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Old 10th August 2010, 05:50 PM   #7091
Paul W is offline Paul W  United States
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Quote:
Originally Posted by g3dahl View Post
Here's the measured response of the Radian 745 in the Azurahorn:

Click the image to open in full size.

Gary Dahl
Gary,
Do you have off-axis measurements of the horn you can share?
Thanks,
Paul
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Old 10th August 2010, 07:33 PM   #7092
Elias is offline Elias  Finland
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One can measure "frequency response" of the LTI system by inserting a number of sinusoids each having infinite duration. Then output will have a number of sinusoids each having infinite length. The "frequency response" is amplitude and phase of these sinusoids at each frequency included in the analysis. When input and output of the system consists of sinusoid of infinite length, the system is at steady state.

One can measure exactly the same "frequency response" by calculating the fourier transform of the system's impulse response.

Since the system can be only at one state at a time, steady state in this case, thus the output of the fourier transform of the impulse response is a steady state response at each particular frequency where the analysis is calculated.

"Frequency response" IS a steady state measure.


- Elias


Quote:
Originally Posted by JohnPM View Post
That is another incorrect statement. FFT is a transform (the clue is in the name ) that we can use to move between domains, it does not know or care what it is transforming. It is as happy being used to generate slices of a waterfall or spectrogram as it is being used to transform a system's frequency response into its impulse response or vice versa. The frequency and impulse response of an LTI system are time invariant.

Last edited by Elias; 10th August 2010 at 07:35 PM.
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Old 10th August 2010, 07:41 PM   #7093
g3dahl is offline g3dahl  United States
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Quote:
Originally Posted by Paul W View Post
Gary,
Do you have off-axis measurements of the horn you can share?
I do, but not with the Radian driver. These were made using a GPA 288-16H:

Click the image to open in full size.

The 10-degree curve follows the on-axis curve almost exactly! From there, it does much what one would expect from the simulations.

These readings were taken fairly close-up...about 26 inches from the front of the horn. Ignore the dB scale -- the gain of my power amp hasn't yet been entered into ARTA.

Gary Dahl
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Old 10th August 2010, 08:35 PM   #7094
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Paul I think Gary's Azura horn is the same as the one I measured from Lynn. Results posted in my sig. Very nice off axis behavior.
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Old 10th August 2010, 08:37 PM   #7095
g3dahl is offline g3dahl  United States
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Thanks Brandon...

Yes, it's exactly the same model of horn (Azurahorn AH-425).

Gary Dahl
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Old 10th August 2010, 09:15 PM   #7096
JohnPM is offline JohnPM  United Kingdom
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Quote:
Originally Posted by Elias View Post
"Frequency response" IS a steady state measure.
"Steady State" has nothing at all to do with it. Frequency Response is more typically measured with a log swept sine, inverse transforming the determined FR to get the impulse response. Is a log swept sine steady state? Is the system's response to the log swept sine steady state? The FR is a characterisation of the system's behaviour and can be determined by examining how the system alters a stimulus passed through it, no steady states required.

Apologies for the off-topic posts on this, I have an aversion to misconceptions. I'll stop now . Steady as you go, Elias.
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Old 10th August 2010, 10:26 PM   #7097
Elias is offline Elias  Finland
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To be accurate, log sweep cannot measure system's impulse response. Not unless you start the sweep from DC. But one cannot do that because it would take infinite time to play the sweep. Anything else yields only approximation of the impulse response. In practise approximations are often sufficient, but it does not remove the (approximate) steady state condition requirement. The more 'steady stateiness' in the log sweep the more accurate is the measured impulse response. That is, the longer the sweep the more accurate is the impulse response. To understand this try to think what will happen if you make your log sweep infinitesimally short in duration.

- Elias

Quote:
Originally Posted by JohnPM View Post
"Steady State" has nothing at all to do with it. Frequency Response is more typically measured with a log swept sine, inverse transforming the determined FR to get the impulse response. Is a log swept sine steady state? Is the system's response to the log swept sine steady state? The FR is a characterisation of the system's behaviour and can be determined by examining how the system alters a stimulus passed through it, no steady states required.

Apologies for the off-topic posts on this, I have an aversion to misconceptions. I'll stop now . Steady as you go, Elias.
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Old 11th August 2010, 01:02 AM   #7098
Few is offline Few  United States
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After over 7000 posts there's little that can be considered off the topic(s) of this thread.

JohnPM: Thanks for your concise, and I believe accurate, descriptions of the nature of frequency response measurements. I think you hit the crux of the matter when you highlighted the fact that the frequency response of a system is just a description of the way the system changes the amplitudes and phases of the various frequency components of any signal that passes through it (sorry for the paraphrasing). The variable t (time) does not appear in the frequency response; the frequency response has no time dependence. Nonetheless--and this seems to be the source of the confusion--the frequency response can still be used to compute the way a system will respond to any time-varying signal, such as music. In short, the system's response to an arbitrary input varies over time but its frequency response does not. For the mathematically inclined, here's another link that describes the relationship between frequency response, impulse response, and transfer function.

On the subject of approximations: It's certainly true that in the real world we make measurements which only approximate the system's true frequency response, but that doesn't alter the definition of the frequency response. It just means we need to take care when making use of our measurements to be sure we only apply them only within the range of their accuracy.

Okay, I'm probably contributing to a subthread that's depleted the patience of some, so I'm going to go fishing for a few days. I hope my input yields the desired output. Wish me luck.

Few
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Old 11th August 2010, 01:29 AM   #7099
g3dahl is offline g3dahl  United States
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Wish me luck.
Good luck!

The worms had better watch out.
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Old 11th August 2010, 01:39 AM   #7100
Pano is offline Pano  United States
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I'm very impressed with how well that little 16.5" horn does. Very nice FR. Nice and compact in size.
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