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Old 23rd June 2012, 11:43 AM   #1
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Default Muffled midrange crossover or driver?

Picked a pair of JPW 215 speakers recently - looked ok at the time. Compared to my Paradigm 9se's the midrange is a bit muffled. Now i have little experience in crossover design but from the little of web browsing i've done i can't make head or tail of whats going on with the midrange and tweeter circuitry - seems overly fussy in a typically English sort of way. Tried replacing the mids with some Paradigm drivers and that improved but am wondering if someone could give me a heads up on the circuit and suggested improvements.Click the image to open in full size.Click the image to open in full size.

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Old 23rd June 2012, 01:53 PM   #2
system7 is offline system7  United Kingdom
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JPW clearly aren't the high-end maker of BBC type small monitors any more. More home cinema now. Doubtless made in China.

I really can't tell what is going on with the tweeter there either. It makes very little sense at all, because you really should never wire all those capacitors in series. They are as good as the smallest one. Is it a piezo tweeter or something?

The rest is straightforward. The bass on the side reinforces the bottom end. It overlaps greatly with the bass/mid which is standard simple CL midpass with the 7.5R/64uF shunt acting as a 2dB attenuator.

I have rewired the tweeter to be conventional soft-dome, though that is just to see what's going on, not a recommendation because the capacitor is way too big in practise. Phase response is very good on these simple filters if my sim serves me well.
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File Type: jpg JPW_215_FreqResp_Guess.JPG (70.3 KB, 28 views)
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Well, there it is! Best regards from Steve in Portsmouth, UK.

Last edited by system7; 23rd June 2012 at 02:06 PM.
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Old 23rd June 2012, 03:51 PM   #3
tvrgeek is offline tvrgeek  United States
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Paradigms are a bit pushy in the mid. More HT than Hi-Fi. Only the studio 20 were reasonably flat. You may want several other listening experiences.

You are putting caps in series in the tweeter. Do you know what the effect is? ( hint, they don't add!) Might start with System7's recommendation and consider it a "kit" starting point.

Please, I am not picking on anyone, but before folks start thinking they can design or even successively modify a crossover, they need to have completed at least a basic AC circuits class. Otherwise you are trusting the calculator or sim without understanding the result. Spreadsheets and sims are only an aid after you understand what you are trying to do. You don't need to go to a trade school as there are plenty of classes online for free and I am sure enough forum members to help with your questions. Designing networks is electrical engineering. Science, math. Sorry.
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Old 23rd June 2012, 04:39 PM   #4
system7 is offline system7  United Kingdom
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You'll notice I wasn't making any recommendations for changes at this stage, tvrgeek!

If my eyes don't deceive me there is a 100uF capacitor in that crossover. It's hard to figure out the network, but not there yet.

This also looks completely bodged:

Click the image to open in full size.

That doesn't even meet any sort of electrical safety or quality requirement. Looks like an odd-on by some previous owner. I'd guess the tweeter has allowance for some sort of crossover to be fitted on the back, but two 1uF non-polars would not be it. 2.7uF does make sense for a tweeter filter though, and the 0.6uF is doubtless involved too.
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Well, there it is! Best regards from Steve in Portsmouth, UK.

Last edited by system7; 23rd June 2012 at 04:42 PM.
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Old 24th June 2012, 12:38 AM   #5
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Isn't that (green thing) a plate for a tube/valve (?!)
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Old 24th June 2012, 01:35 AM   #6
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Thanks for your responses.
The pictures are as i found the speaker and yes some parts of it especially the glue holding the tweeter in position does look very dodgy - i'll post a pic of the midrange cone soon - another shock!!
The crossover is drawn as found.
Thanks for your inputs - i'm just starting out getting seriously interested in HiFi at age 52 its been a long term aspiration. I guess we all need to start somewhere.
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Old 24th June 2012, 02:59 AM   #7
tvrgeek is offline tvrgeek  United States
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WARNING WILL ROBINSON. Hi-Fi can be terribly addictive. Welcome to the club.
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Old 24th June 2012, 11:41 AM   #8
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Quote:
If my eyes don't deceive me there is a 100uF capacitor in that crossover. It's hard to figure out the network, but not there yet.
Yes System 7 there is a 100uF cap in there its paired in parallel with another poly cap underneath - i can't read its values but the combined pair sum to 113uF with a cap meter.
You may be correct about the tweeter being a piezo as well.
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WARNING WILL ROBINSON. Hi-Fi can be terribly addictive.
Too late with the warning - can't ride my bikes as often as i used to - with this as a hobby at least i don't have to leave home and it's not weather dependant.
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