anechoic measurements my self, there are things I would pursue because I like the idea of “perfect” as a goal.
As they are, the SH50’s already do a few things the speakers it is up against couldn’t hope to do.
The idea is scalable to a very high intensity too, where the SH50 is a “100W flood light”, I am working on a “500W spot light” which works the same way but has more drivers.
Again, this would not be a home product either although I did set the dimensions based on getting through my front door haha (seriously I did, same with the SH50).
Anyway, I should get to work but when I talk to Mike or Pat B., I’ll ask about the raw data.
Best,

Tom

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