[95bcwh]

Ok, let me start a newbie question here:

What's the strength & weaknesses of line array speakers compared to traditional 3-way design??

[arthurs]

Start here.....

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

[FredT300B]

Several characteristics of line arrays make them my preferred speaker type:

First, you gain three dB of sensitivity every time you double the number of drivers. Starting with the typical 87dB sensitivity driver, increasing the number to two takes you to 90dB, four gets 93dB, and 8 gets you to 96dB. You have two choices in wiring this array, with one choice getting you 99dB / 4 ohms nominal impedance, the other getting 93dB / 16 ohms. Either way the array is far more sensitive than a single woofer would be. Since each 3dB gain is the equivalent of doubling you amplifer power, you can get by with a far less powerful amp, or you can achieve awesome volume levels with a high power amp. Danny Ritchie once told me he measured 130dB plus from a pair of his Alpha LS speakers. Of course you don't want to play any speaker that loud inside a small room, but even at reasonalble power levels the line array is far more dynamic than a point source speaker using the same drivers. This characteristic also makes a line array a great speaker for use with low powered SET tube amplifiers. My 8 watt 300B will drive my XT-8 arrays much louder than a 120 watt Sonic Frontiers Power 2 would drive my Magnepans.

Second, even the above numbers understate the actual volume gain, because as long as you are listening within the near field a line array's loudness decreases by 3dB per doubling of distance from it versus 6dB for a point source. So at 3 yards listening distance a 93dB line array sounds as loud as a 99dB point source would at that distance.

Third, each driver has to move far less to produce a given sound level versus a point source, reducing the excursion-related distortion. At the volume level where a point source speaker would begin to sound congested a line array using the same drivers would be operating well below its limit.

Fourth, the cylindrical waveform eminating from the baffle eliminates floor bounce, one of the major causes of frequency related peaks and nulls in a point source speaker.

Fifth, line arrays have a larger sweet spot and a more convincing soundstage.

Sixth, they are really cool looking 

The disadvantages are cost, size, and if you're building it yourself, time and difficulty of construction. The cost thing is simple arithmetic: The drivers in a line array using eight woofers and eight tweeters cost eight times that of a two way point source speaker using the same drivers. Line arrays are really big, and women especially don't like big speakers in their homes. It's strictly a cultural thing - my wife had no objection to a 13' high antique "buffet a deux corps" in our entry foyer, but she did hesitate a bit when I told her I was planning to build 6' high speakers. An interiour designer once said to her "You let him have those big ugly things in this beautiful house?" I've trained her to respond "Size does matter". The difficulty factor is simple - a 6' tall enclosure with extensive bracing plus many driver cutouts and recesses is a tough project.

Here's a picture of my first wife when I told her I was building a 7' 4" tall pair of line arrays. As a result of this experience I'm now married to a sweet little old lady who demands nothing and gives me lots of money to build more line array speakers. 
http://fredt300b.smugmug.com/gallery/132721#25172328

[JLM]

Another advantage is elimination of a crossover as the multiple mid/woofers typically used and the efficiency advantages of the line array can normally replace the need of a woofer in a "conventional" three-way speaker.

Disadvantages of line array:

1.  You need lots of drivers (as per the referenced link) to:

     a.) Create an effective line array, the line must be at least 6 feet tall;
     b.) Space drivers close together to avoid comb effect, roughly as close together as possible.

2.  They are tall, heavy, and potentially dangerous (particularly around kids, pets, and party animals).

3.  They are expensive (dozens of drivers and big cabinets), unless you compromise on driver quality.

4.  Cabinets are typically sealed design, the least preferred by most audiophiles. 

5.  They do not provide a point-source (widely recognized as the ideal), they cannot image vertically. 

There is no perfect speaker and I have no axe to grind.  But the main reason for line array seems to be acheiving high sound pressure levels from a box full of medicore drivers.  This logic would be more applicable to a PA than audiophile application.

[FredT300B]

...the main reason for line array seems to be acheiving high sound pressure levels from a box full of medicore drivers... 

I agree with your comments about the disadvantages of line arrays, especially the cost issue. But I don't understand the comment that's quoted above. 

[Daygloworange]

Another advantage is elimination of a crossover as the multiple mid/woofers typically used and the efficiency advantages of the line array can normally replace the need of a woofer in a "conventional" three-way speaker.

How does a line array eliminate the need for a crossover?

5.  They do not provide a point-source (widely recognized as the ideal), they cannot image vertically.

I've never heard any design recognized as ideal.

There is no such thing as vertical imaging.

We've been over this JLM. Please provide proof of vertical imaging, not just your opinion.

http://www.audiocircle.com/index.php?topic=43830.70

But the main reason for line array seems to be acheiving high sound pressure levels from a box full of medicore drivers.  This logic would be more applicable to a PA than audiophile application.

In the DIY world perhaps they would try and build a line array with mediocre drivers. But plenty of arrays are built with great drivers. Some are designed with drivers with truncated baskets so that they can be placed closer together to minimize cancellations.

Most PA systems are horn based systems.

I don't know where you're getting these facts. 

Cheers

[95bcwh]

Fred,
  Thanks for the thorough insight. I didn't realize that you used to have Magnepans!

barry

[bwaslo]

5.  They do not provide a point-source (widely recognized as the ideal),...

It may be "widely" recognized as so (almost universally so by newbies), but certainly not universally recognized as ideal by the rest of the audio world.

In fact, a case might be made that a point source is maybe one of the worst patterns you could have.  A line source completely illuminates the room with sound, the vast majority of the sound reflects off of everything in the room, giving the system the room's distinctive sound, rather the the concert venue's sound.  You get closer to the "Bose 901" ideal of sound, not the ideal of many listeners.

A planar speaker radiates in a plane-wave pattern at higher frequencies, carefully controlling where the sound is going and avoiding reflection.  A dipole avoids radiating at all to the sides.  A line source, though, doesn't radiate up, down, or diagonally -- only horizontally outward.  My taste runs toward dipole line sources, but there are a lot of planar speaker 'philes in the world, particulary in the high end portion of the world.

[JohnR]

A corollary to Fred's point #3 is greater transient capability.

[TONEPUB]

While a line array does not do everything right, they DO do dynamics very well.

Every design is a trade off, but the better line arrays that I've heard from
McIntosh and Pipe dreams are extremely dynamic!

Just depends on what you want from your sound.

[JLM]

FredT300B,

Most of the advantages of line arrays stated and referenced in this thread relate to achieving higher sound pressure levels.  Most speakers are built to a budget of some sort.  So a typical trade off involving line arrays is using 40 (quite ordinary) drivers at $20 each that would cost $800 with 200 feet of internal wiring for another $100 versus 2 or 3 really good drivers with 4 feet of internal wiring.  While not impossible, its almost hard to spend that much for drivers/wiring in a pair of 2 or 3 way speakers.  So the trade off ends up being one of quality versus quantity.

Dayglow,

I'll try to explain again what I'm trying to convey regarding eliminating a crossover.  With multiple mid/woofers (typical line array) the total Sd is sufficient to replace a woofer (if the choosen driver has the needed F3.  This gets back to the above point and the cost/quality challenge of multiple drivers.  But if you disagree, fine, it just takes away a possible advantage of line arrays.

I thought that we had agreed to disagree about vertical imaging and that I should have a right to state my thoughts again on a new thread (it had been awhile).  At the very least admit that we can distinguish point sources vertically in our everyday "real" lives.  The corollary is that we don't use line arrays of mikes to record or ears to hear, so why try to transform the sound from point source mikes to array and then back to the ear?  The mind fills in missing information, but line array's "confuse" the mind with extraneous information.  I'm sorry if you've never heard vertical imaging.

Regarding my "PA" comment, please see my first paragraph from this reply.  PA speakers don't have to be horn loaded.

bwaslo,

The vast majority of the world's high-end speakers have squeeze midrange drivers and tweeters close together, you're comment makes little sense to me.  Many reviewers have also made reference to point source as it relates to speakers.


Just trying to provide balance/perspective.  I'll stop raining on the line array parade now.

[FredT300B]

A quick commentary here: JLM's comments were made in a clear, polite, and non-confornational way. So were the responses to his comments. This is exactly the kind of discussion I hope to see on our new Line Array speakers circle, where polite debate leads to a greater understanding of line arrays. 

[Daygloworange]

FredT300B,

I thought that we had agreed to disagree about vertical imaging and that I should have a right to state my thoughts again on a new thread (it had been awhile).  At the very least admit that we can distinguish point sources vertically in our everyday "real" lives.  The corollary is that we don't use line arrays of mikes to record or ears to hear, so why try to transform the sound from point source mikes to array and then back to the ear?  The mind fills in missing information, but line array's "confuse" the mind with extraneous information.  I'm sorry if you've never heard vertical imaging.

Just trying to provide balance/perspective.  I'll stop raining on the line array parade now.

JLM, we've never agreed to disagree. You are just being persistant, and argumentative on the topic.

There is no such thing as vertical imaging. Period. Stop.

Rinse. Lather. Repeat.

It is not possible with a 2 channel system. I proved it in the other thread beyond a doubt, yet you persist. You are seriously confusing what is possible with speakers and microphones. It is akin to claiming a single diaphragm microphone is capable of playing back in stereo if presented with a stereo source. Your claims are preposterous. Why do you persist?   

http://www.audiocircle.com/index.php?topic=43830.70

I told you you could Google till the cows came home, and you wouldn't find one article to substantiate your claims.

You haven't come back with one iota of proof. I won't ask you to do it again, as it was rhetorical request. It is futile, yet you persist.

Stop posting that your entitled to your opinion on the subject. This is not a matter of opinion. We're talking facts here.

And BTW, stop posting how you feel sorry for me because I've never heard your imagined vertical imaging.

I haven't heard it, because it doesn't exist!!!!!

Cheers

[95bcwh]

The next question I have is that I seems to notice that most line arrays are built with small drivers (less than 8"), so aren't these drivers limited by their inherent limitation to produce frequency below say 50Hz??

[FredT300B]

The next question I have is that I seems to notice that most line arrays are built with small drivers (less than 8"), so aren't these drivers limited by their inherent limitation to produce frequency below say 50Hz??

The size / ctc spacing of the woofers is limited by the crossover frequency for reasons that are best explained in Jim Griffin's white paper. The practical outcome, as you mentioned, is that midwoofers larger than 6" or 7" are seldom  used in line arrays.

The low frequency extension of any given driver is determined by its TS parameters and the enclosure design. It's possible to design a 6" driver/enclosure combination that will extend to relatively low frequencies, say 32hz, which is the frequency of low C on a pipe organ. If the speaker is a simple two way, the 32hz extension capablity probably wouldn't be a good idea because the long excursions required to reproduce that frequency by a single 6" woofer at any reasonably high volume would result in distortion. Better to use a driver/enclosure combination that rolls off around 45 hz or so, or to reproduce low bass make it a three way with a 12" or 15" woofer.

Using 6" woofers in a line array mitigates the problem to a great extent because the multiple woofers' surface radiating area is the equivalent of a much larger single woofer. Consequently, you can achieve relatively high volume levels at low frequencies without the distortion you would hear from a single 6" woofer. By way of example, the now discontinued GR Research Alpha LS, with nine 6.5" woofers, had strong bass response into the 20s'. It will be interesting to see how low the LS-9 will go with twelve.

That said, not every line array manufacturer chooses to use the array's woofers for deep bass. This is simply a design versus cost consideration. Even with a array of high quality 7" woofers the high volume distortion will be less if they aren't required to reproduce deep bass. For example, Rick Craig has just completed a custom array pair with eight 7" Scan-Speak Revelator woofers in sealed enclosures augmented by a a pair of subs, each having a 1Kw plate amp driving four 10" woofers. See a picture on page three of this gallery 
http://www.audiocircle.com/index.php?action=gallery;area=browse;album=299&page=3

[Rick Craig]

The next question I have is that I seems to notice that most line arrays are built with small drivers (less than 8"), so aren't these drivers limited by their inherent limitation to produce frequency below say 50Hz??

Here's something I posted recently on another forum that may help answer your question:

I  use the Clio measurement system and have designed many arrays. In-room measurements aren't very reliable for the lower octaves. Many measurement systems (including Clio) will overstate the numbers because the resolution isn't accurate. Plus your room certainly won't measure the same as mine or the guy down the street from you.

The only accurate way to measure the true low frequency extension of a system is to do a nearfield test where you place the microphone a 1/4" from the woofer (sealed box system) or take a sum of the woofer's output and the port's output in a ported design. This will tell you the real bass response and the method is based on research done by DB Keele, one of the top experts in the industry and former speaker reviewer for Audio magazine.

There's also something called proximity effect where the low frequencies can be exaggerated by certain types of microphones. I think something similar happens when measuring an array and have observed a low frequency tilt that can vary depending on the measurement distance.

The bottom line is that the bass extension is not going to be any different whether you have one woofer (like a compact 2-way) or several woofers in an array. The array will move more air (increased cone area = more displacement); however, it you want true low octave extension you'll need a subwoofer to do that. Without active equalization the best you can expect from a ported 7" driver is a -3db point of 40-45hz. Some drivers I've seen (and measured) in other commercial arrays won't even go that low.

I've found that speaker companies often will quote an in-room response but won't back up their figures with a nearfield or anechoic response curve. The latter is the only way to verify that they're telling you the truth.

[Daygloworange]

There's also something called proximity effect where the low frequencies can be exaggerated by certain types of microphones. I think something similar happens when measuring an array and have observed a low frequency tilt that can vary depending on the measurement distance.

Proximity effect AFAIK, exists in all mics. Condenser mics are much less prone to it than dynamic mics. (I believe calibration and testing mics are all condenser type) It tilts up bass response when placed in near proximity, and rolls off bass with distance.

I'm not sure how that would make for getting a real reading 1/4" away from a driver. It would seem that proximity effect would skew the results, no?

When we mic bass drums for example, we have often have to mic from a distance in order to get proper bass and fundemental pitch, along with tone/overtones. The theory being that the low waveforms are so long that they are missed entirely by close miking. I'm not sure on the theory, but in application, close miking never yields realistic bass response on instruments.

Cheers

[JohninCR]

I've built a number of arrays and sensitivity or SPL capacity would be at the bottom of my list of "why line array?".  Pro or other drivers with high sensitivity can get you there just fine.  Also, cheap drivers can be used very effectively.  Good sounding drivers is what you want, and many cheap drivers sound just fine at moderate levels.  What increases driver price is making them more sensitive and/or increasing the range of their frequency response, neither of which are issues with line arrays.

To me the real advantages of line arrays over all other speakers are:
1.  They fill a room more evenly with sound, not too loud up close or too quiet at a distance.  This is because, as mentioned elsewhere, the SPL from a line array decreases by 3db for each doubling of distance vs a regular speaker that decreases by 6db.  This is a huge difference.
2.  They have a sweet spot that is orders of magnitude larger, a direct result of #1.
3.  The nature of how sound disperses from a line array leads to better in-room behavior.  Not only is floor and ceiling bounce virtually eliminated, but that also eliminates the floor/ceiling room mode from having an influence.
4.  They sound "bigger".

#4 is probably what JLM is attempting to describe with his "vertical imaging" point.  Line arrays can distort the size and depth of the "stereo image", and depending upon the music this skewing of the image can be a negative.  This is the result of time smear caused by the different arrival times to your ears of output from the central drivers and those near the ends of the array, which get to your ears last.  This is why Dr. Griffin advocates power tapering, where the wiring configuration gets more power to the central drivers than those at the ends.  It preserves line behavior, but you can't specifically hear the top and bottommost drivers so prominently and image skewing is reduced dramatically.  Another way to mitigate this effect is with a focused arrays, so all drivers are the same distance from the listening position, but this leads to a very small listening position (both left/right and distance from the speakers).

[bwaslo]

Isn't the "proximity effect" a characteristic of directional microphones only?  I don't think omni condenser mics have a proximity effect.

[Daygloworange]

Yes, you are correct sir. 

It's been a really long time, I almost forgot about that. They are almost never used in studios.

Edit:  Omni's are virtually free from proximity effect. Proximity effect is pronounced in cardioid pattern dynamic mics, it is virtually non existant in (any pattern) condensers.

Cheers