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Old 11th December 2007, 02:38 PM   #11
dlr is offline dlr  United States
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Default The Fiji was nearly linear

Quote:
Originally posted by kevinkr
I had the Fiji, couldn't remember the name of the card I was using..

I was using a B&K with mic pre-amp and calibrator - all borrowed from work. This set up used the line amplifier inputs, and was very accurate.

These days I use a Behringer instrumentation mic with a homebrew low noise mic pre-amp with phantom power, however I don't have a calibrator. This isn't really an issue as I'm not really interested in spl levels per se, but in the response of my speaker system in the room.
I do have a calibrated spl meter which I can use to set the reference point when needed.

The only way you could consider the LAUD setup calibrated is if you bought a microphone and Fiji card that Liberty had measured and created calibration constants for (at that time, no longer in cal after this length of time) or you had a mic calibrator that was known to be in calibration that you use for calibration prior to performing measurements. Technically it would be good to verify calibration before taking measurements each time it is used. The microphone is one variable (its sensitivity, and response flatness) that by definition LAUD cannot know anything about - it has to be provided.
I beg to differ. The Fiji card itself, though not perfect, had very good specs and did not require calibration unless the user needed the small correction of a calibration. I believe it was +/- 0.5db from 20-20K and was primarily the extremes that varied that also made a change of a few degrees in the measured phase response, very minor for most work. It's easy enough to get a calibrated Panasonic electret microphone (recommended by Waslo) for the Fiji mic input. LAUD then uses the supplied calibration file in its post-processing of the measurement that provides a calibrated response. The Fiji could go through a calibration procedure, but as Bill Waslo pointed out, it really wasn't necessary with the Fiji. A mic wand with a pre-installed, calibrated Panasonic electric mic is also available, it just depends on how much DIY you care to do.

I had to replace my first mic due to physical damage after several years and re-measured a driver to compare. The SPL overlay was nearly perfect. Variation in driver response from measurement to measurement has more variation in it than between these calibrated mics.

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Old 11th December 2007, 06:34 PM   #12
EC8010 is offline EC8010  United Kingdom
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Quote:
Originally posted by kevinkr
I had the Fiji, couldn't remember the name of the card I was using..
Pinnacle Fiji? Perhaps Orchid? I used to use the microphone pre-amplifier design given in the LAUD manual to drive the line input of my Orchid but I now use a simpler and better pre-amplifier of my own design. Absolute levels are still dependent on the microphone capsule, but who cares? We're normally interested in frequency response measurements, not sensitivity.
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Old 11th December 2007, 07:39 PM   #13
dlr is offline dlr  United States
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Default Sensitivity as in frequency response for 2.83v @1m

Quote:
Originally posted by EC8010


Pinnacle Fiji? Perhaps Orchid? I used to use the microphone pre-amplifier design given in the LAUD manual to drive the line input of my Orchid but I now use a simpler and better pre-amplifier of my own design. Absolute levels are still dependent on the microphone capsule, but who cares? We're normally interested in frequency response measurements, not sensitivity.
I care, for one. If drivers are to be compared then the drive level has to match (can't really do this from person to person with the various systems) or the measurements need to be adjusted to some absolute reference value, such as the typical SPL for 2.83v @1m. It's useful to be able to provide data referenced to a known drive level such as this.

For example, I have a large number of raw driver measurements posted at my site for download. These were all taken on a 2mx2m board and taken at 0.5m. The auto-adjustment sets it as though it were @1m, so any using them need only subtract 6db to set the level for a 1m reference, easily done. The measurements I made years ago are fully compatible with any taken today insofar as relative levels (sensitivities) are concerned, though I do not keep track of the actual drive level. That, in fact, is not required.

I have at times substituted drivers, say a tweeter or a midrange, in an existing design. I only then have to measure the new driver for the new system design since the absolute frequency response result from LAUD for that driver will be appropriate for the other drivers' measurements, at times made years before. All I need do is make the measurement at the same distance, such as on the tweeter axis @1m. That information IS in the measurements since I (almost) always include that in the comments embedded in the measurement files.

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Old 11th December 2007, 07:42 PM   #14
kevinkr is offline kevinkr  United States
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Quote:
Originally posted by EC8010


Pinnacle Fiji? Perhaps Orchid? I used to use the microphone pre-amplifier design given in the LAUD manual to drive the line input of my Orchid but I now use a simpler and better pre-amplifier of my own design. Absolute levels are still dependent on the microphone capsule, but who cares? We're normally interested in frequency response measurements, not sensitivity.
Turtle Beech Fiji..

I use my measurement system for frequency response measurements and rarely for spl measurements which I have to reference to my questionable spl meter for a baseline cal.
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Old 11th December 2007, 07:46 PM   #15
dlr is offline dlr  United States
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Default Conflicting terms

Quote:
Originally posted by kevinkr


Turtle Beech Fiji..

I use my measurement system for frequency response measurements and rarely for spl measurements which I have to reference to my questionable spl meter for a baseline cal.
Do you mean that you use it for things such as crossover transfer function or driver impedance measurements, but not SPL frequency response (SPL is a form of frequency response)?

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Old 11th December 2007, 09:53 PM   #16
kevinkr is offline kevinkr  United States
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I mostly use it for measuring amplifier performance, frequency response, distortion spectra (FFT) and noise measurements.

I run 24 bits and 96kHz sample rates pretty much across the board - eventually I will probably upgrade to the M Audio 24192 Audiophile, but for now I use the 2496 and it suffices. I can do measurements out to about 42kHz with this set up, almost high enough for bats..
(Well maybe not, haven't checked up on bat physiology for this post.. )

I do use it infrequently to measure my speaker system's frequency response, but usually don't know what the exact system spl is - usually high enough for good snr, and low enough to avoid amplifier compression/clipping. (System measurements are done with the system amplifier, driver measurements with a Dyna ST-80) I just make sure I set everything up the same way each time I do a measurement after making a change to the speaker system.

I can also do all of the standard ts parameter loudspeaker measurements using one of several setups in conjunction with audiotester.

I have a licensed copy of audiotester which I use for electronics mostly, and an eval version of Arta that I use for acoustic measurements. I plan to license it when I start to evaluate my latest cross-over redesign.

The 2496 lives in the media server and primarily serves music via spdif to my dac, but the analog I/O are available anytime I want to do measurements.
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Old 12th December 2007, 11:32 AM   #17
Secips is offline Secips  United States
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Thanks for the help.

However, Liberty Instruments is coming through for me.

Looks like I pre-date you guys. I got LAUD in its introduction right after IMP. I have the preamp and calibrated mic that comes with LAUD. You use an ECHO DSP card with it. I was hoping someone found another card to work with LAUD.

LAUD in its day was an EVOLUTIONARY product. It EMPOWERED hobbyist to develop audio equipment that was first rate. At the time, anything with LAUD's capabilities was 10 to 20 times more expensive. Companies who were using MLSSAs and LMSs were using LAUD as well.

Having the case of "Back-to-the-future" syndrome. I am disheartened upon knowing the demise of LAUD. I am coming from the prespective of a hobbyist/enthusiast. I feel akin to the DIY community as I consider them to be kindred spirits. IMP/LAUD was developed in that light, I remember issues of Speaker Builder magazine. Being in IT, I know how new releases just blindside you. Bill Waslo didn't want this to happen. The development and retraining cost is tremendous, let alone coming up with a product that would measure up to the old standard. In an email to me, Bill Waslo, expressed his disappointment that hardware and operating system upgrades, "Orphaned" LAUD.

Anyway, thank you for all the tips I sure appreciate them. I used LAUD for the development of speakers. During the time FFT transforms, impulse, close-mic measurement gave you data without an anechoic chamber for peanuts compared to what was available. Anyway, I gotta get back up to speed as I haven't done these things in, errrr... something years .

Lastly, I must say that it seems that Bill Waslo, (Liberty Instrument) still "Kept the Faith" lending a helping hand whenever possible.
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Old 12th December 2007, 11:48 AM   #18
SY is offline SY  United States
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I still have (and use) my IMP system. This was a real breakthrough for hobbyists and still does 90% of what I'd want a speaker measurement system to do, albeit with a DOS user interface. When I had some difficulties (software related), Bill sent me his home phone number, figured out the issue, and got me an updated version within a day. Very impressive.

I wish I could cost-justify Liberty's latest-and-greatest. Mmmm, maybe next year...
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