Nice article on correlating speaker measurements with sound

[3db]

Interesting read.

http://www.soundstagehifi.com/index.php/opinion/852-why-i-don-t-infer-a-speaker-s-sound-from-its-measurements

 

[Swerd]

That's a very good article - thanks. I liked all of what he said, especially the part where he said:

"But even if you take enough measurements to better correlate what you hear with what you’ve measured, as Toole did, being able to properly interpret those measurements and correlate accurately with what people hear requires loads of experience and knowledge to draw on – far more than most reviewers have. It’s like interpreting X-rays and CT scans: Almost anyone can draw conclusions from the images produced, but you have to have specialized knowledge and long experience to see anything of real medical significance in such images."

It's all about experience and pattern recognition. This doesn't happen overnight. The graph examples included in the article were examples of decent speakers where little if anything was wrong. I usually learn more from examples that illustrate poor designs.

At the end of the article, he said:
"Unfortunately, what they (measurement graphs) can’t do is what many readers seem to want them to do: tell you exactly how something will sound in your listening room."

One look at those photos of the anechoic room, should tell anyone, this isn't your typical room at home.

 

[3db]

One look at those photos of the anechoic room, should tell anyone, this isn't your typical room at home.

Yeah some bad feng shui happening there.

I like the fact that he mentioned Paul Barton and Andrew Jones.

 

[AcuDefTechGuy]

I bet if we asked a Radiologist if he thinks reading speaker measurements is kind of like reading CT scans and X-Rays, he would probably say, "Oh, hells no, man!"

 

[BoredSysAdmin]

Imma gonna take this article with a healthy pound of salt just because of this part

"Yet as revealing as measuring a speaker’s sound power can be, I know of no magazine that does it: the setup is too complex, it takes too much time, and if you’re renting an anechoic chamber -- the only proper way to do it -- it’s all just too expensive." [Highlight is mine]

Measuring speaker is obiviously preferred way, but it's not the ONLY proper way to do. Close milking woofer and using above 200hz info can provide very accurate results.

Not to mentioned 500 different speaker cables ads all over the site.

 

[3db]

Imma gonna take this article with a healthy pound of salt just because of this part

"Yet as revealing as measuring a speaker’s sound power can be, I know of no magazine that does it: the setup is too complex, it takes too much time, and if you’re renting an anechoic chamber -- the only proper way to do it -- it’s all just too expensive." [Highlight is mine]

Measuring speaker is obiviously preferred way, but it's not the ONLY proper way to do. Close milking woofer and using above 200hz info can provide very accurate results.

Not to mentioned 500 different speaker cables ads all over the site.

Do you know of a magazine that does test correctly? Audioholics does test thoroughly but its not considered a magazine.

 

[BoredSysAdmin]

my comment had nothing to do publishing method such as magazine, blog and other

 

[Dennis Murphy]

my comment had nothing to do publishing method such as magazine, blog and other

I think we do have to interpret the article as part objective commentary, part political prose aimed at not upsetting companies whose speakers don't measure particularly well in the Canadian tests. I pretty much agree with his comments on harmonic distortion. We really don't know how the THD results translate into audible behavior. But if we restrict yourselves to the frequency plots, and just ask whether they can reliably predict the spectral balance that we hear in a room, I think the answer is yes. Just about every speaker I've measured sounded that way in terms of balance. And you don't need a complete set of measurements taken at virtually every angle to predict what you hear. In my experience, off-axis behavior, and in particular extreme off-axis behavior, is dominated by more direct sound. That's what I hear, and that's what you see when you look at measurements with long gate times that show a mixture of on and off-axis arrivals. Although real-life rooms don't look like echo-free test chambers, once you get above the bass and mid-bass regions, room reflections do less than you might think to the basic character of a speaker. None of this goes to directly to sound staging and imaging, although I suspect that the better a speaker measures, the better it will do in these respects.

 

[BoredSysAdmin]

I think we do have to interpret the article as part objective commentary, part political prose aimed at not upsetting companies whose speakers don't measure particularly well in the Canadian tests. I pretty much agree with his comments on harmonic distortion. We really don't know how the THD results translate into audible behavior. But if we restrict yourselves to the frequency plots, and just ask whether they can reliably predict the spectral balance that we hear in a room, I think the answer is yes. Just about every speaker I've measured sounded that way in terms of balance. And you don't need a complete set of measurements taken at virtually every angle to predict what you hear. In my experience, off-axis behavior, and in particular extreme off-axis behavior, is dominated by more direct sound. That's what I hear, and that's what you see when you look at measurements with long gate times that show a mixture of on and off-axis arrivals. Although real-life rooms don't look like echo-free test chambers, once you get above the bass and mid-bass regions, room reflections do less than you might think to the basic character of a speaker. None of this goes to directly to sound staging and imaging, although I suspect that the better a speaker measures, the better it will do in these respects.

Hi Dennis, To correct and highlight my point - I am do not disagree that FR plot is not the only thing (but it pretty important one to have a general idea on speaker performance) that defines a speaker, but as you agreed - it is very possible to measure speaker accurately in less than ideal room ( with minor asterix ofcourse

 

[3db]

I think we do have to interpret the article as part objective commentary, part political prose aimed at not upsetting companies whose speakers don't measure particularly well in the Canadian tests. I pretty much agree with his comments on harmonic distortion. We really don't know how the THD results translate into audible behavior. But if we restrict yourselves to the frequency plots, and just ask whether they can reliably predict the spectral balance that we hear in a room, I think the answer is yes. Just about every speaker I've measured sounded that way in terms of balance. And you don't need a complete set of measurements taken at virtually every angle to predict what you hear. In my experience, off-axis behavior, and in particular extreme off-axis behavior, is dominated by more direct sound. That's what I hear, and that's what you see when you look at measurements with long gate times that show a mixture of on and off-axis arrivals. Although real-life rooms don't look like echo-free test chambers, once you get above the bass and mid-bass regions, room reflections do less than you might think to the basic character of a speaker. None of this goes to directly to sound staging and imaging, although I suspect that the better a speaker measures, the better it will do in these respects.

I think what the author is saying that takes many hours of working eith speakers to correlate the graphs to how the speakers sound. It doesn't suprise me in the least that you are able to do this accurately but many of the readers here can't nor can many of the reviewers found in the magazines, stereophile being the sole exception that I know of.

 

[3db]

my comment had nothing to do publishing method such as magazine, blog and other

Yet you mentioned magazines and other sources. Other than Audioholics and Stereo philosophy what other publications do you know of that go into such detail?

One cannot accurately measure speaker response in a poor acoustically setup room. The best you can hope for is an approximation of the speaker response but that is far from accurate.

It's true that direct radiation (measuring near field) contains most of the energy. However, there are a lot of products out there to treat room acoustic treatment whose job is to treat reflected sound. Those same reflections exist because of driver dispersion. If the dispersion characteristics are not measured one is only getting part of the picture, not the complete picture.

 

[herbu]

One cannot accurately measure speaker response in a poor acoustically setup room. The best you can hope for is an approximation of the speaker response but that is far from accurate.

Seems to me it is a matter of degrees. The test room can be awful, poor, pretty bad, ok, pretty good, etc. So if a competent reviewer uses an "OK" room, can his measurements be sufficient for the consumer?

Somehow I think there is a point at which a room, and thus the measurements, can be good enough that criticism becomes academic. I'm guessing Dennis doesn't have a perfect anechoic chamber in his house, yet I'm thrilled with his speakers. Fair?

 

[Dennis Murphy]

Seems to me it is a matter of degrees. The test room can be awful, poor, pretty bad, ok, pretty good, etc. So if a competent reviewer uses an "OK" room, can his measurements be sufficient for the consumer?

Somehow I think there is a point at which a room, and thus the measurements, can be good enough that criticism becomes academic. I'm guessing Dennis doesn't have a perfect anechoic chamber in his house, yet I'm thrilled with his speakers. Fair?

I think a couple of issues are getting mixed up here. First, you don't need an anechoic chamber to get reliable 1-meter measurements down to around 200 Hz using good software and hardware. Second, an anechoic chamber won't provide more off-axis information than my, uh, slightly less than perfect measuring room. In either case, you have to take off-axis measurements as well. What the anechoic chamber provides is more extended measurements of the speaker into the bass (but it's the speaker response--not the room response), and you can measure further back. The latter is less important, since any decent design software can predict response at greater listening distances once it has the driver locations and sizes, phase, offsets, and the distance the initial measurement was taken at. But none of this goes to the relative importance of off-axis response. My experience has been that it isn't very important once you get past 30 or so degrees off axis. I certainly don't think wave guides are necessary if other precautions are taken, and those guides can color the sound.

 

[3db]

I think a couple of issues are getting mixed up here. First, you don't need an anechoic chamber to get reliable 1-meter measurements down to around 200 Hz using good software and hardware. Second, an anechoic chamber won't provide more off-axis information than my, uh, slightly less than perfect measuring room. In either case, you have to take off-axis measurements as well.

What about reflected energy coming from secondary points? Won't that mess up the measurements?

 

[Swerd]

What about reflected energy coming from secondary points? Won't that mess up the measurements?

No. If the test mike is close to the speaker (1 meter away), you can adjust the time frame during which the measurement takes place (the so-called "time gate"), so that reflected sound arrives at the mike after the gate is closed.

 

[gene]

I think a couple of issues are getting mixed up here. First, you don't need an anechoic chamber to get reliable 1-meter measurements down to around 200 Hz using good software and hardware. Second, an anechoic chamber won't provide more off-axis information than my, uh, slightly less than perfect measuring room. In either case, you have to take off-axis measurements as well. What the anechoic chamber provides is more extended measurements of the speaker into the bass (but it's the speaker response--not the room response), and you can measure further back. The latter is less important, since any decent design software can predict response at greater listening distances once it has the driver locations and sizes, phase, offsets, and the distance the initial measurement was taken at. But none of this goes to the relative importance of off-axis response. My experience has been that it isn't very important once you get past 30 or so degrees off axis. I certainly don't think wave guides are necessary if other precautions are taken, and those guides can color the sound.

Well said. The 'necessity' of Anechoic chambers is a bit overplayed when it comes to speaker measurements and designs. They are nice to have and make the measurement process easier and faster. But it's ignorant to think one cannot accurately design or test a speaker without one.

 

[Dennis Murphy]

No. If the test mike is close to the speaker (1 meter away), you can adjust the time frame during which the measurement takes place (the so-called "time gate"), so that reflected sound arrives at the mike after the gate is closed.

Right--that's why these measurements are often referred to as "quasi-anechoic." They approximate what you would get in a true anechoic chamber, minus some bass information. My software operates in anechoic mode down to around 250 Hz, where it transitions to a room mode showing the effects of room augmentations and cancellations, and also floor bounce cancellation. That can be very useful in speaker design even though rooms obviously vary in their impact on speaker bass response. My room is fairly typical, and always shows a peak in bass response around 70 Hz. The greater the bass capability of the woofer, the higher the peak. I can generally judge where to set the midrange and treble response in relation to that peak, something you really can't do with spliced near-field measurements of the woofer, or measurements in an anechoic chamber for that matter. It's not super scientific, but it seems to work for me, and I know one other popular speaker designer who does the same thing.

 

[3db]

Well said. The 'necessity' of Anechoic chambers is a bit overplayed when it comes to speaker measurements and designs. They are nice to have and make the measurement process easier and faster. But it's ignorant to think one cannot accurately design or test a speaker without one.

I guess thats why we are hear to learn

 

[DukeL]

...there are a lot of products out there to treat room acoustic treatment whose job is to treat reflected sound. Those same reflections exist because of driver dispersion.

At listening distances greater than five or six feet, more sound power is delivered to the listener's ears by the reflections than by the direct sound, for most speakers in most rooms. I believe the audible effects of this reflected energy are significant (which is why there's a room treatment industry, as you pointed out), so I agree with your concern with what's happening off-axis. Toole found that not only the direct sound matters, but also the first reflections, power response (sum of all reflections), and directivity index (how directional the speaker is in general).

 

[Defcon]

The solution to this needs to come from the manufacturers, and Floyd/Olive have said as much. Speaker companies need to be a lot more transparent and publish FRs and other statistics which are measured in a standardized way. Harmon does this and I admire them for it very much, they are also one of the only companies to use proper testing procedures and DBTs to evaluate speakers.

e.g. some subwoofer companies publish CEA specs which let consumers compare the performance. For speakers, there's really no way for a consumer to make a decision except for flowery marketing buzzwords on the company's site and opinions of other users.

Imagine if other components were sold this way - cars would have no mpg figures, cpu's wouldn't quote their speed etc.