Strange phenomenon with subwoofer

Posted by: Phil Levy on 16 October 2003

I have been using a newly acquired kef egg satellite/subwoofer system with my yamaha 800 processor, 72,hi-cap/140 to great effect with DVDs,SACDs etc but wanted to use it in stereo with my Linn LP12 without AV processor. As the subwoofer did not have high level speaker connections (something I was not told about, the older version did) I was supplied with a din-phono connector to run from the hi-cap output to the sub. However I have noticed that whenever this cable is connected to the hi-cap, the output to the left and right channels seems to become mono ie sound comes from both speakers but the balance control has no effect on it. If I send a test tone from the processor the left and right tone cames out of both speakers simultaneously. Can anyone cast any light on this? The system is fine once this cable is removed from the hi-cap but I cant play vinyl using the subwoofer without it. I would like to know if anyone else using this connection with a subwoofer has encountered this or is something faulty?
Posted on: 16 October 2003 by Geoff P
Phil
How are the "ëggs" connected. Are they going through the Subwoofer, or are they connected direct to the 140?
Also does the din to phono connector have 2 RCA plugs or one?
You may be only sending a mono signal simply because you have either joined the two channels together accidentally because of the way the connectors are wired or you are actually losing one channel in the din to phono connector.

regards
GEOFFP
Posted on: 16 October 2003 by Phil Levy
Hi Geoff
It is a DIN to single RCA made by the Chord Co. Audio T supplied this to me when it was realised that the subwoofer didn't have speaker terminals. Therefore the eggs are connected direct to the 140 and the subwoofer is fed from the hi-cap using the supplied cable. As sound was coming from both speakers it took a while for me to realise the problem. It does seem like the channels have been "joined" but I don't think I've lost a channel as there is output from both speakers.
Thanks Phil
Posted on: 16 October 2003 by Geofiz
Phil,

Virtually all subwoofers are designed as mono low frequency units. As a result, the signal is mixed to mono for the cable to the subwoofer. You will also notice the same sort of thing for the center channel speaker as well (if you are using one). Unless you have two separate subwoofers with a cable that splits the the subwoofer out into left and right channels, the subwoofer will always be operating in mono.

There is a school of thought out there that all low frequencies (<40Hz) are mono and omni-directional and can only propagate in a small room in mono. Some audiophiles have gone to the extreme of running dual subwoofers (real subwoofers that handle only those frequencies below 40Hz and have a real output in this range). Frequencies this low are more often "felt" than heard. To generate real low frequencies requires a large dynamic speaker and generally a very powerful amplifier with very could rise time and control so that the subwoofer does not run out of control.

Hope this helps.
Posted on: 16 October 2003 by Phil Levy
Sorry if I am missing something here but I have no issue with the mono signal being fed to the sub. My problem is that the power amp is connected directly to the left and right channels and is sending a "mono" signal to them also, despite being connected in the same way as always before I had the sub. Why would this affect them?
Posted on: 16 October 2003 by Geofiz
Phil,

If you are getting the exact same signal to the left and right speakers then it may very well be a cable wiring problem with the connection between the processor and the Hicap/140.

How exactly do have the system wired up? I would assume that it is a connection/cable/processor setting problem.
Posted on: 16 October 2003 by man
Phil,
You said that the cable is din to single RCA. This means that the cable take both left and right channel from hicap to single RCA. This means your left & right channel has been connected at the same +ve terminal of the RCA plug. Because of hicap output socket are connected parallel (correct me if I wrong), you carry the same signal to the 140 which has been shorted together. That is why you hear the same signal on your left and right speaker.

Hope this help.
Posted on: 16 October 2003 by Phil Levy
Geofiz, this certainly seems to be a cable wiring problem but nothing to do with the processor. As I have said in my first posting, it is when I am listening to vinyl without the processor in the set-up.

I think you may be right, man about the signal being shorted but what is the answer? Would a DIN to stereo RCA fix it? I have also read elswhere that Naim actually suggests this way of connecting a subwoofer to their equipment.

[This message was edited by Phil Levy on FRIDAY 17 October 2003 at 07:43.]
Posted on: 17 October 2003 by Paul Ranson
The answer is to get a sub-woofer designed to work in a stereo system.

If the Kef Home Theatre job doesn't have stereo inputs, either at line or speaker, then you cannot do what you want to. All options are compromised.

1. Listen in mono.
2. Run the subwoofer from either the left or the right but not both.
3. Make a proper cable that uses some resistors to derive the mono signal. This will still reduce the channel separation but may be tolerable. This is what Audio-T and Chord should have provided.
4. Get some separate electronics to do a mono-mix without interfering with the stereo.
5. Listen through the processor.

Basically you need to go back to your suppliers and make them make it work as you want.

Paul
Posted on: 17 October 2003 by Phil Levy
The Kef system does have stereo inputs in the sub and Audio T are getting me a cable to feed both of these from the Hi-cap as opposed to the mono cable they originally supplied. I hope this will rectify the problem. The speaker system was obviously bought with AV in mind, not stereo, but the subwoofer was a new model and we were all surprised that it didn't have speaker terminals which would have solved the problem. My stereo vinyl listening does take second place now to other sources so for the time being it is a compromise I can live with.
Cheers Phil