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acoustic lens technology (ALT) equivalent to line arrays?

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Doonesbury
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Doonesbury posted on Sat, Jul 6 2019 3:32 AM

I happened to read of several speakers (such as McIntosh XRT2.1K) which have columns of tweeters.  This arrangement results in a narrow vertical dispersion with a wide horizontal dispersion.

This made me think that ALT system on many B & O speakers is a more efficient way of getting the same end result (limited vertical dispersion with wide horizontal dispersion).

Are the two types of systems acoustically equivalent?

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leosgonewild
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I am not qualified or educated in anyway for my opinion to matter, but as the Beolab 90’s don’t use the ALT technology, it cannot be the beat option?
Mr 10Percent
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As previous, not qualified to know the real reason.

My assumption is the column line arrays are there to match/companion the power outputs of the mid and base. I.e a single small tweeter can’t deliver the “volume” on its own to balance-out the loudspeaker.

ALT on the other hand is about distributing highly directional sound (high frequencies) through elliptical loci. I guess when a loudspeaker becomes too powerful that the mids and base drown-out the treble, ALT cannot be used because more than one driver is required??

BEOVOX141
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A bit of anecdotal information,- The four midrange speakers in the Pentas is a perfect example of a line array implementation all the way down to the way the X-over is implemented! 

Jeff
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Jeff replied on Sat, Jul 6 2019 2:10 PM

I can see two advantages of a line array of tweeters over a single ALT lensed tweeter. First, power handling, using multiple tweeters will allow higher spl without damage to the tweeters (and tweeters are usually more efficient than mid or lower drivers and their relative output has to be attenuated). Secondly, I expect that the horizontal response/dispersion might well be a tad smoother, the ALT lens does impart some artifacts.

However, the ALT lens is far more compact, allowing for a shorter/smaller speaker, and it's been a while since I looked at the response plots for one but it probably does not "beam" as much as a line array or single traditional tweeter. The higher up the frequency band you go with a conventional driver the more the output moves from being widely dispersed to a narrow dispersion. I believe the ALT addresses this better than a line array does. Which allows you to sit in a wider variety of places, a wider "sweet spot."

Jeff

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poodleboy
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@jeff, I have seen a couple acoustic lens speakers and imagined that if you forced water through an acoustic lens into a room it would do exactly as you say, but will high frequency waves spread the way acoustic lens suggest? Or is it like peeing into a fan ;-)

 

Doonesbury
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I would consider that an entirely different dispersion arrangement

leosgonewild:
I am not qualified or educated in anyway for my opinion to matter, but as the Beolab 90’s don’t use the ALT technology, it cannot be the beat option?

I would consider that an entirely different arrangement from ALT or line array given the BL 90 has drivers pointing in many directions with continuously adjustable soundstage.

Jeff
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Jeff replied on Sun, Jul 7 2019 2:35 PM

poodleboy:

@jeff, I have seen a couple acoustic lens speakers and imagined that if you forced water through an acoustic lens into a room it would do exactly as you say, but will high frequency waves spread the way acoustic lens suggest? Or is it like peeing into a fan ;-)

 

Sound and water behave pretty similarly, so you're probably right in how you think about it. And it's better than something else hitting the fan!

It's a clever device, not perfect but for what B&O wanted at the time, wide dispersion with a fairly small and attractive setup, a good choice.

Jeff

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Millemissen
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Geoff Martin wrote an article where some of these questions are discussed.

Some of you will already know it - it might serve as an inspriration to understand the differences of a speaker based on ALT and one that is line array based.

https://www.tonmeister.ca/wordpress/2014/03/01/bo-tech-curves-are-better-than-corners/

This one might interest too:

https://www.tonmeister.ca/wordpress/2017/08/17/bo-tech-intro-to-acoustic-interference-and-loudspeaker-directivity/

MM

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