Line Array Theory- A question for Danny

Rob Babcock · « **on:** 21 Jan 2004, 02:02 am »

Just how tall/how many drives does a speaker need to begin to act as a "true line source?" I'm curious if the value is arrived at thru some model or thru trial and error? For instance, one tweeter mounted beside a single woofer would obviously not fit the model. But would 3? Or four?

And what happens to a line array turned on its side? Is the imaging the only thing affected, or is the coherence of the entire presentation compromised?

Just curious, no particular reason. I've wondered about this for some time, and Danny, you seem to the resident Line Array expert (along w/Rick Craig)

Thanks.

Danny Richie · « **Reply #1 on:** 21 Jan 2004, 04:19 am »

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Just how tall/how many drives does a speaker need to begin to act as a "true line source?"

Technically it is all distance related.

At a short distance a small line will act as a line source.

At really long distances even a tall line source will at some point behave just like a point source.

The trick is to figure your listening distance and then figure out how long of a line source will be needed to keep you in the near field.

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I'm curious if the value is arrived at thru some model or thru trial and error?

It can all be mathematically calculated.

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And what happens to a line array turned on its side?

It behaves the same way turned on its side. Turning one on its side will allow minimum side wall reflections through upper frequency ranges while allowing a large vertical window. Standing up it is just the opposite.

If you are thinking will it make a good center channel then the answer might be yes, if you stay within the width of the line. Get outside the width of the line and it will loose all the highs.

Peter · « **Reply #2 on:** 21 Jan 2004, 04:50 am »

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Just how tall/how many drives does a speaker need to begin to act as a "true line source?"

Rob,

A truly line source is a speaker with a very narrow and long radiating surface, which is used at frequencies above f = c/2L, where its length L is greater than 1/2 wavelengths and it does not contain dynamic driver units (point radiating units). A truly line source speaker can only radiate sound waves in the vertical direction (which is a huge advantage).

An array or a speaker which contain point source units (equal to dynamic driver units), like for example a line array speaker, will NEVER act as a truly line source speaker. Such a speaker is too wide, the baffle is too big.
The ONLY way to design a truly line source is with planar magnetic ribbons while using a very narrow (or no) baffle, period. The reason is that all the driver MUST radiate the sound waves in vertical direction, and only ELS, ribbons and planar magnetic transducers can do that (but ELS speakers are too wide).
No speaker containing a point source driver (equal to dynamic driver units) will act as a truly line source.

It is very difficult to find a truly line source soeaker, only a very few has been made. Soon we are introducing a truly line source, it is not an inexpensive speaker, two or three new patents are made too.

With the best regards,
Peter

JohnR · « **Reply #3 on:** 21 Jan 2004, 05:08 am »

Well, the problem with using only ribbons or other planars is that you can't get any bass. If you put a couple of bass drivers underneath the line then you have integration problems because of the different radiation pattern. Putting a line of woofers next to the ribbon line seems to be the best (and, as far as I can tell, only) practical way to make a proper "line source" speaker.

Peter · « **Reply #4 on:** 21 Jan 2004, 05:13 am »

But in this way it is still not a TRULY Line Source.

JohnR · « **Reply #5 on:** 21 Jan 2004, 05:31 am »

As I just said, you can't get a "truly" line source as you describe it that produces any bass. There is no such thing. If you know how to do it, then I suggest you say so, as your "FUD" posts in a competitor's forum are not really welcome.

Hank · « **Reply #6 on:** 21 Jan 2004, 02:38 pm »

I never run out of stupid questions, so what does FUD mean? I can extrapolate, based on the comments of the "truly" line source guy, that it means criticizing the competition to hype your own product.

george king · « **Reply #7 on:** 21 Jan 2004, 03:08 pm »

hank,

fear
uncertainty
doubt

Danny Richie · « **Reply #8 on:** 21 Jan 2004, 10:32 pm »

Well , well, if it isn't Peter from Acoustic Reality.

The guy that made popular a series network configuration that I came up with years ago...

Long time, no hear from.

You know Peter, I have heard from several people that your amps and speakers were very good, but the problem was that you rubbed everyone the wrong way on a whole bunch of forums and made more enemies than friends.

I am sure many here can recall incidents from the past.

Here is the just of saying all that. You are welcome to post here all that you like, as long as you are civil.

So what happened to those US distributors you had? I have hardly heard a peep from you or about your products over here for a while.

As for your comments regarding lines sources, well, no, and kind of, and I'll take some of what you said a point at a time.

A true line source can include individual dynamic drivers.

See JBL papers written years ago or Jim Griffins latest "White" paper documentation.

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A truly line source speaker can only radiate sound waves in the vertical direction (which is a huge advantage)

This depends on frequency and length of the array. Lower frequencies can and will radiate in all directions just like a point source. The wavelengths are simply longer than the array and are not cancelled by the other driver in the array.

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An array or a speaker which contain point source units (equal to dynamic driver units), like for example a line array speaker, will NEVER act as a truly line source speaker. Such a speaker is too wide, the baffle is too big.

Point source drivers in an array will begin to behave as point source drivers when the frequency range being played is shorter than the distance between drivers, and to some effect the length of the array.

Baffle width or size has little to do with it even though reflected surfaces do effect the response.

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The ONLY way to design a truly line source is with planar magnetic ribbons while using a very narrow (or no) baffle, period. The reason is that all the driver MUST radiate the sound waves in vertical direction, and only ELS, ribbons and planar magnetic transducers can do that (but ELS speakers are too wide).

Line source radiation patterns can be produced with any size drivers but the larger the drivers the less they will behave as a line source as frequency increases.

Drivers need not radiate only in a vertical direction. Quite the contrary. The more they radiate vertically the greater the interference pattern.

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No speaker containing a point source driver (equal to dynamic driver units) will act as a truly line source.

Not so at all Peter.

In fact even a single driver line source like a long ribbon driver will still have some point source radiation patters as well.

Just take a 54" ribbon and block off 53" of it leaving the top of it only to play.

It will now play with a radiation pattern that exceeds vertically what it could not do before. That is because in no longer has the cancellation effect of the rest of the line.

Guess what. Even with you ear level 50" below it you can hear it plain as day.

You see, every inch of that continuos ribbon still radiates in all directions. It is the cancellation effect of it doing that, (comb filtering within the length of it) that causes it to have a limited vertical dispersion.

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It is very difficult to find a truly line source soeaker, only a very few has been made. Soon we are introducing a truly line source, it is not an inexpensive speaker, two or three new patents are made too.

Hey Peter, you are more than welcome to share whatever info about your new stuff here all you like, so long as it is from an informative standpoint. When it becomes an advertisement is when it might get moved or deleted.

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Putting a line of woofers next to the ribbon line seems to be the best (and, as far as I can tell, only) practical way to make a proper "line source" speaker.

John is correct.

If the dynamic drivers are playing within a frequency range (lower and longer wave lengths) then they all couple and play as one unit with no comb filtering effects.

If frequency ranges increase (higher frequencies) to wavelengths shorter than the line, then in those frequency ranges it will behave as multiple point sources as Peter suggest.

Rob Babcock · « **Reply #9 on:** 22 Jan 2004, 01:45 am »

In rebuking Peter you've actually thoroughly answered my questions, too.

Thanks, Danny. That's what I was wondering.

Jim Griffin · « **Reply #10 on:** 23 Jan 2004, 04:51 am »

Peter needs to read more of the AES papers and other references to understand the conditions for a line array of drivers to be a line source. He can start reading my white paper at:

http://www.audiodiycentral.com/resource/pdf/nflawp.pdf

In my paper I list several of the AES papers which address the conditions for a line array to act as a line source.

It is interesting how Peter comes around DIY speaker forums only when he has a new product to sell. His latest idea will likely be priced well into the five figures $. If his products are worthy of consideration in the commercial marketplace, then he'll have buyers in line to purchase them.

Jim