Room EQ Help - PLEASE

Yup that's a biggish dip. You can see in the results on the calculator that there's a stack of room modes around there (the first 'axial' ones).

I understand that eq can be used for fine tuning but my first port of call would be some bass traps. Having bought in the past I'm now at the point that if I want more I would make them myself, there's plenty of good tutorials and ideas out there.

Child

Scott, that big dip is likely the result of a null. It's what happens when sound waves at one of the room's fundamental resonant frequencies meet themselves 180 degrees out of phase. It's the same thing that happens when you flip the polarity of a track and sum it with the original: anything plus negative same thing equals zip.

There is no EQ that can fix that. The ONLY fix is to trap that frequency. However, bass traps are difficult to implement at that low a frequency - you'd need impractically-thick fiberglass bass traps, like 3 feet thick. The only way that would be practical is if your room was big enough to stack full rolls of pink fluffy in the corners.

If you have a subwoofer, the first thing I'd try is experimenting with moving it to different locations. You'll be surprised by how much difference moving a sub can make.

Given that the rest of the graph looks excellent, you do have the option of simply ignoring the dip. Seriously. Use visual aids to avoid overcompensating for it and have someone else do your mastering and you should be able to live with it just fine.

There is only one other option I can think of, and that would be a tuned resonator. It is possible to build them yourself. You can find DIY examples with photos on the acoustics forums. Google "DIY helmholtz resonator".

Hello everyone!  I suppose this post would have benefited from pictures of the room I'm treating.  You'll see that I've done a bunch of treatment, including BASS TRAPPING.  These pictures are below.

@Bitflipper,
I know we all have to sometimes make concessions with our rooms, this just seems like a big one because it's in such a problem area.   I'm intrigued by what you've said about IGNORING this.  Are you talking about by using a spectrum analyzer during mixing, or something like VOXENGO's Curve EQ?  If you wouldn't mind discussing what you mean by using an example, that would be great, I'm having a hard time visualizing what you mean.  I'm also not super familiar with this technique.

I should mention here too, I ran this test WITHOUT my subwoofer on.  Perhaps I should run it WITH it on?  I didn't turn it on, because I read an old post about calibrating it properly with my system, making sure it's in phase and what not, and I have NO idea how to do that (another thread perhaps?).  I don't really mix with it on much, except to hear if there is any rumble - and I turn it on when clients are here for a wow factor. . . BUT I DIGRESS . . .

I also DID do a bit of research on Hemholtz Resonators, however and think this might be the way to go.  Would I mount something like that on my back wall?

In these travels I also found there are also MEMBRANE RESONATORS which you can tune by drilling holes, which sound like their efficacy is very high - especially in tuning specific frequencies and a small range of frequencies.  This, in conjunction with my broadband absorbers may just be the ticket.

As you said, the rest of that spectrum doesn't look too bad!!   

But, in both techniques, I would need some sort of calculator/plans to find the formula to do this correctly.  I have no issues with DIY, but I hear that this not an EASY fix unless it's done right.  Would you (or anyone reading this) know of a site with plans and calculators to do this.  I wasn't having much luck finding any late last night.



(Since this picture was taken, I've added Auralex bass corner wedges on the corners next to the speakers)

THESE: 






(An OLD picture with my old speakers, etc., but the traps are all still in place.  Notice the ones I have on the floor corners.  I have two in parallel, with matching corner clouds on ceiling.)

Steve,
Thanks for that!  OK, I'll do a reading a bit later and post that to see what differences it makes.  Thank you also for the video tip.  I'm downloading it right now. 

I guess my biggest question then, subwise, is how to calibrate the darn thing.  But I suppose it may be easier than building an absorber!

Check back later please!

Yes, do NOT put those subwoofers too close together either.  I once had two that I put about five feet away from each other by the wall farthest away from an, er, shall we say "volume sensitive?" neighbor.  When I turned everything on the bass seemed missing, then this neighbor rings the bell and asks what the hell is going on - everything in his house is shaking!  Apparently, according to a sound engineer friend of mine, the two bass waves were close enough together to combine and make one, huge, subsonic wave - lol!

One thought that came to mind after reading your threads.  If you didn't have your subwoofer on, are your speakers set up with crossovers that expect it on?  That might account for the dip as well.

One more thing.  I'm getting some advice over at Gearsluts too, and DD over there had me run a FREQUENCY FOLLOWS CURSOR Sine Wave in REW.  Basically this:
THIS IS HIS SCREEN SHOT AS AN EXAMPLE, THAT IS NOT MY TEST PATTERN:


Ok this is pretty cool. I did that test with the sub on and then muted.
 
Around the center of the dip at about 80dB is where I ran it, and with the sub OFF, it wasn't quite as noticeable
 
With sub OFF, I noticed it got quiet right behind where I usually sit.
 
With sub ON, the difference was EXTREME. With the sub ON, and with the mic AND ME in the listening position, that null (which I'm guessing is an EXTREME dip in volume) was directly behind my listening position.
 
When I scooted up to the listening position, with the sub on, the volume incresed dramatically.
 
I hope I described that properly. So with the sub off, at the listening position (mostly behind it), I noticed a slight dip. Barely noticeable. With the sub ON, there was like a quiet HOLE right in the center of the room, right behind where I sit. Where I sit the volume was normal.
 
Thoughts?

Bit, how is it that I find comfort in the fact that your room has some of the same issues as mine!!  LOL.  How sick is that?! 

So I guess my next struggle will be getting my sub calibrated with my system, and perhaps trying a multi-sub listening situation.  I want to make sure I have the thing set right.  I have no idea how to do it, other than by checking my mixes in a car to see if they translate.  I did it with one of the pieces I've been working on, and it was remarkably similar in my car to what I was hearing in the control room.  So that's MUCH better than where I was.  Still, there must be some way to do it right.  My references sound excellent too.

Do you think a multi-sub situation would help, and what did you think of my second test result with the sub on (in green)?

I downloaded the "SECRETS OF THE PROS" video that Steve C. recommended in post #7 but the sound is missing!!!  Tried on my laptop AND in my control room.  Contacted the company late tonight so I wont' have that to reference at the moment. 

And Bit you're absolutely right, I'm a bit of an OCD Egghead when it comes to this stuff, so that book will definitely be on my "must have" list.  I just purchased MIXERMAN's "Zen and the Art of Mixing" which I'm looking forward to diving into as well.  I've heard good things.  I'm also in the middle of reading Bob Katz's book "Mastering Audio" (the new edition).

I also just became aware of Alan Parson's "Art & Science of Sound Recording" video series (http://www.artandscienceofsound.com/) where you can stream video subject segments for $1.99/each online!  I can't wait to dive into those.  I purchased the EQ, STUDIO ACOUSTICS, COMPRESSORS & LIMITERS, and MIXING modules.

Yep, I'll never learn it all, but I'll probably die trying!!!

That's because the sound can only be perfect in one place.

That's the key--there will always be drastic differences throughout the room so the important thing is to get the mix position right.  Now, looking at spindlebox's graph with the sub on vs. off, looks like the sub needs to be turned down. (It's a classic graph of what a sub SHOULDN'T be doing)  What is the crossover point for the sub?  Did you try different sub positions?  There is the oft repeated instruction of putting the sub in the mix position at ear height and then listening at various potential subwoofer positions and hearing where it sounds best--then put the sub there and your ears back in the listening position.  I tried that and it didn't turn out too well.  I just dragged the sub around to various positions, made measurements (graph-wise and listening-wise) at the listening position and went with the best location--well, the best practical location. 

So as long as that dip you described with the sub on is NOT in your listening position, and as long as your listening position sounds good, that's what matters.

If you need to make sure it also sounds good at the client couch, then deal with that next.  Maybe set up a "producer's sub" that you can kick on for a little oomph for the listeners.  But of course anything you add/do differently for the couch will affect your mix position as well.  It's a balancing act for sure.

I got an interesting suggestion in another forum.  Thoughts:

it's likely the floor - ceiling mode causing the dip - consider replacing the overhead cloud with a heavy hard back cloud with an absorptive front. hung on an angle and down from the ceiling. this will help shift the mode. make the panel wide and deep enough to cover most of the area over the front and mix desk - leave about a 12" gap or so around the edges. angle front (low) to back (high) around 15° or 22.5° if possible. use 3/4" MDF and 3/4" plywood with the cloth absorber on the front (bottom) of it.

That's an interesting suggestion. By "shift the mode" I assume he means creating a new mode through the addition of a new boundary to the room.

I'm still trying to puzzle out how that will help you, though. The 62.8Hz resonance will still be there. We're talking rather long wavelengths here - over 16' - so it seems unlikely that a typical ceiling cloud is going to have much impact. But I may be missing something.

Quick suggestion spindlebox if you don't mind....

In the back corners, you would be better suited putting some superchunk or making corner boxes filled with rwa 45 rockwool. This would be much better for levelling out the bass end of the chart. Put the broadband absorbers you have in the corners onto the back wall, but mount them about 2" away from the wall so they have an air gap. This will help flatten the overall response.

Putting those panels in the corner as you have won't do a great deal for the bass response as suggested, the thickness isn't there.

have you seen this interview with Bob Hodas?

My favorite quote from the video: "It takes a looooong time." I forget exactly where and why Hodas said it, but it sums up room tuning nicely. You've got to measure, and add your treatments, and measure, and move stuff around, and measure, and listen, and listen some more, and move stuff, and measure, and listen... you get the idea.

I thought it was funny that almost every time Dave made a comment, Hodas would respond like "well... not really."

With a membrane absorber, yeah, you've got to find the spot where it needs to work and as bitflipper pointed out it might not be practical.

One room I'd like to try building is to start with an anechoic chamber and then adding reflectors and diffusors. So instead of starting with a room where you have to tame resonances, you start with a completely non-resonant, non-reflective room and build it up from there.  Now that's impractical.

thebiglongy:  Yes, the reason I put those like that were because of space considerations; Ethan W from RealTraps thought it would work OK like that, of course, he wasn't there and he never saw one of my tests as a result.  I think I may do some repositioning to see if it works.  I was originally going to do superchunks, but getting that much 703 to build them was out of my budget and again, the space considerations.

@Bitflipper:  thanks for that video; I will watch it tomorrow!  Maybe I'll get lucky I could hang something like that from my ceiling and it will make a difference.  I need  to put more bass trapping along my front wall corners as well.

I'm also convinced I'm going to add another sub as well though.  I'm going to add it at the 3:00 position from my mix position.  The other one is just right of center; I may move it left of center.  That may just take care of it!  I'm working on getting another pair of reference speakers installed too at the moment, so when I get that figured out and the other subs installed I'll do another measurement before I start moving things around.