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  • acousticspeaker
    replied
    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

    Leave a comment:


  • John L. Murphy
    replied
    Re: Murphy Corner Line Array (MCLA)

    Originally posted by Adam Bernau View Post
    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

    Leave a comment:


  • John L. Murphy
    replied
    Re: Murphy Corner Line Array (MCLA)

    Originally posted by Chromedome2000 View Post
    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.


    Originally posted by Chromedome2000 View Post
    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.


    Originally posted by Chromedome2000 View Post
    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.


    Originally posted by Chromedome2000 View Post
    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

    Leave a comment:


  • John L. Murphy
    replied
    Re: Murphy Corner Line Array (MCLA)

    Originally posted by PET-240 View Post
    One other thing John,

    Does your equip rack interfere with the reflected sounds or are they Placed elsewhere? Can you show a photo of your room/setup please?

    Many Thanks!

    My amp rack is at the left and about 4-5 ft in ront of the left array so it is out of the way of the floor reflection. My guitar rack is a little closer. I'll see about posting photos. When I do I'll post a link here.

    Regards,

    John

    Leave a comment:


  • John L. Murphy
    replied
    Re: Murphy Corner Line Array (MCLA)

    Originally posted by PET-240 View Post
    G'day All,

    Still on the learning curve regarding arrays, I have 64 of the Audience A3 drivers in the 16ohm coil config, John I am wondering if you could advise on the freq response from the Audience site and let me know your thoughts in this config as opposed to a bi/dipole config as the Audience does please? Am still in a large learning curve regarding arrays and all the advice you can give would be great.
    http://http://www.audience-av.com/pa...StatsGraph.pdf

    http://http://www.audience-av.com/loudspeakers/

    They do have alot of xmax so that may change the bottom end response in the corner loading, they were also designed for use in arrays so I believe they have a rising freq response in the upper freq to combat combing. Having read your site regarding the corner loading, I would like to avoid using eq if I can as it affects my current setup in regards to musicality, which is part of the reason I also want to use arrays. I want to use these as mains for a 2 channel setup, not too stressed regarding movies, I look forwards to your assistance, hope all had a great Christmas/New Years break!
    Many Thanks!

    Drew.

    Hello Drew,

    Thanks for commenting on the project. The Audience A3 would be a great driver for this project and with 64 drivers on hand you are all set to build a great pair of line arrays. Comb filtering is not a concern (for me) when the "complete" system (composed of the room and two arrays) is considered. Comb filtering from the arrays is probably reduced compared to using two point source loudspeakers placed away from the walls in the same room. This is because the delays between direct and reflected sound are larger for the point source placed away from the walls than for the array placed in the corner. Besides, the type of comb filtering we're talking about here is completely inaudible. (See Floyd Toole's book "Sound Reproduction".) I don't see any practical way to get a flat response (or other controlled response) from the array without corrective EQ. Personally I would not be concerned about the EQ affecting the musicality of the system. A definite advantage of an EQ with memories for storing settings is that you can have multiple voicings available for your playback system. In my experience no single voicing is appropriate for the wide variety of recorded music that exists today.

    Regards,

    John
    Last edited by John L. Murphy; 03-17-2011, 09:31 PM.

    Leave a comment:


  • John L. Murphy
    replied
    Re: Murphy Corner Line Array (MCLA)

    Originally posted by cfelliot View Post
    Just a 2 quick questions:

    Running WinSpeakers for a single driver and a Q of .707, the cabinet volume is much larger than what is used in the array. Is there an advantage in using this larger volume?

    Thoughts on using the array as surrounds in a home theater? I would think that the larger sound source would be excellent in this regard.

    Below some frequency there would definitely be an increase low frequency output as a result of a larger enclosure but it would also tend to cause the drivers to be spaced wider. While the increased output in the low bass would be welcome the wider spacing between the (real) driver and the reflected drivers would not.

    I have not tried it yet but I would expect the corner line arrays to perform well as rear speakers in the rear corners of the room. A variation on the design could be created for placement of surrounds on the side walls. They would lack the additional bass output of the corner loaded systems. The bass EQ would need to be revised for the change in loading. Due to the slow change in SPL as you change listening distance I would hope that the front-to-back sweet area would grow larger compared to point source speakers. With point sources it sometimes seems that the front-to-back listening distance is very critical; Move your head forward or back just 6 inches and it audibly changes the front-rear balance considerably. I use a front projector in my home theater and am considering ways to implement line arrays for center channel use. You could actually maintain corner loading by placing arrays horizontally at the intersection of the ceiling and the front wall and also at the intersection of the floor and the front wall. But what length should they be? I think that they should be long enough that they span somewhat beyond the width of the seating area. In time I hope to try this for myself.

    Regards,

    John

    Leave a comment:


  • Sydney
    replied
    Re: Murphy Corner Line Array (MCLA)

    Originally posted by John L. Murphy View Post
    .... I don't think a small adjustment it would "invalidate the design" but it could have an effect on the frequency response and cause the response to vary more about the room than it would with the more symmetric 45 degree angle.

    Regards,

    John
    Excuse this related question:
    Practically can some of the "effect" be ameliorated by absorbers and/or diffusers near by?

    Leave a comment:


  • John L. Murphy
    replied
    Re: Murphy Corner Line Array (MCLA)

    Originally posted by bjohng View Post
    There has been a lot of discussion concerning different room widths. However, unless I have missed it, there has been no consideration given to changing the face angle from 45degrees to aligning crossing/sweet spot with listening position.

    Does the resulting asymetry invalidate the design?
    The 45 degree angle does establish a regular pattern among the speaker and its three corner reflections. From the top view, each speaker (or reflection) is rotated precisely 90 degrees from those at either side of it. If you were to change the angle of the enclosure you would move the front facing speakers closer to each other and the back facing pair closer together but the front pair would now be rotated further from the rear facing pair (from the top view, again). I don't think a small adjustment it would "invalidate the design" but it could have an effect on the frequency response and cause the response to vary more about the room than it would with the more symmetric 45 degree angle.

    Regards,

    John

    Leave a comment:


  • John L. Murphy
    replied
    Re: Murphy Corner Line Array (MCLA)

    Originally posted by oodesigns View Post
    Thanks for the information.

    Just to get something clear about the speaker cabinet placement

    1) Would it be ok to add a packer to fill the gap between the speaker cabinet and the wall ie a strip of wood around the edge of the cabinet with it removed at the bottom to allow for the skirting board?

    2) How important is the distance of the drive unit away from the walls ie if the cabinet was slightly bigger.

    thanks

    Mike

    Mike,

    1) I don't think it would be a problem to build the enclosure out from the wall by a material thickness to stay clear of the trim.

    2) It's hard to say. I would not expect a big change but when you consider the corner reflections (top view) you would see all four "enclosures" moving apart as you move the enclosure out of the corner. I would expect some effect on the frequency response but nothing dramatic. If you are concerned you can measure the response and customize your EQ settings to compensate.

    Regards,

    John

    Leave a comment:


  • John L. Murphy
    replied
    Re: Murphy Corner Line Array (MCLA)


    Hello Adam,

    Yes, you could build similar speakers with fewer drivers and placed out of the corners, but my measurements and EQ will be of little help to you in that project. Building a passive EQ to correct the response, while perhaps theoretically possible, would be practically impossible given the requirement for a 3 dB/octave corrective slope. The Mini DSP EQ looks like a reasonable and lower cost way to achieve the required EQ.


    I'm still checking on the thread and the project is very much alive...but I have been very busy with a new WT3 software release. Over the next few days I'll try to respond to the discussion here and respond to your questions. Maybe we can stir up some discussion.

    Regards,

    John

    Leave a comment:


  • acousticspeaker
    replied
    Re: Murphy Corner Line Array (MCLA)

    I just joined this forum to find out more about John Murphy's MCLA - and now you guys are telling me he doesn't respond to this forum anymore. Why not? How do I get in touch with him?

    Leave a comment:


  • Adam Bernau
    replied
    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.

    Leave a comment:


  • Chromedome2000
    replied
    Re: Murphy Corner Line Array (MCLA)

    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.

    Leave a comment:


  • Sydney
    replied
    Re: Murphy Corner Line Array (MCLA)

    I would like to make an array of 25 of these drivers which would have to be located some distance from any side walls...
    ...and help develop this speaker beyond just the corner loaded version. Help!
    It already has been in many forms...
    "Line sources" ( as Floyd Toole calls them ) have been around for decades.
    The results can be predicted for the various implementations: Straight or articulated, uniform or shaded, full lines or truncated lines sources
    http://www.eetimes.com/design/audio-...s?pageNumber=2
    http://www.eetimes.com/ContentEETime...tions_fig3.jpg
    http://www.eetimes.com/design/audio-...s?pageNumber=3

    Leave a comment:


  • Chromedome2000
    replied
    Re: Murphy Corner Line Array (MCLA)

    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!

    Leave a comment:

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