Problem with distortion on CM1s

[cholas]

I hope this is posted in the right place. If it is I would greatly appreciate some help with the following problem:

I am experiencing severe distortion via my FL and FR B&W CM1s. It only seems to happen during particularly loud explosions viz: The first bomb going off in The Hurt Locker, the canon fire in Peter Pan or buildings collapsing in War of the Worlds. The explosions happen and produce a very, very loud and unpleasant crackling/ripping/rat a tat tat sound which is quite offensive. Output is from a DVD via Toshiba HD-EP30KB player then HDMI to a Denon AVR-4036. The speakers are set to small and crossover to 80Hz although I've also tried 60Hz to no effect. B&W have been absolutely brilliant in trying to help and have confirmed there is nothing wrong with the speakers. They have also suggested various settings which I have followed to no avail. Currently my channel levels are: FL and FR 0.0dB, centre +0.5dB, SR -7.0dB, SL -6.0dB. My REL 505 sub is set to off in the Denon software. LFE is set. The distortion is slightly worse on a DTS track but not by much.

I have swapped the CM1s for two different sets of older speakers and absolutely no problem occurs. I feel completely out of my depth here so any help will be most gratefully received. Naturally if more info is required I'll be happy to provide it.

Thank you.

[stuofsci02]

What are your older speakers that are working? CM1 is quite a small speaker. Is it possible that the speaker is just distorting because it is too small to play the loud parts of the movie?

[BassThatHz]

With no music playing, press the woofer inward gently while listening for any weird sounds... scratching etc; it should be near-slient until woofer is at its maximum.

If so, the speaker is likely damaged.

If not, the next test is to then disconnect the wiring to all subwoofers and other speakers (rear/sides etc).

Try the scene again with only the one left OR right speaker connected at a time with the grills off, and watch the woofer to see how far it moves.

If it persists, move one of the rear speakers to the front and connect it up.
If both speakers have the same problems then it is likely your amp.

Move the front speakers to the rear, and rear speakers to the front.

Replay the scene to double confirm results.
(I'm assuming your rear channels were/are fine during the scene).

If the problem disapears at any point, back-trace to your last step until the problem re-appears or until the the system is assembled back to normal again, repeating the scene each time.

Through a process of elimination, you are bound to find the defective component at some point.

It could be that you are just simply playing it too darn loud, and need beefier stuff...

[AV-OCD]

BassThatHz gives some very well thought out and thorough troubleshooting advice, but before you do any of what he suggests, lets make sure that you aren't overdriving the speakers. Try a higher crossover point, like 120Hz or higher to see if the problem lessens.

[Space]

The way you describe the offensive sound it could be the amplifier clipping. It would clip at a different level for different speakers depending on the impedance. If you try playing just the left or just the right then the sound might go away, by opening up some headroom in the amp. The solution for this problem would be either a bigger amp or a more sensitive speaker, or lower output levels.

I would guess that if your woofers were damaged then there would be audible problems all the time. That or you could be bottoming on these loud passages, in which case the woofers are in peril of being damaged. As suggested you can avoid that by setting a high pass, if you haven't already. In this case the solution would be using a subwoofer and high-passing the mains.

[Opus007]

It sounds as though you are overdriving the speakers.Going lower from 80 hz to 60 hz would worsen the problem.You would need to go higher up the scale as someone has suggested.
Do you have any sound modes enabled on the Denon?Certain recievers have sound modes like cinema mode,theater mode ect...which will enhance the bass and can cause problems at loud levels.
Your main problem though is that the CM1's are monitor speakers.I would recomend you run them at least at 100hz.You have to keep in mind that they are not full range speakers.The louder you drive those speakers with a low hz setting the more likely you are to bottom them out.
Also Welcome to the forum.

[cholas]

Thanks to you all for a series of very helpful replies. I will work through the suggestions and report back to you.

To answer a couple of specific points: the old speakers which aren't affected are some ancient Wharfedale Denton 2s and a pair of Denon SC-M5Ks. Also the CM1s are new and have been checked out for me by B&W and found to have no faults.

Thanks also for the welcome to the forum; I'm glad I joined.

[BassThatHz]

Make sure all bass enhancement and eq features are turned off.

If you are in DD or DTS mode over HDMI, that would greatly reduce or eliminate the probability of it being a problem with an upstream component.
(Unless the recorded movie-audio signal was recorded clipped.)



With the CM1's you could even go so far as to only hook up the tweeters, which already have a high-pass filter in the +2000hz's range built into the speaker.

If you can hear weirdness out of just the tweeters playing, then something is not right, be it the speakers or amp etc. You should never be hearing crackling/ripping from the tweeters; that is a clear indication that something has died, or is on the verge of dying/blowing up.

[Industrial]

This clipping... Is it the whole speaker or just the tweeter? I find my tweeters clip a lot when playing jazz on vinyl. Not as much now that I istalled a better phono preamp. I know for HT use I have my Rotel 1570 up to 70-80 with no clipping during movies but I do use a ok sub woofer for the lows.

[dknightd]

The speakers are set to small and crossover to 80Hz although I've also tried 60Hz to no effect.

snip

My REL 505 sub is set to off in the Denon software. LFE is set. .

I don't know the denon software, but this seems contradictory. You have the speakers set to small, but the sub off (except for LFE)? Where does the low frequency L and R signal go? Are you sure it is not going to the CM1? What happens if you turn the sub ON in the software?

My guess is you are overdriving the speakers - either bottoming them out, or, clipping the amp. Does it make the horrible sound if you play at a lower volume?

[cholas]

Thank you for yet more helpful replies. I'm a complete novice, and somewhat out of my depth, so the help you are giving me is very much appreciated.

dknightd wrote:

My guess is you are overdriving the speakers - either bottoming them out, or, clipping the amp. Does it make the horrible sound if you play at a lower volume?

Yes it looks like the problem is at least partly volume related. At -13.0dB indicated volume on the Denon, the unpleasant crackling/ripping sound is highly noticeable and offensive but at -21.0dB (ie in my terms a lot quieter) while still noticeable is reduced to a growling rumble.

AV-OCD wrote:

BassThatHz gives some very well thought out and thorough troubleshooting advice, but before you do any of what he suggests, lets make sure that you aren't overdriving the speakers. Try a higher crossover point, like 120Hz or higher to see if the problem lessens.

I tested the differences between 80Hz and 120Hz and found that the problem reduced marginally at each step upwards. However, again, the problem was more noticeable at the higher volume setting and much reduced at the lower level.

dknightd wrote:

I don't know the denon software, but this seems contradictory. You have the speakers set to small, but the sub off (except for LFE)? Where does the low frequency L and R signal go? Are you sure it is not going to the CM1? What happens if you turn the sub ON in the software?

I must say this question of the sub has had me confused. I was advised by the people at B&W to turn it off in the Channel Level settings of the Denon and instead use the subs own volume dial, which is why I have it set that way. However, following your advice I tried turning the sub on and set it to -10.0dB in the Denon's set up. The result being that the offensive noise was still there at the same levels albeit with a slightly more 'rounded' 'bassy' tone.

A number of you have said I am over driving the CM1s and based on my volume tests I suppose that is a reasonable conclusion.

Opus007 wrote:

Your main problem though is that the CM1's are monitor speakers.I would recomend you run them at least at 100hz.You have to keep in mind that they are not full range speakers.The louder you drive those speakers with a low hz setting the more likely you are to bottom them out.

Given that even at 120Hz and a reasonable volume the noise is still there to a degree I guess I am faced with buying some new front speakers. Would anyone care to advise what these should be? My centre is the B&W CM Centre which doesn't exhibit the problem so I imagine it will be okay to stick with that or does anyone think differently!

Thanks again for your interest in resolving my problem.

[jamesdaman]

Cm9?? Does sound like you kicking those cm1's square in the balls lol great speaker but it's still only a 5 or so inch bass mid driver. If you want book shelf you could try get some 805s I'm listening to mine now and love um

[theblue]

as others have hinted I think you're just asking too much from these speakers. I would recommend a higher crossover of 100 or so... you might also find that a better and/or dedicated amp will control the speakers better and allow you to run louder without distortion.

When watching a movie like the hurt locker you really want something like a 683, 804, not a CM1 which is better suited to a small room for listening to audiophile recordings.

[cholas]

you might also find that a better and/or dedicated amp will control the speakers better and allow you to run louder without distortion.

I had been led to believe that the Denon AVR-4306 was a good amplifier; it certainly cost a fortune! Is it really not up to the job do you think? I must say in all other respects it seems to do a good job.

[theblue]

it is a good all around home theater setup after looking at the specs, but it's still a weird match.

how/why did you end up with CM1s? it sounds like you've thrown a small room quiet but detailed audiophile speaker into the middle of a home theater setup.

[cholas]

how/why did you end up with CM1s? it sounds like you've thrown a small room quiet but detailed audiophile speaker into the middle of a home theater setup. 

Due to lack of knowledge I guess and therefore relying on the advice of the people I bought it all from who came over as very helpful. Generally I have been very happy with the set up but this problem with the CM1s has knocked me back a bit and I want to try and rectify matters without throwing everything out and starting again!! I believe choice of speakers can be an absolute minefield for the uninitiated so I'm hoping a bit of gentle hand-holding from this forum can see me right. As indicated earlier I currently have the CM Centre plus the CM1s together with the REL 505 sub and a couple of old Goodmans Arena GLLs as surrounds (I know these need changing - perhaps by using the CM1s?). If I can keep the CM Centre it would be nice and my replacements for the CM1s, assuming replacement it is, must be bookshelf, because of my set up I cannot use stands.

[AV-OCD]

how/why did you end up with CM1s? it sounds like you've thrown a small room quiet but detailed audiophile speaker into the middle of a home theater setup. 

Due to lack of knowledge I guess and therefore relying on the advice of the people I bought it all from who came over as very helpful. Generally I have been very happy with the set up but this problem with the CM1s has knocked me back a bit and I want to try and rectify matters without throwing everything out and starting again!! I believe choice of speakers can be an absolute minefield for the uninitiated so I'm hoping a bit of gentle hand-holding from this forum can see me right. As indicated earlier I currently have the CM Centre plus the CM1s together with the REL 505 sub and a couple of old Goodmans Arena GLLs as surrounds (I know these need changing - perhaps by using the CM1s?). If I can keep the CM Centre it would be nice and my replacements for the CM1s, assuming replacement it is, must be bookshelf, because of my set up I cannot use stands.

Well, the next logical choice would be to step-up to the CM5's and move the CM1 to the rear. The CM5's will give you a bit more head room, but you may still have to be more gentle with the volume.

[theblue]

three solutions:

make money -- trade for 685s with cash on the buyers end

somewhere in the middle -- buy or trade to get some used 705 for the front (this is more what you want for 50/50 music and movies)

spend money -- buy CM5s, move CM1s to rear

[Opus007]

I had been led to believe that the Denon AVR-4306 was a good amplifier; it certainly cost a fortune! Is it really not up to the job do you think? I must say in all other respects it seems to do a good job.

Cholas,
Can you borrow another avr from your dealer?I could be totally off base here but it seems with the hz set at 120 and even driving the cm's at high volume that there should not be a problem.I am wondering if the bass management in the Denon is working correctly.
Do you have a Avia test tone disk?If you do you can use the disk to check to see if the Denon is cutting off the low hz at the setting you have it set to and sending it to the sub.
If you find all is working corectly then I have to go with my original assesment that you are over driving the cm's.
The 685's are not that expensive and would problably fit in ok with you cm center.And as suggested by others you can move your cm1's the rear.