^
Great stuff. My interpretation of Toole quote is that you need an inert cabinet that minimizes internal resonances, a shape that keeps diffraction in check and drivers that need little to no real filtering.
Any good loudspeaker has to start with these parameters - perhaps easier said than done, but it can be done and it does not have to cost you a leg and an arm.
Great stuff. My interpretation of Toole quote is that you need an inert cabinet that minimizes internal resonances, a shape that keeps diffraction in check and drivers that need little to no real filtering.
Any good loudspeaker has to start with these parameters - perhaps easier said than done, but it can be done and it does not have to cost you a leg and an arm.
Yes..
The LS50 is reducing the diffraction related to the tweeter's pass-band. Crossover is 2.2 kHz.
Basically look to wavelength and substantial diffractive (angles).
You'll find DIY'ers that have been doing horns for a long time that have often gone to higher high-pass filters for horn-loaded drivers than what is typically optimal with regard to dispersion. (..with of course the inevitable vertical "aiming" that occurs with horns and drivers.) Sort of a "pick your poison" design-result, and hence and "art".
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Your son has some big shoes to fill if he wants to follow in your footsteps. If I were him I'd become a pastry cook!
Dipoles struggle with same issue as all others - wide range of wavelengths. Even more so, because front/back interference is so crucial! A planar radiating plate is as close to ideal as possible, but B&G Neo3 is as small as it gets, the frame being 6x9cm. Back-to-back domes have smaller diameter, but present pathlength difference in depth.
https://www.diyaudio.com/forums/multi-way/161299-directivity-dipole-tweeters.htmlome
Dipolplus - Alles über offene Schallwände
https://www.diyaudio.com/forums/multi-way/161299-directivity-dipole-tweeters.htmlome
Dipolplus - Alles über offene Schallwände
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Diffraction and roundovers
Gedlee "These are good questions and I would suggest that anyone who thinks that they know the answer would likely be mistaken. The rule in diffraction is how large is the surface curvature relative to the wavelength. Hence this, of course, means that all frequencies see the edge in different ways. I have thought about this in every way that you can imagine and they all seem to be complex enough that it is hard to guess at the answer and I have not seen a study of such, so there is no data that I am aware of. Hence, I just stuck with a circle"
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Gedlee: Several of your comments relate to eliminating nearby sources of diffraction, which make complete sense to me. (cabinets, furniture, etc) And of course the whole idea of cabinet round-overs. Could you comment on the opposite of a baffle round-over? Some vintage speakers, like my EV Marquis, have a very large recessed round-over, behind which the woofer and other drivers reside. It makes the 19" wide speaker look like a shallow horn. The quarter round-over is 2" wide blended into the side walls, and 1.5" deep.
What is your opinion of flush mounting drivers/speakers into a wide wall to ameliorate any of the negative effects you mention? Would a shape like the Marquis make those effects even worse?
Gedlee "These are good questions and I would suggest that anyone who thinks that they know the answer would likely be mistaken. The rule in diffraction is how large is the surface curvature relative to the wavelength. Hence this, of course, means that all frequencies see the edge in different ways. I have thought about this in every way that you can imagine and they all seem to be complex enough that it is hard to guess at the answer and I have not seen a study of such, so there is no data that I am aware of. Hence, I just stuck with a circle"
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Gedlee: Several of your comments relate to eliminating nearby sources of diffraction, which make complete sense to me. (cabinets, furniture, etc) And of course the whole idea of cabinet round-overs. Could you comment on the opposite of a baffle round-over? Some vintage speakers, like my EV Marquis, have a very large recessed round-over, behind which the woofer and other drivers reside. It makes the 19" wide speaker look like a shallow horn. The quarter round-over is 2" wide blended into the side walls, and 1.5" deep.
What is your opinion of flush mounting drivers/speakers into a wide wall to ameliorate any of the negative effects you mention? Would a shape like the Marquis make those effects even worse?
I suppose it is nice to see so much thought applied to this minor artefact by enthusiasts.
The problem seems complex when you are using 7th grade Euclidean thought which simplifies the issue... but, as Einstein said, too simplified isn't good.
Aside from the fact that we aren't ever talking about real point sources with drivers, it is simply a matter of statistical thinking. As long as you think of a point source of sound playing into a circle of edging, you are stuck with big diffraction at a single frequency. But if you think about the range of distances from the driver cone, the diffraction effect is obviously spread across a band. And "spread across a band" is, statically thinking, the same as saying, no problem at all.
The same mode of thought applies to other heart-rending issues in audio. The key take-away is to sometimes aim for heterogeneity so perturbations in sound get averaged out.
B.
Baffle diffraction
BelToronto:
How am I to interpret your comments? That various people on this site who are obviously MUCH MUCH more comfortable with measurements, and other miscellaneous artifacts of sound and design are merely wasting their time on things that don't matter?
I'm not sure what you are trying to do...dispute that this is an issue? I read as much as I could stand today on the topic, and wasn't able to determine any consensus. Your comments, as I've often noted, appear condescending and sarcastic. Is that your purpose?
BelToronto:
How am I to interpret your comments? That various people on this site who are obviously MUCH MUCH more comfortable with measurements, and other miscellaneous artifacts of sound and design are merely wasting their time on things that don't matter?
I'm not sure what you are trying to do...dispute that this is an issue? I read as much as I could stand today on the topic, and wasn't able to determine any consensus. Your comments, as I've often noted, appear condescending and sarcastic. Is that your purpose?
I believe the impact of diffraction is trivial (both absolutely and relative to really important factors in SQ). And easily controlled as per my previous post (for example, by simply not mounting drivers centred).
I post because I'd like to see folks develop great music systems rationally and not according to fad or mistaken interpretation of data. That's why I am willing to get flamed by posts like yours.
Accusing me of sarcasm merits an apology from you. Almost any remark can be heard as sarcastic, whatever is in the intent of the remark.
B.
Diffraction is audible and important to manage if you're looking for the very best- and that's what we try to do in our hobbies. It's relatively easy to use smooth-edged design elements if you're taking the care. My next roundovers will be 6" radius as I have some 12" half-round plywood that's just begging to be built up.
Using a good radius or even bevel will do add more "spreading" to even a complex driver/baffle model. Note line segments A, B, C- this simple 2d model shows the spread- the variance between these paths on the "roundover" area (Between rectangles) is relatively broad, and would be more pronounced in 3 dimensions.
If we want to get REALLY funky, consider the below- I was having this conversation with Dave the felt-man (from the AX article referenced earlier) a couple weekends ago.
These are dual coaxials (one front one rear), in wooden waveguides that mimic the stock hardware with somewhat smoother transitions. Take a look at the stock polars- pretty good performance for a coax (though the 15" from diysoundgroup... dear god....)
These can be wired to move either opposed-force (both voicecoils moving towards or away from their magnets identically) or not (front moves away from magnet, back moves in).
From a thoughts perspective:
What would we expect in each of these cases from a pattern perspective? From a diffraction perspective? What role would absorption play around the "middle" frame in either case? Are the edge bevels helping? Does the offset driver/waveguide placement and asymmetry from front/rear drivers "smooth" things or prevent desired cancellation?
The intent was to have highly similar, relatively controlled forward and rear lobes. The conversation really gets interesting to the sides, in the Low-Mid/LF. The baffles are something like 18"x30", the waveguides are about 12" diameter. The use of the term waveguide may be contentious here but it's about smoothness and directivity so....
https://www.jblpro.com/ProductAttachments/JBL_Ctrl328C_CT.v1.pdf
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
For a contrary view, eyeball the charts in Toole, 3rd ed, Cap 9.
Some charts show what happens when you take a typical bookshelf speaker box and mount it with the face flush with a wall (which ought to eliminate the cabinet edge diffraction).
If you can see non-negligible change in FR between free-standing and flush mounted, let us know.
B.
I would love to see that chart, but I cannot find my Toole. Could someone post it?
Is this it?
Example of the Effects of Room Placement & Baffle Step
That's what a google image search led me to.
Yes, close enough. Seems to be cap 9 in 3rd ed (older folks like me will smile ear to ear when they read the intro). Dunno.
Granted, as my old math prof used to say, "it's just proof by picture" but sort of fits the rhythm of hearing - if your eye can't detect non-negligible differences in that kind of plot then your ear certainly can't.
And now to be contrary to the contrary, Toole is here discussing the important contribution of Allison about cabinet geometry and walls and the power response shown in the plots (not drivers and box edges). I think he concludes that gross cabinet shape and radiation into the room does matter. But bits of felt around the tweeter may not matter, I'd guess.
Surprise, the Allison type of issues are hidden away - far away - in another forum at DIYaudio on acoustics. For sure, that should be the 5th loudspeaker forum, eh.
B.
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I've done enough measurements of my own to validate significant anti-diffraction measures. Hell, just the shape of a foam collar on a 60x40 horn made the difference of "meh" vs. "best and smoothest top octave control I've ever seen".
Whatever data Toole has published (and what I saw there does NOT make your argument, far from it) is irrelevant if it doesn't align to valid experimental data from others. Plenty of folks, myself included, have measured significant variances from diffraction. An article based on the FR response changes from felt treatment has been referenced here, several dB changes over meaningful bandwidths are indeed important.
Matter of fact, here's a goodie.
Improving the Sony SS-CS5 - AVS Forum | Home Theater Discussions And Reviews
Whatever data Toole has published (and what I saw there does NOT make your argument, far from it) is irrelevant if it doesn't align to valid experimental data from others. Plenty of folks, myself included, have measured significant variances from diffraction. An article based on the FR response changes from felt treatment has been referenced here, several dB changes over meaningful bandwidths are indeed important.
Matter of fact, here's a goodie.
Improving the Sony SS-CS5 - AVS Forum | Home Theater Discussions And Reviews
Baffle diffraction
Badman:
Thank you for posting that information, especially on the JBL 8" ceiling coaxial. About a month ago, I stumbled onto some of JBL's offerings under the pro group, and inquired with my favorite dealer if he could get them. Alas, the answer was no.
Without going into a lot of detail, a driver like that might be the only realistic solution in my room, due to all the serious issues to contend with. (Such as 5 doorways, 12 windows, a fireplace, a 30 degree angled wall along the longest wall, etc) If I can figure out how to post a picture, I'll do so.
I'd like to know if you have any comment at all on the DIYSOUNDGROUP coaxial you referred to. I've been looking at it, but for mounting in an end wall. The JBL you posted could be more easily placed in my soffit, and would be much simpler.
Badman:
Thank you for posting that information, especially on the JBL 8" ceiling coaxial. About a month ago, I stumbled onto some of JBL's offerings under the pro group, and inquired with my favorite dealer if he could get them. Alas, the answer was no.
Without going into a lot of detail, a driver like that might be the only realistic solution in my room, due to all the serious issues to contend with. (Such as 5 doorways, 12 windows, a fireplace, a 30 degree angled wall along the longest wall, etc) If I can figure out how to post a picture, I'll do so.
I'd like to know if you have any comment at all on the DIYSOUNDGROUP coaxial you referred to. I've been looking at it, but for mounting in an end wall. The JBL you posted could be more easily placed in my soffit, and would be much simpler.
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