Repairing JBL Balboa Tweeters

[Nordo22]

The tweeters are blown in the Balboa 30s as well as the 2 surrounds (were bought 2nd hand ).

I've watched a few videos on diaphragm/coil replacements and looks very easy.
BTW, none of the videos were specifically for Balboa tweeters.
On ebay diaphragm/coils are available for the Balboa tweeters (or so the ads say).
I've removed a tweeter (see photos), but can't see an easy way to proceed further.

Anyone have any ideas what to do next?
Or maybe know a forum that is more related to speaker repairs?

 

[Penelinfi]

At this point, just search for a compatible compact neo tweeter. At least by measuring Ohms.

You can remove the diaphragm with a little warmth from a heater, remove that foam gasket, then use a not too sharp, not ultra blunt knife to separate the edge of diaphragm from magnet.

Just checking you have confirmed the tweeters are blown by multimeter or test audio directly to tweeter at low volume?

btw, Balboa is a JBL speaker and not Yamaha?

 

[Nordo22]

OOps, JBL.

The resistance of the tweeter with my very old multimeter, is around 3.5ohm. So they may not be blown.
Haven't had a chance to test with a battery or a sweep yet.
The plastic edge of the diaphragm looks like it has been moulded onto the metal casing, so I'm not too sure if I want to proceed.
Would prefer to find a replacement, even it's not a genuine JBL tweeter.

 

[RickS]

Welcome to ASR!

Looks as though the tweeter may be fine. Hard to tell fully without a DATs or a LCR meter. The other suspect would be the crossover, a DATs would help there too. Here one costs about $100. I see the tweeter part one ebay is inexpensive. Could just risk buying a set and seeing if it fixes.

 

[Nordo22]

Thanks Rick.
Often thought about buying a Dayton DATS, but always managed to get away without one (REW is an amazing program, including extracting a full impedance curve from a driver). I have a very early version of DATS, but it's very basic and I haven't used it for over 20 years.

With the JBL Balboas, I'm really just helping my daughter and partner. He's been bitten by the audio bug, and bought a set of 2nd hand Balboas, as well as a Yamaha RX-A660.
After we tested the Balboas and found the severe drop-off above 6kHz in everything except the Centre, he scoured the internet and came up with another set of Balboas.
This time above 6kHz looked good.
The attached graph below shows the old front left main (green), and the newer front left main (blue).
The newer main was maybe 6" further out from the wall behind, but basically in the same position, as was the mic.
The only other difference I can remember between the two tests is that in the first test (green) there was a coffee table between the speaker and the mic.
The broad dip from 2k to 10k is in most of the tests, and I assume has something to do with the untreated room.

As a result of all that, he's given me the older Balboa set (only one of the small 2 way rears), to see if I could fix what was happening above 6kHz.
Whether I fix them or not, I think he will put them back on the market.
Tested the tweeter with a 1.5v battery, and it definitely reacts to the battery.
Regarding the crossovers, I don't have a LCR meter, but visually everything looks OK (no broken wires or obvious cooked components).
I did tighten one of the sliding connectors to the tweeter.
Can't run REW again as I don't have a suitable amp at home for the test.

Not sure what else I can do.

 

[RickS]

As long as the mic was on-axis and no further than a meter away, agree the rolloff of the original looks bad. Does not entirely rule out a failed crossover but without a schematic, am only guessing. If it is worth your time, would order the tweeters and remeasure. Otherwise, could seek out a repair shop or just scrap for parts.

Hope this helps!

 

[Nordo22]

In all cases speakers were in their traditional positions (for 5.1 setup), and mic was at MLP (roughly forming an equilateral triangle with the mains).
i.e. the mains were approx 9' apart and the MLP was approx 9' from the mains.

When I get the chance I'll take some close measurements (maybe outside) to reduce room influence.

 

[Looneybomber]

When I get the chance I'll take some close measurements (maybe outside) to reduce room influence.

At those high frequencies, rooms don’t cause dips that wide and that deep. Rooms cause the choppiness you see in the measurements.

If I were guessing, I’d say whatever speaker is the blue line has an electrolytic cap inline with the tweeter and it’s bad. The capacitance has dropped, which raises the highpass frequency, but I would also assume it would have an increased ESR, which should reduce the tweeter output overall. Guess not? It may also have ferrofluid that’s getting hard and restricting excursion which impacts lower frequencies more than higher ones. I haven’t done a before and after measurement on a rebuilt tweeter with that problem, but I hear it demonstrates similar behavior as shown above.

The green line has a bad tweeter (or bad connection to the tweeter) and possibly bad capacitor too. You can check by swapping the tweeter from the blue speaker into the green speaker since it clearly works fine at 10khz.

 

[RickS]

Swapping tweeters is sound troubleshooting advice. However, a change in the capacitance of an inline cap is not going to affect the high end rolloff as measured. If it comes down to it, a pic of the crossover board may help if no schematic is to be found.

 

[Penelinfi]

Sometimes, people manage to blow up caps with volume, or resistors too.

You could test the tweeter capacitor by using crocodile clips across it (use a 4 Ohm resistor as well if you're worried about short circuit) and play music/measure

 

[Looneybomber]

Swapping tweeters is sound troubleshooting advice. However, a change in the capacitance of an inline cap is not going to affect the high end rolloff as measured. If it comes down to it, a pic of the crossover board may help if no schematic is to be found.

You’re right but you may have misread my post. I was talking about the blue line which has an issue with the low end rolloff of the tweeter, not the high end.

 

[Penelinfi]

As luck would have it, I just picked up some Balboa 30s.
Seems reasonably good, does sound like it's got a lot of "air" around/above 10kHz ; either a little peak somewhere or it's due to the small diameter extra dispersion.

The front baffle is also detaching in some places, so it leaks and starts to rattle as volume goes up. I'll have to investigate that...

 

[Nordo22]

Swapping tweeters is sound troubleshooting advice. However, a change in the capacitance of an inline cap is not going to affect the high end rolloff as measured. If it comes down to it, a pic of the crossover board may help if no schematic is to be found.

Sorry I haven't responded to any recent posts, but I haven't been getting notifications of posts.

Fiddling with the crossover is not really practical.
I have only examined the crossover in the two way rear speaker (the graph above is of two different Balboa 30s), but the crossover components appear to be encapsulated in a resin type substance.

I found a copy of the 3 way crossover for the Balboa 30s.

 

[RickS]

Resin coatings can make things more messy but not insurmountable. Based on the schematic, the tweeter filter is only one cap. As @Penelinfi mention could be jumpered or bypassed as a simple test. If coating is over board contacts, just connect a wire from the positive input terminal to the tweeter positive terminal.

To prevent tweeter damage ensure you limit your frequency sweep to start at 1000 Hz or so. You should also measure close (10 mm) to the driver for best results. When the mic is close, you will need to lower the drive signal level and/or the mic input level. If the drive signal is already set to some reasonable level, would start by lowering the mic signal level.

Hope this helps!

 

[Nordo22]

Resin coatings can make things more messy but not insurmountable. Based on the schematic, the tweeter filter is only one cap. As @Penelinfi mention could be jumpered or bypassed as a simple test. If coating is over board contacts, just connect a wire from the positive input terminal to the tweeter positive terminal.

To prevent tweeter damage ensure you limit your frequency sweep to start at 1000 Hz or so. You should also measure close (10 mm) to the driver for best results. When the mic is close, you will need to lower the drive signal level and/or the mic input level. If the drive signal is already set to some reasonable level, would start by lowering the mic signal level.

Hope this helps!

Thanks Rick, that makes a lot of sense.
I'll try that next time I'm at their place.
I have been meaning to do some close testing (1m) to reduce room effects (to check on the broad dip between 2K and 10K).
But when testing the tweeters, I'll move closer and reduce the gain and sweep range as you are suggesting, and do an A/B test (with and without the jumper).