[Steve Eddy]

Quote:

Originally Posted by SP Wild /img/forum/go_quote.gif
 
 In a sine wave, the positive portion represents a positive pressure and the negative portion is negative pressure.  The rate of change in a sinewave is gradual. 

 
Not sure what this has to do with what we're discussing.
 
Quote:

A transient event is closer to an instantaneous change in pressure, or closer to an infinite acceleration rate.  The closer a driver can instantaneous pressurise and de-pressurise would mean a driver more able to overcome inertia, mass is a variable function of inertia

 
A transient event is simply an event that occurs for a relatively short period of time.
 
If I pluck the low E string on a bass guitar and just a moment later mute it with the palm of my hand, that would be a transient event. If I pluck the same string and let it ring on, that's not a transient event.
 
But in both cases, we're talking about a string that's vibrating at a fundamental frequency of about 41 Hz. And if the peak amplitude is the same in both events, then the string isn't moving any faster during one event versus the other. Neither would two diaphragms reproducing these two events.
 
Quote:

The closer a driver can instantaneous pressurise and de-pressurise would mean a driver more able to overcome inertia, mass is a variable function of inertia

 
It would mean, all else being equal, a driver able to reproduce higher frequencies. Because as I said previously, the driver's velocity only increases if you increase the amplitude or increase the frequency. So if two drivers, one with a lighter diaphragm, are able to produce the same frequency at the same amplitude, then there's nothing "faster" about the driver with the lighter diaphragm.
 
se

 

[Rdr. Seraphim]

I believe there is a transient event (a very short duration, the near instantaneous increase in level) that occurs when the string is first plucked. Otherwise, we would not be able to distinguish it as having been plucked. The sustain is just the decay in level represented over time.  
 
Quote:

 
If I pluck the same string and let it ring on, that's not a transient event.
 
 

 

 

[LiqTenExp]

perhaps the discussion needs to occur that not all audible "things" are developed in the sinusoidal world.  starting simply you could discuss sine vs square vs triangular and how a driver would reproduce those, for lack of a better term, noises.  this may lead you down a path at how a driver could be "quicker" (especially when referencing something as simplistic as a square wave) than another?
 
just a quick google search brought up this interesting read: http://www.physics.mcgill.ca/~moore/P101/Lectures/Lecture-10.pdf

 

[Steve Eddy]

Quote:

I believe there is a transient event (a very short duration, the near instantaneous increase in level) that occurs when the string is first plucked. Otherwise, we would not be able to distinguish it as having been plucked. The sustain is just the decay in level represented over time.   
 

A near instantaneous increase in level would require a near infinite bandwidth.
 
So you're just talking about the diaphragm moving faster due to frequency.
 
se
 
 
 

 

[LiqTenExp]

I think he may be more hinting at where I was going. Some tones (consider pulses here too) have a faster leading and trailing edge transition depending on shape and duty cycle vs. others.  Square vs. triangular for example.  Square ideally is instantaneous but is limited to physics of the amplifier output stage and the driver interactions (electrically and mechanically). 

 

[Nevod]

I suppose that driver becomes "slow" when motive force is not capable of accelerating the emittive surface (diffusor or membrane, doesn't matter) fast enough to match the actual electrical input signal. There is always some lag as air and emitter aren't massless, but it's not very demanding on low freqencies. On high frequencies, it causes phase/frequency shift and reduced amplitude.
This is IMHO..

 

[SP Wild]

I dunno Steve, I can only go by what I hear.  Then I formulate a plausible possibility of why this is so.  Certain headphones can play the pluck part of a guitar with more sting and bite, whilst others tend to smooth out the sting.  This is not necessarily correlated to the square waves I see, in that I can still hear a better sting on some headphones, contrary to how poor the square waves might suggest.  But on two headphones, the LCD2 and SE530, the attacking transients are as good as its square wave suggest.
 
For me, so far, it seems that price of the headphone has been the most consistent correlation of transient attack capability.  Of course this is purely in my opinion and I have no evidence to present that what I hear is indeed fact.

 

[BlackbeardBen]

Quote:

I think he may be more hinting at where I was going. Some tones (consider pulses here too) have a faster leading and trailing edge transition depending on shape and duty cycle vs. others.  Square vs. triangular for example.  Square ideally is instantaneous but is limited to physics of the amplifier output stage and the driver interactions (electrically and mechanically). 

Understand that square, triangular, and sawtooth waves are just an infinite series of sine waves.  What we hear and what is recorded is still limited to 20-ish kHz.
 
Anyway, as far as reproducing bass frequencies (I am unsure if the same is true of higher frequencies but it would not surprise me), overdamped transducers sound "quick" and underdamped transducers sound "slow".

 

[SP Wild]

Quote:

Understand that square, triangular, and sawtooth waves are just an infinite series of sine waves.  What we hear and what is recorded is still limited to 20-ish kHz.
 
Anyway, as far as reproducing bass frequencies (I am unsure if the same is true of higher frequencies but it would not surprise me), overdamped transducers sound "quick" and underdamped transducers sound "slow".

Please explain.  Physically speaking, anything other than critically damped will result in inaccurate bass, and overdamped transducer will exhibit square waves with rounded corners, this is not accurate to the signal and is not fast at all, but in fact slow.

 

[BlackbeardBen]

Quote:

Please explain.  Physically speaking, anything other than critically damped will result in inaccurate bass, and overdamped transducer will exhibit square waves with rounded corners, this is not accurate to the signal and is not fast at all, but in fact slow.

Square waves ALWAYS have rounded corners.  In audio systems with very limited bandwidth (relative to high-frequency electronics), you can see it very clearly with higher frequency square wave.  Luckily we can't hear the difference.
 
And no, overdamping doesn't result in subjectively "slow" sound.  The decay time for the driver is reduced; overdamping the resonance reduces its response (and thus efficiency of the driver) - the tradeoff for giving up efficiency is that extension below the resonance point is relatively higher.  Underdamping results in the opposite - the resonance is under-controlled so you get a response boost at it, and decay time increases as a result.  Critically damped balances efficiency at and above resonance versus extension.  In the name of even frequency response and the "tight" sound of quick decay, often (but not always) slightly overdamped drivers are desirable.