[josh358]

Line sources also fall off as 1/R rather than 1/R^2. So the one meter measurement doesn't directly reflect the SPL at a typical listening distance, say, three meters: if a line source and an omni both have an efficiency of 86 dB at 1 meter, the line source will be louder at the listening position. (To be completely accurate, you'd have to take into account room gain as well.)

[Rclark]

 Yeah even at very low listening levels (one of the reasons I'm in love) it's a big big sound, sounds much louder than it actually is.

 

[Rclark]

Josh do planars require a different measuring technique as far as with a microphone and software, etc? Is there sort of a different way you have to go about it?

[Davey]

I think we can make a pretty good case that MMG's don't behave as line sources.  The transducers are only three feet high and the listening position is most likely in the acoustic far-field for most of the frequency range.  Thus, the SPL drops at something closer to 6db/doubling of distance vice 3db/doubling.

Anyways, we're not talking about a planar versus conventional speaker comparison here.

Cheers,

Dave.

[medium jim]

Dave:

An important clarification.

Jim

[josh358]

Josh do planars require a different measuring technique as far as with a microphone and software, etc? Is there sort of a different way you have to go about it?

Planars are extremely difficult to measure. Some would say impossible. Since the diaphragm is so large, you can't make accurate windowed measurements because of reflections from adjacent surfaces. Also, measurements made in the near field show a huge proximity effect in the bass -- you have to be back far enough to allow the waves from the back to diffract around the front. Furthermore, the amplitude response of a line source changes with distance in a not-very-intuitive way. So, you say, what if you measure them outside, or in an anechoic chamber, or as some people do, make gated measurements with the speakers suspended in an auditorium or gymnasium? There you run into the opposite problem -- line sources are dependent on adjacent surfaces for their response. They require the floor and ceiling reflections to approximate an infinite line source (actually, since the surfaces aren't completely reflective, an acoustically tapered line source, but it's still several times the physical height of the speaker). Also, the reflection of the rear wave from the front wall of the room combs with the front wave and this produces dips in the response that wouldn't be present in an anechoic or outdoor or for that matter gated measurement.

Martin Logan's solution? Measure at the listening seat. I can't think of a better one. But that has its own limitations. In practice, I think the best course is to get the best measurements you can, and evaluate them with a slightly jaundiced eye, e.g., the waterfalls aren't going to be pure, the 1 meter measurement will have elevated bass, etc. You can glean lots of useful information if you know what the handful of pitfalls are. To illustrate, look at the two dreadful-looking 3.6 on-axis frequency response curves at the bottom of the page:

http://www.stereophile.com/content/magnepan-magneplanar-mg36r-loudspeaker-measurements

Looks awful, right? Now look at the in-room 1/3 octave response of the IIIa, at the bottom of the page:

http://www.stereophile.com/content/magnepan-magneplanar-mgiiia-loudspeaker-measurements

There's are some interesting letters appended to the 3.6 review that explain why dipole bass can't be accurately measured from one meter, and incidentally explain something of the theory behind it. (Also the letter in which Grant initially proposed the idea for Maggie stands!)

[josh358]

I think we can make a pretty good case that MMG's don't behave as line sources.  The transducers are only three feet high and the listening position is most likely in the acoustic far-field for most of the frequency range.  Thus, the SPL drops at something closer to 6db/doubling of distance vice 3db/doubling.

Anyways, we're not talking about a planar versus conventional speaker comparison here.

Good point about the MMG. Because of the floor reflection, they behave more like a six foot line source, but at a 3 meter listening distance, a 2 meter line is far field below roughly 900 Hz. (Someone said that Wendell tried stacking MMG's, and said the sound improved.) Then, as the frequency drops below the spatial Nyquist frequency of the images, they should start behaving as an infinite line source, and the radiation pattern will return to 1/R. At an even lower frequency, left and right images will come into play and it will become a plane wave for mono signals, and at a frequency below that, a plane wave for left/right signals as well, and the plane waves won't fall off with distance at all. I used to use this property to use that to good effect with my 1-D's -- if I sat at the same distance from the rear wall as they were from the front, it would cancel all bass modes below that frequency, in effect acting as a single bass array. I don't think very many people are aware of that effect.

[Rclark]

Wow!  And that's why this is the best forum hands down. Josh I can use all of that, thank you 

[Chris Adams]

if I sat at the same distance from the rear wall as they were from the front, it would cancel all bass modes below that frequency, in effect acting as a single bass array. I don't think very many people are aware of that effect.

Thanks for that, Josh. I have my room set up like that because the bass sounded best. Didn't understand the reason, now I do. 

[Davey]

Well, the bass modes exist regardless of where your ears are in the room.  But I understand your point. 

This does somewhat highlight the whole fallacy of "room correction" via "correction" to the loudspeakers response.  (Bass or otherwise.)
Indeed, the whole concept is upside down.....in my opinion.
It's one of those silly audio buzz-phrases that's ubiquitous now.  So, I don't think we're going to change it. 

Anyways, I did some testing on this a few years back and found that with MMG's the SPL drops off at about a 6db/doubling of distance rate very similar to a "conventional" speaker.

Cheers,

Dave.

[josh358]

Thanks for that, Josh. I have my room set up like that because the bass sounded best. Didn't understand the reason, now I do. 

I didn't understand it fully when I first did it either. I could see that the backwave would reflect off the front wall, then tend to cancel the reflection of the front wave off the rear wall at the listener's ears, which is why I tried it. But I didn't realize that below the spatial Nyquist frequency the room reflections would gave you a plane wave (or an approximation, actually, since the surfaces aren't perfectly reflective), making the cancellation complete and nulling all the resonances until I read about the German double bass array setup.

[josh358]

Well, the bass modes exist regardless of where your ears are in the room.  But I understand your point. 

This does somewhat highlight the whole fallacy of "room correction" via "correction" to the loudspeakers response.  (Bass or otherwise.)
Indeed, the whole concept is upside down.....in my opinion.
It's one of those silly audio buzz-phrases that's ubiquitous now.  So, I don't think we're going to change it. 

Anyways, I did some testing on this a few years back and found that with MMG's the SPL drops off at about a 6db/doubling of distance rate very similar to a "conventional" speaker.

I think the reason they did that was because some DSP-based equalizers are intended to compensate for the shortcomings of the loudspeakers, e.g., DEQX (except below the Schroeder frequency where it corrects both loudspeakers and room), while others are intended to compensate for the transfer characteristic of the room (most other units) -- although of course the latter will also try to correct some loudspeaker flaws.

Rather confusing, I agree.

Interesting about the MMG's. I honestly never thought about it, just assumed the sound fell off as 1/R at normal listening distances.

[Davey]

Yes, the DEQX is sort of a two-step process where you initially place the microphone near your speaker to generate a "speaker correction" profile and then pull the microphone back to the listening spot to create a "room correction" profile.  (I apologize if I don't have the exact wording/terminology correct.)

Anyways, who's to say what the original speaker designers objective was in creating the system response.  Maybe he wouldn't appreciate a gadget like the DEQX "compensating for the shortcomings" of his design?

Much of the fiddling I see audiophiles performing nowadays with gadgets to correct this or correct that is to achieve a flat frequency response at the listening position....at the expense of worse response elsewhere in the room.  Is that really a valid "correction?"    Is "flat" frequency response the holy grail?  Is Davey off his rocker? 

What would a "correction" curve for a set of Magnestands look like? 

Cheers,

Dave.

[medium jim]

Davey:

There was a guy on the other place that was extolling the virtues of the DEQX with Magnepan's.  I have to agree with you.  The biggest complaint about Digital when it first surfaced was that it was too sterile and artificial.

Most of my gear is vintage, albeit, some might fine vintage, but I know that it is not perfect, but I would have it over any of the new stuff as my ears and brain have already blueprinted it.

A good analogy would be Carbon Graphite Acoustic Guitars that are perfectly intonated, yet they don't win many shoot outs as they're just too right and without character.  They do record great and some traveling musicians love them as they're impervious to weather/climate changes which means no setting them up at each new venue.   Funny thing is that most who use them on the road, re-eq them to sound like their other guitars, go figure.

I bought Magnepan's because I loved, not liked, they way they sound, not what they could sound like!  Moreover, I surely didn't buy them for how they looked or their size, although they do grow on you.

Jim

[Rclark]

Keeping it stock! And old! Preach on brother man, here comes the Asylum! 

[medium jim]

Rclark:

Absolutley, not to start a debate or negate your choices...for me I got one of the best speakers made by Magnepan and even after replacing the ribbons and doing the repairs myself, am out around $800.00 and couldn't be happier. 

My CDP is a highly modified Marantz 38 with the only things original on it are the case and transport.  My McIntosh MX110 has some improvements to shorten the stage. My Marantz Model 9's have NOS Mullard EL34's (XF2's) and two different sets of Line Stage Tubes, a a quad of 1960's Amperex Gold Pin 6922's and a Quad of Telefunken 7308's.

Different strokes for different folks.  As Davey said, MMG's are ripe canidates for tweaking.   

Jim

[Rclark]

May I ask whereabouts you live? I've never heard a tubed out system like that. I bet warm is the operative word.

[medium jim]

So Cal.  Another misconception that tubes are always going to be warm. I find my system to be nice and natural, very little color. The reason I like tubes is the ability to roll tubes and the beautiful holographic soundstage a good pair of monoblocks produce.

The music just seems to have more weight and depth with tubes.  However, great leaps and advances have been made with SS in the last decade. 

Sorry that I strayed off subject.

Jim

[Rclark]

Eh this place is pretty low key, it's not like we're in a manufacturer thread talking about ham sandwhiches in the middle of a review. It's all good.

My thread, feel free to ramble 

[josh358]

Yes, the DEQX is sort of a two-step process where you initially place the microphone near your speaker to generate a "speaker correction" profile and then pull the microphone back to the listening spot to create a "room correction" profile.  (I apologize if I don't have the exact wording/terminology correct.)

Anyways, who's to say what the original speaker designers objective was in creating the system response.  Maybe he wouldn't appreciate a gadget like the DEQX "compensating for the shortcomings" of his design?

Much of the fiddling I see audiophiles performing nowadays with gadgets to correct this or correct that is to achieve a flat frequency response at the listening position....at the expense of worse response elsewhere in the room.  Is that really a valid "correction?"    Is "flat" frequency response the holy grail?  Is Davey off his rocker? 

What would a "correction" curve for a set of Magnestands look like? 

I've wondered about that. As far as I know, DEQX measures and corrects for on-axis amplitude and phase response. But dispersion is seldom perfect, and power response is at least as important as on-axis response.

I also wonder about the bass reinforcement of close-up measurements of dipoles. The DEQX does room correction only in the low frequencies, using IIR filters rather than the FIR filters used for speaker correction. It's possible that the IIR filter would correct for an error in the FIR filter's curve, but this hardly seems optimal.

That being said, I've heard good things about DEQX and Maggies. And bad things about TacT and Maggies, TacT's algorithms apparently don't like dipole radiators.