Setting subwoofer crossover, info needed.

pieman109 · 3 Mar 2006 at 15:13

Right, I've got an MS avant 302 5.1 surround spkr set and I'm attempting to set the subwoofer crossover point. The knob on the rear of the sub goes from 40-150hz which I understand, but the amp, a cambridge audio CA 540R, has a setting called "LFE" which I'm lead to believe is the option to set the amlifier Xover point (sets the frquency range sent to the sub) and is graduated "-10 db to 0db.
Can someone here tell me which end of this scale sets the higher Xover point, -10db or 0db?
Ie: I want to set 150hz 'frintance, do I set nearer -10db or 0db.

Sorry I haven't explained it very well but I'm hoping someone here understands what I after.

DRZ · 3 Mar 2006 at 15:45

The 'LFE' adjustment doesnt set the crossover point, it sets the attenuation (in dB) that is applied to the sub channel (so you can turn down the bass, basically).

Where you should set the crossover point depends on where the rest of the speakers roll off and how good the low pass filter is in the sub. You want it to give you a seamless descent from mid range to LF so fiddle with it until it does. If you want to do it properly, you can use swept sines to get it as close to perfect as you can.

james.miller · 3 Mar 2006 at 15:56

you're confused there DRZ. the knob on the sub sets the crossover point on the sub, the LFE switch on the amp sets the attenuation

DRZ · 3 Mar 2006 at 15:58

james.miller said:
you're confused there DRZ. the know on the sub sets the crossover point on the sub, the LFE switch on the amp sets the attenuation

Im not confused at all - The LFE adjustment on the amp is graduated, not a switch and sets the attenuation.

The crossover frequency knob on the sub sets the crossover frequency.

How am I confused?

james.miller · 3 Mar 2006 at 16:01

you said adjustment. you didnt say wether you were refering to the knob on the sub or the switch on the amp. forgot i said anything :rolleyes:

DRZ · 3 Mar 2006 at 16:04

james.miller said:
you said adjustment. you didnt say wether you were refering to the knob on the sub or the switch on the amp. forgot i said anything

There wouldnt be attenuation on the sub anyway, only gain

I just posted it like that because of the structure of the OP, didnt think it was needed to point out it was on the amp.

Anyway, it wasnt posted in an agressive tone

Sorry if it came across that way.

If the rolleyes were aimed at me, then, well, OK... but I wasnt being agressive.

darreny · 3 Mar 2006 at 18:27

as has been said a tone sweep is the best method for setting the crossover on the sub, some THX dvd's have this on, if not use the original THX advert

pieman109 · 3 Mar 2006 at 18:39

Thanks for the info guys, I think someone in the past suggested to me that the LFE fuction was crossover point and not attenuation (volume), -10db being the lowest and 0db being the loudest. Where can I get this THX tone sweep thing, I assume when you say advert, its that sort of demo bit you get before a film?

mcmad · 3 Mar 2006 at 20:25

some dvd's have thx tests as an extra.. I'm sure T2 had it ?

oh & as for setting up subs..

If you can hear it, its too loud.

darreny · 3 Mar 2006 at 20:46

or look in the manual of you stereo speakers or specs on the net, it should give a cut off point

pieman109 · 4 Mar 2006 at 12:14

mcmad said:
some dvd's have thx tests as an extra.. I'm sure T2 had it ?

oh & as for setting up subs..

If you can hear it, its too loud.

I've made a few adjustments using the controls on the sub and its improved the sound a fair bit using that THX test you get on some discs. I agree with the sub volume being set very low, I've a few systems where the sub is so loud, it tends to overpower everything else. I've always thought that the saying "if you can hear it, its too loud" is true here. All I need to do is set the relative volume levels of each spkr and I think thats it. Thanks guys.

TONY · 4 Mar 2006 at 16:52

I am always playing with my sub (B&W ASW-2500), I am never quite sure I am getting the best results from it. I am happy with the crossover settings but the sub also has a volume control which I am not sure how high to set before I start compensating with the LFE adjustment on the amp, I have it just past half volume atm with the LFE set to -7db and have left it alone for a while.

pinkaardvark · 4 Mar 2006 at 17:55

Could do with some help with mine too as I don't really know what i'm doing either.

Have Level Input, Crossover Frequency and Gain Knobs and then theres a switch that says Ground In/Out and another that says slope 12/24Db

I don't recall getting a manual with it so i'm at a bit of a loss admittedly. Any suggestions welcome

I have obviously just twiddled the knobs so far until it sounds reasonable but the two switches I have left alone.

james.miller · 4 Mar 2006 at 18:19

ground in/out? ummm. i dont know. what's the make and model of the sub? im sure i cna find out what that is.

Anyway the slope would be the attenuation or the 'steepness' of the crossover. it basically means how steep the frequency responce rolls off after the crossover point. 12db/octave is twice as steep as 12db/octave. From personal experiance, i'd prefer 12db for the sub as it seems easier to intergrate a sub with a shallow slope on the crossover, but just fiddle and see what sounds best for you lol.

pinkaardvark · 4 Mar 2006 at 18:30

It's a Kef PSW 1000.2 came with a 1005 egg kit. Sub has a High pass out set of RCA's so maybe the ground bit has something to do with that.

DRZ · 4 Mar 2006 at 19:25

12dB per octave would be my choice too, but it does depend on a few other factors. The higher the order of the crossover (the steeper the slope) the more ripple you get on the flat part of the crossover, which in turn makes things a bit messier when it comes to the sound.