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Help me tame my out of control bass

Hey all,

Hoping to get some advice on how to tame what appear to be some pretty bad room modes. See my system here:
https://systems.audiogon.com/systems/8800

I’m in a bit of a pickle for a few reasons. First, my NY apartment is on the small side and requires me to set up on the long wall with the listening position against the opposite wall. On top of that I upgraded to my dream speakers, Egglestonworks Kivas. They sound amazing but they’re big and have a lot of low end reach. The combination of these two factors leads to the waterfall you see in my system - a pretty massive bump in low end, particularly at 40-44hz and from 60-70hz.

There’s also a huge bump at 120hz, but I don’t understand how that one is possible. I think that might be a measurement or microphone error - I don’t hear that at all and it doesn’t go away even when I EQ 120hz out completely, but maybe it’s a resonance?

Things I’ve tried so far, each with modest success:
- Plugging the ports gave me about a -5db reduction in the trouble spots (all measurements are with the port blocked)
- I don’t have a ton of placement flexibility but moving them back from their original position gained me about a -3dB reduction in bass
- I added a pair of 5.5” thick GIK bass traps, but they didn’t do much that I’m seeing in the measurements. Maybe a -1-2dB reduction, tops. They honestly helped more with the mids and highs.
- Convolution curve in Roon - this works the best, but doesn’t solve the problem for home theater or vinyl

I’m pretty stumped as to what else I can do. I think that the amount of bass traps needed to fix this is more than my marriage can withstand. I’m considering the PSI AVAA active bass traps, but only if I can do a home trial of them first to see if they’ll actually help - I worry this 8-10dB bump I’m seeing will be too much for even a pair of those. I could get a DIRAC processor from miniDSP and that would at least then work for all digital sources. Vinyl is mostly not a problem since this is so low and most of my vinyl is rock and jazz.

Any other ideas? Rolling tubes that have less bass? Are there any less expensive EQs with digital in and out that I could use as an alternative to the DIRAC for home theater only?
hudsonhawk
hudsonhawk OP
137 posts
 
The odd thing is that 120hz didn’t seem to be there when there’s no signal. This weekend I’ll do some more measuring, there’s been a lot of good hypotheses about what it could be. I’ll run a test tone at 60hz to see if it’s a harmonic, more mic’ing of the room with no signal playing to see if it’s environmental, and with different sources to make sure it’s not an artefact being produced by my DAC or integrated amp.

@rego placement is the correct way to solve this, unfortunately the speakers are quite large and the room allows limited movement of the listening position or the speakers themselves.

Good news is I got in touch with PSI and am in the process of arranging for an in-home trial of the AVAA C20, which could be a good, if expensive, solution to my troubles.

I’m also planning on a few other measurement trials this weekend with different placement of my bass traps, this thread’s given me a ton of ideas thank you all for your thoughtful responses.
erik_squires
16,215 posts
 
I wonder if you have a ground loop from your test signal source? 
audio2design
1,351 posts
 
Odds are the microphone/mic-input is picking up 60Hz and rectifying it (hence 120Hz).
oldhvymec
5,101 posts
 
Hummmm, Maybe that's why I've never see one on my stuff. 2496 Behringer, it's their mic, it's all their stuff. Your saying the equipment the mic is hooked to may have a ground loop? AND that through rectifying it, that causes that spike.

It doesn't sound so "Rectified" "To be made right" A2D
Can you hear a spike like that A2D, or Erik?

OK I'll DMDD, I'll learn.. Maybe:-)

OP, can you hear that narrow spike?

Maybe I need to see if I can make it happen, and give it a listen..

I guess I'm lucky.  I have been in the same home for 40 years,  May..

Regards
lemonhaze
416 posts
 
OP, ignore the comment from @mijostyn that 'bass traps don't work' This is blatantly wrong. Bass traps most definitely work but the 5" thick panels GIK supplied are not proper bass traps, they form broad-band absorbers and are very useful. They are in business to sell so be aware of being sold too many absorbers which will dull the room down.

I see about 10dB between nulls and peaks which really is not too bad. Looking at the CSD you provided I don't see the 120Hz peak being any higher than the other peaks. The suggestions to use EQ to boost the partial nulls will bring no you no happiness. Using EQ to pull down the peaks will work BUT only for one listening position which is rather restrictive.

As I am sure you know, to gain 3dB, it takes a doubling of power. I don't know how loud you listen but to gain 9dB of boost you would need to double the power into the speakers 3 times, so if the 88dB speakers are using about 60 watts average on peaks, then to bring the nulls up to that level would require 480W. If the amp can't provide 480W clean power then it will clip and when it clips the wave begins to take on a square shape and a square wave is just a sine wave with harmonics. Danger!  Harmonics are higher multiples of the fundamental so the crossover does it's job and sends high frequencies to the tweeter which is not designed to handle that kind of power and it politely fries itself.

If the missus won't allow full sized super-chunk bass traps, take heart, you can employ a Distributed Bass Array. Read up on Geddes and Toole on multiple subs and how to deploy them. This will smooth out the modal region below the Schroeder frequency and you will no longer be confined to just one spot. With a smooth power response the whole room sounds good. The 3 or 4 subs recommended randomise the nodes and you get many more but smaller partial nulls and peaks. Needs to be heard.

A DBA is great but although you now have smooth bass it still needs to decay within the correct time for your size room and this of course will need bass absorption. Gearslutz was mentioned and has an acoustics forum with much good info.



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