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Author Topic: Less bass trapping equals more accurate low end?  (Read 2816 times)

Chris Griffith

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Less bass trapping equals more accurate low end?
« on: April 29, 2009, 08:40:52 pm »

Over on gearsluts there is a thread where someone had Bob Hodas come check out there room.  ( http://www.gearslutz.com/board/studio-building-acoustics/370 542-preparing-acousticial-evaluation-friday.html ).  

In case you don't feel like reading the entire thread, in the end they took out some broadband panels and it gave a better low end response.  The room wasn't symmetrical so I'm sure that changes things. Can too much trapping in a symmetrical room be bad?

I'm thinking I might have overtrapped my room.  I have around 20% to 25% of the total cubic volume of the room trapped.  The low end is so 'tight' in there its hard to hear.  From running tones it seems to be very even, its just not full and punchy when you listen to music.  

I had an outside producer (who has a couple gold records under his belt and has worked in tons of top end rooms) recently come do a project and he commented on the same thing.  He had to sit in the back of the room and get some bass buildup to hear the low end.  

I was always under the assumption you couldn't overtrap with broadband absorption.  Now I'm confused.

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Thomas Jouanjean

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Re: Less bass trapping equals more accurate low end?
« Reply #1 on: April 30, 2009, 03:45:11 am »

IMHO, too much of the 'same type' of trapping can be bad (and it usually is). In general, broadband isn't that efficient from 100Hz down. So trapping with only one type can mean and usually leads to an unbalanced room with tight 125Hz and ringing 80Hz for ex.

Also, too much trapping can cause the room to be too dead, and thus uncomfortable (for most) to mix in. But that's also a question of taste... Many of my clients that do Electronic Music are looking for a "headphones" like room = very dead.

Therefore, it's very important to spread the type of treatment, watch your RT and really pay attention at how the energy spread is managed and treated overall in the room. A good room is really like an organic system, with everything in it's right place.

Didn't read the GS thread, but from what you say I'd say there could be interactions between room modes and/or ER that are such that trapping one of the factors actually ends up reducing LF perception at the sweet spot.

What I mean is: if you have one problem that is counter balanced by another on a specific and limited LF bandwidth, if you treat one of them you end-up hearing more of the other (so less bass for ex). But I'd say if your room is like that, then your bass response was ghost-like/phasey to start with, never defined: "there" but not quite there in a way.

About your room, if you have build-up near trapping, it's that it's not efficient enough in the LF. So it means you pbly have problems in those frequencies in your room (maybe you have a ghost-like bass problem?). In this case I would not reduce the amount of trapping, I would modify the type and maybe placement. In Rooms where the low-end is well controlled, wherever you stand in there it basically sounds the same.

Try and move your treatment between 10 and 20cm further away from the wall and see if something interesting happens.
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Thomas Jouanjean
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Ethan Winer

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Re: Less bass trapping equals more accurate low end?
« Reply #2 on: April 30, 2009, 02:04:14 pm »

Thomas gave you good advice. I'll add that the only way to know what you have now is to measure using appropriate software. You need to see not only the LF response, but also decay times and modal ringing. The freeware Room EQ Wizard program is very good, and the only other thing you need is a decent SDC omni microphone.

I'll also add that I do not believe it's possible to have too much bass trapping, at least in a domestic size room. However, you can have an imbalance in absorption versus frequency, which Thomas mentioned.

--Ethan

franman

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Re: Less bass trapping equals more accurate low end?
« Reply #3 on: May 04, 2009, 08:47:52 pm »

ditto (on both posts)... not too much, too much concentrated in one area for sure...
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L_Tofastrud

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Re: Less bass trapping equals more accurate low end?
« Reply #4 on: May 18, 2009, 11:44:55 am »

a lot of LF absorbtion will drain some efficiency from the speakers so it is advisable to do a proper room tuning. If it is a main monitor system you have issues with you can insert an EQ and make adjustments to taste. If it's a small powered monitor system you should make sure it's set to the maximum bass (free space) setting.
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Steve Hudson

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Re: Less bass trapping equals more accurate low end?
« Reply #5 on: May 18, 2009, 12:39:14 pm »

We've trapped the rear and side walls and front wall-ceiling corners of our control room with 703 of varying thicknesses and are out of room there for any new trapping solutions, which leaves the front of the room (I doubt we could install a heavy Helmholz resonater on the ceiling). Would some sort of tuned absorbers work on the front wall or should we consider adding that type of device directly behind the 10" of 703 at the rear of the room?
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L_Tofastrud

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Re: Less bass trapping equals more accurate low end?
« Reply #6 on: May 18, 2009, 01:45:17 pm »

Steve Hudson wrote on Mon, 18 May 2009 10:39

We've trapped the rear and side walls and front wall-ceiling corners of our control room with 703 of varying thicknesses and are out of room there for any new trapping solutions, which leaves the front of the room (I doubt we could install a heavy Helmholz resonater on the ceiling). Would some sort of tuned absorbers work on the front wall or should we consider adding that type of device directly behind the 10" of 703 at the rear of the room?

My initial thought when reading this was "be careful with the 703". If the deepest you have is 10" you might find that midrange and top end is damped too much in comparison to the real LF. 10" isn't gonna help you out much below 300 Hz and worst case, nothing below 100 Hz (and the room will start to sound bass heavy). I say "worst case" because it all depends on how you mount it and how big an area you cover.
The aim of room treatment should be to get the sound to decay somewhat evenly for all frequencies.
This is why I'd recommend corner traps instead of covering the whole wall (at least as a starting point). Corner traps will give you more depth in the pressure zone of pretty much all modes and the limited front area (in comparison to treating a whole wall) will reduce the impact on HF. HF treatment is easy and in my opinion you're better off placing it where you have first reflection from your loudspeakers.
We use tuned absorbers behind porous treatment regurarly - especially in existing rooms to trap a few of the lowest modes and any problem modes we come across. Placement of these traps is very critical though.
Even for DIY room treatment you will need some measurement software - preferably something that is capable of 3D graphs (ETF and Fuzzmeasure comes to mind) so you can see the decay difference between LF and HF. You'll also need a real omni mic like the $50 Behringer ECM8000 (or similar).
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Steve Hudson

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Re: Less bass trapping equals more accurate low end?
« Reply #7 on: May 18, 2009, 03:03:52 pm »

Thanks, Lars. We do have wall-ceiling corner trapping on the whole front wall and extending beyond the first reflection points on the side walls, plus 4" 703 with a 4" gap behind on the side walls, but given the geometry and location of doors in the CR (we didn't build it and can't move the doors), we can't trap any vertical (wall-to-wall) corners except at the rear, where the 10" traps (8' wide) go all the way from the floor to the ceiling. Of course, we could extend the wall-to-ceiling trapping all the way to the back of the CR or mount floor-to-wall traps where they wouldn't impede foot traffic, but our issues are below 100 Hz and as you say there's a limited effectiveness of broadband absorbers at and below that frequency. I also took into consideration the posts above that say to use a variety of LF management solutions, ergo the interest in building and installing panel absorbers instead of just throwing more 703 at the problem..
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"The music business is a cruel and shallow money trench, a long plastic hallway where thieves and pimps run free, and good men die like dogs.  There's also a negative side."

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