Transient response, can you tell in advance???

[Haunz 10+ year member]

I think immacomputer's first post is what everyone should pay attention to.. transient/impulse response will depend on QTS of the system which is a function of all the woofer's T/S paramaters and the enclosure as well as the electrical inductance of the system..

so what is the question? it almost seems that all of the analysis thus far only goes so far as to prove inductance and mass are not limiting factors.
look at the OP's PDF link. the timescale is on the order of 5ms, with visually identifiable events within a fraction of a millisecond. pretty much all of that is stuff that is well above 200hz. the main parts are closer to 2khz it would seem.

This calls into question the validity of the testing -- after all, for car audio someone will be using most likely a 4th order (-24dB/oct) lowpass below 2000hz and even below 200hz. when this is added to the response the "transient" response would likely look almost like a flat line. in the 5ms timescale the filter would largely reject the impulse, except for the lower frequency components, which would not appear "transient" on the 5ms timescale.

further, the zoomed in picture shows a delay difference of what seems to be 1 sample, or 21us. this would be similar to having the woofers located a massive 1/4 to 1/2" further away from you then the rest of the speakers. its likely your time correction features won't even be able to correct for such a small difference.

Not at all.. I think the test was valid.. and shows how the raw driver (which is a mid) responds naturally, and with added inductance or added mass..

I haven't read the whole paper but at first glance you can see in the first two graphs how the impulse response is improved with the added mass (as the added mass lowers the drivers Q)... while the added inductance hinders the driver's impulse response.. you can also see how adding inductance delays the driver's response...

I think these graphs spell out transient/impulse response, what it is, and what affects it quite well..

 

[John_E_Janowitz 10+ year member]

The guys at Stereo Integrity did not pioneer the idea that inductance relates to transient response rather than moving mass, Dan Wigging from Adire Audio did. His tech paper on the subjkect is pretty common knowledge these days. If I wasn't so lazy, Id find the link.

One of the original papers on inductance was done by Nick McKinney from Lambda Acoustics. You can go back to the archive page in 1999 and read it. It's titled BL/Mms = Nonsense.

http://web.archive.org/web/20010810141852/lambdacoustics.com/library/whitepapers/bl_mms.htm

The misconception is that Bl and mass somehow determine an acceleration factor of a driver and determine how "fast" the driver is. In reality how "fast" the driver is is determined simply by what frequency it is playing. The frequency determines how many cycles per second and how fast it needs to move to play this frequency is your speed. The force factor of the driver is not Bl/Mms as some suggst. Force is BL*i which is the current. Lower inductance drivers can play much higher in frequency (faster) as current to the coil is not limited as in high inductance drivers.

There was a lot of discussion on the Basslist back then about it. Many disagreed with Nick on the needed low inductance. Some like Dan Wiggins argued that impedance compensation on a driver provided the same effect, so lowering the self inductance of the woofer wasn't necessary. While impedance compensation does lower the apparent inductance to the system, it does nothing for the self inductance of the driver and the effects of the non-linear inductance. Since then we've found out a lot more about inductance and it's effects on distortion. Lowering and linearizing inductance in a woofer has a huge effect on how it will sound.

For the original post, two things will tell you about transient response. One is going to be the enclosure. In a sealed enclosure, you can tell a lot by the Q of the enclosure for example. The other issue is going to be in the motor of the woofer. What is done to provide linear Bl, low and linear inductance, good heat transfer from the coil, and as a result of all those others, low distortion? Often times one issue is addressed at the expense of making another even worse. For a subwoofer being used under say 100hz, the soft parts are less critical. You need a suspension that moves far enough without physically making noise or limiting travel, but you're not so concerned with resonances and issues far out of the intended band.

Also check out the paper on the Lambda 001 motor design. This is a revised version of the original paper published back in 1999 by Nick McKinney on the motor he designed to address inductance and distortion issues. He had worked at a recone shop for years reconing just about any kind of driver you can think from the pro, home and car industries. He also worked for AIT who at the time was doing JL's woofers. He took all of the knowledge he had from literally back engineering every driver in existence to develop the Lambda drivers.

http://www.aespeakers.com/Lambda001-1.php

John

 

[thch 10+ year member]

Umm... inductance IS reactance. It's the storing of current in the form of an electromagnetic field. When a speaker is playing a frequency near a resonance point and then it stops playing it to play another one, the stored current in the EMF will discharge and the burn off of current will change the response time and will cause a delay in the signal.

Reactance is either capacitive or inductive. Capacitive reactance will cause the current to lead the voltage while inductive reactance will cause the current to lag the voltage. Hmm... sounds like it should be inductance we're looking at, whether it be electrical or acoustical. And that acoustical inductance is what is really going to affect transients.

suspension pulls coil back, mass pulls coil forward. yep, both capacitive and inductive elements can occur mechanically. seems air can also move and compress.

and again, misses the point that resonance isn't the same as inductance or capacitance alone.

 

[Papermaker85 5,000+ posts]

Cone material, mass, efficiency, and bandwidth are not going to affect transient response directly, especially not in the bass frequency range.


Umm... inductance IS reactance. It's the storing of current in the form of an electromagnetic field. When a speaker is playing a frequency near a resonance point and then it stops playing it to play another one, the stored current in the EMF will discharge and the burn off of current will change the response time and will cause a delay in the signal.

Reactance is either capacitive or inductive. Capacitive reactance will cause the current to lead the voltage while inductive reactance will cause the current to lag the voltage. Hmm... sounds like it should be inductance we're looking at, whether it be electrical or acoustical. And that acoustical inductance is what is really going to affect transients.

yes your forward stroke is inductive and rearward is capaitive... but your still not correct "inductance IS reactance"... it isn't, inductance IS what causes the lead/lag reactance is the measure of both the lead and lag... there for the reactance is which alters the FR... reactance is dependant also on frequency and back EMF as well...

since a transducers' inductor moves through a magnetic field after the signal has passed threw(from the dampning on the suspension and inertia) the inductor it causes current to flow in oppsite directions, the upward stroe is inductave so it causes the upward prat of the AC sine wave while rearward flow causes the downward part of the sinewave... its literatilly a generator after the signal has passed thriugh... this goes back to the amp... which most times proper filtering causes very little alterration, but its not soley back emf its a combination of all the factors. inerta,****ing mechanical and electrical, reactance frequency amoung other factors...

cone meterial can affect tranisant resonse.. not directly but it DOES affect mass and stifness as well as acoustic dampning and this crutical to stopping the cone itself from resonating altering both mechanical and electrical damping buy haveing mass that doesn't resonate as a system... the driver resonates as a whole if any other parts start to move nonlinear from its natural centrlized movement it does affter dampning... i will say if all thinngs being equal and hte cones ARE strong enough and light enough there is be no difference is actual sound so it is important and it isn't at the same time... if you get ideal dampning with CF good if you get it with TI good, but mass DOES affect transiant response simply decause it alters dampning and effieiency...PORIORD..

 

[Papermaker85 5,000+ posts]

I think immacomputer's first post is what everyone should pay attention to.. transient/impulse response will depend on QTS of the system which is a function of all the woofer's T/S paramaters and the enclosure as well as the electrical inductance of the system Not at all.. I think the test was valid.. and shows how the raw driver (which is a mid) responds naturally, and with added inductance or added mass..
I haven't read the whole paper but at first glance you can see in the first two graphs how the impulse response is improved with the added mass (as the added mass lowers the drivers Q)... while the added inductance hinders the driver's impulse response.. you can also see how adding inductance delays the driver's response...

I think these graphs spell out transient/impulse response, what it is, and what affects it quite well..

i agree, too much and its not able to properly reproduce signals too little same result. hince FR is dependant on QES as well as FS inductance mass and QMS. where these parameters fall short is there only accuratlly measured @ the woofers reasonance.. it does describe how it will act at other frequencys but its not totally correct becasue every frequency has a different rate of compression... higer dampning means the signal is more controled.. lower compression rates natually require less dampning to be proerly reproduced...

one way to prove this is take a woofer with the same FS and VAS but alter its QES and put them in the same sized box then measure both output through bandwidth at each freuency and frequency response itself... IE take 2 identical coils cones siders and slap it in the same topplate but one with weaker magnets...

the sub with the lower QES will naurally play higher frequencies easier while the woofer with the higher QES will play lower frequencies easier, both having the same actual bandwidth just not frequency response...

mass alters FR periord.. you cannot just add mass and change dampning on one driver while changing nearly everything on hte other... the drivers are both different and therefor output will be different not from inductance but dampning... i disagree here.. the actual change from one signal to another has to do with simply more than inductance as i have explained..

 

[Papermaker85 5,000+ posts]

suspension pulls coil back, mass pulls coil forward. yep, both capacitive and inductive elements can occur mechanically. seems air can also move and compress.
and again, misses the point that resonance isn't the same as inductance or capacitance alone.

this IS the very reason mass does affect FR and futhermore transiant resonse... more mass more inertia stiffer suspension to compencate for the increased inertia higher power handling back EMF and more inductance for a given output... its crutical to output as well as transiant response.. the air around hte driver)compliance also affects the driver. IE larger cabins larger boxes larger ports etc....

 

[audioholic 5,000+ posts]

Dude, we are seriously OT here.. but really what exactly are you trying to argue ???


If we send 1000 watts of power to a woofer at 50hz and then send 1000 watts to the same woofer at 100Hz then the woofer will cycle back and forth at 2x the rate; but the amplitude (xmax) will be cut in 1/2 for the same average velocity...

So how can you possibly say that cone velocity is dependant on frequency ???

Clearly, at any given frequency cone velocity is dependant on amplitude and the amount of voltage we are sending the sub.. And if you vary the frequency then the amplitude will change, but cone velocity will not.. In otherwords, cone velocity depends on the amount of power we send the driver; and has little to do with frequency..

Cone velocity is related to frequency. Acceleration is the element I believe you are unaware of. If you dont believe me that they are related, maybe you will believe some experts:

"Figure 2.30(b) shows how the cone velocity is obtained. Clearly it is proportional to the motor force, BLi. Because the system is mass controlled, the velocity is inversely proportional to frequency and mass." - John Borwick, Loudspeaker and Headphone Handbook

http://books.google.com/books?id=pAOFt1znYr8C&pg=PA72&lpg=PA72&dq=%22cone+velocity%22+frequency&source=bl&ots=3S0kcoFMSZ&sig=Sb9QcaaDWyWuFJf6wMaPXjNcVRg&hl=en&sa=X&oi=book_result&resnum=4&ct=result

If we send 1000 watts of power to a woofer at 50hz and then send 1000 watts to the same woofer at 100Hz then the woofer will cycle back and forth at 2x the rate; but the amplitude (xmax) will be cut in 1/2 for the same average velocity...

Speaker cones have acceleration. They do not instantly stop, reverse direction, and move at maximum velocity. Here's a couple more quotes to show that frequency does in fact relate to cone velocity (thanks to acceleration)...

"there are lots of fast woofers---------but we call them "tweeters"---------since thats what it takes to respond to high frequencies---------the easiest way to evaluate the "speed" of a woofer is its upper frequency response-------the higher it can reproduce the faster it is--------if it can't reproduce high frequencies it ain't fast-----------fortunately to reproduce good bass, woofers don't have to be fast...........RC" - Richard Clark

"Actually, from a physics standpoint, the LOWER you play, the faster you are...

 

Drivers are a constant acceleration device; BLi=ma, and since a driver is a power transformer (electrical power in, acoustic power out), we are transforming current (power) in to audio (acceleration) out. Hence constant acceleration, with a sclar constant (BL/m) relating the two.

 

Now, drop your woofer down in frequency, say one octave, and keep the SPL the same. What happens? Acceleration stays constant (same SPL), but velocity increases (integral of acceleration). Why does velocity increase? You're integrating acceleration over twice the time (drop one octave means halving frequency, which means twice the duration in time for each cycle). So velocity doubles. And of course, if you look at excursion, you get the well-known quadrupling of excursion for every octave you go down (integral of velocity is position, which is excursion, and that means it is quadrupled as you drop an octave).

 

So technically, to the physicist, the fastest woofer would be the one that can play the lowest the loudest. Speed - velocity - increases for all drivers as you drop in frequency and maintain the same SPL.

 

Now, if you're talking transient response, then it's an inductance issue you want to look at. But barring inductance (say the crossover for the woofer is well below the inductive rolloff of the driver), speed is really an issue of who plays lower louder.

 

Dan Wiggins

Adire Audio" - both from: http://www.audiogroupforum.com/csforum/showthread.php?t=2824&highlight=cone+velocity

Two well known experts in the audio field, clearly talking about the relationship between cone velocity, and frequency. Here's another source to explain it yet another way:

"The amplitude, or pressure, of a sound wave produced by a loudspeaker is proportional to the velocity of the speaker cone. The higher the velocity, the higher the pressure that is produced in the air. The velocity depends on the distance the speaker cone moves during each cycle, and the number of time it has to make this movement every second. Clearly, if the speaker cone is vibrating very rapidly to produce a high-frequency sound, then it has to move faster, for the same speaker cone displacement, than if it is vibrating at a lower frequency. This means that, if the speaker cone always moves the same distance during each cycle, high-frequency sounds will have a higher pressure -- and will tend to sound louder -- than low-frequency sounds. Conversely, to reproduce a low-frequency sound with the same pressure amplitude as a high-frequency sound, the speaker cone has to move a greater distance during each cycle." - http://books.google.com/books?id=xdIvItuvXLsC&pg=PA14&lpg=PA14&dq=amplitude%2Bfrequency%2Bcone+velocity&source=web&ots=S4auq51OMb&sig=e5-4PXx-n3c_r7eLBPl0g9duC3M&hl=en&sa=X&oi=book_result&resnum=2&ct=result

As for what Im trying to argue, Im not. I stated my point from my very first post in this thread. It seems to me the one trying to be argumentative here is you, if anyone. If you have evidence to support that frequency has no relation to cone velocity, Id be glad to see it. But Id appreciate it if you would stop acting like Im attacking you.

Have a nice day.

 

[Haunz 10+ year member]

^ WOW you are an idiot...

Everything I posted is factual....

poast another quote ?!?

 

[Haunz 10+ year member]

In reality how "fast" the driver is is determined simply by what frequency it is playing.

It's true when amplitude is equal across the board..

Edit: Audioholic needs to go to audio rehab where he does not try to abuse himself or others.....

 

[SHOemup233 10+ year member]

^ WOW you are an idiot...

Everything I posted is factual....

poast another quote ?!?

I think you just fail to understand the concept. He has tried to explain it to you multiple times, you still don't understand. So he just posted **** to show that even though you still can not grasp the concept, you are without a doubt wrong.

 

[WhoSayWho? 5,000+ posts]

So, does any of this have an effect on whether a sub will wang or not?

 

[Kyle_Keating 10+ year member]

really means a lot of things, more of a general statement that is used without any sort of specific application. traditionally its simply the impulse response of the speaker, and in fact the room has a lot to do with that too. bottom line, is tr is simply the time it takes the system from one state to reach the next. If you're talking about AC its less appropriate because we really dont ever have a steady state.

 

[audioholic 5,000+ posts]

^ WOW you are an idiot...

Everything I posted is factual....

poast another quote ?!?

Yeah I doubt I would even bother trying to dispute Dan Wiggins or Richard Clark if I were you either. Stick to name calling, clearly that is your forte.

 

[Haunz 10+ year member]

I wouldn't dispute Dan or Richard... But, hey.... audiohaulic... why don't you go ahead and explain to the class why the cone excursion of a driver is cut while frequency climbs...

And how exactly are you relating cone velocity to frequency ???

 

[audioholic 5,000+ posts]

I wouldn't dispute Dan or Richard... But, hey.... audiohaulic... why don't you go ahead and explain to the class why the cone excursion of a driver is cut while frequency climbs...

And how exactly are you relating cone velocity to frequency ???

Asked and answered. Must I hold your hand through this?
http://books.google.com/books?id=pAOFt1znYr8C&pg=PA72&lpg=PA72&dq=%22cone+velocity%22+frequency&source=bl&ots=3S0kcoFMSZ&sig=Sb9QcaaDWyWuFJf6wMaPXjNcVRg&hl=en&sa=X&oi=book_result&resnum=4&ct=result

Notice the equation in figure 2.30(b). It clearly indicates what Ive said, cone velocity is proportional to frequency. In basic terms, motor force divided by freq*moving mass.

And yes, you clearly are disputing Dan and Richard. Ive quoted them, explicitly stating frequency is related to cone velocity. Its still up a few posts in black and white for you to read again if necessary.