Active conversion

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Hi All,

I've recently started a diy project. I've converted a pair of Dali 104 speakers to active on a budget. These were only used as a training exercise although the results are pretty good. I will gradually take on bigger and better designed speakers so that while learning I can eventually do my own build. I'm using OpenDRC-DA8 as a crossover and 2 x Sony STR-DB930 amps (allowing a 4 way)

Here's my next project
20140123_201844_inside_jamo.jpg


I'd welcome thoughts as to what you'd do with them. I'd hope to achieve more than just a straight conversion. Possibly replacing the tweeter with a ribbon and adding another 2.5 or 4 inch drive unit. Keeping them as a 4-way.

I've never dealt with such design. I understand the two woofers are wired out of phase.
 
I'll try and edit in a sec from a pc. Pic also available here The speakers are vintage Jamo about 30 year old (Concert 7) It's a 3 way design. 2 x 8 inch woofers facing one another and 6.5 mid plus a 1 inch metal dome tweeter.

I'd like some thoughts from experienced speaker builders on whether it's a good idea to try and turn them into active 4 way by adding another drive unit? Am I likely experience many issues?

In passive form they crossover at 150 and 4000 Hz. 4kHz seems quite a lot for a 6.5 driver so though about adding a smaller drive unit and perhaps doing 150, 2,000, 5,000.

I'm picking them up today so they're an unknown quantity. Or maybe they're rubbish and not worth the effort :)

Spec:

System: 3-way, double chamber bass reflex

Woofer: 2 x 8" compound mounted

Midrange: 167mm (6 1/2")

Tweeter: 25mm (1")

Rated Power: 200 W (300 W music)

IEC Input Power: 80 W

Operating Power: 6.3 W

Frequency Range: 24-22,000 Hz

Crossover Frequency: 150/4,000 Hz

Impedance: 6 ohm

Weight: 28 kg

Dimensions (H x W x D): 920 x 286 x 313 mm
 
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I would first measure them with a mic. Get the Woofer(s), mid and tweeter FR's and distortion with and w/o the XO attached. I would assume having 2 woofers you should be able to get in the low 40's if not 30's. If not, you might leave them alone or make them the best you can without adding much more cost.
I agree 4,000 is quite high for a 6" mid, that is 4" territory. the FR will tell you if it's having issue reaching that high.
You might be better off buying a larger diameter tweeter, so you can move that XO point to 1,500-2,000 which will make the overall speaker sound better mainly due to lower distortion from mid and tweet.
Lastly 150 is quite low for those woofers (but they may need to be that low because they can't play any higher cleanly). I would shoot for 300-500 if they can do it. Again, will make your mid so much happier and play a lot cleaner.
Going active gives you infinite possibilities, but I wouldn't change drivers until you have had a go with stock and then really look at each speaker before you decide which one(s) to replace or add to.
Lots of help on this forum, so ask questions and post pics.
 
Okay, lets take a look...

The original design is effectively a 2-way speaker with a built-in subwoofer. The pair of 8" drivers won't play high up too well. The isobaric mounting and 6th order bandpass enclosure will see to that.

I'd pick a 6" two-way speaker, copy that, and then add the 8"s at around 150Hz (or wherever the 6" driver rolls off in the sealed box), possibly with a seperate amp driving them.

Chris
 
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