Here's a little somethin' for those who believe the theory that proves the bee can't fly. Measurements I took a few minutes ago.
The smooth line is the drive voltage to my giant OB (yes, it is equalized and crossed-over, don't ask). The other is a REW curve using a Radio Shack meter (the calibration boosts the low bass output a small amount) about where my ears are when listening to music in a heavily carpeted room about 10x16x8 feet. 1/6 octave smoothing (which isn't hiding any secrets really). The ancient Stephens woofer has a free-air resonance around 20 or so.
The giant OB is kind of funny shaped. But if any waves wanted to sneak around from the back, the shortest path would be just 30 inches to the meeting place. No kidding. Longest path maybe 60 inches to the common meeting (or 100 Hz cut-off).
15-300 Hz. dBc scale is 10 per box. No fudging around with mic positioning... first curve (after doing a fair amount of test due-diligence).
Looks pretty good to me and maybe to others who have the nerve to publish their real-world results as I am doing. Umm, big roll-off below 20 Hz. Must be that phase cancellation stuff catching up with me. Just kidding, we all know another reason it is rolling off there.
Ben
The smooth line is the drive voltage to my giant OB (yes, it is equalized and crossed-over, don't ask). The other is a REW curve using a Radio Shack meter (the calibration boosts the low bass output a small amount) about where my ears are when listening to music in a heavily carpeted room about 10x16x8 feet. 1/6 octave smoothing (which isn't hiding any secrets really). The ancient Stephens woofer has a free-air resonance around 20 or so.
The giant OB is kind of funny shaped. But if any waves wanted to sneak around from the back, the shortest path would be just 30 inches to the meeting place. No kidding. Longest path maybe 60 inches to the common meeting (or 100 Hz cut-off).
15-300 Hz. dBc scale is 10 per box. No fudging around with mic positioning... first curve (after doing a fair amount of test due-diligence).
Looks pretty good to me and maybe to others who have the nerve to publish their real-world results as I am doing. Umm, big roll-off below 20 Hz. Must be that phase cancellation stuff catching up with me. Just kidding, we all know another reason it is rolling off there.
Ben
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If it is equalized, your only proving the "pro physical laws" position. The original argument in this thread was that it could be done(10 hz?? Sheesh!) without EQ and with "normal" efficiency(What is normal efficiency? Equal to the mains efficiency at 1 khz, and measured at the listening position, with the same amount of wattage going to both..) In fact, a mono sub would need to be 3db more efficient than each individual mains, because the mains are doing bass at the cutoff point in tandem ..
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It can be done without EQ, though, if the woofers have a very high Q and a low resonance frequency- in a box and in a nearfield measurement, the peaked bass is evident. See the Bob Carver speakers for an excellent commercial implementation. Whether through EQ or high Q, the issue still is the tradeoff between extension and efficiency/displacement (read: distortion). But this is irrelevant to the claim of using "reflections" from the room to make up for the inherent comb filtering and cancellation at longer wavelengths, which is utter nonsense.
How many times do I have to repeat that I have no problem with the principles of acoustics? Why are you implying I am a moron or a fool? Do you think I practiced voodoo when I worked at Bell Labs, Murray Hill?
I only argue that the analysis of open baffles in real-world rooms is naive.
Do you want me to say it one more time?
In places the equalization bears a loose resemblance to the well-known suggestion of Linkwitz. In other places, not. In some places, I bet you could eyeball an XdB/8ave drop in speaker output and in other places... a rise.
The net result seems to be not so bad, given the widespread expectation that open baffle output go poof at the half-wave dimension and everywhere south.
Ben
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Not sure what your phrase "utter nonsense" refers to?
I thought that Toole put the notion that anybody can hear comb filtering to rest, as best as I can recall. Engineers love to talk about comb filtering because it is so compelling from a math standpoint even if a non-starter from a hearing point of view.
Can you point to those comb filtering artifacts in my chart? Or could it be that the hypothetical room reflections are really doing a great job masking the hypothetical comb filter faults? And if that is true, then we are back to my point that the "bad rap" OB get from naive theorizing is excessive.
Just returning to the thread topic, if it looks like the simple theory of open baffles with a "point source" cone driver is too simple, then the theory is WAY off base with a planar driver.
Ben
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Read this one more time and address each issue(You won't). You're entering this debate from out of left field..
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Naturally, anyone would want to be prudent in disagreeing with Sy. So, until I get the energy to "drill down" with the curves some more, I'd just say there are always dips and peaks and they always look comb-like. I like 1/6 smoothing as my favorite compromise and as I said, it hides nothing important here.
With any kind of theorizing for practical design purposes, always a choice how deep you want to go. I don't think there is much value in taking a model of a circular baffle (or any other mathematically tractable surface), put a point-like source in the middle... and then try to generalize to an odd-shaped OB in a room at an angle to the walls.
Can we agree to disagree on just where it is productive to draw that line?
Ben
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Jamo, independently tested by stereophile, with two 12" 100db1w/m @200hz woofers per side(The four woofers have a combined efficiency of 106db 4w/1m@ 200hz or 100db 1w/1m @ 200hz). Extension in JA's room hits 25 hz . Distortion figures are not shown. This shows that it can be done, but probably with severely compromised dynamic range and distortion..
Jamo Reference R 907 loudspeaker Measurements | Stereophile.com
Jamo Reference R 907 loudspeaker Measurements | Stereophile.com
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Well indeed, whack enough passive EQ onto the high sensitivity drivers to compensate for the open baffle losses and you can have as much extension as you like, obviously at the expense of efficiency. As you pointed out, by using two high efficiency drivers on a wide baffle and attenuating them down to give you a standard mid band sensitivity of 88dB.
With a baffle 44cm wide you're going to need to start EQing at about 200Hz. At a rate of 6dB/ octave you'd be down 18dB by 25Hz. With a pair of 100dB bass units, giving you 106dB for the pair @ 4 ohms and then attenuated by 18dB you're looking at a midband sensitivity of 88dB, which low and behold is what the Jamo's are.
With a baffle 44cm wide you're going to need to start EQing at about 200Hz. At a rate of 6dB/ octave you'd be down 18dB by 25Hz. With a pair of 100dB bass units, giving you 106dB for the pair @ 4 ohms and then attenuated by 18dB you're looking at a midband sensitivity of 88dB, which low and behold is what the Jamo's are.
Also at the expense of distortion. Necessary consequence of increasing diaphragm displacement.
Now, here is the maggie 3.6R, also measured by John Atkinson. The bass response is self explanatory..
Magnepan Magneplanar MG3.6/R loudspeaker Measurements | Stereophile.com
Magnepan Magneplanar MG3.6/R loudspeaker Measurements | Stereophile.com
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Here is the quad 989..
Quad ESL-989 electrostatic loudspeaker Measurements | Stereophile.com
Quad ESL-989 electrostatic loudspeaker Measurements | Stereophile.com
Apogee stage Mini Grand..
Apogee Stage & Mini-Grand loudspeakers 1994 Measurements | Stereophile.com
Apogee Stage & Mini-Grand loudspeakers 1994 Measurements | Stereophile.com
Yes. To show what the nearfield bass measurements on a dipole should look like in order to get a relatively flat response in the farfield. These measurements also show that even in the near field, the bass wraps around from the back and cancels the front below a certain (Rather high)frequency..
Letter from Linkwitz..
Siegfied Linkwitz comments
Editor: The review of the Magneplanar MG3.6/R in the August Stereophile caught my attention. I am a proponent of open-baffle speakers because of their room acoustic advantages and the absence of sound coloring boxes. So I looked with great interest at figs.2 & 3 on page 89 showing individual driver frequency responses and their summation.
The nearfield measurements of woofer and midrange in fig.2, presumably taken only an inch or so from the driver surface, are a valid set of data. You also could have measured the tweeter at such close range and obtained useful information. Where things fall apart is in fig.3 when you form the complex sum of nearfield measurements and the 50" tweeter "farfield" measurement. This curve does not represent the frequency response a listener might experience at any distance and is therefore extremely misleading.
The nearfield frequency response of an acoustic source is only proportional to its farfield response if the source is small, ie, omnidirectional, and if it is in free-space. Summing a driver diameter corrected woofer nearfield response to a farfield midrange response works for a small monitor on a stand, but already has errors when the speaker is larger and the woofer is close to the floor—when the conditions move away from free-space or anechoic.
The Magneplanar is clearly not a point source and, being open-baffle, it has an acoustic short circuit between front and back. This causes a 6 dB/octave low-frequency roll-off in the farfield response. So from all open baffle nearfield measurements you have to subtract first a 6dB/octave (= 20dB/decade) slope before you can sum the data with other farfield measurements. When you apply this correction to the MG3.6 woofer response you see that it flattens from 400Hz to 60Hz and shows a peak at 47Hz. Similarly the midrange has to be corrected before you can use it for the composite response. The actual room response is still different from this composite, though, primarily due to the effect of the floor on woofer radiation.
You might consider to add a measurement taken with a 50ms time window at your listening position, spatially averaged and half-octave smoothed to include the room. I think as a measurement that allows true comparison between speakers, this would be more useful than the composite data that are correct only in a few special cases.
I hope this letter helps your readers to understand the difficulties in describing a loudspeaker by measurements.—Siegfried Linkwitz, Corte Madera, CA, Linkwitz Lab - Loudspeaker Design.
Hi everybody,
So, now that Sigfried has spoken (what a name : freedom through victory), who has known a splendid success in selling open baffle speakers all over the states and round the globe, it is happily clear that planar sub deserve no longer to be ostracised because of some native characteristics, that can be perfectly treated according to scientific and experimental knowledge, to give finally a very seductive product. Severall well known sound specialists have found them to their taste …
Because this is the case of any driver‘s intrinsic nature. The perfect native driver you believe can use with not the least adaptation to build a perfect sounding system, doesn’t exist. What’s wrong, on the other hand, is to condemn any one or anything by these terrific simple words “that cannot work” ! This is an insult to the human spirit, whose first qualities are intelligence (power of finding solutions) and cleverness.
So I am going to leave you. My aim was only to make you know a typical solution for Maggie lovers, whose bass can so easily be magnified. And I see now that for those who never heard Infraplanar, and LS 50 and 150, that you have little chance to, because till now any US or EC company has taken the opportunity to bring them to you, where they have probably a future. Let’s forget birds names and hot spicy exchanges we had on this thread. So long in the marvelous world of good music and charming sounds.
Tiburce
So, now that Sigfried has spoken (what a name : freedom through victory), who has known a splendid success in selling open baffle speakers all over the states and round the globe, it is happily clear that planar sub deserve no longer to be ostracised because of some native characteristics, that can be perfectly treated according to scientific and experimental knowledge, to give finally a very seductive product. Severall well known sound specialists have found them to their taste …
Because this is the case of any driver‘s intrinsic nature. The perfect native driver you believe can use with not the least adaptation to build a perfect sounding system, doesn’t exist. What’s wrong, on the other hand, is to condemn any one or anything by these terrific simple words “that cannot work” ! This is an insult to the human spirit, whose first qualities are intelligence (power of finding solutions) and cleverness.
So I am going to leave you. My aim was only to make you know a typical solution for Maggie lovers, whose bass can so easily be magnified. And I see now that for those who never heard Infraplanar, and LS 50 and 150, that you have little chance to, because till now any US or EC company has taken the opportunity to bring them to you, where they have probably a future. Let’s forget birds names and hot spicy exchanges we had on this thread. So long in the marvelous world of good music and charming sounds.
Tiburce
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