sub for Quad ESL 988

[opaqueice]

Again, not trying to insist I'm right on this, but even creative part says: "The ribbon is only moving very slightly. So, it can respond very quickly to a signal". So what is this effect that causes opposite results in large ribbons versus large woofers?

Yeah, I share your confusion - I still have no idea what people are trying to say.

Compare two cones, one large and one small, with a pure tone input, but amplified differently so that both speakers produce the same SPL.

First of all, both will oscillate at exactly the same frequency, so neither of them returns to rest sooner than the other - that would be impossible.

Second, all else being equal the larger cone will have a smaller x_max, which means for example that the max speed achieved at the center is lower than for the smaller speaker. Somehow I doubt that this is what's meant by fast, especially considering the Quads have an enormous area (and hence probably move quite slowly).

All that remains is phase. It is true that as you make the speaker larger and larger, it will become more and more damped, and its phase at a given frequency will approach pi/2. But remember that what matters for a speaker is the phase response, in particular the difference in phase as the input frequency is varied, which depends on many factors other than the size of the speaker (like the crossover, for example).

Is this what is meant by "fast" - speakers with a nearly level phase response are called fast?

[Skunk]

First of all, both will oscillate at exactly the same frequency, so neither of them returns to rest sooner than the other - that would be impossible.

Well a speaker is going to be perceived as fast with program material, not test tones.

Consider sequential cannon blasts in the program, and the ability to hear the black background between them.

[opaqueice]

Well a speaker is going to be perceived as fast with program material, not test tones.

Consider sequential cannon blasts in the program, and the ability to hear the black background between them.

We discuss pure tones because any sound - including cannon blasts - can be nicely decomposed into them. Unless the amplitude is so high something clips and the response is highly non-linear, the phase response of the speaker should be prefectly adequate to tell you the answer to that question. If the phase reponse is linear the cannon shot will not be smeared at all, and the background will be black, if not, the sound will get smeared out in time.

So I guess "fast" = close to linear phase response?

[rbl]

darkglobe - thanks very much for your help. Unfortunately the 989/2905 are just too big. I called Gradient in finland and they told me they don't sell anything for the Qauds anymore. Do yo have any experience / knowledge of the Velodyne DD-12?



Regarding the FASTness. I reiterate what i said earlier (which may of course be wrong!). I think the Quads are "fast" since there is no stored energy in the box (as there is no real box). Therefore a canon blast doesn't rumble on as the box (and cone with it) settles down. And of course Quads are low distortion and high phase linearity since they driven over the whole area of the mylar, which helps enormously too (as this creates new harmonics, colour and and i suspect slowness).

[sc53]

What about one of the Martin Logan subs? They seem to be designed to be "fast" to keep up with ML panels. I've only heard one with ML's and the blend sounded terrific.

[Robin Bowes]

opaqueice wrote:

> Compare two cones, one large and one small, with a pure tone input, but
> amplified differently so that both speakers produce the same SPL.
>
> First of all, both will oscillate at exactly the same frequency, so
> neither of them returns to rest sooner than the other - that would be
> impossible.

Not at all. You're assuming ideal speaker behaviour. In the real world,
the mass of the floating part of the speaker has an influence on the
sound produced. Sure, both speakers will oscillate at the same
frequency, i.e. the cones will move at the same velocity. But, the
larger one will have more inertia and will take longer to get going.

> Second, all else being equal the larger cone will have a smaller
> x_max, which means for example that the max speed achieved at the
> center is lower than for the smaller speaker. Somehow I doubt that
> this is what's meant by fast, especially considering the Quads have an
> enormous area (and hence probably move quite slowly).

The speed of the cone doesn't come into it - all speakers must vibrate
at the same speed to produce the same frequency and, apart from
non-linearities, that speed is constant over the whole are of the
driver. A speaker driver is designed to approximate a piston moving in
2-dimensional space.

R.

[rbl]

What about one of the Martin Logan subs? They seem to be designed to be "fast" to keep up with ML panels. I've only heard one with ML's and the blend sounded terrific.

good idea! do you know which one you tried? I tried the Summits which were very good and the bass integrated very well, but unfort i just didnt think the rest of them were as good as the quads.

[opaqueice]

Not at all. You're assuming ideal speaker behaviour.

Actually no, I wasn't.

Sure, both speakers will oscillate at the same
frequency, i.e. the cones will move at the same velocity.

Umm... no. If they have the same frequency but different x_max, the one with larger x_max will move with a greater average velocity, greater v_max, etc. Just think about it for a moment - it has a larger distance to go in the same time.

But, the
larger one will have more inertia and will take longer to get going.

True - that's called phase. As I said before, if the phase response of the speaker is linear or close to it, there will be no "time smearing".

The speed of the cone doesn't come into it - all speakers must vibrate
at the same speed to produce the same frequency and, apart from
non-linearities, that speed is constant over the whole are of the
driver.

The first part is wrong, see above. The second part is also wrong - conventional cones are fixed at the edges, so clearly the speed can not be (and is not) constant across the area.

[Robin Bowes]

opaqueice wrote:
> Robin Bowes;191617 Wrote:
>> Not at all. You're assuming ideal speaker behaviour.
>
> Actually no, I wasn't.

Then you don't understand how a speaker works.

>> Sure, both speakers will oscillate at the same frequency, i.e. the
>> cones will move at the same velocity.
>
> Umm... no. If they have the same frequency but different x_max, the
> one with larger x_max will move with a greater average velocity,
> greater v_max, etc. Just think about it for a moment - it has a
> larger distance to go in the same time.

You said:

> Compare two cones, one large and one small, with a pure tone input,
> but amplified differently so that both speakers produce the same SPL.

"same SPL", i.e. amplitude is the same, i.e speakers are moving the same
distance.

>> But, the larger one will have more inertia and will take longer to
>> get going.
>
> True - that's called phase. If the phase response of the speaker
>
>> The speed of the cone doesn't come into it - all speakers must
>> vibrate at the same speed to produce the same frequency and, apart
>> from non-linearities, that speed is constant over the whole are of
>> the driver.
>
> The first part is wrong, see above.

No, it's not. frequency is directly related to the speed of vibration,
so to produce a certain frequency the speaker *has* to vibrate at a
certain speed.

> The second part is also wrong -
> conventional cones are fixed at the edges, so clearly the speed can
> not be (and is not) constant across the area.

<sigh>

The cone on a speaker is not fixed around the edge - it is mounted on a
suspension ring which flexes as the inner cone moves in and out. Try it
- take the grilles off your speakers and push the cone in gently.

Better still, look here - there's a nice animated diagram that shows
just how it works.

R.

[opaqueice]

No, it's not. frequency is directly related to the speed of vibration,
so to produce a certain frequency the speaker *has* to vibrate at a
certain speed.

No offense, but this is really very basic physics. There's no point in continuing a discussion about this.