I don't think I have seen that stated before, I expected horn resonances plus a primary suspension resonance not harmonically related.
Can you explain that briefly or provide a reference or link to an explanation or analysis?
Best wishes
David
Dave,
Not only do people overlook the resonant nature of the diaphragms in a compression driver, besides where the first breakup mode of the diaphragms are at high frequency but they more than almost always don't seem to understand the acoustical nature of the surrounds used either. There is more noise coming off the surround than you could imagine and this is translated into acoustical output of the device. A holistic approach is needed rather than the simplistic approach that is often used for matching devices to waveguides and expecting exceptional results. Everything I have just stated goes for a dome tweeter also. Surrounds do contribute in a dome tweeter, except that it is often destructive in nature as much of the surface area of the surround is working out of phase to the dome itself.
Not only do people overlook the resonant nature of the diaphragms in a compression driver, besides where the first breakup mode of the diaphragms are at high frequency but they more than almost always don't seem to understand the acoustical nature of the surrounds used either. There is more noise coming off the surround than you could imagine and this is translated into acoustical output of the device. A holistic approach is needed rather than the simplistic approach that is often used for matching devices to waveguides and expecting exceptional results. Everything I have just stated goes for a dome tweeter also. Surrounds do contribute in a dome tweeter, except that it is often destructive in nature as much of the surface area of the surround is working out of phase to the dome itself.
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Kindhornman
I am not sure that I buy this but I am not sure that I understand it either. I have never measured "noise coming off the surround". How would one even determine this to be the case? I think that my understanding of "matching devices to waveguides and expecting exceptional results" is actually pretty good. I am not sure what it is that I am missing here.
I am not sure that I buy this but I am not sure that I understand it either. I have never measured "noise coming off the surround". How would one even determine this to be the case? I think that my understanding of "matching devices to waveguides and expecting exceptional results" is actually pretty good. I am not sure what it is that I am missing here.
Since we're on CD resonances, there's a broad difference between what are otherwise similar devices in terms of impedance spike magnitude. I'm wondering if there's a lot of value in redesigning the back cup of some compression drivers, a la Scan Speak's "AirCirc" dome (carefully damped vented chambers). in many drivers the distance from phragm to back cup is so small as to be seemingly acoustically advantageous (not long enough to set up meaningful resonance), but I wonder if the higher pressure in a CD makes this effectively longer.
Gedlee,
I know that most of the time we measure speaker response at 1 meter and such at one watt to compare devices and have a level playing field. But while developing a new speaker you should look at measuring things much closer with a 1/4" measuring mic and see what is emanating off of different surfaces. You will be in for a surprise how different sections of the speaker are producing sound, a surround definitely does have a noticeable sound signature and different materials sound different also. I know we think it is just the suspension but that is far from the truth, it is a radiating surface that should attenuate the outward wave coming up the cone. It is just something that most designers seem to overlook. A rubber surround sounds much different than a treated m-roll cloth surround. The same thing goes for inside a compression driver, believe me a Mylar surround has a different signature than a metallic surround and it is part of the sound of the device even if you haven't looked at that before. I was pointed in that direction long ago by another designer, something to look at. How lossy is the material and what is the signature of the individual materials used, even the glue line will change the sound by changing the reflective nature of each change in material. Material science is fun!
PS. Earl, you did at one time work for Ford didn't you?
I know that most of the time we measure speaker response at 1 meter and such at one watt to compare devices and have a level playing field. But while developing a new speaker you should look at measuring things much closer with a 1/4" measuring mic and see what is emanating off of different surfaces. You will be in for a surprise how different sections of the speaker are producing sound, a surround definitely does have a noticeable sound signature and different materials sound different also. I know we think it is just the suspension but that is far from the truth, it is a radiating surface that should attenuate the outward wave coming up the cone. It is just something that most designers seem to overlook. A rubber surround sounds much different than a treated m-roll cloth surround. The same thing goes for inside a compression driver, believe me a Mylar surround has a different signature than a metallic surround and it is part of the sound of the device even if you haven't looked at that before. I was pointed in that direction long ago by another designer, something to look at. How lossy is the material and what is the signature of the individual materials used, even the glue line will change the sound by changing the reflective nature of each change in material. Material science is fun!
PS. Earl, you did at one time work for Ford didn't you?
The short answer is "no". The backcup should be as small as practicable, larger serves no purpose. Some damping material might be a good idea, but I would even have suspicions that it was not necessary.
Yes, I worked at Ford for more than 20 years. Left there a little over ten years ago.
The problem with the near field is that there is a lot going on that does not propagate. Why should we be concerned with sound that never reaches the listener? I do not even test as close as 1 meter because 1.5-2 is better. Nearer than that and you will see things that have nothing to do with the far field and should be ignored.
An example of what I mean here, I've shown a raw waveguide then with some arbitrary EQ, pushed the acoustic issues forward and the equalisable ones behind as I'm seeing it.
Seeing HOM's?
Scientists Uncover Invisible Motion in Video - NYTimes.com
Perhaps heating the air for the processor to react to? Maybe a very low level of particulates (i.e. smoke)?
Scientists Uncover Invisible Motion in Video - NYTimes.com
Perhaps heating the air for the processor to react to? Maybe a very low level of particulates (i.e. smoke)?
Earl, I recall from one of your white papers you simulated diffraction/reflections by mixing a second source to be fed via headphones when demonstrating level dependent perception. What about these artifacts when they've been included on a recorded song? Will these on their own be enough to cause this recording to sound worse at higher levels?
I can only guess, but yes, I would say that diffraction that is not part of the instrument would be a degradation. But keep in mind that things that are part of the original recording are all good if the producer wants them there. Its adding or subtracting things on playback that were not in the original that are bad. If the producer was happy with the sound the so be it, if not then they should fix it.
Clearly producers don't always know when something is "good" or how to fix it. That is more than evident from some of the junk in the marketplace. I have seen seriously clipped - audibly so - songs on first rate musicians CDs. How does this happen? Things do see to be slightly out of control IMO.
Clearly producers don't always know when something is "good" or how to fix it. That is more than evident from some of the junk in the marketplace. I have seen seriously clipped - audibly so - songs on first rate musicians CDs. How does this happen? Things do see to be slightly out of control IMO.
I can't say I have much faith in the consistency of recordings. Mostly I dislike what gets done intentionally more than what happens by 'accident'.
The reason I asked is because I'm trying to judge a speaker by listening in mono for changes that happen with level, but when some do sound worse I'm not sure whether it is a clear sign of speaker problems or whether the recording is contributing to it.
The reason I asked is because I'm trying to judge a speaker by listening in mono for changes that happen with level, but when some do sound worse I'm not sure whether it is a clear sign of speaker problems or whether the recording is contributing to it.
That is an interesting test, I've thought about doing that before. Let me know how it comes out. One test that we did once was to record the speakers in an anechoic chamber at different levels and then play them back at a constant level. There was not as much difference as one would suspect. The thing is that the diffraction detection depends on the playback level NOT the recording level. That makes it very difficult to test.
Jumping theads here (Orion beaten by Behringer): wouldn't the same methodology work well to detect audible distortion and/or dynamic compression in loudspeakers?
Dr. Geddes,
in your paper [1], you are discussing radiation impedance for the waveguide, which shows rapid loss of an efficiency below certain value of ka.
Applying Eq. (22) to a waveguide with a=0.5 inch, and theta=45 deg, which you incidentally use in your product, yields cutoff frequency of about 2.4 kHz. Yet, if I remember correctly, you are using the waveguide down to about 900 Hz.
The paper does mention that "in practice it has been found that they [the efficiency restriction] can be relaxed a great deal", but does not go to any details.
Could you comment on the theoretical vs. practical difference? What would be the disadvantage of going to a larger a as Eq. (22) would imply?
Kindest regards,
M
[1] Earl R Geddes, Acoustic Waveguide Theroy, J. Audio Eng. Soc., Vol. 37, No. 7/8, 1989, July/August
in your paper [1], you are discussing radiation impedance for the waveguide, which shows rapid loss of an efficiency below certain value of ka.
Applying Eq. (22) to a waveguide with a=0.5 inch, and theta=45 deg, which you incidentally use in your product, yields cutoff frequency of about 2.4 kHz. Yet, if I remember correctly, you are using the waveguide down to about 900 Hz.
The paper does mention that "in practice it has been found that they [the efficiency restriction] can be relaxed a great deal", but does not go to any details.
Could you comment on the theoretical vs. practical difference? What would be the disadvantage of going to a larger a as Eq. (22) would imply?
Kindest regards,
M
[1] Earl R Geddes, Acoustic Waveguide Theroy, J. Audio Eng. Soc., Vol. 37, No. 7/8, 1989, July/August
I think the first thing that you should remember is that a direct radiating loudspeaker operates almost its entire bandwidth on the upward sloping portion of the radiation impedance, so its not really a "cutoff" effect. That said, I have seen no real cutoff effect from the waveguide, it is dominated by the cutoff from the driver itself (below resonance). Perhaps the efficiency is down below 2 kHz, but the drivers resonance is way up in efficiency in that region.
Posting impulse responses is no problem and step responses are just the integral of the impulse response so they become obvious from the impulse response. I don't plot out phase anywhere, although all of my measurements and plotting is done complex so the phase is there, I just don't have any use for looking at the phase as a stand alone parameter.
What do you want to do with this data? That will help me to decide what to get you.
I could post the HolmImpulse raw data files which will contain the phase if desired, but they can only be viewed from within Holm.
What do you want to do with this data? That will help me to decide what to get you.
I could post the HolmImpulse raw data files which will contain the phase if desired, but they can only be viewed from within Holm.