Peavey Ecoustic 112 - 12" Coax Speaker - Blown Tweeter

[TomCarlos]

Friends....

I thought it would be a good idea to open a new thread and focus on just one thing- the speaker in the Peavey Ecoustic 112. The info in this thread could apply to other Peavey Speakers, but let me stick to this particular speaker.

This speaker is a 4 ohm, coax. The tweeter has it's own terminals and uses fuses and a single cap for the crossover. I found a 6.8uf cap solders to the terminals. So I am guessing that a single order crossover means this falls in the neighborhood of a 6Khz crossover. I could be wrong.

The cap is open and the diaphragm melted. Its mostly also a 4 ohm diaphragm.

I have contacted Peavey to see if they have a replacement part and specs for this speaker and the tweeter. Perhaps we'll get a reply.

In the meantime, here are some photos.

While waiting for Peavey to respond, I am going to search and see if I can find a 3rd party replacement.

And then... the crossover. I don't know if a simple cap will suffice. Perhaps I will look for a high pass filter or 2 way. And the cut over will depend on the diaphragm specs. The woofer will go full range.

[The Dude]

I looked through my "box-o-diaphragms" and don't have anything similar. This might work?

Titanium Dome Hi Frequency Tweeter Diaphragm 8 Ohm 25 4mm Length 83 5mm | eBay

It's 8 ohm, but I doubt it would matter much. Are you sure the original was 4 ohm anyway? I very rarely (almost never) see 4 ohm high frequency diaphragms.

[TomCarlos]

That is a good question... I don't know. That is why I hope Peavey can provide some specs on the diaphragm. I'll take a look at that link.

Thanks!

[J M Fahey]

*Looks* reasonably close, but the proof of the pudding lies in the eating: both seem to be 1" nominal diameter voice coil, but each factory has its own take on that, problem is that even fractions of a mm matter: too thin and voice coil touched polepiece; too fat and it scratches "outside" , against the pole plate hole walls ... if it ever could get inside the gap.

Precision in measurement is paramount.

FWIW even *this* diaphragm might fit:
Diaphragm Horn Tweeter for Foster Fostex N30 025H30 FT300H FT50 H025N08 | eBay



2 replacement diaphragms for U$12

the "pcb" type base will not fit yours, but that's not the main problem, you can work around that, the main problem is exact voice coil fit.
Don't you have one of these around, even if burnt?

[Enzo]

A simple cap is a 6db/octave crossover.

[TomCarlos]

Monte.... that diaphragm looks dawg-on close.

Juan... Yes I have a working Fostex type diaphragm... I will see if I can carefully remove it from the existing board and transplant it onto the frame. Delicate work indeed.

[The Dude]

Looking at the gap in your pic, there appears to be quite a bit of tolerance. It's a wider gap than many. Of course that still doesn't mean 100% that some semi-random diaphragm won't fit. My bet is that the one I linked will.

[J M Fahey]

Don't actually remove the diaphragm from the PCB type frame until certain it works.

Just pull full diaphragm assembly from the Fostex horn, measure coil diameter, in fact put it edge to edge with the burnt voice coil and if and only if they are same diameter you connect a small radio or equivalent to the Fostex diaphragm, play some music, and try to insert it in the Ecoustic tweeter magnet gap.

The radio serves both as a functionality tester and as a centering device by ear, since you are sending the full range an d not just highs, diaphragm is centered when it sounds best and horrible/hollow/thin/weak if not.
Quite noticeable if you test it yourself.

Only if diaphragm works perfect in the Ecoustic you can either unglue Fostex diaphragm in the ecoustic phenolic frame (possible but very delicate job) or kludge some way to permanently mount the Fostex diaphragm there.

A Dremel with a cutting wheel or rotary file can work wonders, as long as:
a) cover the gap with tape to avoid filling it with debris
and
b) cut/grind only plastic or pot metal or aluminum but never ever iron, filings will *fly* straight to the gap and render the magnet unusable.

That said, please show how is original tweeter mounted, there is some kind of center post involved but no picture shows it.

You might very well remove old tweeter magnet and epoxy a small new tweeter there, with same or lower cost as a new diaphragm, and with guaranteed results, while repair is iffy unless you find the exact same diaphragm.

I sometimes cut generic Piezo tweeters to make them fit between adjacent speakers or in some small free corner, you might create a small coax-capable one with a sharp bandsaw or a few minutes with a coping saw.

[Enzo]

Geez, shouldn't we wait until we know if Peavey has the exact same part that will drop into place before we go inventing something?

[The Dude]

Certainly can't take it as gospel, but I read in another forum that the speaker is discontinued by Peavey.

[TomCarlos]

The Peavey KB3 Amp uses a similar speaker - except that it is 8 ohms.

Perhaps the impedance of this dome tweeter is not critical since the woofer is running full range and we are merely providing a crossover for the tweeter. I did notice that there are some dome type diaphragms that are 4 ohms. So that is why I asked about impedance.

Enzo.... yes and definitely, if a direct replacement is available from Peavey, I will snatch that up. I want to see what they would send me.

Juan.... I am adding another photo that shows the diaphragm sitting in the two notches on the tweeter frame.

The link that Monte provided drove me to a similar item, Smooth Titanium Dome Hi-Frequency Tweeter Diaphragm 8 ohm. Looks identical (or at least fairly close to what I have.

[TomCarlos]

I received a reply from Peavey today. They do not carry the diaphragm as a separate part. You need to buy the entire speaker. The new speaker part number is 70777226. It is a 4 ohm speaker and tweeter.

I found another blog posting today where a guy was doing a simple solder fix to the diaphragm of the same speaker. The photo below shows him checking the diaphragm- there it is - 3.71 ohms. So Peavey was using a 4 ohm diaphragm!

I ordered the 8 ohm diaphragm that I mention in post #11. Let me see if that works.

And if not, one can either do a transplant as Juan suggested OR go with a separate Piezo or horn (with a crossover) as I did on the KB60 project. See Peavey KB60 KB60A Speaker Replacement.

I'll get back to this when the diaphragm arrives.

Tom

[The Dude]

I believe it was mentioned before, but you would be better off not using an electrolytic cap for the crossover. Since yours is bad and needs replacing anyway, I'd go with something better and maybe slightly smaller value. There's a calculator here for quick figuring of crossover frequency.

Speaker Crossover Calculators by V-Cap

[Enzo]

Schematic calls for a 4 ohm load. You know, if you installed an 8 ohm version, it would only lose you a couple of decibels, no one would notice.

[The Dude]

And probably less likely to smoke again. I wouldn't worry even a little bit about using an 8 ohm diaphragm. The only thing is that it will change the crossover frequency, which is why I would use a slightly smaller value film cap (since the original is bad anyway). Perhaps something like this:

475MMR250K Illinois Capacitor | Capacitors | DigiKey

Edit: assuming the ordered diaphragm works.