Room nodes

[swgiust]

I played around with my subwoofer (SVS PB12-Ultra/2) yesterday. Taking new measurements and such. I have a huge bump at 63hz. +13 db! Even with the parametric eq maxed out!

I have a feeling that eq will not cure this bump. I do have a Feedback destroyer but
have not hooked it up yet.

My question is this, if a room node is so large an eq can not cure it, what are the fixes?
My room is 18x18 with a vaulted ceiling. My sub currently sits in the back right hand corner.

I also have powered towers (mains and surrounds) that I tested as well, seperately, and they also show the same bump. Normaly I run them "small" so they don't interfere with
the main sub.

[kexodusc]

This one's a bit baffling. Your perfect square room isn't ideal but it EQ'ing the bump down should work. Is the Parametric EQ you're using one of those single, wide band settings? A lot of sub plate amp P EQ's aren't really that useful (and the few I've seen have been pretty lously in fact). You might benefit a lot from a precision cut at 63 Hz, the BFD is great for those.

It's hard for me to believe that cutting it 10-20 dB or whatever it takes wouldn't work, surely the 63 Hz hump doesn't show up when the system is off, and it must increase relative to the SPL of other frequencies, hence an EQ should work. Since you already have the BFD, I'd try that.

Moving the sub around can make a bid difference sometimes as well, but presumably you've already found your ideal position?

What SPL meter are you using to take the readings? Most SPL meters become pretty inaccurate below 125 Hz, the Radio Shack SPL meter is the only one I know with available correction values, though I've heard the latest batch requires new ones. IF you use the RS meter, a search at the forums here should give you what you need.

[Sir Terrence the Terrible]

I played around with my subwoofer (SVS PB12-Ultra/2) yesterday. Taking new measurements and such. I have a huge bump at 63hz. +13 db! Even with the parametric eq maxed out!

I have a feeling that eq will not cure this bump. I do have a Feedback destroyer but
have not hooked it up yet.

My question is this, if a room node is so large an eq can not cure it, what are the fixes?
My room is 18x18 with a vaulted ceiling. My sub currently sits in the back right hand corner.

I also have powered towers (mains and surrounds) that I tested as well, seperately, and they also show the same bump. Normaly I run them "small" so they don't interfere with
the main sub.

You have a room MODE not a node. A node is a place where there is a cancellation of output. The best thing I think of is to move the sub little by little out of the corner until the peak lies within the ability of the eq to correct the remaining output.

I am surprised that you are getting identical peak readings from all of your towers. Usually if bass drivers are located in different places within the room, they will exibit quite different frequency responses. Are they all sitting in identical places in relationship to the side and rear walls? Are all the peaks totally identical?

[swgiust]

Thanks for the replies.

I did use a radio shack meter. I have the corrections on a spreadsheat for SVS.

My towers are 2 mains, left and right, and my side surrounds. They are actually
in the same place all around the room. About 1' out from the wall and 3' from the
corners.

I played with all sorts of settings and got the same hump everytime. I am going to
set up may BFD tonight and see if I can just center in on the 63hz.

For all you bass freaks out there, It was fun! When I started I had my system WAY
to loud, I was getting like 112db at some frequencies. It wil move inside parts of your body!
I also found many things in my room that like to rattle.

[Sir Terrence the Terrible]

Thanks for the replies.


My towers are 2 mains, left and right, and my side surrounds. They are actually
in the same place all around the room. About 1' out from the wall and 3' from the
corners.

.

Just as I figured. You located all of you bass drivers in high pressure zones that are exciting a mode that peaks at 63hz. Its a good thing you keep them on small!

[Woochifer]

Sounds to me like the parametric filter on your sub is not targeting the center frequency precisely enough. If you measured the peak at 63 Hz, then a parametric filter should be able to attenuate it, IF you have the center frequency correctly set to 63 Hz. If this peak occurs within a narrow frequency range, then it will be very easy to miss using those rotary controls provided on your subwoofer.

If that peak at 63 Hz is the only major issue that you measured, then you should play around with the center frequency setting on your subwoofer's parametric filter some more before you resort to connecting the BFD. I have a feeling that you just need to find the correct position on the subwoofer parametric EQ's frequency dial that actually corresponds to 63 Hz, and that will improve your measurement and sound quality dramatically.

If through trial and error you can't attenuate that problem frequency using the sub's internal parametric EQ, then go ahead and plug in the BFD. It won't take much time to set up a -13 db parametric filter at 63 Hz (probably using 1/6 octave bandwidth) using the BFD.

The advantage of the BFD is that it is digital, and allows you to very precisely set the center frequency for the parametric filter, and you can create multiple bass response curves (each using up to 12 parametric filters) depending on the source that you're listening to. The disadvantage is that it can raise the noise floor (clearly audible in the midrange and highs, debatable how much it affects the lows), and it introduces a 1-2 ms delay into the signal path that can detract from how well the sub integrates with the mains (if you use a newer AV receiver, you might be able to compensate for this by decreasing the subwoofer distance in the setup menu by 1 to 2 feet).