Bass "speed" (or timing) as it pertains to frequency response

[Vaughan Odendaa]

No, don't worry this thread isn't about bass speed as it pertains to woofer size, but more as it pertains to our subjective impressions.

I'm having a disagreement with someone I know on another forum who argues that frequency response aberrations can't affect our perception of bass speed and/or timing. Now to my knowledge, frequency response is transient response. If you flatten the frequency response that should improve the subjective impression of bass being "on time". Even an amplitude shift can affect things.

If you cut several peaks coinciding with a bass note in a piece of music I can't imagine how that wouldn't affect the "timing", or "speed". Just to clarify, he agrees that modal effects can affect our perception of bass speed, he is only disagreeing about frequency response issues.

What do you guys think?

[trnqk7]

I'm going to say I don't know about perception per se of bass "speed". As to frequency response though, I don't think you have all the terms and stuff straight. What we talk about with frequency response here is the amplitude of the signal at a certain frequency made into a nice little line graph, although you could get fancy and make a 3d graph that incorporated distance/angle from source etc I suppose if you wanted to. That's not what we typically talk about though. But flattening the frequency response only means the amplitude of the signal is more equal for any given frequency. The only place perception comes into play here is that humans apparently have a harder time hearing lower and higher frequencies, so even if a low frequency signal has the same amplitude as one several hertz higher, it will probably be perceived as being quieter. That's a limitation in our hearing though, not a true difference in amplitude.

An amplitude "shift" doesn't move anything forwards or backwards in time at all. It merely raises or lowers the maxima or minima of the waveform's amplitude. It doesn't move it forward or backward, only up or down. So in no why shape or form could that possibly affect the "timing".

I'm going to go out on a limb here and say that your friend, at the very least, is more correct than you are. I won't pretend to know everything about the subject, but just the basic math principles I have/had a fairly good grasp on. It's not meant to be a boast-but I took 4 semesters of calculus and 3 semesters of circuit theory, 2 of which dealt with waveform transformations. I've forgotten way more about it than I remember. However, the basics are still pretty clear and I don't think we are moving anywhere past the basics right here.

[Vaughan Odendaa]

But flattening the frequency response only means the amplitude of the signal is more equal for any given frequency. The only place perception comes into play here is that humans apparently have a harder time hearing lower and higher frequencies, so even if a low frequency signal has the same amplitude as one several hertz higher, it will probably be perceived as being quieter. That's a limitation in our hearing though, not a true difference in amplitude.

Okay, so you flatten the response and the amplitude of the signal is more equal. Are you saying that this won't have any effect whatsoever on our perception of how articulate, "quick" and tight the bass will be? A ragged response with uneven energy throughout the frequency range with large peaks everywhere isn't going to affect things? Perhaps I'm imagining all these changes.

An amplitude "shift" doesn't move anything forwards or backwards in time at all. It merely raises or lowers the maxima or minima of the waveform's amplitude. It doesn't move it forward or backward, only up or down. So in no why shape or form could that possibly affect the "timing"

Then I don't understand. If you have reflections in the room causing peaks of 6 dB's and you cut them down flat, you are telling me that it won't affect the subjective impression of "speed". Perhaps bass articulation is a better term to use.

I would imagine a more reasonable octave to octave balance of energy would improve ones perception of bass articulation/tightness, but you seem to be suggesting that I'm wrong. Perhaps I am. Perhaps "shift" was the wrong term to use, but that's a minor nitpick.

I'm going to go out on a limb here and say that your friend, at the very least, is more correct than you are.

In what way would I be wrong? I don't mind being wrong, but I would like to know how he would be right. My observations are contradicting his views. Simply moving speakers or subwoofers around the room will alter the frequency response and so far I've noticed big changes related to the tunefulness of the bass. It sounds subjectively "quicker" (although bass isn't fast, that's a misnomer), more tight, controlled - insert whichever term is appropriate.

[trnqk7]

Merely flattening the response shouldn't have an effect on "speed" or "articulation" of the bass response. You will notice that with a flat frequency response you will typically find the lowest and highest frequency ranges quieter than those more in the middle range. Again, that has nothing to do with "timing".

Reflections in a room being cut, whether by a filter or just a better design, will not change the "speed" or "articulation". You still are doing nothing to shift the frequency forwards or backwards in time. Shift probably was the wrong term for you to use, but it's not a minor nitpick as far as the mathematical terminology goes. Plus shift is correct as far as an amplitude shift (up or down, not forwards or backwards).

Your very last sentence is correct-in that moving speakers or subs around will alter frequency response and "articulation" (although I think that's still an incorrect term, I think your original phrasing of "speed" is more adequate here). The reason it's correct is that reflections, standing waves (peaks/nulls), and direct sound all play a part in what we hear from a speaker. Moving a speaker will cause those parameters to change (I'm thinking, and will gladly be corrected if I'm wrong, that the direct sound radiated from the speaker will have little to no difference in it's frequency response from this scenario. However, I know that the other parameters will greatly change and affect what we hear). As far as the "speed" goes, that will "change" only because the physical distance between you and the speaker changes. The sound will either have to travel farther (more time=slower) or less far (less time=faster). Also factoring into that would be the reflections-their distance traveled will also change, thereby slowing or speeding up the time it takes for their sound to reach you vs. the directly radiated sound. This is mostly likely what results in a blurred, muddy sound (inarticulate for your phrasing?).

Frequency response however still has nothing to do with the articulation/speed/whatever. That is how, in the original post, I posit that your friend is more correct. You aren't completely wrong, but the basis for what you hearing is wrong. You have your cause/effect relationships mixed up imo. Frequency response /= speed and articulation. Room placement can and does have an effect. This is why room treatments are often discussed. They not only help level out frequency response, but in some applications could probably lower it so much that for a reflection as to eliminate (for all practical-ie audible puroses) that source of sound. Thereby potentially fixing or improving the impression of "speed" or "muddiness" or "articulation". I use the quotes not to mock, but just to point out terms that are subjective and difficult to quantify.

[Vaughan Odendaa]

First, thanks for taking the time to offer your views on this. I do appreciate it. You've taken a great deal of time typing all that out and I can't really follow up on what you said, but I do have a question :

Frequency response however still has nothing to do with the articulation/speed/whatever.

So transient response isn't tied to frequency response? I thought that was some fundamental truth.

[trnqk7]

Transient response is the response of a system to something that takes it out of equilibrium or its steady-state. Step responses and impulse responses are examples of transient responses (think along the lines of them being members of a family and transient is just "father" or "mother" figure whichever you prefer-much like a square is a type of rectangle). Transient response can be an on/off event or just a response outside of the normal steady-state.

However it is just an amplitude thing at a given frequency (this is my understanding and a VERY quick google search seeming confirms this-again, I could be wrong and would welcome someone to explain it better). It doesn't shift anything in time. It may alter a frequency, ie, raise or lower it (50hz instead of 75hz or vice versa). But that doesn't effect the "speed" at which it travels, only the speed of oscillation. Sound travels at a relatively fixed rate, especially over these short distances. Distance is the main mechanism to change the perceived "speed" of sound. And you should only notice this from direct radiated sound from a speaker itself vs. the reflections from the room environment.

[Vaughan Odendaa]

I'm pretty sure the bass waves don't physically travel quicker - if that were the case you would've changed the frequency. But if you have a more reasonable energy per octave vs a ragged response with huge amplitude variations and you cut those peaks down to size, as it were, it sounds *as if* the bass is quicker and tighter. At least those are my thoughts.

If I move a subwoofer around the room and the bass sounds tighter in one location vs another then what could aid in this perception? The big thing that changed was the frequency response. Even moving a subwoofer half a meter can radically change the response.

So I then deduce from this that the frequency response affects my subjective impressions. Again, this is how I've reached my conclusions. I've measured plenty of rooms before, I've applied EQ on occasion so I feel some of my observations must carry some kind of weight. I'm a big believer in acoustic treatment and especially bass trapping as I have floor to ceiling absorption in my front corners which made a big difference. But simply changing position, whether it's my seated location or the sub position absolutely changes how the subwoofer sounds - it sounds less boomy, tighter etc - it might be semantics, but slow = boomy, and fast = tight/articulate?

Dan Wiggins wrote the paper on woofer speed and there he says that transient response basically is frequency response and vice-versa. Thanks again for your views on this. It doesn't seem so cut and dry as other people are giving me different explanations, so I'm just weighing the explanations. Don't know what's correct, what's wrong etc. I could be wrong and you could be right. You know how it goes, everyone has an opinion.

[TLS Guy]

There are three issues here.

The speed of sound is the same for all frequencies.

There is no such thing as fast bass, and it has everything to do with frequency response. A sharp transient is essentially a square wave, and you can't reproduce a square wave without an extended frequency response. A sub by itself such rumbles. It needs to integrate to the rest of the system which needs to be excellent to have any hope if having "attack".

The real issue as I have explained is total system Q, which is the quality of the bass resonance. High Q in the 0.7 range or above will sound like spreading glue, which is most ported subs.

A system Q in the region of 0.5 will be achieved by a lot of sealed subs and all properly designed aperiodic transmission lines.

To make a bass drum or kettle drum, sound exactly like the real thing , requires a well integrated total system of extended and smooth frequency response, with a total system Q in the bass range of 0.5, so it is what is known as critically damped.

Anything else will come up short.

[Vaughan Odendaa]

There is no such thing as fast bass, and it has everything to do with frequency response.

I agree, bass isn't technically fast. But you have subjective descriptions of what bass sounds like in a room. Perhaps "fast" isn't the correct term, but it's used all the time, not to describe the mechanics, just the subjective quality. So if the frequency response determines how the bass is going to sound (boomy, tight/ slow .. fast, whatever) then basically I am right in my observations.

[TLS Guy]

I agree, bass isn't technically fast. But you have subjective descriptions of what bass sounds like in a room. Perhaps "fast" isn't the correct term, but it's used all the time, not to describe the mechanics, just the subjective quality. So if the frequency response determines how the bass is going to sound (boomy, tight/ slow .. fast, whatever) then basically I am right in my observations.

Frequency response is not the determinant of whether bass is boomy or not, Q is and its interaction with the room is.

Some rooms have unfortunate bass peaks due to reinforcement by reflections.

However a high Q system will sound boomy even in a good room. A critically damped system will sound excellent in a good room and minimize the deleterious effects of poor rooms.