There is a direct correlation between your room's size and shape and the placement of your speakers. In a "long" room set-up, with the seating located in the middle of the room, it is best to mount the surround speakers on sidewalls parallel to the main seating position. If they were mounted on the rear wall in this room configuration there may be a pronounced "hole" in the sound stage, with sounds "jumping" from front to rear rather than there being a smooth transition. In a "short" room set-up with seating on the rear wall you might get away with speakers being mounted on the rear wall. Furthermore, depending on the distance of the side walls from the listener, you might prefer to use floorstanding speakers as surrounds instead of dipoles.

Only by selecting the proper speakers for your room you will have high quality sound. Do you need a simple stereo or a modern multichannel system? Keep in mind that modern multichannel home cinema systems are good not only for movie reproduction but also for high quality audio reproduction - SACD (Super Audio CD), DVD-Audio - as well as modern games consoles such as the X-Box and Playstation. You can listen to your favorite albums in a multichannel mix and feel a truly new experience.

Once you decide on a stereo or multichannel system (we recommend a modern multichannel system), consult the Crystal Audio Room Acoustics Designer - RAD®, a unique utility which helps you place your Home Theater in the optimum way into your own room. You can choose different types of speakers, according to your preference and room dimensions. At the same time you will be properly consulted for the correct placement of the speakers in the room based on the room dimensions, furniture etc.

Room Acoustics Designer® is more than a simple programme that selects loudspeakers based on the input of the user.

• It takes into consideration the furnishing of the room and the dimensions of the video display or TV, to place the loudspeakers in optimal locations
• It offers the suggestions to the user in a friendly graphical way
• When the user changes the listening position, then simultaneously all the components of the system (display, speakers) are moved, so that the acoustic rules are followed

Room Acoustics Designer® is a patented software, accessible free of charge at the Crystal Audio website.

When a wave hits a hard boundary (in our case the wall/floor/ceiling of a room) it is reflected back. The reflected wave adds with the original wave and depending on the ratio of the wavelength to the dimensions of the room, the sum of the two waves creates points in the room where specific frequencies are emphasized and points where they are attenuated. The result from the wave sum is called standing wave, as it does not propagate in space but rather creates a 'standing' field that selectively boosts and attenuates different frequencies. An alternative naming for this phenomenon is room modes, where each mode represent the standing wave that is caused by each separate boundary and affects a specific frequency.

In the end of it all the multiple reflections result in different frequencies being boosted or attenuated by a different amount in different places in the same room, all depending on the position of speakers.

For typical 'small' domestic listening rooms, low frequencies are the ones affected my this wave effect. Hence the attention we must pay in correctly placing the subwoofer in the room so as to minimize the standing waves.

Rooms with different height, width and length are preferable for best low frequency performance and for the minimization of resonance problems, but obviously you must work with the room available to you. If possible, place the speakers so they are firing along the longest wall. In other words, if the room is 5 meters wide and 10 meters deep, place them along the 5-meter wall. There will be less wall reflection and therefore a more natural sound.

When building a new home theater room or renovating an old room, here are some good rules to follow:

• Shape has direct effect on sound quality. One dimension should not be divisible by another, for example 4 x 8 x 15 is bad, while 4 x 9 x 15 is good
• Stick with rectangular rooms, which minimize wide-open archways into adjacent rooms. Irregularly-shaped rooms do not avoid standing waves; they simply make them harder to predict and minimize
• Avoid any concave curved shapes as they focus sound reflections
• Control sound reflections and echoes with the use of absorption or diffusion materials
• Control reverberation times using the right absorption
• Good sound isolation allows use of the room anytime, and minimizes background noise

The table that follows indicates the Sound Pressure Levels dB SPL, of various sound sources. It helps you realize yor requirements in sound level.

• Rocket 194 dB
• Jet engine 160 dB
• Propeller Airplane 140 dB
• Pain Threshold 135 dB
• Jets' take off (60m) 120 dB
• Closed off space with Loud music 115-120 dB
• Symphonic orchestra 113 dB
• Piano solo (peak RMS, 1/8sec) 110 dB
• Piano solo 103 dB Large truck 100 dB
• Minimum audio level for Hi-Fi system evaluation 96 dB
• Noisy office 80 dB Train (30m) 70 dB
• Vacuum cleaner (3m) 70 dB
• Speech (30cm) 70 dB
• Conversation 60 dB
• Secluded office 50 dB
• Quiet residence 40 dB
• Recording studio 30 dB
• Rustle of leaves 20 dB
• Limit of hearing 20 dB

The table below indicates the Sound Pressure Level of a pair of speakers with 90 dB/2.83V/m sensitivity and 8Ohm impedance. Note that a stereo pair produces 90 + 3 = 93dB of SPL, that is a 3dB increase (as opposed to +6dB which you would be inclined to think).

Using the 3 rules of calculation of the sound level, you can calculate the SPL of your speakers for various distances and amplifier output power depending:

• On the distance of speakers and listener:

  • Doubling the distance results in a 6dB reduction of the sound level

  • At half the distance the sound level is increased by 6 dB

• The sensitivity of our speakers:

  • Two speakers deliver 3dB more than one speaker

• The impedance of the speaker:

  • The sensitivity is expressed in dB at 2.83V (modern amps are constant voltage sources), which is equivalent to 1Watt at 8Ohm. If the impedance is different than that, ie. 4Ohm, the sensitivity will correspond to a power of 2Watts (P=V2/R, so P=2.832/4=2W), hence the SPL will be half (-3dB) at 1Watt. Download the simple Sound Pressure Level calculator and insert the exact sensitivity & impedance of the speakers you intend to buy and find out the produced SPL at different distances and for various amplifier powers, for a Stereo pair

• The power of our amplifier:

  • Twice the power (watt) results in a 3dB increase of the SPL (under the assumption that the speakers can handle the extra power without distortion or damage)

No matter how careful the design of the home theater room is, there still exist standing waves and speaker/room boundary interactions. In both circumstances a proper equalization can restore accurate spectral and tonal balance. During the 60’s and the 70's graphic equalizer use (or shall we say abuse) resulted in highly unsatisfactory sound. Equalizers were used for everything from tone controls to means of forcibly obtaining flat frequency response from grossly inaccurate loudspeakers and in the process lost their appeal with the audiophiles. Today, sophisticated algorithms, implemeted by some niche manufacturers, provide corrections both in frequency and the time field (that is they correct the frequency response as well as the phase of the waves) resulting in a much better (although still not perfect) undoing of the effects of the room acoustics.