Need advice on subwoofer settings please.

tony kop77

Well-known Member
I have the kef 2005.2 and would like help on setting the sub. On the back of the sub there is a a switch and I can have it on either slope 12db or 24db which of the 2 would you recomend I have it on?
My volume on my amp is normally -20.
I also notice there is a switch for ground in and out which I dont know what it means.
I have some knobs saying adjust level crossover frequency and phase adjust. My bedroom is 12ft by 10ft can you recomend on what levels I should have these on please and what they do.

Ian J

Your amplifier is best controlling the crossover for the bass management so it is a good idea if the crossover frequency control on the subwoofer is switched to it's highest possible setting.

I can't help with the other questions as I don't have a KEF sub and am unsure what the controls do but hopefully one of the very many KEF sub owners here will give you a hand

Ian J

Originally posted by Jase
The 12db setting would give you a more a gentle roll off of the frequency at the chosen cutoff point whereas the 24db setting would give you a sharper roll off.

At 24db there is less of an overlap of the frequencies as it were and can help to reduce boom around the crossover point.

The Phase dial helps you maintain the phase between the satellites and the subwoofer, ideally you need a Test Disc with frequency sweeps such as AVIA to help with this. Get the phase right (along with the crossover) and the sat/subs will sound like one big speaker rather than two seperate entities.


Active Member
What process do you actually need to go through to set the phase? If you have a range of test sweeps, how do you use it to choose the best phase setting? Is it by ear, or is there a more scientific way?




Sub phase affects peaks and dips only when your main speakers are putting out similar content (at the same low frequencies) as your subwoofer.

If the wave arrives from sub and mains together then you get a peak in the response at your listening position. (Summing)

If the wave arrives from the mains before or after the sub then there will be a trough in the response at the listening position. (Cancellation)

You can only set phase correctly for one particular frequency. Since the wavelengths are so long it is difficult to match more than one frequency. Use an SPL meter on slow sliding test tones in the bass at the listening position and see where exactly you have large peaks or troughs. (if any)

If you can't flatten the response by moving the sub then try adjusting the phase knob to minimise troughs and peaks at the listening position. Moving the sub is NOT the same as adjusting the phase control since it affects all bass frequencies.

None of this is very easy to achieve. If you want to do it by ear then run a sliding test tone and see if you can hear a peak. Then have somebody adjust the phase knob (or switch) to lower the peak while you sitting in the hot seat.

Troughs can't easily be detected by ear as far as I know. The absence of something is not easy to detect except on an SPL meter.

If I remember correctly REL simply suggest you set the phase to sound loudest in the bass. You can check their instruction online to confirm this. SVS also has good online instructions for setting up a sub. Both probably put it better than I do using half as many words. ;)


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