This is correct. Sound compression and rarefaction is purely a mechanical phenomenon.
It is an interesting topic, suggest starting a thread for this discussion?
_-_-bear
Hi
I would agree with much / most of what you say, the differences being mostly a different way of seeing how the driver properties tie together.
How a loudspeaker driver works can be explained in great detail but rarely does one hear discussion of how sound works and what a driver really does. I like to say so far as size and time, sound is something like a set of Russian dolls, the traditionally smallest one (20KHz) only 5/8 inch tall while the largest at 20Hz is 1000 times large. You see this volume relationship with woofers, if you want the same sensitivity but an octave lower corner F, it requires you cube the volume not double it.
If you lower the corner frequency an octave but keep the size the same, the sensitivity goes down 9dB.
A lower frequency is larger in wavelength and naturally takes a longer time too.
For that reason, when looking at an event covering a wide bandwidth, time is often not a good frame of reference as the natural period for any event is directly related to frequency.
For example, some foam about subwoofer group delay without considering that any response feature always occupies twice the time if it happens an octave lower, that is to say a large GD is part of a low frequency response corner. In fact the phase response is locked into the amplitude response, any change in one causes the change in the other.
Conversely, a better way to view these things would scale the Russian dolls to the same size so that only deviations from the design are shown, like Cumulative burst decay or in wavelets. Here what would be ime is now related to the wavelength or period (like phase) for that particular frequency.
You thoughts about pistonic motion are mostly right, nothing in infinitely stiff so nothing is absolutely ridged. Conversely, when operating as a piston radiator, when a small fraction of a wavelength across, then the small amount of flex is averaged out as total displacement. In a high pressure design like some at work, the flexure of the cone is visible as an un-accounted for compliance between the horn and driver.
Cone breakup (and any other sharp resonance driven by the system) is really bad! Breakup magnitude relative to that below is sort of a radiator badness indicator.
The drivers motor is the primary distortion generator, the nonlinearity between the signal Voltage and motion. If one had a breakup that was say 20dB tall at 3KHz, then one might be tempted to think, ‘I can cross that out at 1500 with a 96dB /oct crossover and all is well. Yes, when you measure the response the effect of the breakup is not visible, cool!.
Do a distortion tracking measurement and you see that there is a large mound of 3rd harmonic at 1KHz, a similar mound of 4th harmonic at 750Hz and at every submultiple of the mound at 3K, that same resonant gain is applied to the existing motor nonlinearity and that harmonic and raise about 100X or 20dB.
When a woofer is acoustically small even what it does may not be obvious.
For example, what is known for sure is that if you put a microphone or pressure transducer inside a sealed box enclosure with a woofer mounted, one see’s that the internal pressure is directly related to the driver excursion at any frequency (where the enclosure is small compared to the wavelength).
In the range where one is in the box roll off (-12dB/oct) one finds that the driver excursion does not increase as the frequency falls, -12 dB per octave is a constant displacement slope.
Yet, if one monitors the internal microphone, one see’s flat response and a square wave in equals a square wave pressure what gives????
If you wanted such a woofer to produce a flat response externally, one needs to have the excursion increase by four times each time you go down an octave. This is to offset the changing radiation resistance which has a radiator size term relative to the wavelength look into radiator. With that requirement, what does the excursion look like required to produce a square wave now?
This is a constant acceleration response. Here it is the moving mass and the current to force transduction, in series with it’s Rdc makes it an acceleration device. That is why / how one can add mass to a given driver’s motor and NOT have an effect on it’s attack, speed of response step response or whatever measure of time one would apply. It is already controlled by mass, adding more only lowers the main resonance F and the efficiency etc. Conversely, the reason why large massive woofers do not respond quickly is because they have a larger motor which has more series inductance and this is what rolls the response off / slows its rise time.
Like the Russian dolls again, drivers can be suited to a frequency range, a big slow subwoofer driver maybe perfect doing that job even being slow because everything coming out of the low pass crossover IS slow.
You are concerned with an issues near to my heart, also the Manger is a driver I have had some time to play with and measure. In time response, it is the best driver I have ever measured, it occupies one point in time, over a very broad band and radiates as a simple source. AS you suggest it REALLY needs to be crossover over in the lower mid as it’s harmonic distortion skyrockets even at 1w @ 200Hz.
Understand what it does, it radiates a very simple portion of a sphere (read my other post about disappearing), it does that by producing a disturbance at the center which radiates outward at the speed of sound in air and then is absorbed. From that standpoint, it is conceptually similar to a Quad ESL-63 which constructs a portion of a spherical radaiton with sequential rings of ess radiators.
Our Synergy horns produce this also but by producing the high frequencies at the apex of a conical horn and progressively adding the mid and lower frequencies in time with the wavefront as it progresses forward (compensating for the order they emerge form the crossover) radiating a spherical segment that appears to have been from one source at the apex.
One thing that is required to act like a single source like the manger is the drivers acoustic phase must be around zero degrees over a broad band and the Manger does that and will reproduce a nice square wave. A woofer with flat response can’t do that until way above the low corner because of it’s acoustic phase.
Anyway, some random thoughts, time for turkey Phase II.
Best,
Tom
I would agree with much / most of what you say, the differences being mostly a different way of seeing how the driver properties tie together.
How a loudspeaker driver works can be explained in great detail but rarely does one hear discussion of how sound works and what a driver really does. I like to say so far as size and time, sound is something like a set of Russian dolls, the traditionally smallest one (20KHz) only 5/8 inch tall while the largest at 20Hz is 1000 times large. You see this volume relationship with woofers, if you want the same sensitivity but an octave lower corner F, it requires you cube the volume not double it.
If you lower the corner frequency an octave but keep the size the same, the sensitivity goes down 9dB.
A lower frequency is larger in wavelength and naturally takes a longer time too.
For that reason, when looking at an event covering a wide bandwidth, time is often not a good frame of reference as the natural period for any event is directly related to frequency.
For example, some foam about subwoofer group delay without considering that any response feature always occupies twice the time if it happens an octave lower, that is to say a large GD is part of a low frequency response corner. In fact the phase response is locked into the amplitude response, any change in one causes the change in the other.
Conversely, a better way to view these things would scale the Russian dolls to the same size so that only deviations from the design are shown, like Cumulative burst decay or in wavelets. Here what would be ime is now related to the wavelength or period (like phase) for that particular frequency.
You thoughts about pistonic motion are mostly right, nothing in infinitely stiff so nothing is absolutely ridged. Conversely, when operating as a piston radiator, when a small fraction of a wavelength across, then the small amount of flex is averaged out as total displacement. In a high pressure design like some at work, the flexure of the cone is visible as an un-accounted for compliance between the horn and driver.
Cone breakup (and any other sharp resonance driven by the system) is really bad! Breakup magnitude relative to that below is sort of a radiator badness indicator.
The drivers motor is the primary distortion generator, the nonlinearity between the signal Voltage and motion. If one had a breakup that was say 20dB tall at 3KHz, then one might be tempted to think, ‘I can cross that out at 1500 with a 96dB /oct crossover and all is well. Yes, when you measure the response the effect of the breakup is not visible, cool!.
Do a distortion tracking measurement and you see that there is a large mound of 3rd harmonic at 1KHz, a similar mound of 4th harmonic at 750Hz and at every submultiple of the mound at 3K, that same resonant gain is applied to the existing motor nonlinearity and that harmonic and raise about 100X or 20dB.
When a woofer is acoustically small even what it does may not be obvious.
For example, what is known for sure is that if you put a microphone or pressure transducer inside a sealed box enclosure with a woofer mounted, one see’s that the internal pressure is directly related to the driver excursion at any frequency (where the enclosure is small compared to the wavelength).
In the range where one is in the box roll off (-12dB/oct) one finds that the driver excursion does not increase as the frequency falls, -12 dB per octave is a constant displacement slope.
Yet, if one monitors the internal microphone, one see’s flat response and a square wave in equals a square wave pressure what gives????
If you wanted such a woofer to produce a flat response externally, one needs to have the excursion increase by four times each time you go down an octave. This is to offset the changing radiation resistance which has a radiator size term relative to the wavelength look into radiator. With that requirement, what does the excursion look like required to produce a square wave now?
This is a constant acceleration response. Here it is the moving mass and the current to force transduction, in series with it’s Rdc makes it an acceleration device. That is why / how one can add mass to a given driver’s motor and NOT have an effect on it’s attack, speed of response step response or whatever measure of time one would apply. It is already controlled by mass, adding more only lowers the main resonance F and the efficiency etc. Conversely, the reason why large massive woofers do not respond quickly is because they have a larger motor which has more series inductance and this is what rolls the response off / slows its rise time.
Like the Russian dolls again, drivers can be suited to a frequency range, a big slow subwoofer driver maybe perfect doing that job even being slow because everything coming out of the low pass crossover IS slow.
You are concerned with an issues near to my heart, also the Manger is a driver I have had some time to play with and measure. In time response, it is the best driver I have ever measured, it occupies one point in time, over a very broad band and radiates as a simple source. AS you suggest it REALLY needs to be crossover over in the lower mid as it’s harmonic distortion skyrockets even at 1w @ 200Hz.
Understand what it does, it radiates a very simple portion of a sphere (read my other post about disappearing), it does that by producing a disturbance at the center which radiates outward at the speed of sound in air and then is absorbed. From that standpoint, it is conceptually similar to a Quad ESL-63 which constructs a portion of a spherical radaiton with sequential rings of ess radiators.
Our Synergy horns produce this also but by producing the high frequencies at the apex of a conical horn and progressively adding the mid and lower frequencies in time with the wavefront as it progresses forward (compensating for the order they emerge form the crossover) radiating a spherical segment that appears to have been from one source at the apex.
One thing that is required to act like a single source like the manger is the drivers acoustic phase must be around zero degrees over a broad band and the Manger does that and will reproduce a nice square wave. A woofer with flat response can’t do that until way above the low corner because of it’s acoustic phase.
Anyway, some random thoughts, time for turkey Phase II.
Best,
Tom
Great post, thanks!
Hi Tom,
Thanks so much Tom there is lots of great info in your reply, I will take a day to digest it and hopefully come back with some worthwhile ideas to explore further.
Thanks Bear, I will start a new thread for this and please contribute if you have time, your opinon also is a good'un!
Cheers
Derek.
Hi Tom,
Thanks so much Tom there is lots of great info in your reply, I will take a day to digest it and hopefully come back with some worthwhile ideas to explore further.
Thanks Bear, I will start a new thread for this and please contribute if you have time, your opinon also is a good'un!
Cheers
Derek.
in this case I start a similar topic:
http://www.diyaudio.com/forums/mult...8535-ess-amt-beymas-tpl-150h.html#post4191426
http://www.diyaudio.com/forums/mult...8535-ess-amt-beymas-tpl-150h.html#post4191426
Additional supplement: detailed datasheet from Fostex brochure:
Attachments
I was working on the thread title.
FWIW, I have 2 15"/ch each with 14mm Xmax to 60Hz LR8.
"Nope, not at all. "
You can't hear (or it doesn't bother you listening to gargling sounds).
One decade of coverage (3.3 octaves) at 5.5mm cone excursion cause about 3% frequency modulation distortion. Its strictly a function of the square of the bandwith in octaves, and how far the cone moves. It's also independent of cone diameter (although bigger cones play louder for a given excursion).
You can't hear (or it doesn't bother you listening to gargling sounds).
One decade of coverage (3.3 octaves) at 5.5mm cone excursion cause about 3% frequency modulation distortion. Its strictly a function of the square of the bandwith in octaves, and how far the cone moves. It's also independent of cone diameter (although bigger cones play louder for a given excursion).
Hi bear,
I've found the large surface area combined with high BL and low MMS as Tom mentioned to sound to best to my ears. Your requirement for 50Hz makes it extremely tough to find a reasonable driver. I only have direct experience with a couple of drivers.
Kappa Pro 15A ported, datasheet is pretty close to my measurements and high MMS to BL ratio, but large enclosure. Does not have the cone peaking on upper pass band. Midrange sounds dynamic.
15TBX100 has less ratio but might not sound dynamic enough for you. I found the 15TBX100 to sound as dynamic as the 18" goldwood open baffle H-Frame suggested by Martin King though. That is the extent of my direct listening/comparision for 15" drivers. All of the pro drivers are night and day difference to the high mass low BL drivers to my ears.
I'm moving to BC 12MH32 and taking it down to 100Hz as I could not find a driver that had high ratio that went much below 100Hz.
Hope you check back in when you have made your choice. I'd like to hear the AE drivers but too expensive for me.
I've found the large surface area combined with high BL and low MMS as Tom mentioned to sound to best to my ears. Your requirement for 50Hz makes it extremely tough to find a reasonable driver. I only have direct experience with a couple of drivers.
Kappa Pro 15A ported, datasheet is pretty close to my measurements and high MMS to BL ratio, but large enclosure. Does not have the cone peaking on upper pass band. Midrange sounds dynamic.
15TBX100 has less ratio but might not sound dynamic enough for you. I found the 15TBX100 to sound as dynamic as the 18" goldwood open baffle H-Frame suggested by Martin King though. That is the extent of my direct listening/comparision for 15" drivers. All of the pro drivers are night and day difference to the high mass low BL drivers to my ears.
I'm moving to BC 12MH32 and taking it down to 100Hz as I could not find a driver that had high ratio that went much below 100Hz.
Hope you check back in when you have made your choice. I'd like to hear the AE drivers but too expensive for me.
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