Magnepan LRS Speaker Review

[KaiserSoze]

As far as I understand the argument, the reflections from the back wall are an integral part of the transmission chain, and hence dipoles should be measured in a room and in a position that generate the right reflections. But in my humble opinion (as owner of a room with windows, and furniture that severely restrict speaker positioning) this means these speakers will only sound good by accident, or when the room has been designed to specifications (which don’t seem to exist).

I think that all of this is correct, however it misses the point that I wanted to make. Unless, perhaps, the reflections from the back wall are supposed to somehow resolve the inconsistent tonality in the forward radiation space. I am skeptical that this would happen, and I don't think anyone has provided a persuasive argument that it would happen. This is why I say that if a dipole speaker is mounted on a pole outdoors and measured, the tonality in the forward radiation space, in the speaker's horizontal place, should be as uniform as it is generally expected to be for a conventional forward-radiating speaker. I can't think of any valid reason why this isn't a fair and reasonable expectation.

 

[KaiserSoze]

The mathematics is not limited to describing a point source. It only uses the spherical coordinate system (in this case). You can take a look at this paper to see an example of the application of this method to characterize the sound radiation pattern from a vibrating rectangular plate and the comparison to the theoretical prediction.
https://www.xlrtechs.com/dbkeele.com/PDF/Keele (2006-10 AES Preprint) - Full Sphere Measurements Using HELS Method.pdf

That's what I tried to say!! Except, I didn't say it nearly as well, and it took me 10x as many words to say it less well.

 

[Robbo99999]

My point was different. The conversation you barged into was whether there was a low frequency roll-off inherent to Maggies or not, smooth or not wasn't the point being made. I posted two different examples of one without a roll-off until about 100hz so if this LRS really rolled off at 300hz as interpreted (incorrectly in my opinion for reasons I have explained many times), then it would be a worse speaker than the 25 year old SMGa. I also posted another Maggie that did have an early roll-off and that is the smallest one.

The scale wasn't relevant to the above but since you insinuated, I posted the second scaling. It has nothing to do with the point you are making and I am not interested in that discussion.

I know, but I wanted to make that side point, which I made.

 

[mac]

If Linkwitz' Orion or LX521 were measured by Amir using the same setup he used for this small Maggie, the Linkwitz' speaker would in all likelihood measure exceptionally well without the difficulties that Amir encountered in taking measurements of this speaker.

I'm going to partially disagree with you on this, speaking as someone who owns LX521's and has used mainly dipoles and planar speakers for the past 20 years. I think they'd measure much better than this low-end Magnepan did but I wouldn't be surprised if a Revel or cheap JBL measured as well or better. OTOH, I think that if someone were to listen to a pair of properly engineered dipoles properly setup in a room they'd hear things not conveyed by a positive Klippel NFS analysis. No science to back up my hunch as I don't have a Klippel NFS system setup in my garage.

Some reading to backup my hunch.

 

[TheGhostOfEugeneDebs]

Actually you will get accurate and consistent results of wheel power from a specific dyno, as that is what a wheel dyno measures, power to the ground. Different wheel dynos measure and calculate power differently resulting in variances depending on which you use. You have to extrapolate to estimate engine horsepower, as different drivetrains have different losses. Usually the extrapolation is done by comparing the wheel dyno numbers of a stock vehicle to the factory power numbers and using a power factor. It is very inexact for calculating actual engine horsepower, but a great tool for measuring modification and their improvements (or detriments).

This is getting off topic, but I generally ignore anyone in the scene that tries to pass off estimated engine power like it's some kind of dick measuring contest. Who cares what your engine makes if you've got 30% parasitic loss through your fancy AWD setup anyway?

But... Uh... Yeah, so magnepans. How about that?

 

[Joppe Peelen]

The mathematics is not limited to describing a point source. It only uses the spherical coordinate system (in this case). You can take a look at this paper to see an example of the application of this method to characterize the sound radiation pattern from a vibrating rectangular plate and the comparison to the theoretical prediction.
https://www.xlrtechs.com/dbkeele.com/PDF/Keele (2006-10 AES Preprint) - Full Sphere Measurements Using HELS Method.pdf

Thanks !
Woei ! it does have a different formula ! by the looks of it. Thats really nice. then everything i just wrote might be bullocks if that one was used. and only applied for a normal measurement. might dive a bit more into that paper ! thanks !

 

[LTig]

Thats a nice write up !!! read it a few times ! although i dont agree on maggies being bad.

I did not want to say the Maggies are bad per se - I had them for 13 years and liked them for what they did right. It was just that the first listen of the O300D made totally clear what they did not right.

Gaithain'? never heard of them since called monitors i thought some , studio monitors... but they are not. they are coaxial, i do agree very pleasing , fullranges or coax every now and then, they can sound really nice. never heard this pair though

https://www.me-geithain.de/en/

- Distance tweeter woofer. is 7 mm, and crossover is half that of any monitor, should not be any problem. the fact the tweeter is rather wide compared to a dome might be a problem ! and beams

You may be right, but the width of the woofer also plays a role - does it not?

- The fact it does not look like a line source, and maybe you meant that is it should go to the ceiling. and it does not.

To have the effect of a line source in a room the driver has to reach to the floor to get the effect of a mirrored source. At least this is how I understand @Floyd Toole. Going much higher than the LRS also helps.

- Acoustic shortcut is just how open baffles work just like the dispersion being almost 0 @ 90 degrees. its the same problem.. although i dont see them as a problem. an open baffle might not PUMP as hard as a closed speaker, allot of people like them, and weirdly enough this is how many of the beloved drum solos are recorded with the most wanted mic... neuman U87 , mostly used as a dipole..

I'm not sure a dipole mic suffers from acoustic shortcut since it doesn't produce sound.

cool you mentioned the hump , also to make use of the back wave, you would have to need more then 3.5 meter behind the speaker hihi thats allot for a small speaker.

When you calculated the 3.5m did you take in account that the back wave is 180 degree out of phase? Which frequency did you choose? Honestly I did not calculate it. I had them about 1m from the front wall (same as the O300D), and audiophiles I know maybe 1,5 to 2m.

 

[KaiserSoze]

Most monitors cross at 3 khz.... a maggie does that much lower . while even being closer to the woofer then any dome? not ,many domes can cross at 1200hz-1400hz so it should be better then most domes crossed over. so if you got a 8 inch woofer.. thats like 20.4 cm diameter, most of the magnepans are around 24 cm wide (of witch driven area is even smaller) and of witch 3 to 4 cm is the tweeter (yes the tweeter is big compares to a dome thats why the top end still beams) @ 7khz , and above even worse. but the crossover region is no problem, its much better then most speakers.

I have a very difficult time following what you are saying, but I believe I understand you well enough here to be able to say that you misunderstand, and you do so in a way that strikes me as peculiar. You seem to be comparing the crossover point used in this speaker, where the "woofer" and the "tweeter" are located side-by-side, with the crossover points commonly used in monitors, between a midrange and tweeter that are arranged in a vertical stack. Why would you think this would be a useful comparison? The general presumption, which I am confidant is valid, is that the angular spread of the "sweet spot" needs to be several times greater horizontally than vertically. The typical crossover point between midrange and tweeter is even higher than you suggest. When there is a true midrange, the typical crossover point is probably around 3 kHz, with wavelength 11 or 12 cm, which is typically between 2 and 3 times greater than the separation distance between the centers of the midrange and tweeter. As such, nulls that are due to interference (phase cancellation) typically occur 20 to 50 degrees above the horizontal and 20 to 50 degrees below the horizontal, such that the angular "thickness" of the main forward lobe, measured on the vertical polar plane, is typically 40 to 100 degrees. This is the angular thickness or width of the "sweet spot", in the vertical direction. The speaker that was measured here, the small Maggie, has the woofer and tweeter located side-by-side. I haven't bothered to obtain measurements of the width of the woofer portion and the width of the tweeter portion, but it isn't important because Amir clearly identified a major null in the forward radiation pattern, a sort of vertical stripe from top to bottom, and not especially skinny in either spatial width (horizontal width) or frequency width. And this null was located only about 25 degrees off-center. Thus, a listener at this location, but within the speaker's horizontal plane, would hear the snare very differently from a listener located directly at the center of the speaker.

This is another example where you seem to be trying to say something by insinuation. Here, you seem to be saying that the angular spread of the main lobe should be just as great vertically as horizontally. Since this is what you are really saying, why not just say this in a plain, direct manner?

At the very end you did say something definitive. You wrote: "but the crossover region is no problem, its much better then most speakers". No it is not. It is much worse than it is with most speakers, the reason being simply that with most speakers the individual drivers are arranged such that the nulls that are inherently difficult to avoid, which occur due to interference between the individual drivers, restrict the angular width of the main lobe in the vertical direction, whereas with this speaker the individual drivers are arranged such that the nulls restrict the angular width of the main lobe in the horizontal direction. With this speaker, a listener located in the same horizontal plane with the speaker and moving from center toward the direction where this null occurs (I'm not sure whether it is toward the tweeter side or the woofer side), from center to one side, will pass out of one main lobe, across the null and then into a secondary main lobe. The null has a specific spreading both spatially and in frequency.

And by the way, this is all stuff that most all speaker designers have understood since about when they first began contemplating the design of loudspeakers.

 

[Joppe Peelen]

To be direct you are not writing in a manner sufficiently precise for other people to comment on what you say. In particular, "...its not a sphere... a sphere indicated a point source and extrapolates from there. a big planar speaker is far from a point source...."

What exactly do you mean when you say, "...a sphere indicated a point source ..."? Implicitly you are saying that if the radiation source is not a point source that it is not valid to represent the radiation pattern using magnitude values at points on the surface of a sphere. This is what you seem to be wanting to say, but you didn't give any reason why this would not be valid. I don't know why this wouldn't be valid irrespective of whether the radiation source is or isn't a point source. Why would it be necessary for the distance from the surface of the sphere to the radiation source to be a singular distance in order for this to be valid? The explanation for this seems to be missing from what you are saying. To me at least, but I'm not certain I understand what you're saying. If I understand you, this is essentially what you are arguing, that the distance from the surface of the sphere to the radiation source would need to be singular before it would be valid to capture/represent the radiation pattern using magnitude at points on a spherical surface. This seems to be essentially what you are saying, but I did not see anything in the way of and explanation for this perspective.

If the radiation field/pattern is represented on the surface of a sphere with a given radius, and that sphere is replaced with another sphere with radius twice as great, the energy density will change as the change in surface area. The area of a sphere scales as the square of the radius, thus if the radius doubles, the area will increase by a factor or four, which means the energy density at the surface will decreased by a factor of four. As Amir explained (not that I understood all of it ...) the measurements are taken at points on the surface of a sphere, at a particular distance that is the radius of that sphere, and because the measurements are taken at points on the surface of a sphere, it is possible to extrapolate to other spherical surfaces with different radii. Where it gets complicated is with extrapolating to spheres that are smaller than the sphere where the measurements are taken. It is over my head to understand how this is possibly done if the source isn't a point source, but as Amir pointed out, there are not any speakers that are true point sources. The great majority of the speakers he measures are two-way speakers with the tweeter mounted in a waveguide and with a port on the front or rear or a passive radiator on the rear. These are not point sources. And if the physical size of the non-point-source radiator were ordinarily a problem for taking the measurements, he would have had problems with some other speakers he has measured.

in short the thing you describe can still be a point source no matter how many woofers and or bass ports it depends on what frequency they produce. everything low can be still be further away from each other , but i must say i read some more in the paper and i understand only 1/4th of it (or less). so for all i know they found a solution to do it correct. and assumed according to methods normally used... you cant do it like this. so i might be wrong. still everything i said i think is true. be it i might utterly incorrect if the klippel works the way people say it work. and i need to do some home work on the measurement system used in this case.

 

[Sancus]

Surely this kind of dispersion leads to a very different in room response compared to a conventional box speaker. IMV this is not a flaw but a characteristic feature. No side reflections should lead to less room influence, OTOH throwing the same sound at 180 degree phase shift leads to more room influence above Schröder.

I mean we know what the reflection curves are, they're in the review, and they are indeed different from a normal box speaker. What that means is anyone's guess, since floor and ceiling reflections aren't too well-researched.

I don't know why people keep saying Magnepans have no side wall reflections. They have a narrow band with no output at 70-110 degrees, sure, but they still have plenty output at 80 and 110 degrees, which is going to reflect off the side walls at some distance depending on how you have them toed.

 

[Joppe Peelen]

I did not want to say the Maggies are bad per se - I had them for 13 years and liked them for what they did right. It was just that the first listen of the O300D made totally clear what they did not right.

https://www.me-geithain.de/en/

You may be right, but the width of the woofer also plays a role - does it not?

To have the effect of a line source in a room the driver has to reach to the floor to get the effect of a mirrored source. At least this is how I understand @Floyd Toole. Going much higher than the LRS also helps.

I'm not sure a dipole mic suffers from acoustic shortcut since it doesn't produce sound.

When you calculated the 3.5m did you take in account that the back wave is 180 degree out of phase? Which frequency did you choose? Honestly I did not calculate it. I had them about 1m from the front wall (same as the O300D), and audiophiles I know maybe 1,5 to 2m.

yeah woofer is around 20 cm , so a large normal woofer would almost be the same it surely does play a role. they might be playing longer then normal and that might be the trouble? could well be

the mic does the same yeah. it also has cancellation for massive low end you would chose an omni directional that is pressure sensitive, kind of like closed speakers pressurize the room. thats the fun thing about mics they are very similar/interesting.

the 3.5meter was just a random frequency of 50 hz and then half wave from speaker to wall and halve wave from wall to speaker to add up.

about the line source, i understand also only half of it, but what i noticed not true line sources have some really annoying peaks and nulls. as posted above in some pictures. its amazing small panels like small esl's on a woofer exist when i look at it. made a few myself. but lately not liking the way it works.


by the way nice looking speakers !!!

 

[Joppe Peelen]

I mean we know what the reflection curves are, they're in the review, and they are indeed different from a normal box speaker. What that means is anyone's guess, since floor and ceiling reflections aren't too well-researched.

I don't know why people keep saying Magnepans have no side wall reflections. They have a narrow band with no output at 70-110 degrees, sure, but they still have plenty output at 80 and 110 degrees, which is going to reflect off the side walls at some distance depending on how you have them toed.

well at least almost no low end witch usually is the biggest problem in a room i believe ? surely is in mine

 

[Blumlein 88]

For you guys wondering about Klippel measuring a dipole or box, a long tall speaker or a regular one. It DOES NOT MATTER.

The Klippel could be used to measure the sound output of an HVAC air handler/blower box. It would present you with all the info near and far field of what is being measured.

 

[KaiserSoze]

Other than stated by several posters I do think that @amirm has done enough measurements to describe the behaviour of the LRS in anechoic conditions. Even enough to somehow find the cause of the 'magic' sound. We just don't have enough knowledge (or done enough work) yet how to correctly interpret the results into how the LRS sounds in a room where it is optimal positioned. Clearly neither the Klippel's on axis FR nor @John Atkinson 's FR show directly what one would expect to hear in an optimal room, especially below Schröder.

All good, but the expectation, that the problems that Amir identified will simply vanish when the MiniMaggie is placed in a room, has thus far not been justified by any argument that anyone has given. The room will affect the sound, and for many people this sound will be more pleasing. But no matter how much more pleasing it may be, the problems that Amir identified will not be eliminated, avoided, or rendered moot. These are the problems you identified, and I want to comment on a couple of them.

Where the LRS is different compared to a conventional box speaker:
...

• Tweeter and woofer side by side with too large distance.

This is a major flaw and leads to a bad horizontal dispersion. It could be improved by using a DSP crossover with very steep flanks (48 dB/octave) to minimize the region where the flaw is audible.

I am so glad that you did not omit this. Analogous to comments that Mr. Toole has made concerning what can't be corrected using EQ, this problem can be corrected across the frequency domain for a specific location, but not for all locations. You can fix it so that somewhere close to the midpoint of the null, where the cancellation between the "woofer" and "tweeter" is near its greatest, the response will nevertheless be flat. But the only way to do this is to apply a whole lot of boost at 1 kHz, which will affect the sound at all other locations. At any location that isn't close to where the null is located, you will hear an unnatural emphasis at 1 kHz. As such, it would seem reasonable to say that it cannot be fixed using EQ.

• Large moving area means for the same SPL excursion of the foil is lower compared to a conventional box speaker.

This should lead to low distortion since distortion increases with excursion. However with magnets on one side of the foil the membrane does not move in a constant magnetic field which increases distortion - at least in the low frequencies where excursion is high. I have no clue which effect is stronger..

I don't think it is useful to try and compare the two different kinds of drivers in this way. The linearity of the foil's stiffness is also a major factor. But fortunately the distortion measurements speak for themselves, and if you only look at higher frequency, from upper midrange and up, it is surprisingly good. From lower midrange down, it isn't good but neither is it especially bad until you get below about 150 Hz. In this respect it is probably fair to compare it with a typical small bookshelf speaker with a 5" conventional woofer. The need for a subwoofer is more or less the same as it with a speaker of that type.

• Acoustic shortcut in the bass

This is a flaw, but one which cannot be circumvented. Some posters claim that placing the LRS on the floor dramaticely improves bass compared to the measurements taken off the floor. This cannot be true. Most of the bass gets lost via the short side. There will be an improvement but only a minor one. To get better bass you must place the LRS at such a distance to the front wall that the wave leaving the back of the panel reflects such at the front wall that it sums up with the wave leaving the front of the panel at a frequency where the shortcut has damped the far field SPL by 6 dB.

There is a reason why Linkwitz put so much effort into subwoofer design! By the way he left us with a ton of useful information on how to design good subwoofers. As for the effect of the reflection from the wall behind the speaker ... with conventional speakers the reflection from the wall is coherent with the direct radiation at very low frequency. As frequency increases, eventually the roundtrip distance from the baffle to the wall and back will equal 1/2 wavelength, at which point a dip will occur. With conventional speakers in a typical home setting this dip occurs somewhere in the rough vicinity of 150 Hz. But with this speaker, the effect is different. At very low frequency the reflected sound is fully out of phase with the direct sound. As frequency increases, eventually the reflected sound will be in phase with the direct sound and a peak will occur; the specific frequency depends on the round-trip distance. The distance can be varied as a way to control where this reinforcement peak occurs, but since you can only set it to one distance, it will only happen for one frequency. The attenuation due to cancellation at the sides increases with decreasing frequency, so it makes sense to place the speaker as far from that wall as you possibly can. In a typical room the lowest you could reasonably expect to locate this peak would be maybe around 200 Hz. There isn't really any way to fix the bass thing except by augmentation with subwoofers. Linkwitz to the rescue.

• Very low sensitivity (~78 dB when one ignores the unwanted hump at 250 to 900 Hz)

This is comparable to the sensitivity of most "full-range" drivers. Which suggests that you could do just as well, possibly better, by buying two or three large full-range drivers and mounting them in a vertical array on an open baffle. The treble would beam, but it is probably better for the treble to beam than to have the effect encountered with this speaker, where that null occurs in the forward radiation pattern. Anyone who didn't like the beaming treble could maybe add two or three tweeters. They could be placed in the same vertical array with the big midrange drivers, interspersed with the big midrange drivers. The result would probably be at least as good as this speaker. It would cost a lot less and would be ridiculously simple to build. And then you would be on the same path that Linkwitz took when he first started tinkering with dipole speakers.

 

[Joppe Peelen]

I have a very difficult time following what you are saying, but I believe I understand you well enough here to be able to say that you misunderstand, and you do so in a way that strikes me as peculiar. You seem to be comparing the crossover point used in this speaker, where the "woofer" and the "tweeter" are located side-by-side, with the crossover points commonly used in monitors, between a midrange and tweeter that are arranged in a vertical stack. Why would you think this would be a useful comparison? The general presumption, which I am confidant is valid, is that the angular spread of the "sweet spot" needs to be several times greater horizontally than vertically. The typical crossover point between midrange and tweeter is even higher than you suggest. When there is a true midrange, the typical crossover point is probably around 3 kHz, with wavelength 11 or 12 cm, which is typically between 2 and 3 times greater than the separation distance between the centers of the midrange and tweeter. As such, nulls that are due to interference (phase cancellation) typically occur 20 to 50 degrees above the horizontal and 20 to 50 degrees below the horizontal, such that the angular "thickness" of the main forward lobe, measured on the vertical polar plane, is typically 40 to 100 degrees. This is the angular thickness or width of the "sweet spot", in the vertical direction. The speaker that was measured here, the small Maggie, has the woofer and tweeter located side-by-side. I haven't bothered to obtain measurements of the width of the woofer portion and the width of the tweeter portion, but it isn't important because Amir clearly identified a major null in the forward radiation pattern, a sort of vertical stripe from top to bottom, and not especially skinny in either spatial width (horizontal width) or frequency width. And this null was located only about 25 degrees off-center. Thus, a listener at this location, but within the speaker's horizontal plane, would hear the snare very differently from a listener located directly at the center of the speaker.

This is another example where you seem to be trying to say something by insinuation. Here, you seem to be saying that the angular spread of the main lobe should be just as great vertically as horizontally. Since this is what you are really saying, why not just say this in a plain, direct manner?

At the very end you did say something definitive. You wrote: "but the crossover region is no problem, its much better then most speakers". Not it is not. It is much worse than it is with most speakers, the reason being simply that with most speakers the individual drivers are arranged such that the nulls that are inherently difficult to avoid, which occur due to interference between the individual drivers, restrict the angular width of the main lobe in the vertical direction, whereas with this speaker the individual drivers are arranged such that the nulls restrict the angular width of the main lobe in the horizontal direction. With this speaker, a listener located in the same horizontal plane with the speaker and moving from center toward the direction where this null occurs (I'm not sure whether it is toward the tweeter side or the woofer side), from center to one side, will pass out of one main lobe, across the null and then into a secondary main lobe. The null has a specific spreading both spatially and in frequency.

And by the way, this is all stuff that most all speaker designers have understood since about when they first began contemplating the design of loudspeakers.

"And by the way, this is all stuff that most all speaker designers have understood since about when they first began contemplating the design of loudspeakers"

And thats why they are in business for 50 years now

"I appreciate your tone of civility, which sets an example for me to follow. "

But i do think you lost that at attitude quite fast. i have a feeling you know me and i know you but i surely never had the honor to meet a Kaiser/Emperor so who are you ?

 

[KaiserSoze]

Well the thought was, its not about being open baffle or not so much. but being a line source. mseauring a needle point is much easier then measuring huge membrane that does lows and heighs. since the lows will reach the mic. and the highs wont.. so you get a weird result. you cant do it. close by.

It does not seem to me that a large speaker would be any different from a small speaker with an uneven radiation pattern, which is to say, any small speaker. Whether you are talking about a large speaker that does not behave like a point source, or a small speaker that behaves more like a point source but not completely so, what you end up with is much the same: an uneven distribution of energy over the surface of a virtual sphere. The general theme of what you have been saying is that this sort of representation of the radiation field doesn't work unless the radiation source is a point source. But the closest you have come to explaining your reason, so far as I can tell, has to do with the difference between near field and far field. You seem to be implying that in the near field this can work for point source radiation but not for larger radiators. But you haven't explained why this would be. It seems to me that it isn't fundamentally different from what it is with any real speaker with an uneven radiation pattern. I don't follow why it would be, and thus far I don't think you've done a good job of explaining why you think it would be.

 

[KaiserSoze]

Thats a nice write up !!! read it a few times ! although i dont agree on maggies being bad. ...

If i may add some of what i think.

- Distance tweeter woofer. is 7 mm, and crossover is half that of any monitor, should not be any problem. the fact the tweeter is rather wide compared to a dome might be a problem ! and beams

As I discussed in another reply to one of your other posts where you commented more at length on this, your understanding of this problem is not properly informed, in that the assumption underlying your take on the question is that there is no reason for the main lobe to be angularly thicker in the horizontal than in the vertical. There is very obviously a very good reason why the main lobe should be several times thicker horizontally than vertically. The only exception that comes to mind is where someone places a ladder at the ideal location in the room and each person chooses a rung upon which to sit while listening to music.

And as for the suggestion that the distance between the tweeter and woofer is only 7 mm, barely 1/4 inch, this tells me that you have now abandoned any pretense of sincerity. We are talking about interference between two sources emitting radiation at the same wavelength, and you are suggesting to me that instead of the distance between the centers of the two finite sources, what matters is the distance between the edges at the closest point between the two drivers.

 

[Joppe Peelen]

It does not seem to me that a large speaker would be any different from a small speaker with an uneven radiation pattern, which is to say, any small speaker. Whether you are talking about a large speaker that does not behave like a point source, or a small speaker that behaves more like a point source but not completely so, what you end up with is much the same: an uneven distribution of energy over the surface of a virtual sphere. The general theme of what you have been saying is that this sort of representation of the radiation field doesn't work unless the radiation source is a point source. But the closest you have come to explaining your reason, so far as I can tell, has to do with the difference between near field and far field. You seem to be implying that in the near field this can work for point source radiation but not for larger radiators. But you haven't explained why this would be. It seems to me that it isn't fundamentally different from what it is with any real speaker with an uneven radiation pattern. I don't follow why it would be, and thus far I don't think you've done a good job of explaining why you think it would be.

So i need to read more about the klippel method for sure since NTK posted a pdf where they also did a rectangular source(so i presume more line source like ?) ! so im not sure right now of the above quote (from me) might be faulty with this method used in the pdf. (might be , and that would be in fact great, since they are a pain to measure to begin with) but on a normal measurement i dont have to explain you, you wont capture anything decent close on a 120cm long midrange or tweeter that resembles anything the speaker would measure 1 or 2 meters away.

 

[MRC01]

...A dyno measures torque. Horsepower (or KW output) is calculated from the torque and RPM.

That's actually backwards. Power is conserved, Torque is not. By this I mean power at the engine crankshaft equals power at the dyno drum (minus frictional losses). Torque at the dyno drum is R times torque at the engine crankshaft, if the engine crankshaft spins R times as fast as the dyno drum (R is the overall gear ratio from crankshaft to drum).

For example, consider a 300 HP engine that makes 250 ft.lbs. of torque, where 2nd gear is 3:1 and the differential is 3:1. When you run this on the dyno in 2nd gear, the dyno drum receives 300 HP of power, and 250 * 3 * 3 = 2,250 ft.lbs. of torque. So what the dyno drum directly senses in power is the same as at the engine crankshaft. But what the dyno directly senses in torque is 2,250 ft.lbs. and the dyno has no idea how much torque the engine makes at the crankshaft, unless you tell it engine RPM so it can calculate the gear ratio and divide it out.

Thus, the dyno can directly measure the engine's power output. But the dyno cannot sense the torque at the engine crankshaft, which is what you want to know. It can only sense torque applied at the drum. These are not the same, because Torque is not conserved. To give engine crankshaft torque, the dyno must know the engine RPM so it can compute R (the overall gear ratio), and divide it out.

If that's not convincing, try this practical experiment: run the car on the dyno without connecting the dyno's engine RPM sensor. The dyno will still tell you the engine's power output, but it can't tell you the engine's torque output.

 

[KaiserSoze]

Hey everyone Amir made a mistake. Now we can't trust anything he ever says again. For those who are sarcastically impaired, the foregoing was sarcasm.

A dyno measures torque. Horsepower (or KW output) is calculated from the torque and RPM.

Now that's very weird. The first sentence is manifestly true, so long as it is not interpreted to mean that dynamometers do not measure anything other than torque. That would be silly, because it would be silly to think that you have not taken the measure of some quantity that you have measured.

The second sentence is worded strangely. Does it mean that power may be derived from measurements of torque and rpm, or does it mean that the only way it is possible to obtain measurement of power on a dynamometer is by first measuring torque and rpm? It would be a silly statement if it only meant the first thing. So it must mean the second thing. But this is much sillier than if it meant only the first thing.

It is absolutely not true that it is necessary to first measure torque and rpm in order to measure power. There are any number of ways to obtain the measure of power without first measuring torque and rpm.

This notion is popular within automotive circles where a closely related, similarly popular belief is that torque is "real" whereas power is merely an abstraction of torque. The notion, about dynamometers being able to measure only torque, is used to justify the notion that whereas torque is "real", power is only an abstraction of sorts.

Notions of this variety are not substantive. They are contrivances thought up by people who think this kind of thing is clever. Why they think it is clever is anyone's guess.

CDMC, please do not take any of this personally. This is something that goes way back with me, that has been a pet peeve of mine for a long time. It bothers me because people don't understand that two different methods for measuring some given physical quantity are entirely equivalent except for the differences in accuracy and resolution. Differences in accuracy and resolution are very important, but when there are no differences in accuracy and resolution, two different ways to measure something are 100% equivalent.

Now I will give, off the top of my head, a few ways that might be used to power power, that do not involve taking measurements of torque and rpm.

1. Couple the spinning drum of the dynamometer to a hydraulic pump that pumps water into an overhead tank. Use a measuring stick and a stopwatch to figure out the rate of increase of the water level in the tank. From this rate of increase, apply a linear conversion to the rate at which work is performed. This linear conversion is equivalent to a conversion of units of measure.

2. Couple the spinning drum to a dynamo that produces current that generates heat within a big resistor and in the air surrounding the resistor within a container. Use a couple of thermometers and a stopwatch to measure the rate of temperature rise. Apply the thermal mass of the resistor and the air in the container to obtain the rate of heat generation, expressed in customary units for the rate of work performance.

3. Attach a trailer to the car and add weight as necessary so that when driven up a steep hill with known, constant slope, the speed will stabilize with the throttle held full open. Measure the speed of the car, factor in the slope and the total mass, convert to rate of work performance.