Frequently Asked Questions - Rooms & Acoustics

Here are our answers to the questions we get asked the most. If the answer to your question isn't here, send us an email and we'll add the most popular new questions.

What’s so important about room acoustics?

How do I measure the frequency response of my room?

My room is too boomy, some notes rattle the windows.

The sound is muddled, I can’t make certain instruments out.

How can I soundproof my room?

What’s so important about room acoustics?
Your listening room is the last link in the audio chain and is also the weakest link. After all the precision and care taken in reproducing the original sound through the electronics and the speakers, the room has to convey the sound from the speakers to your ears. It is in this last stage that the sound can be grossly corrupted from reflections off of just about every surface in the room. The room’s ability to store sound energy, known as reverberation, also impacts the sound quality. Even the most expensive sound system can sound truly awful when installed in a bad room.
People talk about how “live” a room is. Halls, gymnasiums and bathrooms are examples of live rooms. A subway carriage full of people, a well-stocked library and a closet full of coats are dead rooms. The difference has to do with the rooms resonance.
The two key measurements you need to evaluate a rooms acoustic properties are the frequency response and the time decay response of those frequencies. Unfortunately, these measurements can be different at each point in the room. In reality you need to average a many measurements taken at a number of points in space including those where people sit.

How do I measure the frequency response of my room
You need a high quality, calibrated microphone, some test signals and an audio analyzer. These days a soundcard and a laptop have all the tools to perform audio analysis and many good programs exist.
The simplest method is the swept sine method where you play a sequence of single sine tones through your system at a constant amplitude and measure the sound pressure level at each frequency and point in the room. You average all the points for each frequency and voila.
Other methods use a very short pop or impulse or a special noise sequence to measure every frequency at once. These methods  require special techniques and good math skills to ensure accurate data.
The tricky part is knowing what to do with the results. There will be many peaks and dips and it may look more like a mountain range than the flat line you were expecting. Fixing problems requires some detective work and some imagination.

My room is too boomy, some notes rattle the windows.
This is the usual impression of a room with modal resonance problems. Certain low frequencies are accentuated and seem to hang in the air for a long time while others are feint. A scale played on the bass will seem to fade in and out, each note playing differently.
Easiest thing to try is moving the speakers around paying attention to distance from the walls and proximity to corners. Next search for hard, parallel  surfaces on opposing walls. Measure the distance between these surfaces and see if they relate to the wavelength of the problem frequencies. Here’s a chart for reference:

The sound is muddled, I can’t make certain instruments out.
When the direct sound from the speaker is mixed with many equal level reflections from nearby furniture with large hard surfaces, clarity is lost. The ear cannot catch enough of the direct sound to distinguish it before the barrage of reflections confuses the sound.
Solving these problems requires either moving the speakers to a more open location, moving the furniture or hard surfaces away from the speaker or treating the hard surfaces to make the absorptive or diffractive. Both techniques reduce the level of the first reflections making the direct sound dominant.

How can I soundproof my room?
There is often need to block sound from being heard in adjacent rooms, in an apartment or next to bedrooms for example. Making a room completely soundproof is pretty much impossible as a retrofit, but you can usually make a significant difference. Here’s a list of things to check and consider in order of effectiveness.

• Achieve an air-tight seal around doors and windows. Sound moves through air and so can pass through the smallest crack. If you can feel a draught under a door or around a window then there’s a lot of sound getting in and out too.
• Don’t mount speakers on walls shared with bedrooms or neighbors. Speakers are heavy and require rigid mounts. Unless properly treated, these mounts will couple sound into the wall structure and cause the entire wall of the adjacent room to act as a passive loudspeaker.
• Consider heating and air conditioning vents. These are usually a large open pipes connecting all rooms together. However, reducing acoustic coupling in air vents usually works against their intended purpose of moving large quantities of air. Be careful any modifications don’t overload your ventilation motor.
• Add more diffractive furnishings. By diffusing the energy more evenly around the room, coupling hot spots can be reduced. This can be a powerful technique.
• Add more absorbent furnishings. By deadening the room you reduce the energy in the room and so reduce the coupling to adjacent areas. This can degrade your sound quality though if too much absorbency is added.
• Use a rug to reduce noise to a room below. Even if you have carpet and felt, a good rug in the right place can help.