Diagnosing lack of tweeter output (Rti8)

mmcculloch

Greetings,

I have a pair of RTi8's (purchased new 7 years ago) serving as the front speakers for a fairly old Onkyo AVR (TX-DS494). I've had this configuration for 18 months or more, but a couple months ago swapped the RTi8's out for other speakers temporarily. Now I've switched back to the Rti8's, and much to my consternation, found no tweeter output from either of them.

My other speakers still sound great on the same channels, so I know the amp is okay. I suspect that the Rti8's probably went south before I disconnected them but I failed to notice, at the time, perhaps because I had a 5.1 setup at the time and used 4-speaker stereo mode for music, so I was getting enough high end from the center speaker while watching TV/DVDs, and from the rear speakers while listening to music. However, in two channel mode it has become painfully obvious that I have zero high end from the Polks.

As well as ruling out the amp, I have pulled both tweeters and measured their impedance, which is about 3.8 ohms apiece. I believe that indicates the tweeters should be fine, but please correct me if I'm wrong there.

My questions is what can I do next to troubleshoot this?

By the way, in terms of possible causes, I wonder if my Polks have been damaged by a horrendous screeching sound that my DTV receiver occasionally emits when trying to decode a less than ideal signal (I watch good old over-the-air TV). It is loud, high pitched, usually lasts about a second, and used to happen a few times a week at least. Can that sort of thing damage speakers? (It damages my nerves.)

Also possibly worthy of note is that these speakers were shipped by sea all the way from Oregon to Australia two years ago.

Cheers,
Murray

[Deleted User]

Hello Murray,
Just to be sure, are the binding post jumper plates making good contact on the rear of the speaker's cabinets?
Regards, Ken

tonyb

In addition to what Ken said ^^^^, your receiver is a tad on the light side for power running all channel stereo for 4 speakers yet, especially if you tend to crank on that volume dial. You may have clipped those tweets long ago as you said, but didn't notice. Polks customer service can help you out in that department but first I would take a look at the crossovers and see if you notice any burn marks on the boards.

mmcculloch

Kenneth Swauger wrote: »

Hello Murray,
Just to be sure, are the binding post jumper plates making good contact on the rear of the speaker's cabinets?
Regards, Ken

Ken, you sir are a dead-set certified legend. Previously I was binding with bare wire, but upon reconnecting the speakers I switched to banana plugs. I never screwed down the posts again. And I never knew this was important! Problem solved!!

And now I'm curious why the wiring of the speaker would be done in such a way that not **** down the posts would be a problem when using banana plugs. I assumed all four posts had a hard connection to the internals. Maybe only the top post do (I'm using the bottom posts).

tonyb, thanks for the suggestions and the note about the power of the receiver. I intend to upgrade the receiver this year so I will be sure to bump up the power then.

Thanks again guys. Huge relief!

Murray

[Deleted User]

Hello Murray,
I'm glad you were able to fix the problem. The idea behind the two posts to to give owners a way to isolate the tweeter and its portion of the crossover from the mid-range and bass sections and their crossover sections. Sometimes people use a thicker, lower resistance wire for the lower connection and a thinner, less inductive speaker wire for the upper connection. Or, they place a small value resistor between the upper and lower binding posts if they wish to reduce the tweeter's output (in a highly reflective or "bright" listening room). Sometimes owners will try one type of power amp for the lower frequencies and another type for the upper (one of which needs to have a volume adjustment capability).
Or, if this kind of experimentation isn't appealing just keep the connections intact with the binding post jumper plates, or substitute a short section of your favorite speaker wire.
Enjoy, Ken

mmcculloch

Thanks Ken, I didn't know any of that. I always had a feeling there must be a better reason for the additional binding posts than what I could guess.

Cheers!
Murray