Home studio: Introduction

Home studio: Listening position

Home studio: Speakers placement

Home studio: Use of acoustic treatment

Speakers placement - distance from the wall

Can't hear enough bass from your speakers? The distance between the wall and the speaker has a huge impact on low frequencies!

Especially at low frequencies, the speakers are practically omnidirectional, which means that the sound waves are also propagated backwards, towards the wall in front of the listening position. When the sound wave hits the wall, it is reflected and then interferes with the sound waves coming directly from the speaker.

The second problem we observe is when placing the speaker off the wall one quarter of the wavelength for a certain frequency. In this case, there is a disturbance of the sound wave of that frequency (the sounds wave gets almost cancelled), and such a decrease horribly affects the resulting sound.

Behavior of the reflected sound wave

Watch an animation of a sound wave bouncing off a border. After reflection, the sound pressure is zero at 1/4, 3/4, 5/4, etc. wavelength from the boundary (points in the wave that do not move). These points are called nodes and are places where direct and reflected sound always cancels each other out.

Let's say it's a sound wave with a frequency of 60 Hz. If you place the speaker on a node (1/4 wavelength from the wall), it will cause a zero or significant decrease of frequency response at 60 Hz.

As the opposite, 1/2 wavelength from the wall is the so-called antinode. This is the point where the two waves meet, and placing the speaker here will increase the frequency response at 60 Hz.

Remember: the frequency is always interrupted at ¼ the distance of the wavelength from the wall. A quarter of the wavelength from your wall means that the sound wave bouncing back on itself will hit half the wavelength (a quarter there, a quarter back). The reflected and direct sound is thus 180 ° "out of phase", with phase interference - the interference of the waves with each other.

The term for this effect is called speaker-boundary interference response (SBIR).

SBIR causes deep drops in bass responses below a certain frequency and can affect your low frequency response even more than the room modes. Because this effect cannot be corrected by software, two reliable means must be used: the correct placement of the speakers and the use of acoustic treatment.

How far from the wall should I place the speakers?

In general, we distinguish between three placement options, which we will describe:

• Placement in the wall

• Speakers as close to the wall as possible

• Speakers far enough from the wall

Flush mounting the speakers in the wall - absolute win

The only way to really eliminate the SBIR effect by one hundred percent is to embed the speakers into a hard, solid wall. Sound waves do not have the ability to bounce off the front wall because the speakers form the surface of the wall.

This kind of placement is used in the world's most expensive and best studios, but we hardly ever encounter it in our home conditions. This is a relatively expensive variant of the acoustic solution, but if you decide for it, do not forget to think about the following:

• Not all speakers are suitable for wall mounting. Consult the manufacturer first or refer to the user manual.

Option 2: Place the speakers as close to the front wall as possible

Even if you don't mount the speakers into the wall, you can still enjoy the proximity of the wall behind them. This is your second best choice for placing nearfield speakers, which we encounter most often in home studios and listening rooms. In this way, a quarter of the wavelength distance is shifted to higher frequencies, which are easier to handle by acoustic treatment.

In general, a gap of 0 to 20 cm between the speakers and the front wall is a good starting point for minimizing the SBIR effect on the sound. However, check the speaker specifications for the recommended minimum distance in the user manual (e.g. for cooling).

At very close distances, acoustic absorbers with a thickness of 10 cm behind the speakers can do a great job. As the distance of the speaker from the wall increases, absorption is less effective.

Option 3: Speakers far enough from the front wall

This placement option is demanding in terms of space, so it is especially suitable for large rooms. The speakers must be spaced far enough away from the front wall so that the lowest disturbed frequency is outside the frequency range reproduced by your speakers.

The easiest way to calculate the distance of the speaker from the wall is to use the following formula:

Distance min (m) = (1.4 * 343) / (4 * f-3dB)

Where f-3dB is the low cutoff frequency of your speaker. For example, if your speakers have a -3dB limit at 55 Hz, the minimum distance from the wall = 2.18 meters. Check the manual from your speakers to find out this value.

Little hint and simple summary

In general, you want to avoid the SBIR effect for low frequencies between 40-200 Hz. For typical home studio conditions with two speakers setup, this means (in most cases) the following speaker position:

• Ideal: Flush-mounted in the wall or as close to the wall as possible (see manufacturer's recommendations)

• Good: up to 1 m from the wall

• Avoid: 1-2.2 m from the wall

• Good: from 2.2 m from the wall