Hi All, I have got my hands on a pair of KEF Q55 speakers. This is a 3 way system. Both tweeters are blown. I have done a fair amount of research on line and from what I can see, these tweeters are delicate and go quite often. They are concentric mounted in the center of the midrange speaker. The only one I can find is a replacement part from KEF for about $100/pr.
I am wondering if it would be better to replace these with a cabinet mounted tweeter that would be more robust. The tweeters are 4 ohm Any thoughts?
These are the specs for the KEFQ55:
System type: 2½-way, floor standing Enclosure type: Reflex Dimensions (H x W x D): 852 x 207 x 276mm (33.6 x 8.2 x 10.9 inches) Weight: 13kg (29 lbs) Nominal impedance: 8 ohms Power Handling: 150W Frequency response: 40Hz to 20kHz +/-3.0dB (-6dB at 37Hz) Sensitivity: 91dB at 1m for 2.83V Maximum output: 112dB Finish: Black Ash, Mahogany, Video Grey System: SP3317 Drive units: B160 Bass unit (SP1395), B160 Uni-Q (SP1449) [NT19 tweeter (SP1446)] Crossover network: SP2338
You're likely better off replacing the stock part (and leaving the volume down a bit) than trying to find an electrical match in an alternate driver. You likely already know you can't just look at the impedance of the driver, it's much more complicated than that.
I'd also ask what you are driving the speakers with (ie what amp) ? An amp driven beyond it's limits will be a common cause of driver failure. A driver shouldn't be so delicate as to blow under reasonable use.
I got these with the blown drivers. I don't know what amp blew them. I will be driving these with a Denon AVR 1604 or a Yahama RX-V361. Both around 100w. I'm sure I wouldn't be pushing these amps to the max. I'm really not that knowledgeable about all this. When I looked on line and saw all the posts from others with the same problem, I assumed these drivers were a weak link in this system. I was hoping that I could replace the drivers with something more readily available, but like you say, "It's more complicated than that"
Distortion in high frequencies generates a lot of power. It is either the amp can't drive the speaker or the speaker is simply demanding more of the amp than it can deliver.
The '100 watt HT receiver' is certainly nothing like 100 watts in actual use. When drive hard....near redline, I'd suspect more like 60 or so per channel for 5.1 or 7.1 installations. Certainly no more.
See if you can borrow an amplifier. connect it to preamp outputs from either receiver....if available....and give a listen. Try to be a little more sensitive to the obvious distortion at high levels.
We seem to be missing the point that you were not responsible for blowing out these tweeters. Yes, the general rule is, when you hear distortion, turn down the volume. Got that? Let's move on.
As far as replacing the tweeters in your KEF's, they are your speakers and you can do whatever you want with them. However, the intent of the KEF coincident driver technology is to create a "point source" from which all frequencies in music will originate. This design offers many audiophile advantages with increased coherence and stable soundstaging. Timbre and tone of the individual instruments are improved in this design. Since all instruments have what are known as "overtones" or harmonics, the sinic character of the drivers must meld into a whole unless you are simply not concerned about good sound. Are you interested in these advantages? If so, then you should rebuild the drivers with components from KEF which will restore their original design. Replace the tweeter with a driver not identical to the KEF and all of those values are no longer there. The speaker might make sound but that sound will be compromised anywhere from "noticeably" to even the most casual listener to, possibly, a complete waste of money.
If you don't really care about the intricacies of the KEF design and you just want sound, then you can add aftermarket tweeters to the system and go. Unfortunately, just adding tweeters to the system isn't an especially simple repair. There are a few technical issues you'd need to resolve if you wanted even mediocre performance. You'd need a tweeter with the same electrical "sensitivity" to ensure a proper frequency balance from the system. Impedance and polarity of the original driver would need to be matched. You should know the crossover filter frequency and filter order before you order any replacement driver.
Then you'll need to find a driver that actually fits inside the speaker cabinet. Where were you going to place this new tweeter? The Q55 cabinet doesn't have room for another driver. Even if you don't care much about audiophile values, you need to pay attention to the overall rules of good speaker design if you don't want to waste your money. Cutting into an existing cabinet to make an appropriately sized hole and then providing the rabetted edge around that hole isn't a job for someone with just a jigsaw. Booger up the mounting and again you've wasted a fair amount of money and time plus you've made the Q55's a pile of trash with no value to anyone.
You can do anything you want, these are your speakers. To do something that won't waste your money, the best choice is to rebuild the drivers as they came from the factory.
Why don't you contact PartsExpress and get a second opinion?
I have replaced both of my Q55 speakers and one on a pair of Q80's.-Blown by previous owner. My Q55's made it 8 years before failure. I think it is in design and characteristic of a tweeter. I have run a Yamaha Rx-V663 and a RX-N600 receiver tp power them. I have sold many audio brands in A/V retailers for many years and think Kef had the best sound for your dollar in the 90's.