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" DJ8MTM "

Origins

I love to rock as well as listen to the classics. I don't mean at average listening levels. I'm talking about levels comparable to a live performance with depth and realism. I listened in just about every high end audio parlor in the area for a loudspeaker system that would deliver what I wanted without having to second mortgage the house. Although I loved the sound of many of the name brands I heard they just couldn't deliver the kind of pain inflicting realistic volume levels that I dreamt of or could fit within a modest budget. The thought occured to me to use my woodworking skills along with some modest electro-acoustic knowlege and construct my own. After much research and scouring the internet for ideas I found a design I really was impressed with. The MTM (midwoofer, tweeter, midwoofer) arrangement (also known as a "D'Appolito" alignment) really intrigued me and I was also quite impressed with the look.

Drivers

The very affordable yet surprising high performance for the cost, Dayton 8" woofer and the popular 1-1/8" silk dome tweeter are the drivers of choice in these bad boys. These things need a large cabinet to really crank. The Dayton 8" is suitable to both sealed and ported cabinets. I opted for the ported design as I was looking for a lower F3.

The Crossover

Thanks to Wayne J. at Speakerbuilder.net I didn't have to worry about designing a crossover. From reading about the experiences with several of his other designs (D3's, VD Monitor and DHT) I could not think of a better way to go and would build these as proposed. 

 

Parts List

Below you will find my suggested list of parts for the DJ8MTM all from Parts Express...

 

Part Number Description Qty. Price Ext. Price
004-20  DAYTON 20 OHM 10W NON-INDUCTIVE..  2 $1.25 $2.50
027-344  15uF-100V NON-POLARIZED CAPACIT..  2 $0.70 $1.40
027-354  50uF-100V NON-POLARIZED CAPACIT..  2 $1.00 $2.00
027-430  DAYTON 12uF-250V POLYPROPYLENE ..  2 $3.55 $7.10
266-313  .27mH 14 GA. PERFECT LAYER INDU..  2 $6.88 $13.76
266-320  .40mH 14 GA. PERFECT LAYER INDU..  2 $8.03 $16.06
266-812  .33mH 18 GA PERFECT LAYER INDUC..  2 $3.30 $6.60
275-070  DAYTON 1-1/8" SILK DOME TWEETER..  2 $15.50 $31.00
295-310  DAYTON 8" WOOFER ..  4 $16.65 $66.60
027-429  DAYTON 7.5uF-250V POLYPROPYLENE..  2 $2.40 $4.80
004-2.4  DAYTON 2.4 OHM 10W NON-INDUCTIV..  2 $1.25 $2.50
004-4.7  DAYTON 4.7 OHM 10W NON-INDUCTIV..  2 $1.25 $2.50
    Total $156.82

Notes

Parallel the 50uf and the 22uF to make the 72uF cap
Use the 15uF for the 16uF
Use the 7.5uF for the 7.2uF
Use the 12uF for the 11.5uF
Use the 2.4 Ohm for the 2.5 Ohm
Use the 4.7 Ohm for the 4.5 Ohm
Use the .4mH for the .45mH
Use the .33mH for the .35mH
 ***You may notice that some of the parts aren't exactly as specified in the crossover. That's OK as they are close enough and this will not produce any difference audibly.

The Cabinet

If you don't have a large listening area, you might want to build a different speaker. I have these things in my living room and they are large indeed, they need their own postal zip code. OK now here are the specifics:

The internal dimensions of the cabinet are 49 x 16.5 x 9.5 (around 4.4 cu. Ft). I used (3) 7"x9.5" braces inside the cabinet to try to tie the sides together. You could brace more if you wanted but it is not necessary. A tuning of 32 Hz was employed to get the lowest F3 and flattest response possible. If you build the cabinet as described. just use a PE 260-328 port in it and you will be dead on. If you want to make one out of PVC pipe and save 30 cents, make it 4" ID x 4.5" long. The driver spacing that I used left 3/4" between the woofer frame and the tweeter face plate. The tweeter is offset 3/4" also. The sides and the rear baffle are covered with egg crate foam. There is also about 1/2 pound of Poly Fill behind the drivers. I also used (not in parts list) some vinyl floor tile from the local hardware store and adhered them to the interior to even dampen the cabinet even more. I should draw some sort of diagram for the cabinet but you should be able to figure it out. The crossover was mounted to the outside rear of the cabinet. I utilized a Radio Shack black plastic project box for each. They had to be rather large as the crossover when built takes up some space. I felt this was better in keeping things cool and easily accessible for future tweaking if needed. The external finish was very involved and took as much time as the box construction. I used 15 coats of a satin black latex mixed 50/50 with a satin clear latex sealer and rolled it on with a very fine foam sponge roller and steel wooled between each coat. The effort was worth it for the finish is smooth, satiny and very durable.

How do they sound?

These things definitely sound real, dynamic and definitely rock hard. You do not need a subwoofer with these monsters, just a cold brew, some Jack D and a copy of the "Lamb" CD/album by Genesis. The sound is like I have never heard in my living room. The bass rattled things off of my fireplace mantle without a hint of sounding strained.

On the serious side though, these things do sound fantastic and lifelike. I put on an Eric Clapton live CD and he sounded like he was in the room. Another quality of these speakers is the unbelievable wide stereo image they project. Even when standing beside them you never loose the other channel. As a package these are possibly the best all around deal I have seen in DIY speaker projects. For around $160 bucks in parts you can really wake up the neighborhood. Check out at my other site and sign the guestbook. Intruder LC 1500