Dim tweeter

Ben Lawrence

Ben Lawrence

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Mar 2, 2011
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I have been getting ready for an event and running through a few matching passive speakers. It sounds like one of them has a dimmer sounding tweeter. What is the most likely culprit? Crossover, actual driver? It is still functioning just not as crisp as the other 3. The only other issues I have had in the past with tweeters they blew and were completely out. Can they be compromised and continue to run or am I more likely looking at a crossover issue?
I guess when I have a moment I can do a swap with one of the functioning units.
 
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What model speaker do you have,
Could be the crossover and or driver.

A quick test measuring the drivers with an ohm meter could be
telling of an issue, disconnect at lest on lead to the driver from the crossover first.

Swapping drivers between cabinets would narrow it down.
If it's the driver maybe something gotten into the driver and
removing the diaphragm and cleaning out the voice coil gap, the diaphragm
it self may take care of it.

While it's a part check the voice coil for damage, signs of burning high heat, ect.
Some drivers that used Nomex voice coil formers and some times they would
"de-form" and develope bumps that would then drag in the voice coil gap
 
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JBL SRX 715. Im going to try a swap later today hopefully. I would be surprised if junk got in there as these have the foam covering the grill. We shall see. It looks like a diaphragm is hopefully an easy swap. The crossover might be a little harder to come by I would imagine.
 
I swapped them and the lower tweeter followed the speaker I put it in. I popped it apart and everything looked fairly clean. I didnt take it all the way apart as I have not replaced a diaphragm for a tweeter before that I can remember and hoping to use these this week even in the compromised state. Guess I will order a replacement diaphragm. Hoping it is easier than reconing a woofer. Scraping that glue is a pita.
 
Sometimes a coil can just get "weak". I see that when fixing speakers, the tweeter will look alright, but the coil is just fading away.
Measuring the impedance/resistance of each of them might tell you that, but not necessarily. They should be pretty close, whichever the resistance of the good one is. Even just a little swelling of the coil can slow it down, but not enough to physically feel it.
If it's a half decent tweeter, the coil may be replaceable, that'll save some money, because aside from some trauma like overheating or dropping, the magnet part rarely fails. Coils can range anywhere from $20 and up, and the whole thing can be anywhere around $100 and up, naturally the brand, etc can throw that number off, or even make it so the coil isn't replaceable.
 
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The compression driver for the SRX 715 (and SRX 712) is JBL 339894-002X aka 2431H / 2431HPL. Rather pricy at close to $400 from reputable parts stores in the USA. The diaphragm kit is called JBL D8R2431 and is a quite frankly shocking $210. Ouch. Oh, I see, this is a ferrofluid filled driver. Yuck.

Replacing diaphragms is relatively easy, there is no glue involved. It is generally a question of removing a number of screws or bolts that hold the 2 halves of the driver together. The diaphragm is sandwiched between the 2 halves of the driver. In your case, it appears to be a lot of screws... check YT for how to videos. I also don't see anyone replacing ferrofluid, so not sure what the deal there is.

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Roy Andrews said:
The compression driver for the SRX 715 (and SRX 712) is JBL 339894-002X aka 2431H / 2431HPL. Rather pricy at close to $400 from reputable parts stores in the USA. The diaphragm kit is called JBL D8R2431 and is a quite frankly shocking $210. Ouch. Oh, I see, this is a ferrofluid filled driver. Yuck.

Replacing diaphragms is relatively easy, there is no glue involved. It is generally a question of removing a number of screws or bolts that hold the 2 halves of the driver together. The diaphragm is sandwiched between the 2 halves of the driver. In your case, it appears to be a lot of screws... check YT for how to videos. I also don't see anyone replacing ferrofluid, so not sure what the
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Ben Lawrence said:
Thanks for the heads up on the ferrofluid. Just watched a couple videos. Looking like this might be a bit of a learning experience.
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The aftermarket speaker kits can save you some money, it's just a matter of finding a good manufacturer. I used to have a good one that had almost everything I had needed, but he shut down over the pandemic. The few times I bought parts at Simplyspeakers they were good, they have factory and aftermarket.
Ferrofluid is neat but messy stuff. It's kind of cool to see it crawl like it's alive towards a magnet. It doesn't need very much and there might still be enough in there or salvage what comes out on the coil. Most will stay in the magnet, since it's attracted to it, so if the aftermarket part doesn't come with it, it's not a big deal, as I was told in the past that it's mainly used for cooling when really pushing the driver, and will work good without it or with what's left in there.
 
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One other thing that I'm not seeing in YT videos that I always do, although ferrofluid will complicate this somewhat:

I always clean the magnetic gap before installing a new diaphragm. This is especially important if the diaphragm shattered or otherwise cracked or split (or in the case of Mylar, melted or burned). It doesn't take much dirt or schmooze in the magnetic gap to cause distortion, and one oddball thing about compression drivers is that a small piece of grit or other material can cause distortion at a particular frequency(s) meanwhile every other frequency sounds great. And it can also happen that you don't notice until it's all back together, in the cabinet, and running at concert volume, because it sounded perfect at lower test volume in your shop.

I like to get Pec-Pads - a strong, but soft & perfectly lint free cloth used for cleaning the sensors of digital SLR cameras ($12 for 100 pack on Amazon USA). Cut a small finger of thin & stiff but flexible plastic (often the clamshell packaging the diaphragm comes in is perfect for this), fold the Pec-Pad so it covers both sides of the piece of plastic, then insert that in the gap & wipe it around & around. You can wet the pad with alcohol to help pick up dirt. Use a can of compressed air (or a real air compressor with a blower handle on the end of the hose) to blow out the gap. Repeat the Pec-Pad wipe & compressed air blowing if anything still looks sus after the first round.

Only THEN go ahead & install the new diaphragm. This should ensure a prefect job that returns the compression driver to a state indistinguishable from new.

The strangest thing I've found in a compression driver so far is dried coffee with milk & sugar. How??? Just how??? That was about 6 passes with the Pec-Pads, alcohol, & blower. New diaphragm for good measure, even though the old one still looked serviceable after some cleaning. Sounded fine after repair.
 
Good point. Ours that have the ferrofluid have always been from units that have the hf drivers tucked away from "spoilage", and clean from burns etc., just dealing with the infamous Vertec speakers with cracked domes/separated coils of the hf driver making it rattle at higher volumes. I seem to recall the coil separation made them too quiet, I guess it would be like having no cone joined to it on a woofer.

I was going to say use a magnet and wax/parchment paper to trap/save the ferrofluid, but I guess it would bring any metal material with it,
and it would have to be a much stronger magnet to overcome the other one, so not a good idea I guess now that I think about it more.
 
Paul Lewendon said:
I was going to say use a magnet and wax/parchment paper to trap/save the ferrofluid, but I guess it would bring any metal material with it,
and it would have to be a much stronger magnet to overcome the other one, so not a good idea I guess now that I think about it more.
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In my opinion, trying to save the ferrofluid is a terrible idea. You might compare it to re-coning a woofer & re-using the old spider, although that is very inexact comparison. You have zero confidence that ferrofluid is clean & free from debris caused by the failure of the diaphragm.

The genuine JBL replacement comes with a bottle of fresh ferrofluid, or at least that's what FullCompass claims. Their reps are knowable and ready to answer questions, worth talking to them. I'm not in the US, but I end up buying most of my repair parts there to be freight forwarded to my country.
 
Paul Lewendon said:
The aftermarket speaker kits can save you some money, it's just a matter of finding a good manufacturer.
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Look, it boils down to this:

Are these speakers important to you? Does your reputation depend on them working strong & solid, night after night? Or are they end of life ratted out cabinets that are going to be retired soon??

If it's the former, then why risk your reputation to save money on a chinesium diaphragm of unknown quality. Get the original, do the cleanup I talked about above, & get your cab back on the job, confident that you did the job right.

If it's the latter, then put any old junk in it just to get it over the finish line until you start using your new cabs.

Only you can make the decision, but that is my thought process when I fix my own equipment.
 
The ones I ordered in the past from the supplier that closed its doors, I think he said he was building them, they looked almost identical to original, if anything they seemed to look more robust. I tested in the Vertec using my ears and the sweep pattern in the JBL program (Performance manager?), and then a music test, it seemed to sound the same, my ears couldn't tell the difference, but I likely won't be able to find the same quality again. I think he was re-using the aluminum ring from the old ones if I recall.
 
Ben Lawrence said:
Man thanks again. This place is such a treasure trove of information. It is very much appreciated.
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Ben,

The ferrofluid itself, not the diaphragm could be the cause of lower output, if it has partially dried out, its viscosity increases. Think of running your hand through a bucket of syrup compared to water, and you get the idea of the difference the coil experiences.

As well as aftermarket diaphragms seldom being equal to the original, ferrofluid has dozens of different types.
If you bought the cabinets used, very possible some crap generic ferrofluid was put in, or contaminated old stuff left in place.
Even the wrong amount of the right stuff will affect the response.
If you want original performance, the old ferrofluid must be cleaned out, gap completely cleaned, Roys suggestion of Pec-Pads, followed with masking or artist's tape until the tape shows no sign of debris is needed.

Then, after putting in the measured quantity of ferrofluid, the diaphragm must be aligned.
Alignment pins or rings on the JBL diaphragms generally will center the diaphragm adequately to prevent rubbing and buzzing, but they do not guarantee it.

A narrow frequency band, sometimes only a few Hz wide, may trigger a “buzz” distortion. For that reason, misalignment distortion may not be at all evident except with certain musical passages, making music, pink noise, or even specifically spaced sine wave tones near useless for alignment.

In most cases, low frequencies of several octaves below the usual pass band will make the harmonic distortion most audible. After determining a reasonable mid pass band output level, slowly sweep from 200 Hz up, listening for "buzz". Most times the range between 200 Hz to 800 Hz will reveal the "buzzing", but I have found a few diaphragms that only buzzed when driven at anywhere from 800 Hz to 5kHz or so.

The horn, or even the long throats of "old school" drivers like Altec, JBL, or TAD makes the diaphragm output much louder, which will mask a dragging voice coil distortion component. Removing the driver from the horn, or stuffing the horn with rags, or laying it mouth down on a rug or carpet makes the buzz easier to hear.

To align the diaphragm, re-install the diaphragm with it's screws just loose enough to not rattle, but tight enough to allow one to tap a portion of the screw ring in the direction that eliminates the buzz, then re-sweep to determine this did not cause a buzz at a different frequency, then tighten the screws fully, and test again. Lather, rinse, repeat ;^).

Art
 
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Eventually ferrofluid get thicker, stickier, and will affect free movement of the voice coil. This will show up as an impedance variation (compared to a reference unit) and will have audible/measurable magnitude differences.

I'm not a fan of "aftermarket" HF parts. The closest we ever found were made by Radian and while not exactly to JBL spec, were pretty consistent in our inventory of 2445 drivers. The rest that we tried were shit, frankly. See Riley's post.

Art's advice on ferro, diaphragm alignment, and freq sweeping is spot on.
 
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