I think I've got quite constant directivity in this design surrounding an ATH-enabled waveguide with small woofers in front to extend pattern control, then adding additional woofers on all sides for a cardioid response to extend pattern control even further.
Full range line array for wall or corner placement
see post 1427
so far, this design exists only in paper and Vituix simulation
the thread started out as a line array which was built but then went in a different direction...
Full range line array for wall or corner placement
see post 1427
so far, this design exists only in paper and Vituix simulation
the thread started out as a line array which was built but then went in a different direction...
Constant directivity designs come out on top in double blind listening tests, done by the scientific experts in this field.
Something is wrong with your assumptions.
There was a rainstorm and wind here, and today I started CPR (Body Postural Rehabilitation) sessions so I apologize but I will not be able to respond individually to all the answers. Thanks for that !
Indeed, my curiosity was about how CBT can achieve DC with multiple speakers on a curved stand.
Much has already been said and there is currently a CD thread using horns, so I opened this separate thread.
Here is a paragraph that caught my attention, and that seems to be quite extraordinary if true....😉
Don Keele's CBT (Constant Beamwidth Transducer) Page
“Figure 18.3 shows a small sample of the informative sound field simulations in the paper. (……….) How did (e) and (f) sound? Excellent—at least that is the author’s opinion from a biased, sighted test. It was distinctive in how little the sound level and timbre appeared to change with location in the room and how the loudspeaker did not get “loud” as one walked up to it.”
Indeed, my curiosity was about how CBT can achieve DC with multiple speakers on a curved stand.
Much has already been said and there is currently a CD thread using horns, so I opened this separate thread.
Here is a paragraph that caught my attention, and that seems to be quite extraordinary if true....😉
Don Keele's CBT (Constant Beamwidth Transducer) Page
“Figure 18.3 shows a small sample of the informative sound field simulations in the paper. (……….) How did (e) and (f) sound? Excellent—at least that is the author’s opinion from a biased, sighted test. It was distinctive in how little the sound level and timbre appeared to change with location in the room and how the loudspeaker did not get “loud” as one walked up to it.”
Attachments
I'm not making assumptions. A massive amount of work has been done on this over decades by Floyd O'Toole, Sean Olive and others.
Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms (Audio Engineering Society Presents)
If you search that book for "constant directivity" you will get lots of hits; none of which argue against its use
"A good loudspeaker for this purpose would therefore be one that has two qualities: wide dispersion, therebypromoting some amount of reflected sound, and a relatively constant directivity index, so that the direct sound and reflected sounds have similar spectra."
"e
requirement for loudspeaker design, therefore, seems to focus on flat on-axis frequency response and constant directivity, so that direct and reflected sounds have similar spectra—assuming that the surface of the room boundary does not ange the reflected spectrum."
"A good loudspeaker for this purpose would therefore be one that has two qualities: wide dispersion, therebypromoting some amount of reflected sound, and a relatively constant directivity index, so that the direct sound and reflected sounds have similar spectra."
"e
requirement for loudspeaker design, therefore, seems to focus on flat on-axis frequency response and constant directivity, so that direct and reflected sounds have similar spectra—assuming that the surface of the room boundary does not ange the reflected spectrum."
There might be an issue of semantics going on here. "Constant directivity" has a very specific meaning in professional audio engineering, and that behaviour is not necessarily conducive to achieving good sound reproduction quality in a domestic sized room.
The main requirement that O'Tool documents for a domestic loudspeaker system is freedom from discontinuities in the power response, the second is a power response that tilts gently downwards as frequency rises. It is the second condition that constant directivity designs for public address loudspeaker systems attempt to overcome, so that everyone over a wide seating area has essentially the same transfer function. In a domestic room this will make the sound too 'bright' to be natural.
If the objective is to create sound in a room that is analogous to a real life performance, it is necessary for the loudspeaker to emulate the power response of real life acoustic sources. Of course there is a broad range of different power responses and directivities of real acoustic sources, so any loudspeaker is a compromise. However investigations since the 1970s by Floyd O'Tool, John Dunlevy, Sean Olive, Wilfried Ehrenholz, David Griesinger, et al, have determined the generally desirable slope of power response for loudspeakers for reproduction of recorder sound in rooms.
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" ..........have determined the generally desirable slope of power response for loudspeakers for reproduction of recorder sound in rooms. "
Something like the BBC slope?
What is meant by "BBC rise"?
Something like the BBC slope?
What is meant by "BBC rise"?
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Maybe, I'm not sure about that. Many people in many organisations at many times have come up with preferences for in-room loudspeaker responses, starting with the Academy of Motion Picture Arts and Sciences 'N' (normal) curve back in 1938, AKA 'the Academy Curve'.
Note typo in my text quoted: "recorder sound" should be recorded sound by which I mean the playback of naturally produced sounds whether speech, music or environmental, as opposed to synthesised sounds which have no natural analogue and therefore no basis for comparison when reproduced by a loudspeaker.
Describing what is meant or interpreting what others mean always appears to be a problem. Constant seems to have a simple meaning but still means different things to different people in this context.
"In all of our loudspeaker evaluations, over several decades now, the highest scores have gone to those with the most uniform directivity, not the highest or any particular directivity. In fact one of the highest scoring loudspeakers for a period of time in the NRCC double-blind evaluations was an essentially omnidirectional bipole design, which would generate maximum reflections from all vertical surfaces. This makes sense in that the precedence effect would remain intact because there is a spectral similarity between the direct and reflected sounds. That was a learning experience".
This quote from Floyd Toole and similar ones from others seem to say to me that there is no particular directivity per se that rates higher than others. It is a combination of a number of factors that result in a speaker being preferred.
A cone and dome speaker with flat on axis sound will tend to have a rising Directivity index and falling power response. Earl Geddes is probably the most noteworthy person who is in favour of a completely flat and quite high directivity index. He tilts the on axis response of the speaker to compensate for the perceived brightness. As you said above a flat DI from a true constant directivity source will likely sound too bright if the on axis response of the speaker has also been made flat. It seems to me that there is too much music already produced on speakers with a falling power response to make it possible to switch to a flat DI without a corresponding falling on axis.
Something about the sound of the BBC, Sean Olive included .
Gundry Dip or BBC Dip?
I understood what you wanted to say despite my bad English , but it is worth the clarification, thank you .
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Returning to my specific concern, I believe that the cost of building a system with the CBT principle is the cause of the few who dare to experiment.
Buying a large number of speakers, spending a lot of time and money on construction, and then being let down by the sound shouldn't be pleasant. I really thought I was going to get some response from some constructor here, but it didn't ......
Buying a large number of speakers, spending a lot of time and money on construction, and then being let down by the sound shouldn't be pleasant. I really thought I was going to get some response from some constructor here, but it didn't ......
You can find CBT threads in the full range forum; in particular one by Jim Griffin. He usually responds if he notices discussion about CBT. You should be aware though that CBT is constant vertical directivity. Its horizonal directivity is that of the drivers of which its made, which for a full range driver means narrowing pattern as frequency rises.
If you are impressed by a speaker whose sound image holds together even up close, you should look into Synergy. According to Tom Danley, you can stick your head into the mouth of a Synergy horn and it will sound the same - like a point source. And its also constant directivity, both in H and V over a frequency range corresponding to the size of the horn.
If you are impressed by a speaker whose sound image holds together even up close, you should look into Synergy. According to Tom Danley, you can stick your head into the mouth of a Synergy horn and it will sound the same - like a point source. And its also constant directivity, both in H and V over a frequency range corresponding to the size of the horn.
This is not because it is a synergy. You get this effect with a low diffraction single driver waveguide of sufficient bandwidth. I also feel that point source isn't the point, only a side effect.
Keele explored multi-dimensional arrays.
the wonder of the synergy is that its a multi-way that sounds like a single driver/point source up close. What other multi-way is like that? Not at all surprising for a single driver waveguide. Add a woofer below that single driver waveguide for the same response bandwidth as a Synergy and then try again!
Hi,
It all depend on what you call close but ime coax loudspeakers can have this effects too.
I've got experience with Tannoy's System 15 dmt II and 215 dmt ( and other smaller models but i find them showing less this effect, probably because of the higher xover point and lesser control on 'important' range- as described by GM previously 500hz and up) and they share this attribute
But of course they don't allow for same control of directivity on high bass/ low mid region and aren't constant directivity ( that said some recent coax do tends to have a range in which they could be considered close to constant directivity up to 10khz).
Horizontal isobar at the end of the datasheet:
http://westlab-audio.com/sites/default/files/downloads/2017-05/Datenblatt LR12.pdf
It all depend on what you call close but ime coax loudspeakers can have this effects too.
I've got experience with Tannoy's System 15 dmt II and 215 dmt ( and other smaller models but i find them showing less this effect, probably because of the higher xover point and lesser control on 'important' range- as described by GM previously 500hz and up) and they share this attribute
But of course they don't allow for same control of directivity on high bass/ low mid region and aren't constant directivity ( that said some recent coax do tends to have a range in which they could be considered close to constant directivity up to 10khz).
Horizontal isobar at the end of the datasheet:
http://westlab-audio.com/sites/default/files/downloads/2017-05/Datenblatt LR12.pdf
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Yep, the newer KEF speakers come close...
KEF Q350 Preference Rating - Google Drive
KEF R3 (Amir) Preference Rating - Google Drive
Making it appear high in the sorted list of CD designs (*):
Speaker Data (beta) - Google Drive
(*) testing at AVR rates speakers against the list of parameters as Harmon/Toole disclosed them.
KEF Q350 Preference Rating - Google Drive
KEF R3 (Amir) Preference Rating - Google Drive
Making it appear high in the sorted list of CD designs (*):
Speaker Data (beta) - Google Drive
(*) testing at AVR rates speakers against the list of parameters as Harmon/Toole disclosed them.
Then you should actualy read it.
The front cover of the 3th edition has the spinorama of the JBL M2 on it, that speaker is alway's comming out on top in DBLT's (together with the Revel Salon 2). This is a constant directivity design.
Hi, i built a pair of CBT's using 24 TC9's per speaker.
They have been the most room-neutral, even coverage, speakers I've built.
Very nice sound, particularly the midrange. No directivity index issues at all, after EQ. (they did require subs for my taste)
I think a big part of their design, over and above the typical line array used by the prosound industry, is the curvature that works with floor reflections to minimize combing. (May work with the ceiling too, but i'm not so sure there, given differences in home ceiling heights.)
The cost really wasn't that much. Gotta love the price of TC9s 🙂
Two 4x8 sheets of 1/2 baltic-birch covered the cabinet. Biggest challenge was building a 22ft diameter circle jig for the router, to cut the arc needed.
Well said.
A synergy is about a multiway for higher output (SPL) and also getting as much of the frequency range to mimic a point-source as possible.
Any full-range single driver with a wave guide is also trying to get as much of the frequency range to mimic a point-source as possible, albeit with greatly reduced output capability (and almost certainly reduced frequency extension).
Same thing for coaxes... another point point-source mimic, but with more output and frequency range extension than a full-range with waveguide.
If you really want clean SPL and freq extension from a box that tries to act like a point source, .....Synergies rule (to my ears).
Agree with most all you say...good points 🙂
The freedom from discontinuities in the power response seems most important to me.
I'm not so sure about the importance of a power response that tilts gently downwards as frequency rises. I think that depends alot on listening preferences, type of music, etc. You know the whole ambiance thingy...
I use prosound constant directivity boxes in home, and have found it takes a more strongly sloping downward house curve to make them sound just fine...spectacular really.
The narrower the speaker's pattern, the greater the downward slope of course. It's no problem at all.