http://cgi.ebay.com/ebaymotors/NEW-...ewItemQQcategoryZ38647QQitemZ8043182458QQrdZ1
Here check these out, for the price they should be fun to play with. Later
Here check these out, for the price they should be fun to play with. Later
The whole thing about 18" drivers being "slower" due to "increased moving mass" is definitely B.S. because the moving mass of almost all 18" PA drivers is just between 100 and 150 grams, while the moving mass of most exotic Hi-Fi 10", 12" and 15" subs that are routinely mentioned in that forun is in the 150 to 300 gram range.
In my opinion, the slow thing are all those Hi-Fi subs, because the extremely high moving mass together with the high coil inductance and the low BL products prevent them from playing anything except awful *rumble* due to mass roll-off and very poor electrical damping. Also, 18" PA drivers are useable up to much higher frequencies than Hi-Fi subs, they may be happily crossed over at 250hz directly with the midrange (producing dip-free sub-bass and bass at the same time), while this approach does not work for heavy Hi-Fi subs at all.
Furthermore, any physics book will tell us that given the same driver and SPL output:
- Cone displacement is proportional to 1/freq^2 (a widely known fact).
- Cone velocity is proportional to 1/freq (velocity is the derivative of displacement!!).
- Cone acceleration is constant regardelsss of the frequency (acceleration is the derivative of velocity), and its value is given by a=force/mass.
Thus, the higher the frequency, the slower the cone has actually to move!!! Being the lower frequencies the ones that require greater cone speeds!!!
Indeed, those that talk about speaker "velocity" and "speed" doesn't usually have a clue about physics. Also, anyone that has worked with horn-loaded 15" and 18" drivers in PA knows that these arrangements can produce far louder and cleaner "fast-punch" bass (in the 80Hz to 400Hz range) than any heavy Hi-Fi direct-radiator.
p.s.: From time to time, I'm asked to design and tune low frequency enclosures of all kinds (sealed, reflex, 4th/6th band-pass, horns) and by now I have had to face almost every kind of existing driver due to market trends and customer tastes (actually I'm seldom allowed to chose driver). So far, my favourite drivers are the low moving-mass high efficiency paper cone PA-like ones.
In my opinion, the slow thing are all those Hi-Fi subs, because the extremely high moving mass together with the high coil inductance and the low BL products prevent them from playing anything except awful *rumble* due to mass roll-off and very poor electrical damping. Also, 18" PA drivers are useable up to much higher frequencies than Hi-Fi subs, they may be happily crossed over at 250hz directly with the midrange (producing dip-free sub-bass and bass at the same time), while this approach does not work for heavy Hi-Fi subs at all.
Furthermore, any physics book will tell us that given the same driver and SPL output:
- Cone displacement is proportional to 1/freq^2 (a widely known fact).
- Cone velocity is proportional to 1/freq (velocity is the derivative of displacement!!).
- Cone acceleration is constant regardelsss of the frequency (acceleration is the derivative of velocity), and its value is given by a=force/mass.
Thus, the higher the frequency, the slower the cone has actually to move!!! Being the lower frequencies the ones that require greater cone speeds!!!
Indeed, those that talk about speaker "velocity" and "speed" doesn't usually have a clue about physics. Also, anyone that has worked with horn-loaded 15" and 18" drivers in PA knows that these arrangements can produce far louder and cleaner "fast-punch" bass (in the 80Hz to 400Hz range) than any heavy Hi-Fi direct-radiator.
p.s.: From time to time, I'm asked to design and tune low frequency enclosures of all kinds (sealed, reflex, 4th/6th band-pass, horns) and by now I have had to face almost every kind of existing driver due to market trends and customer tastes (actually I'm seldom allowed to chose driver). So far, my favourite drivers are the low moving-mass high efficiency paper cone PA-like ones.
let me read this again
Thus, the higher the frequency, the slower the cone has actually to move!!!
I don't get it, your saying that a cone vibrating at 100Hz moves slower than 10Hz?
Thus, the higher the frequency, the slower the cone has actually to move!!!
I don't get it, your saying that a cone vibrating at 100Hz moves slower than 10Hz?
Hayden said:
Exactly. Consider that the cone has to travel 100 times more distance at 10Hz than at 100Hz, but the time available to complete such displacement is only 10 times higher, so the speed has to be another 10 times higher. It's elemental physics.
Eva said:
That is the tried and tested recipy for woofers and most people will agree with you.
You sound like a smart person Eva so help me out here as my maths is like weak root beer.
The reason I think hi-fi woofers have heavy cones is to get the Fs down to the low notes like 25Hz, they normally have all the 100Hz signal quite flat from the main speakers, anybody agree?
The only thing I believe worth a mention is the direction change or TDC and BDC of the cone, if a woofer cone has to change dirrection 100 times a second and the excursion is say 3mm this creates just as much stress as a cone moving at 20mm at 50Hz , this stress deforms the cone in different ways, i believe this is why so many large cones have eccentric ribs to brace the cone, anyway,,
Cones do not travel 100 times more at those frequencies your talking about?, 2F = E/4 is this correct?
At 200Hz lets say we have 2mm excursion and at 20Hz we have 20mm excursion, this is more realistic i think?, there is a relationship between freq and excursion, you can not get 20mm excursion at 200Hz as the mass of the cone would increase to much because of the cone travel and speed, so the cone can only travel 2mm maybe less if it wants to stay together i think.
I always thought of a woofer as just a mass accelerator, with small variables in the design that changes the sound quality?
Am i wrong?
Before entering deeper considerations, you have to understand that if a direct radiator has to move 10mm to produce 90dB SPL at 20Hz, it will have to move 0.1mm to produce the same SPL at 200Hz. Air "stiffness" is proportional to frequency, and wave lenght is inversely proportional to frequency, these are the two facts that yield a quadratic relationship between cone displacement and frequency. It's actually the air who asks for 100 times less cone displacement to get the same SPL at 200Hz.
This is how things work when operating conditions are the same, and the only way to alter the quadratic relationship is to create frequency-dependent operating conditions, such as what happens in reflex or horn-loaded systems.
This is how things work when operating conditions are the same, and the only way to alter the quadratic relationship is to create frequency-dependent operating conditions, such as what happens in reflex or horn-loaded systems.
Here's an article about the 60" subwoofer...
http://www.digitalgrabber.com/audio/the_60_inch_subwoofer.html
http://www.digitalgrabber.com/audio/the_60_inch_subwoofer.html
I guess if you put it in a ported box it would throw massive amounts of air at low frequencies around say 10Hz 
Hayden said:I guess if you put it in a ported box it would throw massive amounts of air at low frequencies around say 10Hz
That's pretty much the frequency it was operating at anyway (10-15hz) If there ever was a sub to test the "brown note myth" this is it 😀
Hi everyone,
I am also fascinated with this topic. I made a thread at HTF in the speaker section dealing with this topic. There are some things that are confusing me.
My manager at work told me that an 18" driver would never be able to move as quickly as a 12" driver. And that for simulated effects, like explosions, an 18" driver would not move fast enough.
It would move too much air which would mean that it would be too slow. Now I understand that he was wrong for a simple reason. He left out BL motor strength. You could move a 50" driver as quickly as an 8" driver provided it has a stiff enougn suspension and an appropriate motor assembly.
I understand that. But I hear some people on HTF saying that mass doesn't effect the bass range that the drivers are working in. I do not doubt their advise but I don't understand it and it's confusing me.
I hear some people here and on HTF make the same car analogies. And they make perfect sense. But then I also get people telling me that the mass isn't even the problem either. That in the drivers respective bassband, both drivers would accelerate the same, regardless of mass.
This is what is confusing me. If the mass isn't the issue then why do people even use the car analogy if it's a nonissue to begin with ?
I really need someone to clear up this confusion. Thank you !
--Sincerely,
I am also fascinated with this topic. I made a thread at HTF in the speaker section dealing with this topic. There are some things that are confusing me.
My manager at work told me that an 18" driver would never be able to move as quickly as a 12" driver. And that for simulated effects, like explosions, an 18" driver would not move fast enough.
It would move too much air which would mean that it would be too slow. Now I understand that he was wrong for a simple reason. He left out BL motor strength. You could move a 50" driver as quickly as an 8" driver provided it has a stiff enougn suspension and an appropriate motor assembly.
I understand that. But I hear some people on HTF saying that mass doesn't effect the bass range that the drivers are working in. I do not doubt their advise but I don't understand it and it's confusing me.
I hear some people here and on HTF make the same car analogies. And they make perfect sense. But then I also get people telling me that the mass isn't even the problem either. That in the drivers respective bassband, both drivers would accelerate the same, regardless of mass.
This is what is confusing me. If the mass isn't the issue then why do people even use the car analogy if it's a nonissue to begin with ?
I really need someone to clear up this confusion. Thank you !
--Sincerely,
Anyone ?
I also found out from one knowledgeable poster that acceleration is proportional to SPL. So an 18" driver will be able to accelerate as quickly in it's passband compared to a 12" driver because it requires less excursion to reach the desired input level.
The longer it takes for the voice coil (in a 12") to reach the required acceleration to react to the input signal because it moves less air compared to the bigger 18" driver. So, this means that the 18" will be able to move just as quick or quicker in this case.
Is that correct ? Does it sound correct ? But then what of BL ? And how does that factor into this ? If mass isn't important here then the BL motor force isn't as important as what we thought because if both low mass and high mass drivers aren't required to move quickly to reproduce the input signal at low frequencies then what benefit would there be to have more "horsepower" ?
--Sincerely,.
I also found out from one knowledgeable poster that acceleration is proportional to SPL. So an 18" driver will be able to accelerate as quickly in it's passband compared to a 12" driver because it requires less excursion to reach the desired input level.
The longer it takes for the voice coil (in a 12") to reach the required acceleration to react to the input signal because it moves less air compared to the bigger 18" driver. So, this means that the 18" will be able to move just as quick or quicker in this case.
Is that correct ? Does it sound correct ? But then what of BL ? And how does that factor into this ? If mass isn't important here then the BL motor force isn't as important as what we thought because if both low mass and high mass drivers aren't required to move quickly to reproduce the input signal at low frequencies then what benefit would there be to have more "horsepower" ?
--Sincerely,.
Its all simple calculus.
Acceleration is NOT the only factor in SPL
cone velocity is NOt the only factor in SPL
dv/dt I believe is
Acceleration is NOT the only factor in SPL
cone velocity is NOt the only factor in SPL
dv/dt I believe is
Mark Seaton believes that acceleration is a function of SPL. Is he wrong ?
Just asking. And I also would like to know something. Amplifier damping factor. Is it as important as we are led to believe ? Or is the mechanical damping of the suspension of the driver more important ?
My manager always harps on the fact that the amplifier in the speaker controls the abilitiy for it to stop and start. Is he correct on this ? Some advise would be appreciated.
--Sincerely,
Just asking. And I also would like to know something. Amplifier damping factor. Is it as important as we are led to believe ? Or is the mechanical damping of the suspension of the driver more important ?
My manager always harps on the fact that the amplifier in the speaker controls the abilitiy for it to stop and start. Is he correct on this ? Some advise would be appreciated.
--Sincerely,
I'll do some work on this in my spare time and try to get this entire subject condensed into a few equations. Basically though The derivitive of position with respect to time will be velocity, and the derivitive of velocity with respect to time will be acceleration.
SPL will be equal to the derivitive of pressure with respect to time(I think) which will be related to the volume displacement
Looks like its time to get out the old physics book again
SPL will be equal to the derivitive of pressure with respect to time(I think) which will be related to the volume displacement
Looks like its time to get out the old physics book again
BassAwdyO said:
This quote is the best proof that people talking about 18 inch driver "speed" does not have a clue about physics.
dv/dt is the mathematical expression of acceleration
There are two reasons why bigger drivers have more trouble playing higher frequencies:
- Propagation of mechanical energy from the voice coil to the outer perimeter of the cone is not instantaneous, it takes some finite time to happen and is subject to reactive mechanical characteristics of cone materials (energy storage and resonances). Given the same cone material and construction, the bigger the cone diameter the least coherent cone movement will be (and more self-cancellation will hapen at high frequencies due to phase differences between cone regions). Indeed, one of the reasons for diaphragms to be cone shaped is to provide some phase lead to the radiation from the outer perimeter and compensate a bit propagation delays.
However, all these mechanical phenomena are highly dependent on cone material technology, so you may as well find some cleverly designed 18" cones that self-filter, thus preventing the outer regions of the cone from even receiving high frequency energy. PA drivers and some full-range gems are a good example of that, while Hi-Fi subwoofers cones are terrible (very heavy and with very slow energy propagation).
- Off-axis radiation depends stongly on cone diameter and on the effective diameter of the region of the cone that is actually radiating at each frequency (remember self-filtering effects that may prevent HF to reach outer cone perimeter). In principle this means that drivers with higher cone diameters are going to be more directive at higher frecuencies (due to self cancellation of the out-of-phase radiation coming from different places of the cone), but this is usually circumvented with self-filtering (again), making the radiation pattern highly dependent on cone technology.
As I have previously pointed out, speed is not an issue because it is actually much higher for lower frequencies. Acceleration isn't the problem because it is *not* frequency dependent. Moving mass is also not an issue because it only lowers efficiency and the said "mass rolloff point" (that is just a harmless mechanical low-pass filter), but this is easily compensated with higher BL and higher radiation surface (yielding most bigger drivers more efficient, or how else could some PA 18" produce 100dB/W at 1Khz???).
OOps
Damn can I be stupid... By Dv/Dt I meant displaced volume with respect to time, not the derivative of velocity. I guess I should have written dDV/dt(And defined DV)
We are in the subwoofer forum here, 1khz doesnt matter a bit, neither do dispersion patterns.
Speakers are indeed very complex mathematical workings with a huge number of variables. Basically when it all boils down though, a 18" driver will move less to produce the same SPL at the same frequency than any speaker with a smaller radiating surface. Therefore the cone will have a lower peak velocity and less acceleration.
If the cone were just as light, and just as rigid, and the suspension had the same compliance, and with the same motor, we could make some simple models, but the real world isnt like this...
Damn can I be stupid... By Dv/Dt I meant displaced volume with respect to time, not the derivative of velocity. I guess I should have written dDV/dt(And defined DV)
We are in the subwoofer forum here, 1khz doesnt matter a bit, neither do dispersion patterns.
Speakers are indeed very complex mathematical workings with a huge number of variables. Basically when it all boils down though, a 18" driver will move less to produce the same SPL at the same frequency than any speaker with a smaller radiating surface. Therefore the cone will have a lower peak velocity and less acceleration.
If the cone were just as light, and just as rigid, and the suspension had the same compliance, and with the same motor, we could make some simple models, but the real world isnt like this...
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