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Dean Markley BC215D = Sunn 200S? By Sid of Stone Marmot August 6, 2016 I recently acquired a two 15 inch speaker cabinet that a neighbor was throwing away. The cabinet was a Dean Markley BC215D which was missing the speakers and needed a significant cleaning. But the wood and Tolex were in reasonably good shape, though someone had painted the tan Tolex black, with a lot of the paint now missing. This cabinet looked to be a lot more trouble than it was worth the first time I rode my bike past it, looking and smelling pretty bad. But when I rode past a second time, I noticed it had the unusual port design of the Sunn 200S. Closer examination showed its dimensions were almost identical to the 200S. So I decided it was worth salvaging. Prior to the mid 1960's, there were few, if any, reasonably sized cabinets that could reproduce bass frequencies at the loud volume levels desired for larger concerts. The Sunn 200S was one of the first that did a good job of producing loud bass in an reasonably transportable cabinet. Consequently, this cabinet and it bigger brother, the 2000S, became staples for large rock concerts in the late 1960's, until the Ampeg SVT and the various folded horns, most famously represented by Acoustic, became available. So, the Sunn 200S and 2000S became the recognized sound of concert rock bass guitar for the late 1960's. Part of the reason for the 200S and 2000S cabinets capabilities was the use of the JBL D130 or D140 (later K130 and K140) speakers. These JBLs, though expensive in their day, were much more efficient than the typical speaker available then, though EV and Altec also had speakers that were comparably efficient (and expensive). But the JBLs weren't the whole story, as many manufacturers offered JBL (Fender, for example), Altec (Ampeg, for example), or EV upgrades for their existing cabinets, none of which really cut it for concert volume level bass. The thing that really separated the 200S from the other cabinets in its day was the cabinet design. Figure 1 shows a drawing of the front and a side cross-section of the 200S. The front showed a port running across the entire width of the cabinet between the speakers (the "D" dimension). A number of traditional bass reflex cabinets also did this. But traditional bass reflex cabinets maintained a constant cross-sectional area throughout the entire depth of the port. The 200S had a port cross-section that got progressively smaller as the sound exited the cabinet, as seen in the Figure 1 side cross-section view (refer to the parts with the "E" and "F" labeled dimensions).
Figure 1 - Sunn 200S style cabinet drawing. Though Sunn sometimes called this a "rear loaded horn," it wasn't a typical horn as the cross-sectional area of a horn gets bigger, not smaller, as the sound leaves the cabinet. I also suspect that typical bass reflex design criteria, such as those popularized by Thiele and Small, don't work too well in explaining the function of this cabinet, either. It was an inspired design (the creator said the idea came to him in a dream) that just seemed to work, and work well. Some manufacturers came up with their own versions of this design. This Dean Markley BC215D, which was introduced about 20 years after the 200S was, is almost an exact copy of the Sunn 200S. Table 1 compares the BC215D and a consensus of the 200S dimensions found on the web. Refer to Figure 1 for what each dimension refers to. In both cabinets the board labeled "F" and its mirror image complement directly above it are at a 45 degree angle to the boards labeled "E." This table shows that there is no more than 0.5 inches difference between any dimension between these two cabinets. Table 1 -Comparison of Dean Markley BC215D and Sunn 200S Dimensions
Figure 2 shows a front-right view of the BC215D after I cleaned and painted it. As usual, I didn't think of creating an article on it until I was mostly finished refurbishing it, so I don't have any before pictures. But I had to scrub both the inside and outside a couple of times with bleach to clean it and try to get rid of the smell, which smelled like cat piss. After it thoroughly dried, I painted both the inside and outside to try to seal in any remaining smell. This figure also shows that I had stapled fiberglass on all the inside walls to minimize standing waves. The BC215D originally did have fiberglass on all the walls, which I had to throw away because it smelled bad.
Figure 2 - Front-right view of the BC215D. Figure 3 shows a close up of the front port.
Figure 3 - Close up of front port. I found little information on the Dean Markley BC215D. But what little I found indicated it was usually shipped with 15 inch EV Force speakers. I didn't have any EV Force speakers or any of the 15 inch JBLs used in Sunn 200Ss. But I did have a pair of EV EVM-15L speakers available. The EVM-15Ls are closer in performance to the JBL K-140s than to EV Force speakers. Personally, I feel the EVM-15L is probable the best sounding 15 inch bass speaker ever made. It is a so-so PA speaker, though (I salvaged these from a pair of Ramsdell PA cabinets). Figure 4 shows the BC215D with the EVM-15Ls installed.
Figure 4 - BC215D with the EVM-15Ls installed. Two 2 inch cone tweeters were also added. These tweeters were salvaged from a Roland/Rodgers C-100 digital keyboard that had built in amps and speakers. This C-100 was sitting in a neighbors garbage with half the keys on the keyboard broken, though all the electronics still worked. I originally built a crossover with 2.2 kHz crossover frequency feeding the tweeters, but found the cabinet sounded way too bright. I rebuilt the crossover for a 4.5 kHz crossover frequency, which sounded much smoother. Figure 5 shows a picture of the crossover mounted inside the cabinet. There is also a switch mounted in the top of the left recessed handle to completely switch the crossover and tweeters out of the circuit. Figure 6 shows a schematic of the cabinet, including the crossover.
Figure 5 - Crossover mounted inside the cabinet.
Figure 6 - Schematic of modified BC215D speaker cabinet. The grill that was with the salvaged BC215D was originally maroon. Someone tried to paint it black. It also had multiple tears and smelled real bad. So I removed the grill cloth from the frame and cleaned and painted the frame. I then added some spare shade cloth, as discussed in this article, to the frame to use as grill cloth. The frame is attached to the cabinet with Velcro-like fasteners, with two black cloth tabs at the top to make it easier to remove. Figure 7 shows the final result. It sounds great both with and without the tweeters switched in. Obviously, it has a more vintage sound without the tweeters and a more modern sound with them. So far I've only tried it with my modified 1972 Ampeg VT-22 head (100 Wrms, see this and this article for the mods) and my Ampeg SVT-2 Pro (300 Wrms). I get a great bass sound out of both of these amps through this cabinet with both my basses (1978 Rick 4001 and a late 1960's Conrad hollow body violin shaped bass), even with the tone controls on both amps set flat. The output sounds smooth, with no detected resonances or boominess and all the notes down to low E are well defined.
Figure 7 - Final fully assembled BC215D speaker cabinet. You can hear the cabinet in the song "Miss Chameleon" found here . The bass is most prominent in the bridge of this song. I always question the value of these listening examples, as you are not only hearing my BD215D speaker cabinet, but also my amp (modified 1972 Ampeg VT22), tone control settings (flat with ultrahi on), bass (late 1960's Conrad violin shaped bass), microphone (Joe Meek JM47), preamp (Echo Layla3G), bass strings, guitar pick, microphone positioning, room acoustics, etc., all adding their color to the sound. But this song is an example for those who value these sound samples. By the way, it also sounds great with guitar, but only with the tweeters switched out of circuit. Otherwise, it sounds way too shrill. © 2016 Stone Marmot Enterprises, all rights reserved. |
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