Burnt out KSN-1141 piezo :-( - diyAudio
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Old 19th December 2005, 09:20 AM   #1
Ovation is offline Ovation  United Kingdom
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Angry Burnt out KSN-1141 piezo :-(

Hi All,
I've come to a point where I urgently need some help and advice again!
We were doing a disco on Saturday night when we kept hearing strange brief hissing noises. Suddenly one of the speakers went to white noise and then let out a deafening high pitched squeal. After that there was no more treble from that speaker, and a slight 'blown up capacitor' kind of burning smell :-(
Luckily we had some spare speakers, and the show went on.

We are using some large pre-manufactured cabinets which are unbranded and un-spec'd:
They're about 60cm high x 40cm wide x 30cm deep and very solid.
The venting is strange - The front baffle bends towards the back of the cabinet low down, and then leaves a gap the entire width of the speaker, which is about 10cm wide)
The drivers are Eminence Delta 400 8ohm (12 inch), and the tweeters are KSN-1141 Piezos which we've been using successfully in both our pairs of speakers.
We were driving them with a Lyonforge A400 Amp which is 200W into 8ohms, and the tweeters are currently wired direct in parallel with the drivers.

I need to fix these speakers before wednesday, which means I need to order parts before the end of today. Obviously I can order another KSN-1141, but I'd really like some advice on how I can protect these units in future (particularly as the specs say they have built in protection!!)

(As a brief history - we did have a problem with these speakers where the treble output really over-powered the bass output. We have since removed most of the wadding (there was *no* space for any air!) and the bass response has improved dramatically.
In our other speakers we are extremely happy with the frequency response with no x-overs)

If a crossover would protect these tweeters - Can you recommend a pre-manufactured Eminence crossover that's any good? (I say Eminence because I can buy them from www.cpc.co.uk and get them Guaranteed Next-Day today.

If I'm not going to use a crossover, would a second piezo help to lighten the load? (It'd have to be something like KSN-1165 for space reasons.)
Or if I went with a Crossover, could something like an Eminence APT80 be mixed with a piezo?

Many Thanks (In advance)
Jonathan
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Old 19th December 2005, 09:30 AM   #2
Ovation is offline Ovation  United Kingdom
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Oh dear - It looks like I won't be able to buy a KSN-1141 from CPC as they're out of stock!!
The only similar thing they've got that *is* in stock is a KSN-1016 - I might have to get one of these as a temporary replacement.

Anyone know where I can get a new KSN-1141 in the UK - to arrive tomorrow?

Thanks
Jonathan
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Old 20th December 2005, 02:18 PM   #3
Wizard of Kelts
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Seems a little strange to be answering from over here, but nobody else has responded, so I'll try.

First, the 1141 seems to have been discontinued. However, the discontinuance seems to be fairly recent, so I would call a couple of music stores locally and see if they have any hanging around. They very well might.

Second, a model which covers the same range as the 1141 is the KSN 1165. A friend of mine uses 2 per cab with his his Eminence Kappas. You can probably get away with one per cab. The shape is somewhat different-you might have to cut a piece of plywood to fit.

Theoretically the KSN 1016 only goes down to 3,000 Hz, not 2,000 Hz like the 1141, but in fact piezo response is so uneven, I doubt anyone would notice. I would use it in a pinch, if I had to.

Lastly, since the thing you are playing is tomorrow night, I might point out that all the Motorola tweeters, including the 1141, use the same drive element! So if you can get hold of any old piezo tweeter that works, take a hacksaw and cut off the back and remove the wafer from the new piezo. Perform similar surgery on the old 1141-what have you got to lose? Just transplant the wafer and solder the connections. Now you have your old KSN 1141 ready to go.

You might have to bypass that "protection circuitry" with a wire-if didn't pprotect the element, what are you losing? Piezos without protection circuits have been functioning for years. Gluing the plastic case back together? My guess would be Krazy Glue, or any cyano type glue. Should work for awhile-ie, weeks or more. Maybe forever.

Maplin's has the 1165 at various stores around London. Fill in the Search box at the top of the page with "ceramic tweeters", scroll down to the part where they list KSN 1165, and they will direct you to the London stores which have them in stock, store phone numbers, and directions.

Just for the heck of it, here is a listing of London stores and their stock for the KSN 1165:

Holborn, 2
Bishopsgate, 0
Tottenham Court Road, 2
Great Portland Street, 2
Marble Arch, 0
Queensway, 2
Stratford, 2
Wood Green, 4
Hammersmith, 2
Forest Hill, 0

Good luck.
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Old 20th December 2005, 03:02 PM   #4
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How are the piezos wired? They do not need a crossover as they roll off naturally, but they do need attenuating. A series resistor is not the correct method and can lead to excessive capacitive load on the amp, which can lead to instability. Maybe this is what happened to you?

Regarding your removal of the wadding. From your description I would hazard a guess that the stuffed box and 'vent' configuration produced a form of aperiodic loading. Removal of the wadding will probably have had the effect that the cone is now unloaded at quite a high frequency -- I suspect you are on a razors edge with the reliability of your bass units. I would look seriously at modifying the cabinet to a proper vented design.
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Old 20th December 2005, 08:56 PM   #5
Wizard of Kelts
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Of course, if you don't want to cut into the cabinet, you can make a small stand or enclosure with the two, (or one) KSN 1165 in it. The stand might consist of no more than two pieces of half inch pine nailed at a right angle. Spray it black with Krylon, Rustoleum or whatever instant drying paint if you are worried about appearances. Fasten to top of cabinet with Velcro fasteners available at sewing stores, just tack the bottom Velcro piece down. Or you can choose your own fastening method. Heck, the thing might stay upright of it's own accord, if you make the base of the stand large enough.

The two KSN 1165's should be joined in parallel. Simply unhook the 1141, but keep it in the cab for appearance's sake.

Assuming you have a small reciprocating saw, that would be all you need to make the holes.

Or you can get creative and make your own method of installing the KSN 1165's into, or on top of, the cab. These are just quick suggestions to get you through an emergency, though you might decide to keep the change permanent.

Wires can run inside, or outside the cab depending on whether you feel like drilling holes.

As stated before, a friend who runs a DJ business in Cork, Ireland has cabs, both for himself and his employees, consisting of an Eminence Kappa 15 and two KSN 1165's. He's been running them for years, is quite satisfied with the sound.

Pardon the crude illustration below, just wanted to illustrate the idea.

Good luck.
Attached Images
File Type: gif emergency piezo cabinet.gif (4.0 KB, 183 views)
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Old 20th December 2005, 09:27 PM   #6
Wizard of Kelts
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As regards the series resistor, the KSN 1165, as a 2 kHz horn, would appear to have a built in series resistor. So would the 1141.

If you use the KSN 1016, though, a series resistor is recommended, since that is a 3 kHz horn.

Quote:
If such an [100kHz capable] amplifier is used, particularly with an array of tweeters, a small series resistor is suggested (Figure 9). For CTS tweeters with a low-end cutoff of 3 kHz to 6 kHz, a 50 ohm, 2 watt resistor wired in series with each tweeter will prevent this resonance problem without noticeably affecting the response. It should be noted that this problem is uncommon in automotive applications since these amplifiers usually roll off at 20 kHz. The 2 kHz horn products do not require an external series resistor since one is built into each unit. The KSN1086 mid-range driver and KSN1090 and 1103 voice range products should be protected with a 20 ohm, 10 watt series resistor.
This information is from in a CTS, (Motorola) application note which is on the web here.
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Old 21st December 2005, 01:37 AM   #7
alfa147 is offline alfa147  Turkey
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you should connect serial 30 ohm(approx.) resistance to tweeter.By the way ksn 1141 15$ in Istanbul.
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Old 21st December 2005, 05:26 AM   #8
Wizard of Kelts
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Well, here's a place in London that appears to stock them.

And here's contact info.

For all enquiries please call: 0845 230 6 230

Lines Open:
Sales: Monday to Saturday 9am - 6pm
Customer Services: Monday to Friday 10am - 5pm

eSpares Ltd
14 Chelsea Wharf
15 Lots Road
Chelsea
London
SW10 OQJ

Hope things work out.
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Old 28th December 2005, 10:20 AM   #9
Ovation is offline Ovation  United Kingdom
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Hi All,
Thanks a lot for your suggestions! Unfortunately by the time you all started replying I had been forced into buying *something* as an emergency replacement.

"Something" ended up being a couple of KSN-1016 horns (5 each) as everything else has been discontinued or was out of stock (The only place that could get a KSN-1141 to me next day wanted 40 in total!!!!)
Silly me didn't pay attention to the size of the KSN-1016 - it is much smaller than the 1141 but a bit of gaffer tape has masked its hole for the moment and I've now ordered another 1141 from espares.co.uk

I took some advice from http://www.planet10-hifi.com/piezo-XO.html (As posted by planet10 in response to the thread: "Having major problem with speakers"

So now, I have got the following ( sorry , crap drawing!):

+   PIEZO    &n bsp;-
|        & nbsp;       &nb sp;   |
39ohm       &nb sp;   |
|        & nbsp;       &nb sp;   |
| <--22ohm-->  |
|        & nbsp;       &nb sp;   |
4.7uF       &nb sp;    |
|        & nbsp;       &nb sp;   |
+  DRIVER   -
|        & nbsp;       &nb sp;   |
+     AMP      -

I've done this to both speakers - One still has a KSN-1141 in it - Only the one that we blew has got the temporary KSN-1016.

So now I need to know:
1) When I get my new KSN-1141, I'd like to use the full range it provides. How can I calculate where this crossover crosses over?
Please can someone point me in the direction of a page/thread that gives the BASIC formulae behind Crossovers (and cabinet design if possible).
2) Any comments about the pros/cons of the XO circuit I've added?

Many Thanks
Jonathan
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Old 28th December 2005, 10:25 AM   #10
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fc (approx) = 1/ (2 * pi * 22 [Ohms] * 4.7E-6 [F] ) = 1.5 kHz.

I.e. the mechano-acoustical crossover function of the piezo is still dominant but the piezo is heavily relieved from LF content, which should make it sound less harsh.

Regards

Charles
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