No one mentioned about the proportion issue in nature.
In general, area increases in proportion to the square of length (of one side, if the enlargement is happening in both x and y directions). And then the volume increases in proportion to the cube of length (of one side, again).
For the same material (density), the mass is in proportion to the volume. So the mass increases much faster than the single dimension length, it's the power of 3. That's about the proportion of the strength needed for supporting a larger stuff by itself.
And that's why an elephant has to be so much stronger and bigger than a deer in its skeleton and muscle, or it would collapse on itself. Not to mention why it can not make a turn as sharp as a cheeta can.
And, how terrible is that if it can!? Imagine an 18-wheeler can stop as quickly as an F1, than how could we judge the safety when crossing the street? The driver of that 18-wheeler would say, don't worry, it's not going fast so I can stop this thing in the last several meters in front of you. Can you comfortably believe that?
Of course not, it's just against the nature.
So, bigger drivers must be slower than those smaller one if all other things being equal. Period. Nothing wrong about that. One can argue that 18s can be made of lighter cone and stronger motor etc to be 'fast'. Funny that the same thing can be done in 15s, so 15s win again (in acting faster). It's endless and meaningless.
It's all about compromises for the applications. So 18s also don't have to be sorry for its slowness. Actually we need that slowness all the time !!
Someone please give me a veeerryy slow woofer, say, slow as 10Hz... 😀
In general, area increases in proportion to the square of length (of one side, if the enlargement is happening in both x and y directions). And then the volume increases in proportion to the cube of length (of one side, again).
For the same material (density), the mass is in proportion to the volume. So the mass increases much faster than the single dimension length, it's the power of 3. That's about the proportion of the strength needed for supporting a larger stuff by itself.
And that's why an elephant has to be so much stronger and bigger than a deer in its skeleton and muscle, or it would collapse on itself. Not to mention why it can not make a turn as sharp as a cheeta can.
And, how terrible is that if it can!? Imagine an 18-wheeler can stop as quickly as an F1, than how could we judge the safety when crossing the street? The driver of that 18-wheeler would say, don't worry, it's not going fast so I can stop this thing in the last several meters in front of you. Can you comfortably believe that?
Of course not, it's just against the nature.
So, bigger drivers must be slower than those smaller one if all other things being equal. Period. Nothing wrong about that. One can argue that 18s can be made of lighter cone and stronger motor etc to be 'fast'. Funny that the same thing can be done in 15s, so 15s win again (in acting faster). It's endless and meaningless.
It's all about compromises for the applications. So 18s also don't have to be sorry for its slowness. Actually we need that slowness all the time !!
Someone please give me a veeerryy slow woofer, say, slow as 10Hz... 😀
I think you are looking at it backwards
you seem to forget the obvious
namely that a bigger driver also moves less
but a small driver depends on much larger stroke
and that will need a stronger 'motor'
you need some amount of weight to play deep bass
and I suppose each 'weight' has certain 'optimal cone size
and then comes the compromises, suspension stifness, etc etc
and not to forget SPL
not going to exstremes tend to make life easier
I think some people waste valuable time, and money, trying to do the impossible
if you focus more on how to make it work, you may realise that you really don't need very fancy components
or like saying, if you plan to travel to the moon in a car, you wont find any good cars anywhere
and it would be a waste of time to try and build one that could
you seem to forget the obvious
namely that a bigger driver also moves less
but a small driver depends on much larger stroke
and that will need a stronger 'motor'
you need some amount of weight to play deep bass
and I suppose each 'weight' has certain 'optimal cone size
and then comes the compromises, suspension stifness, etc etc
and not to forget SPL
not going to exstremes tend to make life easier
I think some people waste valuable time, and money, trying to do the impossible
if you focus more on how to make it work, you may realise that you really don't need very fancy components
or like saying, if you plan to travel to the moon in a car, you wont find any good cars anywhere
and it would be a waste of time to try and build one that could
The "speed" you are referring to would technically be the driver's ability to perform the leading edge of an impulse.
This is a direct function of the upper bandwidth limit on the system, nothing more.
As the frequencies required of a subwoofer will never reach the kHz region, the ability to reproduce such high frequencies is totally irrelevant.
To expand a little on your analogy, lets say both the truck and the F1 car have to accelerate very slowly to a given speed, then slow to a stop very slowly.
Both will perform this exactly the same. Sure, the F1 car could be doing the same much faster, but this is never required for subwoofer duties.
Chris
Ha, yeah. Even if you had a huge array of ideal tweeters, they would behave pretty much the same (or even worse) as a big old sub.
Here is something to try. You take one of these "slow" 18" woofers and measure it in REW with the mic right up close to the cone, then you look at the waterfall response. It looks very neat. You do the same with a fast little woofer. Add some EQ so they both run as deep. Then put the mic in your listening position and measure again with one then the other.
Nearfield you see something like this:
Except maybe without the roll off on the top end (that one is a sub). Surprisingingly they look quite similar. Then in the listening position you see something more like this:
Suddenly everything becomes dominated by the speed of the room. Potentially you could get an 8" and an 18" woofer to sound the same in a fair comparison.
I like 18" drivers for bass because they are the largest economical woofer size. No need for multiple drivers, it's all you can eat bass at home. At that size you don't even really need ported and it will probably run up high enough to cross to your mids. Of course, an 18 will be different to a pro 15" because it will nearly always be designed as a dedicated woofer. The VC will be larger, the inductance will be larger, some of them start rolling off quite early. A 15" might be used as a mid, but an 18 is always going to be a woofer.
You can always trust audiophiles to get funny ideas about what matters in audio and to have elaborate descriptions behind how they have connected the dots. I'm far more interested in things like the quality of the motor design, the room treatment and the way the bass is integrated than about the size of the driver and its moving mass or whether it has an evil port or not. Start with a good quality driver, pair it with enough power, integrate it sensibly with the speakers, treat the room, get the integration with the room right (and that is quite a process), and you will get a good result. The size of the driver/s is just a means to ensuring you get your desired output with some headroom. If the automotive world were as nutty as audio, then we'd be languishing on freeways at 40kph! Well, if the first 40kph aren't quality ks, what's the point in having any more?!
Nearfield you see something like this:
Except maybe without the roll off on the top end (that one is a sub). Surprisingingly they look quite similar. Then in the listening position you see something more like this:
Suddenly everything becomes dominated by the speed of the room. Potentially you could get an 8" and an 18" woofer to sound the same in a fair comparison.
I like 18" drivers for bass because they are the largest economical woofer size. No need for multiple drivers, it's all you can eat bass at home. At that size you don't even really need ported and it will probably run up high enough to cross to your mids. Of course, an 18 will be different to a pro 15" because it will nearly always be designed as a dedicated woofer. The VC will be larger, the inductance will be larger, some of them start rolling off quite early. A 15" might be used as a mid, but an 18 is always going to be a woofer.
You can always trust audiophiles to get funny ideas about what matters in audio and to have elaborate descriptions behind how they have connected the dots. I'm far more interested in things like the quality of the motor design, the room treatment and the way the bass is integrated than about the size of the driver and its moving mass or whether it has an evil port or not. Start with a good quality driver, pair it with enough power, integrate it sensibly with the speakers, treat the room, get the integration with the room right (and that is quite a process), and you will get a good result. The size of the driver/s is just a means to ensuring you get your desired output with some headroom. If the automotive world were as nutty as audio, then we'd be languishing on freeways at 40kph! Well, if the first 40kph aren't quality ks, what's the point in having any more?!
Hi,
You quoted my entire post and said "that's not how it works".
May I ask, is my entire post above incorrect? Or which sentence(s)?
Show me a 15" midrange. Of course, that depends on what your definition of midrange is.
Any 15" is going to struggle to get to 1 kHz. After that the physics kick in and directivity begins to beam considerably.
Completely, utterly irrelevant. Was your point that a larger woofer will have higher Mms? We knew that already.
Analogies never amount to anything.
Two problems here. First, you have not defined what is fast and what is slow. Second, you have not proven that bigger drivers are slower than smaller drivers, nor have you even given lip service to appropriate premises required to back up your argument, only poor analogies.
You missed the point that the proportion of one-dimension size and mass is not linear. Far from it.
Take 5" cone and 10" cone of the same material, the latter should be 8 times in mass to maintain the same strength. While it has 'only' 4 times of area.
So, there's indeed a 'proper' size for any particular application.
I know this analogy is not precise and ignoring technologies in material itself and the construction, but the trend is still there, clearly. It's happening everywhere in mother nature.
Quite the opposite. It applies to everything.
Don't have to define what is fast and what is slow. They are relative, that's enough.
Why do you need any proof to "bigger drivers are slower than small drivers"?
Or, why do you think the opposite? Do you really think a bigger driver can be faster then a small one? Do you use 18s for tweeter job?
Why do you make the assumption that thickness must grow as well?
B&C SPEAKERS
B&C SPEAKERS
The 12TBX100 has an Mms of 119 g and Sd of 531 cm^2. The 18TBX100 has an Mms of 209 g and an Sd of 1210 cm^2. Doing the math, that gives us a ratio of 0.224 g/cm^2 for the 12" vs 0.173 g/cm^2 for the 18".
Whoops, did they actually thin out the diaphragm? Strange... 😉 Things like that might happen because the voice coil mass stays the same, but the point is, analogies don't really work, because if all the facts were known, analogies would be useless but for being pedantic.
I don't think it's worth my time to argue this particular point with you. If you can't be bothered to quantify what is slow and what is fast, anything can be slow and anything can be fast.
Serious question?
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its easier to pick the only one that made just a little sense 😀
again, a 6" woofer reproducing 30hz needs to move faster than a 15" moving maybe 1/10 of the 6"
now, a 6" may be fast, but which one will play most 'accurate'
so tell me, which one ends up being too slow ?
and lets not forget that a 100mm short Xmax voice coil is different beast than a 40mm with long Xmax
And a driver designer would take this into account when designing the driver so that he might, for example, produce two equivalent drivers of different sizes which differ only in their intended frequency range but otherwise behave the same within their range.
The intended frequency range of different sized drivers is usually constrained by other issues. For example...
...a larger driver will typically have a lower frequency of cone breakup, lower frequency where directivity becomes an issue, and higher voice coil inductance. (Might not be right to mention full range drivers at this point but they do address some of these issues relevant to this discussion.)
If not for these issues could we maybe make an 18" tweeter?
It's a giant leap from talking about elephants and cheetas to woofers. Interesting topic though. You could also talk about fleas vs elephants, but what gets overlooked there as well is that there are more factors involved. The flea must be extremely athletic because it is so small but has to survive in a big world. If the flea were as slow as an elephant relative to its size, it would not survive. So it is a design issue, insects must be high performance. They are extremely light, extremely strong and very fast and powerful. An elephant is much slower and weaker in relative terms, but it is as strong and fast as it needs to be. Whatever we might learn from any of this may not translate very well into woofers.
Far too simple. You have to consider all the relevant factors and mass can't be considered in isolation. A bigger driver with higher mass can be given a more powerful motor. Of course, this will also affect the Q and the suitable box size. Making the motor stronger gives a lower Q and this leads to a less efficient driver as a general rule. A balance is needed here.
In terms of acceleration, inductance is something to be considered, but if you look at the actual transient response then there are factors like the suspension system that also come into play. A larger driver in a bigger box will see less excursion and less power, and also less internal pressure changes. Less compression, lower thermal and mechanical dynamic effects.
In terms of the subjective impression, the quality of the motor itself is also very important. So you have a whole lot of factors going on all at the same time, as well as the room itself.
"Slow" also causes a lot of confusion, especially when it's not clear if you mean it literally or not.
Woofer size tells us little about the final result.
The upper harmonics or "slap" of a bass drum are quite a bit higher than that, there's a lot of energy in the 2KHz-8KHz range.
But that's the job of the midrange and high frequency elements of the system, doesn't matter if the 18" can do that or not. Any woofer is gonna sound "slow" after you've fed it through a low-pass filter.
I find that when someone complains about their woofers or subwoofers being 'slow' the real problem is that they havent or don't have the equipment to time align the system to account for the delay imposed by the crossovers, and/or that the crossover slope is too steep. That ~7ms can make a difference if the ist harmonic is on the other side of the crossover.
Fact of Physics
Rhetorical Question:
Over what distance must a given driver’s [Sd] be accelerated/decelerated in a fixed time interval (determined by frequency) to produce a given [Vd]?
The driver diaphragm with larger [Sd] has to travel the shorter distance.
So, it is the smaller driver that needs to move faster and will probably overshoot signal peaks the most.
The only limitation of the larger driver is bandwidth. But for that sacrifice, the impedance mismatch with air is reduced, so a bump in efficiency is delivered at the low end, right where it is needed the most. Thus, for a given frequency and SPL an even smaller excursion is required by the larger driver. That fact makes it slower still!
If the larger driver, crossed over at a lower frequency, sounds "slower", what probably is being heard is a limitation of the mid-range driver and/or the intervening crossover. At the point where the "punch" signal components are at issue, is the place in the frequency band where the mid-range driver is becoming displacement limited.
For a sub-woofer, if space for a larger footprint is available, drivers with larger [Sd] are preferred, given that a constant level of quality between the smaller and larger drivers being considered is maintained.
Regards
WHG
Rhetorical Question:
Over what distance must a given driver’s [Sd] be accelerated/decelerated in a fixed time interval (determined by frequency) to produce a given [Vd]?
The driver diaphragm with larger [Sd] has to travel the shorter distance.
So, it is the smaller driver that needs to move faster and will probably overshoot signal peaks the most.
The only limitation of the larger driver is bandwidth. But for that sacrifice, the impedance mismatch with air is reduced, so a bump in efficiency is delivered at the low end, right where it is needed the most. Thus, for a given frequency and SPL an even smaller excursion is required by the larger driver. That fact makes it slower still!
If the larger driver, crossed over at a lower frequency, sounds "slower", what probably is being heard is a limitation of the mid-range driver and/or the intervening crossover. At the point where the "punch" signal components are at issue, is the place in the frequency band where the mid-range driver is becoming displacement limited.
For a sub-woofer, if space for a larger footprint is available, drivers with larger [Sd] are preferred, given that a constant level of quality between the smaller and larger drivers being considered is maintained.
Regards
WHG
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