More Accurate Yet Less Bass?

[wesarvin]

After treating my control room, I've gotten a pretty satisfactory response in the room. Bass lines are clear and even, and imaging is incredible. However, the really low frequencies (sub 70hz) seem to disappear only at mix position. I realize that I'm mixing without a sub, but how come I heard the lows before trapping and not after, except along the back wall or in the next room?

The only graph I can locate is a little numerically challenged. It's the default RoomEQ Wizard window up to 200hz.

[danbronson]

Are your monitors out of phase?

Okay probably not, right? But that seems impossible to me. The bass response should change noticeably, but it shouldn't disappear.

[Ethan Winer]

Originally Posted by guitarwes

the really low frequencies (sub 70hz) seem to disappear only at mix position.

You need more bass traps, or better speaker placement, etc. I imagine the bass is now flatter than it was, but maybe by contrast things seem thin? The only way to know is to measure. If you have REW, let's see some graphs. But don't stop at 200 Hz. Let's see 20 to 300 Hz.

--Ethan

[avare]

[QUOTE=guitarwes;2022569I realize that I'm mixing without a sub, but how come I heard the lows before trapping and not after, except along the back wall or in the next room?[/QUOTE]

Working with what you wrote, psycho-acoustics are involved. You probably were hearing the second and third harmonics of the notes and your mind was perceiving the fundamental.

A good psycho,
Andre

edit: inserted the word "were" in the last sentence to make logical.

[wesarvin]

This is a graph that the numbers were messed up on. I will re-test later today. Should I use my API312 or Presonus Firepod as the pre for the ECM 8000? I think the API has a low-mid bump.

[wesarvin]

and include a waterfall plot*

[Ethan Winer]

Originally Posted by guitarwes

I think the API has a low-mid bump.

Doubtful. The worst POS preamp will be flat from 20 to 20K within half a dB. A really good room will be off by 10 dB in five places all below 300 Hz.

--Ethan

[wesarvin]

Ok thanks for all of the help so far. Here come the plots!

[wesarvin]

What is the bump before the null at around 60hz? Might it be floor resonance (this is an attic studio after all)?

[avare]

Originally Posted by guitarwes

What is the bump before the null at around 60hz? Might it be floor resonance (this is an attic studio after all)?

It might be. I just looked over the the thread and saw specifics about your room's construction. Mind I am to fall asleep and it may be there.

Andre

[Glenn Kuras]

Yea if you could list your layout and how you have the acoustics set up, that might help a little more.

Glenn

[bpape]

Agreed. If we had:

- Room dimensinos
- Seating location
- Speaker location

that would give us a lot better idea of what the potential issues might be. Have you tried running a set of measurement with the mic back or forward 6" to a foot - or side to side 6" over? That'll give a quick and dirty idea of what it is or isn't and help narrow down the possibilities.

Bryan

[jwl]

There are a few possibilities, but as the others say it's impossible to tell for sure without more specifics about your room.

My guess is that your listening position or your speakers are set up in a null point of the room. If this is the case, you'll want to rearrange.

Everyone always needs more bass trapping. (I'm only half kidding)

Double-check and make sure your speakers aren't out of phase, though I doubt if they are because that is a null, and not a dropoff over the entire bass range. But double-check just to be sure.

What treatments do you have in the room now?

[wesarvin]

Wow, thanks for the responses. This is my first time with Sketchup, so bear with me. The room dimensions are 17' x 11' 4". The ceiling is 6' 11". There are dormer windows on the sides of the room. The mix position is 5'6" from the front wall, and the speakers are 3'4" away from the wall, at an equilateral triangle. If you need any more dimensions, let me know. BTW, the corner traps are 2 layers of 10 inch R-30, and the wall traps and clouds are 1 layer of the R-30. An earlier post of mine has the pictures of the room. Finally, does cable length make a difference in the phase of active speakers?





Thanks again for all of the help!!!!

[Glenn Kuras]

that would give us a lot better idea of what the potential issues might be. Have you tried running a set of measurement with the mic back or forward 6" to a foot - or side to side 6" over? That'll give a quick and dirty idea of what it is or isn't and help narrow down the possibilities.

I think this is the best advice you are going to get.

Glenn

[wesarvin]

Ok cool, here we go.

1 ft back--


6 inches Left--


6 inches Right--


For kicks, I moved some traps from my live room into the control room to see what adding more traps would do. I put 2 behind the monitors, one horizontally above the one on the back wall, another vertically next to it, and two on the back wall corners adjacent to the corner chunks. That makes for a total of 17 traps in the room. Sounded pretty good, but was it overkill? It didn't kill the big null!!--



Also, I replaced a long xlr cable going to the monitor with a shorter one of the same length as the other monitor. My gut tells me that this helped and it could have been a phase problem, but we all know that the only answer is to measure with hard numbers!

[danbronson]

Were those measured with the new XLR?

It's actually pretty good response except for ~65 and ~230 Hz. 230 Hz is not hard to take care of if you position the trap right, but 65 Hz will go straight through a lot of traps without a problem. That one could be pretty tough.

If that were my room, I'd probably cover the wall you're facing with thick traps and stick traps in all the ceiling/wall and floor/wall corners as well. You only have one of those covered atm. If you're not DIY, it would be pretty expensive.

[wesarvin]

Yes, those tests are with the new XLR.

Thankfully I'm DIY. The two rooms together cost under $250 in supplies ($150 for control room, $90 for 11 traps in live room). Would sacrificing 2-4 traps in the live room be better, without having to spend all the friggin' time building more traps?

[avare]

Can you marker the low null? If you can, is it near 84 Hz? That is the SBIR null for speakers 3'4" away from a wall behind it.

Andre

[danbronson]

Originally Posted by guitarwes

Yes, those tests are with the new XLR.

Thankfully I'm DIY. The two rooms together cost under $250 in supplies ($150 for control room, $90 for 11 traps in live room). Would sacrificing 2-4 traps in the live room be better, without having to spend all the friggin' time building more traps?

Yeah, sure. At least see if it makes a difference. Hope it does!

[wesarvin]

Ok this is a regular graph of the new cable and the regular trap setup (as seen in the sketchup model).

[aluman]

Originally Posted by avare

Can you marker the low null? If you can, is it near 84 Hz? That is the SBIR null for speakers 3'4" away from a wall behind it.

Andre

Try to move your speakers a little closer and further to the wall to see if the frequency of the null moves .

[avare]

Thanks Guitarwves. You could in the middle of the null from the side walls. Next time you measure room, do a test with the microphone right against one side wall or the other.

Andre

[jwl]

I'd suspect that the length of the room is related to this.... the wavelength for 65Hz is near 17'. As a result, I'd add more bass trapping to the rear wall, as well as the front wall directly behind the speakers.

I'd also try moving my speakers and/or my listening position a bit, a few inches left/right, as well as backward/forward. Make sure you aren't in a null.

[bpape]

Since you moved the seating position back 1' and still had the null in approx the same place, I'm guessing that it's not related to seating position with regard to the length. I think Andre is on the right track with the SBIR issues.

What was the thickness of the panels you placed behind the monitors and where did you put them height wise?

Bryan

[Glenn Kuras]

FYI
Learn what is SBIR (Speaker Boundary Interface Response).
Just in case

Glenn

[Glenn Kuras]

Before the question is asked.

SBIR (Speaker Boundary Interface Response) - This is a term to describe how the proximity of a speaker to a hard boundary (wall/ceiling/floor) will change the response, especially in the low end. This is something that not a lot of people understand nor consider when planning a room.

Sound radiates from a driver in different ways. Higher frequencies act like a ray and move in straight lines from a point. As you get lower in the spectrum, they begin to radiate more like a sphere. By the time you get below 500Hz or so, you're getting pretty spherical radiation. By the time you get to 125, it's purely spherical.

That said, imagine sound coming from a driver at say 100 Hz that is coming directly at you. There are other waves that are wrapping around the cabinet and bouncing off the front wall and then back at you. When 2 waves of the same frequency meet in this way (one direct, one having bounced off the front wall) there is an interface of the 2 waves (some describe this as interference).

Constructive interference occurs when the 2 waves happen to be in phase with each other. This yields a reinforcement of that frequency or a peak in response. Destructive interference occurs when the 2 waves are 180 degrees out of phase. This yields a partial cancellation of that frequency (the bounced wave has less amplitude) resulting in a dip or null at that frequency.

This can cause WILD variations in frequency response. However, one can sometimes use this to your advantage. If you play with speaker positioning in relation to the front wall (behind the speakers) and the side wall, you can 'tune' the response changes. This can be beneficial when attempting to smooth overall response.

Let's say that you have peak at your listening position at a given frequency. If you can find a place that images well and works with the video positioning that will create a slight dip due to SBIR, the net effect is a smoother response at your seat. It's kind of like using an EQ without having to put one in your system.

Generally, you're best off if the distance from speaker face to front wall, driver centers to side wall, and driver center to floor are 3 different dimensions in order to not reinforce any specific set of harmonics by having all the boundaries generate the same SBIR effect.

If you still have issues, you can treat the walls directly beside and/or behind the speakers with appropriate materials to further reduce the intensity of the reflected wave to it's imact when interacting with the direct wave is minimized. If you have issues say from 125Hz up but OK below that, then a thinner panel may be in order - say 2". If you have problems all the way down, then something thicker may be appropriate.

Also remember that there will be interactions between the sub and boundaries and also between the sub and mains and their boundary responses.

[wesarvin]

Thanks guys. I just measured and the speakers are almost smack dab in the middle of all three measurements (about 3 ish feet from all walls, including floor/ceiling. I'll move and measure them in the next hour. And Andre, before moving them, I'll measure near the side wall too. BTW, do you prefer the waterfall plots or line graphs?

Oh... the traps on the front wall were 4 inches and vertically on the floor (quick and dirty setup).

[avare]

Thanks for the quick reply Guitarwves. Right now I would prefer line graphs if it has to be one or the other. Mostly because determining actual frequencies is easier.

If I had a choice, I would want both.

Andre

[wesarvin]

Ok this is the mic against the side wall--



This is when I moved the speakers about two feet to the right. It is slightly impractical to have them there (makes me feel claustrophobic in a corner of the desk).


And finally, here it is with the speakers in thier original location and 4 additional traps, 2 on the front wall and 2 on the side walls in front of the rfz panels, All propped up against the wall about 2 feet off the ground.



If stealing traps from the live room, which 4 would be the best to steal? (there are 3 in a cloud above the drums)