Murphy Corner Line Array (MCLA)

[John L. Murphy]

Re: Murphy Corner Line Array (MCLA)

The shape of my listening room precludes corner mounting. I would like to make an array of 25 of these drivers which would have to be located some distance from any side walls. I'm wondering what volume the cabinet should ideally be and if a Mini DSP system could be used for EQ? What should I expect as far as bass performance? Modeling the system I come up with about 39L for the internal volume, does this sound about right? I like the efficiency provided by a line array and would really like to experiment with the ND90 driver in this application. Thoughts, ideas?

For a given input power level I would expect 6 dB less output in the region below resonance as a result of changing from a 1/4 space (pi steradians) acoustic load to a 1/2 space (2 pi steradians) load. See: Spatial Loading Tech Topic


A larger enclosure would allow for more bass output below resonance changing the required EQ but the excursion limited maximum acoustic output would not be increased. Technically, the maximum volume velocity (U) of the system is that of the driver alone. Changing the enclosure size changes the shape of the frequency response curve but not the maximum output capability. Changing the acoustic load does change the maximum output capability. The system requires precision EQ correction regardless of the enclosure so ultimately I see no clear advantage to using a larger enclosure. Measurements and Custom EQ correction would definitely be warranted.

One other thing. I noticed in the MCLA design the drivers are rear mounted with a flare routed into the front of the baffle. It seems the ND90 has a thin mounting flange and I was wondering what the effect of surface mounting the drivers would be. Surface mounting would greatly simplify the construction of the baffles, though at the same time would make a grill harder to fabricate. I realize the rear of the baffles would need to be chamfered to allow the driver "breath". I guess what I'm trying to ask is, would surface mounting cause any real problems with diffraction effects or something else I haven't considered?

It's hard to say precisely what the difference would be but there would likely be some small but measurable difference in frequency response. I don't see any real problem with this change. My motivation for rear mounting them was to provide a little protection for the drivers.

Another question, what about using these in and open baffle design. I'm sure in such a design a subwoofer would become a necessity but according to some (Linkwitz comes to mind), dipoles may be the "almost holy grail" as all speakers are compromises. This thread doesn't seem to be getting much activity of late and I'm hoping some of you speaker gurus will chime in and help develop this speaker beyond just the corner loaded version. Help!

A dipole (open baffle) design would offer no corner or flush placement options but could be an interesting project. Free space loading would reduce the output below resonance considerably which would necessitate a subwoofer as you note. I once prototyped a full-range focused dipole line array which sounded quite nice. That prototype may have been the beginning of my affection for full-range speakers.

I've read the papers you've linked to and Dr. Griffin's white paper on line array theory. What I'm looking for are more specifics on this particular driver (Dayton ND90) and an enclosure for out of corner use. Also, can the Mini DSP be used in this application. Any help would be greatly appreciated.

You could certainly use my enclosure (or similar) placed out of the corner but you would probably want to customize your EQ and add subs because of the reduced bass output. Just because you move it out of the corner doesn't mean the reflections go away..they just move further away from the real array instead of being clustered tightly in a single coherent bass radiator as in the corner line array. Consistency as you move about the room may not be as good as with corner placement.

Regards,

John

[John L. Murphy]

Re: Murphy Corner Line Array (MCLA)

It seems like Dr. Murphy is not coming here or to the Diyaudio forum anymore. i like his idea, but i believe that the corner positioning may be a problem for lot of people, i am also worried that even if you have the listening position in the ideal center of the room and if you can place the speakers in the corners, if it is the longer side of the room the stereo-imaging and localisation might be a problem.

Hi Adam,

Thanks for the promotion but the US Air Force allowed me just 2 years for graduate study after I was commissioned upon graduation from college. In those 2 years I managed to squeeze in an MS in physics. After that I went on active duty as a Space Systems Analyst for NORAD. What an eye opener that was to see behind the "black curtain" of our secret missile warning systems. After becoming familiar with one satellite based system I was tasked with writing/editing a secret book concerned with the detailed flight characteristics of the various ballistic missiles deployed by nuclear armed nations at that time (late 1970's Cold War era). Even as I was simulating mass missile raids by day I was studying loudspeaker design by night. That's when I connected with Bob Ashley and took his wonderful course on Loudspeaker Design at the University of Colorado. At that time Dr. Ashley had recently been responsible for having Neville Thiele's landmark paper "Loudspeakers in Vented Boxes" (re)published in the AES journal. Science based loudspeaker design had just been born. Since serving in the US Air Force my professional focus has been on all things audio.

Oops...sorry for rambling. Yes, the corner placement will definitely be a problem for many people. This project is really only suitable for select rooms where the arrays can be placed across the narrow end of the room. I would not recommend placing the arrays across the long wall of the room. If you are lucky enough to have a suitable room for corner line arrays then I believe you will be very happy with the performance of this system.

Regards,

John

[acousticspeaker]

Re: Murphy Corner Line Array (MCLA)

John,

Glad to see you back answering on this forum. I joined specifically because of what I read about your MCLAs. I think I have an ideal room for some corner speakers - the room is rectangular and the speakers would be placed in the corners on the short wall which is about 11' wide. I was all ready to purchase some Allison Threes which would fit in the corners quite well also. But then, in searching corner speakers, I came across your MCLAs. So now I am torn as to what to do. Tha Allisons would seem to take advantage of many of the corner loading advantages that you speak of - but they are not line arrays - but they are already built, etc. Any comments that you have that would help me would be appreciated greatly.

Thanks,

John

[John L. Murphy]

Re: Murphy Corner Line Array (MCLA)

John,

Glad to see you back answering on this forum. I joined specifically because of what I read about your MCLAs. I think I have an ideal room for some corner speakers - the room is rectangular and the speakers would be placed in the corners on the short wall which is about 11' wide. I was all ready to purchase some Allison Threes which would fit in the corners quite well also. But then, in searching corner speakers, I came across your MCLAs. So now I am torn as to what to do. Tha Allisons would seem to take advantage of many of the corner loading advantages that you speak of - but they are not line arrays - but they are already built, etc. Any comments that you have that would help me would be appreciated greatly.

Thanks,

John

Hi John,

The Allison Threes, as you note, are one of the few speakers designed for corner placement. You can imagine the top view of the speaker with its three corner reflections and see that it is a good configuration compared to placing the same point source speaker away from the walls. A point source corner speaker could be a good fit for your room. While the point source in the corner would bring the front wall and side wall reflections together in a controlled way that group would not be particularly well integrated with the ceiling and floor reflections. Also the point sources would not have the slow falloff with distance that you get with the arrays. I think this slow change in level with distance is responsible for the "walk around image" effect that people talk about with line arrays. The image of the performers across the soundstage is nicely consistent as you walk about the room. I guess it largely depends on whether you are interested in a speaker building project or want something ready-made. If you play a wide variety of music the arrays will offer the advantage of variable voicing (via the EQ) where you can use a flat response for the latest reference recordings or have a more traditional voicing for older recordings so that they sound good also. Keep an X-Curve voicing at the ready for movie playback.

If you do decide to build the arrays please report on your progress and results.

Regards,

John

[acousticspeaker]

Re: Murphy Corner Line Array (MCLA)

Hi John,

The Allison Threes, as you note, are one of the few speakers designed for corner placement. You can imagine the top view of the speaker with its three corner reflections and see that it is a good configuration compared to placing the same point source speaker away from the walls. A point source corner speaker could be a good fit for your room. While the point source in the corner would bring the front wall and side wall reflections together in a controlled way that group would not be particularly well integrated with the ceiling and floor reflections. Also the point sources would not have the slow falloff with distance that you get with the arrays. I think this slow change in level with distance is responsible for the "walk around image" effect that people talk about with line arrays. The image of the performers across the soundstage is nicely consistent as you walk about the room. I guess it largely depends on whether you are interested in a speaker building project or want something ready-made. If you play a wide variety of music the arrays will offer the advantage of variable voicing (via the EQ) where you can use a flat response for the latest reference recordings or have a more traditional voicing for older recordings so that they sound good also. Keep an X-Curve voicing at the ready for movie playback.

If you do decide to build the arrays please report on your progress and results.

Regards,

John

Thanks for reply, John.

The Allison Ones, although not meant for the corners, were another consideration of mine, as they would be backed up to the wall. However, I don't know how they would work on an 11' wide wall without getting to close to the sidewalls. The Allison IC20s, although no longer available, did have a small line array of MTTM on each panel to supposedly help with the floor ceiling reflections you spoke of - but I don't see how just adding one more tweeter and midrange on each panel would help that much. The "room" that my speakers would be in is about 11' x 18' - but the other 11' end is really a half height entryway wall with a 3' opening in the middle. On the other side of the entryway is the kitchen. So one could actually be on the far wall of the kitchen, some 30' away from the speakers, and clearly see at least the top half of the speakers - the halfwall would block the view of the bottom half. In other words, people could be listening to music some 30' away. I would then think that your line array would have an advantage over the Allisons. In your earlier posts, you had talked about designing your own equalizer with some preset hardwired settings. Are you still considering doing that? If yes, would you be able to switch between some different EQ curves depending on the music?
Finally, has anyone come forward to offer to fabricate (for a price of course) the front panel of your MCLA? It appears making all of the routered holes is the most difficult part of the project for the builder.

John

[John L. Murphy]

Re: Murphy Corner Line Array (MCLA)

Thanks for reply, John.

The Allison Ones, although not meant for the corners, were another consideration of mine, as they would be backed up to the wall. However, I don't know how they would work on an 11' wide wall without getting to close to the sidewalls. The Allison IC20s, although no longer available, did have a small line array of MTTM on each panel to supposedly help with the floor ceiling reflections you spoke of - but I don't see how just adding one more tweeter and midrange on each panel would help that much. The "room" that my speakers would be in is about 11' x 18' - but the other 11' end is really a half height entryway wall with a 3' opening in the middle. On the other side of the entryway is the kitchen. So one could actually be on the far wall of the kitchen, some 30' away from the speakers, and clearly see at least the top half of the speakers - the halfwall would block the view of the bottom half. In other words, people could be listening to music some 30' away. I would then think that your line array would have an advantage over the Allisons. In your earlier posts, you had talked about designing your own equalizer with some preset hardwired settings. Are you still considering doing that? If yes, would you be able to switch between some different EQ curves depending on the music?
Finally, has anyone come forward to offer to fabricate (for a price of course) the front panel of your MCLA? It appears making all of the routered holes is the most difficult part of the project for the builder.

John

Hi John,

Yes, I would expect the arrays to sound better at 30' than the point sources. I like to crank mine to an extreme level in the music room and then step into the adjacent kitchen and enjoy the music while I make pizza from scratch. I've had occasion to cover my ears and turn it up to the threshold of clipping and then step out of the room to evaluate the sound quality. From the next room I could hear that there was no audible distortion even at levels that were so high I could not comfortable stay in the same room with the speakers without guarding my ears. At these levels and with a little EQ tweak (more bass typically) they can provide a fair illusion of a live band in the next room. (If you could ever believe Fleetwood Mac was really performing in the next room!) But they can reach those kinds of level comfortably with just my small amp with no signs of stress.

Have you ever had a loud party where people wanted to dance but because of the loud crowd you could barely hear your stereo when you cranked it up to clipping and beyond? I have. How embarrassing. That will never happen with the MCLAs. They have enough output to totally dominate any loud party that might unfold at your place. But truly powerful dynamics are just one facet of the outstanding performance of these speakers.

I have a design completed for the all-analog EQ with voicing options but have not completed a circuit board layout yet. That will happen as time allows.

The front panels were definitely a pain to make...especially the cutouts for the 25 drivers. I am in discussions with a supplier to offer an enclosure kit and will announce any progress toward that offering right here. Any readers who might be interested in an enclosure kit should let us know by commenting here.

Regards,

John

[acousticspeaker]

Re: Murphy Corner Line Array (MCLA)

Hi John,

Yes, I would expect the arrays to sound better at 30' than the point sources. I like to crank mine to an extreme level in the music room and then step into the adjacent kitchen and enjoy the music while I make pizza from scratch. I've had occasion to cover my ears and turn it up to the threshold of clipping and then step out of the room to evaluate the sound quality. From the next room I could hear that there was no audible distortion even at levels that were so high I could not comfortable stay in the same room with the speakers without guarding my ears. At these levels and with a little EQ tweak (more bass typically) they can provide a fair illusion of a live band in the next room. (If you could ever believe Fleetwood Mac was really performing in the next room!) But they can reach those kinds of level comfortably with just my small amp with no signs of stress.

Have you ever had a loud party where people wanted to dance but because of the loud crowd you could barely hear your stereo when you cranked it up to clipping and beyond? I have. How embarrassing. That will never happen with the MCLAs. They have enough output to totally dominate any loud party that might unfold at your place. But truly powerful dynamics are just one facet of the outstanding performance of these speakers.

I have a design completed for the all-analog EQ with voicing options but have not completed a circuit board layout yet. That will happen as time allows.

The front panels were definitely a pain to make...especially the cutouts for the 25 drivers. I am in discussions with a supplier to offer an enclosure kit and will announce any progress toward that offering right here. Any readers who might be interested in an enclosure kit should let us know by commenting here.

Regards,

John

John - I would definitely be interested in an enclosure kit. The enclosure is what is holding me back from building your speaker. It's not like I have to build a pair tomorrow so I look forward to progress in your discussions.
p.s. I didn't mean to turn this forum into a discussion of Allison speakers - they were my alternate choice - but I am going to hold off for now.

[Chromedome2000]

Re: Murphy Corner Line Array (MCLA)

I too would be interested in a cabinet kit. However, as I posted earlier, I would have to place them a fair distance from any corners. So, if possible, an out of corner cabinet kit would be appreciated. I realize EQ would have to be done on an individual basis but a kit would be nice to get started on a set of these speakers. If an entire kit is out of the realm of possibility, just a precut baffle would truly be appreciated as this would be the most difficult part to fabricate. Keep the info flowing.

[russ_L]

Murphy Corner Line Array (MCLA) Enclousure Kit

Hi John,

The front panels were definitely a pain to make...especially the cutouts for the 25 drivers. I am in discussions with a supplier to offer an enclosure kit and will announce any progress toward that offering right here. Any readers who might be interested in an enclosure kit should let us know by commenting here.

Hi John- I've been following this thread since its beginning. I'm most interested in your MCLA as it should adapt very nicely into my 13'x22'x7'3" basement home theater. The room is currently being built, but is a year behind schedule (life always seems to get in the way of things).

In that regard, I'd be interested in two enclosure kits, but perhaps not at the moment. I hoping in the interim that you might work out a center channel solution.:D

Regards,

Russ

[EricTheBlue]

Re: Murphy Corner Line Array (MCLA)

I too would be interested in a cabinet kit. However, as I posted earlier, I would have to place them a fair distance from any corners. So, if possible, an out of corner cabinet kit would be appreciated. I realize EQ would have to be done on an individual basis but a kit would be nice to get started on a set of these speakers. If an entire kit is out of the realm of possibility, just a precut baffle would truly be appreciated as this would be the most difficult part to fabricate. Keep the info flowing.

+1: I suspect many (myself included) who will want to build this kind of speaker will not have symmetrical corners available, and even if they did, may prefer traditional off-rear-wall placement. With this though in mind I have a few suggestions:

Develop at minimum two basic enclosure types: One with the size and shape of the original corner loaded, 25 driver array, and a more traditional infinite baffle design approximately 6 feet tall using 16 drivers. It is understood that the infinite baffle version will likely not have much extension below 80 hz but that's what subs are for.:D Because I've spent more time thinking about the the infinite baffle enclosure than anything else, I have a few more suggestions for it:

• I recommend an enclosure height of approximately 6 ft. because if the driver placement is right (see next bullet), owners should hear a more or less identical tonal balance when seated or standing.
• The bottom driver of sixteen should be place approximately 1 foot above the ground for a few reasons. For starters, doing so fulfills the previous item because 16 ND90 drivers should form an array approximately 5 feet tall. Second, when seated, no one is going to be listening to drivers within a foot of the floor so it makes more sense to get the bottom driver closer to ear height so the entire driver array can be taller. Third, when you raise the height of the driver array closer to the ceiling the listener will get the benefit (IMO-it's a big part of the reason why I prefer tall arrays) of a tall sonic soundstage and images when seated. I know this to be true from owning AV123's LS9 array up to a year ago. Finally, though I wouldn't necessarily recommend this for the first generation of enclosures, if one inserted a solid horizontal wall within the enclosure just below the bottom driver, the enclosure would essentially be split in two. The upper chamber would hold the array drivers, and a lower one could incorporate a shallow depth, side firing woofer (8-12 inches assuming the enclosure is deep enough) to allow for a close to-if not full range-speaker via external crossovers and bi-amping.
• Make the enclosure as narrow across the front as possible. Given the diameter of the ND90, I would think the enclosure need not be more than 6 inches wide. Having a tall skinny enclosure offers three benefits: Better SAF, a design that can be used in smaller rooms because the speaker isn't in the owner's face physically, and a speaker that disappears better than a typical tall, wide line source like Magnepan's larger planars. The enclosure can be as deep as necessary within reasonable limits (12-14 inches?).
• Brace the internal enclosure well.
• Optional but recommended-include internal damping and absorbing material.
• Ensure the front baffle can be user removed for driver installation and repair as necessary.

[lasse]

Re: Murphy Corner Line Array (MCLA)

Hello,

this is the most interesting development I´ve seen for my sound system up until today.

I have a lot of questions, both on the practical side and the basic tecnology but that comes later.

Does anyone know if the EQ can be fixed with a DCX2496? It would be nice to limit the investment in time and money to two towers of 30-32 drivers imported to Sweden from USA and make use of the EQ I have, at least to verify the merits of the setup.

2nd thoughts: One basic question on the fundamentals: I think I understand that one of the things with an array is to focus the sound in the center and thus limiting the bounce effects from ceiling and floor. The longer the array, the more focus. Now, what happens if you have an infinitesimal (Spelling??) array as in ths case? And isn´t the floor/celilg-effect what makes this array so long?

Regards/lasse

[Sydney]

Re: Murphy Corner Line Array (MCLA)

and thus limiting the bounce effects from ceiling and floor.

Not necessarily; some arrays are designed to use floor/ceiling ( boundary reflection ) to become a virtual extension of the real line.
Some are amplitude shaded depending upon whether being free flown or boundary loaded.

[John L. Murphy]

Re: Murphy Corner Line Array (MCLA)

Hello,

this is the most interesting development I´ve seen for my sound system up until today.

I have a lot of questions, both on the practical side and the basic tecnology but that comes later.

Does anyone know if the EQ can be fixed with a DCX2496? It would be nice to limit the investment in time and money to two towers of 30-32 drivers imported to Sweden from USA and make use of the EQ I have, at least to verify the merits of the setup.

2nd thoughts: One basic question on the fundamentals: I think I understand that one of the things with an array is to focus the sound in the center and thus limiting the bounce effects from ceiling and floor. The longer the array, the more focus. Now, what happens if you have an infinitesimal (Spelling??) array as in ths case? And isn´t the floor/celilg-effect what makes this array so long?

Regards/lasse

The Behringer DCX2496 is a fine crossover but it may not offer enough EQ flexibility to correct the 3 dB slope of an array. If it is an existing EQ you could always try it out before getting the DEQ2496 which has the real EQ power you need for line array projects.

Yes, it is precisely the floor and ceiling bounce (reflections) that make the effective array so long. Because the listener is at a listening distance small compared to the (effective) length of the array he is said to be in the near-field.

The "focus" you describe is probably a reference to the narrow beam width that arrays exhibit in the FAR-field (distances large compared to the array length). This thinking applies to concert line arrays which are designed for far-field use. The MCLA does not behave this way because you listen to it in the NEAR-field where the sound field does not change with listening height. There is much confusion in casual speaker discussions about this very important distinction between how line arrays perform in the near-field versus far-field. The two situations are quite different and it is important to understand the distinction. Much of the analysis that applies to concert line arrays does not apply to line arrays in small rooms. Concert lines are almost always heard in the far-field. Small room line arrays have the potential to create infinite line sources if they are used in a room with parallel ceiling and floor and the array covers essentially the full floor to ceiling height. With the infinite line array the listener is fully immersed in the near-field of the array. This is when the acoustic magic happens.

With most point-source multi-way loudspeakers there is an audible change in sound with a casual sit-down/stand-up test. I have observed that in a casual sit-down/stand-up test the sound of the array is completely unchanged...as expected. The behavior of the MCLA array is essentially ideal with respect to vertical directivity. However, the horizontal directivity is precisely that of a 2.5" piston. Many people would consider this to be too large for use up to 20 kHz but with corner placement the listening angle is automatically restricted to +/- 45 degrees which allows the 2.5" piston to illuminate the complete listening area very nicely...even in the top octaves. If I listen carefully as I move from the listening area forward to the front wall I can hear the highs fall as I approach the wall. If you think about it, the arrays probably maintain a better response near the front wall than any point source speaker placed away from the walls because you would be about 180 degrees off-axis for the point source speaker at the front wall but only 45 degrees off-axis from the corner line array. The geometry nicely compensates the largish diameter of the driver regarding high frequency dispersion.


Hey Chromedome2000,

I like your suggestion of just a pre cut baffle. I'll mention this to my potential source and see if we can get at least a pre cut baffle offering. So far it is still just loose talk...

Regards,

John

[lasse]

Re: Murphy Corner Line Array (MCLA)

The Behringer DCX2496 is a fine crossover but it may not offer enough EQ flexibility to correct the 3 dB slope of an array. If it is an existing EQ you could always try it out before getting the DEQ2496 which has the real EQ power you need for line array projects.

Yes, it is precisely the floor and ceiling bounce (reflections) that make the effective array so long. Because the listener is at a listening distance small compared to the (effective) length of the array he is said to be in the near-field.

The "focus" you describe is probably a reference to the narrow beam width that arrays exhibit in the FAR-field (distances large compared to the array length). This thinking applies to concert line arrays which are designed for far-field use. The MCLA does not behave this way because you listen to it in the NEAR-field where the sound field does not change with listening height. There is much confusion in casual speaker discussions about this very important distinction between how line arrays perform in the near-field versus far-field. The two situations are quite different and it is important to understand the distinction. Much of the analysis that applies to concert line arrays does not apply to line arrays in small rooms. Concert lines are almost always heard in the far-field. Small room line arrays have the potential to create infinite line sources if they are used in a room with parallel ceiling and floor and the array covers essentially the full floor to ceiling height. With the infinite line array the listener is fully immersed in the near-field of the array. This is when the acoustic magic happens.

With most point-source multi-way loudspeakers there is an audible change in sound with a casual sit-down/stand-up test. I have observed that in a casual sit-down/stand-up test the sound of the array is completely unchanged...as expected. The behavior of the MCLA array is essentially ideal with respect to vertical directivity. However, the horizontal directivity is precisely that of a 2.5" piston. Many people would consider this to be too large for use up to 20 kHz but with corner placement the listening angle is automatically restricted to +/- 45 degrees which allows the 2.5" piston to illuminate the complete listening area very nicely...even in the top octaves. If I listen carefully as I move from the listening area forward to the front wall I can hear the highs fall as I approach the wall. If you think about it, the arrays probably maintain a better response near the front wall than any point source speaker placed away from the walls because you would be about 180 degrees off-axis for the point source speaker at the front wall but only 45 degrees off-axis from the corner line array. The geometry nicely compensates the largish diameter of the driver regarding high frequency dispersion.



Regards,

John

Hello and thanks for the feedback.

Yes, I have a lot of understanding to catch up with in this field, and that is a part of the fun, I think, to try to fully understand why the system is working the way it is.

Is it fair to say that there could be a problem with the doppler distortion, using the same driver in the whole range? Is that the main trade-off with the liberty from XO phenomena?

Mind you, I understand that there are more on the up-side with this system.

A detail from your material on the system, John. I cannot track the applied EQ in appendix 1 to the measurements in fig 5-7. Perhaps the process of coming to the EQ is a iterative process and not just a measure-and-adjust??

Regards//lasse

[superspeeder]

Re: Murphy Corner Line Array (MCLA)

Subscribing... I find this project very interesting, though I must admit I'm a bit skeptical since the project has been out there for over two years (I think) and not one person beyond the original creator has duplicated this system and reported on it with real detail.

It really does sound like an awesome system, John. To your knowledge has it been duplicated AND documented anywhere else?