If you can feel it vibrate, most likely the total volume of displacement would not be that much less than the driver itself. Why would it not be of any importance? I could imagine that if other aspects of stored energy mask this, then it would less significant, but not for good speakers.gedlee said:
Rick Miller said:
I think that I have been clear on that point. My breathing in the listening room affects the cone motion, of that I have no doubt. That it is insignificant, I have no doubt about that either. It is classic audiophile to raise an effect to a level of importance way beyond its actual significance simply because "it has to happen".
Should I say;
"That the Earth revolves around the sun is if no importance to me at all"
Oh please...
Come on Earl. You play all scientific, then shoot yourself in the foot like that. Really makes me doubt your ideas, all of them - and that's a shame as you have many good things to say.
You can shrug it off if you want - why should you care what I think? But you quickly loose your audience when you ignore basics like this.
I, for one, will take whatever you say with a large grain of salt from now on. This is not only your loss, but mine - and perhaps that of many other readers.
panomaniac said:
Should I say;
"That the Earth revolves around the sun is if no importance to me at all"
Oh please...
Come on Earl. You play all scientific, then shoot yourself in the foot like that. Really makes me doubt your ideas, all of them - and that's a shame as you have many good things to say.
You can shrug it off if you want - why should you care what I think? But you quickly loose your audience when you ignore basics like this.
I, for one, will take whatever you say with a large grain of salt from now on. This is not only your loss, but mine - and perhaps that of many other readers.
Pano...you're kidding right?
With all Earl's brought to these discussions you can say something like that?
Maybe it would be appropriate for you to ask why "DR." Geddes feels that way?
Frankly, I've been watching this thread from the beginning. I don't pretend to be the design gurus so many of you profess to be but one thing is very, VERY, clear. There is not one consensus on "design".
Furthermore, Lynn, himself, has comments on the absolute precision and stunning dynamics of the Summas. That's quite a commentary. I've also read reviews comparing the Summas to other OB speakers and the reviewers actually commented that the Summas were, not just better, but, FAR superior.
As an acknowledged layman, I have found just how complicated so many of you make of every design issue and, as is often the case, trying to conquer all usually degrades the end result. One thing that's glaringly clear, at least to me, is that Dr. Geddes has chosen what he feels are the most important issues in speaker design (to him) and clearly demonstrated it's viability through scientific methodology and proof. Supporting opinion of the outcome of his "opinions" have been among the most stunning I have EVER heard.
So, I think it only fair you get off that horse.
It's okay for people to have differing opinions...what's not okay is to throw stones at someone just because the opinion is different than yours or your version of a "consensus".
Really, wasn't the same ridicule directed at many of our society's greatest inventors? In retrospect...are they not all considered today...genius?
I'm with Pano on this one. I wonder just how much there is to learn on these forums when the people who are self professed experts, and sometimes even proven experts, seem unable to agree on anything much at all, no matter how basic is the facet being discussed.
Second to that if interpretations of the so called data cannot be agreed on perhaps the subjectivists carry some weight in the arguments. Don't ask me which ones as there are too many over the years I have been in this and other forums.
I have also noticed a trend lately for questions which are more of a theoretical nature than " how do you do this?" which come from those of us who are not so well educated or informed to be ignored.
People with a proven practical background such as Pano, GM and few others have my admiration for the way they freely share their experience.
jamikl
Second to that if interpretations of the so called data cannot be agreed on perhaps the subjectivists carry some weight in the arguments. Don't ask me which ones as there are too many over the years I have been in this and other forums.
I have also noticed a trend lately for questions which are more of a theoretical nature than " how do you do this?" which come from those of us who are not so well educated or informed to be ignored.
People with a proven practical background such as Pano, GM and few others have my admiration for the way they freely share their experience.
jamikl
I have to say I also have a lot of sympathy for Earl's impatience with some of the discussion points and his resulting hand waving on design issues he thinks are secondary. The order of magnitude of the problem really matters, it determines what to attack first, and here it's not about what is measurable at all, but what does subjectively matter the most. Not to mention that what matters the most may not be the easiest to measure.
Before I became a bit more competent in judging the issues in acoustics, and in building and measuring speakers, I also tried a lot of the usual suspect audiophile tweaks. Even with the benefit of builder's bias I often could not hear any difference and whenever I did, I could not tell for sure if the difference was an improvement. One of the things that supposedly mattered in say the mid 80's to 90's period, was spikes under your speakers. Cables of course. Binding posts. And what not. And what turns out to be actually important? Power response. Directivity and its angle and shape. High order harmonics even in small quantities. Everything that has nothing to do with contemporary audiophile obsessions.
John K to offer a comment on your graphs: the different FR bumps for box and u-frame vs. truly open baffle can be explained with not too much trouble by resonance of the box (the air that is) and the cavity resonance of the u frame. This does not have to mean that the cone itself is "leaking" rear radiation. Not to claim it doesn't exist but if such leakage truly was a major problem then compression drivers would have to be deemed completely useless due to their rear chamber no?
I also use dipole mids and bass drivers and love them dearly, but I have to admit, the perceived extra clarity may have to do just as much with the power response of the dipole (read: less total radiated bass energy than from a box assuming identical on axis FR) as it does with box modes. And I did not find it easy either to equalize the u-frame modes away even though I use a very shallow and wide u-frame (24wx40hx7"d).
Before I became a bit more competent in judging the issues in acoustics, and in building and measuring speakers, I also tried a lot of the usual suspect audiophile tweaks. Even with the benefit of builder's bias I often could not hear any difference and whenever I did, I could not tell for sure if the difference was an improvement. One of the things that supposedly mattered in say the mid 80's to 90's period, was spikes under your speakers. Cables of course. Binding posts. And what not. And what turns out to be actually important? Power response. Directivity and its angle and shape. High order harmonics even in small quantities. Everything that has nothing to do with contemporary audiophile obsessions.
John K to offer a comment on your graphs: the different FR bumps for box and u-frame vs. truly open baffle can be explained with not too much trouble by resonance of the box (the air that is) and the cavity resonance of the u frame. This does not have to mean that the cone itself is "leaking" rear radiation. Not to claim it doesn't exist but if such leakage truly was a major problem then compression drivers would have to be deemed completely useless due to their rear chamber no?
I also use dipole mids and bass drivers and love them dearly, but I have to admit, the perceived extra clarity may have to do just as much with the power response of the dipole (read: less total radiated bass energy than from a box assuming identical on axis FR) as it does with box modes. And I did not find it easy either to equalize the u-frame modes away even though I use a very shallow and wide u-frame (24wx40hx7"d).
It would be interesting actually to hear and measure the output of any particular cabinet by totally isolating it from the frontal output of the speaker by means of, for example, clamping the speaker to an appropriate sized weather-strip-sealed aperture in a cement walled soundproof room into which the speaker drivers and port fired.
Hi John,
That's a nice set of amplitude responses you present there.
What is most often NOT said however is -
that these are the *steady sine* responses, and
that these do NOT become established or applicable until AFTER the drive waveform has become a steady sine at the frequencies measured;
ie. after the LS/cab/baf energy exchanges have become fully stabilised in Time.
However, Music is not steady sines, and it has its basis in Time.
During the first 90 degrees of waveform, say around 150Hz, all of the exampled loudspeakers will be transducing relatively linearly, though the boxed driver will be driving against additional resistance as it compresses enclosure air.
After 90 degrees (say 3mS) the cone motion of the boxed driver becomes considerably modified over a range of frequencies centred upon system resonance, this by energy exchanges between the driver itself and the enclosed air as cabinet returned energy either destructively decreases or resonantly increases the cone's amplitude response.
This is why we *hear* the rear pressure reflections upon cone transducers when they are 'boxed' and reproducing Music (as compared to test sines).
Your responses show that even the U-baffle sides will become audible circa 300Hz wrt the flat baffle via ongoing Music reproduction.
Music Waveform Amplitudes become modified in Music Time by energy returned from within the box or frame; this assymetrically and independently modifies the reproduced amplitude response of the driver cone in Box or Frame Time !!!
If there are any cabinet/frame induced pressure reflections impinging upon the rear of any driver cone, then every time there is LF content (especially percussive drum and guitar) the linearity of amplitude transduction and harmonic relationships of all reproduction becomes inconstant in Time.
With your boxed example this is first noticeable at 60Hz which makes for 16mS (related to Q) of typical waveform amplitude distortion in Music Time; while for the exampled U-frame similar audibility would likely appear at 240Hz / 4mS.
Such time constants have considerable bearing upon what we hear. They modify the amplitude response of ALL frequencies reproduced by the same driver with respect to the waveforms reproduced by any other drivers !!!!!
For this reason the only LF drivers I have are large OB, because I can no longer stand the sound of those entirely *avoidable* internal box pressure 'reactions' which so distort music reproduction.
Quality is what really counts; not quantity .
Cheers ........ Graham.
That's a nice set of amplitude responses you present there.
What is most often NOT said however is -
that these are the *steady sine* responses, and
that these do NOT become established or applicable until AFTER the drive waveform has become a steady sine at the frequencies measured;
ie. after the LS/cab/baf energy exchanges have become fully stabilised in Time.
However, Music is not steady sines, and it has its basis in Time.
During the first 90 degrees of waveform, say around 150Hz, all of the exampled loudspeakers will be transducing relatively linearly, though the boxed driver will be driving against additional resistance as it compresses enclosure air.
After 90 degrees (say 3mS) the cone motion of the boxed driver becomes considerably modified over a range of frequencies centred upon system resonance, this by energy exchanges between the driver itself and the enclosed air as cabinet returned energy either destructively decreases or resonantly increases the cone's amplitude response.
This is why we *hear* the rear pressure reflections upon cone transducers when they are 'boxed' and reproducing Music (as compared to test sines).
Your responses show that even the U-baffle sides will become audible circa 300Hz wrt the flat baffle via ongoing Music reproduction.
Music Waveform Amplitudes become modified in Music Time by energy returned from within the box or frame; this assymetrically and independently modifies the reproduced amplitude response of the driver cone in Box or Frame Time !!!
If there are any cabinet/frame induced pressure reflections impinging upon the rear of any driver cone, then every time there is LF content (especially percussive drum and guitar) the linearity of amplitude transduction and harmonic relationships of all reproduction becomes inconstant in Time.
With your boxed example this is first noticeable at 60Hz which makes for 16mS (related to Q) of typical waveform amplitude distortion in Music Time; while for the exampled U-frame similar audibility would likely appear at 240Hz / 4mS.
Such time constants have considerable bearing upon what we hear. They modify the amplitude response of ALL frequencies reproduced by the same driver with respect to the waveforms reproduced by any other drivers !!!!!
For this reason the only LF drivers I have are large OB, because I can no longer stand the sound of those entirely *avoidable* internal box pressure 'reactions' which so distort music reproduction.
Quality is what really counts; not quantity .
Cheers ........ Graham.
I would be interested in reading the reviews that you mention. Are there any links to those reviews? Up to now, I have not been able to find any reviews that specifically addresses music source + other speakers compared + specifically addresing music passages where people can listen for on their own systems.Teh said:
MBK said:
The near field response curves I show are directly indicative of the cone motion. That the sealed box and U-frame results show clearly the effect of the enclosure resonances is an indication of the "acoustic" transparency of the cone (or maybe it should be called translucent). Lynn said cones a transparent. Earl said they are not. I said it not so black and white. Also as I said a while back, when the term transparent is used it does not mean the box/u-frame resonances passes through or leak through the cone. It means the rear resonances which impinge upon the back side of a cone transfer some of their energy to the cone to excite it to vibrate in a different manner than it would in the absence of the resonance. This difference in vibration is then reflected in the front side SPL response. To what extent this happens depends on many factors including the difference between the acoustic impedance of the cone and and air, the thickness of the cone, the internal damping of the cone... to name a few. Your comment about compression drivers applies equally to any driver with a closed chamber, like a dome mid, or tweeter. In all cases the rear chamber must be correctly designed, and possibly damped, so as to minimize or eliminate the effect of chamber resonances on the response in the desired passband.
Graham,
You always seem to take a simple process and convolute it into something incomprehensible. What you are looking at in my plots is the representation of the system impulse response in the frequency domain via FFt. The addition of the resonances does not change the linearity of the system. Given the impulse response I measured, it could be convolved with any input signal to get the output. It has noting to do with SS sine waves, except that in the input was a SS sine wave the output would be reproduced with amplitude as shown in th FR plots.
Any system which does not have a perfect impulse necessarily add some decay tail to the input. Therefore, if you like, any system with a non perfect impulse adds time smear. This goes back to the discussion on stored energy and linear distortion.
I would get in to low frequency sources and what the box does. It's been don't to death in these discussion groups and isn't relevant to midrange reproduction.
You always seem to take a simple process and convolute it into something incomprehensible.
What you are looking at in my plots is the representation of the system impulse response in the frequency domain via FFt. The addition of the resonances does not change the linearity of the system. Given the impulse response I measured, it could be convolved with any input signal to get the output. It has noting to do with SS sine waves, except that in the input was a SS sine wave the output would be reproduced with amplitude as shown in th FR plots. Any system which does not have a perfect impulse necessarily add some decay tail to the input. Therefore, if you like, any system with a non perfect impulse adds time smear. This goes back to the discussion on stored energy and linear distortion.
I would get in to low frequency sources and what the box does. It's been don't to death in these discussion groups and isn't relevant to midrange reproduction.
Regarding the discussion about cone transparency two things got constantly mixed that should more clearly be distinguished from each other IMO.
1.) first part that is related upon mirroring the back wave
2.) the other part is about the different acoustic resistance a driver has to work against in OB, back open or closed box or whatever
Ad 1.) I have shown in
http://members.aon.at/kinotechnik/diyaudio/diy_audio/BDMD/Introducing_BDMD.htm
that this actually shows the "real" transparency of diaphragms (if you refuse to accept Lynns great arguments about building cardboard speakers and monitoring rooms with paper walls)
For this part we have to be aware of the nature of the mirror actually in duty – if you have not only one mirror in the back but rather many of them - the effect is different (smeared it is) as outlined with several simus – also giving different impression of box coloration with different shapes of boxes
(Horn honk due to reflection at points of strong impedance change actually is of the same nature - only difference - its a reflection from the front not from the back)
The main thing to keep in mind with this part also is that the distortion occurs after a certain time – related to the time of flight diaphragm > mirror > diaphragm.
Meaning there actually *is* a time window where there is *no* distortion through that effect
Ad 2)
This is a completely different part as the driver "sees" the acoustic impedance form the very beginning of cone movement.
Here there is *no* early time window of cone movement that is *not* affected by the shape of your enclosure.
Regarding this effect the cone movement is throughout determined by the shape of the box (in overlay with its own parameters).
For this effect we also could say the cone is transparent, but more precisely we possibly should say its coupled – what in the end turns out to be roughly the same from a perception point of view.
Michael
1.) first part that is related upon mirroring the back wave
2.) the other part is about the different acoustic resistance a driver has to work against in OB, back open or closed box or whatever
Ad 1.) I have shown in
http://members.aon.at/kinotechnik/diyaudio/diy_audio/BDMD/Introducing_BDMD.htm
that this actually shows the "real" transparency of diaphragms (if you refuse to accept Lynns great arguments about building cardboard speakers and monitoring rooms with paper walls)
For this part we have to be aware of the nature of the mirror actually in duty – if you have not only one mirror in the back but rather many of them - the effect is different (smeared it is) as outlined with several simus – also giving different impression of box coloration with different shapes of boxes
(Horn honk due to reflection at points of strong impedance change actually is of the same nature - only difference - its a reflection from the front not from the back)
The main thing to keep in mind with this part also is that the distortion occurs after a certain time – related to the time of flight diaphragm > mirror > diaphragm.
Meaning there actually *is* a time window where there is *no* distortion through that effect
Ad 2)
This is a completely different part as the driver "sees" the acoustic impedance form the very beginning of cone movement.
Here there is *no* early time window of cone movement that is *not* affected by the shape of your enclosure.
Regarding this effect the cone movement is throughout determined by the shape of the box (in overlay with its own parameters).
For this effect we also could say the cone is transparent, but more precisely we possibly should say its coupled – what in the end turns out to be roughly the same from a perception point of view.
Michael
john k... said:
This is what I meant exactly in my comment above (also corresponds to Michael's "ad 2)"). But this also means that the graphs do not show anything related to a "transparent" or translucent cone in this situation. It just means the cone as an electrodynamic spring mass system is influenced in its own resonant behavior by the ordinary and usual resonances / impedances it encounters. Additional bracing or adding tons of lead to the box won't change any of that because it's the air volume really that does it - that's the fundamental spring. And, if the design of the box / u-frame etc takes proper account of the resonance it must not necessarily be a problem.
The discussion started along the lines of "disorderly box modes may leak through the cone". I just wanted to point out that John K's graphs showed something else, it showed the response of the driver's resonant system to coupling with the box or u frame resonant system. I think we are finally in violent agreement here. And, I don't even like boxes - I am not using any (OK OK I do: my tweeter has a rear chamber).
MBK said:
Yes, exaclty, this is what is meant by "transparent". That is, the effects of the box resoances alter the mechanical motion of the cone such that these resonances, or there effect on the cone, are then re-radiated from the front side. Perhaps it is the term transparent that is the source of confusion which is why I tried to explain (9define) it a while back.
The terms transparent and opaque are just lables being applied to indicate that either the cone reacts mechanically to the internal resonances, thus their effect impacts the radiated sound, or the cone does not.
If we
- are accepting my theoretical work, simus and measurements about BDMD "back diaphragm mirror distortion" to be valid
- and we also accept to distinguish between the two effects (delayed and non-delayed overlay of cabinet behaviour) described in my last posting
- then we possibly also can state some conclusions of interest that apply to the discussion at hand, regarding impacts of "box cabinet resonance" (more so about mechanisms involved than its sonic significance though).
If we take a standard closed box, all walls can be considered to be mirrors for the back wave. If the walls vibrate
– one effect is that there is sound radiation towards the surrounding - ie. directly into the listening room.
– the second effect is that the mirror is vibrating – hence modulating the reflection of the back wave and also re-radiating sound towards the driver
For that part of box cabinet vibration created by the reaction forces of cone acceleration (rather than by pressurising the cabinet) - that ideally could be avoided by massive construction or free suspension of the driver - we also can state that there is *additional* energy radiated from the diaphragm.
The part of "from box wall generated sound" that's transitioning through the cone my easily be perceived as distortion of the driver – what isn't correct in a more precise understanding of second order effects.
Michael
- are accepting my theoretical work, simus and measurements about BDMD "back diaphragm mirror distortion" to be valid
- and we also accept to distinguish between the two effects (delayed and non-delayed overlay of cabinet behaviour) described in my last posting
- then we possibly also can state some conclusions of interest that apply to the discussion at hand, regarding impacts of "box cabinet resonance" (more so about mechanisms involved than its sonic significance though).
If we take a standard closed box, all walls can be considered to be mirrors for the back wave. If the walls vibrate
– one effect is that there is sound radiation towards the surrounding - ie. directly into the listening room.
– the second effect is that the mirror is vibrating – hence modulating the reflection of the back wave and also re-radiating sound towards the driver
For that part of box cabinet vibration created by the reaction forces of cone acceleration (rather than by pressurising the cabinet) - that ideally could be avoided by massive construction or free suspension of the driver - we also can state that there is *additional* energy radiated from the diaphragm.
The part of "from box wall generated sound" that's transitioning through the cone my easily be perceived as distortion of the driver – what isn't correct in a more precise understanding of second order effects.
Michael