REW finds peaks but doesn't find valleys???

[ghstudio]

I've done some measuring with REW and just got a BFD1124. From my graphs it looks like I have some frequencies that I should want to boost.....but REW only finds those peaks that need to be reduced. I suspect that the dips are caused by the room...but boosting them does seem to change the curives.

Can someone explain why REW doesn't suggest adding gain to frequencies???

On a related note.....REW doesn't seem to tell me how wide (bandwidth) to make the cuts on the 1124P if I want to enter them manually. How do I set the bandwidth of each cut correctly, or is trial and error?

[brucek]

Can someone explain why REW doesn't suggest adding gain to frequencies???

Dips are caused by phase cancellations, where the sound reaching the measurement point is a combination of an original direct soundwave and a reflected sound that is 180 degrees out of phase at the dip (one half wavelength).

When you add a gain filter at that dip frequency, not only does the direct sound increase by the number of dB of the filter, but unfortunately the 180 degree out of phase signal also applies an equal and opposite signal to counteract. The result is that your dip is still there and you have wasted the gain you've thrown at it in decreased headroom.

Consider what creates a peak. The direct signal arriving at the measurement point is combining with a reflected signal that is in phase at the peak. When we apply a cut filter, not only does the direct signal drop, so does the reflected signal drop at the same time. The peak is easily reduced.

REW doesn't seem to tell me how wide (bandwidth) to make the cuts on the 1124P if I want to enter them manually. How do I set the bandwidth of each cut correctly, or is trial and error?

REW tells you the frequency, gain and bandwidth of every filter in the EQ Filters panel. Where are you looking that it doesn't tell you the bandwidth? Hopefully, you have the 1124 selected as the equalizer type.

brucek

[Wayne A. Pflughaupt]

ghstudio wrote:

Can someone explain why REW doesn't suggest adding gain to frequencies???

REW is designed to eliminate extended signal decay (aka “ringing”) by crafting filters to counteract room modes. In truth, it will recommend EQing down everything appearing above the Target Curve, modes or not.

From my graphs it looks like I have some frequencies that I should want to boost.....but REW only finds those peaks that need to be reduced. I suspect that the dips are caused by the room...but boosting them does seem to change the curives.

It sounds like you have some nulls with the sub in its current position; nulls don’t respond to EQ boosts. It’s not hard to identify them; nulls are usually sharp, plunging and narrow depressions, like you see below at 38 and 65 Hz. The best way to deal with nulls is to try a different sub position, if that option is open.

On a related note.....REW doesn't seem to tell me how wide (bandwidth) to make the cuts on the 1124P if I want to enter them manually. How do I set the bandwidth of each cut correctly, or is trial and error?

Not sure what you mean there – in manual mode, REW makes no recommendations of any kind – frequency, boost/cut or bandwidth. However, you can watch the dotted line on the graph and see what REW predicts you’ll get from a manual filter.

Regards,
Wayne

[Eric D]

A related newbie question re the valleys. Would a helmholtz resonator suckout (such as from an opening into the rest of the house) show up as a broader valley - more like an upside down resonance peak?

Thanks.

P.S. After my first, simplistic, measurements with REW, I was able to reposition my subs and eq them a little and they are kickin'. I plan to do much more measuring and moving, but I made sure to record these positions in case I lucked into the sweet spot right off. It's not based on any of the usual writeups, but if it is as good as it seems, I'll have to share what I did.

enjoy!

[edit] I promise to be good - thanks for being gentle. [/edit]

[NCDave]

Wayne A. Pflughaupt wrote:

nulls are usually sharp, plunging and narrow depressions, like you see below at 38 and 65 Hz.

Oh, sure! Use my horrible plot as an example of bad stuff!

You can TRY to add a boost to those nulls, but it's like spitting in the ocean. The sharp nulls will just suck it down and the poor ol' sub will give it the college try...all for nothing.

After I get done pouting about my utter failure thus far (on another thread--not hijacking yours), I'm planning on move the sub to some location far from where it is now...maybe the big nulls will go away. You could try that.

[Wayne A. Pflughaupt]

NCDave wrote:

Oh, sure! Use my horrible plot as an example of bad stuff!

LOL - sorry about that Dave, yours was fresh on my mind and readily available.

But here's another one, from a buddy of mine's house, before and after EQ. You can see once again that the 50 Hz null is narrow and deep, and while EQ helped everywhere else, it had no effect on the null.

Baseline



With Equalization

Regards,
Wayne

[NCDave]

Wow, mine is not so bad, then.

Take heart, ghstudio, there is hope. I got something a bit flatter; even the nasty null is not so bad, but can get a lot worse with only a few tweaks.

http://www.hometheatershack.com/foru...red-mains.html