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DCM KX-12 Midrange question

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dsime42

New Member
I was recently given a pair of DCM KX-12 speakers.
As always when I get speakers I see "what's inside". I was surprised to find that the "modified transmission line" seems to be describing the fact that the internal brace running vertically from side to side and only extending down to the top of the rear-firing ports. Seems to be an odd arrangement but I am not an engineer, however the 6" midrange and the 12" woofer share the internal volume. No the mid is not sealed. It seems to me that the woofer would be driving the midrange with bass pressure and that the speaker could be improved with internal baffles and some silicone sealant.
BUT, I am not an engineer. :-)

Comments?

I'm concerned that if I add a baffle to protect the midrange, which is at the top of the cabinet, the woofer will have less volume an the box will be detuned.

How much volume would the 6" midrange need for whatever band it reproduces? The crossover is VERY odd too, so I don't know where the filters split up the freqs.
 
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I too have a pair of KX-12's and once I got a look inside, I considered that "modified transmission line" to be basically BS.
An idea I have involve using a "port tube" from Parts Express. The tube would form an enclosure between the front baffle and that divider. That divider would have holes drilled in it to vent it and be stuffed with poly-fill. This way the sound waves from the woofer wouldn't have such a short path to the midrange. If you wanted to take the isolation further, you could take another "port tube" and extend this "enclosure" to the rear baffle. Keeping it sealed or venting it.

What really is a shame about these speakers is the way they did the crossovers. With some better parts and things properly spread out, these speakers would improve alot.
 

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js1138 said:
Never heard of that model, but older DCM speakers were carefully designed and tuned.
Click to expand...

The KX series are really MTX designs. They are carelessly designed and tuned.

At least, my KX-6 sounded bad right off the (thrift store) shelf, and the crossover network produced a lot of "lolwut?" reactions. As though someone handed them 1 resistor, 1 coil, and 1 capacitor and said to just stick them in there.

Edit: To be fair, my KX-6 sounds pretty alright with the crossover reworked into something that actually makes some kind of sense. The drivers are good, the cabinet is reasonable, they just severely dropped the ball on the implementation.
 
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I had a pair of the KX-12 series II. I thought they were fine for the money. Threw up a decent soundstage, were efficient and handled some power. I had a lot of fun with those and a Carver A-760X. I don't know if I'd mess with them. They weren't the ultimate in resolution, but they did seem to be tuned pretty well for even frequency response. Messing with them might mess that up. How much better are they going to sound with those drivers anyway?

If I ever see a pair of KX-212, I probably won't be able to resist...

The crossovers pictured look quite different from the series II crossovers. The series 2 were 8 ohm speakers and there were automotive light bulbs used to protect the mid and tweeter. Not sure if they sounded pretty much alike or not. I didn't think the series II were bad at all, considering the price and the amount of destruction they could do.
 
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audio1025 said:
Don't confuse the KX series with the CX series. The CX-17 I just stumbled on are quite nice.
Click to expand...

I have CX-17s in the computer room, so I listen to them more than any others. I love them. They aren't the best in the world, but they're remarkable anyway.
 
The CX series are goodspeakers. The CX 27 has the same woofers and tweeter used in the Timeframes. I use a pair as my rears in one of my surround systems with Timeframe 600's in the front.

I recapped a pair of KX 12's that I had for a while and they sounded good with my SX 1010. A friend of mine and myself were talking about the midrange and the next day he came over with a new tube of silicone and two shallow tuperware bowls and he wanted to glue them on the back. Well he left the bowls and silicone and later I sold the speakers.

Some poly caps make them sound better. I had them about 4" off the ground.
 
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dsime42 said:
It seems to me that the woofer would be driving the midrange with bass pressure and that the speaker could be improved with internal baffles and some silicone sealant.
BUT, I am not an engineer. :-)

Comments?
Click to expand...

As an easy experiment, you could take some folded up polyester batting and stuff it up there around the mid. This may provide a measure of soundwave isolation dor the mid. FWIW, being a ported design, I don't think there's as much pressure going on in there as a sealed speaker. But hey, I'm no engineer either.
 
royphil345 said:
I had a pair of the KX-12 series II. I thought they were fine for the money. Threw up a decent sound stage, were efficient and handled some power. I had a lot of fun with those and a Carver A-760X. I don't know if I'd mess with them. They weren't the ultimate in resolution, but they did seem to be tuned pretty well for even frequency response. Messing with them might mess that up. How much better are they going to sound with those drivers anyway?
Click to expand...

The KX-12 Series I's do have a pretty nice sound. I could listen to these for a long time without feeling the need to turn them off. I do believe they could use a better tweeter however. I just look at the construction of the crossovers in the Series-1's and wonder how much improvement there'd be if they were done "right".

Mebby I could get away with replacing just the woofer LP & mid HP inductors, split the crossovers into two seperate boards, use one of these for that mid sub-enclosure :scratch2:
 
RickeyM said:
The KX-12 Series I's do have a pretty nice sound. I could listen to these for a long time without feeling the need to turn them off. I do believe they could use a better tweeter however. I just look at the construction of the crossovers in the Series-1's and wonder how much improvement there'd be if they were done "right".

Mebby I could get away with replacing just the woofer LP & mid HP inductors, split the crossovers into two seperate boards, use one of these for that mid sub-enclosure :scratch2:
Click to expand...

The tweeters aren't the best and I thought about replacing them. But, I was impressed with the overall tonal balance for the price and didn't want to chance messing that up. Really, the highs were better than what Cerwin Vega had out at the time for twice the price. They were durable too. I tortured those speakers and ended up giving them to my brother in perfect working order. The first series may not be quite as tough, without the light bulbs to protect the mid and tweeter.
 
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Better than given credit for.

royphil345 said:
Really, the highs were better than what Cerwin Vega had out at the time for twice the price. They were durable too. I tortured those speakers and ended up giving them to my brother in perfect working order. The first series may not be quite as tough, without the light bulbs to protect the mid and tweeter.
Click to expand...

Wow, highs better than then current C-V's :music: Check the thumbnail of the crossover, upper right hand corner. Is that the bulb for mid & tweeter protection you're referring to? If so, the Series-1's have it too :thmbsp:

I agree with you about the KX-212 thing :D A pair of those at a good price? Talk about temptation :naughty:
 
RickeyM said:
Wow, highs better than then current C-V's :music: Check the thumbnail of the crossover, upper right hand corner. Is that the bulb for mid & tweeter protection you're referring to? If so, the Series-1's have it too :thmbsp:

I agree with you about the KX-212 thing :D A pair of those at a good price? Talk about temptation :naughty:
Click to expand...

Yeah, there it is! The series II used 2 in each speaker and I thought the crossovers looked a little more complex. It's been a GOOD while though and I may be wrong.
 
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RickeyM said:
...
I just look at the construction of the crossovers in the Series-1's and wonder how much improvement there'd be if they were done "right".
...
use one of these for that mid sub-enclosure
Click to expand...

I looked at the crossover and quickly determined that I couldn't even guess what it was supposed to be doing. It does seem that some better inductors, properly oriented, with mills resistors and some polypros "might" improve the sound. :yes:
Does anyone have a schematic of the crossover? Or even just the crossover points?

That said, yes that PE part is along the lines I was thinking.
How much volume should a sealed 6" mid have?
Do you think that removing that volume from the woofer will change the box tuning much?

ericj said:
The KX series are really MTX designs. They are carelessly designed and tuned.
Click to expand...

Thanks. That does go quite a way toward answering my "detuning" concern. :D


I think that I'll try a temporary insert, probably leaky but should be able to get an idea of the consequences.
 
Seven years later, I acquired some of these, if you're really pushing bass out of it it will definitely take hold of the midrange and push it where it doesn't belong making a terrible noise. I'm going to look into protecting that mid against my bass tests.
Matt
 
It do think it protected the mid range from the woofer. I think it reduced the bass a little bit so it backfired, I'm somewhat of a bass head. If you don't care about excessive bass, it could be a good move.
 
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