What are the advantages and disadvantages of line arrays?
Music Lover -- Fri, 07/08/2011 - 08:35
Jon Valin's CJ ART and GAT blog has spurred this question. Jon has the CJ gear hooked up to the Scaena speakers. I looked this design up in Robert Harley's latest edition of the book, but unfortunately it is not covered. I'm guessing line arrays are a small, small niche since Robert's encyclopedic book leaves them out.
Nevertheless, these designs may be coming back. Genesis has been around for a while and may have been resurected recently. Scaena has been getting a lot of good press at shows the last 5 years or so. Harry Pearson loved the Scaena in his review, calling them "electrostatic like in the midrange", but with realistic bass. He loved their "realism". How do these speakers create their" realism"?
Is this true of all line array designs or just Scaenas? How good can the midrange drivers get? Are they really electrostatic like? (Heck can any non-electrstatic midrange driver hold a candle to an electrostat?)
How much of it is great cross-over design?
The downsides I can see are adequate space, setup, and cost. Scaena is $60K+ and Genesis may be $100K+. What are the other downsides?
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ML: Either Paul Seydor or Robt. Greene reviewed the Dali Megaline line array speaker several years ago for TAS. In describing the performance of that super-speaker (cost: about $45K at the time of the review), the author also discussed the design philosophy and performance benefits of line array speakers in general. The article is well worth seeking out.
Dali also published a white paper which describes the R&D process and performance features of the Megaline. Follow the link: http://www.dali-denmark.com/admin/filer/MegaLine%20WP.pdf
Wiki also has an interesting discussion on line array speakers, although I am not qualified to decipher all the techno-bable. Here is the link: http://en.wikipedia.org/wiki/Line_array
Good reading.
Amandela77
I may be over generalizing a bit, but line arrays are generally referred to as multiple conventional drivers, all lined up in a line. Line sources, are generally thin film element lines (planar magnetic, ribbon, etc...). True line sources are theoretically better than line arrays, as they do not have issues with all of the small drivers creating potential lobing problems, and they are one element not requiring a crossover, like multiple small midrange cones will with a tweeter element. One of the main advantages of line sources is that they have virtually no dispersion above and below the line itself- which is why the line is generally 4 to 7 feet long. If you put your ear above or below the line, then there is very little above around 500 hz, or so. This basically eliminates the floor and ceiling reflection of your room- allowing you to get closer to what is really on the recording.
Line source speakers also disperse differently into the room. Below is an excerpt describing this, copied from the Wisdom Audio site:
" Line source loudspeakers distribute sound more evenly into a room than do point sources. Specifically, the rate at which the sound decreases with distance is half that of normal, point source speakers.
The standard Speaker Sensitivity specification is measured at a distance of one meter (1m). This is a convenient measurement, but not particularly real-world -- few of us are so close to our speakers when listening. A four meter (4m) distance is probably more representative of how people actually use their speakers.
But here is the catch: at a distance of 4m, point source loudspeakers (including our own) will have lost 12 dB of volume due to propagation loss. By contrast, line sources will have lost only 6 dB of volume, based on the physics of how they disperse sound.
So if what you are really concerned with is how loud the sound is at the listening position -- which seems the most meaningful measure -- a line source will be 6 dB louder than a point source which has the same 1m sensitivity measurement. Thus, its "4m equivalent sensitivity" will be 6 dB higher than what you measure at 1m.
Another way to think of this is to ask what the sensitivity of a normal, point source speaker would have to be in order to achieve the same result as the line source being measured. At a distance of four meters, the point source would have to be 6 dB more sensitive than the line source simply to yield the same result for the listener."
Basically, the only disadvantage a line source has, is that they are generally fairly expensive, but, if you want to get to what is on the recording, and take more of your room out of the equation, they are the way to go.
As stated, propagation loss from a point source is -6_dB with each doubling of distance.
The math is 20log(scalar change in distance) = SPL reduction in dB.
And likewise popagation loss from a line source is also -6_dB with each doubling of distance, but only in the far field. In the near field, propagation loss from a line source is -3_dB with each doubling of distance, and
the math is 10log(scalar change in distance) = SPL reduction in dB.
That nearness of that near field is a function of line height, listening distance, and frequency, well described in Jim Griffin's whitepaper linked elsewhere in this thread. Acousticly reflective room boundaries in close proximity to the ends of the lines (floor and ceiling) can serve to extend the effective length of the line, extending the near field region.
A single short ribbon tweeter is a line source, but because of its short height will transition to far field at the lower end of its frequency range well before reaching the listener at listening distances commonly used in domestic applications. A very tall array of those same ribbons can extend the nearfield across the listening region of a domestic listening environment, but gaps in the spacing will introduce combing.
Spectral balance can vary significantly across the listening region within the audible passband as spectra transition near to far field at different propagation distances. Horizontal lobing in the polar response through the crossover is troublesome given the horizontal spacing between the the vertical tweeter line and the vertical midrange line.
Done right they can perform well at creating a pleasant sounding illusion that we are seeking from audio playback, but the engineering is more complex; and as with all loudspeakers, anything short of a well engineered design will not sound good in unbiased listening.
For a very good description of technical aspects written for a layperson, I suggest the whitepaper:
"Design Guidelines for Practical Nearfield Line Arrays", by James R. Griffin, PhD.
Download the PDF with this link: http://www.audioroundtable.com/misc/nflawp.pdf
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JRT- thank you for posting that- a good read. I should mention, the Scaena is what I would refer to as a "line array", due to the fact that it is multiple drivers lined up vertically and also crossed over passively to a tweeter element. A true line source would be a single element with no lobing effects to be taken into account due to the multiple drivers lined up. Think of a thin line of a single element from floor to ceiling as the ideal. A ribbon or thin film element that is full range down to where woofers can cross it over is technically more correctly described as a "line source". It's a small technical difference, although many "line arrays " share many of the true line source advantages.
More experimentation and less buying & trying ... this is the creed of a true audiophile.
You want to know what a line array sounds like ... cut a long piece of plywood and bolt as many drivers as you can afford to it. Wire them in series parallel, hang them from the ceiling where you normal box speakers live and take a listen ... you'll be shocked how good they sound.
Yes I am talking open baffles line array's here!
You will however need high quality low frequency modules (subs) as there's virtually "no" bass coming from the naked drivers. Most subs you can buy are too slow to keep up with open baffle drivers so plan to build your own using large pro audio woofers. The higher effecient the driver, the less the woofer will cone will move ... this is what you want for open baffles drivers and matching subs. For sub drivers look for something around 15" and near 100db/1 watt. On the cheap the $67 Peavy Pro 15's work great in a 3cu/ft cabinet. For 5X the price the Electro Voice EVX-155's rule. Purchase 3 cu/ft 15" sub cabinets & 240 watt plate amps from Part Express and you are ready to roll.
To keep costs down you could take apart an old pair of Bose 901's, you'll have 18 very effecient 4" drivers. Look for the Series 1&2 as they have cloth surrounds so chances are they'll be in great shape. Bolt 8 per side to a piece of wood (2 spares), wire in series parallel. Use the the Bose 901 EQ to fill in the top & bottom end of the now naked 4" drivers. The open baffle line arrays with Bose EQ will play from around 140hz to 14kHz (room and baffle placement dependent). Place the subs near the baffles and tune the subs to fill in where "line arrays" roll off, then be prepared to have a Depends momemt.
No passive crossivers, no tweeters, no BS ... the sound will blow you mind!
(If you can still hear above 14Khz, mount a single tweeter dead center between the 8 drivers and add a 1uf cap on the + wire.)
Total project cost under $1000, results, experiance, and knowledge gained ... Priceless!