Technical Assistance

Positioning the loudspeakers
Free standing or suffit mounting
Flush mounting
Rear speakers
Definition of sound
Reverberation
Room acoustics
Audio system and room acoustics are the total solution
Resonance treatment
Reflections treatment

1. Positioning the loudspeakers

Placement of the monitors strongly affects the mixers perception of the sound. For the low frequency, the relation with the real wall and the size of the room will be predominant. For the mid and the high frequency, the relation with the axes of directionality will also be predominant. For the complete frequency range, the relation with the distance between the speaker and the mixer will be predominant.

An equilateral triangle has to be formed between the speakers and the mixing position. This easy geometry is as efficient in near field listening as in mid or far field listening. Place each speakers at the same distance from their respective walls. Keep perfect symmetry between the speaker and its distance from the left wall and the second speaker its distance from the right wall. The axes of directionality should be focused on the mixer (either vertical axe as the horizontal axe).

2. Free standing or suffit mounting

The biggest problem at low frequency is the interference between the sound generated by the speaker and the reflection from the rear wall. These reflections come back towards the listeners. The addition of direct and delayed reflection causes phase interference in the low frequency signal. Interference are recognised by cancellation dips in the frequency range. To be sure that this problem will not affect your listening, place your speakers at ¼ wave length of the lowest frequency that your speaker can generate (e.g. if your speaker's lowest frequency is 50 Hz, place it at 1,7 meters from the rear wall).

If you don't have space, put the speakers close to the wall and use the deep switches at the rear of your speakers to decrease the level of low frequency reflected from the speaker.

3. Flush mounting

Flush mounting, the speakers will put you in half-space conditions. Of course, low frequency will increase up to 6db. But you will reduce all diffraction effects and eliminate unwanted sound radiation from the cabinets. Of course, the speaker will be at a maximum of pressure and for that reason will excite more standing waves in your room. It is very important to properly build this flush mounting. Build a support as heavy as possible and put the speaker on line with the external surface. Precision, transient response and stereo image will be much better. The mounting should be as tight as possible. The speaker should just fit in the hole, with as little space as possible left between the top and the sides and the hole itself.

4. Rear speakers

The rear speakers have to be placed at the same height as the front speakers in order to guaranty acoustical symmetry. To guaranty the best surrounding environment, please use a min. of 4 rear speakers. This way you will reduce directivity problems and you will create a much bigger comfort working zone all around the mixing position. All the surround have speakers to be at equi distance from the listening area to be covered.

5. Definition of sound

As a basic description, we can say that sound consists of waves containing amplitudes and frequency characteristics :

- the amplitude is the energy of the waves and is measured as sound pressure level (SPL) and is expressed in db.

- the frequency is the speed at which a wave, crest to crest , completes its cycle per second and is expressed in Hertz (Hz).

One frequency alone is a pure tone, like a sine wave. Music or speech characteristics are not easy. They include a wide range of frequencies occurring simultaneously and are original frequency. Human hearing is limited to a spectrum starting at 20 Hz to 20000 Hz :

- 20 Hz is a very long wave length (low frequency), the woofer will generate these frequencies (20Hz-150).

- 500 Hz is a medium wave length (mid frequency), the mid range will generate these frequencies (150Hz-2000Hz).

- 8000 Hz is a small wave length (high frequency), the tweeter will generate these frequencies (2000Hz-20 000Hz).

6. Reverberation

The reverberation time tells you how long it takes for reflected sound to decrease to 60 dB, called RT60. In a small room, it is frequently impossible to measure a 60 dB decay, so we do it for 40 or 20.

The reverb time described by Sabine is a world wide reference to know how live your rooms, the level of the first reflections will be more significant. The delay of these first reflection will let you know how long large the room is. Reflection is function of the volume of the room and its absorptivity (the x value). Optimal reverberations are given by several charts.

A Standing wave is a wave that resonates between two surfaces of a room. Its amplitude is continually reinforced. The value of the lowest one is twice the value of the room's largest dimension.

7. Room acoustics

The difference between a good and bad recording can come from acoustical qualities or lack thereof your room. Room acoustics can create the best or the worst atmosphere, isolate instruments or mix them in an infernal common blur. We call this part of acoustics : the "technical way". These aspects are the first evidence of results, but don't forget the secondary effect of poor acoustics. When playing in good acoustics, musicians will perform enthusiastically because they are pleased, because they can communicate with each other. We call this part of acoustics : the "emotional way". To get good working conditions, room acoustics must be a priority either in professional or home studios. Of course solutions must be financially adapted.

The owner of the studio has to be precise about the desired acoustics.

8. Audio system and room acoustics are the total solution

The audio system is half of the solution. The room acoustics are the other half of the solution. A room (anechoic room expected) is never neutral, it always affects your listening perception because room, boundaries act like a filter affecting phase, and thus frequency response. The low frequencies are "non directional" and so can diffract and bend around most objects in the room.Take care about own modes, standing waves. At such low frequencies we have to consider that the room acts as a resonant chamber and so directionality is not a critical factor. The mid and high frequencies are highly directional and don't diffract but always reflect on objects or boundaries (never forget the relationship between the size of the objects and the wave length). At such high frequencies we have to consider that the room acts as a reflector and so directionality is a real critical factor. The way of light method will help you to find the reflections you have to avoid.

9. Resonance treatment

To keep a good brightness according to the size of your room, note that a slight roll off of frequencies above 10 kHz is good for large rooms while an equivalent roll of above 15 kHz is the one needed for a small room.

As shown before, low frequency creates resonance problems. These own mode or standing waves are very powerful (max of energy), and influence your perception of the low frequency in quality and level.

To avoid these problems, you can use the FAR basstrap pannels.

10. Reflections treatment

As explained before, quality of the speakers directivity is in close relationship with the walls reflections. These reflections don't contain much energy, but modify dramatically your perception of stereophonic and your frequency curve.

Good reflections and bad reflections : in a listening environment, you need to add to your direct sound the early reflections (below 20 milliseconds) and the late reflections (after 20 milliseconds). The listener generally perceives the early reflections as part of the direct sound, and these cause phase cancellation, break the stereo image and mask the reverb already recorded on your tape.

To avoid these problems, you can use the FAR absorptive panels. The absorptive panels are very efficient and the listener perceives the late reflections as an open and natural feel to the listening space. To get the decay of these as regular as possible, diffuse them the most you can using FAR diffusers. Too many diffusers can make the room sound larger than reality. Efficient diffusion conditions enable everybody to hear the identical balance.