Thank you. I am sure I will.
To my embarrassment, no I don't remember that standard room. A typical room will depend on whether you are talking about urban or suburban situations. My current room is around 25' by 16' by 7.5', which is larger than the NRC listening room in Ottawa (in which I spent some time back in 1996) but around the same size as Michael Fremer's and Wes Phillips' rooms, though Wes has an 8' ceiling.
Neither. I use a chirp, implemented in SMUG Software's FuzzMeasure. A very useful program, though it is Mac only. The computer calculates the impulse response from the chirp then uses FFT analysis to give you the frequency response. The impulse can be windowed to include as much or as little of the room as you wish.
I still have my SA3050A but almost never use it these days. (There's now a great spectrum analyzer available for the iPhone and iPod Touch, BTW, from Studio Six Digital) For my published in-room measurements, I use spatial averaging in a 36" by 18" grid centered on the position of the listener's ear in his seat, which smooths out most of the peaks and dips, leaving a curve that does seem to correlate quite well with a speaker's perceived balance.
You can find Kal Rubinsons review of Floyd's book, which is excellent, at Stereophile: Book Review: <I>Sound Reproduction: Loudspeakers and Rooms</I> . Everyone with a serious interest in loudspeakers should have this book in their library.
John Atkinson
Editor, Stereophile
That ceiling height has to be a drawback to getting really good sound.
With all Macs around here not a hardship, althou i've finally just gotten a Leopard capable machine so i can run 3.x (i was one of the very 1st, if not 1st user (after Chris), of FuzzMeasure)
I've been holding off an an iPhone, but this software will push me to get an iPad when the arrive.
Can you tell us where the microphone locus are in that grid?
dave
9 positions: ear +/-9" vertically, repeated 18" on either side. Each speaker is measured individually to avoid combing and I weight the average slightly to the center with a 10th measurement.
Please understand that this is entirely empirical, but it works relatively well at combining the direct sound with the influence of the reverberant field, and reducing the effect of LF room modes.
John Atkinson
Editor, Stereophile
Thanx. It may be empirical, but with all the times you have generated this metric, it has become somewhat a standard.
dave
Yes, but the ear/brain expects combing (ref Toole), so measuring each individual speaker removes how combing would confound the FR, making the measurement more useful for interpretation.
dave
I pointed out the bass bump in Stereophile's measurements back in 2005 on the Classic Speaker Pages and also noted that it was a measurement issue since measurements at the NRC did not agree:
AR-303 Comments and Observations - Acoustic Research - The Classic Speaker Pages Discussion Forums
The older threads over there have become mangled, unfortunately due to forum updates and upgrades. Even the order of the posts became scrambled and most links are broken.
AR-303 Comments and Observations - Acoustic Research - The Classic Speaker Pages Discussion Forums
The older threads over there have become mangled, unfortunately due to forum updates and upgrades. Even the order of the posts became scrambled and most links are broken.
I have always been clear in the magazine that this bump is due to the nearfield measurement technique, which assumes a 2pi acoustic environment. You can consider that nearfield and anechoic are the two extreme conditions; in all but very very large rooms, the actual bass performance will be somewhere between these two extremes.
John Atkinson
Editor, Stereophile
Hi John thanks for responding,
I'm familiar with the near field measurement method and the differences associated with 2pi and 4pi environments. Yes, if a speaker is designed with baffle step compensation for in room listening and you measure it near field we should see the baffle step compensation curve with, roughly, a gradual rise from about 1K to plus 3 or 6 dB (depending on how much compensation was designed in) at 100 Hz and below. That is assuming worst case the actual difference depends on where you make the splice from near field with the gated measurement. But we don't see anything like this, rather the curves often look like a higher Q alignment with something more like peaking in the bass. I don't have a good answer for what is going on with that peak. Actually, you should not use any gating for the near field measurement, you can use a swept sine. Gating could be a source of error if you use it for the near field measurement.
Here is an old near field measurement that I made of the SPICA TC-50 woofer through the crossover using a swept sine. Note the rise from 1K down to about 100 Hz as would be expected for a system with very close to full baffle step compensation. Also note that since there is only a mild rise from 300 Hz down so that if the splice is made near 300 or below the baffle step compensation hardly shows up:
http://baselaudiolabs.googlepages.com/MT5ANRFW.PNG
The curve has nearly text book agreement with the measured Fc and Qtc for the system:
T&S parameters: Fc = 69.5 Hz, Qtc = .79
It should be roughly 2 dB down at 69.5 Hz and it is very close considering that the woofer should be driven directly for full agreement and not through the crossover.
I'm familiar with the near field measurement method and the differences associated with 2pi and 4pi environments. Yes, if a speaker is designed with baffle step compensation for in room listening and you measure it near field we should see the baffle step compensation curve with, roughly, a gradual rise from about 1K to plus 3 or 6 dB (depending on how much compensation was designed in) at 100 Hz and below. That is assuming worst case the actual difference depends on where you make the splice from near field with the gated measurement. But we don't see anything like this, rather the curves often look like a higher Q alignment with something more like peaking in the bass. I don't have a good answer for what is going on with that peak. Actually, you should not use any gating for the near field measurement, you can use a swept sine. Gating could be a source of error if you use it for the near field measurement.
Here is an old near field measurement that I made of the SPICA TC-50 woofer through the crossover using a swept sine. Note the rise from 1K down to about 100 Hz as would be expected for a system with very close to full baffle step compensation. Also note that since there is only a mild rise from 300 Hz down so that if the splice is made near 300 or below the baffle step compensation hardly shows up:
http://baselaudiolabs.googlepages.com/MT5ANRFW.PNG
The curve has nearly text book agreement with the measured Fc and Qtc for the system:
T&S parameters: Fc = 69.5 Hz, Qtc = .79
It should be roughly 2 dB down at 69.5 Hz and it is very close considering that the woofer should be driven directly for full agreement and not through the crossover.
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I won't jump in on the measurment argument, but I will say that after 20 years of designing subwoofers and speakers, that part of the design process is maxmizing output through the calculations. We can manipulate the performance of the driver through the cabinet. In my days of high end mobile audio, it took me months to re-train the sale staff from selling the most expensive woofer with crap amplifiers. We made some very nice sounding systems with cheapo woofers and quality amplification. Any good speaker designer can "force" the alignement (within limits) to get, or get close to the desired performance. The amplifier is extremely important for a sub, as with any speaker or speaker system. I spent many hours on my enclosures for the speakers in my two channel room. I used inexpensive 8" drivers and get decent response down to 38Hz. But this is after a lot of modeling, and not what the manufacturer supplied. I personally don't think there is anything wrong or unethical about a manufacturer tweaking a cabinet to push driver performance. As far as I am concerned, that's the fun part of loudspeaker design, seeing just how far you can push the gear without letting the smoke out....
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