18Ti Problemette...

[meaculpa]

Hi, new to the forum today and my first post. I have a pair of 18Ti's that I bought in Saudi Arabia sometime in '88 or early '89 when I was working over there. For as long as I can remember the output from one speaker has been way different to the other but I always thought this was by design. If I channel all the audio through the right speaker (as I have them set up) the sound doesn't change much at all but I channel everything through the left one it's really hardly audible though you can hear the song...it sounds really tinny and completely devoid of bass or 'loudness' in general. I'm no audiophile so I'm explaining it best as I can.

I now live in Canada and was told by a JBL tech that the 18Ti's were never sold in Canada so I suppose I have two questions...what is likely causing my speaker to sound like it does and can it be fixed here in Canada (availability of parts etc) ?

As an extra bit of info I swapped the wires round to check that the amp was ok..ie I put the wires that were feeding the defective speaker into the good speaker and vice versa and the condition still existed in the same speaker (ie the left one).

Any help greatly appreciated,

Rob

[Robh3606]

Pull the drivers on the bad speaker. Check the connections and the network for obvious loose connections or cooked resistors. Hook up the woofer directly to the amp and see what you get. Do the same for the tweeter at low levels but have a series cap say 3Uf to protect it. See if they sound OK when not connected to the network. Go from there.

Rob:)

[meaculpa]

Hi Rob, thx for the reply...I should have mentioned that I know little of what you say. I have the spec sheet in front of me for these babies and I can see the network that you spoke about. I'm thinking that I should be looking for loose or broken connections first (the obvious signs) and any obviously damaged or broken components on the network card.

I'm not sure how to hook up just the woofer and / or just the tweeter (is it done by bypassing the network completely or is it simply a case of just attachine the relevant wire (ie black or red) to the relevant terminal on the Network ?

Rob

[whizzer]

I think you want to bypass the card in order to find out if the problem resides there. Each of the drivers has terminals, usually posts of some sort, probably marked red and black for positive and negative. Since you describe what presently comes out of this one enclosure as "tinny," it seems likely that little if anything is being produced by the woofer. Luckily, it cannot be damaged by a full-range signal; be careful about the HF driver (tweeter), though, for it may be severely damaged by low-frequency material. So, what you want to do is attach the speaker cable directly to the woofer's own input terminals and play something through it at low level in order to see if it produces sound. If so, and if more clearly than what you've heard previously, then you know that the signal is getting lost somewhere between the input terminals on the rear of the enclosure and the card's outputs. I hope this helps.

[Robh3606]

The connections are easy with the 115H's. They have polorized spade connections so you can't put them back in the wrong positions. To remove the woofer you just take out the 4 mounting screws and it should come right out. The network will most likely be against the back of speaker. To see if the woofer is OK you can also just take it out of the cabinet and leave the network connected. Use aligator clips to attach light gage speaker wires directly to the spade connectors on the woofer. Be careful you don't short the speaker wires while you are doing this. Power it all down, make sure you have good connections and then power it up. Don't try changing connections on the fly with the amp on. If it works fine like this there is something wrong it the network. It could be as simple as a bad solder joint. If you look at the schematic there is only an Inductor right before the woofer. Inductors typically don't go bad. So it's either a loose connection or it could be the woofers voice coil. I will post a picture in a little while.


Rob:)

[meaculpa]

Thx Whizzer...that's what I'll do...hopefully it's the woofer that's the issue (actually I'm hoping for a losse or missing connection as that would be the easiest to fix without having to pay for a specialist).

Rob

[GordonW]

Try taking the woofers in both speakers, and SWAP them left-for-right, in the cabinets (ie, the woofer from the "problem" in the "good" cabinet, and vice-versa). If the problem stays in the problem cab, then it's a crossover issue, most likely. If the problem moves with the woofer, then it's the bad part.

Regards,
Gordon.

[opimax]

I really hope you fix your problem . If you don't and want to sell the speakers I thought i would chime in real quick that I would be intersted.

Being very careful if you push the speaker in and let it come out, say a 1/4", does woofer on the suspected bad have a crunchy feel to it? Please don't do this if you don't understand...I will try another explanation

Mark

[Robh3606]

Being very careful if you push the speaker in and let it come out, say a 1/4", does woofer on the suspected bad have a crunchy feel to it? Please don't do this if you don't understand...I will try another explanation

Don't do that. Every JBL owners manual has a note basically saying that the tolerances in JBL speakers are very tight and you could accidentlly force the cone out of alignment.

Rob:)

[opimax]

sorry, usually the one of things I check when diagnosing bad noises...

Mark

[meaculpa]

OK, update time...I took out the woofer from the bad speaker and isolated it and connected it up and I got nada out of it when I played a cd so there we go. Next question would be how do i source a new 115H ?

Rob

[Robh3606]

Damn that stinks. They show up quite often on Ebay. You could also start a thread in the Market Place Forum here on the site. Someone might have a spare they can part with.

Good Luck

Rob:)

[meaculpa]

I done got me a 115H-1 off Ebay...thx everyone

:applaud: