Murphy Corner Line Array (MCLA)

[Chromedome2000]

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?

[D, Rose]

Re: Murphy Corner Line Array (MCLA)

Hey John! Interesting design. I was thinking about using a line array at my church. Its a long room with a high peaked ceiling, walls go up about 10' before going up to that classic "cathedral" design. I could put two of these in the front corners. We have a praise band for the contemporary service, and a choir for the traditional service. Think this would work? Thanks for your time on this thread.

[Chromedome2000]

Re: Murphy Corner Line Array (MCLA)

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?

[Chromedome2000]

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!

[Sydney]

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-design/4210985/Loudspeakers--Objective-evaluations---Part-1--Sound-source-radiation-patterns?pageNumber=2

http://www.eetimes.com/ContentEETimes/Images/loudspeakers_objective_evaluations_fig3.jpg

http://www.eetimes.com/design/audio-design/4210985/Loudspeakers--Objective-evaluations---Part-1--Sound-source-radiation-patterns?pageNumber=3

[Chromedome2000]

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.

[Adam Bernau]

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.

[acousticspeaker]

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?

[John L. Murphy]

Re: Murphy Corner Line Array (MCLA)

Dear John,
I am an architect, living in Prague and DIY audio in general is my hobby.
I was very inspired by your MCLA design and i have decided to build one pair, but i will be happy if you can answer my possibly entertaining and also maybe a bit stupid questions.
First of all, i want to ask : Can i build the speakers like normaly positioned " towers " ? I have issues with the corner placement because my corners are too far away and i do believe that the stereo-base will be destroyed. I also do like to have realistic bass response, can i still have reasonable spl when i will compensate the bass drop with the eq ?
I was also thinking about trying something smaller with the Daytons ND-90 like a smaller " towers " with maybe only 10 or 16 speakers per side and desktop/PC monitors for my work table with maybe two or three. In the last two cases, the compensation of the frequency response via the Behringer that you have used for the big speakers seems inadequate, so i wanted to ask what do you think about the posibilities of compensating them passively. I am unfortunately not much educated in electronic circuits and i dont know if it will be better to use the mini DSP or try to go the crossover way.
I have read through the great article of the man who designed Mcintosh speakers and he says that he was equalizating the response to be flat between 30 Hz-18 kHz, that was done with passive filtering i take it ? He is selling some equalizing box with his last project but i don´t know what is inside.
I was also thinking about putting the speakers in their separate sub-enclosures , would you see that like an improvement ?

Thank you very much for going through my questions !

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

[John L. Murphy]

Re: Murphy Corner Line Array (MCLA)

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

[John L. Murphy]

Re: Murphy Corner Line Array (MCLA)

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

[Sydney]

Re: Murphy Corner Line Array (MCLA)

.... 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?

[John L. Murphy]

Re: Murphy Corner Line Array (MCLA)

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

[John L. Murphy]

Re: Murphy Corner Line Array (MCLA)

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

[John L. Murphy]

Re: Murphy Corner Line Array (MCLA)

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