I think I can add a bit to this, if I remember correctly.
The radiation impedence increases with frequency, so the cone meets a stiffer resistance from the air it has to move as the frequency increases. This makes the radiation of sound more efficient at higher frequencies. It levels off when the wavelength of the sound is of similar dimension to the radiating area. Similarly, a horn makes the air stiffer at the throat, hence the increased efficiency, but over a wider frequency range.
Another effect is that sound travels along the cone from the voice coil to the surround at a speed depending on the cone material. It is this that causes cone breakup, and the radiating source to shrink towards the coil at higher frequencies.
Not sure what added clay does to it though
The radiation impedence increases with frequency, so the cone meets a stiffer resistance from the air it has to move as the frequency increases. This makes the radiation of sound more efficient at higher frequencies. It levels off when the wavelength of the sound is of similar dimension to the radiating area. Similarly, a horn makes the air stiffer at the throat, hence the increased efficiency, but over a wider frequency range.
Another effect is that sound travels along the cone from the voice coil to the surround at a speed depending on the cone material. It is this that causes cone breakup, and the radiating source to shrink towards the coil at higher frequencies.
Not sure what added clay does to it though
Is it possible that there is another effect here too. Cone break-up is as I understand it standing mechanical waves in the membrane. These would primarily occur in the radial direction between the coil and the suspension. In the acoustic case (inside boxes) we kill such waves with stuffing. Could the clay do something similar to the cone break-up? Would this smoth the response in the upper frequency region.
a little more info
These drivers were pulled from a pair of Infinity Qjr's BUT I'm pretty certain that they are not original to the speakers. I've owned them for 25 years or so but I bought them used.
The cone is very very heavy paper treated with something resembling glittery cement. Very rough tough texture. I weighed the clay, which is ordinary plumbers clay, and it weighed 11.5 grams.
They worked quite well in the Infinities fairly large sealed box using the Qjr x-over crossed at 600hz. I noticed that the midrange was run out of phase in the original Infinity xovers but in the pair that these woofers came out of it was the woofers that were out of phase.
Ahh well I was just curious what you all thought, thanks for your input
incidently ...everytime I look at them I think 30 year old Sansui. I don't know why ... just one of those mind tricks but thats what I think they are are.
P.S. the pic is missing because I just changed the DNS for my website and its hasn't replicated fully yet.
These drivers were pulled from a pair of Infinity Qjr's BUT I'm pretty certain that they are not original to the speakers. I've owned them for 25 years or so but I bought them used.
The cone is very very heavy paper treated with something resembling glittery cement. Very rough tough texture. I weighed the clay, which is ordinary plumbers clay, and it weighed 11.5 grams.
They worked quite well in the Infinities fairly large sealed box using the Qjr x-over crossed at 600hz. I noticed that the midrange was run out of phase in the original Infinity xovers but in the pair that these woofers came out of it was the woofers that were out of phase.
Ahh well I was just curious what you all thought, thanks for your input
incidently ...everytime I look at them I think 30 year old Sansui. I don't know why ... just one of those mind tricks but thats what I think they are are.
P.S. the pic is missing because I just changed the DNS for my website and its hasn't replicated fully yet.
Here's the crossover schematic on the Jrs:
http://oellerer.net/infinity_classics/Quantum_Jr/body_quantum_jr.html
And here http://oellerer.net/infinity_classics/Quantum_Jr/Quantum_Jr_brochure_02.jpg is the added clay
official 'explanation' (see the 12" woofer paragraph):
http://oellerer.net/infinity_classics/Quantum_Jr/body_quantum_jr.html
And here http://oellerer.net/infinity_classics/Quantum_Jr/Quantum_Jr_brochure_02.jpg is the added clay
official 'explanation' (see the 12" woofer paragraph):Thanx for the links. I already had both but the effort is appreciated. The brochure makes no mention of clay or any other mass added in and around the voice coil area. I beleive the "special damping treatment" referred to the coating they put on the cone.
As I mentioned earlier, I am quite certain that these are not Infinity woofers. To begin with they are the wrong color. Infinity woofers had black cones till they changed to the opague poly cones which I happen to own a pair of as well.
As I mentioned earlier, I am quite certain that these are not Infinity woofers. To begin with they are the wrong color. Infinity woofers had black cones till they changed to the opague poly cones which I happen to own a pair of as well.
sreten said:
I agree that increased mass can limit midrange output. That seems fairly obvious. I'm not sure that its a good way to do it unless it's tuned close enough to the xover point that it is simply increasing the roll off slope. I have no equip to measure the results so I won't be able to say for certain what it accomplishes in this instance.
I think that it is just as likely that it was done to tune the effiency of the driver. I mean if you can decrease the effiency and most of the the change in tonal quality occurs above xover then that might have been the goal as well.
Without being able to indentify them, and hence the matching cross over design, it's all just guesses ...I guess
I will spend some time listening to them in various states and see what I hear before deciding. I will be trying this on other speakers as well.
I know this is somewhat OT for this thread, but I thought I'd add a little more about cone behavior.
The variables of mass, radiating area, and the frequency-dependant acoustic impedence of the air load have already been mentioned. Also add the variables of bending wave transmission velocity and the degree of horn loading the cone profile provides.
These, along with motor-related damping and inductive rolloff, are what the designers of full-range drivers juggle in their quest for flat on-axis FR.
Basically the ideal is for bending waves to traverse the cone at the speed of sound for ideal coupling to the air. Trouble is, bending wave velocity increases with the square root of frequency. If the bending wave surpasses the speed of sound, beaming and lobing is the result. So engineers settle for trying to keep the wave velocity below the speed of sound over the desired BW. Assuming good cone damping and termination, the wave dissipates as it travels outward from the cone center due to the circumference increase with radius, and the acoustic pressure wave mimics that of an ideal point source (any resonant cone breakup is just due to poory damped cone material).
At higher frequencies where most of the cone area is effectively decoupled and the mass of the VC has become a significant portion of the total moving mass, further cone area decoupling becomes insufficient to keep the mass rolloff behavior from dominating. Provided the bending wave velocity is still below the speed of sound, this is where the cone profile can contribute a degree of horn loading. When that runs out (due to bending wave velocity or horn "throat" dimension becomming too great), a 2nd-order rolloff will dominate.
The variables of mass, radiating area, and the frequency-dependant acoustic impedence of the air load have already been mentioned. Also add the variables of bending wave transmission velocity and the degree of horn loading the cone profile provides.
These, along with motor-related damping and inductive rolloff, are what the designers of full-range drivers juggle in their quest for flat on-axis FR.
Basically the ideal is for bending waves to traverse the cone at the speed of sound for ideal coupling to the air. Trouble is, bending wave velocity increases with the square root of frequency. If the bending wave surpasses the speed of sound, beaming and lobing is the result. So engineers settle for trying to keep the wave velocity below the speed of sound over the desired BW. Assuming good cone damping and termination, the wave dissipates as it travels outward from the cone center due to the circumference increase with radius, and the acoustic pressure wave mimics that of an ideal point source (any resonant cone breakup is just due to poory damped cone material).
At higher frequencies where most of the cone area is effectively decoupled and the mass of the VC has become a significant portion of the total moving mass, further cone area decoupling becomes insufficient to keep the mass rolloff behavior from dominating. Provided the bending wave velocity is still below the speed of sound, this is where the cone profile can contribute a degree of horn loading. When that runs out (due to bending wave velocity or horn "throat" dimension becomming too great), a 2nd-order rolloff will dominate.
Sreten, it appears that you were correct as to the primary purpose of the clay. I have played with these drivers extensively since rebuilding them.
I have come to the conclusion that the clay was not a modification of the driver, but rather was part of the original design. On close inspection it can be seen that both the voice coil and the cone were designed to accept and hold the clay.
The drivers cloud the midrange quite badly with out the clay. As well the bass output is not as tight. On deep organs, kettle drums, etc. the drivers seemed to lose control. With the clay added the drivers are tight, clean and well controlled.
The driver is currently mated with another 12" in a WMTW configuration. Although the resulting speakers is rather large by todays standards I am very pleased with the sound.
I have come to the conclusion that the clay was not a modification of the driver, but rather was part of the original design. On close inspection it can be seen that both the voice coil and the cone were designed to accept and hold the clay.
The drivers cloud the midrange quite badly with out the clay. As well the bass output is not as tight. On deep organs, kettle drums, etc. the drivers seemed to lose control. With the clay added the drivers are tight, clean and well controlled.
The driver is currently mated with another 12" in a WMTW configuration. Although the resulting speakers is rather large by todays standards I am very pleased with the sound.
Well its very difficult to say as you appear to saying these are not
the original drivers for the speakers, so the application they were
designed for remains a mystery.
However its more likely the clay was not part of the original design.
Its more likely a driver was modified with an extended voice coil
former and the clay to suit a new application. As the original
and new applications are not known its still hard to be absolute.
All I'll say for definite is that modifying a 12" drivers parameters
by adding ~ 11g of clay around the voice coil will have a profound
effect on top end response of the driver.
For a 2 way I'd be certain the clay is for response shaping.
For a 3 way its probably changing parameters, but with a
possibly unexpected but beneficial side effect.
Perhaps I should have said the primary effect of the clay.
sreten.
the original drivers for the speakers, so the application they were
designed for remains a mystery.
However its more likely the clay was not part of the original design.
Its more likely a driver was modified with an extended voice coil
former and the clay to suit a new application. As the original
and new applications are not known its still hard to be absolute.
All I'll say for definite is that modifying a 12" drivers parameters
by adding ~ 11g of clay around the voice coil will have a profound
effect on top end response of the driver.
For a 2 way I'd be certain the clay is for response shaping.
For a 3 way its probably changing parameters, but with a
possibly unexpected but beneficial side effect.
Perhaps I should have said the primary effect of the clay.
sreten.Glancing quickly at the Peerless CCC 12" and a Blaupunkt 12" woofer, I get cone mass of 80g and 105g respectively.sreten said:
All I'll say for definite is that modifying a 12" drivers parameters
by adding ~ 11g of clay around the voice coil will have a profound
effect on top end response of the driver.
For a 2 way I'd be certain the clay is for response shaping.
For a 3 way its probably changing parameters, but with a
possibly unexpected but beneficial side effect.
Assuming this about average, adding 11g of clay to a 12" speaker would be increasing the cone mass, (Mms), about 10-15%.
Playing with Bullock and White's BoxModel freeware, which calculates these things, I see that increasing cone mass by 12% lowers sensitivity by 0.7dB, and decreases Fs by about 5%.
If you can smooth midrange performance and give up only 0.7 dB in exchange, most people would call that a very good tradeoff. If you can make the woofer roll off naturally at the high end by doing this, eliminating the need for an electrical crossover on the woofer, most people would call that an even better tradeoff.
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