Tweakers' Asylum

Technical detail

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In Reply to: RE: Sorry, I'm a technical nut.. posted by cheap-Jack on November 05, 2007 at 10:56:09

Hey C-J...here's a post by Al with some more technical details...characteristic impedance matching, corner frequency, etc.

Technical discussion (Open in New Window)

Follow Ups:

If RFI can affect loudspeaker cables so much, ... - cheap-Jack 13:29:15 11/05/07 (0)
Hi.

We better shield up our loudspeaker boxes completely as there are inductors/caps inside the box which only make the RFI effect worse.

On the contrary, I placed the X-over networks for my loudspeaker system outboard, which should be affected by RFI much much more. How come my music sound so good???

c-J
All roads lead to Rome. - cheap-Jack 13:15:42 11/05/07 (1)
Hi.

Don't try to corner yourself in a dead-end alley.

Yes, the characteristic impedance of a cable for wave transsfer is a crucial factor for any audio interphases.

I agree we have to pay due attention to RFI on powerlines & audio front ends where RFI intermodulation can cause complex audo waveform deformation upon amplification, affecting the sound.

But we are now dealing with strong audio signals going through the loudspeaker cable into a very low impedance passive loudspeaker load.
How much sonic effect, if ever detectable by our ears, such RFT can act on the strong signals at the end of the audio journey??

Use common sense, please.

R-C shunt filters when hooked up across the loudspeaker terminals, do change sound due to something else more relevant, e.g. damping factors, not simply RFI.

c-J
- All amp ports admit RF noise. - Al Sekela 15:19:58 11/05/07 (0)
  The speaker output ports of your power amp admit RF noise from the speaker cable. There are plenty of locations inside where the parasitic capacitances allow noise energy to penetrate to the gain sections of the amp, and many amps have feedback networks that couple a fraction of the output directly to the input.
  
  Once RF noise gets to the gain sections, it intermodulates with the audio signal. One outcome of this intermodulation is production of spurious audio-band tones that mimic natural musical overtones. These spurious tones are most obvious as the bright, spitty treble of enhanced sibilants and mushy cymbals, but also cause a dry and disconnected midrange and a vague bass. The soundstage is brought forward and compressed. Massed voices and instruments are blurred together. A low level of RF noise pollution causes just a little treble enhancement and often is mistaken for an increase in "detail." However, careful listening tests reveal that the true detail in the recording is suppressed by RF noise.
  
  These R-C networks help by loading the speaker cables to reduce their resonant quality factor. Cable resonances takes broad-spectrum background RF noise and amplify it at the resonant mode frequencies. This is true for all cables, but the methods to treat power cords and interconnect cables are different. The strong resonant tones of undamped cables are usually the biggest contributor to audio degradation from RF noise.
  
  Once the audio cables are damped, further improvements can be had by damping resonances in the house power wiring network, and placing filters on the AC power feeds to noisy non-audio appliances. These are two different actions, and complement the other measures to reduce RF noise pollution.

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