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

[brucek]

I feel that I have done everything I can with REW and the FBQ

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

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

brucek

Here is the measurement:


Waterfall:


Corrected:


Ideas?

[brucek]

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...

[brucek]

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

[Kal Rubinson]

brucek wrote:

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.

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

Kal

brucek wrote:

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

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...

[JohnM]

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?

[clubfoot]

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

[Bob_99]

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

Bob

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.

[OvalNut]

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

[Wayne A. Pflughaupt]

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?

Like the others who have commented, nothing’s jumping out at me that would explain the loud jump in volume that you’re hearing. The 20 Hz bump should not be audible with music. However, most music has a lot of energy in the 50-80 Hz range, where your baseline chart does show elevated levels.

You indicate that you have an FBQ, but I’m kinda curious about your “corrected” chart. The dotted line indicates that it’s what REW is predicting equalized response to be, not an actual sweep of equalized response. So do you even have an equalized graph for us?

If all else fails in tracking down the “10 dB jump in volume” issue, try running per-frequency sine wave test tones. You can download some at our Downloads Page and burn them to a CD. That should make it obvious where the problem is, as you’ll hear a severe increase in SPL when the offending frequency plays. It may be a good idea to record the SPL level of each tone, for later analysis. It’s highly possible that the problem is a range of frequencies, not just a single one.

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?

REW is an aide for equalization, which has nothing to do with relative levels between the mains and subs. After equalization, set the levels with the receiver’s test tones as usual.

Regards,
Wayne

[JohnM]

Wayne A. Pflughaupt wrote:

REW is an aide for equalization, which has nothing to do with relative levels between the mains and subs. After equalization, set the levels with the receiver’s test tones as usual.

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.

[m-fine]

Wayne A. Pflughaupt wrote:

REW is an aide for equalization, which has nothing to do with relative levels between the mains and subs. After equalization, set the levels with the receiver’s test tones as usual.

Regards,
Wayne

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.

[m-fine]

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.

[jerome]

lardawge wrote:

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.

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'.

Here you go:

[m-fine]

The first isue I see is the room has virtually no absorbtion, except for the loveseat. If you could do something to treat the corners either with LENRD's, corner traps or open back panels spannig the corners, and maybe some of the wall reflection points it would help, but you need to be realistic about what can be done below 50 hz or so. I also understand that approach my not fit your desires or budget.

The second issue could be that your sub is simply overpowering your mains. That little SVS is still pretty potent and the cube mains probably can not keep up as you push the volume levels. The first thing I would do is take some sub+ main sweeps beyond 200 hz so you can see the relative levels and also see if your crossover is in an appropriate spot. With satelite speakers you may be better off moving the crossover point above 80 hz maybe to 150 or more depending on their response capabilities. It also looks like you are employing a house curve, which is OK, but it is a matter of taste and in your room it may not be to your tastes. You mention it sounds like the bass is turned up 10 db, and from your target curve, I am guessing 6 db of that is due to a house curve you have EQ'd in. Once the response looks good, try some sweeps at slightly higher volume levels and see if the curve shape holds or if the satelites are giving up before the sub.

[jerome]

A thick carpet on the floor would probably help to get less 'echo' in your room. It won't help much with the very low frequencies but might give you a more confortable sound stage (by confortable I mean that you don't get tired of listening to music).

As stated earlier in the thread I am replacing the current speakers with 5b/4c/4b bookshelves from Aperion. That should help the mains achieve a better crossover and not get over powered. They will be here early next week at which time I will reevaluate. I am also going to get a rug to go under the coffee table which was already in the plan but haven't found one I like (carpeting the whole floor is not an option.

At this point I have flattened the house curve and leveled the mains and it has done wonders to my ears. Quick question about the LENRD's, I read that the sponge doesn't really do much for bass frequencies. Is that correct?

[Kal Rubinson]

lardawge wrote:

At this point I have flattened the house curve and leveled the mains and it has done wonders to my ears. Quick question about the LENRD's, I read that the sponge doesn't really do much for bass frequencies. Is that correct?

Not much is better than none. Compressed fiberglass corner traps will do better.

[bkspero]

At this point I have flattened the house curve and leveled the mains and it has done wonders to my ears. Quick question about the LENRD's, I read that the sponge doesn't really do much for bass frequencies. Is that correct?

It took a lot of Lernd's in our room of similar size (16, 2 ft segments) and it still wasn't fully effective. In our studio we found that it was helpful to sit on different bass frequencies that showed problems. It often showed the source of the reflection causing the issue. Open the generator dialog box, select sine wave, and check the box for frequency to follow the cursor. Then open up a measurement graph and move to the peaks and nulls. At one resonance frequency we heard the windows rattle behind us (a front to back issue), at another it was the closet doors to our right. We never noticed them before. Just eliminating their sound helped, and the bass traps pretty did end the ringing on the waterfall (down to about 40 Hz). At about 20-30 Hz in a similarly sized room to yours we still have a resonance and ringing in the waterfall from floor vibration. The frequency is low, but the feel of it makes it seem loud. Could you be having a similar issue? We have a wall to wall rug on the floor, but that is of little help because the whole floor is resonating. The best we could do so far is to place the subwoofer on two thicknesses of 5/8 inch rubber pads to help isolate it from the floor. We will be testing more material, and material made specifically for sound management. You might want to try the same thing for your lowest freq. issue.