Loudspeaker Distortion
 

Hi all, I have a problem I need some guidance on please. I have recently acquired a pair of IQ Ted 3 loudspeakers. They are of German manufacture from the 80’s and from what little information I’ve been able to get, were not a cheap item. The spec label reads as follows:

NENNBELASTBARKEIT 110watt
MUSIKBELASTBARKEIT. 160watt
FREQUENCY 32 ~ 24000 KHertz
EMPHORLEN FUR VERSTARKER VON 4 ~ 8 OHM

I am driving them with a vintage Rotel RA-1312 rated at 80W per channel RMS into 8ohms 20 ~ 20K Hertz.

My problem is that at reasonably ‘normal’ listening levels the output is very good and clear but if I turn the volume anywhere over 60% the sound rapidly distorts into unlistenable garbage. It’s not that I want the house to move but sometimes it’s good to ramp it up a bit.

From what I’ve read online I’m wondering if the amp is under powered to drive the speakers. What do you think?

At the same time in a separate room, I am driving a pair of Linn Kabers actively wired through three Linn LK100’s via the pre out connections on the amp. This achieves nowhere near the same volume levels as the directly wired IQ’s and there is no evidence of distortion.

Any guidance will be gratefully received.

Re: Loudspeaker Distortion
 

I would suggest you're driving your amplifier into clipping. IF, the speakers are in good condition and the cone surrounds are OK, it still brings me back to the amplifier.

One thing you did not state was the "efficiency" of the speakers. This is normally expressed in dB/watt, or decibels per watt. Some modern speakers require a large amplifier to even get started, many old speakers will be roaringly loud with only a few watts supplied. For instance, I have late 1960's Tannoy speakers made in England. I drive them with a home made amplifier of seven watts RMS per channel. Anything over about 4 on the dial will have the wife after me with the broom.

After that little rave, it might also be that the speakers are "poling". That means the voice coils are rubbing on the magnet and pole assembly. Caused by two main problems:-

1: the speakers have been "flogged" and the voice coils have been overheated.
2: the suspension system has deteriorated and the cones have sagged from gravity,

AND once again the voice coils are poling.

A few closeup pics of the fronts with the grille removed might very well make it much easier to answer.

Regards, Joe.

Re: Loudspeaker Distortion
 

Speaker power ratings is a very inexact science.

One wattage number doesn't cover it. 110W rated power, but at what frequency? That's enough power to quickly ruin tweeters if it's applied at a frequency which reaches them. All manufacturers are guilty of giving single, misleading numbers. Music and speech have a roll-off characteristic where higher frequency components are normally progressively less powerful.

So, is the amplifier hitting its end-stops at the level you're trying to drive these speakers, or are the speakers hitting their end-stops?

If the amplifier, current limiting could be coming into play, or the amplifier could simply be reaching the limits of its voltage swing. I'd assume voltage clipping is more likely as usually Japanese amps are switched for two pairs of speakers, so their design is pitched towards low-Z loads.

A shufti with an oscilloscope would show if the amp is flat-topping. If so, it doesn't really matter if it's hitting a current or voltage limit. That Rotel is styled to look much hunkier than its electronics delivers.

You could try it with a pair of headphones, suitably attenuated and with long enough cable to put you in another room. If you hear the distortion, blame the amp, if you don't it's definitely the speakers.

David

Re: Loudspeaker Distortion
 

I wonder if the speaker voice coils could be slipping on their formers?

Re: Loudspeaker Distortion
 

The output is probably only about 50 watts per channel with both channels driven. I suspect you are just trying to get too much from the amp. As others have said there might be a problem with the speakers. You should be checking with tone controls flat or switched out, if there is a switch, and any loudness compensation turned of. Trying with bass turned up can quickly reach the maximum the amplifier can deliver without distortion.

Re: Loudspeaker Distortion
 

Even 50wpc driven to clipping should sound very loud indeed in a typical domestic environment. I wonder if there is a problem with the amp (maybe a power supply fault).

Re: Loudspeaker Distortion
 

Another thing you may want to consider is what I discovered about my ageing ears.
If I go to one of my sons gigs all I can hear is distortion, which ruins the enjoyment for me. I thought it was the PA system being driven into clipping, but if I put my fingers in my ears the distortion goes. So the conclusion I have come to is I can no longer stand chest thumping sound levels like I used to. As I have got older apart from the severe drop in top end frequency (around 10k now) my ears can not handle the heavy vibrations any more.

I have just noticed your signature, "Small Scotch, New Aids and Happy Ears" if you do wear hearing aids take them out and test again.
Mike

Re: Loudspeaker Distortion
 

Hi,
In post #2,
Just a thought, have you tried turning the speakers upside down?

Stuart.

Re: Loudspeaker Distortion
 

I would try listening in MONO, through 1 speaker at a time.
Its a bit easier to hear whats going on and a difference between speakers / amplifier channels could be revealing.

dc

Re: Loudspeaker Distortion
 

Another thing, try an 'air gapped acoustic attenuator' :) if your hearing is in doubt, i.e. stand further away! I quite often think the bass sounds muddled at home until I stand in the kitchen and can follow the bass player without issue. I guess this is down to standing waves when I am closer ...

dc