Murphy Corner Line Array (MCLA)

[spasticteapot]

Re: Murphy Corner Line Array (MCLA)

A friend of mine wants to build some PA speakers for his barn, and I was wondering if a set of MCLA-style arrays might do the job. The barn is approximately 20x30, with walls that are about 15' high before you hit the slanted sections that form the roof. For reasons of cost, the arrays would likely be limited to 18 drivers per side; as such, the benefits of running floor-to-ceiling would be lost (though with the slanted roof, I'm not so sure how well they'd work anyway.)

Assuming a subwoofer was crossed in at about 80hz, do you think this would work?

[broncosaurs]

Re: Murphy Corner Line Array (MCLA)

Thanks John for your reply. Do you think adding some more drivers say 5-6 to each side would help or is adding drivers a diminishing return?

I got two drivers and made a mini-MCLA to get an idea of the sound. My ears tell me the highs seem a little dull. Remember, I love ribbons. Any thought on a tweeters just for the upper octaves? I understand not having an xover is part of the love using a full range speaker. Maybe bring in an array of tweeters some where above 4khz (highest note on piano) which should keep any xover problems well above voice and most instruments. Maybe a small mylar on a bracket between and in front of each full range? I guess cost comes into question by doing this. Even a cheep tweeter would almost double the cost of the speaker. Well, just an idea. I didn't think of the cost while I was typing this.

Brad

Thanks for the kind comments Brad. Your 18' x 30' room could work well with the lines 18' apart across the short wall. With an array that is less than the ceiling height you will still get ceiling reflections but the "equivalent system" (consisting of the direct sound source and its reflections) will have gaps in the infinite array due to the "missing" drivers. Short of simulating the system along with its first few reflections it is hard to say how it would perform. My intuition says to expect some loss of low end output and a somewhat more variable response around the room. But if you were to build the system and then custom EQ it to flat (X-curve, or other) I have no doubt it would sound quite fine. My system EQ would be a good starting place but would probably need some adjustments.

Regards,

John

[richidoo]

Re: Murphy Corner Line Array (MCLA)

broncosaurs,
In your single driver experiment that sounded rolled off, did you use the Behringer DEQ2496 EQ to flatten frequency response?


John, I am just about ready to go ahead. But I have one more question. I am not sure if this is what Jack was talking about above with doppler effect, or if it is what you mention in your article regarding comb filtering. I thought you were talking about wall reflections, but maybe you meant direct sound as well. Specifically, what I am concerned about it the phase error between the ear level driver and the highest driver is huge at high frequencies. 13kHz is 1 inch wavelength, and the different distances to ear between closest and farthest drivers are several inches. So the drivers will have interference and comb filtering, as will also happen from wall reflections. Is this something that I should be concerned about? I worry that high frequencies will sound smeared. I am familiar with the digital EQ methods and will use RTA to verify flat response.

Thanks for your input!
Rich

[Jim Griffin]

Re: Murphy Corner Line Array (MCLA)

Rich,

You asked:

"Specifically, what I am concerned about it the phase error between the ear level driver and the highest driver is huge at high frequencies. 13kHz is 1 inch wavelength, and the different distances to ear between closest and farthest drivers are several inches. So the drivers will have interference and comb filtering, as will also happen from wall reflections. Is this something that I should be concerned about?"

No. Go to my "Near Field Line Array White Paper" (see link below) and study Figure 2A. You are in the near field so the energy flow is outward without minimal overlapping. No smearing as the direct energy flow is parallel to the floor and ceiling.

Jim Griffin

http://www.audioroundtable.com/misc/nflawp.pdf

[jerrald]

Re: Murphy Corner Line Array (MCLA)

Jim, this is the first I've seen of your comments on this project. Do you have any other observations on using full-range drivers this way?
I know that comb filtering happens with all speakers but what about this design?
I also believe if the driver has the right specs then a broader frequency response is possible. But a digital EQ will still be necessary.

[Jim Griffin]

Re: Murphy Corner Line Array (MCLA)

Jerrald,

John has freely shared his design and we should all appreciate his expertise and efforts. But, I am not an advocate of a full range driver line array as I feel that you compromise the low and high frequency ends of the band. EQ helps but EQ alone will not eliminate these issues. Best bet in my mind is to use a three way line array system (or effectively a two way line array with active subs to carry the low end of the band). The builder of a line array needs to decide whether he can live with the compromises of a full range driver design but with no crossover.

Jim

[raiderone]

Re: Murphy Corner Line Array (MCLA)

Jerrald,

John has freely shared his design and we should all appreciate his expertise and efforts. But, I am not an advocate of a full range driver line array as I feel that you compromise the low and high frequency ends of the band. EQ helps but EQ alone will not eliminate these issues. Best bet in my mind is to use a three way line array system (or effectively a two way line array with active subs to carry the low end of the band). The builder of a line array needs to decide whether he can live with the compromises of a full range driver design but with no crossover.

Jim

I really am enamored with the sound of line arrays, but I am not sure exactly why. It started with the Infinity RS1B many years ago. Then Pipedreams and recently Dali Megalines. I'm pretty sure it is the low distortion and effortless dynamics, but it might be the way line arrays propagate sound into the room. Sorry for the rambling, my question is if we only have room for one array, which one would be easier to crossover to: Low array + conventional speaker or Mid array with tweeter and subs? Thanks.

[richidoo]

Re: Murphy Corner Line Array (MCLA)

Jim, thanks for sharing your paper. I enjoyed reading it, although I think it reinforces my concern about phase error being an issue at high freqs with this non-curved design.

A friend of mine has Pipedreams, which use separate tweeters, he says the high freqs are excellent, no sign of smear or incoherency. Unfortunately he lives too far away for me to audition, and it would not equal auditioning MCLA anyway. I would just like to understand the benefits and compromises of the MCLA design in the high freq region. Testing shows 1kHz to be very low distortion, with HF spectra likewise low. The aluminum drivers do not seem to have any propensity to ring in this high sensitivity application.

Jim, what specifically are the issues you have with full range drivers covering high freq and low freqs? I can imagine you mean the large drivers will beam at very high freqs, and not big enough for low freq linearity. I think the low freq response will be excellent when EQ is applied. I'm planningnto use 30 drivers per side and hope to achieve 25Hz flat response at moderate levels that i listen to music from 3 meters away. And the beaming of high freqs might actually reduce the perception of phase error at higher freqs, but will lihgt up the walls more than the direct sound, so some wall treatment may be needed.

I am especially attracted to the MCLA because of the full range no crossover feature. I have built other crossoverless speakers and I am convinced of their musical superiority, but always open to learning something new!
Rich

[John L. Murphy]

Re: Murphy Corner Line Array (MCLA)

A friend of mine wants to build some PA speakers for his barn, and I was wondering if a set of MCLA-style arrays might do the job. The barn is approximately 20x30, with walls that are about 15' high before you hit the slanted sections that form the roof. For reasons of cost, the arrays would likely be limited to 18 drivers per side; as such, the benefits of running floor-to-ceiling would be lost (though with the slanted roof, I'm not so sure how well they'd work anyway.)

Assuming a subwoofer was crossed in at about 80hz, do you think this would work?

I think it would be a great system provided it is EQ'd for a flat (or other targeted) response.
I would suggest they go in the corners of the shorter (20') wall.

John

Thanks John for your reply. Do you think adding some more drivers say 5-6 to each side would help or is adding drivers a diminishing return?

I got two drivers and made a mini-MCLA to get an idea of the sound. My ears tell me the highs seem a little dull. Remember, I love ribbons. Any thought on a tweeters just for the upper octaves? I understand not having an xover is part of the love using a full range speaker. Maybe bring in an array of tweeters some where above 4khz (highest note on piano) which should keep any xover problems well above voice and most instruments. Maybe a small mylar on a bracket between and in front of each full range? I guess cost comes into question by doing this. Even a cheep tweeter would almost double the cost of the speaker. Well, just an idea. I didn't think of the cost while I was typing this.

Brad

Hi Brad,

Adding more drivers to extend the line closer to the (18') ceiling would help assure adequate low frequency output capability and extend the range of near field behavior.

I'm glad you auditioned the ND90 drivers. Unless you EQ'd them it is reasonable that the high end was less than perfect. You were likely hearing a response not terribly different from this:



This is the uncorrected ground plane measurement of the ND90 in a 0.1 cubic foot closed box. The upper octaves are shy and diffraction is causing the bass to droop. Not bad for a raw driver but the EQ'd flat response will sound much less colored.

Personally, I love the sound of a good full range driver when EQ'd flat in the top end. But there is no reason not to implement the corner line array as a 2-way system if you feel you must. Smaller drivers (say 1" domes) would broaden the (horizontal) high frequency dispersion in the top octaves compared to the slightly narrower dispersion of the 2.5" piston of the ND90. But remember that your listening angle is limited to lass than 45 degrees with the corner line array. This compensates for some degree of the concern about horizontal dispersion; vertical dispersion is not an issue since the high frequency response is expected to be near constant at any height within the length of the array.

If you were to implement the system as a 2-way I would encourage you to keep the crossover frequency as low as possible to minimize the overall audibility of the crossover. While you may gain increased horizontal dispersion at high frequencies you introduce the audible veil of a crossover along with a heap of added cost, complexity and failure modes. The simplicity of the full range crossover-less array is sweet.

Since you have two ND90's try a test where you compare listening to one driver full range to listening to two drivers crossed over at say 1k Hz. The crossed over pair SHOULD sound the same as a single driver...but does it??? Is the crossover audible??? How audible???

John

<snip>John, I am just about ready to go ahead. But I have one more question. I am not sure if this is what Jack was talking about above with doppler effect, or if it is what you mention in your article regarding comb filtering. I thought you were talking about wall reflections, but maybe you meant direct sound as well. Specifically, what I am concerned about it the phase error between the ear level driver and the highest driver is huge at high frequencies. 13kHz is 1 inch wavelength, and the different distances to ear between closest and farthest drivers are several inches. So the drivers will have interference and comb filtering, as will also happen from wall reflections. Is this something that I should be concerned about? I worry that high frequencies will sound smeared. I am familiar with the digital EQ methods and will use RTA to verify flat response.

Thanks for your input!
Rich

Hi Rich,

Any time you audition a sound source via multiple pathyways at once you introduce very complex comb filtering into any single point measured response. No loudspeaker can escape this reality unless it is auditioned in an anechoic chamber. And then, consider that listeners do not prefer the way music sounds without the usual room reflections (and attendant comb filtering). Listeners prefer the complex sound of a rooms compared to the single path (comb free) sound of an anechoic chamber. So you can relax your concerns about comb filtering and interference among the drivers at different distances. The sound from the multiple drivers all arrives well within the 20 to 30 millisecond fusion time window our ear-brain system employs to identify sound events.

For me, the subjective effect is that the line array (with its near field behavior) actually sounds more focused and detailed than any other speakers. In my testing I do not hear changes as I move my head while listening. Certainly there is no audible "flange" effect as is clearly heard when electronically combining two signals with different time delays. Such as when used as a studio sound "effect". To me, percussive clicks are defined as well as (or better than) on the best point source systems I've heard. While recorded material is compelling in this regard, it is playing my guitar through the arrays at close range that really convinces me that the line arrays can render the briefest percussive clicks and pops with absolute precision. I've worked professionally with quite a few electric guitar players over the years and have learned that they have an unusually intimate connection with the "sound" of their "rig" and are typically sensitive to little distortions that audiophiles playing recorded music would never notice in a thousand years of listening.

Regards,

John

[richidoo]

Re: Murphy Corner Line Array (MCLA)

Thank you for sharing some additional subjective impressions, John. :D
Rich

[FredT]

Re: Murphy Corner Line Array (MCLA)

Here's the link to a picture of the almost completed pair of ND-90 line arrays I'm building. The design is similar to Johns MCLA's except the room I'll be using these in doesn't have any corners, so the enclosures will be positioned a few feet out from the wall and will not take advantage of close-to-corner placement. I'll be using a subwoofer, and equalization & crossover to the sub will be accomplished by a dbx DriveRack PA+. Also, each speaker consists of two 12-driver stacked enclosures for easier transport.

http://fredt300b.smugmug.com/Hobbies/Speakers/132721_wacsQ#864865296_eqa7i

[blair]

Re: Murphy Corner Line Array (MCLA)

Too bad you will not have those for LSAF!

Blair

[John L. Murphy]

Re: Murphy Corner Line Array (MCLA)

I'd like to announce that the MCLA web site has been revamped and new project documents are available for download.

http://www.trueaudio.com/array

The original project document .pdf was created from multiple source documents and had the look of a printed web page, which is exactly what it was. The new document has been redesigned in M/S Word and the layout is much improved. The document name is unchanged in order to preserve all links to it.

I have also condensed the full 51 page document into a 12 page Project Brief. This is the document handed out at the 2010 Midwest Audio Fest. We had hoped to demonstrate a working pair of MCLA enclosures but there were assembly problems with one enclosure and the demonstration was cancelled. Perhaps next year we can demo a complete MCLA system.

Regards,

John

[oodesigns]

Re: Murphy Corner Line Array (MCLA)

Hi, I am new to this group...

I am intrested in making these also... but I have the same issue as another member, i quote:

"I've had the MCLA's running for 4 days now but my first impressions have not been that great, mainly because of the distance between corners in my room. My corners are 17 ft. apart along my front wall, and my listening position can be 12 ft. max back from the front wall. As a result I'm getting too much separation between the left and right channels.

In the MCLA article, I can't see where John mentions anything about optimum spacing between speakers. I don't have any experience with using equalizers. Would optimum equalization settings minimize this problem?"

In my case I have no choice but to have the speaker further apart than I will be sitting. Will this make this design reduntant? or using could using other features of the equalizer help.

[auracle]

Re: Murphy Corner Line Array (MCLA)

Hi John,

Just curious if you've had the chance to experiment with sound absorbing materials on the walls adjacent to the line arrays to see what impact it might have on imaging, tonal balance, and a sense of depth.

Having experimented a fair amount myself with line arrays, I agree wholeheartedly with some of your earlier observations about the actual percentages of direct/reflected sound in point source configurations versus line source. Given the comments I've read in various places, I think this aspect of line arrays is one of the most overlooked - concentrating the source of excitation in one place in most real environments produces greater contrast in both reflection time and intensity - often making reflected energy more noticeable.