How to tame resonance?

So I have recently purchased a new sub and FBQ. After reading through numerous days of reading and pouring over documentation I feel that I have done everything I can with REW and the FBQ. I Still find a very annoying loud vibrating resonance when music gets down in the lower frequencies (my guess is 30hz and lower). It sounds as if it has jumped in volume 10dB+. I can visually see it in the waterfall as well.

My question is, What can be done to tame this beast?

Room 10x12 square
SVS PB10-NSD

I would be happy to post graphs if it would help...

Thanks,
Larry

Let's see the response.......

brucek

Here is the measurement:


Waterfall:


Corrected:


Ideas?

Response looks good to me.

What's the problem?

brucek

Sorry bruce, your too fast! I realized I posted the graphs from my living room not the entertainment room... New graphs up. There is a hump that I cannot get rid of just before 20hz and I think that is what I am hearing...

Most people would die for that response. I don't know what to suggest. A small hump like that at 20Hz isn't too significant.

How does the response look like with the mains turned on. Maybe the sub is simply too high in relation to the mains...

brucek

I suspect that a 3dB bump below 20Hz is inaudible. What is bothering you must be something else.

Kal

For some reason I cannot find a graph with the mains... although I did create one. I will see if I have some time tomorrow to measure again. Thanks for the help so far...

Those graphs look like they include the mains, the level at 200Hz seems much too high to be from a sub alone if it is driven through a crossover. If that is the case the target should be set to full range rather than subwoofer and the sub level looks very high compared to the mains, at least through the range shown. Better to get things working well and levels reasonably matched without a house curve in the target then try a house curve after that to see if it does what you want.

Hi John,

Great Program BTW!

Yes, you are correct. I remeasured and dropped my level of my sub to be in line with the mains. I think my biggest problem at this point is that my main freq starts at 150 & my sub starts dropping off around 80 even without a crossover... I am waiting for a new set of mains to arrive which should help a lot.

Question, I am setting my sub based on my receivers test tones which leaves it well above my mains. Should I just use REW and leave it at that?

Try setting your mains to small, set final levels using your receiver test tones and take another measurement.

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My HT pics

The response looks good but I think you could use some room treatment to tame the low end.

Bob

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"There is always hope, even if it is just a fool's hope."

This room is so small that room treatment is not really an option which is why I am trying to tame it at least a bit with an eq.

I'll chime in here primarily in agreement with what has been said. The response looks very good, and the bump below 20hz can only help IMO.

What would make a big audible difference would the the addition of good well placed bass traps. What you're probably hearing is the ringing as shown on the waterfall graph. You'd quite likely be able to bring up the null some at 97hz, and knock down most of the ringing you're getting down into the mid 50's or so. The result would be smoother integration with your mains and a more detailed sound. The ringing below 40hz is pretty going to stay there though without more dramatic measures.

Realizing that extensive room treatments are not really an option in this case, you may be pretty much stuck with what you have. And not too shabby though. Really.


Tim

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He drove a black and white pirate ship at 190 mph.
- Dale in the #3 will never be forgotten. Thanks for the memories.

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A little harsh, REW is also a comprehensive measurement tool. A measurement of subs+mains together shows the relative levels very nicely. I would ordinarily also recommend using the receiver's test tones, but if the result is a very high sub level the receiver's sub tone may not be correct.

YIKES! I could not disagree any stronger. Pink noise and a RS meter is a very primitive method of setting levels compared to REW. It is sensitive to peaks and in no way compensates for a person's desired response curve. Are you not the guy who champions the house curve in these parts?

The way I use REW to set level is as follows.

1) measure and EQ the sub only first, as generally recomended.

2) Take a much longer sweep with the sub plus one speaker at a time, starting with the center. I like to go about 4 octaves up from the crossover, so for an 80-100 hz crossover run it up to around 1.5khz.

3) turn on smoothing in the display. Most mains in real rooms will show a fairly jagged response, but with 1/3 or 1/2 octave smoothing, or even 1 octave smoothing if necessary, you can get a real good idea of the average level of the mains compared to the sub, even if the mains have peaks and nulls and the sub has a house curve. Adjust levels as necessary, re-sweep to check. (Note: Look on either side of the crossover point and not at what happens in the middle, see number 4 to get the area at the cross correct)

4) take some sweeps about 2 octaves on either side of the crossover without smoothing and adjust your delay or phase to get the best results.

5) Move on to the next speaker + sub combo until the front 3 are done.

6) I just use the RS meter for the rears but you could use the same method if you like.

Here are a couple pics of step 3 in progress. Obviously the scale is non standard so you can see what is going on. In practice I was looking a couple octaves higher to get a wider picture of the level of the main speaker by scrolling.

First, sub plus one speaker, no smoothing. Is the main at target or not?





Now with 1/2 octave smoothing it is fairly easy to see the main is below target 3-4 db. Note, there is more influence from nulls, so I probably adjusted the level up about 3 db not the full 4.



Also, the null at 80 and 140 or so is probably a phase issue, so I am ignoring those at this point and will correct with the delay setting later. The details of that are another topic but I think most will get the point.

Could you describe your room? Or post a picture?

I think too that you should add some room treatment (bass traps) to minimize the low frequencies. Your waterfall diagram clearly indicates that you have too much information remaining in your room below 80Hz (decay time is high). In my opinion, reducing the low frequency levels using an FBQ will not fix your problem, it will only make it less 'visible'.

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