Not ultracritical but look at the angle of the column and move the system fore and aft until the presenters are right off the end of it. That angle has lowest output for all frequencies. I.e. presenters are 90 degrees below firing axis.
David S.
The bottom of the array being 9 feet above the presenter will be okay with no feedback problems if you believe speech only extends to 400 Hz , and you apply a high pass to filter out the speech frequencies that exists below 400 Hz.
If you plan to do that, there are many PA horns that can provide defined coverage to 400 Hz for a fraction of the price of a mini line array.
So, Art, I translate the above, "It won't work, don't do it???"
Our current front speakers--twin angled JBL floor monitor boxes run full-range--are currently 9' above and 4' forward of the presenter's head, and they haven't caused feedback problems... Judging by their squat dimensions, they must have less vertical control than this array will... ?
Our current front speakers--twin angled JBL floor monitor boxes run full-range--are currently 9' above and 4' forward of the presenter's head, and they haven't caused feedback problems... Judging by their squat dimensions, they must have less vertical control than this array will... ?
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And this isn't exactly the first church in the history of PA that wants to install a line array!
David
If you are presently using a pair of floor monitors, the mini line array should be an improvement in coverage, as would large horns offering pattern control not relying on interference to achieve said pattern control.
With a speaker with a strong voice and a close mic, pattern control is not a feedback issue, it is possible to achieve a level roughly the same at the back of the hall as at the microphone.
I recently measured my voice at over 132 dB peak at the microphone.
I have worked with announcers that create less than 70 dB at the microphone. With that type of announcer, the demands placed on the sound system in terms of gain before feedback are several orders of magnitude greater than your situation.
Absolutely true, a "line array" presently will usually be considered the best choice even when it is not.
Sometimes I think about finding, buying, and reselling church PA systems which often go through multiple installations before arriving at a viable solution.
Then I think of how much stuff I own I'd like to sell and have not been able to, and let the thought go..
I'm going ahead with the purchase of a CBT70J and CBT70JE later today. I found some demo units, so the total price is about $1200, which seems like pretty good bang for the buck to me.
Again, thank-you to those who donated their expertise and opinions.
Getting back to the home audio side of things, I got curious how well a wall-mounted 70J would work in a large home listening room or home theater if its top was up against the ceiling. The CBT calculator doesn't simulate interaction with surfaces, but I figured a single 70J against the ceiling might behave somewhat like a free-space unit whose length is doubled with a 70JE extender, since the ceiling adds an image.
So here is an approximation of a wall-mounted 70J (set to narrow mode) whose top is against a 9ft. ceiling in a 30ft.-deep room. First at the seated position, and then standing. Pretty tight coverage when seated. 3-4dB spread beginning @~12ft. to the back of the room from 400Hz up. Not a bad seat in the house. When heard from a standing position, the spread opens up, and the array behaves more like a standard speaker.
Compared to the competition at the high-end home-theater level, it seems to me that the 70J might be a bargain, even at full retail price.
Again, thank-you to those who donated their expertise and opinions.
Getting back to the home audio side of things, I got curious how well a wall-mounted 70J would work in a large home listening room or home theater if its top was up against the ceiling. The CBT calculator doesn't simulate interaction with surfaces, but I figured a single 70J against the ceiling might behave somewhat like a free-space unit whose length is doubled with a 70JE extender, since the ceiling adds an image.
So here is an approximation of a wall-mounted 70J (set to narrow mode) whose top is against a 9ft. ceiling in a 30ft.-deep room. First at the seated position, and then standing. Pretty tight coverage when seated. 3-4dB spread beginning @~12ft. to the back of the room from 400Hz up. Not a bad seat in the house. When heard from a standing position, the spread opens up, and the array behaves more like a standard speaker.
Compared to the competition at the high-end home-theater level, it seems to me that the 70J might be a bargain, even at full retail price.
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I have extensive line array use, they have their place. I use a line array for mains on 90% of the shows I work.
In a tall room with extensive reverberant problems, the narrow vertical pattern can really "clean up" the sound. For long throws, the more even level response from front to back, compared to a "point and shoot" box is a big plus.
In a smaller home environment, the attendant comb filtering that is responsible for the narrow vertical pattern can be a distraction.
Having compared a simple 2 way design using an 8" and tweeter (and subs) to both commercial and "Home Brew" line array in my living room (listening position 11 feet from the speakers) I have stuck with the standard cabinets.
If pattern control is an important issue to you, I'd recommend the DSL Synergy horns (available in many different patterns) over a line array.
The Synergy achieves pattern control from a virtual single source point, eliminating the problems "built in" in to a line array.
Art
I'd love to hear some Danley SH50's in a home theater. About $3,500 per channel, though, right?
I'm not a line-array fanboy by any means, but I am intrigued by CBT's ability to create relatively constant SPL over a distance. I know that carefully aimed CD horns can do this--and maybe better?--but there seem to be some size and price tradeoffs.
I'm not a line-array fanboy by any means, but I am intrigued by CBT's ability to create relatively constant SPL over a distance. I know that carefully aimed CD horns can do this--and maybe better?--but there seem to be some size and price tradeoffs.
That's what Don Keele says, anyway. The ceiling can work as the acoustic mirror just as the floor does.
Maybe I'm not sensitive to comb filtering (I don't notice it on multi-cell horns) but I didn't hear any on Don's prototype CBT array - either very close or very far away. They seemed very smooth and uniform.
Hi
A full range CD horn does allow this under the right conditions.
Part of the magic of the synergy horns is that there is never a clue there is more than one driver even when you stick you head into the horn itself, it radiates like one driver, only has one lobe, no interference pattern visible in a series of lobes and nulls.
While they are always a point source, they also have a directivity envelope, a single lobe.
The idea is you raise the speaker off the ground and aim it at the farthest seat.
In that way, the shape of the bottom of the lobe (often shown as an equal loudness balloon / polar plot) is used to keep the SPL at the audience nearly constant or within + - 1dB in some cases.
Ironically, this is an ANCIENT approach that was used with single horns and not usable with multi-way speakers because they do not have a single behaved lobe. It is this same reason that when used in the home, a speaker with a lobe should be aimed at the seat kitty corner (if you had a couch) or the toed in configuration.
That way, to the degree the sweet spot is amplitude related, it makes it a little wider.
Here is the closes I can come to a demo at the moment, I hope we can get into hifi eventually.
These are larger Synergy horns than the SH-50 and I think the first time these were used in an indoor installation.
After a side by side comparison with some factory set up line arrays from out west, the designer chose these.
The speakers cover a ground floor and balcony space and let’s just say he has some extra headroom. If you record a conventional system and walk around, you really hear the variation from place to place. Try some good headphones for the video
First Baptist Goodletsville w/Danley JH90 cabinets Main floor on Vimeo
First Baptist Goodletsville Tn Balcony W/Danley JH90 Speakers on Vimeo
His nice review.
Live Sound: First Baptist Church Upgrades With Stereo Pair Of Danley Jericho Loudspeakers - Pro Sound Web
Best,
Tom
David,
Thanks for linking my article on your speaker. I stumbled across the Xpanding array when I was about 22 years old, and the technology really impressed me. I've written a ton of threads on Unity and Synergy horns, and I think many of the concepts are shared between the two designs. (IE, great minds think alike!)
Speaking of Synergy horns, I think there's an improvement that can be made to Keele's CBT 36. After reviewing the design, there's one big flaw with it. You can't get the tweeters close enough to sum properly.
Here's what I mean by this:
To get a pair of radiators to sum well, you want them very close. Ideally within one quarter wavelength. For instance, if you have a pair of 12cm woofers with a center-to-center spacing of 12cm, their upper frequency limit is dictated by their size. In this case, it's 708hz. (34000 cm per second / 12cm / 4)
The CBT 36 uses extraordinarily small tweeters - but it's upper limit is still just 6692hz.
Here's a frequency response graph of MK's CBT speaker - note how the directivity and frequency response loses control about 6khz - I believe this is due to the size of the diaphragm.
That pic is from MK's CBT by the way. Keele's CBT has been measured, but the measurements are in PDF so I can't post the results here in the forum. But it's the same idea.
Anyways, long story short, I think this is a shortcoming.
BUT -
It can be fixed.
There are two ways to do it. The first is to use your invention - the xpanding array - for the tweeter line. Basically the tweeter at the bottom of the array will run full range, and then the other tweeters are low passed progressively. So the tweeter at the bottom will play from 1khz to 20khz, and by the time you get to the top the tweeters are only playing perhaps one or two octaves. By low passing the tweeters you eliminate the destructive interference that's screwing up the directivity and frequency response in the CBT designs. So basically the woofer array is a CBT and the tweeter array is an xpanding array AND a CBT.
Naturally, this makes for a very complex crossover! I shudder to think how long it took to make the crossover in those Snells from the 90s!
The other way to 'fix' the upper response of the CBT is to stick a Paraline in there. The Paraline has wide horizontal directivity and narrow vertical directivity - basically it's a great match for the CBT. Best of all, the Paraline elements don't really interfere with each other the way that a line of domes do, because the Paraline sharply restricts vertical directivity.
The use of a Paraline introduces a second problem however. The Paraline inserts a delay, because the sound wave has to pass through the Paraline labryinth. There are two ways to solve this. The first is to use DSP to delay the woofers.
The second - and simpler solution - is to simply stick a coupling chamber in front of the woofers. The coupling chamber resonates with the woofer, the resonance creates a delay, and the delay virtually 'moves the speaker backwards.'
Of course, if you did that, you'd end up with something very similar to what Keele himself recommends on page 110 of his presentation! The Vertec VT4886 is a passive design with a coupling chamber in front of the woofers.
I agree on most of your remarks, but in a home setting when extreme spl is not needed there may be better solutions than the paraline coupling. Why not use ribbons or planars that can be mounted close together to form a continous line. I have been working on a such design on paper, but have realised it will be too expencive.
hi John
the grating lobes started to occur beyond one wavelength as evidence in dr. Don paper below, page 13-14: http://audioartistry.com/Papers/CBT Paper4 PracticalImplementationCircularArcCBTArrays.pdf
Hi Folks,
I have barely discovered the CBT36, looks great on paper!
I have a problem. My home is made of concrete, and the ceiling is very low, only 2.3m high.
I have been using dipoles for a while and would like to try a line source to tame the ceiling reflexions, it's just too low to put treatment on it (my wife is a dictator).
I was thinking using the B&G RD-75, a couple other forum members have reported it sounds very good, with a dipole sub line array floor to ceiling, crossed around 150hz, because I think dipoles do sound better in the bass. So, RD-75 vs CBT36, any thoughts? (I have printed some papers from Don, will read them tonight)
Thanks!
I have barely discovered the CBT36, looks great on paper!
I have a problem. My home is made of concrete, and the ceiling is very low, only 2.3m high.
I have been using dipoles for a while and would like to try a line source to tame the ceiling reflexions, it's just too low to put treatment on it (my wife is a dictator).
I was thinking using the B&G RD-75, a couple other forum members have reported it sounds very good, with a dipole sub line array floor to ceiling, crossed around 150hz, because I think dipoles do sound better in the bass. So, RD-75 vs CBT36, any thoughts? (I have printed some papers from Don, will read them tonight)
Thanks!