Fast/Slow Speaker Article

[two4fifteen]

hope you recupperate soon glass

[GlassWolf]

oh I'm alright.. just had the indignant joy of going through an endoscopy and EGD. found out I have an ulcer :) Also had to deal with some stuff regarding organ donors.
made for a long 3 days.

[geolemon]

thanks. after (during) 3 days in the hospital, I wasn't in the mood to type even half of that stuff.

3 days in the hospital! I hope you at least had some cute nurses.

I think they should supply WiFi through the hospitals, so you could use a laptop on broadband inside the hospital. That would be cool.

Anyway, good luck with the ulcer... I've been lucky enough not to have had one of those yet, but the way my life has been pulling in 10 opposing directions, I'll probably be right there with you soon...

[solacedagony]

Oh ok, so that article was actually talking about woofer speed in a different way than I was taking it. I'm still slowly absorbing Glass' link. A lot of info there as I'm still learning how all this stuff collates together.

Edit: Hope everything turns out alright Glass! And thanks Geo/Glass for trying to straighten me out on that. I'll probably have more questions just based on Geo's reply. Thanks!

[GlassWolf]

the speed of a driver generally refers to how quickly it responds to the input signal fed to it by the output of the amplifier driving that speaker.
There's a common misnomer that larger speakers are slower and play deeper bass, and smaller subs tend to be faster (quicker, tighter, snappier) but don't play as low.
All horse hockey.
a smaller sub can usually play to higher frequencies without coloration from various things like cone flutter, and larger subs usually have more output at lower frequencies just due to moving more air, and a general trend toward lower Fs numbers on larger subs, but nowhere is this all carved in stone.

[geolemon]

Oh ok, so that article was actually talking about woofer speed in a different way than I was taking it...

Think about it...
...what other way really IS there to think about it? ] functions as part of the subwoofer's suspension.

Some people hear one sub (say a quick kickdrum) and hear a tight response, with instant silence following it... and then hear another sub and hear more of an overhang, or maybe even distortion.

That contributes to SQ, and you could say relates to transient response, but isn't related to the motor at all (save for a case where you are simply using the wrong sub in the wrong type of box - particularly a 'sealed box' sub in a vented box), and in fact may not have any relevence to the suspension either - like a cone distributing breakup modes or other flexing that's causing distortion. That's just general build quality stuff.

It's definitely important, if 'tightness' or 'quickness' and realism are important to you, to not only select a subwoofer that has properties condusive to that, but also that it's in an enclosure well suited to letting the sub actually demonstrate those properties, as well as that enclosure design itself being tweaked to your goals.

But as far as the woofer itself being "fast" or "slow", there's really nothing other than inductance slowing you down (ie. preventing you from playing higher - faster - frequencies).

[solacedagony]

I was thinking more in the transient response manner than the literal LPF manner.

Edit: I can't seem to find anything on the net on the effect of BL on a speaker. I'll check out my Loudspeaker Cookbook in a little bit and see what info that has.

[geolemon]

I was thinking more in the transient response manner than the literal LPF manner.

It's basically the same thing - how fast can the speaker move from one point (perhaps "at rest") to another point (perhaps something close to Xmax in one direction or another).

You can look at this as just one portion of one cycle if you like, but it's the same thing as looking at an entire cycle, or multiple cycles, since sound doesn't exist until you actually have multiple cycles, creating pressure nodes that move through the air. ]Edit: I can't seem to find anything on the net on the effect of BL on a speaker. I'll check out my Loudspeaker Cookbook in a little bit and see what info that has.[/QUOTE]
Motor strength (I'll use that instead of BL, because as I mentioned before, BL isn't motor strength, and it's motor strength that controls these dynamics) helps a speaker work in smaller enclosures, but at the expense of low frequency response.

This is perfectly predictable using Hoffman's Iron Law (which states that 'small enclosure size', 'low frequency extension', and 'high efficiency' are all mutually exclusive items in a sub/box alignment).

A higher motor strength helps a subwoofer push through the higher air pressure "spring" forces inside a small enclosure.

Similarly, a higher motor strength helps a speaker perform better in vented enclosures, where you don't just have the static air pressure forces of the air trapped in the enclosure, but you also have the speaker contending with the pressure forces of the moving mass of air inside the port, which further increases the pressure forces inside the box. And, it doesn't help that the port air motion is slightly out of phase with respect to cone motion, so you have another dynamic that could actually set the cone into non-linear motion, if the cone isn't well controlled by it's motor.

A higher motor strength doesn't directly lower the subwoofer's Fs, but it increases the resonance of the subwoofer/box combination in actual use, raising the mechanical damping factor, making the subwoofer more efficient in the higher frequencies, sacrificing the lower frequencies a bit. If you will, this is the Fs of the sub and box in combination, with power.

Higher motor strength isn't really all a good thing, unless you are an SPL competitor.

And stop thinking "BL = motor strength" - BL can be one indicator of motor strength, but not in a comparative way - one subwoofer with a BL of 14 and a 2 ohm impedence has more motor strength than a 4 ohm subwoofer with a BL of 21.
BL is an indictor of motor strength, but if used comparitively, Qes is arguably a better one - a lower Qes indicating a higher motor strength.
Or, for that matter - just calculate BL^2/Re, and you have a true comparitive number for actual, isolated "motor strength" - IF that's for some reason important to use.

[GlassWolf]

the enclosure you choose has some effect there as well.. ported adding some group delay, etc..

[thnking]

So would the inductance be affecting motor control than?
Edit: I guess what I'm asking is what determines motor control. BL would be the strength, but there must be more to it than just the strength.

Motor force generated, as was alluded to in the Adire article is
F=B*L*I
Inductance does affect the transient response (ie. Fourier transform of the frequency response), it's considered a ”static impedance".
Factors affecting motor control are a much more complex concept.