dip in HF with 2 speakers

[peteys1]

I'm starting to take some measurements now and am wondering why I'm getting a dip in the FR from 6 to 14k when I measure with 2 speakers compared to no dip with one speaker.

By the way, I just wanted to say thank you to the originator of this software. It is outstanding.

The room is 34 by 23 with 8 foot ceilings. There are are 2 foot knee walls that slope up to the 8 foot ceiling, so it's not rectangular. I am facing the short wall about 38 percent. I presently have about 30 4 inch traps in the room so far.

The pics have 1/24 octave smoothing and the speakers are full range. They only go down to 45 hz.

I'm also getting a pretty big dip at 140hz. I still need to play with the positioning which may help. I posted this also and this has no smoothing.

I also posted a waterfall and just noticed that I have ringing at 36 hz. Any idea what could be causing this as the speakers only go down to 42.

Sorry for all the questions.

[JohnM]

peteys1 wrote:

I'm starting to take some measurements now and am wondering why I'm getting a dip in the FR from 6 to 14k when I measure with 2 speakers compared to no dip with one speaker.

Measuring with both speakers active is extremely sensitive to mic position, the tiniest difference in the distance from the mic to each of the speakers causes comb filtering due to the phase differences between the signals as they arrive at the mic. It can be useful to run both speakers when looking at low frequencies but does not give useful info higher up.

peteys1 wrote:

By the way, I just wanted to say thank you to the originator of this software. It is outstanding.

You are very welcome

peteys1 wrote:

I also posted a waterfall and just noticed that I have ringing at 36 hz. Any idea what could be causing this as the speakers only go down to 42.

Speakers do not have a sharp low end cut off, their output rolls off gradually. Your room has a modal resonance at 36Hz that is being excited by the speakers.

[peteys1]

Thank you , John. It definitely does seem to have that resonance. I'm wondering if the null at 140hz is related and if I should I be concerned with this.

I've posted a couple of graphs and was wondering if anybody had any thoughts on how they look. I've got 34 traps in the room now. My wife is gonna kill me. Anyway, I seem to still have some modal ringing. Should I try to address this more, or does this look pretty good.

It definitely sounds better. And I've notice a marked improvement in using REW to place traps and position speakers. I'm really having fun with this.