Testing...testing...
Thanks to everyone for helping me out with the Kefs.
I have purchased a power amp...an Adcom 555 (II). I also purchased a power conditioner, and replaced all RCA cables with 3-foot Acoustic Research audio cables with gold-plated connectors. In short...I threw some money at the problem.
So my current setup is.....
Pioneer CD Player --> Carver Receiver (HR-755) --> Adcom Power Amp (555-II) --> Kefs (Q55.2). I am using the receiver in CD direct mode (no eq), and its preamp outputs to connect to the Adcom amp.
In one word...WOW! I am not an audiofile, but this setup sounds amazing to me. The bass and drums are crystal clear, and the vocals/guitar are nice and bright...just the way I like them. One thing I observed...the volume control on the Carver now has a very "linear" feeling to it. I have gone beyond comfortable listening levels with the same material that previously destroyed the Kef drivers, and the Kefs just hang right in there. I listened to the entire Lateralus cd (Tool) on Saturday night, and just walked away completely blown away by these speakers.
I'll grant you that I may have masked the problem by not solving it analytically, but my spare time is almost nil with 4 kids and a job with a start-up company.
Thanks again for the helpful suggestions, and for not blasting me for the off-topic (DIY) subject matter.
Have a great summmer!
P.S. - please be kind when I come back with my tail between my legs and a broken Kef driver.
Thanks to everyone for helping me out with the Kefs.
I have purchased a power amp...an Adcom 555 (II). I also purchased a power conditioner, and replaced all RCA cables with 3-foot Acoustic Research audio cables with gold-plated connectors. In short...I threw some money at the problem.
So my current setup is.....
Pioneer CD Player --> Carver Receiver (HR-755) --> Adcom Power Amp (555-II) --> Kefs (Q55.2). I am using the receiver in CD direct mode (no eq), and its preamp outputs to connect to the Adcom amp.
In one word...WOW! I am not an audiofile, but this setup sounds amazing to me. The bass and drums are crystal clear, and the vocals/guitar are nice and bright...just the way I like them. One thing I observed...the volume control on the Carver now has a very "linear" feeling to it. I have gone beyond comfortable listening levels with the same material that previously destroyed the Kef drivers, and the Kefs just hang right in there. I listened to the entire Lateralus cd (Tool) on Saturday night, and just walked away completely blown away by these speakers.
I'll grant you that I may have masked the problem by not solving it analytically, but my spare time is almost nil with 4 kids and a job with a start-up company.
Thanks again for the helpful suggestions, and for not blasting me for the off-topic (DIY) subject matter.
Have a great summmer!
P.S. - please be kind when I come back with my tail between my legs and a broken Kef driver.
Fixed
Yup, some amps just burn tweeters.
Glad that you have found a much better soloution.
PS - It is sounding like you had an rf instability problem.
Eric.
Yup, some amps just burn tweeters.
Glad that you have found a much better soloution.
PS - It is sounding like you had an rf instability problem.
Eric.
I'm compelled to ask several questions no one else has.
How big is your room? Carpeted or non-carpeted? Curtains?
How far away from the speakers is your listening position?
Do you know for a fact what the db output is at 1 meter at your prefered listening, volume level?
If I were you I'd purchase an SPL meter from Radio Shack and get a rough idea of what you're asking your Kef's to do at 1 meter.
The fact that they sound better and don't appear to be having any problems (yet) with the new Adcom amp points back to the simple possibility of clipping distortion(whether your ears can hear it or not) from the previous lesser powered amps. Tweeters will be the first thing to go if you want an SPL level that forces an amp to clip. If you've got a big room or even a small or medium sized dead room the bottom line is you need head room.
Sorry, thats a bad limerick. But your problem could be as simple as that.
How big is your room? Carpeted or non-carpeted? Curtains?
How far away from the speakers is your listening position?
Do you know for a fact what the db output is at 1 meter at your prefered listening, volume level?
If I were you I'd purchase an SPL meter from Radio Shack and get a rough idea of what you're asking your Kef's to do at 1 meter.
The fact that they sound better and don't appear to be having any problems (yet) with the new Adcom amp points back to the simple possibility of clipping distortion(whether your ears can hear it or not) from the previous lesser powered amps. Tweeters will be the first thing to go if you want an SPL level that forces an amp to clip. If you've got a big room or even a small or medium sized dead room the bottom line is you need head room.
Sorry, thats a bad limerick. But your problem could be as simple as that.
To Timo
Thanks for the comments Timo. The room is a family room, 16' square. The Kefs are located approx. 4 feet from the corners of the room on either side of an 8-ft sliding door. They sit on a hardwood floor and are directed towards a chair on an area rug that is 8-10 feet away. There are curtains on the sliding door as well as windows.
I guess my preferred volume level is higher than most people, but when I blew the Kefs, the listening level did not seem as high as what I would normally listen to on my Advents. I was really trying to be faithful to the recommended break-in, especially after the first time I blew a driver. It was not as if I were trying to find the Kefs breaking point (I really doubt that I was approaching the 114db max limit). I think anyone would have been surprised at the volume level when these speakers blew. But I suppose this is just subjective rambling.
It would be interesting to know what the listening levels are...perhaps I will purchase an SPL meter if they are not too expensive. My friend Dave says I'm just playing it too damn loud...and turn that **** down. Sorry...that's just me...I'll probably need a hearing aid in a few years.
In the end, this new and improved stereo sounds incredible to me, and well-suited to my taste. I'm really glad I stuck with the Kefs and hope to own and maintain them for a long time.
Thanks for the comments Timo. The room is a family room, 16' square. The Kefs are located approx. 4 feet from the corners of the room on either side of an 8-ft sliding door. They sit on a hardwood floor and are directed towards a chair on an area rug that is 8-10 feet away. There are curtains on the sliding door as well as windows.
I guess my preferred volume level is higher than most people, but when I blew the Kefs, the listening level did not seem as high as what I would normally listen to on my Advents. I was really trying to be faithful to the recommended break-in, especially after the first time I blew a driver. It was not as if I were trying to find the Kefs breaking point (I really doubt that I was approaching the 114db max limit). I think anyone would have been surprised at the volume level when these speakers blew. But I suppose this is just subjective rambling.
It would be interesting to know what the listening levels are...perhaps I will purchase an SPL meter if they are not too expensive. My friend Dave says I'm just playing it too damn loud...and turn that **** down. Sorry...that's just me...I'll probably need a hearing aid in a few years.
In the end, this new and improved stereo sounds incredible to me, and well-suited to my taste. I'm really glad I stuck with the Kefs and hope to own and maintain them for a long time.
KEF Q55 Problems...cont'd
Ok - I'm back. The bad news is that I lost my job in August. The good news is that I now have time to look at this problem.
Since we last spoke, I have blown the tweeters in my KEF Q55.2's five times, the most recent occasion was over the past weekend. My dealer has been replacing them at no cost to me.
Let me add to this thread that I like my music REAL LOUD, and my dealer claims this is the problem (that I'm over-driving the speakers).
To refresh, these Q55.2's are complimented by a Yamaha subwofer which I use as a cross-over for the KEFs (I was blowing the tweeters before I gt the sub). I am driving the KEFs with an Adcom 555-II (200w/ch), and a Carver preamp and Pioneer CD.
Where do I start to try to trouble shoot this? I'm inclined to blieve the dealer....that I am over-driving these things...but would welcome sme feedback.
Thanks for you time,
Tom
Ok - I'm back. The bad news is that I lost my job in August. The good news is that I now have time to look at this problem.
Since we last spoke, I have blown the tweeters in my KEF Q55.2's five times, the most recent occasion was over the past weekend. My dealer has been replacing them at no cost to me.
Let me add to this thread that I like my music REAL LOUD, and my dealer claims this is the problem (that I'm over-driving the speakers).
To refresh, these Q55.2's are complimented by a Yamaha subwofer which I use as a cross-over for the KEFs (I was blowing the tweeters before I gt the sub). I am driving the KEFs with an Adcom 555-II (200w/ch), and a Carver preamp and Pioneer CD.
Where do I start to try to trouble shoot this? I'm inclined to blieve the dealer....that I am over-driving these things...but would welcome sme feedback.
Thanks for you time,
Tom
What is the sesitivity of this speakers. If they are in the low range, you might be trying to achieve levels that you are use to with other more sensitive speakers. If that is the case you are pumping more power, but getting less output. That eventualy leads to clipping and to blown speakers. Just as an example: 15W amp driving 100dB speaker is equal of 200W amp driving 87dB speaker.
Sorry to hear that you are going through so much trouble.
Sorry to hear that you are going through so much trouble.
I would be inclined to think that your dealer is right about this. High frequency speakers are usually the first to let go, especially if you are overdriving your amp (which might be more possible than you think, with a dynamic source, loud levels, and speakers with a normal efficiency.) Maybe it's time to bi-amp? This would at least keep your mid/treble amp from clipping and save some tweeters. I see that you're using a sub.. that's good. At the levels you are listening at, you could be chucking woofers very easily. I have sent a couple woofers out of service doing this (that's what good clean power is capable of, haha)
Try bi-amping...would really help...and dun on them too loud...guess Puddle of Mudd proves you listen to rock...so I dunno...guess it would really pain us to see your hearing gone after we helped you fix the problem...have you checked to see if the CD-palyer has got some crap coming out of it?? Using a scope...
A normal sound wave is a nice rounded wave, like you would see at the beach. However, when you drive your amp too hard, the amp cuts off the top peak and the bottom peak of this nice rounded wave, causing it to resemble a square wave.
Most music waves, except for a pure tone, have harmonics in them. However, these harmonics are very muted.
When you turn the volume up, the smooth music wave gets driven to where the top gets flattened. See crude, badly drawn illustration below. Wave A is what the music wave looks like, (sort of, LOL), when the amp is not overdriven. Wave B is wave A when the amp is overdriven. This B wave no longer resembles the music on the source-it now begins to resemble a square wave.
As a non-engineer, I was shocked to know that a combination of simple sine waves can manufacture a square wave. It does not seem logical, but a square wave is composed of many sine waves. So a square wave, or a flattend music wave, is suddenly going to have a lot of high volume harmonic content that was not on the music signal. Normal smooth music waves do not have a lot of loud high frequency content.
Since this harmonic content is higher in frequency than the fundamental, it mostly gets sent to the tweeter. Tweeters are delicate mechanisms, compared to sturdy woofers. The reason tweeters get away with being so delicate is that most natural music content has few high harmonics that are very loud. However, with the high volume high frequency content generated by the square wave, (the music wave with the flattened top and bottom), the tweeters get overloaded and blow out.
Believe it or not, the cure is to get a more powerful amp, so that the top and bottom of the wave does not get flattened in the first place. It's not the power that blows the tweeters usually, it's the music waveform being deformed into a square wave that blows the tweeters. A more powerful amplifier can see to it that the music waveform does not deform due to the amp being overdriven.
Of course, all this is assuming that there is nothing wrong with the signal coming out of the CD player in the first place.
Most music waves, except for a pure tone, have harmonics in them. However, these harmonics are very muted.
When you turn the volume up, the smooth music wave gets driven to where the top gets flattened. See crude, badly drawn illustration below. Wave A is what the music wave looks like, (sort of, LOL), when the amp is not overdriven. Wave B is wave A when the amp is overdriven. This B wave no longer resembles the music on the source-it now begins to resemble a square wave.
As a non-engineer, I was shocked to know that a combination of simple sine waves can manufacture a square wave. It does not seem logical, but a square wave is composed of many sine waves. So a square wave, or a flattend music wave, is suddenly going to have a lot of high volume harmonic content that was not on the music signal. Normal smooth music waves do not have a lot of loud high frequency content.
Since this harmonic content is higher in frequency than the fundamental, it mostly gets sent to the tweeter. Tweeters are delicate mechanisms, compared to sturdy woofers. The reason tweeters get away with being so delicate is that most natural music content has few high harmonics that are very loud. However, with the high volume high frequency content generated by the square wave, (the music wave with the flattened top and bottom), the tweeters get overloaded and blow out.
Believe it or not, the cure is to get a more powerful amp, so that the top and bottom of the wave does not get flattened in the first place. It's not the power that blows the tweeters usually, it's the music waveform being deformed into a square wave that blows the tweeters. A more powerful amplifier can see to it that the music waveform does not deform due to the amp being overdriven.
Of course, all this is assuming that there is nothing wrong with the signal coming out of the CD player in the first place.
Attachments
I agree clipping is most likely
Hi,
I used to blow tweeters all the time and mids sometimes too (at parties). I allways thought it was because the power handling of the speakers was too low, but people here told me that it was probably my amp clipping. Recently I was trying to debug my amp and did some measurements. Too my surprise I was able to clip the amp (100W RMS/Channel) with the volume control at about 3/4 with only a 0.2V 1Khz sine wave as input (and a cd player will deliver in general up to about 2V!)
Results of this testing here (with the unclipped and clipped waveforms). --> http://www.diyaudio.com/forums/showthread.php?postid=248708#post248708
Note that based on the measurements that I did, my amp was delivering 190W/channel when clipping, compared to the nominal 100W/channel rating.
GM gave a good explanation of clipping the amp with CD as source here --> http://www.diyaudio.com/forums/showthread.php?postid=224298#post224298
Regards,
Tony.
Hi,
I used to blow tweeters all the time and mids sometimes too (at parties). I allways thought it was because the power handling of the speakers was too low, but people here told me that it was probably my amp clipping. Recently I was trying to debug my amp and did some measurements. Too my surprise I was able to clip the amp (100W RMS/Channel) with the volume control at about 3/4 with only a 0.2V 1Khz sine wave as input (and a cd player will deliver in general up to about 2V!)
Results of this testing here (with the unclipped and clipped waveforms). --> http://www.diyaudio.com/forums/showthread.php?postid=248708#post248708
Note that based on the measurements that I did, my amp was delivering 190W/channel when clipping, compared to the nominal 100W/channel rating.
GM gave a good explanation of clipping the amp with CD as source here --> http://www.diyaudio.com/forums/showthread.php?postid=224298#post224298
Regards,
Tony.
Clipping can also be an indication of the "lousy" amp?? or overratted amps...?? So a 5% margin for between amps and speakers will do the tweeters good then??
I think the key is the dynamic range of the music source, ie the difference between the softest and loudest bits. If most of the track is recorded at fairly low levels but there are a few very high level bits in there as well, then you will generally be driving the amp quite hard to get loud levels from the music which has a low level, and when the high level bit comes along the amp clips.
It's not because the amp is necessarily bad, it's just reached its physical maximum. The amp may be able to deliver full power from a low level input signal say 0.5V, if it is doing that and then you suddenly increase the input level to 1.0V or 1.5V, the amp is allready at the wall delivering full power, and now you have asked it to give more, it can't so it clips, the only way to stop the clipping is to have a more powerfull amp.
I don't think the power rating of the tweeters comes into it. Even if you have a 100W amp and a tweeter rated at 105W (system power) and suitably crossed over, you can still blow the tweeters. As GM said (paraphrased) in the thread I linked to before probably the safest thing would be to have a 1000W amp! (even if your tweeters are only rated at 100W system)........
Regards,
Tony.
It's not because the amp is necessarily bad, it's just reached its physical maximum. The amp may be able to deliver full power from a low level input signal say 0.5V, if it is doing that and then you suddenly increase the input level to 1.0V or 1.5V, the amp is allready at the wall delivering full power, and now you have asked it to give more, it can't so it clips, the only way to stop the clipping is to have a more powerfull amp.
I don't think the power rating of the tweeters comes into it. Even if you have a 100W amp and a tweeter rated at 105W (system power) and suitably crossed over, you can still blow the tweeters. As GM said (paraphrased) in the thread I linked to before probably the safest thing would be to have a 1000W amp! (even if your tweeters are only rated at 100W system)........
Regards,
Tony.
Trade em
Trade em in for Klipsch or JBLs. You need very sensitive tough speakers. You are a rocker. Ask for something with a compression HF driver in it.
Trade em in for Klipsch or JBLs. You need very sensitive tough speakers. You are a rocker. Ask for something with a compression HF driver in it.
I used to own the original GFA-555's about 15-20 years ago, and in a 16x16 room with average efficiency speakers, I doubt you would get significant clipping until you hit insanely loud levels, as in insanely serious ear-damaging levels.
So, given that the dealer couldn't blow them in his setup, and the pretty tough nature of the 555, I vote for the cdp sending garbage down the line.
...either that, or you're are insane - and this is going to to be a short-lived hobby. 😉
So, given that the dealer couldn't blow them in his setup, and the pretty tough nature of the 555, I vote for the cdp sending garbage down the line.
...either that, or you're are insane - and this is going to to be a short-lived hobby. 😉
Monster cables are highly inductive (relatively) and can setup HF ringing conditions.
Try lower inductance cables for cleaner and less tweeter cooking and ear bleeding highs.
Eric.
Try lower inductance cables for cleaner and less tweeter cooking and ear bleeding highs.
Eric.
hmmm....try other cables...replace the CD Player and then at last the amp..if it doesn't work out...get a new pair of speakers...sounds very expensive to me...
reply
These following tips have worked for me:
1. Fit a miniture lightbulb in series with the tweeter closet to the
+ terminal as possible,if the amp clips,the bulb will light up,and if it clips severely then the bulb blows,saving the tweeter from burnout.
2. Don't use a receiver instead use an intergrated or even better pre and power amp or better than that monoblock poweramps and a pre-amp.
Most receivers can't deliver more than 50w rms[clean,unclipped power].There's a very small amount of receivers which are decent quality [like the Parasound receiver which is 5x 100w rms.]
Sony is normally good quality but can't compaire to the Parasound which is superb pro hifi quality.[Sound quality and parts quality]
3. Fit a polyswitch or special circuit breaker or relay to protect woofers since these don't act as fast as minture lightbulbs.
4. Use a 18db filter to protect the tweeters ,or a 12db minimum.
6db octave[first order network] still lets some of the bass into a tweeter.
5. Amp clipping,DC fault on amp,not using a high enough crossover point are all things which can blow tweeters.
6. Also to consider that paper cone and dome tweeters are easier to blow than titanium bullet ring radiator or compression tweeters[but you'd still blow them with heavy clipping or no crossover.] The only one which can take hard clipping and uses no crossover is the piezo tweeter.But the piezo tweeter is very harsh and 'hissy' sounding the type of tweeter which makes your ears bleed at high volume levels.
Although the piezo is cheap and doesn't need a crossover it isn't used for much except cheap disco/pa speaker cabinets and used in guitar combos[amp plus speakers in cabinet with tone controls].
As piezos only reproduce super high frequencies well good for the crash of cymbols or a snare drum,but apart from that they are junk,because any frequency below 7khz they reproduce is a very harsh unnatural sound[NOT what u want for hifi or studio monitors]!
These following tips have worked for me:
1. Fit a miniture lightbulb in series with the tweeter closet to the
+ terminal as possible,if the amp clips,the bulb will light up,and if it clips severely then the bulb blows,saving the tweeter from burnout.
2. Don't use a receiver instead use an intergrated or even better pre and power amp or better than that monoblock poweramps and a pre-amp.
Most receivers can't deliver more than 50w rms[clean,unclipped power].There's a very small amount of receivers which are decent quality [like the Parasound receiver which is 5x 100w rms.]
Sony is normally good quality but can't compaire to the Parasound which is superb pro hifi quality.[Sound quality and parts quality]
3. Fit a polyswitch or special circuit breaker or relay to protect woofers since these don't act as fast as minture lightbulbs.
4. Use a 18db filter to protect the tweeters ,or a 12db minimum.
6db octave[first order network] still lets some of the bass into a tweeter.
5. Amp clipping,DC fault on amp,not using a high enough crossover point are all things which can blow tweeters.
6. Also to consider that paper cone and dome tweeters are easier to blow than titanium bullet ring radiator or compression tweeters[but you'd still blow them with heavy clipping or no crossover.] The only one which can take hard clipping and uses no crossover is the piezo tweeter.But the piezo tweeter is very harsh and 'hissy' sounding the type of tweeter which makes your ears bleed at high volume levels.
Although the piezo is cheap and doesn't need a crossover it isn't used for much except cheap disco/pa speaker cabinets and used in guitar combos[amp plus speakers in cabinet with tone controls].
As piezos only reproduce super high frequencies well good for the crash of cymbols or a snare drum,but apart from that they are junk,because any frequency below 7khz they reproduce is a very harsh unnatural sound[NOT what u want for hifi or studio monitors]!
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