The correlation comes about because heavier moving masses tend to come not from heavy cones, but longer/larger/heavier voice coils. Which also have considerably higher inductance. So it's not the mass that's causing a lot of the audible and measurable "slowness". It's the limited bandwidth and increased eddy currents from the increased inductance.
So the effect of mass is a typical byproduct when you go to a larger inductive voice coil. IF you cut back the mass to the same point as originally existed, but increased the inductance, you will also have the same measurable and perceptual decrease in "speed" of the driver.
It's not the mass, it's the inductance. However, with most drivers it's hard to increase inductance without increasing mass (and the inductance is increased in a pursuit of higher power handling and higher linear stroke).
Dan Wiggins
Adire Audio
So the effect of mass is a typical byproduct when you go to a larger inductive voice coil. IF you cut back the mass to the same point as originally existed, but increased the inductance, you will also have the same measurable and perceptual decrease in "speed" of the driver.
It's not the mass, it's the inductance. However, with most drivers it's hard to increase inductance without increasing mass (and the inductance is increased in a pursuit of higher power handling and higher linear stroke).
Dan Wiggins
Adire Audio
isnt the major factor in inductance the number of coil turns? So if we reduce the number of turns of coil we also reduce BL correct? isnt the only way to have lower inductance and still achieve the same BL is to use stronger magnets and have more flux? how then does that effect the impedence? I really dont know enough about this stuff to know that I'm right, but wouldnt the best motor use an extremely long gap with the highest possible amount of flux and the lowest possible inductance? I'd imagine once you get past a certian point it wouldnt be good to lower inductance any more. I.E. you would never use a single turn of wire no matter how much flux it was saturated in correct?
I do plainly see your point about the decay time that lags behind impulse or step response brian. I'd say thats probably what most people refer to when they talk about fast subwoofers, because just like Dan's paper says, the acceleration is merely a function of the current running through the coil. Critically dampened sealed enclosures would seem like they do the best job to prevent a resonant system. the self dampening of the suspension probably plays a good role too.
I do plainly see your point about the decay time that lags behind impulse or step response brian. I'd say thats probably what most people refer to when they talk about fast subwoofers, because just like Dan's paper says, the acceleration is merely a function of the current running through the coil. Critically dampened sealed enclosures would seem like they do the best job to prevent a resonant system. the self dampening of the suspension probably plays a good role too.
Well you don't listen at a lower volume just because your speakers are less efficient, you turn up the volume instead. So all else being equal, a speaker with higher moving mass will need more power and thus suffer from thermal compression earlier.DanWiggins said:
BassAwdyO said:
I do advocate tight gaps and large magnets. Higher BL without increase in inductance leads to a better control of cone motion over the piston operation frequency range (in subwoofer, it is most likely the midbass region and below). As the frequency goes up, the cone resonance will take over. I know some Bose midrange drivers used single turn of wire. I am neutral on Bose so don't flame me 😀
I agree. Most of my listensing experiences pointed to that, with the same driver, a lower Q response does sound better. The exceptions are either the drivers are too good or too bad 😀 So different drivers can still sound differently even with their Q values and extension set to the same. Also, I think there are more in the decay time analysis than what we consider now. Most people consider thermal compression as an issue of output reduction or even frequency response deviation which is a static view. Thermal compression is also a memory effect, which is a dynamic view. For example, let us say we apply a burst sequence of say, 10 cyles of sin waves. The thermal buildup is a gradual process and the amount of buildup depends where we are in this burst tone. At the end of the burst tone, the voice coil is at a slightly different temperature which leads to a different decay time characteristic (because Re is now different). Should this type of analysis be also included in decay time analysis? I know a sensitivity analysis (not the speaker sensitivity if you know what I mean) will suffice. Maybe someone already did it!!
Brian Ding
Rythmik Audio
directservo said:
A misquote here. Some Bose midrange drivers used "single layer" voice coil in short gap cofiguration. Single turn only makes sense for long gap configuration. I need to also clarify a few thing. Driver design is series of trade-offs. I have long believed the so-called fast bass is caused by better performance (distortion, thermal compression,...) in the midbass range. And that has always been our focus on driver design. To achieve that, we used tight gap (vs wide gap) and other tricks. Using 6-layer voice coil (to achieve higher BL) which can widen the gap so much and at the same time increase inductance just doesn't cut it when we finaly sit down and listen to it.
Brian Ding
Rythmik Audio
All else being equal, yes. HOWEVER, you'll never find two drivers that are identical save for moving mass. It's not a real-world situation. Most mass changes come from voice coil winding changes; typically heavier moving mass comes from more voice coil (or aluminum, not Kapton, formers) which means better power handling.Mr Evil said:
In the abstract, you are correct. In the real world, heavier moving mass drivers tend to have LESS power compression because of where that mass usually resides.
Dan Wiggins
Adire Audio
directservo said:
Really? Sub systems in a first order analysis are completely modeled by mass/spring/damper systems. Higher order analyses only make some constants variables dependant on temperature, humidity, power density, etc. in various parts of the system.
And the "removal" time of a mkc system is defined by it's Q.
RHosch said:
Removal time does not solely depend on Q value. One hysteresis characteristic is called creep. Hysteresis is a memory effect. The best way to show a creep is the step waveform analysis. It makes the system slower to return to steady state, which affects the removal time. The point here is an analysis/simulation model is based on what we believe the system should be made of. As of today, most models are still based on time-invariant systems (which assume there is no memory effect, no "time-variant" thermal compression effect,etc).
I have found again that my comment is taken out of context. Let us focus on the intension of the comment, why the speed is only determined by how fast it arrives, but not how fast it stops?
Brian Ding
Rythmik Audio
Brian, you talk so much about step response. What exactly does a step response signal look like?
The ideal unit step response is y=0 at t<=0, and y=1 at t>0. It has a DC component. So a speaker cannot reproduce a perfect step response. The response from a speaker will most likely look like this: it goes up very fast immediately after t=0, and then graduately come back to 0 (it may take more than 100ms). Mathematically, it is the integral of impulse response. That means its spectral energy is inversely proportional to frequency. Am I on the right track to answer your question?
Brian Ding
Rythmik Audio
Brian Ding
Rythmik Audio
Basically it's just a spike right? I've drawn two ideas of what I concieve it may look like. The first I believed was an impulse or transient signal, the second is more/less a half cycle of a square wave, but mostly just the only other idea I had of what the signal might look like.
BassAwdyO said:
BassAwdyO,
What you showed in the second pic was a pulse waveform. A step waveform is a pulse with an infinite pulse width.
Brian
so a step would basically be the equivilant to hooking up a battery to a speaker? DC can fry voicecoils last I heard. How wide does the width need to be for all practical purposes?
well i was a bit bored, and I though I'd find out what it would take to get a speaker cone up to the speed of sound. For 20hz, about 9 feet one way excursion. I'm pretty sure that for every double in frequency the excursion is reduced to half, so that above 20k only about 3mm each way would be needed. I really wonder what the actual output would look like from something like that. I'm certian it would achive low pressure clipping due to the fact that you just cant get any below a vaccum. Wouldnt that be neat!
BassAwdyO said:
The next logical question to ask is if Doppler effect is significant enough to consider. There were papers related to that for low frequency transducers and their conclusion was negative. Now I think the issue should be more serious at high frequency based on the numbers you have just written out 😀
Brian
I used the sin function and calculated the derivative at x=0. If the form Bsin(Ax) is used. B is a factor of amplitude and A is a factor of period. For a 20hz signal, using radians the equation can be written Y=Bsin(40(pi)x), where Y=displacement. The derivative of the equation gives slope, which is velocity. I used feet as the Y unit, and seconds were the x unit. Since a sine function crosses the x axis at zero this was the point used to calculate maximum slope. Since I'm too lazy to actually calculate the derivative myself I simply plugged the equation into my graphing calculator and it did the work for me. I started with B=1 and worked my way up finally to 9, where the slope became greater than 1125. Therefore at 9 feet one way excursion a 20hz tone should bring a speaker beyond the speed of sound when it crosses the center position.
I only assumed it would take about 3mm each way at 20k, but calculation seems to differ. For every doubling in frequency the speed increases by a factor slightly less than 2 to keep the same excursion. My calculator wont do the derivative of sin(40000piX) so I'm not sure quite what it would take up there. I just wanted to see if it was possible at all to get a cone moving faster than the speed of sound. I really dont think so.
My question is, if the speaker cone moved faster than sound, then wouldnt it make a sonic boom? When it moved in, it would probably create a better vaccum than space.
I only assumed it would take about 3mm each way at 20k, but calculation seems to differ. For every doubling in frequency the speed increases by a factor slightly less than 2 to keep the same excursion. My calculator wont do the derivative of sin(40000piX) so I'm not sure quite what it would take up there. I just wanted to see if it was possible at all to get a cone moving faster than the speed of sound. I really dont think so.
My question is, if the speaker cone moved faster than sound, then wouldnt it make a sonic boom? When it moved in, it would probably create a better vaccum than space.
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