Murphy Corner Line Array (MCLA)

[ROTECH]

Re: Murphy Corner Line Array (MCLA)

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]

Re: Murphy Corner Line Array (MCLA)

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]

Re: Murphy Corner Line Array (MCLA)

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]

Re: Murphy Corner Line Array (MCLA)

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]

Re: Murphy Corner Line Array (MCLA)

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 [email protected] 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]

Re: Murphy Corner Line Array (MCLA)

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]

Re: Murphy Corner Line Array (MCLA)

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]

Re: Murphy Corner Line Array (MCLA)

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]

Re: Murphy Corner Line Array (MCLA)

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

[dkatr]

Re: Murphy Corner Line Array (MCLA)

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]

Re: Murphy Corner Line Array (MCLA)

[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]

Re: Murphy Corner Line Array (MCLA)

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]

Re: Murphy Corner Line Array (MCLA)

[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]

Re: Murphy Corner Line Array (MCLA)

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]

Re: Murphy Corner Line Array (MCLA)

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