An Open Loudspeaker Design Project
by John L. Murphy
3. MCLA Project Details
5. Array Test Results
6. Line References/Links
7. Project Log
8. MCLA Discussion Thread
3. MCLA Project Details
The Dayton Audio ND90 3.5 inch speaker is available from Parts Express here: Dayton ND90 at Parts Express
Per the Parts Express web site pricing for the ND90 is as follows:
1-10 units: $19.70 each
10-49 units: $16.90 each
50+ units: $12.90 each (this is nearly 35% off the single unit price)
The MCLA system employs 24 speakers per corner line array enclosure. If you are considering building a pair of MCLAs I recommend buying at least 50 speakers to allow you the freedom to reject one or two for quality reasons and/or to have a replacement driver to set aside.
Total Cost for 50 ND90 speakers: $645.00
At $645 for the drivers alone this may not be a low cost speaker system, but when you consider the high level of performance that this system delivers, the value is quite large.
My initial prototype enclosures (Prototype #1) were built out of 1/2" (actually 15/32") plywood. I am a minimally skilled woodworker so my prototypes are a bit rough, but they are fully functional. I ended up covering the entire face of the line enclosures in black grill cloth. I have seen some of the fine looking enclosures that DIY speaker builders create so I am looking forward to seeing better implementations of the MCLA than my Prototype #1. Please send pictures of your finished systems and I will post them here.
Figure 3-1 shows an overview of the plans for Prototype #2. The detailed plans are available in .pdf form below.
The recommended enclosure at this time is Prototype #2. The plans are provided in a .pdf file for easy reference and easy printing.
With 24 drivers of 8 Ohms each it is necessary to employ a series/parallel wiring arrangement in order to achieve a net load impedance near 8 Ohms. The simplest ways to wire the drivers are either six parallel groups of four in series or four parallel groups of six in series. I chose the first case in order to achieve an impedance that falls between 8 and 4 Ohms (5.33 Ohms). Figure 3-2 shows the wiring diagram. The other arrangement with four groups of six drivers in series would yield a net impedance of 12 Ohms which I decided was just too high.
Here is a link to the wiring diagram as a .pdf file: MCLA Wiring Diagram.pdf
Eventually I may design a custom analog EQ to voice the MCLA. For now however, I am using an off-the-shelf digital 1/3rd octave equalizer. I strongly recommend that you use this same EQ in order to directly implement my EQ settings for the MCLA. The equalizer I am using is the Behringer Ultra-Curve Pro DEQ2496 shown in Figure 3-3 below. This unit is available from Parts Express for $299.99. The thing I especially like about this unit is the accurate correspondence between the boost/cut settings and the amount of boost/cut actually achieved. There is minimal interaction between bands and being digitally implemented the EQ is perfectly repeatable. It would not be possible to convey my settings to other users and get precisely repeatable results with anything besides a digitally implemented EQ. If you want to precisely reproduce the MCLA voicing you will need to use this equalizer. I will tell you exactly how to set it so that should not be a concern.
Here are links to the EQ's page at Parts Express and the product brochure.
The Ultra Curve Pro at Parts Express: Behringer Ultra-Curve Pro DEQ2496.
Product Brochure for the Ultra-Curve Pro DEQ2496: Behringer DEQ2406.pdf
The Equalizer Settings
Here are the equalizer settings I have arrived at for the MCLA systems in my music studio room. Shown in figure 3-4 below are the average settings for the two channels.
I use separate EQ settings for my Left and Right channels. By swapping the two enclosures and measuring each way I determined that the two prototype enclosures are very consistent but that there is a small difference between the two positions. My corners are actually not ideal as one has windows at either side and the other has a window to one side and a door to the other. So I have prepared a PDF file containing one page of settings (each) for my current left and right positions along with an average of the two. In general, I would recommend using my average EQ unless your corner configuration closely matches one of mine.
MCLA EQ Settings as of 3Oct2009: MCLA EQ 3Oct09.pdf
Each page has the three settings for the Graph Equalizer portion of the Behringer EQ. These settings correspond to:
In addition to the Graphic EQ settings I have included settings for the Parametric EQ portion of the Behringer unit as well. These adjustments are just as important as the graphic EQ settings. I recommend you enter the data for the FLAT setting and then save this to three different memories. Then you just need to edit the second two memory locations to create the small-room X-curve and X-curve EQ settings. Note that the only modules of the EQ unit that I am using are the Graphic EQ and Parametric EQ. All other modules are bypassed at the unit's bypass pages.
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