Response after cutoff

[Testpattern]

I'm new to this so please bear with me.

I've notice there's a significant amount of response above cutoff which is shown on my graphs when playing with the sub only. It is down about 20-30 db but there appears to be something present. I would anticipate an octive or two after cutoff should look like a flat line way down in the mud?

Is this normal for REW or most likely I've done something dumb?

Thanks

[brucek]

I would anticipate an octive or two after cutoff should look like a flat line way down in the mud?

The crossover is not a brick wall. It's a 4th order that slopes at 24dB/octave.

Here's what an 80Hz crossover looks like up to two octaves above......

80 hz crossover.jpg


brucek

[Testpattern]

Thanks for the feedback Brucek.

I agree and understand the slope of the response would look like the curve you've provided. What I'm seeing is a sound trace which jumps around between 48 and 56 db (ref your graph) and remains more or less constant up through 400 hz. Sorry, I don't have a graph to submit since I'm at work. It appears as though there's sound energy being measured past the cutoff but nothing "should be there".

I would expect my RX-V2700 sub cutoff at 80hz to attenuate anything coming through the system rather quickly given the filter rolloff rate. I am sweeping up to 400hz so there is a signal present. I just cannot imagine why something remains on the graph after the 80hz crossover.

Thanks....

[brucek]

I am sweeping up to 400hz so there is a signal present

Huh, and this is coming from the receiver? Simply do an REW sweep with cables that includes the receiver as the input and the sub out as the output to and from your soundcards line-in and line-out. First sweep the cable only to ensure a flat response). Adjust the Check Levels and you have an analyzer that will do a response of the crossovers in your receiver. Then you'll know for sure....

brucek

[Testpattern]

Forgive me. Poor wording on my part.

When I said I was sweeping up to 400hz I meant I had set up REW to sweep to 400hz. I did this to check the transition from sub to mains when running all three. However, when disconnecting the mains I still see acoustic response past the cutoff up to where the sweep terminates. I was expecting the rolloff of the A/V LFE filter to quickly eliminate signal after the 80hz crossover frequency. It does follow the filter's rolloff down to about 56db then things randomly fluctuate between 56db and 46db on out to the sweep termination at 400hz.

I can play with filters and various curves and see direct effects in the area below the cutoff where I'm working, but every graph I get has this acoustic information out beyond the cutoff for some reason.

Thanks for the patience on this.

Alan...

[brucek]

I was expecting the rolloff of the A/V LFE filter to quickly eliminate signal after the 80hz crossover frequency. It does follow the filter's rolloff down to about 56db then things randomly fluctuate between 56db and 46db on out to the sweep termination at 400hz.

Yep, and I do get what you're saying. My suggestion is to test to see if it is caused by the receiver itself. Do an REW response test of the receiver itself. NO speakers.

Feed the receiver just as you are now from line-out of the soundcard to the AUX input of the receiver, except this time connect a cable from the receivers subwoofer line output to the line-in of the soundcard. Delete the meter calibration file, but leave the soundcard file in REW.

Do a Check Levels setup in REW and you'll have to adjust the receiver volume control a bit.

Sweep from 0-400Hz. You'll see what the crossover looks like...............

brucek