Baffle Diffraction

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Can you post the felt and no felt impulse responses overlaid rather than a difference ?

Here you go. Blue: no felt; red: with felt
Felt_impulse_comparison.png
 
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2dB difference at 3Khz - that will be very audible. 3Khz is literally where our hearing is most sensitive and it is a key frequency affecting imaging.

True. Also, a lot of speech intelligibility relies on the 3 kHz range.

A difference graph is good for frequency responses but a bit confusing for impulse responses. Can you post the felt and no felt impulse responses overlaid rather than a difference ?

I made that plot to see what the diffraction looks like in time domain. Delayed and smeared, as I thought. Below is the FR plot of the difference. Bare in mind that my methodology is not the best -- no access to anechoic chamber and the felt treatment doesn't nullify diffraction. My measurements should be interpreted carefully and not to be taken as an absolute truth, but I think they still offer some insight into what's going on.

Felt_difference_FR.png

I've come to understand that steady-state measurements like this show only one aspect of diffraction, basically the irregularities in FR are symptoms and an indicator that something's going on, but the real causes of diffraction audibility lie in time domain.
 
I made that plot to see what the diffraction looks like in time domain.
OK, is anybody still arguing you can hear diffraction?

I guess the "importance" of it has moved to stereo image and smearing.

Time... isn't that about the human inability to hear phase information?

With heads stuck into the textbook, posters are imagining a perfect source of sound in a perfect room that sends a perfectly identical image to the two mic's.... and they come out of two perfectly matched drivers in boxes perfectly matched for diffraction and, unlikely of all, a room with perfectly balanced acoustics. If not, then the irregularities of diffraction are just a spit in the ocean of disparate tonal influences between the first violin section and you.

(Actually, some of the previous paragraph doesn't apply to many of the recordings posters are moaning the lost of stereo location about: if they are the common pop-music 100% cooked stereo made by panning. As far as I'm concerned, losing the stereo "localization" of cooked sound is no big loss.)

Yes, the physics of diffraction are real. But how it upsets human perception for sound from speakers*, singly or as stereo pairs in normal rooms, is a different question.

B.
*or anywhere else in real life
 
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"I've come to understand that steady-state measurements like this show only one aspect of diffraction"

I agree. That's why a lot of the measurements taken are usually in steady state which does not nearly capture how the our ears detect sound. A lot of people take freq. response or jitter plot in steady state and came to erroneous conclusion.
 
However this is not the norm for ABX testing which typically wants the listener to make decisions about what they are hearing quickly, with the mistaken belief that if you can't identify a difference of two 5 second samples of audio after several random selections of them that there is no audible difference.

Again, it's all about the experimental design, and yes it's very often done poorly. The statistical analysis will tell you that.

For example, in our latest double blind test, the first round came out absolutely significance free, meaning that the test design was wrong. I recognized what the problem was and we changed the design, a new signal source, and got much better data with some significant results. The fact that the first signal did not show anything was in itself noteworthy, so no data is ever totally useless.
 
Thank you. So, this picture is a representative of our temporal resolution?
View attachment 709343

Yes, exactly. All models of human hearing use GammaTone filter banks, it's just the way that we hear. It is generally believed that the bandwidth of the filters should be approximately the same as the ERB of Moore (Equivalent Rectangular Bandwidth.) You can see how at HFs we resolve signals (the impulse response has settled) at ever shorter time periods. Any diffractions or reflections that occur within the impulse response are fused with the direct sound and will smear the image. Lidia and I have direct evidence of this fact coming out in a paper shortly.
 
2dB difference at 3Khz - that will be very audible. 3Khz is literally where our hearing is most sensitive and it is a key frequency affecting imaging.

A difference graph is good for frequency responses but a bit confusing for impulse responses.

Some data from Moore suggests that our best resolution is actually at 2 kHz, but that not a big difference.

I have often used impulse response differences when looking at diffraction type problems.
 
Any argument that nobody can sense the minor re-arrangement of bumps-and-dips caused by diffraction in the as-if steady-state FR applies far more strongly to non-steady-state listening.

Ben - this is clearly not true and in fact it is the exact opposite of what actually happens. Consider group delay, for example, it is a proven fact that we can hear group delay under various conditions. But there are group delays that have no effect of the frequency response. Hence, how could your statement possibly be true.

As to feedback in a loudspeaker, this has been done so many times and for so long (Dave Clark did this some four decades ago.) It has never been shown to have any significant effect on audibility for a "good" driver. It might make a really bad driver better, but even this is doubtful.
 
Most definitely, but I use such a big driver for directivity, not "filling a room". But it does "fill the room" nicely even down to 20-30 Hz which your 6" woofer is going to choke on. There is also the efficiency and the extremely low distortion, not to mention the MaxSPL that is achievable. No small woofer is going to get you those things.

I am designing for a DI in the 9-12 dB range. A 6" woofer would be lucky to get 4 dB.

I can't imagine a 15" woofer having much finesse at lower volumes but idk. Most speakers transition from omni to more directive sound, so then when in this optimal? I would imagine it depends on the room and what early reflections you're dealing with?

Finally I do also take issue with fanatical devotion to blind A/B testing as the only method that works or matters when deciding whether something is audible or not. While it certainly has its place and I have used it to test some things, it does have a major shortcoming - some types of subtle changes in frequency response, especially those that affect imaging, are not always immediately apparent in rapid A/B switching and take some hours or even days to form an opinion on, based on a wide selection of music.

Speakers are like shoes, it takes time to develop preferences and notice problems. At this point I subscribe to the least amount of fatigue as the most important goal, above dynamics and everything else.

Right. So as narrow as possible with as much of a roundover as possible. Vivid Audio Giya and Estelon XB come to mind. Quite hard for the average DIY guy to do these shapes, though. 3D printing the front baffle maybe?

One can stack 1/4" MDF into a pyramid shape and then grind it into a smooth rounded surface with a powerful belt sander. Might want to wear a dust mask.

Ben, it's not solely a FR problem. It's a direct-radiation-reflection interfering with direct-radiation, that presents itself both as comb filtering of FR and smearing time delivery.

I agree the FR component may probably never be reliably discerned. But I strongly think the time component is there to hear reliably.

Diffraction IMO is simply another form of early reflection. It manifests itself in the FR but doesn't behave the same as if the sound was coming directly from the driver, since it isn't.

One of the things that even experienced people seem to forget is that its not the measurements per se, but how our brain interprets them. So looking at an FR graph visually doesn't tell us how offensive something will sound.
Diffraction makes the FR messy but in some ways the brain adjusts to it better than say cone break up. But still it's an issue if we want speakers that can "disappear" and image solidly.
 
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I can't imagine a 15" woofer having much finesse at lower volumes but idk. Most speakers transition from omni to more directive sound, so then when in this optimal? I would imagine it depends on the room and what early reflections you're dealing with?

"Finesse?", I don't know that term in science language. There is no science that would suggest that a bigger speaker handles small signals any worse than a smaller speaker.

The polar pattern of the woofer should match that of the waveguide at the crossover. The narrower the directivity the better the imaging will be in a small room. All small rooms have early reflections and diffractions that are problematic. A high DI minimizes them.
 
Diffraction IMO is simply another form of early reflection. It manifests itself in the FR but doesn't behave the same as if the sound was coming directly from the driver, since it isn't.

They are very similar and yet fundamentally different. Both can be thought of as creating image sources. In a reflection the virtual image is exactly that of a mirror - some distance behind the reflector. On the other hand, diffraction results from a boundary change and it too creates a virtual image source, but positioned exactly at the diffraction point (or line or whatever.) Hence diffraction will always be much closer in time to the direct sound than a reflection will. A very significant difference.
 
towl trick -> cowl trick?

If one can suspend judgment on the dubious design and decor consequences of this idea, might a lot of edge diffraction be reduced if, instead of the apparently little effect a felt ring has, instead do a variation on the "towel trick" used with success on horns (but to reduce the cavity resonance), as follows: fabricate what I'd call a hood (cowl?) around the driver(s), sort of a partial funnel or torus around it. This would, I would think, greatly reduce any waves to the side and to nearby diffraction-prone edges.
 
the mirror analogy doesn't work for me because a mirror would reflect the entire spectrum of light, instantaneously (as in all frequencies) with diffraction you have frequency selectivity (determined by physical size vs frequency) so there's a filter effect and then the time difference between the two sources which causes comb filtering that we hear.
 
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