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Old 12th February 2010, 02:17 AM   #611
soongsc is offline soongsc  Taiwan
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Quote:
Originally Posted by gedlee View Post
You know, I mis-spoke. That its free is irrelavent. I'd gladly buy it if I had to. I insisted that my Chinese client switch over to HolmImpulse since they were using old B & K and LMS stuff. Holm danced circles around both of those.
I agree that LMS has limitations, and that the key "old" is very critical. Lots of audio companies cannot afford new B&K equipment. Not that the new equipment is better, but that B&K seems to put more focus on noise related aspects rather than driver design related aspects.

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- Its free
- It uses a log sweeps which puts the nonlinearities at precise points on the impulse response as individual impulses - nothing else does this and its key to any view of nonlinearity that is going to mean anything
...
I am quite interested in this point because even if it did put the nonlinearities at the precise points, it still takes more effort to allocate the cause of such nonlinearity in a way that an adequate driver fix can be predicted. I have never seen any paper on this subject just looking at impulse data. If any is available out there, I certainly would appreciate the information. Additionally, with only single channel impulse, how would one differentiate between nonlinearity in the driver, interaction between driver and amp, vs. driver. I don't believe there is any paper out there that addresses this either.
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Old 12th February 2010, 10:03 AM   #612
Jmmlc is offline Jmmlc  France
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Hello Soongsc,

http://pcfarina.eng.unipr.it/Public/.../134-AES00.PDF

http://pcfarina.eng.unipr.it/Public/...154-AES110.PDF

http://www.anselmgoertz.de/Page10383...wp-english.PDF


Best regards from Paris, France


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I have never seen any paper on this subject just looking at impulse data. If any is available out there, I certainly would appreciate the information.
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Old 12th February 2010, 10:54 AM   #613
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I've been after Bohdan to add the Farina approact to SE for some time. Hasen't happen yet.
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Old 12th February 2010, 01:19 PM   #614
soongsc is offline soongsc  Taiwan
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I have seens these before, and I browsed through them again. I see a different means of extacting data that is available via other commonly available means of measurement, but I still fail to see how it assists in further diagnosis of the DUT. Even if it provides more distinction under certain circumstances, is the cause due to complicated acoustic wave interaction? Is it due to the mic? or the DUT?

When I look at an impulse created using MLS test signal, I do see various effects as I tweak drivers. I can see reflections from mic clamp. Even with this kind understanding, there are still some areas where I hear differences, but cannot quite find the correlation in data. The method described in these papers desmonstrates some valid mathematical methods, but does not seem to write off what is caused by the measuring equipment. It also brings more uncertainties when only using single channel to do the measurement.
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Old 12th February 2010, 01:30 PM   #615
gedlee is offline gedlee  United States
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Originally Posted by soongsc View Post
I am quite interested in this point because even if it did put the nonlinearities at the precise points, it still takes more effort to allocate the cause of such nonlinearity in a way that an adequate driver fix can be predicted. ... Additionally, with only single channel impulse, how would one differentiate between nonlinearity in the driver, interaction between driver and amp, vs. driver.
When one is dealing with any type of transducer, the nonlinearities in the transducer will swamp out those in the amp, unless its a very bad amp, which you should not be using in a measurement system.

You can check the amp with a simple load to be sure. The amp will tend towards higher orders of nonlinearity while the transducer will have very large lower orders.

And whose to say that the driver needs to be "fixed" because it has nonlinearities? There are papers on that and they imply that chasing nonlinearities in loudspeakers is a waste of time.
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Old 12th February 2010, 03:35 PM   #616
soongsc is offline soongsc  Taiwan
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Originally Posted by gedlee View Post
When one is dealing with any type of transducer, the nonlinearities in the transducer will swamp out those in the amp, unless its a very bad amp, which you should not be using in a measurement system.

You can check the amp with a simple load to be sure. The amp will tend towards higher orders of nonlinearity while the transducer will have very large lower orders.

And whose to say that the driver needs to be "fixed" because it has nonlinearities? There are papers on that and they imply that chasing nonlinearities in loudspeakers is a waste of time.
Interaction between the amp and the driver is still significant. Unless the amplifier has been verified under different types realistic nonlinear loading, I think the amplifier factor still needs to be taken out by using a reference channel. I have measured distortion right at the speaker terminals under mainy situations during one of the projects we've been working on. I have also seem many measurements Stereophile has made public. Basically the results have similar trends compared to mine.

I really think whether anything needs to be fixed or not is really a design tradeoff. But you have to have enough data showing what part is causing what kind of distortion before one makes that decision. Nothing is going to be perfect, just an engineering judgement as to whether it's worth fixing or not. No two engineers will have the same opinion. There are things that I can't determine through listening. But if data shows a certain part is producing higher levels of problems than other parts, that is surely an aspect to at least consider. If that improvement produces audible improvement, then we've learned one more thing. Whether it's worthwhile to make it into a product is a different issue. I'm sure there may be some forms of nonlinearity to be a waste of time to consider.
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Old 12th February 2010, 04:17 PM   #617
gedlee is offline gedlee  United States
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But you have to have enough data showing what part is causing what kind of distortion before one makes that decision.
First you must PROVE that any of it even matters in the perception of the end product. In the case of loudspeakers and distortion, it doesn't. End of the need for any more data.
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Old 12th February 2010, 04:47 PM   #618
soongsc is offline soongsc  Taiwan
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First you must PROVE that any of it even matters in the perception of the end product. In the case of loudspeakers and distortion, it doesn't. End of the need for any more data.
I like the improvement, implement it, and the customer likes it. To me, that is proof enough. Others can choose what they want to do. Life is too valuable to try and convince those beyond their will. If "chasing nonlinearities in loudspeakers is a waste of time", then "puting the nonlinearities at precise points on the impulse response as individual impulses" would be of no value either.
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Old 12th February 2010, 06:13 PM   #619
gedlee is offline gedlee  United States
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I like the improvement, implement it, and the customer likes it. To me, that is proof enough. Others can choose what they want to do. Life is too valuable to try and convince those beyond their will. If "chasing nonlinearities in loudspeakers is a waste of time", then "puting the nonlinearities at precise points on the impulse response as individual impulses" would be of no value either.
Yes, if you (think) that you hear something and that's good enough for you, that's fine. I'm more scientific than that. I don't believe something until it can be shown subjectively AND objectively. I'm not willing to except one OR the other.

I'd be interested in the nonlinearities more for electronics than loudspeakers because nonlinearities in electronics IS audible (loudspeaker nonlinearities CAN BE audible, but they can also be inaudible. In my speakers they are inaudible). But without having the distinct orders seperated out you can't tell the good from the bad for anything. Thats why HOLM is so valuable.
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Old 12th February 2010, 06:33 PM   #620
Pano is offline Pano  United States
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And another reasons its valuable is that it's free. Ooops!
Seriously, I tried many different measurement softwares - free, pay, share - and settled quickly on HOLM when it showed up.

It has really helped my measurements because it's both good and easy to use. Being both, it tends to spur further work, measurement technique and investigation. That's a good thing.
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