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Discussion Starter · #1 ·
Hi all,

I just registered here at the Shack today. I was drawn in by REW, however it is nice to see another HT forum around. I'll be sure to post in the introduction thread when I have some time.

For now I'm just curious to know how my first attempt at a room mode measurement compares to what the more experienced REW users have gotten.

I took this sweep just off of the listening position using an external SB and ECM8000 mic and I do have quite a few room treatments already. It looks close to what I was expecting, just looking for a bit of confidence in what I'm doing with a new tool.

TIA,

Dan
 

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Yeah, looks fairly typical - good job.

Once you start measuring above subwoofer frequencies you can use the smoothing feature which removes the sharp peaks and dips and gives a more readable display. This feature (on the left panel of REW under Trace Adjustments) allows various octave settings. (Be sure to turn this feature off before finding peaks and creating filters for a sub though).

You have a typical peak around 35Hz that could easily be removed with a parametric equalizer. You'd be surprised at the difference it would make in your low end.

The dip at 20hz may be caused by sub placement and might be cleared by moving your sub.

The dip at 70-80Hz may be caused by the crossover interference and interaction between your sub and mains. Adjustment to sub phase can usually clear that up. REW is handy for that job.

brucek
 

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Discussion Starter · #3 ·
Bruce,

Thanks for the confirmation and tips. I get quite a bit of noise from my PC when I connect the external SB to my preamp input. I can actually hear when I move the mouse and when the video card changes the overlays. The next step I guess is to try my laptop.

You have a typical peak around 35Hz that could easily be removed with a parametric equalizer. You'd be surprised at the difference it would make in your low end.

The dip at 20hz may be caused by sub placement and might be cleared by moving your sub.

The dip at 70-80Hz may be caused by the crossover interference and interaction between your sub and mains. Adjustment to sub phase can usually clear that up. REW is handy for that job.

brucek
Sorry to mislead you here. I don't really have a sub, just a bass horn that rolls off pretty quickly below 35 Hz. I'm surprised to see that hump at 20Hz.

I agree with you that there is probably some interaction with the bass and mid-bass in the 70-80Hz region. Since that is the cutoff point of the mid-bass it couldn't be in a worse spot. But that's my goal, getting the crossovers correct.

Here's a sweep just with the bass horn that shows the 70-80Hz region is really there.
 

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I get quite a bit of noise from my PC when I connect the external SB to my preamp input. I can actually hear when I move the mouse and when the video card changes the overlays. The next step I guess is to try my laptop.
Huh, strange about the noise. Both my PC's with different soundcards are completely silent. Perhaps your cables have a bad ground or the connector (1/8" phono - worst connector in the world) is not mating properly, etc?

Watch out with the laptop. Normally everyone uses an external USB soundcard with those, since they don't usually have a line-in, only an unsuitable mic-in.

Yeah, lots of peaks and valleys with that horn for sure. With the typical external sub it can be moved around and EQ'd quite easily..... The horns have a unique sound though...

brucek
 

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Discussion Starter · #5 ·
My PC is probably 8 years old. It's a P3 so it does have plenty of cpu power but . . .

I bought the external USB SB card just in case I'd have to try the laptop. We'll see. If I still hear noise it's probably a connection, as you say.

I do have the horn sub on casters. I was thinking ahead on that one. :bigsmile: It is located pretty close to the front wall in a corner. I don't have the room mode calculations I made with me so I haven't yet compared those with what I'm getting.
 

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Discussion Starter · #6 ·
Looks like my noise issue is in the circuits in the PC. I can actually hear digital noise when the hard-drive is writing. :thumbsdown:

Doesn't really matter for measurements in the lower frequencies. I'll try the laptop tomorrow.
 
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