got hole in my 200Hz. to 300Hz. range

[sonic-man]

I just ran a couple tests on my 'control room' and found it has a bumpy response but the bumpyness is fairly even across the spectrum except for a hole in the 200Hz to 300Hz. range. The 'bumps' are >6dB in many cases and the hole is >9dB in places. So i'm going to try to address the hole first and hopefully the rest can be smoothed out as well.

The room dimensions are 30' by 10' with 8' ceiling. I'm limited in where i can put the console/speakers so they are approximately against the middle of the 30' wall length, speakers about 6' apart. I have a feeling the 10' wall by 8' ceiling is just about right to produce a standing wave that supresses roughly ~250Hz. or so.

So, i have a feeling that treating the ceiling directly above and walls directly infront and behind the speakers somehow might do the trick. I'm thinking thick absorbers in the mixing area ceiling and walls behind the speakers and the opposite wall 10' behind the mixing position. Or should i look at tuned traps maybe? or... what you think?

[suprstar]

Bass traps in the corners. 4 2'x8' panels with 4" OC703 can be put together for a couple hundred bucks, that'll definately soak up a lot of lows and calm those nulls and voids down. Sounds like you've realized the response is different in diff. locations in the room. Do some trial and error, you can find the best spots to place your amps and mics.

Putting a panel behind your monitors or on the ceiling is for killing off 1st reflections, which are gonna be your higher freq's anyway. That's all good too, but controlling bass freq's is more important imo. What are the walls and ceiling made of?

[yancrazy]

Here are some basic rules that are pretty standard do's and dont's.

(1) Nearfield positioning: make sure that both speakers are pointing directly at the spot where you'll be mixing.
Ideally you need a 60º angle between the monitors, and if they are above the height of your head, make sure
they're pointing down towards your ears. Remember that for critical work (such as mixing) you need to be sitting in
the sweet spot to get the correct impression of the music you're listening to. Moving out of the sweet spot will
detrimentally affect the sound you're listening to, so don't make any major decisions while away from your desk.
Also, make sure that your nearfields are, indeed, in the nearfield; anything between 0.7 and 2 metres between
your speakers and your ears is okay.

(2) Nearfields, in most cases, should be mounted on stands. Mounting them on the meterbridge may be
convenient, but you'll get a whole load of reflected sound off the panel of the mixing desk, whereas you really only
want to listen to direct sound. Mounting them on stands will avoid this, and is also a solution to problems caused
by mixing in front of a computer monitor. It's also preferable to mount nearfields vertically, though of course some
models are designed specifically for horizontal use.

(3) Symmetry of installation: it goes without saying (I hope) that your monitors should be the same distance from the listening point, but they should also be symmetrical within the room (i.e. the same distance from the side
walls). Why? Because you'll hear reflected sound off these walls, and you need to hear the same on either side, or
it'll mess up your stereo imaging. The same goes for gear in front of the monitors, which should also, if possible,
be symmetrical, so if you have a rack in front of the desk on one side, try to have an identical one on the other
side.

[yancrazy]

Tuning a room is quite often a massive mathematical problem to deal with and as you have already run some tests on your control room i think you can handle some more info that i dug up from an future music mag i have at home.


Why is it that you always seem to hear people talking about problems with bass in their studio, and rarely with
high frequencies? Why does it seem to be that those low frequencies are so problematic? Or is it just myth? Well,
it is true that low frequencies are more problematic, and the reason has to do with the radiation space in a room.
The radiation space is the geometrical surroundings of a speaker, and is frequency dependent. If the speaker is in
the middle of a field (for example), there are no limitations to its radiation space and it's known as 'free standing'.
As soon as you place it in a room, however, the radiation space starts to be limited. If your speakers are soffit
(wall) mounted, or right next to the wall, they can 'see' only half the space now, and if placed by two walls, the
radiation space is divided by four. A typical corner, with two walls and a floor would cut this to an eighth of the
radiation space of our monitor in the middle of a field. But what does this mean in practise?
A decrease in the radiation space means an increase in energy density in that immediate area (i.e. higher SPL
levels), and the theoretical value is 6dB for every time the space is halved. So soffit-mounting your speakers will
give 6dB of boost, and in a corner (with two walls plus floor) this will give 18dB of boost. But remember that we
said earlier that this is frequency dependent, and the way it works is that the radiation space is limited by
'reflecting surfaces that are large compared to the wavelengths'. So for low frequencies this means the walls, the floor and the ceiling, for mid frequencies it's mainly the speaker baffle and objects near the speaker, while for high
frequencies it's entirely the speaker baffle and driver itself. Now you understand why it's the bass frequencies that
cause all the trouble?
1. +6dB bass boost at boundaries: Now we've understood the effects of limiting the radiation space of a
speaker (i.e. placing it in a room), and that it's the low frequency effects that are most apparent, let's look at some
practical examples. Many big studios choose to soffit-mount their monitors (Wall mount), and by
doing this they will experience a 6dB boost in the low frequencies, since the radiation space is halved. In this
case, the bass response of the speaker should be cut by at least 6dB to compensate. Placing a speaker very
close to the back wall will also have a similar result, and the same action should be taken.
If your speakers are in the corners of a room, you'll experience a bass boost of between 12dB and 18dB,
depending on how close they are to the floor (above about 1.3m the floor won't have a significant effect). Again,
this needs to be rectified by cutting the bass response of the speaker. Great - your bass frequencies are under
control? Or are they? There's another factor that has to be taken into account when deciding how far away from
the walls you place them...
2. Frequency cancellation caused by wall reflections: Another reason why many studios wallmount their
speakers is to avoid cancellation of frequencies caused by wall reflections. This effect is easy to explain: if a
speaker is a quarter wave-length away from a reflective wall, the reflected wave returns to the speaker with a halfcycle
phase difference (2 x 1/4 cycle, kapiche?) - i.e it's in antiphase.
If this is a perfect reflection then the cancell-ation will be complete, though in reality this is unlikely to be the case
(due to absorption by the surface). Nevertheless, the effect can be very audible indeed, and a problem that needs
to be solved. Naturally, this will occur in more than one direction too, so several frequencies may experience
cancellation.
The solution? Apart from flush mounting (which eliminates reflections) you can either place the speaker very close
to the wall, or considerably away from the wall. In the first case, the cancellation frequency is so high (work it out
yourself using the following equation: wavelength = velocity of sound (343m/s) / frequency) that the effect is
overlapped by higher directivity and higher density of room resonance modes.
If you take this option, remember that placing your speaker close to the wall will result in 6dB of bass boost
(covered in point 4) and you'll need to take corrective action.
The other solution is to move your speakers well away from the walls, where the cancellation frequency is so low
that it'll have little effect on the music anyway. But just how far away? Well, using the above equation, a distance
of three metres will give a cancellation frequency of 29Hz, which isn't going to cause anyone problems. Even at
two metres, the cancellation frequency is an acceptable 43Hz (2 x 4 = 8, 343/8 = 42.875), but of course this all
depends on how much space you have to spare.
3. Positioning of subwoofers: Subwoofers have been used increasingly in recent years in conjunction with
nearfields to give an extended frequency response in the absence of (a) a large room (b) budget for a pair of fullrange
speakers and (c) both of the former. But does it really matter where you place the subwoofer?
Frequencies in this bandwidth are omni-directional anyway, so surely it doesn't matter where they're placed? Well,
not quite... (you knew I was going to say that, didn't you?). Firstly we should look at the +6dB effect at boundaries
(covered in point 1). If you have a large room, you can place the subwoofer 3m away from the closest walls, and
you'll avoid the 1/4 wavelength frequency cancellations covered in point 2.
The subwoofer can be either facing the floor, or into the room, but you will have to adjust the unit's response to
take into account the effect of the boundary (the floor) by taking off 6dB of gain. In a smaller room, the unit should
be placed close to the front wall(s) (between 20 and 80 cm) to avoid any frequency cancellation due to the 1/4
wavelength phenomenon. If this is in the centre of the room, with two boundaries (floor and wall) then the
response of the unit should be adjusted by 12dB, and in a corner (three boundaries) it should be adjusted by
18dB.
There is another factor to take into account, and that's the general room behaviour, its standing waves and axial
modes. We will be covering these issues in next month's instalment, so we won't go into too much detail here.
However, a quick explanation would be that by placing the subwoofer in a pressure minima (which, coincidentally,
would generally be the case if you placed the unit on the floor behind the mixing desk and between the nearfields
in a small room) it causes the subwoofer problems in generating high enough SPLs. One solution is to move the
sub slightly off the centre line, which puts it in a more balanced sound pressure zone.

Sorry for the wall of text.

[yancrazy]

As you can see it becomes very complex when everything is being taking into consideration which is why if you are chasing that perfect sounding control room then its probably worth paying a professional to come in and tune the room for you....no idea about cost on that though sorry.

[yancrazy]

Originally Posted by suprstar

Sounds like you've realized the response is different in diff. locations in the room.

Remember there is only a small area around the sweet spot that will sound as intended....thats why its always important to allow the client to sit in your chair when it comes to show and tell time.

[sonic-man]

Great! Thanks for the info guys! Yancrazy, ...So i will start by moving the monitors closer against the wall because they are ~about 1 wavelenght[4'] away at 200-300Hz. and see if that alters the pattern.

I realize the ratio given for the null is 1/4 the wavelenght so there should be a null at somewhere around 66Hz. if my room were big enough. I still think the speaker to wall distance may be the culprit.

The other thing i can do is open 4 doors into an almost equal sized space on the other side of the back wall. Each doorway will act as a resonant trap i guess eh? So if i put damping i the door ways they could become collosal traps, right? something like that anyway. Ok, i'll try some stuff.

BTW - I found some nice fat US made moving blankets on the internet, and they also have extra plush ones for movie sets and recording studios. You get 12 80"x72" for about $125. They can put things in them for hanging. you ever tried these things? The good thing is they don't have to go against the walls so you can extend the damping to low frequencies.

[yancrazy]

Yeh you are onto the right kind of thing m8, like i said its a science at the end of the day and it all starts with nearfield placement. If im honest 66Hz is not great but its probably better than what you had. You will find that you will for sure get some confusing signals when mixing Kick and sub bass into your mix. Also something that may help a lot is making sure that the nearfields arent grounded....make sure they are sat on some kind of foam or rubber so that the low end isnt travelling through your whole desk lol...sounds obvious but so many ppl miss it.
Also pay particular attention to "speakers and equal distance apart from the side walls otherwise you may get an off balanced mix.

Moving Blankets sound like a nice cheap way of soaking up some of the unwanted low end return....let me know how you get on with them.
Also BrandonFury found a neat way of encasing guitar amps in some material....might be worth seeking that post out...sorry i couldnt track it down for you

[yancrazy]

Here is a link for anyone in the UK looking for a cheap solution to acoustic treatments for their studio.

Advanced Acoustics - Studio Acoustic Treatment - Rockwool Flexi Slab

They would probably ship to U.S aswell although i think its more cheaper for you guys to buy it over there.

[brandondrury]

So, i have a feeling that treating the ceiling directly above and walls directly infront and behind the speakers somehow might do the trick.

I think you are definitely on the right track, but corners are where I would start.

I'm thinking thick absorbers in the mixing area ceiling and walls behind the speakers and the opposite wall 10' behind the mixing position. Or should i look at tuned traps maybe?

In order to absorb a frequency with sheer thickness, your absorber needs to be half the wavelength of that frequency. If you do the math you are going to be shocked at how long a 100Hz wave is so the only practical solution is to use a tuned absorber.

Brandon