The faster it goes the more difficult it is to stop and change direction, that I think is fundamental.
At lower SPL its no problem fore a small sub to get as low as the big one, but trouble starts at higher SPL where a small unit must produce very large strokes and begins to get into trouble, and starts to "smear"(if that the right word) - in other words, it starts to get at bit behind and out of control.
Zaph writes about it in some way - he claims that the driver with the shortest voicecoil is always the best sounding, within its limitations.
At lower SPL its no problem fore a small sub to get as low as the big one, but trouble starts at higher SPL where a small unit must produce very large strokes and begins to get into trouble, and starts to "smear"(if that the right word) - in other words, it starts to get at bit behind and out of control.
Zaph writes about it in some way - he claims that the driver with the shortest voicecoil is always the best sounding, within its limitations.
18" Woofers
I use four JBL 2245H 18" woofers in my home theater - they are NOT "slow" as some suggest. Their passband is from 20 Hz to 80 Hz - and my 4th order (24 dB per octave) active crossover is setup that way. I have tried the JBL 2235H (the 15" version) and have found it to be no more FAST than the the 2245H. The 2245H just supplied MORE bass output in the final octave..
I use four JBL 2245H 18" woofers in my home theater - they are NOT "slow" as some suggest. Their passband is from 20 Hz to 80 Hz - and my 4th order (24 dB per octave) active crossover is setup that way. I have tried the JBL 2235H (the 15" version) and have found it to be no more FAST than the the 2245H. The 2245H just supplied MORE bass output in the final octave..
This driver is about 3” and it’s seriously modified, recoiled at .5ohms in a sealed 12mm MDF box it produces very low frequencies that can shake a filing cabinet next to it
http://img208.imageshack.us/my.php?image=cimg33415jf.jpg
http://img208.imageshack.us/my.php?image=cimg33415jf.jpg
Steve, I am not going to apologize for what seems like a long and slow understanding of this issue.
Have you read all the threads on this issue on this forum ? Because I have read most of them and most of them end up with a less-than-clarified conclusions.
Which is why I'm asking questions here. I know that I don't know this very well and I don't like to feel pressurized into just accepting things, but I don't think you should push me into understanding something (something you apparently know far better) because you seem aggitated.
With all these conflicting opinions going around here, how can this issue be very simple ? Simple to whom ?
BTW, SY, I thank you very much for your input. Again, much appreciated, as well as everyone else's contribution. I still don't see how this issue can be as simple as others make it out to be if there are so many conflicting opinions (even on this very site).
--Sincerely,
Have you read all the threads on this issue on this forum ? Because I have read most of them and most of them end up with a less-than-clarified conclusions.
Which is why I'm asking questions here. I know that I don't know this very well and I don't like to feel pressurized into just accepting things, but I don't think you should push me into understanding something (something you apparently know far better) because you seem aggitated.
With all these conflicting opinions going around here, how can this issue be very simple ? Simple to whom ?
BTW, SY, I thank you very much for your input. Again, much appreciated, as well as everyone else's contribution. I still don't see how this issue can be as simple as others make it out to be if there are so many conflicting opinions (even on this very site).
--Sincerely,
The simple part is, a 8" driver CAN be equally fast(velocity) as an 18" driver if the cone excursion and frequency being reproduced are identical. However for the same SPL and frequency the 18" driver will use far less excursion and thus move slower.
The part that is often unclarified is the issue of 'fast bass' and what objective qualitys contribute to it's subjective sound.
The part that is often unclarified is the issue of 'fast bass' and what objective qualitys contribute to it's subjective sound.
Well, how does motor strength factor into this ? Because I've seen a lot of car analogies in this thread and yet I believe these analogies are confusing things even more.
First, in this thread, it was said that if an 18" driver had a magnet assembly of sufficient size compared to an 8" driver, it would be able to move just as quick.
Now we know that we don't even have to have a sufficiently scaled motor to compare with a smaller motor of a smaller diameter driver as long as there is low distortion and it can move enough air needed to reproduce the frequency in question.
But what about current changes ? How does that factor into all of this ? Dan wrote a paper on this but I don't fully understand this.
So now the amplifier plays a big role in "speed", in objective terms ? If an amplifier can supply large amounts of current to the driver, it will have all the "speed" required for dynamic transients ?
Can you explain ?
--Sincerely,
First, in this thread, it was said that if an 18" driver had a magnet assembly of sufficient size compared to an 8" driver, it would be able to move just as quick.
Now we know that we don't even have to have a sufficiently scaled motor to compare with a smaller motor of a smaller diameter driver as long as there is low distortion and it can move enough air needed to reproduce the frequency in question.
But what about current changes ? How does that factor into all of this ? Dan wrote a paper on this but I don't fully understand this.
So now the amplifier plays a big role in "speed", in objective terms ? If an amplifier can supply large amounts of current to the driver, it will have all the "speed" required for dynamic transients ?
Can you explain ?
--Sincerely,
If an 18" driver has a motor structure proportional to that of a beefy 8" driver, then the capability would be there for the 18" cone to move just as fast as the 8" cone. However, since the 18" cone has much more surface area then the 8" cone, for the same amount of movement, the 18" cone will displace more air. To reproduce a given frequency at a given output level, it doesn't have to move as far as the 8" cone in the same amount of time, and thus, it doesn't move as fast. This is incorrectly interpretted by some as "slow bass".....a phrase which doesn't even make sense to begin with. That phrase gives the impression that the 18" driver can't move as fast as it should be moving and it is producing copious amount of distortion - that is false, the 18" driver is moving exactly as fast as it needs to, which for a given frequency and output level, is slower than the 8" driver. The fact of the matter is that the 18" driver is more efficient and it will produce the bass cleaner with less distortion in probably 99% of all implementations.
The amp is an outside variable, I assume the end user has an amp that will be capable enough to handle the 8" or 18" driver adequately. Over at AVS, Ilkka did some testing of a beefy class AB amp vs a digital hybrid BASH amp (with filters in place) powering a sub to play a 20hz sine wave. He was measuring how fast it took the sub to reach full amplitude with the sine wave, and the class AB amp enabled to sub to reach full amplitude in about half the time as the BASH amp. If the amp can supply large amounts of current at the drop of a hat (I believe this is measured as slew rate, not completely sure), then yes, it is one aspect that will help the driver reach full amplitude faster with demanding material. A class AB amp always has some current running through it while it's on, a class A amp always has full current running through it, that's why those types of amps will get warm. A digital amp has little to no current running through it when no signal is present, making it more efficient and allowing it to run cool, but also putting a greater load on it with dynamic peaks. As a poor example, if it were a race, a digital amp always has to start from rest, wheras the class A amp is always in full stride, and the class AB amp is always at a steady jog. Too bad the BASH amp was using filters, otherwise we could have concluded the digital amp wasn't as capable as the class AB amp.....I'm not a fan of digital switching amps for subwoofer use
Starting to make sense?
Steve, thank you ! This is all starting to make sense for me now. One question : if I had an 18" driver with a magnet structure less strong compared to a beefy 8" driver, would the outcome still be that the 18" driver would need far less movement in a given time to reproduce any given low frequency, or could it mean that the 8" driver would need the same amount of time to reproduce that frequency ?
The reason I ask is because just as there are 12" drivers that can outperform 18" drivers in air moving capability, I'm sure there are some 8" drivers that can move more air than 18".
What do you think ? Again, thank you for your explanations.
--Sincerely,
The reason I ask is because just as there are 12" drivers that can outperform 18" drivers in air moving capability, I'm sure there are some 8" drivers that can move more air than 18".
What do you think ? Again, thank you for your explanations.
--Sincerely,
I don't think discussing different types of speakers' ability to 'accelerate' is the issue here. A manufacturer of any decent driver will ensure the motor assembly is capable of doing the job.
I mentioned this earlier, but it seemed to go unnoticed:
We don't need to prove this with mathematics - it is already a well accepted fact:
The main benefit with large drivers is that they have an inherently better accoustical match to the environment.
Illustration:
Blow air quickly in and out of your mouth - there are negligable infrasound waves launched.
If, however, you were able to move a 20 metre square panel back and forth at the same frequency, displacing the same amount of air as you did with your mouth, a significant wave would be launched.
Liken this to the comparison between an 8" driver and an 18" one. The differences aren't as extreme as in my example, but still exist.
The main disadvantage with a large driver is the resonance of the air mass enclosed within the large cone, which can apparently cause colouration. This, I believe, is one of the main reasons why hi-fi manufacterers avoid large drivers.
PA driver manufacturers however recognise the efficiency of larger drivers and 18" is the norm for high output bass units.
I mentioned this earlier, but it seemed to go unnoticed:
We don't need to prove this with mathematics - it is already a well accepted fact:
The main benefit with large drivers is that they have an inherently better accoustical match to the environment.
Illustration:
Blow air quickly in and out of your mouth - there are negligable infrasound waves launched.
If, however, you were able to move a 20 metre square panel back and forth at the same frequency, displacing the same amount of air as you did with your mouth, a significant wave would be launched.
Liken this to the comparison between an 8" driver and an 18" one. The differences aren't as extreme as in my example, but still exist.
The main disadvantage with a large driver is the resonance of the air mass enclosed within the large cone, which can apparently cause colouration. This, I believe, is one of the main reasons why hi-fi manufacterers avoid large drivers.
PA driver manufacturers however recognise the efficiency of larger drivers and 18" is the norm for high output bass units.
Excellent points, Andy. Although I don't understand what you mean with large drivers having resonance problems because of the air mass trapped in the cone. Not too sure what you mean. Perhaps you can elaborate ?
Concerning the better acoustical match with larger drivers, that is because they have a better impedence match to air. Correct ?
--Sincerely,
Concerning the better acoustical match with larger drivers, that is because they have a better impedence match to air. Correct ?
--Sincerely,
Hi,
I'm not sure the Hi-Fi manufacturers know either.
Yes, they strive for the best quality they can achieve in their respective price band, but they have, in general, sacrificed all semblance of efficiency by selecting smaller drivers to try to keep the speakers at an acceptable size (and probably other sound reasons). Although in the last decade they have managed, by design and better driver understanding, to get back some of that lost efficiency.
There does seem to be a correlation between small displacement distances (not displacement volume) and distortion. It so happens that small displacement goes hand in hand with efficiency for a particular SPL. Could it be that the true correlation is efficiency vs distortion, or is that stretching things too far?
For that first reference to "best quality" you can substitute "most profit per unit" if you are so inclined.
I'm not sure the Hi-Fi manufacturers know either.
Yes, they strive for the best quality they can achieve in their respective price band, but they have, in general, sacrificed all semblance of efficiency by selecting smaller drivers to try to keep the speakers at an acceptable size (and probably other sound reasons). Although in the last decade they have managed, by design and better driver understanding, to get back some of that lost efficiency.
There does seem to be a correlation between small displacement distances (not displacement volume) and distortion. It so happens that small displacement goes hand in hand with efficiency for a particular SPL. Could it be that the true correlation is efficiency vs distortion, or is that stretching things too far?
For that first reference to "best quality" you can substitute "most profit per unit" if you are so inclined.
The 18" driver would still only need to move some fraction of the distance the 8" driver would - that realtionship is static.
Now if comparing two 18" driver with the same size cone in the same size enclosure, one with a vert strong and efficient motor and the other with a weak, less efficient motor, it will take less power for the the more efficient motor to move the cone the SAME amount of distance as the less efficient motor. So in the end, while the two driver would be displacing the same amount of air, and both cones would be traveling the same distance, the more efficient motor could do it with say 16 watts while it might take 128 watts for the less efficient motor.
This comes down to excursion. The 8" cone has a certain amount of surface area and the 18" cone will have a certain amount more surface area - depending on how far the cones can travel, you can figure out their air-moving capability. I don't think there is any real case in which an existing 8" driver can displace more air than an existing 18" driver - by giving an 8" driver as much excursion as it would need to move more air than an 18" driver, you are getting a lot of negative side effects as a result. Manufacturers would just move up to a larger size driver.
Looky, Looky, Looky...
It might not be an 18" but they are sweet looking.
http://www.partsexpress.com/webpage.cfm?&WebPage_ID=3&filter=rss390h&raid=25&rak=Day15&wt.sv1
It might not be an 18" but they are sweet looking.
http://www.partsexpress.com/webpage.cfm?&WebPage_ID=3&filter=rss390h&raid=25&rak=Day15&wt.sv1
Re: Looky, Looky, Looky...
I had no idea 15" versions were being produced. Nice find!J.k.Wilson said:
Eva Referencing page 13 where you said
...As acceleration is just force/mass :
a = (I*BL/M) * sin (wt)
Where (I*BL/M) is a constant that does not depend on frequency, thus acceleration is not frequency dependent, it only depends on the amplitude of the input signal.
'I' is the current through the vc caused by voltage from the amp, this current is not constant. The higher the frequency the higher the slew rate(am I saying this right). If we assume a constant amplitude and frequency then 'I' will follow a sinusoidal form and I*BL/M will vary with both time and frequency.
Unless Im missing something again.😀
...As acceleration is just force/mass :
a = (I*BL/M) * sin (wt)
Where (I*BL/M) is a constant that does not depend on frequency, thus acceleration is not frequency dependent, it only depends on the amplitude of the input signal.
'I' is the current through the vc caused by voltage from the amp, this current is not constant. The higher the frequency the higher the slew rate(am I saying this right). If we assume a constant amplitude and frequency then 'I' will follow a sinusoidal form and I*BL/M will vary with both time and frequency.
Unless Im missing something again.😀
Re: The Ascendant Alliance 18" driver, I used Martin King's mathcad worksheet to figure out a pretty good design (in terms of very low frequency response).
Theoretically, you can reach 10Hz at about 82db before equalization with a 120" long Transmission line.
Alternatively, you can change the port size and maintain 90db down to about 15Hz.
And this is without room gain added in....
Theoretically, you can reach 10Hz at about 82db before equalization with a 120" long Transmission line.
Alternatively, you can change the port size and maintain 90db down to about 15Hz.
And this is without room gain added in....
http://www.mtxaudio.com/caraudio/products/subwoofers/jackHammer.cfm
Check this out. 6000 watts.
Dominick
Check this out. 6000 watts.
Dominick
john, if that driver ever comes out, and it lives up to its specs, it can do much better than that. A ~700 liter enclosure with a ~13.5hz tuning using an 8" diameter port will behave pretty similarly to my Avalanche 18 sub.
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