Pop Sound in my speakers when driven loud from studio recorded CD sources.

I’m afraid there is no rattle or anything loose when I shake the speakers. I would revise my description of the sound though, from a "pop" to something more like a "fart" or "burp"... sorry folks, that's what it sounds like ;-).

As far as amplifier clipping is concerned. A recently completely restored Marantz 2275, which was bench tested at about 85 wpc is what the Hales speakers are working with. I don’t know enough about clipping to know if it possible that my amplifier is producing this effect. Playing the same CD passages at lower volume does not produce any of the "pop" "fart" sounds.  It only happens at higher volumes.

Stringreen... thanks.  It's not a particular CD.  The 'pop' correlates to certain sounds on any number of CD recordings.  For instance, a hard slap of the snare drum or tom tom drum by a drummer.  So the pop coordinates with certain sharp staccato sounds like that.  That's why I thought it had something to do with possible errant mechanical movement of a driver.  Perhaps, for all those years of being stored and not used, the actual membrane materials are not as supple as they were.

But I will definitely do the shake test and get back to you.

This is all helpful... So, the output of the DAC is <50 ohms.  Is that relevant?

Doing some research on clipping. My issue does seem to be (and sound like) amplifier clipping.  Only specific 'sharp' sounds seem to cause the speaker drivers to shutter.

Anyone want to confirm this? The amplifier in the Marantz receiver does not have a gain control. Is my only option playing at lower volume? A more efficient, powerful amp.  I really thought 85 wpc would drive these speakers properly.  Thanks.

The Cambridge CXC CD Transport does not have the DAC in it... it's just a transport.  I'm running all digital signals through the Cambridge DAC Magic Plus.  It's a digital converter and preamplifier (I'm not using the preamplifier part). Output impedance of the DAC component is <50 Ohms

I have another Marantz... the 2245. Also fully restored and putting out about 58 wpc. Probably not a good for testing with the 8 ohm Hales.

Thanks all!  

Simao: Cambridge Audio CXC Dedicated Transport.  It says "Output Impedance" <75 ohms.

Filter capacitor: Not likely. They were all replaced & upgraded (along with a lot of other internal components) in the Marantz’s restoration process, only a couple of months ago. The unit was also extensively bench tested before it was returned to me. But, you never know...

Yes, they're ported.  What will blocking the ports do??

Hey... I got an email that member "almarg" posted to this thread, but I don't see the full post here.  The partial post I got in the email is below.  Almarg, if you are out there I would like to know your full response.  Not sure why it didn't get posted here.
"Given the 180 mv sensitivity of the Marantz receiver and the 2.1 volt maximum output level of the DacMagic+ unbalanced outputs, it seems very conceivable to me that the problem may be due to overdr....."

Al,  Thanks for reviewing your original response.  Most here seem to think that the amp is clipping.  Is that what you are describing by saying: 

"...Given the 180 mv sensitivity of the Marantz receiver and the 2.1 volt maximum output level of the DacMagic+ unbalanced outputs, it seems very conceivable to me that the problem may be due to overdriving whatever circuitry in the Marantz precedes (i.e., is "upstream" of) its volume control."

On the other hand, Rodman thinks:

"...You might be hearing the woofer voicecoils, bottoming out, or- when woofers exceed their max excursion, things can sound really nasty...."

If the woofers were really bottoming out, wouldn't that mean the speakers were being seriously overdriven (too much power)?  Simao, disagrees with that and says this:

"...The Hales are 86db at 8ohms - that might be a pretty difficult load to drive at high volume for most amplifiers less than 100 watts..."

The Marantz was bench tested recently at about 85 wpc.  Therefore it may not be driving the speakers efficiently enough.

Am I understanding all of these comments correctly?  Thanks!

Al, Thank you! This is an education for me. I think I understand your detailed explanation. In summary, you are saying if I were to rule out some electronic or mechanical failure in either the Marantz or the Hales, it is most likely inadequate amplifier power based on your calculations of the published specs... or in your words, "...clipping of the power amp section of the receiver." Only solution to that, is a more powerful amplifier I presume.

If it is volume dependent clipping, the other simplest solution would be to live within my equipment’s boundaries and not play the CD’s too loud to the clipping point... and potential destruction of my gear! The problem with that, is that the effect is more pronounced with recordings on CD that are more compressed, which generally you want to listen to louder to give the sound more ’presence’ in the room. As you also pointed out, the more ’spacious’ recordings, within my system can definitely be played louder without the clipping effect emerging... no question about that.

Any other observations would be welcome from all... thanks again!

Kanjit, The covers on the Hales are nearly impossible to remove.

Erik, I did try blocking the ports, but no change.  In fact it may have made the phenomena worse... hard to tell.

Al... thank you again. I think that we are understanding the terms "compressed" and "spacious" in the same way in terms of dynamic range. It’s just that I handle the volume issue with each, differently than most, I guess. The truth is, I enjoy the wide dynamic range sound much more so than the narrow range employed in many of today’s recordings. Wide feels more live and ’in the room’ where as narrow sounds canned or unrealistic to my ears... hence my impulse to crank it up and make it feel more real. Perhaps a fool's errand ;-)

You’ve also added thermal overload, either in the amp or the speakers as a possibility. Is it possible that my Hales speakers, which I purchased new nearly 20 years ago and have spent the overwhelming majority of that time in storage and unused until very recently, may have some material degradation of say the membrane materials?

Hi All... I’m dredging up this 1+ year old thread because I think I discovered the solution to the problem I brought up here (I’m the orginal poster).

I had complained of a pop or burp sound when I was playing CD’s and there was a brief spike in sound, like when the drummer slaps the snare drum. This would happen at fairly loud volume. So, it was preventing me from turning the volume up on my amp to a nice loud concert level. If you want to know more, see the original post at the top.
All of my digital sources are routed through a Cambridge Audio DAC Magic Plus. This DAC has a "pre amp mode" with a volume control knob that is activated when headphones are plugged into the DAC... or when it is purposely selected by the user for speaker listening. Until now, I have been using the DAC without that pre amp mode selected... and THAT is when I find that the amp’s volume knob tops out early and the popping/burping sound starts happening coincident with the brief spikes in sound.
Now, I am using the DAC in pre amp mode and putting the amp’s volume knob much higher and then adjusting the DAC volume knob to get the music to a good listenable loud concert level... and to my surprise, I no longer get those pops/burps in the same instances that I was before. I believe that one of the posts earlier in this thread hints at trying that very thing out. But it was not until now that I tried it.  I'm still working on the optimal ratio between the two volume knobs.

Of course, I’m happy about this, but what I would like to know from you all, is what might be happening within my system between the receiver (pre amp/amp) and DAC (with pre amp volume control activated). Now there’s actually 2 pre amps working simultaneously. I don’t really have the technical knowledge to know why it’s working better, but I’m sure curious. Thanks!

Wow... Thank you again Al.  I'll continue to monitor the situation and try various other CD's where I know the "pop" was happening before.
As you point out, the mystery may be within the Marantz's circuit design:

Detailed knowledge of the Marantz' circuit design might be required to explain that

At this URL, scroll down to the bottom, and there are links to PDF's for "schematic" and "diagram" for the Marantz 2270 I'm using:http://spacebullet.net/marantz-2270.html.  If you feel like it, take a look; my curiosity continues!  Best, Mike

Hi Al... further experimentation with using the DAC in pre amp mode is proving that I can play at higher volume now, without inducing the "pops".  Thanks for your help!  I'll make any updates here.  If you have any further thoughts, post here.