Loudspeaker Measurements Explained

Stereoeditor · Mar 27, 2011

If anyone is going to SSI in Montreal or Axpona in Atlanta and wants to know more
about how I measure loudspeakers for Stereophile and what those measurements
mean, I will be giving presentations on this subject at both shows.

At SSI, my presentation will be on Sunday April 3 at 2pm. The Show takes place at the
Hilton Bonaventure in downtown Montreal.

At Axpona, I will be giving the presentation on Saturday April 16 and Sunday April 17,
at 3pm on both days. The Show takes place at the Sheraton Atlanta Downtown.

John Atkinson
Editor, Stereophile

c1ferrari · Mar 27, 2011

Excellent Opportunity

and very exciting, John! Any consideration to offering the talks at either "T.H.E. Show Newport Beach" and/or RMAF, this year?

Best regards,

Sam

Stereoeditor · Mar 27, 2011

c1ferrari said:
and very exciting, John! Any consideration to offering the talks at either "T.H.E. Show Newport Beach" and/or RMAF, this year?

Rocky Mountain for sure, but the Newport Beach Show is the same week as my youngest daughter's high school graduation.

John Atkinson
Editor, Stereophile

caesar · Mar 27, 2011

I am really not a dumb guy, but looking at the measurement section of the magazine or your website is kind of like looking at the Mesopotamian or Greek exhibits at the Museum of Art. http://www.metmuseum.org/toah/hd/wrtg/hd_wrtg.htm#slideshow1

I am not sure if you guys have meant for this to come about, but it seems only a few "elites" know how to read them and to correlate to what is heard. Any chance you guys can tape it and post it on the web?

c1ferrari · Mar 27, 2011

Stereoeditor said:
Rocky Mountain for sure, but the Newport Beach Show is the same week as my youngest daughter's high school graduation.

John Atkinson
Editor, Stereophile

Wonderful, John, on the occasion of your daughter's graduation! I'll look for you at Rocky Mountain, then

Steve Williams · Mar 27, 2011

when is T.H.E. Show in Newport and at which hotel

ack · Mar 27, 2011

Stereoeditor said:
If anyone is going to SSI in Montreal or Axpona in Atlanta and wants to know more
about how I measure loudspeakers for Stereophile and what those measurements
mean, I will be giving presentations on this subject at both shows.

At SSI, my presentation will be on Sunday April 3 at 2pm. The Show takes place at the
Hilton Bonaventure in downtown Montreal.

At Axpona, I will be giving the presentation on Saturday April 16 and Sunday April 17,
at 3pm on both days. The Show takes place at the Sheraton Atlanta Downtown.

John Atkinson
Editor, Stereophile

Great subject! I hope you post your presentation here also, and cover the controversial subject of which amplifier technology is best for such measurements - you know, Mr. Karsten is a bit bitter on a'gon about your insistence on using SS for these measurements.

c1ferrari · Mar 27, 2011

Steve Williams said:
when is T.H.E. Show in Newport and at which hotel

Hi Steve,

The particulars:

T.H.E. Show Newport Beach will take place across from the John Wayne/Orange County Airport at the Hilton Hotel, June 3rd through the 5th, this year.

Best,
Sam

NorthStar · Mar 28, 2011

Yes good stuff, with speaker's waterfall plots. Is that how you descibed those?

Phase versus Impedance is also quite revealing.

EDIT: Sorry John for my prior sense of humor.

Stereoeditor · Mar 28, 2011

ack said:
Great subject! I hope you post your presentation here also...

It is an updated version of the articles on speaker measurements I published in Stereophile at the end of the 1990s:
http://www.stereophile.com/features/99/index.html
http://www.stereophile.com/features/99/index.html
http://www.stereophile.com/features/103/index.html

and cover the controversial subject of which amplifier technology is best for such measurements - you know, Mr. Karsten is a bit bitter on a'gon about your insistence on using SS for these measurements.

Ralph Karsten tends to get a bit bitter about many things

Seriously, to get repeatable speaker measurements, you need to use an amplifier with a very low output impedance, which means solid-state as far as I am concerned. If you use a tube amplifier, you get arbitary changes in response due to the interaction between the output impedance of the amplifier and the manner in which the speaker's impedance changes with frequency. If you do wish to use a tube amp with a speaker that has been reviewed and measured in Stereophile, it is a simple matter to examine how the response will be changed by that interaction.

John Atkinson
Editor, Stereophile

mep · Mar 28, 2011

John-I appreciate your posts here on WBF because I do value your experience and judgement. You just touched on something again in your above post which you have talked about numerous times before, and that is how the output impedance of tube amps interacts with speakers to cause changes in the speaker's frequency response.

So here is a question for you: If we say we prize accuracy in our stereo systems, are we deluding ourselves if we use tube amps? We know that tube amps aren't capable of the bottom end control that SS amps have due to a number of reasons including poor dampening. So in addition to less than stellar bass response with a tube amp, are tube amps also acting as a tone control on your speakers due to varying the response (which I assume doesn't happen with a SS amp)? And this is coming from someone who owns a Jadis Defy 7 MKII and is undergoing a *crisis* created by sticking in an old Phase Linear Series 2 amp into my system and hearing things that makes me question my belief systems.

Stereoeditor · Mar 28, 2011

mep said:
I appreciate your posts here on WBF because I do value your experience and judgement.

Thank you.

If we say we prize accuracy in our stereo systems, are we deluding ourselves if we use tube amps?

There's no easy answer other than "it depends." The accuracy of any particular speaker and amplifier need to be considered as a system. For example, some speakers will have a bass alignment that benefits for a tube amp; others will sound too "lumpy" and undercontrolled.

John Atkinson
Editor, Stereophile

fas42 · Mar 28, 2011

mep said:
If we say we prize accuracy in our stereo systems, are we deluding ourselves if we use tube amps? We know that tube amps aren't capable of the bottom end control that SS amps have due to a number of reasons including poor dampening. So in addition to less than stellar bass response with a tube amp, are tube amps also acting as a tone control on your speakers due to varying the response

I would just repeat a comment that I have made before that the better the system the less relevant the frequency response accuracy is to the listening experience. So, a well performing tube amp, irrespective of its output impedance, can do the job of reproducing enjoyable sound as well as SS, provided its behaviour characteristics are not disturbed by a speaker to the point where extra non-linear distortion elements are introduced.

Frank

mep · Mar 28, 2011

Stereoeditor said:
Thank you.

There's no easy answer other than "it depends." The accuracy of any particular speaker and amplifier need to be considered as a system. For example, some speakers will have a bass alignment that benefits for a tube amp; others will sound too "lumpy" and undercontrolled.

John Atkinson
Editor, Stereophile

John-Here's the funny thing. My speakers are the Def Tech BP7000SC speakers. They have their own built in 14" woofers with an 1800 watt amp. However, the amp for the sub gets its connection through the binding posts for the speaker. On the surface, you wouldn't think that the amp powering the speakers could affect the bass from a powered woofer, but it does. There is no doubt the bass is stronger, deeper, and tighter when a SS amp powers the speakers and not my Jadis.

Mark Seaton · Mar 28, 2011

mep said:
John-Here's the funny thing. My speakers are the Def Tech BP7000SC speakers. They have their own built in 14" woofers with an 1800 watt amp. However, the amp for the sub gets its connection through the binding posts for the speaker. On the surface, you would think that the amp powering the speakers could affect the bass from a powered woofer, but it does. There is no doubt the bass is stronger, deeper, and tighter when a SS amp powers the speakers and not my Jadis.

...and not surprising at all, as the differences in the amplifiers response/interaction for the passive section of the speaker will affect the relative level of all the harmonics of any bass instrument, and should be expected to be audible. I've been rather surprised on a couple occasions now when I've measured the acoustic output of a "hifi" speaker when nothing was changed but the amplifier (solid state amps at that!). Of course many times this points directly back to choices made by the speaker / crossover designer making for some wild loads for the amplifier to drive.

mep · Mar 28, 2011

Mark-I made a correction to the post you replied to. I meant to say that you wouldn't think that the amp powering the speakers could affect the bass from a powered woofer. There are four 6 1/2" drivers in each BP7000SC and I don't know how far they go down to before they are crossed over to the sub. My guess is that they are run full range because the subs appear to be crossed over very low.

ack · Mar 29, 2011

Stereoeditor said:
Seriously, to get repeatable speaker measurements, you need to use an amplifier with a very low output impedance, which means solid-state as far as I am concerned. If you use a tube amplifier, you get arbitary changes in response due to the interaction between the output impedance of the amplifier and the manner in which the speaker's impedance changes with frequency. If you do wish to use a tube amp with a speaker that has been reviewed and measured in Stereophile, it is a simple matter to examine how the response will be changed by that interaction.

John Atkinson
Editor, Stereophile

Well, this is what makes the whole thing controversial, and to paraphrase Mr. Karsten on a recent a'gon thread on Wilson speakers, some speakers are designed - he claims - to be used with tubes, therefore said interaction is part of the design (the thread is on tweeter harshness with Wilsons and some SS). Specific (I believe) to the Sophias, the tweeter fluctuation you measured isn't going to be as pronounced with tubes - this is from memory reading that thread about 2-3 weeks ago, so apologies if I have twisted some claims.

But in the end, Mr. Karsten does have a point in at least indirectly raising the question - isn't it all about system matching?

Kal Rubinson · Mar 29, 2011

ack said:
But in the end, Mr. Karsten does have a point in at least indirectly raising the question - isn't it all about system matching?

Agreed but why design a product that requires compensation from another, especially if you do not supply that other component (as with an active speaker system)?

ack · Mar 29, 2011

Kal Rubinson said:
Agreed but why design a product that requires compensation from another, especially if you do not supply that other component (as with an active speaker system)?

Why indeed, and I wouldn't be able to answer accurately. But this practice won't stop, so perhaps the indirect take-away from this is, why not test with both technologies (which in turn implies testing with various tube designs)? Or perhaps consult with the manufacturer as to the more desired amplifier technology to test with? To take this further, why not also test with class-D or -T et al as well, especially when 'D' has been shown to be sensitive to speaker impedance? And even further - what's the real purpose of speaker measurements, and wouldn't be nice for them to show some good matching amplifiers for the subject?

Kal Rubinson · Mar 29, 2011

ack said:
Why indeed, and I wouldn't be able to answer accurately. But this practice won't stop, so perhaps the indirect take-away from this is, why not test with both technologies (which in turn implies testing with various tube designs)? Or perhaps consult with the manufacturer as to the more desired amplifier technology to test with? To take this further, why not also test with class-D or -T et al as well, especially when 'D' has been shown to be sensitive to speaker impedance? And even further - what's the real purpose of speaker measurements, and wouldn't be nice for them to show some good matching amplifiers for the subject?

Well, I cannot speak for JA but one reason for testing with an amp that is insensitive to speaker impedance is for consistency over time and for the results to be unbiased. OTOH, if the amp is "sensitive" to impedance variations, the amp itself is a variable as one would presume that the interaction would not be the same for all such amps.

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