A Tale of Sound Nodes and DB Readings

It has been a few days since my last post. Okay, actually almost an entire week. It has been a busy one for sure. Chris was spent all week working at home and I spent as many days/evenings as possible over there working on getting everything up and running with him.

Chris spent most of his time setting up gear (computer, synths, etc) and wiring all of it together. A slow, methodical process that is extremely important with the amount of cable that will be required. We cannot have a rats nest back there because it would be a nightmare to manage or re-route anything if we have to. We are talking a few hundred cables that have to be managed and this is not something we can slack on.

Chris has also begun the fun chore of organizing everything. We have tons of boxes sitting around. Some contain important parts, cables, and accessories that we will need as our gear gets setup. Other boxes are full of old parts and cables that are worth keeping but not needed at the moment. We are slowly moving the un-needed stuff from the studio into the basement of the house. It is amazing seeing the space change as pieces are getting set-up and boxes are being moved out.

I spent the last three studio work days on tuning the room. I don’t know if this is the correct “technical” term for what we are doing, but it is a good description of the end goal.

The ideal control room should have a neutral sound. What this requires is special sound foam and diffusers to help stop sound reflection off the walls and ceilings that create sound nodes and anti-nodes.

Here is a little sound primer for anyone that is actually reading this. Sound reflects off surfaces just like light. So when a sound wave is generated from a speaker the wave goes off in all directions. When the sound hits a hard surface (such as a wall) it will reflect off the wall at an angle (think skipping a stone off water). As the wave bounces off one wall it can hit another wall and reflect again. This reflection or bouncing off walls creates echo or reverb.

The problem with reverb is that as the waves bounce around they can collide with other waves in the room. A couple of bad things can happen when two waves collide. If the waves collide and they are at the same amplitude in the wave they will be added together and create a larger/louder wave.

This additive wave creates a node and the sound (most apparent with bass) is much louder and prominent in this position. If you try to mix while sitting in a node then all the music will sound heavy in the sound range that the two waves are at. For example, if two low frequency waves collide it will create a bass heavy sound. This extra bass will effect how you EQ the song and cause the balance to be off.

An anti-node has the same effect, but in the opposite way. When two waves collide and they are at the opposite amplitude of the wave they will cancel each other out. This means that if you mix from this position everything will sound baseless.

An ideal room has no nodes and this means that you can sit anywhere in the room and it sounds the same. To do this you need to minimize reflection or disrupt the reflection so that waves will not collide. To do this you use studio foam and diffusers.

A diffuser is an oddly shaped piece of plastic. The shape is designed is such a way that as waves hit the diffuser they get sent in many different directions. This helps limit direct reflection and limits possible node points.

Studio foam come in many different thicknesses (1 inch – 3 feet) and stop different frequency ranges depending on the thickness and mass of the foam. We are using 4” foam on the front walls, 2” foam on the side walls and ceilings, and 1’ thick foam on the back corners. The 4” and 2” foam trap and stop high and mid range frequencies from reflecting. The 1’ foam (called Venus bass trap) is designed to catch the low end frequencies. We have also placed 6 diffusers on the ceiling to help diffuse any reflections.

The shape of the room is also important. A box room will cause much more reflections so you want to avoid 90 degree angles. Our room is oddly shaped and we only have one 90 angle in the entire room. This design will also help prevent reflections and also direct where certain reflection end up.

After our first pass at tuning the room we realized that we have some nodes. This is kind of a bummer, but it is to be expected. We are having a professional room designer come in and help us determine where the nodes are coming from and more importantly what we have to do to make them go away. We hope that it is a simple task and that we don’t have to invest a lot more into foam and diffusers.

The other interesting thing that happened this weekend is that we where able to set-up the drum kit. With the kit set up we got our first true test of the live room’s sound proofing. Unfortunately we did not ace the test. The room got a B+ but we think that we can do a few things and get it up to an A.

We broke out the DB meter to get a reading of the SPL (Sound Pressure Levels) to see how loud we are outside the room. We got a 68 db reading right by the door. That is pretty damn loud, but not bad since I had the meter practically up against the door.

The next reading I took was from the gate/fence between the house and the neighbor’s yard. This is the critical reading, because we only care how loud it is for the neighbors. There we where getting a 52 db rating. Much, much better but it still is too loud for late night sessions. We need to get the reading down to about 45 db* for us to have a late night jam session and not piss of the neighbors.

We talked about possible solutions and we think that once we rig up a blocker for the window, hang our foam in the room, put the drums on sound risers and create a heavy drape for the door we can shave off 6-8+ db. If this is the case we can get really close to the 45 db goal and night drums here we come!

*The 45 db rating is coming from the law books. If we can get below or at a rating of 45 db at night then there are no legal repercussions anyone can use on us. Realistically if we can shed 3 db then it will be hard for anyone to really complain about that. Sadly, there is a neighbor we are concerned about and we are doing everything possible to not disrupt or bug them.