30 db dip

[bobgenie]

Hi,

Can't post the curve as had limited time and now at work. I've been dabbling awhile with REW etc and have a fairly nice curve with minor fluctuations or around 2 to 3 db...except one huge dip at exactly 90 hz of about 30 db not alot I can do about it with electronics so any ideas guys. I guess it's modal (whatever that means)
Cheers.

[brucek]

not alot I can do about it

This is where you have to consider how wide the dip is and whether it's worth trying to move the subwoofer around to see if that has an effect. Sometimes it's best to ignore a narrow dip.

I have a narrow dip that is the result of a resonant frequency created when I have my kitchen door open. If I run REW there is a rather large dip that I can completely eliminate by shutting my kitchen door. Very weird, but my point is that I can't hear any difference in music or movies either way. I believe it's because the dip is so narrow.

At 90Hz, it would seem that perhaps you have a phasing interaction with your mains at the crossover. Does it occur with the sub only? Have you moved the sub around at all? Have you tested at various microphone positions to see if it's isolated to a particular spot in the room?

brucek

[Josuah]

It may also be you have to move your speakers. It could be their placement is bad for 90Hz at your listening position even without the subwoofer?

[bobgenie]

Fast replies - thanks guys. I have changed the crossover on the subs from 80 hz right through to 100 hz. I've also changed the crossover on the mains to see if that worked. If i move the mic it moves the dip a little but it's always there. I've tried moving subs, and mains but all that does is create another dip elsewhere as well. Actually it is a fairly narrow dip and the music sounds pretty good but it would be good to get this last little thing sorted

With the subs on their own they roll off at about 80 hz quite steeply. I've got two PB12+s and have one port blocked with each. I wonder if i should take the plugs out and go up to the 20 hz tune.