Murphy Corner Line Array (MCLA)

[johnlmurphy]

Re: Murphy Corner Line Array (MCLA)

And yet again, all the heads turn to the JVC 3x5s. That is the obvious choice i presume, same Fs, freq extension. But much less xmax, but then much cheaper, so u can use as many as u want!

I think alot of people will come in to say that, its one of those situation where without a tweeter line, it sounds perfectly good and extends high enough etc. etc., Yet, when a tweeter line IS added, you'd notice whats missing. Hence I've been living with my JVC3x5 tweeterless arrays happily, making sure that I DON'T get to hear one with a tweeter line

I am sure these MCLA sounds fantastic, but I am also confident that you can do just as well with cheaper drivers like the JVCs, or peerless, TB, Aura, etc. etc. 2-3" fullrangers with some calculated comprimises - e.g. distortion OR SPL, and ovals are A PAIN IN THE *** to drill, when u have a 100 ovals to cut.....

To me this is just a good old full range line array stuffed in a coner, so as opposed to a "novel design" its more like a "novel placement/positioning" ? I mean, not many speakers designs here would ask you to do corner loading, other than subs. But as far as a "fullrange line array" is concerned, how much more designing is required other than finding a fullrange driver, and putting them into a correct size box? Maybe spend a little time on an EQ. But sounds like the drilling and cutting will be much much more effort!

A 3x5 should be fine. The Xmax may be adequate or not depending on the low end output the listener requires. I would encourage everyone to experiment if they have the time and inclination. You will almost certainly need to determine and setup your own custom EQ but that's not really hard to do. Don't expect the stunning bass capability of the MCLA with the ND90-8 if you use a less capable driver...but you may not need that level of output for your application. Remember I designed the MCLA to also use as the sound system for my band which is a much more demanding than the usual CD playback or home theater applications.

Regarding "missing highs" that some people report with line arrays: I still have my older 2-way line arrays (with 16 dome tweeters) which I listen to regularly as I have for 30+ years. I can't perform a quick A/B comparison because the old and new systems are in separate rooms on different floors. (apologies to Kathy Mattea) But I can definitely say that nothing appears to be missing in the new full range arrays...except for the crossover coloration. As a musician I definitely feel that I would hear if there were any missing harmonics. I can very easily hear the slightest "flanging" or "chorus effect" when I deliberately apply that type of effect to my guitar sound. Flanging is where you deliberately introduce a comb filter and then slowly sweep the notches around as a "sound effect". While I have definitely heard flanging with large scale concert sound systems when I walked the room while listening to pink noise, I have never heard it on either of my line arrays. In my opinion, there are no missing highs. The high end sounds constant as I walk around the room and as I change my listening height by sitting down or standing up. The MCLA is actually more consistent this way than my 2-way line arrays because I hear a very slight shift in response due to the crossover as I move laterally which changes the phase relationship between the woofers and tweeters. To me the full range array is more "ideal" with respect to shifting horizontal position.

Yes, it was a pain in the **** to cut 48 of those 3" holes. I can't imagine cutting ovals. This is why man invented NC machinery.

Yes, it is a full range line array stuffed in the corner. But I do believe the "image friendly" enclosure design is sufficiently novel that a US patent would have been possible. But that does not mean much these days...they still will patent things that have been in the public domain for seemingly forever. That's why I made such a fuss over the public disclosure. I want to make it easy for the patent examiner to deny anyone's patent application for a line array "stuffed in the corner". Someone could still obtain a patent and then have their lawyers hound anyone who was making the enclosures. The builders would then have to mount a lawsuit to overthrow the clearly bogus patent. That takes time and money. With the backing of the company I was working for I did manage to shut down harassment from attorneys for a patent holder trying to extort licensing fees for a "derived" crossover I was using in one of our products. I was rather arrogant in my response to their demand letter and explained to them how their patent was worthless because they had foolishly patented a circuit that was CLEARLY in the public domain long before their patent application was even filed. I included copies of the published papers detailing crossovers derived by subtraction and I never heard from them again. So I felt it important to make it very clear that this design is now in the public domain.

As you note, the design part for this closed box system was really quite simple. All that nasty crossover design stuff just vanishes...so does the nasty crossover sound coloration. I used to find myself making the case that a 2-way was always preferred over a 3-way (or higher) speaker because crossovers were a "necessary evil" that should be avoided whenever possible. Now I find myself making the case against using any crossover at all. While crossovers remain "evil", in my opinion, they are no longer "necessary" to achieve the highest quality sound reproduction.

Try this thought experiment...or maybe even try it for real. Imagine two identical wide range drivers (say the ND90) in separate closed boxes but with the drivers located close together. Now you add a crossover at, say, 2 or 3 kHz so that each driver operates over only a portion of the frequency range. Next you rig a switch to change between the crossed over pair and a single driver operating with no crossover. Then you conduct a listening test asking only if you can hear any difference. Do you think you could hear a difference? When I tried this test (around 30 years ago) I could always hear the difference. The crossover was always audible even in this "ideal" application of crossing between two identical wide range drivers in the middle of their operating range. In real 2-way systems we are always crossing between a larger driver and a smaller driver which just adds another layer of audibility as we introduce the "dispersion discontinuity" that attends the shift from a narrowing dispersion woofer to an ultra wide dispersion tweeter. All those audible effects completely go away when you eliminate the crossover. Try it yourself and tell us what you hear.

In the end I spent days measuring and tweaking the EQ to get it "just right". I am hoping that those who precisely clone my MCLA will not really need further EQ tweaking; or at least that it will be minimal. For me the hard part was building the enclosures. But I know that many DIYers excel at woodworking and I look forward to seeing some really good looking implementations of the MCLA. I guess I'm getting long winded here on this lazy Sunday afternoon.

Regards,

John

[johnlmurphy]

Re: Murphy Corner Line Array (MCLA)

John,

Any chance on posting some frequence responses of the speakers using the exact same eq outdoors or as close to anechoic as possible, to compare to those taken in the room.

I would like to see that measurement also...but with cold weather arriving and my other projects heating up it may take a while to get to that.

Regards,

John

[johnlmurphy]

Re: Murphy Corner Line Array (MCLA)

John,
Thanks for posting the design. I find it very intriguing. There are some old and new ideas presented.

I've been thinking a lot lately about corner-loaded speakers. Klipsch "cornered" :rolleyes: this market once upon a time, but you don't see it anymore ,and I'm not sure why this is. (Of course, I don't have my speakers in the corners, either)

I guess the thing I'm left wondering after reading your writeup is that you continually describe the "corner reflections" as mirrored images. This makes sense to a point; however as you know, not all frequencies behave the same directionally (bass = omnidirectional, treble = directional, midrange = transition). So I'm just sort of wondering how you factor this frequency discrepancy into the design to keep the overall FR "flat" (or x-curve or whatever your desired FR needs to be)

Again, it's a very interesting design; I only wish I could hear it. Reading about it and the theory behind it doesn't take the place of an in-person experience.

Ahh, the classic K-horns.

Speaker enthusiasts traditionally say that bass is omnidirectional and that the treble is directional. In the context of a typically sized speaker enclosure this makes sense because the baffle is usually about as wide as middle frequency wavelengths where 1 kHz has a wavelength of about 1 foot. At higher frequencies the baffle is an obstruction which limits rearwards radiation and imposes half-space loading. At longer wavelengths (lower frequencies) the baffle is small with respect to the wavelength and the bass radiates omnidirectionally in spite of the baffle obstruction.

In general, the directional characteristics of a sound source depend on the dimensions of the source and the dimensions of nearby obstructing and reflecting surfaces. Here's a simple example that clearly contradicts the speaker enthusiasts rule-of-thumb that bass is omnidirectional. If a 1 foot (12inch) woofer beams above about 2 kHz a 100 foot woofer would beam ((radiate in only a narrow angle) above 20 Hz. That is, a 100 foot diameter woofer would produce highly directional bass. From this extreme example we see that bass frequencies are only omnidirectional because of the (relatively) small size of our usual speaker enclosures compared to bass wavelengths.

Today line arrays are finding increasing application in large concert venues because they provide a degree of low frequency pattern control due to their long length. This tends to improve the sound of these large rooms where low frequency reverberation times can be unusually long and troublesome. Long line arrays can limit the low frequency radiation to a narrow vertical angle (compared to smaller sources) and direct less energy into the room and more on the concertgoers. This holds down the tendency of these large venues to ring obnoxiously in the bass range.

In-room the MCLA system has wide frequency dispersion throughout the frequency spectrum. It does narrow slightly and smoothly in the top octave but offsetting this is the fact that the listening angle is automatically restricted to less than 45 degrees by virtue of the corner placement. Because all frequencies are handled by the same driver there are no abrupt changes in directivity such as occur when crossing between a larger woofer and a small tweeter.

Build some and tell us what you think.

Regards,

John

[billfitzmaurice]

Re: Murphy Corner Line Array (MCLA)

And yet again, all the heads turn to the JVC 3x5s. That is the obvious choice i presume, same Fs, freq extension. But much less xmax, but then much cheaper, so u can use as many as u want!

I originally loaded my TLAH with 69 cent NSBs and 29 cent Onkyos, and recently builders have used the JVCs and those same Onkyos with equally good results.

But sounds like the drilling and cutting will be much much more effort!

It's called 'sweat equity'. Line arrays do allow very good results with very inexpensive drivers. But there being no such thing as a free lunch what you save on the drivers you expend drilling holes and wiring drivers. Which is best for you depends on what you have the most of to spare, time or money.

[johnlmurphy]

Re: Murphy Corner Line Array (MCLA)

John,
Thanks for sharing your design. The benefits are articulated well in your article but I had a few questions about the trade offs. These aren't "gotcha" questions by any means since the research tends to vary on these effects. Since you've lived with this arrangement so long, hoping you have some experiences to share in these regards.

Some psycho acoustic research indicates that short delay lateral reflection colour the timbre and lead to spreading of the individual image sizes. Have you noticed anything to this effect with the MCLA? For example are image sizes the same as traditional speakers out in the room? Does the timbre sound similar to a box out in teh room that measures about the same, anechoic wise?

Other questions are in regards to imaging. One of the benefits of having the cabinets a few feet out from the walls is that this positioning can enhance the perception of width and depth. How do you find this trade off working for the tight corner design? Also do you miss any sense of spaciousness? Cabinets 5 or more feet from the boundaries can enhance this perception.

Thanks again,

Dave

Thanks for your comments Dave. I'll have to get subjective here but I'll do my best to not get too poetic.

Overall, I perceive the sound as more intimate in the sense that headphones are intimate but with the image located between the speakers. The image of an artist or instrument is sharply located in space. I can close my eyes and point to a voice or instrument without hesitation. If I change my position vertically as by sitting, standing or laying the image moves with me vertically such that it is located at the height of my ears.

Moving from side to side the image shifts differently depending on the listening distance. Up close (where I like to play guitar) the image seems to more quickly snap to one side as you move away from the center line. This sort of reminds me of the behavior of near-field monitors where center-line seating is critical and the image readily pulls to either side as you move left-right. Further back in the room the image seems to stay centered longer as you move away from the center line. With a vocal performance I hear the artist firmly located as I walk about the room just as if they were standing at the front of the room. I can turn my back and walk about much of the room and the artist is always firmly located in place.

On a side note I'd like to comment about how speaker or player-to-player distance affects musicians when we are playing music. Musicians hate latency. That is, we hate to have any delay between playing a note and hearing it. The lower the latency the better we can perform. If I have to sit even 15 feet away from my speaker that 15 millisecond delay will cause me to play with sloppy timing and mess me up. Similarly, I need to be close to my band mates when we play acoustically. We can't be 15 or 20 feet apart and deliver a "tight" performance. We need to be closer than that to hold the time delays down to musically acceptable levels. That's why when I play through the line arrays or my guitar amp I always sit up close so that I can have a good tight musical connection with the sound. That's also why I considered it so important that the reflected images be in tight proximity to the array. Speakers placed away from the walls manage to reduce the amplitude of the room reflections but unfortunately this also increases the delays between images themselves and between the images and the source. Perhaps this creates more of a sense of spaciousness but that's the last thing I want as a player. If I want a spacious effect I will dial it in deliberately with my effects units; I don't want the speaker doing it automatically. I want the intimacy that comes with the very tight arrival of all the sound with inter-image delays as small as possible. The brain nicely fuses all the images arriving within 15-20 milliseconds into just one perceived sound event. Sound arrivals beyond this time do lend a sense of spaciousness, and eventually echo and reverberation. But I want my monitoring system to be as free from audible delay effects as possible in order to be as "honest" as possible.

Cheers!

John

[audiorasp]

Re: Murphy Corner Line Array (MCLA)

Hi John. I've decided to go ahead and build the MCLA, and in spite of my vaulted ceilings, I've already ordered the drivers.

Regarding driver mounting, is the 1/2" radius on the driver hole made on the inside of the front baffle? Also, do you use any gaskets between the driver and baffle?

Thanks,
Geo

[brianpowers27]

Re: Murphy Corner Line Array (MCLA)

Some psycho acoustic research indicates that short delay lateral reflection colour the timbre and lead to spreading of the individual image sizes. Have you noticed anything to this effect with the MCLA? For example are image sizes the same as traditional speakers out in the room? Does the timbre sound similar to a box out in teh room that measures about the same, anechoic wise?

Other questions are in regards to imaging. One of the benefits of having the cabinets a few feet out from the walls is that this positioning can enhance the perception of width and depth. How do you find this trade off working for the tight corner design? Also do you miss any sense of spaciousness? Cabinets 5 or more feet from the boundaries can enhance this perception.

Thanks again,

Dave

I imagine that the audible effect of these short distances is the same effect that one hears from the line array. With a line array the impulse is unclear due to the multiple sources. In the grand scheme of things, how audible is this?

I would be interested to hear John's impressions.

[DDF]

Re: Murphy Corner Line Array (MCLA)

John, thanks for taking the time to share your detailed impressions! I was especially interested to hear that the images stayed so sharp.

The design definitely does a good job of managing reflection delays if a high direct/reverb ratio (headphone like presentation) is the ultimate goal.

The first reflections are very short in delay and being largely in the same direction as the speakers helps reduce their audibility. The reflection off the ceiling and floor make it look like a line source much longer than its physical length, to greatly minimize ceiling and floor reflections (which also affect timbre). Finally, the next longest delay would probably be the back wall. 15' long room puts this beyond 20ms for an average seating position.

The corner placement excites all room modes the most. Some like this, some don't. Do you find the need for extra room diffusion or bass traps? The longer RT60 from the corner placement no doubt helps add some warmth given that all delayed reflections are > 20 ms or so out.

The vertical column also smooths out the combined response of vertical reflections (similar effect to placing more subs in a room to smooth the low frequency in room response).

Neat design!

I tend to like some spaciousness from a strong delayed side wall and some "artificial?) depth from the front wall, but old habits die hard. It'd be nice to hear this some day (can't build it at home, my room wouldn't suit).

Dave

[curt_c]

Re: Murphy Corner Line Array (MCLA)

Hello Tech Talk!

This is John Murphy, the guy who operates TrueAudio.com. I am the designer of the MCLA and author of a couple of audio software applications and a book on loudspeakers.

Hello John,

Nicely done, and a great write up! The design suits the ND90 attributes well. I’ll hopefully be unveiling a design of a bit more modest construction using the ND140’s shortly. –I'm patiently waiting for the drivers to arrive.

I notice you didn’t utilize power tapering in your array. Had you considered it, and found it wanting, or did the simplicity of the straight power array outweigh any potential improvements in resolution or image bloom?

I've been thinking a lot lately about corner-loaded speakers. Klipsch "cornered" :rolleyes: this market once upon a time, but you don't see it anymore ,and I'm not sure why this is. (Of course, I don't have my speakers in the corners, either)

I’ve been giving the corner loaded design some thought as well. The seemingly incongruent requirements of many’s HT systems of both a small unobtrusive speaker, and one with high sensitivity and SPL capabilities suggest corner loading as one possible solution. Of course, pushing the speakers back into the corners will most likely result in the loss of soundstage depth, but with multi channel HT, that probably isn’t an issue. It’s still not a panacea, as you can’t realistically corner load the center channel…

C

[danakruse]

Re: Murphy Corner Line Array (MCLA)

John,

Thank you first of all for making your ip public.

From reading the text and looking at the diagrams, if an MCLA system were to be constructed for use in a room with 9 foot ceilings, would it be better to add drivers to gain the additional height (retain a 3.5" driver spacing) or increase the spacing to "fit"?

If a higher strength material were used for the baffle, would closer spacing and more drivers present any worthwhile improvement, as long as the volume per driver remains at .0451 cubic feet?

I presume that if the cabinets were true triangles with the 22.28 square inch internal area, that they would function much the same as yours. I am thinking specifically of the possibility of attaching cleats to the wall surface and applying the baffle or baffle sections to the cleats, eliminating the need for a free-standing cabinet.

Dana

[MagicO309d]

Re: Murphy Corner Line Array (MCLA)

Thanks for publishing!

Your design seems to answer what I was looking for next from my 2-channel audio system, reference level headroom that fits/works in my room. As it is now, even in my large room I still have to hump my small towers out and center for critical listening sessions. Speakers that I don't have to "put away" when I'm done "playing with them" would be awesome!

I'm in the same boat with 9' ceilings but I also have an old house with big crown moldings and 9" high baseboard trim that I can't touch. What would be the desired workaround for MCLA's in this case?

Thanks Again!

[johnlmurphy]

Re: Murphy Corner Line Array (MCLA)

Hi John. I've decided to go ahead and build the MCLA, and in spite of my vaulted ceilings, I've already ordered the drivers.

Regarding driver mounting, is the 1/2" radius on the driver hole made on the inside of the front baffle? Also, do you use any gaskets between the driver and baffle?

Thanks,
Geo

Geo,

That 0.5" radius was in error. I just uploaded revised enclosure plans changing that to a 0.25" radius. There is only 0.5" between driver cutouts so the .5 radius would remove far too much material between drivers. The radius would be on the outside of the baffle toward the listener. I did not use any gaskets in my prototype. But a gasket would be a nice refinement and would minimize any air leak noises.

Here is a link to the revised enclosure plans:

http://www.trueaudio.com/array/downl...nclosure_2.pdf

Happy Thanksgiving,

John

[johnlmurphy]

Re: Murphy Corner Line Array (MCLA)

I imagine that the audible effect of these short distances is the same effect that one hears from the line array. With a line array the impulse is unclear due to the multiple sources. In the grand scheme of things, how audible is this?

I would be interested to hear John's impressions.

Yes, the array generates multiple (tightly spaced) impulses but compared to a point source with its multiple widely spaced impulses, arrays seem to do quite well. The secret may be that the array delivers more of its energy within the 15-20 millisecond time range where the brain can fuse the impulses into one perceived sound. Because of the longer reflection distances involved, a typical point source speaker may have lots of energy arriving late and being perceived as spaciousness separate from the primary sonic event.

Regards,

John

[johnlmurphy]

Re: Murphy Corner Line Array (MCLA)

The first reflections are very short in delay and being largely in the same direction as the speakers helps reduce their audibility. The reflection off the ceiling and floor make it look like a line source much longer than its physical length, to greatly minimize ceiling and floor reflections (which also affect timbre). Finally, the next longest delay would probably be the back wall. 15' long room puts this beyond 20ms for an average seating position.

The corner placement excites all room modes the most. Some like this, some don't. Do you find the need for extra room diffusion or bass traps? The longer RT60 from the corner placement no doubt helps add some warmth given that all delayed reflections are > 20 ms or so out.

The vertical column also smooths out the combined response of vertical reflections (similar effect to placing more subs in a room to smooth the low frequency in room response).

Neat design!

I tend to like some spaciousness from a strong delayed side wall and some "artificial?) depth from the front wall, but old habits die hard. It'd be nice to hear this some day (can't build it at home, my room wouldn't suit).

Dave

Thanks for the comments Dave.

My listening room is about 12' x 27' with the corner lines at the front of the room spaced 12' apart. This means the rear wall reflections are delayed about 34 ms or so from the usual listening area (about 10' from the front wall) and even more (around 46 ms) from my guitar playing location at the very front of the room. The room itself has no additional acoustic treatment beyond its normal furnishings and with its hardwood floor is rather "live" by most standards. Fortunately I've liked the sound of the room from the day it was built and I've been happy with the sound it imparts to live acoustic guitar as well as to my recordings of (my buddy's) voice and acoustic guitar. If the room sounded unpleasant I would be more inclined to damp it.

Yes, as Dave notes, the corner placement does maximally stimulate the room modes. I hear some bass variation with room position but I do not hear a big increase in bass as I approach the walls. This was something that bugged me about the point source speakers I previously used in this room. This is not too surprising as work done by prominent loudspeaker researchers Dr. Floyd Toole and Tom Nousaine supports the corner placement of subwoofers.

Regards,

John

[johnlmurphy]

Re: Murphy Corner Line Array (MCLA)

Hello John,
<snip>
I notice you didn’t utilize power tapering in your array. Had you considered it, and found it wanting, or did the simplicity of the straight power array outweigh any potential improvements in resolution or image bloom?


I’ve been giving the corner loaded design some thought as well. The seemingly incongruent requirements of many’s HT systems of both a small unobtrusive speaker, and one with high sensitivity and SPL capabilities suggest corner loading as one possible solution. Of course, pushing the speakers back into the corners will most likely result in the loss of soundstage depth, but with multi channel HT, that probably isn’t an issue. It’s still not a panacea, as you can’t realistically corner load the center channel…

C

I deliberately chose not to do power tapering or high frequency tapering in light of the reflections of the lines in the ceiling and floor. If tapering were used then each ceiling and floor reflection would also have a tapered response. Instead if decreasing in output as distance increased the first reflections in the ceiling and floor would be backwards and would increase in output with distance. The second reflection would taper off correctly but then the third reflection would be backwards again. So power tapering or high frequency tapering of line arrays will not give the intended result in the presence of ceiling and floor reflections. The giant acoustic array that results when a single real array is placed between a parallel ceiling and floor has a naturally occurring taper as a result of the loss incurred with each successive reflection. The in-room result is an effective acoustic line array that extends to infinity in each direction but is tapered with each reflection growing progressively weaker and more diffuse. Here is an idea of what the in-room effective array would look like:




Curt raises the issue of home theater center channel where corner placement at first seems impossible. I've been thinking about the center channel problem and am considering two short lines located at the center of the front wall but placed horizontally at both the floor and ceiling. Perhaps 12 drivers in a corner enclosure placed horizontally at the intersection of the front wall and floor and another placed at the ceiling would be a good solution. The image should appear nicely centered on the screen.

Regards,

John