High or Low

[admin_exported]

Hi,

I have a sub connected from amp's speaker posts to high level inputs on a sub. Today I felt that the main speakers seems duller than before. I disconnected the sub and the main speakers seemed cleaner. I am wary because this conclusion is based on perception, and I may well be mishearing differences. It has been on my mind for a while.

Is there any electrical reason why a sub connected to the amp's speaker post would affect the sound of the main speakers?

The sub has low level RCA inputs. Would it better on balance to use these, even if the run is 6 metres from sub to amp? It is a shame if this is better because it uses up the input I could have used for an AV amp. I thought that low level signals didn't like long runs.

 

[Anonymous]

The most probable cause for the "dull" sound is not an electronical issue, but the subwoofer interfering with the bass of the main speakers. This is why three-way speakers with bad cross-overs tend to sound "muddy" because effectively two sets of drivers are producing the same sound at some frequencies and because the drivers will not be exactly the same in design, or in the same position, it will sound "dull". The sub will hardly put any load on the amplifier (basically, only the load of the wire which is minimal), so I see no reason to change it to the line-level inputs. However, this may sort out some issues, perhaps increasing the "slam" and the "timing" of the subwoofer, however it is unlikely that any difference will be heard.

You shouldn't have much of a problem using a line-level cable over 6 metres though - as long as it is high-quality shielded cable from the likes of QED or Atlas, there should be hardly any difference - besides, the voltage from the output of the amp should be quite high (more than 2V) and the higher the voltage, the less likely distance is to degrade the signal (just how high-tension high-voltage power lines work).

However, I would leave the sub as it is. Check the connections again, make sure there are no short circuits etc and then turn the subs cut-off down a bit. This will stop alot of the "dull" sound in the 100-200Hz range and will improve the "timing" of your system.

Good luck!

 

[Anonymous]

Thanks Hughes,

I am grateful for the electrical advice. I take from your thoughts that any differences can't be due to these factors.

I had a suspicion about the drivers interfering with each other and your objective assessment further pushes me down this path. I have set the crossover to 90hz, which would be in vocal range. I might play with the phase, but moving the crossover near min (40hz) is more likely the answer.

I posted some measurments on another thread for information, and the graphs do show some effect to the music from 120hz. This further tallies with your suggestion. My work desktop does allow the active controls, so I pasted the thread, rather than an active link.

http://whathifi.co.uk/forums/t/168867.aspx

I have to confess, I don't think I need a sub for music, as my speakers go down to 30hz, and I have a massive room mode at 40hz. Puting more sub bass will affect this modes, and at lower volume be not noticeable.