Polar plots
Getting back to this important point. I am certainly confused. Tho I "think" that I saw horizontal polar plots in Keele's Powerpoint presentation, I don't see them in the AES paper. I didn't get a CD with a copy of the Powerpoint.
Has anyone else seen the horizontal polar plots? I don't remember a significant shift in tonal balance off axis, but would love to see plots. Thanks
Getting back to this important point. I am certainly confused. Tho I "think" that I saw horizontal polar plots in Keele's Powerpoint presentation, I don't see them in the AES paper. I didn't get a CD with a copy of the Powerpoint.
Has anyone else seen the horizontal polar plots? I don't remember a significant shift in tonal balance off axis, but would love to see plots. Thanks
I have suggested on another site that those DIYers interested in experimenting with CBT might rationally begin with the simpler and significantly more modest group delay steered 50LA design:
http://www.jblpro.com/catalog/support/getfile.aspx?doctype=3&docid=1402
For which complete documentation is available here:
http://www.jblproservice.com/pdf/CBT/CBT 50LA-WH.pdf
Am I way off base with this? If not, what driver might be appropriately used?
http://www.jblpro.com/catalog/support/getfile.aspx?doctype=3&docid=1402
For which complete documentation is available here:
http://www.jblproservice.com/pdf/CBT/CBT 50LA-WH.pdf
Am I way off base with this? If not, what driver might be appropriately used?
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DIYers could build their own shaded array with any favorite full range driver. My paper shows a 16 element short line that performed pretty well, if not quite to the CBT standards. It was split into 4 electrical groups with relative levels of 0dB, -1dB, -3dB and -10dB. These would apply respectively to the center 4 elements, the 2 above and below the central 4, the next two above and below them, and the final two outer pairs. Resistive padding could achieve the level drop if you confirm the frequency response remains fairly flat.
Laid sideways the element strengths are like this:
-10 -10 -3 -3 -1 -1 0 0 0 0 -1 -1 -3 -3 -10 -10 (dB)
If your lines go floor to ceiling you don't need to do any of this. It is only for the short to medium lines that the arrays become very variable in vertical performance.
David
Drivers like that have a great packing factor when mounted end to end. That helps push off the lobing frequency.
David
Hi,
This might be a driver option:
Rated power handling 3 W
Impedance 8 Ω
Mean sound pressure 76 dB
Transmission range 120…20000 Hz
2.73€ each in 100pc lots.
http://www.diyaudio.com/forums/full-range/165942-small-32mm-wide-ranger-veco-32kc08.html#post2169012
https://www1.elfa.se/data1/wwwroot/assets/datasheets/03020757_1.pdf
- Elias
This might be a driver option:
Rated power handling 3 W
Impedance 8 Ω
Mean sound pressure 76 dB
Transmission range 120…20000 Hz
2.73€ each in 100pc lots.
http://www.diyaudio.com/forums/full-range/165942-small-32mm-wide-ranger-veco-32kc08.html#post2169012
https://www1.elfa.se/data1/wwwroot/assets/datasheets/03020757_1.pdf
- Elias
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Hello David,
You are right.
However, since most of the conclusions in psychoacoustic studies are done based on listener preference comparing a loudspeaker against another loudspeaker, and not a loudspeaker against reality, And since almost all the loudspeakers used are conventional monopole boxes, I really wish to see a study where line arrays are used.
After all, for example in case of early reflections, line arrays provide completely different pattern in temporal, magnitude and spatial domain than a conventional monopole box, it can be questionable if the conclusions based on available listener preference are valid.
Myself, I've been using dipole line array for several years. It's a straight array, no tapering, no delay, no curving, simple as it can be. I'm very pleased in it's behaviour in the normal living room acoustics. It delivers me more of the recording venue acoustics and less of the listening room.
- Elias
You are right.
However, since most of the conclusions in psychoacoustic studies are done based on listener preference comparing a loudspeaker against another loudspeaker, and not a loudspeaker against reality, And since almost all the loudspeakers used are conventional monopole boxes, I really wish to see a study where line arrays are used.
After all, for example in case of early reflections, line arrays provide completely different pattern in temporal, magnitude and spatial domain than a conventional monopole box, it can be questionable if the conclusions based on available listener preference are valid.
Myself, I've been using dipole line array for several years. It's a straight array, no tapering, no delay, no curving, simple as it can be. I'm very pleased in it's behaviour in the normal living room acoustics. It delivers me more of the recording venue acoustics and less of the listening room.
- Elias
Look up the AES papers of Salmi. He was exploring the interaction of a loudspeaker with the room and how it impacts our perception of frequency response. He found that early boundary reflections were objectionable and advocated greater vertical directivity. He ended up designing a short line array to reduce the floor bounce.
You will like his conclusions.
David Smith
A "piece of carpet" over a hard floor will not be sufficient to simulate many home conditions, imo. PM me to continue that discussion offline
(Don - great to see you here!).
_-_-
@Don & speaker Dave,
Again Don, fabulous to have you on here!
Speakerdave, i still don't fully understand your design - you made a few references that didn't (to me) seem clear, but it's just a "standard" CBT then?
Don, (and David) when I look at the nice color images showing the vertical "strata" for radiation in Don's paper (the first referenced one here) I think I see that while the levels in the listening plane are equalized nicely that there is a substantial amount of radiation that rises above the plane of the top of the speaker.
What I am saying is that while this may not be an issue, I have some concerns about it (even if it is attenuated) in the home environment where the ceiling is not a long distance away (as it is in a typical medium to large venue) or in a testing facility with high ceiling heights. I am not suggesting that it is a fatal flaw, just something that the figures in Don's paper illustrates, and that is worthy of some discussion...
_-_-bear
Again Don, fabulous to have you on here!
Speakerdave, i still don't fully understand your design - you made a few references that didn't (to me) seem clear, but it's just a "standard" CBT then?
Don, (and David) when I look at the nice color images showing the vertical "strata" for radiation in Don's paper (the first referenced one here) I think I see that while the levels in the listening plane are equalized nicely that there is a substantial amount of radiation that rises above the plane of the top of the speaker.
What I am saying is that while this may not be an issue, I have some concerns about it (even if it is attenuated) in the home environment where the ceiling is not a long distance away (as it is in a typical medium to large venue) or in a testing facility with high ceiling heights. I am not suggesting that it is a fatal flaw, just something that the figures in Don's paper illustrates, and that is worthy of some discussion...
_-_-bear
Well in the hotel meeting room the ceiling was somewhat high, maybe 12'. But there was a wide soffit at 8'. Don's array was at the inner edge of the soffit. From the pattern charts, I don't think much if any energy was hitting the soffit. It was probably hitting the ceiling 9 or ten feet away. Just FWIW.
@bear,
Yes I agree that the carpet over a hard floor will not simulate a living room, however it will be a first order estimate of carpet's impact on the floor's reflection and if/how it affects the speakers frequency response. I think it is best to take one step at a time, so after we get past this test we can move to a more representative room that approximates a normal living space.
-mk
Yes I agree that the carpet over a hard floor will not simulate a living room, however it will be a first order estimate of carpet's impact on the floor's reflection and if/how it affects the speakers frequency response. I think it is best to take one step at a time, so after we get past this test we can move to a more representative room that approximates a normal living space.
-mk
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You might download and read the 4 part paper I attached a couple of pages back. It includes everything I know on the subject.
I wouldn't call mine a CBT as Don uses that name for his particular design. It is a short (not infinite length) array that uses a shading technique to improve its off axis performance. By "shading" this means that the elements aren't all the same strength. It was found by acousticians before Don and I, (and also by antenna designers as there is analogous performance with antenna arrays) that reducing strength of elements towards the end of an array can improve the off axis smoothness. In my case I was working on a 16 tweeter line for a McIntosh sytem and wanted to have less variation in response for standing vs. sitting. The shading technique I described worked very nicely at that.While there may be radiation above the top of the speaker, it is considerably less with any line array than it would be from a conventional non-arrayed system.
David
Is that Geddes (on left) and Linkwitz belittling the need for a loudspeaker to play loud?
I know my Dad likes to brag about being an "old" guy, but at least he doesn't need hearing aids.... oh but maybe that would be great, cause you know he'll try to utilize the miniature drivers somehow!
It may be that I do not understand what I am seeing in Don's paper. But I am comparing the Legendre shaded 50 driver array figs 62-5 with 41-3 for the straight line source.
I seem to see energy going up vs. energy not going up??
So, perhaps I'd prefer a taller speaker??
No matter what, the "shaded array" is a neat idea.
@ Dave, i think i read your pdf, and if your speaker is explained fully there, I'm as yet unclear - but this seems to be a trend with me??
I seem to recall the McIntosh line source speakers - too bad the technology wasn't really "disclosed" in the marketing... although perhaps I am thinking of much earlier speakers from them??
_-_-bear
I seem to see energy going up vs. energy not going up??
So, perhaps I'd prefer a taller speaker??
No matter what, the "shaded array" is a neat idea.
@ Dave, i think i read your pdf, and if your speaker is explained fully there, I'm as yet unclear - but this seems to be a trend with me??
I seem to recall the McIntosh line source speakers - too bad the technology wasn't really "disclosed" in the marketing... although perhaps I am thinking of much earlier speakers from them??
_-_-bear