# MYTH: The fact that we talk about "transient response" means we know what it is



## 24th-Alchemist (Jun 16, 2011)

*MYTH: The fact that we talk about "transient response" means we know what it is*

Can anyone define "transient response" as it pertains to speakers and sound reproduction?

Is there a relationship between transient response and frequency response?


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## S3T (Sep 21, 2008)

*Re: MYTH: The fact that we talk about "transient response" means we know what it is*

Well, transient response = step response = impulse response = the way the systems resembles "step" waveform = react to single change.
In the perfect world you should get a clean step without trails.
You should see the square wave on the microphone while playing square wave thru the system.

That's what i call a good step response.

The problem is it never happens.


The impulse response is closely related to FR and phase responses thru Laplace transform.
If you take the Laplace transform on the impulse response, you get Bode plots (FR/Phase). If you take the FR/Phase plots and transform them back - you get the impulse response.

The perfect impulse response = flat phase and FR plots.

Group delay (GD) is function of phase response. GD is derivative of phase on frequency axis = dPh/dF.






How to make "transient-perfect" system?
- Make sure the signals come from different speakers at the same time = acoustical centers matching. These acoustical centers vary on the applied frequencies, for example it could be a midway between the dust cap and speaker edge for 2kHz and at the dust cap for 4kHz.
- Make sure the crossovers don't introduce phase change (impossible to do with all but FIR crossovers and some "weird" active crossover implementations involving substractions of signals).
- Make sure the speakers themselves don't introduce phase issues.
- Make sure you don't have reflections/echo.
...


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## envisionelec (Dec 14, 2005)

*Re: MYTH: The fact that we talk about "transient response" means we know what it is*



24th-Alchemist said:


> Can anyone define "transient response" as it pertains to speakers and sound reproduction?
> 
> Is there a relationship between transient response and frequency response?


Start two more threads of similar titles with the subjects of slew rate and headroom. :laugh:


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## 24th-Alchemist (Jun 16, 2011)

*Re: MYTH: The fact that we talk about "transient response" means we know what it is*



> You should see the square wave on the microphone while playing square wave thru the system.
> 
> That's what i call a good step response.
> 
> The problem is it never happens.


So if we can't achieve a perfect transient response, is there a metric for evaluating whether one imperfect transient response is better than another? And what would "better" mean?


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## Calum (Aug 13, 2008)

*Re: MYTH: The fact that we talk about "transient response" means we know what it is*

Fourier analysis - Wikipedia, the free encyclopedia

Or the condensed version; the higher the frequency response, the better the amp will be better at changing voltage levels faster.


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## 9mmmac (Dec 14, 2010)

*Re: MYTH: The fact that we talk about "transient response" means we know what it is*

I always thought of transient response as the "attack" or "bite" one notices when the first instant of a sound is heard. Good transient response denotes an aura of believability or fidelity, whereas a sound with poor transient response will sound dull, lifeless or weak. Good transient response can be found in bass as well as treble. 

Glue a couple of quarters to a speaker cone and I suppose it will have a damaging effect on transient response. 

I don't think frequency response is directly related to transient response. I think you can have excellent transient response in a bandwidth limited speaker. In fact, limiting cone excursion to a range of frequencies favorable to the speaker should improve transient response.


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## minbari (Mar 3, 2011)

*Re: MYTH: The fact that we talk about "transient response" means we know what it is*



envisionelec said:


> Start two more threads of similar titles with the subjects of slew rate and headroom. :laugh:


slew rate is pretty easy and completely measureable. its just the speed at which an amplifier can change voltage or current. higher the slew rate, the more acurate an amplifier is. usually measured as V/uS

headroom, I beleive is how much extra "oomph" an amplifier has left, power-wise. an amplifier with poor headroom will not handle dynamic music content very well.


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## envisionelec (Dec 14, 2005)

*Re: MYTH: The fact that we talk about "transient response" means we know what it is*



minbari said:


> slew rate is pretty easy and completely measureable. its just the speed at which an amplifier can change voltage or current. higher the slew rate, the more acurate an amplifier is. usually measured as V/uS
> 
> headroom, I beleive is how much extra "oomph" an amplifier has left, power-wise. an amplifier with poor headroom will not handle dynamic music content very well.


Both are "pretty easy and completely measureable." Whether they have any useful impact on sound quality is quite subjective. 

A high slew rate could mean the amplifier has too great a HF power response; the type that breaks into oscillation on highly inductive loads.... no impact on sound quality? It could. Reliability is definitely diminished!


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## 14642 (May 19, 2008)

*Re: MYTH: The fact that we talk about "transient response" means we know what it is*

Basically, Slew rate determines the amount of distortion present at high frequencies at high power. 

Transient response refers to the speaker's ability to start moving as soon as it receives a signal and to stop moving as soon as the signal goes away. Speakers include all kinds of components that degrade transient response, but all of them are required to make a speaker that works. The voice coil's inductance is required to make motion (it generates the magnetic field) but it also stores energy--that results in poor high frequency response which equates to a delay in starting the motion. This is one reason why we don't use 15" woofers with 4" coils as tweeters. The suspension is a mechanical capacitor which also stores energy and results in a delay in stopping the movement of the cone when the signal goes away. 

In an acoustic system that includes a room, the transient response includes reflections which contribute to plenty of "degradation" if one is looking at measurements. 

I'd say the answer to the OP's question is that "NO, being able to talk about transient response doesn't mean that one knows what it is." I've read plenty of marketing materials from a certain speaker "manufacturer" that illustrates this perfectly.


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## minbari (Mar 3, 2011)

*Re: MYTH: The fact that we talk about "transient response" means we know what it is*



envisionelec said:


> Both are "pretty easy and completely measureable." Whether they have any useful impact on sound quality is quite subjective.
> 
> A high slew rate could mean the amplifier has too great a HF power response; the type that breaks into oscillation on highly inductive loads.... no impact on sound quality? It could. Reliability is definitely diminished!


I never said it would have good or bad impact on sound, lol.  just that it would more accurately follow the input. at some point (for audio) it is all academic. 20Khz is the highest freq we are worried about, slew rate doesn't need to be the same as you would need to an RF amplifier.


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## cvjoint (Mar 10, 2006)

*Re: MYTH: The fact that we talk about "transient response" means we know what it is*



Andy Wehmeyer said:


> Basically, Slew rate determines the amount of distortion present at high frequencies at high power.
> 
> Transient response refers to the speaker's ability to start moving as soon as it receives a signal and to stop moving as soon as the signal goes away. Speakers include all kinds of components that degrade transient response, but all of them are required to make a speaker that works. *The voice coil's inductance is required to make motion (it generates the magnetic field) but it also stores energy--that results in poor high frequency response which equates to a delay in starting the motion.* This is one reason why we don't use 15" woofers with 4" coils as tweeters. The suspension is a mechanical capacitor which also stores energy and results in a delay in stopping the movement of the cone when the signal goes away.
> 
> ...


So both Andy and the 24th-Alchemist are ok with interpreting more limited bandwidth as a decrease in the transient response. Good enough for me. 

Then we can also say there is a bit of truth when snotty audiophiles replace their single 18" sub with 20 7" units to get better transient response.


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## SSSnake (Mar 8, 2007)

cvjoint said:


> Then we can also say there is a bit of truth when snotty audiophiles replace their single 18" sub with 20 7" units to get better transient response.


This is only true if those 20 7" subs are capable of playing higher freqs than the 18". Also, once you throw in a low pass filter what happens? You guessed it, the transient response suffers ( at least on paper). IMO if phase and freq response of a driver ate flat within the passband you're golden. Which brings me to the question why are pro audio components so much more dynamic than typical home/car audio drivers? Of course this assumes a relationship between transient capabilities which I believe are closely related but not the same thing. Can lower power compression be the main difference?


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## cvjoint (Mar 10, 2006)

*Re: MYTH: The fact that we talk about "transient response" means we know what it is*



SSSnake said:


> This is only true if those 20 7" subs are capable of playing higher freqs than the 18". Also, once you throw in a low pass filter what happens? You guessed it, the transient response suffers ( at least on paper). IMO if phase and freq response of a driver ate flat within the passband you're golden. Which brings me to the question why are pro audio components so much more dynamic than typical home/car audio drivers? Of course this assumes a relationship between transient capabilities which I believe are closely related but not the same thing. Can lower power compression be the main difference?


Sure thing, the subs would be from the same line for example so that size differences are the only differences. 

Well, depends on how you test the decay performance. Naturally the low passed impulse response will show slower decay. But say you compared both the pack of small drivers and the large kahuna both with the same lowpass. The intrinsic slower decay artifact in the CSD for example applies to both, it's a wash. The only thing that does remain is the true decay performance differences. If broader bandwidth means quicker decay due to inductance and suspension differences then it should show up. 

Another matter would be to look at the low pass filter itself as a transient variable. Is it true that the LP filter itself affects decay or it's simply an artifact in the generation of a CSD? If the first is true then we should try to have our drivers reproduce the largest frequency band possible.

Is it proven that PA drivers have better transient qualities? I'm not sure what you mean by dynamic capabilities. The biggest difference I see is that PA has room for large drivers. They focus more on high efficiency. In HT and car audio space is at a premium, motor linearities are more important to develop higher excursion small drivers. Only lately have PA drivers migrated over to HT and I'm loving it. B&C and Faital have products that whop on the HiFi camp. I'm waiting for them to make high excursion subs. While the hi fi and car audio world has been crafting fancy cones the PA world worked on advanced motors and it's paying off now.


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## subwoofery (Nov 9, 2008)

*Re: MYTH: The fact that we talk about "transient response" means we know what it is*

Is it fair to assume that a 2-way front (mid playing a wider bandwidth) will sound "snappier" than a 3-way front with the midbass playing 63Hz to 160Hz? 

Wonder if it's the primary reason why Andy Wehmeyer always recommended we LP our midbass around 800Hz-1000Hz. 

I understand the concept from Scott Buwalda of having 1 driver play as much midrange freq as possible (160Hz to around 8kHz) but this thread has me wondering now... 

I remember one guy on DynamicAutoAcoustics stating that he wanted to go back to a 2-way front coz it sounded more dynamic to his ears but never asked why he thought that... 

Kelvin


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## andrave (Jan 20, 2011)

*Re: MYTH: The fact that we talk about "transient response" means we know what it is*

my transient response is usually something like "Get a job, you bum!"


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