Murphy Corner Line Array (MCLA)

[johnlmurphy]

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!

Yes, the system has a tiny footprint and is unobtrusive in the room. You'll have to come up with a customized enclosure to deal with the baseboard and moldings. You might consider Dana's suggestion of a system built into the corner where the room walls serve as the rear walls of the enclosure.

Regards,

John

[johnlmurphy]

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

Dana,

Where greater height is needed I recommend extending the array with more drivers spaced at the same 3.5" interval (minimum spacing). For 9' ceilings 28 drivers would allow for a 4x7 wiring arrangement with a net impedance of either (4/7)*8 = 4.6 Ohms or (7/4)*8 = 14 Ohms. I would recommend the 4.6 Ohm configuration with 7 strings of 4 series drivers wired in parallel.

A higher strength material would be interesting but the drivers cannot be spaced any closer than 3.5" as this allows only about .015" or so between drivers. You might devise a layout using essentially two lines side by side but staggered so that the driver spacing is effectively halved. You might orient the driver with corners up and down to allow the two lines to fit closely together. The horizontal spacing between the two lines could probably be held below 2" this way. That might be a good way to implement a larger number of even smaller full range drivers. Perhaps a tight spaced dual line of 2" drivers would achieve sufficient linear displacement capability to deliver sufficient bass output. Let's see, that would be something like 72 drivers per side.

A triangular shaped enclosure would work fine. That's actually the shape I was drawing as I started the project. It was only as I applied image analysis to the problem that I saw the improvement offered by the octagonal shape. I changed to the five sided enclosure because when it is reflected in the front and side walls it more closely approximates a cylinder. The cylinder shape is desirable because its diffraction will introduce no ripple into the frequency response. The square shape that will result when the triangular enclosure is combined with its three side reflections will have sharp corners which will contribute some amount of ripple to the frequency response. I like your idea of building the enclosure "into" the corner. That way you would need only the baffle and top and bottom caps to form a complete enclosure without concern for the enclosure buzzing against the wall.

Regards,

John

[Paul Carmody]

Re: Murphy Corner Line Array (MCLA)

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.

Will there still be room to fit people and furniture with all these drivers in the room? :D

[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

[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)

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)

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

[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!

[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

[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

[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

[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.

[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

[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

[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.