I was just responding to your comment saying "I would have agreed with you on this except when I went back and reread Floyd's claim" where you went on to point out that the comparison was done with equal amplitudes - I was just pointing out that I was aware of that and mentioned it already and thus didn't think we were actually in disagreement.
I had a quick look and found two different mentions speaker dave made in relation to the audibility of cabinet resonances with changes in Q:
http://www.diyaudio.com/forums/mult...a-speaker-based-t27s-b110s-6.html#post4166507
and
http://www.diyaudio.com/forums/multi-way/245965-cabinet-sound.html#post3710117
To me that's pretty clear advice that when a mechanical resonance is involved - whether a panel resonance or a driver cone resonance, that improving the damping of that resonance to lower it's Q will make it less audible, and that is certainly my experience.
As you point out another way of looking at it is the amount of energy in the resonance - the high Q resonance will have more energy in it, how could it not ?
The artificial scenario of different Q resonances with the same peak amplitude, which doesn't happen in mechanical resonances when you are only varying the damping just serves to confuse the situation.
Last edited:
Simon - you see I completely agree with your previous comments (#200). I think that we are on the same page. The difference between fused signals and non-fused ones IS fundamental.
As to "I was just responding to your comment saying" - you are correct, I worded that badly. I should have stated that "I agree with you, however ..."
As to "I was just responding to your comment saying" - you are correct, I worded that badly. I should have stated that "I agree with you, however ..."
Last edited:
No, my speakers have a huge sweet spot which I think is because of the brick wall crossover around 1000 hz. They're actually on both sides of a plasma tv, and I know I get reflections off the TV so that could affect things as well.
That's really the issue. Diffraction might result in simple peaks and dips in the frequency response at a position. However, I assume our brains process these peaks and dips to form a picture of what's going on.
Its not just the instantaneous FR but the changes in FR over time as the later reflections arrive. Its a bit like lobing.
The fact that we have two ears and can locate sounds so well suggests that we must be very sensitive to timing. I don't understand the whole phase thing, but if the FR is flat across time and direction that is the best. I would think phase isn't as issue till it affects the FR in some way.
Yes, but this is the thing. At small timing differences from the direct it may only affect the response, but at slightly higher differences it can cause fatigue trying to sort it out. Then at large differences it becomes an echo, ie ambience, which is fine if it is nicely balanced.
What I'm saying is that with diffraction and early reflections what we actually hear are the changes in FR. Out of phase waves are interfering with the sound in various ways over time. Also differences in how the direct sound itself reflects off the baffle. Our brains process the change in FR and tell us one speaker sounds boxy and another smooth.
I think this is the case for all linear distortion, its the various changes in FR over time, and probably the difference between sounds that reach our two ears. Nonlinear OTOH is basically extra noise. I think its easier to mentally adjust to nonlinear.
Last edited:
I think too much is getting lumped together here. What we hear is more complex, timing clearly plays a role, so its more than just FR.
For example, in our latest study (incomplete at this time, but dozens of screened listeners in controlled double blind testing) we can not detect image location blur for steady state random noise signals, but we can with the same FR impulsive signal. But, on the other hand the noise signal is best at detecting coloration, and finally each is relatively immune to what the other is best at. Clearly there is more to things than just FR.
For example, in our latest study (incomplete at this time, but dozens of screened listeners in controlled double blind testing) we can not detect image location blur for steady state random noise signals, but we can with the same FR impulsive signal. But, on the other hand the noise signal is best at detecting coloration, and finally each is relatively immune to what the other is best at. Clearly there is more to things than just FR.
Yea that's what I took away from his lecture. Basically the frequency response decays over time.
So even if the direct sound from a speaker is flat the sound that arrives later might not be. This creates a mismatch. This is why we can hear things like an off axis suckout.
Apparently its part of how we locate sounds which we are designed to be sensitive to.
I assume that FR and the changes to it are how we can tell phase. Lobing is essentially a phase problem and is creates a different FR at a different angle.
Of course it's all relevant, and you should understand everything that Floyd says because it's all valid. But when we talk about the nuances of image that might result from cabinet diffractions, it's kind of beyond what Floyd is talking about. Think of it as Floyd's comments are the basics that you must understand to really follow what we are talking about in regards to diffraction. Floyd's stuff is the big picture and here we are into the details.
Without getting into Toole and pinna theory, I will point out that dipoles and de-emphasis on room colouration (such as with neutrality of non-direct sound) help reduce the salience of room cues relative to the reproduced signal.
My point is that you can't escape sound cues that tell your brain you are in your room. No way.
B.
My point is that you can't escape sound cues that tell your brain you are in your room. No way.
B.
Last edited:
I finally had the opportunity to make some quick grill on, grill off measurements of my main speakers, so as promised, here they are.
I was able to move the speakers to get a little to get a bit more reflection free time however the measurement environment was still far from ideal, so I've still had to use a rather short gate time of 2.5ms, so the measurement is only sufficiently detailed down to perhaps 1Khz.
So, not ideal, but it does give some idea of the effect of the grill cloth and it's frame on higher frequencies. The front panels are flat, 39cm wide 59cm tall, the "midbass" driver is centrally located while the tweeter is about half way between the mid bass and the top of the cabinet with a 20cm centre to centre spacing. The crossover is a 4th order LR at 3Khz.
The grill cloth is very simple - a wooden frame about 15mm tall and 10mm wide with black acoustic cloth pulled tight. There are no struts or braces - just a frame around the perimeter. The mounting pegs cause there to be about a 3mm gap between the frame and the surface of the panel.
The first is an on axis measurement:
The blue grill off measurement is clearly significantly smoother right from about 2Khz up to about 15Khz. In particular notice the peaks at 8Khz and about 6.5Khz.
Subjectively, putting the grill on loses some of the "airiness" of the treble and sounds slightly sibilant, but not to an objectionable degree. There is no sibilance with the grills off. The peaks at 6.5Khz and 8Khz in particular explain this sibilance.
There are noticeable dips at 3Khz, 4Khz, 9Khz and 11Khz that all probably contribute to a small loss of presence and airiness when the grill is on.
Next is 30 degrees off the horizontal axis:
In this one the difference between grill on and off is significantly less at lower frequencies, with only a small dip at about 4Khz being present until about 7Khz.
It's obvious though that the peak at 8Khz is still the same as is the dip at 9Khz.
This suggests the 8Khz peak and 9Khz dip is a cavity resonance formed between the tweeter and the grill cloth, and this peak/dip combination is probably present at most if not all off axis angles.
On the other hand most of the fluctuations seen at lower frequencies on axis are gone off axis, suggesting that the frame of the grill cloth was responsible for those.
Despite both drivers having a significant amount of high frequency directivity the frame of the grill cloth still has a significant effect, although nowhere near as bad as the Technics speaker I posted earlier.
On the other hand, the cavity resonance at 8Khz could probably be avoided by reducing the distance from the grill cloth to the tweeter. If it was halved it would shift it up to 16Khz so a bit less than half the gap should move it out of the audible region.
Unfortunately I can't move it any closer because while the tweeter is flush mounted on the panel the mid bass drive is mounted on the front of the panel. (For various reasons) So I had to make the frame of the grill cloth a lot taller than I would have preferred.
Do these grill cloths and frames introduce the horrific response aberrations of the Technics speaker I posted earlier in the thread - absolutely not. That was an example of how bad it can be if grills are designed with no consideration for diffraction. By comparison the changes here are much more subtle, and they still sound good with the grills on.
But there is an obvious improvement in the quality with them off, both subjectively and in measurements, so for critical listening I always remove them.
Attachments
Last edited:
I just bought one of these waveguided tweeters. It has a nice rainbow off axis response (at least to 45 deg)
Dayton Audio ND25FW-4 1" Soft Dome Neodymium Tweeter with Waveguide 4 Ohm
I don't think I would bother building a speaker without dealing with diffraction in the high frequencies. Its just not worth the trouble. A waveguide is easier than making a rounded enclosure.
The choice comes down to either more or less directionality. Directionality is better in a large room or if the speakers are near walls or objects.
Dayton Audio ND25FW-4 1" Soft Dome Neodymium Tweeter with Waveguide 4 Ohm
I don't think I would bother building a speaker without dealing with diffraction in the high frequencies. Its just not worth the trouble. A waveguide is easier than making a rounded enclosure.
The choice comes down to either more or less directionality. Directionality is better in a large room or if the speakers are near walls or objects.
It seems to me that the exact opposite would be the case. High directivity limits the early reflections that are so problematic in small rooms. Directivity is also advantageous in large rooms to direct the energy to where it is needed - both advantageous, but for different reasons.
In a larger sense, it isn't only dispersion control (that Earl favours for his well-argued reasoning) but what tone colour reaches your ears.
For days, I've been thinking that diffraction is not much different than "borrowing from Peter to pay Paul". Maybe the best analogy is "gain management" theory, really the same concept.
Subject to EQ etc, a driver emits whatever it emits and according to its Toole total polar plot, and room structural acoustics and furnishings*. The question is what gets to your ears and how we "colour manage" it.
Of course, folks who love dipoles (and we are a very dedicated lot) just laugh at talk of box diffraction since our systems diffract all over the room and we love the ambience... and think there's got to be more important stuff to think about.
B.
*pity the new acoustics forum was hidden away, far away
Last edited:
Too much direct sound without enough late reflections will sound lifeless and fatiguing. This is more true for music than home theater. Music is meant to interact with a space and produce reverb and harmonics.
Which leads to a much larger point, which is that most people (including me) don't have a properly sized and treated listening room. So most people are getting too much direct sound and not enough indirect. And the indirect they get may not be very good.
So FWIW in my hobbyist opinion, the reason why people gravitate towards certain kinds of lower fidelity options like tube amps and vinyl is they are unwittingly trying to dirty up the sound a bit and replace some of the harmonics that are missing.
If you are stuck with a small space something like a small spheroid high dispersion speaker might be your best option but only then if you can clear the area around it. Another option might be a larger speaker with a more resonant cabinet design.
Last edited:
Small dead rooms are indeed bad. That's why mine are as lively as possible. High DI gives a good clean direct sound with low early reflections and the room adds in the later reflections because it is reverberant. A small reverberant room with a low DI speaker will have poor to no imaging. A low DI speaker in a dead room just sounds dead.
I would assume if the room is dead you would want to have more dispersion and less directivity.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.