SPL Meter - AVS | Home Theater Discussions And Reviews
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Old 03-26-2014, 02:55 PM - Thread Starter
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What is the best, inexpensive meter? Apple has an app for my ipod 5 Touch for $0.99. Does anybody know if it's good?
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Old 03-27-2014, 11:06 AM
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The Radio Shack models have been the old standby for most. I tried one of the SPL apps on my IOS device and got similar results when balancing channels. Neither of them is calibrated for actual SPL readings but if you are only using them for balancing the difference in channels I'm sure they are both acceptable.

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Old 03-27-2014, 11:42 AM
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The old Radio Shack meter works. But I have difficulty with it for sub levels.

(LCD - Sony KDL - XBR4) (Receiver - Sony STR-DA4ES)(Blu Ray - Oppo BDP-83) (PS3)( Dish Hopper DVR With Sling) Speakers (L & R - Paradigm Studio 20) (Center -Paradigm CC-470) (Surrounds & Back Surrounds - Paradigm SA-15R in walls) (Subwoofer 1 - Sunfire HRS-12) (Subwoofer 2 - Paradigm PW-2100)
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Old 03-27-2014, 08:17 PM - Thread Starter
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I downloaded the free app, my wife downloaded one that cost &0.99. The latter was a bit easier to read, but both worked fine for adjusting speaker trim. I can't do any EQ by frequency, so I'm basically done. If I could adjust bass response, it would be worth buying a better meter.
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Old 03-28-2014, 01:33 PM
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Keep in mind that the transducer (microphone) being used has a non-linear frequency response, and has cutoff points.

That will limit the accuracy or usefulness of any setup you use above or below its frequency limits.
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Old 03-28-2014, 01:48 PM
 
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Quote:
Originally Posted by commsysman View Post

Keep in mind that the transducer (microphone) being used has a non-linear frequency response, and has cutoff points.

That will limit the accuracy or usefulness of any setup you use above or below its frequency limits.

The following is the measured frequency response of the microphone in a commonly-used SPL meter:

http://realtraps.com/art_spl.htm



The following is the measured frequency response of several generations of iPhone:

http://blog.faberacoustical.com/2010/ios/iphone/iphone-4-audio-and-frequency-response-limitations/



http://blog.faberacoustical.com/2009/ios/iphone/iphone-dock-and-headset-io-frequency-response/




Can't find comparable data for the iPhone 5, but the general trend (based on other web resources) has been for it to about be the same for the iPhones 3 and later.

Looks like the earlier models might be better choices, but the iPhones 3-4 aren't bad for general work - not so good for subwoofers.
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Old 03-28-2014, 06:33 PM - Thread Starter
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Thanks, Arny, that's very useful and explains why my sub reading was low. Seems like my ipod isn't too bad. Certainly adequate for adjusting speaker trim. The test tones put out by my Oppo 103 are just noise, not deep bass.
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Old 03-28-2014, 08:05 PM
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Arny, I am almost certain the response you show from Ethan's site is that of a room, not of the microphone.

If you want a comparison to a measurement mic, throw in the curve for my Earthworks M30...

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
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Old 03-29-2014, 04:41 AM
 
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Quote:
Originally Posted by DonH50 View Post

Arny, I am almost certain the response you show from Ethan's site is that of a room, not of the microphone.

If you want a comparison to a measurement mic, throw in the curve for my Earthworks M30...

You are right - I made a mistake in my haste to get to an appointment.

This page is probably what you may be looking for:

http://realtraps.com/art_microphones.htm

Sample:



The Earthworks mic tested above is the QTC-1 which I understand to be closely related to the Earthworks M50. Not that the M30 does not need to be apologized for. I know some well-known speaker reviewers who base their work on it. It is just fine.

The whole microphone price/performance thing changed dramatically when Panasonic started selling the P9932 (number from memory) omnidirectional electret microphone capsule for less than $2. Other than being noisy due to its small diameter, and mediore dynamic range due to the low voltages it is designed to work at, it has great frequency response and works well for measurements and some recording. I am told that a Chinese clone of it is the basis of the popular Behringer ECM 8000. I believe that the first public observance of its performance was in an article by Dr.Bernhard Muller and I that was published in Audio Amateur now Audio Express) in the (if memory serves) late 1970s. As they say the rest is history!

I believe that later versions of the iPhone have an intentional roll off in their bass response for same reason that vocal mics do. Cuts wind noise, popping and the like. The mic element that is in them probably has the little Panny omni in its heritage.
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Old 03-29-2014, 07:40 AM
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No problem Arny. Ethan's measurements still show room influence at low frequency and do not match the manufacturer's data broadband, probably because he could not (well, he could, but maybe did not for lack of time and finances) make a perfect anechoic chamber, but as a relative comparison among mics is a great reference. Along with all the other great stuff on his site, natch!

The QTC (Quiet Time Coherent) series looks similar to the M (Measurement) series but QTC mics target recording, not measurement. I have not looked lately, but when I got my M30 the QTC series was not quite as flat (intentionally) and I don't think they came with an individual cal sheet. However, I think they had a lower noise floor. IIRC, even though the QTC claims time coherency, both were similar in phase response and time response (i.e. durn good!) I thought the QTC-1 was similar to the M30 but do not recall. The current model QTC-30 is similar to the M30. The M50 and M30 are virtually identical through the audio band; the M50 extends out to 50 kHz for noise applications and those who need ultrasonic response. I did not need more than 30 kHz and did not want to pay for it (the M30 is around $650 last I checked). Frankly, I'd have to ask Earthworks for the differences among the M, QTC, and TC (Time Coherent, presumably not as quiet wink.gif ) series mics.

What is great, as Ethan's plots show, is that today you can get a pretty inexpensive mic that has performance basically the same as a measurement mic. If only I had known about them back then! Actually, I believe Radio Shack had a dirt-cheap electret that was very popular because it had very good (flat) response; maybe it used that Panasonic capsule? I don't know.

You are correct about the iPhone; there have been articles about that in various engineering trade rags. The early models generated a plethora of audio apps ranging from free to several thousand dollars (a friend has one of those) that provided great results. the newer models require processing to compensate the low-end roll-off. Apple said the newer models provide greater vocal clarity with less noise. it is the right trade for vocals, but would have been neat if they had left full-range response and given us the choice (or processed digitally). I suspect the mic was overloading the preamp with LF content.

Nice to have your historical perspective Arny, thanks! - Don

"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
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Old 03-30-2014, 05:41 PM
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Studio Six Digital http://www.studiosixdigital.com/ is a great company that sells audio apps for the idevices. Their software takes into consideration the device's microphone limitations and curves - although anything lower than 40-50Hz can pretty much be ignored. They additionally sell reference mics (even a type 1) than can be connected directly to a 30 pin. These are good people that make good software. The software is not free by any means, but it is quality.

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