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  • Room Acoustics

  • How should my listening room ideally be?

    • Does the size and shape of my room affect the set up of my surround sound system?

      There is a direct correlation between your room’s size, shape and loudspeaker placement.

      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.

    • What are the steps for the correct selection of speakers that match your space?

      Decide which stereo or multichannel system you like best and run our RAD on-line application.

      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.

    • What are the standing waves or room modes?

      When a wave hits a solid boundary (e.g a wall) it gets reflected, causing a so called “standing wave

      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.

    • What are the ideal room dimensions for best speaker performance?

      You must work with the room available to you.

      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.

    • What rules to follow for a home theater room construction?

      Room shape, reflections, reverberation time and isolation, are key elements you must consider.

      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
    • What are the realistic Sound Levels that you need in your Space?

      They range up to 194dB SPL! Check the following table.

      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
    • Which combination of Amplifier/Speaker/Room give the dB that you require?

      According the table below.

      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:[image]

      • 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)


    • What is Room Equalization?

      An audio correction algorithm to counteract the effects of room resonances and standing waves.

      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.

  • How to place my speakers?

    • Where is the best place for my surround sound speakers?

      The best placement is between 90° to 110° from each side of your listening position.


      The best surround speakers are Dipoles. Their role is to offer a wide dispersion of sound in all directions, giving benefits such as a transparent and detailed sound and rear channel effects that are similar to a true cinema experience, created by the rows of side loudspeakers.

      The best placement of Dipoles are between 90° to 110° to each side and about 70cm or higher above the listener's ears.


    • Placement of the Main Speakers

      Please refer to the drawing.


      • The greater the distance of the speakers from the walls the better their response

      • Place the main speakers slightly in front of the TV and not at the same line with it, so that he distance of the main speakers from the listening position is identical to that of the center speaker. Placing the speakers this way also reduces the reflections from the TV screen

      • The speakers must form an isosceles triangle with the listening position. The speakers are placed in font of us just like a live orchestra

      • The greater the distance between the main speakers, the wider is the stereo image that we get. However we must be careful not to place the speakers too far apart, or we will create an acoustic hole between them

      • The tweeter must be placed at the ear level when seated at the listening position an there should be no objects in the direct path of the sound to our ears

      • Slightly turning the speakers towards the listening position improves the sound focus but it reduces the dimensions of the sound image. This affects some speakers more than others. Trial is the best way to determine this...

      • All speakers must be broken in for some time. Use your speakers for at least for 100 hours in mid to low listening levels, before they can perform at their best.

    • Placement of the Center Speakers

      Please refer to the drawing.


      • Align its facade with the TV screen, to reduce diffraction. Diffraction is the secondary sound generated when sound meets a discontinuity

      • If the speaker is placed below the TV, tilt it upwards, towards the listeners. If it is placed above the TV, tilt it downward towards the listeners

      • Make sure that the central speaker is not placed above or below the tweeter level of the main speakers by more than 60-70 cm

    • Placement of the Surround Speakers

      Please refer to the drawing.


      • The reflections from the Surround speakers are useful, in reverse of the reflections of the main speakers that are destructive to the sound quality

      • The tweeter must not aim at your ears

      • The sound must be directed towards a wall so that it reaches our ears after a reflection

      • It is preferable that they are placed at least 50 cm above the ear level of the seated audience

    • Placement of the Subwoofer

      Experiment with various locations based on herebelow suggestions

      The successful placement and adjustment of a subwoofer is the result of many trials. A correctly placed and adjusted subwoofer generates sound that cannot be localized as coming from a separate speaker.

      Place the subwoofer near the listening position. Play a jazz piece with acoustic bass and many succeeding notes "walking bass". Get down on your knees (beware of your neighbors...) and find the exact point of the room where the bass sounds the clearest. Now change position, place the subwoofer at this spot and sit at your listening position.

      Avoid placement of the subwoofer equidistant from the two walls. If, for example, the width of the room is 8 m, do not place the subwoofer at the middle of this distance (4 m).

      Do not place the subwoofer in the corner and at the same distance from the two corner walls.

      Place the subwoofer as close to the listening position as possible. This way you will experience more of the direct sound of the subwoofer instead of the reflections of the room.

      The use of two subwoofers, to the left and to the right of the listening position, is the ideal albeit more expensive solution.

      The ideal location for the subwoofer may not be practical. Think of the decor of the room and make sure the subwoofers are not in the way.

      Experiment with various locations based on the above suggestions. You will be rewarded with much better sound without additional cost.

    • What is the benefit of using two or even four subwoofers?

      You will enjoy uniform, fully extended low frequencies with minimal to none standing waves.

      Extensive THX and AES (Audio Engineering Society) research has proven that the use of two and - even better - four subwoofers is the best solution for achieving a uniform bass performance for many seats around the listening area.

      Each subwoofer creates its own modes, which overlap randomly with the modes of the other subwoofers in the room. Statistically, this results in a more uniform result, with the big dips and peaks in the low frequency response being mitigated considerably.

      Overall, the use of at least two or even four subwoofers, leads to the following advantages:

      • Significant alleviation of room resonances
      • Enhanced low frequency coverage
      • Even excitation of all modes in the listening area, not just for the main listening position
      • Significant reduction of the frequency variations from seat-to-seat
      • Effective equalization over a wide seating area, rather than a small sweet spot or even a single listening position

      For the ones craving the most realistic LFE experience, the extra cost is definitely worth the effort!