If you limit yourself to AES only, you'll miss whole a lot of news ! 🙄
Besides, all the perceptual models I've encountered use bandwidths of about 1/3 octave or wider. The need for a narrower bandwidth is questionable from the listener point of view.
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Please stop that disrespectful behavior of rolling eyes and making wrong assumptions about me as a person. I don't limit my reading to AES publications. You asked for reference and I pointed to one possible source.
Regarding perceptual models - perceptual models of what? Loudness? Again, this is not what I was talking about.
With a parametric EQ it's easy to simulate what modes can do to music. It's easy to over-emphasize single fundamentals of instruments like a (electric) bass or drums with much smaller bandwidth then 1/3 octave. This is exactly what can happen in acoustically small rooms. Looking at 1/3 octave smoothed data doesn't reveal the correct physical parameters that would allow proper assessment.
All the sounds going to brain through ear canals are filtered by (about) 1/3 octave fiterbank. If you want to bypass perception the efforts beyond that become irrelevant for the listener. In other words it could be claimed anything not visible in 1/3 octave analysis is not perceptible.
Lets say we have a 12 dB peak with Q=6. Do you think this will be most annoying at 3 kHz or 30 Hz ?
You can claim whatever you want but that doesn't make it an objective fact.
You could easily come up with a case where audible magnitude irregularities won't be visible through a 1/3 octave filter.
As I said before, it's easy to do your own experiments. In the end you'll find that your claim is wrong for low frequencies.
Do you have access to the AES journal?
Not sure how this is related to what we were discussing? Nevertheless, due to room effects such an isolated peak is more likely to happen at 30Hz than at 3000Hz.
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According to the BBC article, the peak is more likely to be audible at 3kHz. Fletcher Munson suggests that we will be more sensitive to 3KHz than 30Hz.
Does this mean we should build our speaker cabinets not to be as stiff as possible but rather to optimize them for damping. Damping, I believe, is more effective at higher frequencies.
That's not correct. It takes more SPL to make lower frequencies audible but once you're past the threashold a low frequency sound is perceived proportionally louder than a higher frequency sound.
You need only a 10dB increase at 30Hz to get from 80 to 100phon but a 20dB increase at 3000Hz:
I was thinking of a peak in the speaker's own response. Surely a 3k peak would be far more audible. It's easy to test this out using a parametric equalizer.
Within a room you will not get a single peak caused by room acoustics isolated only at 3kHz (we will have peak and dips across the entire frequency range), but at 30 Hz we surely will because of room modes.
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I was looking at it from the perspective of an audibility threshold, not a relative increase in sound level.
Anyhow, I'm now thinking this is the wrong way to approach the question. The F-M curves, if I remember, deal with the perception of loudness as a function of frequency. They do not represent our ability to perceive a peak at a frequency on a background of music covering many frequencies. The BBC testing looked at the perception of colouration against the background of a music signal that spanned many frequencies and as such I think their data is more relevant than the F-M curves. For starters, the psychoacoustic effect whereby an existing signal masks adjacent signals may play a role in our perception of colouration. This is something Hugh Dean has exploited in some of his amplifier designs.
Bigun, now you're mixing two separate discussions. Elias was rewarming a discussion about room resonances that started here.
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I don't understand what you are saying. I was talking about the question raised by Stig, which you responded to in post 76. Sorry, but you've lost me completely, not sure what it has to do with Elias.
I was under the impression that http://www.diyaudio.com/forums/multi-way/215133-box-colourations-really-39.html#post3097447 was a direct reply to Elias' post.
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De-coupling the driver from the cabinet and other experiments
Thanks, Speaker Dave, for the link to the BBC paper.
I would agree with you on the potential effects of de-coupling the driver from the cabinet a la the KEF speakers. Four years ago, I used visco-elastic grommets and a sorbothane gasket to de-couple a large full-range driver from a bass-reflex cabinet (see the E-A-R Composites website for grommets and graphs and a nice paper on 'The Four-Fold Method of Noise and Vibration Control') at frequencies >15Hz. I used a stethoscope to listen to the cabinet before and after de-coupling the driver. I heard a marked diminution in sound transmitted into the cabinet, especially for frequencies >100Hz. It follows that sound radiated from the excited panels also diminished, though this was harder for me to conclusively discern when listening from 3 metres away.
The panels (14mm ply, screwed and glued, no work of art - this was an experiment!) were then damped (on the inside) using Dynamat Extreme constrained layer damping. This time, my listening through the stethoscope was less conclusive. I thought that the panels became a little quieter again, notably at a 'hot spot' I'd previously found on a side panel. I could hear no difference in sound from my listening position.
The panels were then covered (on the inside) with 25mm of Latimer Acoustics 'Acoustop' polyether foam. Listening through the stethoscope, I could not hear any difference to the sound transmitted to the cabinet. From my listening position, I could hear a difference to bass tones, which I attributed to the effect of increased acoustic damping of the air enclosed in the cabinet, and some improvement in speech and sung tones.
I removed all the foam except a panel on the rear wall of the cabinet directly behind the driver. My perception of improved speech and sung tones remained, the change to bass tones was gone.
I removed the de-coupling grommets and gasket and constructed an isobaric chamber from large diameter PVC tube, mounting two full-range drivers with the option of connecting only the front or the rear driver to the amp, or both in series, or both in parallel (always in phase, whether in series or in parallel). I retuned the cabinet (the volume was halved with plastic bags full of sand, the port tube trimmed) to suit the composite driver. The chief finding (apart from confirming the Thiele-Small analysis for frequencies <1kHz) was that, with the front driver disconnected, the rear driver could clearly be heard, though diminished, through the front driver, especially at higher frequencies.
I returned to using a single driver, directly mounted on the front panel, and experimented (played?) with acoustic foam on the side and top panels immediately adjacent to the driver and, finally, with wedges of foam attached to the arms of the driver basket immediately behind the cone. The latter brought clearly audible improvements to spoken and sung tones.
As a result of these amateur experiments, I concluded that I would, in future, pay attention (in priority order) to:
I would probably only tackle de-coupling the driver and cabinet again as a last resort. It's not a straight-forward task and I did not find it as audibly rewarding as other measures I took, especially reducing reflections back through the driver cone.
Bondini
Thanks, Speaker Dave, for the link to the BBC paper.
I would agree with you on the potential effects of de-coupling the driver from the cabinet a la the KEF speakers. Four years ago, I used visco-elastic grommets and a sorbothane gasket to de-couple a large full-range driver from a bass-reflex cabinet (see the E-A-R Composites website for grommets and graphs and a nice paper on 'The Four-Fold Method of Noise and Vibration Control') at frequencies >15Hz. I used a stethoscope to listen to the cabinet before and after de-coupling the driver. I heard a marked diminution in sound transmitted into the cabinet, especially for frequencies >100Hz. It follows that sound radiated from the excited panels also diminished, though this was harder for me to conclusively discern when listening from 3 metres away.
The panels (14mm ply, screwed and glued, no work of art - this was an experiment!) were then damped (on the inside) using Dynamat Extreme constrained layer damping. This time, my listening through the stethoscope was less conclusive. I thought that the panels became a little quieter again, notably at a 'hot spot' I'd previously found on a side panel. I could hear no difference in sound from my listening position.
The panels were then covered (on the inside) with 25mm of Latimer Acoustics 'Acoustop' polyether foam. Listening through the stethoscope, I could not hear any difference to the sound transmitted to the cabinet. From my listening position, I could hear a difference to bass tones, which I attributed to the effect of increased acoustic damping of the air enclosed in the cabinet, and some improvement in speech and sung tones.
I removed all the foam except a panel on the rear wall of the cabinet directly behind the driver. My perception of improved speech and sung tones remained, the change to bass tones was gone.
I removed the de-coupling grommets and gasket and constructed an isobaric chamber from large diameter PVC tube, mounting two full-range drivers with the option of connecting only the front or the rear driver to the amp, or both in series, or both in parallel (always in phase, whether in series or in parallel). I retuned the cabinet (the volume was halved with plastic bags full of sand, the port tube trimmed) to suit the composite driver. The chief finding (apart from confirming the Thiele-Small analysis for frequencies <1kHz) was that, with the front driver disconnected, the rear driver could clearly be heard, though diminished, through the front driver, especially at higher frequencies.
I returned to using a single driver, directly mounted on the front panel, and experimented (played?) with acoustic foam on the side and top panels immediately adjacent to the driver and, finally, with wedges of foam attached to the arms of the driver basket immediately behind the cone. The latter brought clearly audible improvements to spoken and sung tones.
As a result of these amateur experiments, I concluded that I would, in future, pay attention (in priority order) to:
- Reducing sound reflected from the driver basket arms back through the cone;
- Controlling reflected sound from the rear wall of the cabinet;
- Judicious use of acoustic foam in the enclosure; and
- Judicious use of constrained layer damping on 'hot-spots'.
I would probably only tackle de-coupling the driver and cabinet again as a last resort. It's not a straight-forward task and I did not find it as audibly rewarding as other measures I took, especially reducing reflections back through the driver cone.
Bondini
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Very interesting and really nice to hear of first hand experiences.
You put some real time and effort into those experiments and got some really good information out of it. The idea with the pvc tube was really neat.
I'd like to learn more about the foam on the driver basket - what it looked like and how it was attached ?
You put some real time and effort into those experiments and got some really good information out of it. The idea with the pvc tube was really neat.
I'd like to learn more about the foam on the driver basket - what it looked like and how it was attached ?
I thought of the foam on basket arms to diminish reflections back into cone when I was putting caulk on my woofers the other day. I was assuming someone had done it before, but had never actually heard or seen it... Glad you did! This is why some very high end speakers have well designed baskets with small, rounded arms and small magnets. Large cheap woofers, not so much (like subs and PA woofers and Econowave stuff).
I am going to assume that putting absorbing material on the arms of the speaker basket would only really help with drivers that play full range, or crossed over high, as a thin layer of foam is only going to block frequencies in the 2-3k range minimum at that depth? Is this really going to help with people who are running larger woofers to 1.2k or even lower like in the econowave speakers? I would assume subs would see no benefit at all. I am assuming this, as room treatment panels need to be at least 3 inches thick to get anywhere near upper midrange frequencies. Even 300hz with good absorption is hard to do... Most drivers don't have 3 inches of room to spare as far as foam in between cone and arm. (I hope it's a low excursion driver 😀 )
I have seen the open baffle and baffle-less guys who use foam or rubber on basket to decouple from baffle and also use o-rings on the mounting bolts to not allow direct contact to basket. I may try it for giggles, but will not bet on it doing that much my lead ears can hear (especially with no measuring equipment).
I think that if you decouple the woofer from the cabinet, it's important to sound deaden (through dampening) the woofer basket (especially if it's cast aluminum). I know the woofers in the speakers I have now rung like a bell before I put caulk on them.
#3 is the most effective, and will help with #2 (if you don't want to build a non paralleled rear wall).
I am going to assume that putting absorbing material on the arms of the speaker basket would only really help with drivers that play full range, or crossed over high, as a thin layer of foam is only going to block frequencies in the 2-3k range minimum at that depth? Is this really going to help with people who are running larger woofers to 1.2k or even lower like in the econowave speakers? I would assume subs would see no benefit at all. I am assuming this, as room treatment panels need to be at least 3 inches thick to get anywhere near upper midrange frequencies. Even 300hz with good absorption is hard to do... Most drivers don't have 3 inches of room to spare as far as foam in between cone and arm. (I hope it's a low excursion driver 😀 )
I have seen the open baffle and baffle-less guys who use foam or rubber on basket to decouple from baffle and also use o-rings on the mounting bolts to not allow direct contact to basket. I may try it for giggles, but will not bet on it doing that much my lead ears can hear (especially with no measuring equipment).
I think that if you decouple the woofer from the cabinet, it's important to sound deaden (through dampening) the woofer basket (especially if it's cast aluminum). I know the woofers in the speakers I have now rung like a bell before I put caulk on them.
#3 is the most effective, and will help with #2 (if you don't want to build a non paralleled rear wall).
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Not sure how much help foam would be on basket arms but I suspect the effect on woofer baskets to be close to zero due to the wavelengths involved.
May be if one would just some hard material to change the angle of reflection thereby directing those reflections away from the cone and into the box where one would have better a chance in eliminating them?
May be if one would just some hard material to change the angle of reflection thereby directing those reflections away from the cone and into the box where one would have better a chance in eliminating them?
Porous absorption works by dissipating "air movement" into heat. So it's best placed at velocity points. This is not at a boundary.
Hi Bondini,
Sounds like some very interesting experiments and results. I am a bit surprised that you felt the decoupling made a dramatic difference but still put it at the bottom of the list for further development. It can be tricky to do correctly since adequate woofer mounting will tend to be at odds with good decoupling.
I'd also note that you made your changes cumulatively, that is the woofer was still decoupled when you added constrained layer damping. Since we are generally trying to get wall radiation to that 30dB below point it is always possible that the first change gets you there and the subsequent changes are "gilding the lily" and not so audible. In this case the order that you make the changes might alter your view of what was effective.
For sound transmission through cones I have seen some measurements by Freyer wher he measured a broadband 25dB loss through a cone with 2 major transmission spikes. One was at fundamental resonance and the second was close to 2k and looked like a typical coincidence frequency transmission, with only 6 dB loss. This means anything bouncing around inside the box has about a 25dB barrier to getting back out (this dependent on cone mass).
I haven't experimented with chassis reflections. I suspect that they can only matter for full range drivers because the dimensions are pretty close to the cone. As for those who dribble damping goop on woofer chassis legs......
David S.