"Fast" bass is one of those audiophile terms that doesn't really mean much on it's own.
Generally speaking there is a consensus that there are two big things that people tend to identify as making for "fast bass".
One is a great to perfect integration of the bass and midbass. This is very easy to get wrong, and you will end up muddying and smearing the signal in time and/or get a wonky frequency response near crossover. Perfecting the crossover preserves the attack that goes with percussive hits and gives the impression that the sub frequencies are somehow faster.
Another is a downward sloping half space response. A lot of people identify an exaggerated low end as boominess and think it sounds "slow". A subwoofer that slopes downward in half space will have it's lower end made up for by room gain and sound more balanced to those who prefer that tone. This is another identified factor that makes people think bass sounds "fast".
There are plenty of other things that can contribute. High harmonic distortion subs can sound more aggressive and "punchier" than low distortion subs.
People disagree about how important group delay is in judging "fastness", but you'll find a lot of people believe that higher group delay makes for slower bass, which in a way is technically true.
But as for your original question, no, driver size does not predict anything about "fastness" of bass.
Generally speaking there is a consensus that there are two big things that people tend to identify as making for "fast bass".
One is a great to perfect integration of the bass and midbass. This is very easy to get wrong, and you will end up muddying and smearing the signal in time and/or get a wonky frequency response near crossover. Perfecting the crossover preserves the attack that goes with percussive hits and gives the impression that the sub frequencies are somehow faster.
Another is a downward sloping half space response. A lot of people identify an exaggerated low end as boominess and think it sounds "slow". A subwoofer that slopes downward in half space will have it's lower end made up for by room gain and sound more balanced to those who prefer that tone. This is another identified factor that makes people think bass sounds "fast".
There are plenty of other things that can contribute. High harmonic distortion subs can sound more aggressive and "punchier" than low distortion subs.
People disagree about how important group delay is in judging "fastness", but you'll find a lot of people believe that higher group delay makes for slower bass, which in a way is technically true.
But as for your original question, no, driver size does not predict anything about "fastness" of bass.
Horsepower is a calculated figure that has little correlation to measurable power (force or torque) since the calculation is varied by speed, time, and/or frequency, in this case. Though popularly used in conversation, horsepower is a meaningless and very misleading term.
"Think of the mass corner as a kind of power-to-weight ratio for loudspeakers."
Thats a better statement... my apologies... I can't help myself, but must correct that horsepower nonsense every time its mentioned.
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Fail!
Horsepower is an arbitrary mathematics CALCULATION, derived over time, from a known measure of power (and for mechanical devices requires a divisible 5252 constant!)
Only power (force) can be directly measured. Horsepower cannot be directly measured by any device or through any scheme. Power must be measured and known first, before horsepower can be calculated.
Its an untruth to imply that horsepower is a measure of power when it cannot ever be measurable. A measured power figure can be greater than, equal to, or less than, a calculated horsepower figure, depending on implementation of device. I speak from experience, having designed and built and measured many racing motors that produced a greater measured power figure than calculated horsepower figure, and vice-versa, with horsepower calculations derived using the same time (RPM) factor and constant in each calculation. Since horsepower cannot be measured and can result in any arbitrary figure above, equal to, or below measured power figures, its a useless calculation.
Its important that we use proper terms and offer corrections when and where its shown that many are being deceived. I will continue to correct people because equating horsepower with power or force in conversation is the same as lying to people.
If you were to research the origins of the horsepower myth you would find that it was created for use as a standardized marketing tool in response to requests from corporate marketing departments. There was a lot of discussion preceding the invention of that word. The corps wanted something they could use in marketing their products that common, technically ignorant people could relate to, when advertising power output of their products. Since everyone in that era understood horses and the relative amount of work that a draft horse can do, the Horsepower term was invented out of thin air to fill that purpose. As you (hopefully) understand by now in your adulthood, most marketing = lying. Some things never change.
Horsepower is a unit of power, not work.
Force = Mass x Acceleration
Work = Force x Distance
Power = Work / Time
The way that I was taught to remember the definition of power, more than 60 years ago, was that if you were powerful, you could work overtime, that is "work over time" or "work / time". I have never forgotten the formula thanks to this simple memory aid
.And the result from each horse will differ from another!
Define "standard horse". Define the ground your horse is stomping on. Now remove the arbitrary time component that is required for some, but not all calculations. Remove the silly constant thats required to fudge some, but not all calculations, so that those calculations correlate to other, fully measurable forms of force. Show humanity how you can provide an honest power output figure from any device, without regard for frictional (and other) losses within the closed system, without first taking those factors into account (and showing them) in all your calculations.
If you can accomplish all of those you will be a great pioneer. Not just a great pioneer in your field, but will have challenged the basis of the laws of physics.
This isn't an unobtanium science. It is a deception. Is there a value or an interest in that sort of behavior here?
I'm done... this is so far offtopic I'm probably at risk of being labelled a ben.
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Horsepower is used to describe all of those in conversation. It is a calculation taken from measurable forms, not a measurement itself. The deception lives on.
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Who was the head of the corporate marketing department when James Watt and Matthew Boulton (and possibly William Murdoch) defined and started using horsepower to describe their steam engines?
I came in this thread to post this:
http://www.adireaudio.com/Files/WooferSpeed.pdf
Very informative and relevant to the topic at hand.
But while I'm here-
Horsepower is power. One horsepower is 745.7 watts. One horsepower is one foot-pound at 5252 RPM. You posted that yourself previously. I'm really lost as to what you're arguing. Of course horsepower is measurable. That's precisely what dynamometers are for, as you should know.
Of course colloquially 'horsepower' is an abused word much like 'power' is in that it's often used in a context inconsistent with its scientific/engineering definition. When djk said horsepower, he was technically referring to the driver's effectiveness at converting current to motor force.
And of course you can argue much like Walmart subwoofers advertised at "2000watts!!" and such, horsepower figures are abused in advertising of cars and engines and whatnot. And of course the nature of speakers means that using "horsepower" as a descriptive figure in the context of loudspeakers doesn't make a whole lot of sense. That still doesn't mean horsepower is any less valid as a unit of power.
http://www.adireaudio.com/Files/WooferSpeed.pdf
Very informative and relevant to the topic at hand.
But while I'm here-
Horsepower is power. One horsepower is 745.7 watts. One horsepower is one foot-pound at 5252 RPM. You posted that yourself previously. I'm really lost as to what you're arguing. Of course horsepower is measurable. That's precisely what dynamometers are for, as you should know.
Of course colloquially 'horsepower' is an abused word much like 'power' is in that it's often used in a context inconsistent with its scientific/engineering definition. When djk said horsepower, he was technically referring to the driver's effectiveness at converting current to motor force.
And of course you can argue much like Walmart subwoofers advertised at "2000watts!!" and such, horsepower figures are abused in advertising of cars and engines and whatnot. And of course the nature of speakers means that using "horsepower" as a descriptive figure in the context of loudspeakers doesn't make a whole lot of sense. That still doesn't mean horsepower is any less valid as a unit of power.
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The essential question is whether horsepower or force provides a more meaningful parameter or which communicates the reality of performance better apropos drivers (or possibly apropos speakers)*. As with engines, drivers operate at different speeds and so it makes no sense to talk about horsepower or force except in relation to frequency and output.
And it makes no sense to to talk about either until the concept of "fast woofer" is clarified.
Ben
*As it happens, I've spend several very informative if expensive hours running my motorcycle engines on dynamometers. In terms of forward motion, just a matter of meaningfulness whether you talk about horsepower or torque-over-time for a given engine RPM band or given gear ratio, as with speakers and crossovers.
And it makes no sense to to talk about either until the concept of "fast woofer" is clarified.
Ben
*As it happens, I've spend several very informative if expensive hours running my motorcycle engines on dynamometers. In terms of forward motion, just a matter of meaningfulness whether you talk about horsepower or torque-over-time for a given engine RPM band or given gear ratio, as with speakers and crossovers.
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