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Old 23rd September 2007, 09:10 AM   #1
dynapos is offline dynapos  Norway
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Default JMLab Profil7 upgrade

I have been planning to upgrade my JMLab Profil7 speakers, it is a speaker with two 7" midbass\bass woofers (I think it is Focal 7v4211 or 7V014) and TC120K tweeter in d`Appolito configuration. See attached pictures.
I have now bought the Focal TC120TD5 tweeters and I think this will be a big upgrade to the sound of these speakers.

I have also been planning to change out the woofers with Focal 7W4411 and from the reviews all over the audiophile world this should be a very big upgrade, the problem is that Elliot @ Zalytron suspected that the existing woofers were 4 ohm and therefore I would need to change the crossover, the crossover in the speaker now is a 3 way 18dB\octave and my question is if it is easier to rebuild the existing crossover for the higher impedance or if the best solution is to use the already proven good crossover from Zalytron.
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Old 23rd September 2007, 11:52 AM   #2
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Rebuilding the existing crossover for the different impedance isn't really an option because the drivers are different. Everything changes, it would be a completely new design.

You could measure the DC resistance across your speaker terminals. If it is somewhere around 8 ohms, you have two 4 ohm woofers in series. If it is around 4 ohms, you have 8 ohm woofers. If you have 8 ohm woofers you might get passable results using the existing crossover. One issue is the cone breakup modes are probably different frequencies and amplitudes.

Elliot's crossover designs are a decent if you don't have the ability/desire to roll your own (I used his kits a couple times when I re-started this hobby). As long as your cabinets are within an inch or so of the width of the cabinet Elliot recommends for the project it should work well.

If you want to get into it, you can do better, though. IIRC Elliot's crossover kit for 7W4411/TC120TD5 crosses over around 2,400 Hz, without much attention to the woofer breakup at 2,700. There's also a bobble in the FR and impedance curves around 1200 Hz, which indicates that the 7W4411 would probably be better suited as a woofer than a midwoofer. At least the breaup modes aren't as nasty as some metal cones.

Were I to design a crossover for this driver combination, I'd push it lower and higher order. My 6W4254/TD120TD5 sound much better crossed over at 1,500 Hz (8th order LR initially) than they did at 2,400 Hz (4th order LR) , even though I notched out the woofers' breakup.

Going from the K to TD5 will be a big improvement. While still not a high excursion tweeter it does a lot better crossed lower. I have an old copy of Speaker builder with an ad for the T120K recommending a 3500-4000 Hz crossover point depending on which version.

I haven't compared W cones to V, but compared to the treated paper cones, the W is a LOT cleaner. However, there are quite a few drivers with better performance for less money available. They don't look as nice, though.
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Old 23rd September 2007, 02:21 PM   #3
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Quote:
Originally posted by BobEllis
Were I to design a crossover for this driver combination, I'd push it lower and higher order. My 6W4254/TD120TD5 sound much better crossed over at 1,500 Hz (8th order LR initially) than they did at 2,400 Hz (4th order LR) , even though I notched out the woofers' breakup.

Going from the K to TD5 will be a big improvement. While still not a high excursion tweeter it does a lot better crossed lower. I have an old copy of Speaker builder with an ad for the T120K recommending a 3500-4000 Hz crossover point depending on which version.

Thanks for the reply Bob,
I suspected that I had to change out the X-over if I will change the woofers, but I will try the tweeters first and see the improvement, but I think I will change the capacitors on my x-over with MCAP Supreme caps, was thinking of changing out the smallest spool for a high grade foil spool. ( See attached photo of crossover)
I am very happy with the sound of these speakers and I have had them for over ten years now, have been buying new speakers three times the last five years, but I play the new speakers for a while and then it's back to the old ones, these speakers have a soul and that you can feel when you sit down and put on a nice cd (especially female voices, Norah Jones \ Diana Krall etc) So I hope I will be even more happy with the sound after the new tweeters are installed.

If I decide to buy the woofers I will have to build a new crossover and will only use premium caps \ spools, do you have drawings of any crossover you think might suit this project?
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Old 23rd September 2007, 02:21 PM   #4
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Specifications of JMLab Profil7
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Old 23rd September 2007, 02:49 PM   #5
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It doesn't look like the crossover has enough parts to make any attempt to tame the T120K's peaking top end. That ought to really make the TD5 sound sweet in comparison.

The crossover also doesn't look like a three way to me, but 2.5 makes sense. That accounting for baffle step may be what makes you like them better than your other experiments.

You'd probably get more bang for your bucks upgrading the caps than coils. The thing to be aware of is that they probably designed the filter with the ESR of the electrolytic cap in mind. Going to a low ESR cap may change the shape of the transfer function.

I generally think foil inductors ae too expensive for questionable benefits in the audio band. Just use the heaviest gauge regular inductor that you can find. Even then, you'll be hard pressed to match the DC resistance of those ferrite core coils, so replacing them will likely change the sound character.

I don't have any suitable crosover plans. Use Zalytron's as a starting point. My system is actively filtered.
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Old 23rd September 2007, 04:49 PM   #6
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Hi Bob and thanks for the reply,

I think I will play with the TD5 on the crossover as it is for now, will build a new crossover when I invest in the new woofers, I can't wait to get the TD5's next week and get them in the speakers, I think I will be pleasantly surprised with the upgrade from the kevlar tweeters even if I keep the x-over as is for a while.

I checked out your website and I understood you was into active crossovers, I hope to learn from it when I make my new crossover, will go for Elliot @ Zalytron's crossover, but I will also consult with Eltek in Oslo for their opinion.

(Regarding 3 way x-over, I just saw the text in the specs for my speakers saying: Number of electric ways - three ways)

Thank you very much for your input Bob.
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