Speaker "Speed"

[antcollinet]

Is this a thing? The upper is the input signal and the lower is the speaker output, so if there is a difference between speakers in how fast it is to get up to a given amplitude?
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No, that is not how speakers work.

As long as the input signal is within the bandwidth capability of the speaker, the speaker will just match the input. It doesn't take time to ramp up the amplitude.

 

[antcollinet]

Apologies if i am misreading some posts…..

Is the idea that higher mass takes longer to stop and start moving not really applicable to audio?

No, it's applicable. But if a speaker is designed well enough to provide the specified frequency response, then the motor force is capable of starting and stopping the mass of the driver fast enough for the maximum rated frequency of that speaker. A speaker with bigger mass will just require a bigger/more powerful motor.

(motor here means voice coil in the permanent magnet)

Think about it : with the speaker playing its maximum frequency at it's maximum output, it is starting, accelerating to full speed, stopping, reversing and accelerating again twice every cycle. So if the driver can do 2kHz, it is doing that 4000 times a second.

 

[DonH56]

Apologies if i am misreading some posts…..

Is the idea that higher mass takes longer to stop and start moving not really applicable to audio?

I am not a speaker designer, but have dealt with a few over the years, and piddled with a few speaker designs. My first subwoofer was a servo-controlled DIY thing I made ca. 1980 and the whole "speed" debate was much on my mind at the time. I was taking a grad course in acoustics, which I expected to be a "fun" class, but it was a lot of work! Started with wave equations and ended with fairly detailed models of things like speaker systems. Since then I have mercifully forgotten most of what little speaker design knowledge I had so take my comments with a grain of salt.

Higher cone mass is but one part of the system. There is also the magnet, voice coil, spider, and surround that influence its response, and the amplifier driving the speaker is a major part of the system to overcome the inertia of the driver (speaker) itself. A high-mass cone with a large voice coil and magnet driven by a good amplifier will have no problems "stopping" and "starting". A light cone with tiny magnet and voice coil driven by a small tube amp may sound "muddy". The lighter cone may also be more susceptible to break up, where modes form on the cone in motion that cause distortion (depends on the cone's material, natch).

FWIWFM - Don

 

[Basic Channel]

No, it's applicable. But if a speaker is designed well enough to provide the specified frequency response, then the motor force is capable of starting and stopping the mass of the driver fast enough for the maximum rated frequency of that speaker. A speaker with bigger mass will just require a bigger/more powerful motor.

(motor here means voice coil in the permanent magnet)

Think about it : with the speaker playing its maximum frequency at it's maximum output, it is starting, accelerating to full speed, stopping, reversing and accelerating again twice every cycle. So if the driver can do 2kHz, it is doing that 4000 times a second.

Yeah it makes sense, especially the latter part. But I still (wrongly) think that when you stop sending that 2k sine it takes some time to stop moving. Would I be correct in thinking that a driver that kept moving after 0.000025 ms (of no signal) would distort playing a 20k sine?

 

[NTK]

Yeah it makes sense, especially the latter part. But I still (wrongly) think that when you stop sending that 2k sine it takes some time to stop moving. Would I be correct in thinking that a driver that kept moving after 0.000025 ms (of no signal) would distort playing a 20k sine?

You mean a driver diaphragm that is capable to produce a movement like below? That abrupt stop will require the driver to have an infinite bandwidth.

 

[Blockader]

Yeah it makes sense, especially the latter part. But I still (wrongly) think that when you stop sending that 2k sine it takes some time to stop moving. Would I be correct in thinking that a driver that kept moving after 0.000025 ms (of no signal) would distort playing a 20k sine?

It does take some time for the movement to stop, but this duration does not exceed the time corresponding to the frequency being played. If it does, it reflects itself as a roll off in the frequency response.

The driver's response time doesn't affect its distortion directly, as long as the driver can respond quickly enough.

The linearity of a loudspeaker driver, particularly how its performance changes as the voice coil moves away from its central position, has the biggest impact on its distortion/linearity. This concept is often quantified by Bl(x), which measures the motor strength, or force factor, of the driver at different positions x of the voice coil relative to the center of the magnetic gap.

Bl(x) represents how the magnetic flux density B and the length of the wire l in the voice coil exposed to this flux interact as the coil moves. Ideally, Bl(x) should remain constant as the coil moves within its operational range, ensuring consistent motor force regardless of the coil’s position.

Bl(x) is just one of the factors. There are more but I just wanted to explain the most prominent factor in driver design which affects distortion.

 

[Cbdb2]

Apologies if i am misreading some posts…..

Is the idea that higher mass takes longer to stop and start moving not really applicable to audio?

From a=f/m more mass does take longer but only if the force is the same but the force can be adjusted to get the same acceleration. With sine waves an increase in mass (decrease in acceleration) just lowers the amplitude, so as stated by purifi it just lowers the efficiency. But it also decreases the bandwith. This is similar to a RC network. Increasing the C slows the step response down ( increases the time constant ) but with a sine it just lowers the amplitude, and decreases the bandwith.

 

[JohnnyAudio]

From my experience designing motion systems there are two important factors that affect speed.

1. Load inertia, what is the measurable inertia, friction, resistance that the load contributes? For a speaker the load is air. What is the amount of air the driver has to move and at what speed? Factors affecting this are, air pressure, altitude, moisture in the air and the resistance of the speaker enclosure, including the influence of ports.

2. Machine inertia, the materials in the motor (speaker) that slow it down. This would be the mechanical parts like, cone, voice coil, surround and magnet. One could also consider the drag or acceleration of the enclosure or mount.

So, reducing inertia will allow speed to increase .

In my system, the edge less woofers in the TAD TSM-300 are a big plus. For the Lii P-10's the 22 lb magnet can really get things moving, as well as stopping the bass notes when they are complete.

Of course the right size amplifier is important to deliver the voltage and current required.
This is a rather simple view, as frequency has quite a bit to do with how speed is achieved. Then there is the alchemy of it all.

We are lucky as audiophiles to have speakers as our race cars.

 

[TankTop]

No, that is not how speakers work.

As long as the input signal is within the bandwidth capability of the speaker, the speaker will just match the input. It doesn't take time to ramp up the amplitude.

I’m asking because I do not know but what if speed could be the cone not returning fast enough to reproduce the next frequency at a high enough amplitude. I know many subs have been tested by test tones but randomizing test tones at maximum volume over time would the driver of say an 18” woofer always have time to return to a “zero” position so that it could always reproduce the next frequency at the required amplitude? If it could would that be interpreted as speed? I’m guessing correctly designed subwoofers do and that was the difference between ported and sealed subwoofers until recently where box and port size have been mostly correctly engineered giving the driver enough “back pressure” to operate correctly.

Sadly my question exposes my lack of understanding

 

[Jim Taylor]

Sadly my question exposes my lack of understanding

Never feel bad about that. No one knows everything, and everyone has to learn. Right now you're simply on one step of a stairway that goes a lo-o-o-ng, lo-o-o-ng way.

Jim

 

[tmtomh]

Apologies if i am misreading some posts…..

Is the idea that higher mass takes longer to stop and start moving not really applicable to audio?

@antcollinet has given you an excellent answer.

In short, frequency is speed.

It's not an intuitive idea until you take a moment to think about it; it took me some time to really absorb it and grasp the implications.

Same holds true for digital audio sample rates: the fact that 44.1kHz can encode all the frequencies that humans can hear means it's "fast" enough to capture the full "resolution" of music (and any other audible sound).

 

[Newman]

the difference between ported and sealed subwoofers until recently where box and port size have been mostly correctly engineered

The work of Neville Thiele and Richard Small derived the 'correctly engineered' ported cabinet equations at least 50 years ago. Is that what you mean by 'recently'?

 

[TankTop]

The work of Neville Thiele and Richard Small derived the 'correctly engineered' ported cabinet equations at least 50 years ago. Is that what you mean by 'recently'?

No, I mean it wasn’t mass produced and implemented widely until recently. Just because the science was settled 59 years ago doesn’t mean subwoofer manufacturers cared. Maybe I’m mistaken but looking at available products subwoofers have come a LOOOOONG ways in the last decade.

 

[GXAlan]

I don’t know anyone who talks about speed is arguing the frequency response or the speed of sound in air is different.

It’s actually easier to think about headphones. Open air headphones can seem to have a different sound than closed ear headphones.

SoundStage! Solo | SoundStageSolo.com - Is It Possible for Headphones to Sound Fast? (Or Slow?)

Reviews of headphones, earphones, and headphone amplifiers

www.soundstagesolo.com

But this article suggests that speed is reflective of FR

 

[wwenze]

Speed is speed.

Fast movements have larger amounts of high frequency components when you break down that movement using math.

 

[rynberg]

I didn't read through all five pages, but the thing that always strikes me on these arguments for speed, at least when they are used for bass: a driver creates sound with total excursion (movement + area), so isn't it odd to think a smaller woofer is "faster" than a larger one when it has to move much further to generate the same output?

Then again, there never was actual logic or physics knowledge behind this audiophile theory in the first place.

 

[TankTop]

I didn't read through all five pages, but the thing that always strikes me on these arguments for speed, at least when they are used for bass: a driver creates sound with total excursion (movement + area), so isn't it odd to think a smaller woofer is "faster" than a larger one when it has to move much further to generate the same output?

Then again, there never was actual logic or physics knowledge behind this audiophile theory in the first place.

I don’t like you, tried to get the Paradigm Signature Sub 2 out of my head but here it is back again.

 

[welwynnick]

I didn't see this old thread until Eric Alexander recently made a name for himself. He was trying to assert his skills as a successfull loudspeaker designer, but fell into the same trap as many people, and I posted this in the Legal fund for Reviewers/Erin? thread a few weeks ago.

Eric Alexander behaves as if he’s a great speaker designer, but he proved the opposite with his own speakers, so the evidence is out there. He makes a feature of using a tweeter array to perform mid-range duties. The argument is that they’re lighter, so they can mechanically respond to the electrical input more quickly, but there are a few problems with this:

1. Tweeters are small, so they have to move further than a mid-driver, which undoes the supposed advantage.
2. The ability to react quickly is reflected in the frequency response. If it's flat – it’s right.
3. Tweeters have very short travel, and will cause high distortion in the mid range, even when there are several of them.
4. A tweeters ability to play in the mid-range is limited by it's own system resonance.
5. Speaker drive units are dynamic transducers, not static, which is a crucial difference that few understand, including Eric.
6. If it really was a good idea, everyone would do it.

Here’s what dynamic means. At very low frequency, the time varying displacement of the drive unit diaphragm is roughly in phase and in proportion to the applied electrical signal. The resistance to motion comes from the mechanical and acoustic suspension. The displacement amplitude is roughly constant with frequency, and the acoustic output increases with frequency. In this state, a light drive unit would indeed respond to the electrical input more quickly than a heavy drive unit. This is static transducer behaviour, and this is what happens below the drive unit’s normal operating frequency range (the pass band).

Fortunately drive units don’t work like this in their pass band, otherwise you’d never get a flat frequency response. Within their pass band , drive units work as dynamic transducers, and the resistance to motion is predominantly the mass, not the suspension. The force generated from the electrical signal into the motor goes into accelerating the heavy drive unit back and forth, and it’s that acceleration of the diaphragm and hence the air that creates the loudness – not the position, nor the displacement, nor the velocity. The acoustic output comes from the second derivative of the displacement. When a signal is applied, the drive unit starts accelerating, and when the signal is removed the drive unit carries on what it’s doing – moving, stationary, whatever.

So – does reducing the mass must improve the “speed”? No – it increases the efficiency, not the speed or the bandwidth. The drive unit accelerates the instant the force is applied, not after it’s had time to move, it’s immediate. Reducing the mass will increase the acceleration, so you get a higher output for a given input, which is higher efficiency. The upper frequency limit is generally constrained by the driver’s ability to maintain pistonic motion, and not it’s mass.

It's just well that drive units are heavy because otherwise they would never have a flat frequency response - the displacement would be constant against frequency, but the acoustic output would be steeply uptilted.

So reducing the driver mass doesn’t make it faster. Proper speaker designers know this, and unless it’s all a cynical con, Eric clearly isn't one of them, and I guess that's why this thread woke up again.

 

[antcollinet]

So, reducing inertia will allow speed to increase .

But it will never go faster than the maximum frequency it is specified for - and it can already do that.

 

[Sokel]

What people think of it wrongly is because of observation.
They see a small woofer traveling far further than a big one who hardly moves (if you're lucky to see it) to reproduce the same tone at the same amplitude and SPL and they think,"well,this travel distance must take longer time for in and out" .

It's visual really.And as all visuals has it's place on affecting what we think we hear.