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Old 17th September 2012, 01:14 PM   #451
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No idea what spl the measurement was taken at as this doesn't really matter. Probably around 75-80dB, normal listening levels for that speaker.

If you say it's only accurate down to 1.2kHz then how come all measurement programs, that show you the accuracy cut off for the given gate length, say different? ARTA says this is accurate down to just below 300Hz providing I've set the gate accordingly, as does Holm. They ain't gonna lie about something which is presumably calculated mathematically.

Besides what makes you choose 1.2kHz?
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Old 17th September 2012, 02:17 PM   #452
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I spent about 9 years working with Meyer's SIM2 and SIM3 measurement systems doing repair for a Broadway rental house. The truth is you can get some funky traces depending on the environment you are measuring in. The beauty of those particular system's is you have a visual indication of where the software isn't sure of the result- for SIM it's the Coherence trace. Many other pieces of measurement software do this, but SIM always seemed to perform a bit better. Then you can adjust the measurement window to suit the environment and look at your relative phase trace to get the best result trace.

What we ended up doing to have the best chance indoors was use a bunch of acoustic absorption panels. We used Sorber panels made by ClearSonics which are commonly used for vocal and drum booths for live concerts and shows. We made a sort of portable booth surrounding the SUT with 10 feet or so of panels on the floor in front of the SUT and a couple behind the measurement mic (usually a DPA 4007).
This was in early 1900's converted railway warehouses with finished plywood floors and parallel brick walls.
We found that compared to manufacturers traces done in their own anechoic chamber, we could get very close. Certainly close enough to confirm a within spec window of +/- 3 dB.
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Old 17th September 2012, 02:50 PM   #453
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I suppose back then things we're quite a bit different indeed. ARTA lets you view the impulse response directly, whilst setting the gate. This gives you a very good visual representation of what the captured response (room included) is like and you can see the response captured in time, seeing when each of the reflections arrive at the mic.

The issue at the moment, at least from my point of view, is that the data captured is accurate and the gate has been set accordingly. With those conditions ARTA says the data is accurate down to around 300Hz, but A.wayne say's it's only accurate to 1200Hz, what I want to know is why he thinks that and why then is ARTA being misleading.
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Old 17th September 2012, 03:58 PM   #454
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.....We found that compared to manufacturers traces done in their own anechoic chamber, we could get very close. Certainly close enough to confirm a within spec window of +/- 3 dB.
and that is what I thought: could have the process meaasurement have been done wrong on stereophile's hand?
Could this cause in your opinion a significant discrepancy with the manufacturer's trace?
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Old 17th September 2012, 04:09 PM   #455
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What is this thread about again?
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Old 17th September 2012, 04:13 PM   #456
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Old 17th September 2012, 04:40 PM   #457
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Without knowing what software was used (I went back a bit to find the article in the thread but no luck) all I can say is it's possible to interpret the results incorrectly.
However, the software that I have used- SIM, SMAART, and Spectrafoo all show you when to question the measurements. If the phase trace looks good, the coherence trace looks good, your mic is good, and you've reasonably treated the area for spurious reflections if indoors you have an excellent foundation for good data.

5th,
I'm pretty sure the all of the above software does impulse response. SIM doesn't do the pretty spectral maps, but SMAART and Foo certainly do.
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Old 17th September 2012, 04:44 PM   #458
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the measurements discussed are made by stereophile, here is the link

http://www.google.com/url?sa=t&rct=j...vDs6g2l1CqEhFw
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Old 17th September 2012, 04:54 PM   #459
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Old 17th September 2012, 05:01 PM   #460
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and that is what I thought: could have the process meaasurement have been done wrong on stereophile's hand?
Could this cause in your opinion a significant discrepancy with the manufacturer's trace?
Well with either measurement technique what you're doing is effectively isolating the direct sound from any reflected sound. An anechoic chamber doesn't have any reflections and the gated measurement only looks at the first few milliseconds of sound and so isolates it that way. If everything is set up correctly, the only way that the gated measurement is going to become compromised is if you set the gate incorrectly and allow too many reflections in. This looks quite horrible on the frequency response. You can see a little of this in the response I posted above, superimposed over the frequency response you've got small wiggles, up-down-up-down, like passband ripple in a DACs brick wall filter (it's effectively comb filtering in this case). If you let more reflections in these get progressively worse to the point where you don't know if its coming from the loudspeaker or if its a reflection. One can counter this to a degree by using smoothing, but smoothing will obviously smooth out any peaks that are actually there, so anything beyond 1/12/octave is usually shunned, at least by me. John Atkinson's measurements don't show telltale signs of being heavily smoothed so he must be gating his measurements correctly and using an appropriate hardware set up to allow a reasonably large gate.

Even so, the shortfall of gated measurements is their low frequency accuracy, measuring 3.5kHz accurately is extremely easy.

As you can appreciate B&W could easily apply smoothing to their curves to lessen the impact of this peak and if they wanted they could simply photo-shop it out, it wouldn't be the first time that manufactures have done this.

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