Murphy Corner Line Array (MCLA)

[ROTECH]

Nice project and write-up JM.

Although it has been mentioned, I thought that it might be useful to re-mention that there is a tool called a "hole saw". It attaches to a drill and can be used to cut/drill 3" diameter holes with relative ease.

I dont know if many of you have seen these hole-saws yet. They are meant for wood, they are incredibly cheap too. I picked up an 8pc set 1''-3'' for like $18.99. They work the nutz, they do not bind or collect MDF cuttings.
http://www.homedepot.com/h_d1/N-5yc1...1&keyword=hole saws&storeId=10051

[Sidi]

They work especially well in a large drill press. Mark and pilot each one for a line array, and it's just pull, shift, pull, shift, pull, shift. And take the blank out in between of course.

For tweeters, a forstner bit makes it even easier. Just have a shop vac running and you can get 40 holes in 30 minutes.

[dmontella]

Update time:

1. Pictures for the project are attached
2. I've gotten better at using the DEQ2496 (RTA, GEQ, PEQ). I have 3 memory settings at this time (a. MCLA specified settings-flat response, b. RTA AutoEQ, c. my ear/interpretation)
3. I still am very dissappointed with the sound. Very colored, minimal impact.
4. I have not done measurements, but it appears as if the off access reponse drops off very quckly.
5. Positives- bass response appears to be pretty good. Nowhere near as good as my infinite baffle sub in my family room.

Next steps:
1. Continue to muck around with my ear/interpretation curve
2. I'm going to give it a couple more weeks. If I'm not happy at that time I'll sell the speakers (for cost of the drivers) without the DEQ2496.

I'm open to suggestions.

[dmontella]

After much consideration and discussion with others more experienced than me I've decided to chalk this project up as a total failure. The comb effect and poor high frequency performance are too profound and I don't want to spend anymore time on the project. I plan on repurposing the drivers. If anyone in the Boston area is interested in the cabinets you can have them - no charge.

It was a great winter project and I hope that I've helped in some way to shed some light on the concept. Perhaps someone with more experience can pick up the project and achieve better results.

[John L. Murphy]

After much consideration and discussion with others more experienced than me I've decided to chalk this project up as a total failure. The comb effect and poor high frequency performance are too profound and I don't want to spend anymore time on the project. I plan on repurposing the drivers. If anyone in the Boston area is interested in the cabinets you can have them - no charge.

It was a great winter project and I hope that I've helped in some way to shed some light on the concept. Perhaps someone with more experience can pick up the project and achieve better results.

Hello dmontella,

I have not been getting notices and am just catching up with your project...

Before you abandon the project can we discuss it just a bit. The line arrays are acoustic chameleons and can be made to sound like pretty much anything depending on the overall EQ you have achieved with the finished system in your room. It sounds like you are not happy with your overall frequency response. Fortunately that can be fixed.

As the first person to complete a pair of corner line arrays and report your results here on this thread (even if they are negative so far) I would like to offer you a free license to TrueRTA Level 4 to use in measuring the in-room frequency response of the new line array system. Just contact support@trueaudio.com and mention this thread.

If you measure the response and tweak the EQ to get the actual in-room spatially averaged response flat (or some other preferred house curve) your opinion of the arrays is likely to change according to the achieved EQ. The bass can be boomy or tight depending on the EQ coloration. The high end coloration can be adjusted to be soft, exaggerated or flat.

With customized EQ I'm confident you can have the arrays sounding excellent in your room. My own EQ has actually changed a bit from what is currently posted at the project site (as a result of replacing most of the drivers over the course of 2 years). My tweaked EQ may improve your system but there is no substitute for customized EQ based on your own in-room measurements averaged around the listening area. I usually collect about 16 measured responses over the listening zone and then take an unsmoothed average of these responses. Finally I apply 1/6th octave smoothing to the grand average response and shift it so that it is centered on 0 dB. I then use this response to setup the initial EQ for the system. Then I measure again and make smaller adjustments as needed to remove coloration from the response. I am usually happy after the second round of adjustments. Then I do a final round of measurements to confirm the final response.

dmontella, In any event thanks for completing the project, posting photos and reporting your observations. If you will stick with it for one or two rounds of measurement based EQ tweaking I expect that your opinion of the product of your labor will change for the better. What do you say?

Regards,

John

[v01d]

Hi John.

Hopefully you're still about.

I'm very interested in the MCLA. But I cannot commit what is essentially 1000$ AU for my first build. So I'm thinking about the Aurasound NS3 as a cheap alternative driver.

The NS3 seems inferior to the ND90 especially in the bass department. However, I'm hoping that it will at least be a good start and I can replace the drivers further down the track with the ND90.

Do you think that it would be at least decent?

A quick question also; I didn't notice in your project details a reference to how much room gain there is for bass, by using the corner. I may have missed it though. Is there a rough estimate as to the gain one might get?

Cheers.

[John L. Murphy]

Hi John.

Hopefully you're still about.

I'm very interested in the MCLA. But I cannot commit what is essentially 1000$ AU for my first build. So I'm thinking about the Aurasound NS3 as a cheap alternative driver.

The NS3 seems inferior to the ND90 especially in the bass department. However, I'm hoping that it will at least be a good start and I can replace the drivers further down the track with the ND90.

Do you think that it would be at least decent?

A quick question also; I didn't notice in your project details a reference to how much room gain there is for bass, by using the corner. I may have missed it though. Is there a rough estimate as to the gain one might get?

Cheers.

Hello v01d,

The NS3 seems like a perfectly good alternate choice to me.

The gain in the bass range from corner loading is largely the difference between half-space and quarter-space loading or 6 dB. But when the array gain is included the system will produce over 100 dB SPL at 100 Hz with 1 Watt of input at 1 meter. See figure 5-4 in the array test results for more insight into the gain of the array compared to a single driver.

Regards,

John

[John L. Murphy]

I'm still pondering dmontella's negative results and have a couple of thoughts. He mentioned using an optical output and I wonder if he used the optical input to the Behringer DEQ2496. If so, it would have been absolutely necessary to reduce the EQ's overall signal level by 10 dB in order to avoid clipping the EQ. The first time I used the optical link from my CD player directly into the EQ I noticed that clipping was spoiling the sound so I investigated and found that I needed to reduce the "Gain Offset" to about -10 dB at the EQ's Utility menu.

The digital signal from the CD player has peaks at 0 dBFS or at digital "full scale". There is NO headroom so any attempt at boosting the signal level immediately results in clipping. So before we go boosting the signal at the EQ we first need to reduce the signal level so we have some working headroom. That's why it is necessary to set the "Gain Offset" down to about -10 dB when using the optical input. (see the Utility menu, page 1)

When driving the EQ from an analog source it is possible to overdrive the unit but if you are connecting to typical hi-fi gear you may have just the opposite problem. With analog sources you need to make sure you have enough signal level that signal peaks are getting into the top 10 dB of the operating range. This is a Pro Audio equalizer so you may find it may be necessary to drive it from a pro audio mixer. I strongly recommend using balanced analog connections. In my setup I first tried single ended (unbalanced) connections but audible hum forced me to upgrade to all balanced connections. With my current all balanced setup there is no audible hum even with audio paused at the highest playback levels.

For analog playback I control the signal level before the EQ so it is not necessary to adjust the "gain offset" to prevent clipping. I just set my mixer's output level to get into the top 10 dB but not clip the EQ. Then I trim the actual listening level using the power amp's input level controls. This way I can keep the signal level optimum at the EQ regardless of the actual playback level. For example, I can listen at whisper quiet levels while still operating the EQ at full level and maximum resolution. If I were to leave the volume up on the power amp and simply reduce the mixer output level it would lower the volume as intended for all practical purposes. But operating digital audio gear at 30 dB below full scale is asking for trouble in the form of noise and grungy distortion. For "critical" listening we always want to be operating the digital EQ so that peaks are hitting in the top 10 dB but never clipping. With typical hi-fi gear this can be a bit tricky.

Anyway, I'm wondering if maybe dmontella experienced bad sound as a result of signal level issues with the EQ.

Regards,

John

[NickJ]

It would be cool to get some more info and experimentation on this...it seemed like such a cool project.

[dkatr]

Hello to everyone,

I am a newcomer to this forum.
Congratulations to John Murphy for offering this project to public domain.

I have two questions:
1. Are there any step responce and CSD plot of the loudspeaker?
2. Instead of the DEQ2496, could someone use a DRC processor, such as Copland DRC 205 or Lyngdorf RP 1?

Best regards

Dimitris

[brokencrank]

[QUOTE=dmontella;1825510] If anyone in the Boston area is interested in the cabinets you can have them - no charge.

QUOTE]

I sent a PM regarding these cabinets since I have some NS3 on hand, but have not heard back. I will likely build something similar in the near future as line sources have me very intrigued. The tough part for me is not having a room with more than one corner that that is free of door or window trim...

Mr Murphy, if something similar in shape is constructed and tucked as close to the corner as possible (again, 3/4" thick casings, etc will not allow for these to be completely 'in the corner' in nearly any room in my home) will the effect still work?
I would also like to know about different processors as I have a minidsp, and with 31 band eq plug-in, I think that your settings should be able to be replicated?

[John L. Murphy]

Hello to everyone,

I am a newcomer to this forum.
Congratulations to John Murphy for offering this project to public domain.

I have two questions:
1. Are there any step responce and CSD plot of the loudspeaker?
2. Instead of the DEQ2496, could someone use a DRC processor, such as Copland DRC 205 or Lyngdorf RP 1?

Best regards

Dimitris

Hello Dimitris,

1. All my data is at the project web site. I have no CSD or impulse response data.

2. My only concern with the DRC units is their total range of correction. They need to be capable of +/- 15 dB of EQ correction. I've seen somewhere that these units are limited to a small dB range of correction. Perhaps someone will post the actual limits.

Regards,

John

[John L. Murphy]

[QUOTE=brokencrank;1838676]

If anyone in the Boston area is interested in the cabinets you can have them - no charge.

QUOTE]

I sent a PM regarding these cabinets since I have some NS3 on hand, but have not heard back. I will likely build something similar in the near future as line sources have me very intrigued. The tough part for me is not having a room with more than one corner that that is free of door or window trim...

Mr Murphy, if something similar in shape is constructed and tucked as close to the corner as possible (again, 3/4" thick casings, etc will not allow for these to be completely 'in the corner' in nearly any room in my home) will the effect still work?
I would also like to know about different processors as I have a minidsp, and with 31 band eq plug-in, I think that your settings should be able to be replicated?

You will start to get "corner gain" as you begin to move an array into the corner. I don't think the 3/4" casing will be a problem at all unless it creates an opportunity for something to buzz in sympathy with the bass.

The minidsp units with 1/3rd octave EQ would seem to be a good fit for the project and are lower cost than the Behringer EQ. You could start with my settings and then perhaps do your own custom measurements to fine tune your EQ even further.

Regards,
John

[jerrald]

I've been meaning to post this for some time but kept forgetting:
"Comb Filtering: Common Misconceptions", Axiom Audio
"Why We Believe: a common sense explanation of audiophile beliefs", Ethan Winer
"Hearing, Columns, and Comb Filtering", Roger Russell

[jerrald]

I've been meaning to post this for some time but kept forgetting:
"Comb Filtering: Common Misconceptions", Axiom Audio
"Why We Believe: a common sense explanation of audiophile beliefs", Ethan Winer
"Hearing, Columns, and Comb Filtering", Roger Russell

[zeus]

Would a 27 driver array using the Dayton ND-4s be appropriate for a room with a 9 foot ceiling? The 27 drivers could be divided into 3 sets of nine drivers in series, for an approximate impedance of twelve ohms.

[John L. Murphy]

Would a 27 driver array using the Dayton ND-4s be appropriate for a room with a 9 foot ceiling? The 27 drivers could be divided into 3 sets of nine drivers in series, for an approximate impedance of twelve ohms.

Hello Zeus,

Yes, assuming that the ceiling is parallel to the floor. I also assume that you are referring to the 4" ND drivers...the ND-90-4 or even the ND-91. 27 drivers seem ideal for the 9' height and the impedance works out fairly well. You would want to use a fairly high powered amp to have plenty of voltage swing headroom for the higher impedance. The good news is that the power amp will only be lightly loaded with little stress resulting in lower distortion than with its rated load.

If you need very high sound levels or are using it in a very large room (like a club) you may want to reconsider the 12 Ohm configuration and shoot for a lower system impedance. It just depends on your needs.

Good luck with your project. Please keep us informed of your progress if you would.

Regards,
John

[Tin_Ears]

Bill's were the PE Pioneer NSB Buyout . I have enough of those drivers to build 2 corner-loaded arrays and a center channel. How do you think these would perform in an eight foot tall corner-loaded array? One corner of my room has only 4 inches of space so I'd be limited to that width. Just to get the Qtc down to 1.0 would require a box 4x10x96 with internal dimensions of about 3x9x94 which is about .065 ft3 per driver after subtracting the truncated 45 degree corner for the driver baffle. I guess my biggest concern would be the asymmetrical shape of the box, being 4 inches across the back and 10 inches on the side. The center channel would be mounted at the joint between the front wall and the ceiling.

[Ron_E]

Ron,

Yes! The SPL increase due to corner loading is greatest in the bass range. So corner loaded sub-woofer arrays would make sense to me...unless they are competing for the location with a full range line array. Then I would let the full range array have the corner location.

Regards,

John

Is there a way to estimate how much gain I would get with a sub only array? My listening room is 12'x10'x7.5' with the speakers on the 10' wall. With a slightly staggered line I could get 16 of the Aura NS6-255-8A woofers in each corner. http://www.parts-express.com/pe/show...number=299-030 I modeled them in Winspeakerz in 5 cu.ft. with 600 watts and this is what I came up with. The longest dimension in the room is 17.4' so I included room gain set at 32 hz.



I plan to run them stereo and I have Ultimate Equalizer to take care of any EQ. http://www.bodziosoftware.com.au/ The rest of the system will probably be 3 way with ribbon tweeter, planar mid, and woofer. I assume I can integrate all of this together since this is a dedicated listening room with fixed listening position. Any input is much appreciated.

Ron

[Catfish]

Now this is a very interesting project indeed.

I was one of those audio professionals to whom Mr. Murphy refers as having heard his original line arrays in his living room. Twenty something years ago, I worked at an audio electronics company where John was working as Chief Scientist. I used to annoy him with questions every chance I got and he was always gracious to answer and explain with patience. I credit him with giving me my start in what has been a wildly successful career in pro audio product design and manufacturing. John has the heart of a teacher and it doesn't surprise me to read that he's placed his design in the public domain so others can enjoy and build upon his work.

Those original line arrays were something. I was skeptical at first, but hearing was believing. Of course, those cabinets looked like coffins and took up way too much living room to ever pass the "wife test." Using the corner effect to simulate increased cabinet volume is a novel idea. A bit of designer grill cloth and these could disappear into the architecture. I'm curious if these could be built in smaller segments to give them some modularity. Could one, for example, make two 4-foot arrays and stack them vertically to get the same result as a single 8-foot array? This might make them more commercially viable for portable sound systems and even cabinet makers to build and ship via UPS.

The need for frequency shaping appears to add a level of complexity to the project. I suppose your average home-built speaker is expected to deliver correct response from flat amplified audio. Call me a gear-snob, but that Behringer EQ isn't shouting "audiophile" to me. Maybe a more elegant solution would be to build the equalization into the speaker box. Okay, passive components working with powered signals are probably not realistic; it's difficult enough to build a passive crossover.

So instead, maybe the MCLA becomes a powered speaker. Powered speakers offer many benefits over passive speakers. The amplifiers can be matched perfectly to the drivers. The internal wiring can be known and compensated. Power limiting and protection can be optimized. Low level audio can be sent to the speaker cabinet eliminating long speaker wires which can be lossy and sometimes introduce instability. And of course, in this case, the front end to the power amp can have the frequency-shaping circuitry. Maybe a few dip-switches to flip if the MCLA is moved from a corner (eighth space) to a wall (quarter space), etc. Or some trimmers for calibrating speaker-to-room response.

Conversely, if powering is not desired, one could still make the electronics box and insert it into the signal chain between source and power amp. Maybe we could design this box and publish the schematic and bill of materials in the same way that John published the MCLA design so the more adventurous hobbyists could build their own. Just thinking out loud here.

Anyway, cool project. And to the poster who feels like tossing in the towel on the project, hang in there. I suspect with some frequency shaping tools, you're going to be very happy with the results.

Mike Dosch aka Catfish