RTA 12 - driver slap when used as "Large" fronts with no sub in HT

[Escher]

Just wanted to run this by everyone to make sure I'm not having an issue with my baby's.

I just went full 5.1 in my Den - using a Marantz 5006 receiver. I had originaly set up the system with my RTA12's as my fronts, a Monitor 5 as my Center, and no sub.

Last night I was watching "Wrath of the Titans" at pretty low volume, say under 60Db... and kept hearing the clicking/slapping noise.

I isolated the section that it was most obvious on (if you have the movie - its the section where Andromeda is talking to Festus, around 44:08 if I remember correctly).

I found that the two Left front drivers were actually bottoming out - tons of excursion... and causing a slapping noise.

I turned my sub on, and crossed my fronts over at 60Hz... problem went away.. So its like the super low frequencies used in movies are too much for the Polks since they dont have enough excursion or something.

ANyone else ntoice this? I dont have any issues with music and can rock them out quite loud.... I'm thinking its just due to the "movie" type digital bass they add for effects.. I also remember hearing the same sound during Transformers "Dark of the Moon"..

Anyone else seeing this happen? I'm assuming its a non-issue, but want to make sure!!

[drumminman]

That sounds like a front end/set up issue. I run RTA 12C's (modded) as my front L-R mains, powered by a Carver TFM-42, set up as full range and I can get it to reference levels without distortion.

Your AVR is spec'd as 100WPC, with 2 channels driven. I'm guessing that it simply doesn't have enough power. The RTA 12's like lots of clean, high current power and they're not getting it. Running volume levels that high with only the AVR providing amplification can destroy the AVR, the RTA 12's or both.

The Marantz has pre outs for the front L-R mains - I suggest buying a power amp to drive the RTA's.

[Jim Shearer]

I disagree with drumminman. Movies often have lots of low freq effects which you may not even know exist until you hear it on a system capable of reproducing them. You state that the drivers are bottoming out (which is a rather unmistakable issue), so you have enough power to make that happen. Not saying that you aren't clipping, which could cause other issues that would endanger your speakers.

I don't know what the box tuning is on your RTA-12's, but you should know that at freqs below the tuning freq, a vented enclosure (which the RTA-12 is, even though the 'vent' consists of a passive radiator) the drivers become unloaded and start to flail around uselessly. So either turn down the volume or use a filter to cut off the low freqs from the RTA-12's (as you did) and let the sub do the job it was designed to do.

Cheers, Jim

[Mystery]

I was playing a surround test or thx test in youtube and at one point in the track, all mid drivers moved like crazy.
One of the dimensional drivers was slapping and making rattling sound but the other speakers SDA driver did not.
Some tracks do have way low frequency to move them more than what they are used to.
I'll see if I can find that video. It was around 10 minutes long with some world war II scenes at the end.

[smglbrth]

Anytime I've had drivers "slap" was when they were on the verge of blowing altogether, which they eventually did. Couldn't at all be the problem but you never know...

[SDA1C]

The wife did this to my 11t trying to blast some Crazy Frog something or other for the kids at school. After quickly rescuing them from the clutches of death, replacing them with some CV, taking then home to verifying the damage and sneaking up on them with real power, it was decided that the lack of quality power to them from her AVR at school was the culprit. I have no doubt permanent damage was done but as surrounds they do not seem to be dying just yet.

Maybe not what you want to hear but it was the over driven amp and low powered receiver causing the issues. 100w per channel on a 7.1 receiver doesn't leave a lot of headroom. Turn them down AND filter them if you want to keep them alive.

[Escher]

I understand what you guys are saying, but Jim has to be right on this one. This was at midnight with my 2 and 3 year old sleeping - probably around 50-60 dB.. NOT loud, maybe 2-3 watts... Its not the amp.

I did another test, and switched my PS3 to Bitstream, sending an uncompressed Masteraudio signal and using only the Polks with no sub as before - problem goes away... Even at much higher volume levels..

So - Heres my thoughts - digital graininess in the signal lower quality signal caused some signal spikes. The cleaner signal doesnt have the same issue..