This calculator provides an easy and accurate method to position loudspeakers for critical immersive audio monitoring in professional control and mastering rooms. It also checks some parameters of the room design for compliance with the requirements of ITU-R Rec. BS.1116, which contains a commonly used specification for critical listening rooms.

Begin by entering the room dimensions and desired loudspeaker configuration on the Loudspeaker Positions tab, then the Room Modes tab will show if the loudspeaker placement meets BS.1116 requirements. The Layout tab explains how the dimensions shown on this page can be transferred to the room where the loudspeakers will be mounted.

Note that:

• The Loudspeaker Positions tab includes a table that is also useful for understanding the ideal loudspeaker positions for panning and rendering in audio production.
• Background information on low-frequency room modes, which can greatly affect bass reproduction, is provided on the Room Modes tab. The frequency distribution of room modes is controlled by the dimensions of the room.
• You may wish to measure your ear height at the listening position using your chairs or equipment to determine an appropriate value for the Listening Height.
• BS.1116 specifies that loudspeakers should be at least 1 m from walls. Additionally, loudspeakers less than 1m from the listener may offer too much direct sound to replicate normal listening.
• If the ceiling is too low, it is possible to place the upper loudspeakers closer to the listening position (enable the Upper Loudspeaker Radius value on the Loudspeaker Positions tab) and delay their signals.
• A popular configuration for immersive monitoring is 7.1+4H.

To layout loudspeakers in your room, you will need:

• Dimensions of your room and the dimensions specified by this web page
• A measuring tape
• String, preferably nylon mason’s twine that does not stretch
• A plumb bob (or substitute)
• Painter’s tape or other means of marking locations
• Some microphone or light stands or similar objects
• (optional) laser level and adapter to mount on mic or light stand, or tripod

Plotting the loudspeaker locations:

1. Set a microphone or light stand at the listening position with its top at the desired listening height. Tie a string to the stand at this point. You may wish to permanently mark this position on the floor for future reference. A screw driven into the floor is a popular way to do this.
2. Mark the acoustic center of the loudspeakers, perhaps with a mark on painter’s tape stuck to the front of the loudspeaker. Professional loudspeaker manufacturers usually specify this position.
3. Place another mic stand close to the front wall at listening height and centered horizontally on the wall. Stretch the string between the stands. Measure the loudspeaker distance on the string from the listening position with the measuring tape. Mark this distance on the string with tape, marker, or a knot. This will be the M0 or center loudspeaker position.
4. Stretch another string from the top of the listening position stand and mark it at the loudspeaker distance. Use the measuring tape to position this string at the distance specified from the center loudspeaker position and at the listening height above the floor to find the position of the next loudspeaker. The combination of the distance from the M0 position and the distance from the listening position sets the desired angle in the horizontal plane. Maintaining the same distance from the floor insures the new point is in the horizontal plane.
5. Position a loudspeaker at this point, or mark its position with another mic stand.
6. Repeat the measurements for the next loudspeaker in the horizontal plane, until all the loudspeakers have been located. Measuring back to the center loudspeaker position will reveal the closure error in your measurements and thus the likely error in position of the loudspeakers.
7. For overhead loudspeakers: Move a string to the position of the mid-plane loudspeaker underneath the desired loudspeaker. If there is no such mid-plane loudspeaker, mark the position of an imaginary one as shown on the diagram. Attach another string to the plumb bob and mark two points the vertical distance apart on the plumb bob. Move the other string so it’s marked listening distance is coincident with one mark on the plumb bob string and the other mark on the plumb bob string is coincident with the mid-plane string. This establishes the position of the upper loudspeaker.
8. Repeat this for each overhead loudspeaker.
9. If lower-plane loudspeakers are used, repeat the procedure as for the upper loudspeakers, marking the specified vertical distance on the plumb bob string.

Notes:

A laser level positioned at the listening position can eliminate the need to measure distances from the floor, particularly if the floor is not level or is uneven. For field work, the measuring tape can be locked and held by the end hook as an improvised plumb bob. If a plumb bob is not available (usually sold at hardware stores with the twine and measuring tapes), a heavy washer can be used instead.

Frequently Asked Questions:

Should I angle the loudspeakers toward the listening position as shown here?

Yes, high frequency response of loudspeakers often degrades substantially when they are not pointed at the listener.

Where should subwoofers or LFE channel loudspeakers be placed?

Loudspeaker configuration CICP13 (22.2) defines loudspeaker positions for LFE channels. For other configurations, Fraunhofer recommends placement of the subwoofer (or multiple subwoofers driven in parallel) for even response at the listening position. See footnote 7 on the Room Modes tab for more information.

Can I just connect the subwoofer to the LFE channel of my mixing console or DAW interface?

Usually, this is incorrect. A subwoofer output contains the LFE channel, perhaps with +10 dB gain, and the lowest bass frequencies of all the other channels, including the overhead and lower loudspeakers. Note that the LFE channel must be low-pass filtered to 120 Hz to simulate the audio encoder's filtering. A professional subwoofer will usually have appropriate filtering for 5.1 or 7.1 loudspeakers built-in, but lack inputs for the other channels. The other channels will have to have appropriate filtering applied elsewhere and their lower bass components added to the subwoofer signal (perhaps using the "sub in" input of the subwoofer). This can be successfully tested and aligned using the LFE Level Alignment signal at https://mpegh.com/academy/testing-and-qa/test-signals/. Industry guidelines¹ recommend that no content that is very significant to the program be placed in the LFE channel, as the channel will be reproduced with less gain in stereo or binaural playback.

What if the ceiling in my room is too low for correct placement of overhead loudspeakers?

If the ceiling can't be raised (for example, in a mobile truck), flat loudspeakers built for ceiling mounting may be an option. The electrical signals to the loudspeakers can be delayed so that they are aligned with the mid-plane loudspeakers.

What if I want to flush mount loudspeakers?

Mounting loudspeakers flush with a wall or mis-named “soffit” helps to prevent diffraction effects (loudspeaker boundary interference) from the loudspeaker enclosure and the effect of adjacent walls. However, it will require a different equalization of the loudspeaker than that used for playback away from walls or corners. Consultation from a room acoustics professional is suggested in this case. Note that loudspeakers with a rear-facing or side-facing bass port or woofer are not intended for flush mounting.

What acoustic treatment should be used in the room?

General acoustic design is beyond what is presented here, and it may be desirable to retain an acoustic consultant. However, if the reverberation times and other parameters specified by ITU-R Rec. BS.1116 are met, it is likely the room will have been treated appropriately. Lack of bass absorption is the most common issue requiring acoustic treatment in most rooms. A quick survey using the software referenced on the Room Modes tab will be very valuable in determining what treatment is required. The large number of first reflection points in immersive listening rooms require careful distribution of broadband absorbers and diffusers.

I want to set up loudspeakers for listening as a group.

BS.1116 recommends that listeners be placed within 0.7m for a loudspeaker radius of 2-3m. Careful control of room modes and loudspeaker dispersion is needed to ensure uniform response over a large listening area.

What if there is a fire sprinkler, light, door or other object interfering with mounting the loudspeaker in the correct position?

A different loudspeaker configuration might be used, or a custom rendering matrix used to account for the mis-placement of the loudspeaker. A small placement error is not critical to the sound image and can be tolerated except for the most critical listening.

I can’t stretch a string to the desired position since something is in the way.

In this case a different listening position is needed or a different room, or a different loudspeaker configuration.

How do I mount loudspeakers from the ceiling?

Some manufacturers offer tilting mounts for loudspeakers that can be attached to poles mounted to the ceiling. Light stands or tall loudspeaker stands can be also be used. Many facilities use lighting trusses for this purpose. A welding or metal fabrication contractor may be useful in making and installing custom loudspeaker brackets.

Why not measure the angles with a protractor?

This can be done for approximate or field setups. Angles measured with a protractor will not usually be as accurate as those with this technique, as the protractor would need about 0.1 degree accuracy for comparable accuracy of location. Machinists and surveyors have devices to measure angles this accurately, but they are expensive compared to string and a measuring tape.

Footnotes:

¹AES Technical Council, Multichannel surround sound systems and operations, AES Technical Document, Document AESTD1001.1.01-10, 2001. Available from: http://www.aes.org/technical/documents/AESTD1001.pdf.

Background. Aside from listening outdoors or in an anechoic chamber, all rooms will have resonances and reflections. Their effects are determined by the dimensions of the room, and by the placement of the loudspeakers and listeners. Typical studio control rooms or listening rooms are of a size¹ where the resonances or modes² at bass frequencies occur only on certain musical notes, leading to those notes being amplified or suppressed relative to the others. At higher frequencies, the modes and reflections become more finely spaced and less objectionable. The graph below shows the un-smoothed, measured frequency response of a small room with fairly rigid walls and no acoustic treatments.³ The loudspeaker used has a flat response within 1-2 dB; the large peaks and dips in the response are due to room resonances and reflections.

At the very lowest frequencies (termed the pressure region), the room is too small for resonances to develop, and the response is uniform. Above the pressure region are the modal region frequencies where sparse resonances or modes lead to a very rough response. Then there is a transition region, often specified by the Schroeder frequency criterion, where the modes become more tightly spaced. In the higher reverberant region, the sound waves are small enough that modes are very tightly distributed and their effects overlap. Interference from reflections is still present but is to some degree averaged by the ear.

Modal resonances are similar to those present on a stretched string: the amplitude or volume is zero at the ends and varies along its length, and energy is stored in the string, gradually dissipating after being plucked. Thus, a room mode can cause a peak or a null, or have little effect depending on the listening position. This can be easily experienced by playing a sine tone through a loudspeaker at a resonant frequency and walking around a room. Nulls of 30 dB or more are quite common in an untreated room. Energy storage in modes causes a long decay of bass transients or “boomy bass”. Both the strength of the peaks and nulls and the lengthened decay of transients caused by modes can be reduced by adding acoustic absorbers that are effective at the mode’s frequency.

Classic room ratios. In classical acoustics practice, the ratio of room dimensions is chosen to optimize the distribution of modes so they are less objectionable. Criteria developed by Walker⁴ at the BBC is specified in EBU⁵ and ITU⁶ standards for listening rooms:

Many other room ratios have been proposed over decades of research in this area and optimization programs have been developed that attempt to find the optimum room dimensions and loudspeaker and listening positions for a given set of constraints. Many room mode calculators assume rigid uniform walls. Most walls that are not made from concrete or brick are not rigid at bass frequencies, so this assumption is not valid in those cases.

Room simulation. The freeware program Room Eq Wizard has a simple room simulation tool that takes surface absorption into account for rectangular rooms. For non-rectangular rooms or more precise results, Boundary Element Method or Finite Element simulation is typically used to solve the acoustic wave equations at the room perimeter.

Measurement and treatment. If an existing room is being considered for use as a listening room, measurement of the room modes is more accurate than simulation. Although a tone generator and sound level meter can be used to find modal frequencies, software based on Farina (exponential) sweep techniques is freely available and can completely measure a room’s response for a given loudspeaker and listening position in seconds. A popular program for this purpose is Room Eq Wizard. Classical 1/3 octave real time analyser applications will likely have insufficient resolution.

Proper use of acoustic absorbers can greatly improve the response degradations caused by room modes. Traditional absorbers made of fiberglass, mineral wool, or plastic foam operate by modifying the velocity of air molecules – which is zero at a wall boundary. Thus they must either be very thick (perhaps 1/10 or preferably 1/4 of a wavelength) or spaced sufficiently away from the wall. Room corners are the most effective location for absorption as all modes are present there. While some audio enthusiasts will construct one meter thick mineral wool absorbers in room corners, untuned diaphragm or membrane absorbers are more effective in terms of room volume. Many rooms made of gypsum wall board mounted on steel or wood studs over insulation batts already act as diaphragm absorbers to a degree, and modes in these rooms may already be less powerful before treatment is added.

Subwoofer placement. Since room modes require a specific acoustic pressure distribution in the room to exist, it is possible to place one or more subwoofers or full-range loudspeakers where troublesome modes are not excited by the loudspeaker radiation. Several subwoofers may be driven in parallel to reduce the modes excited.⁷ As these acoustic signals obey the reciprocity effect, a common technique is to place a loudspeaker at the listening position and then take measurements at various locations around the room to find an optimum position for the loudspeaker.

Immersive listening reduces room options. Many of the techniques and criteria for listening room or control room design were developed during the era of stereo sound. Immersive sound involves loudspeakers positioned over an entire hemisphere and thus a simplified and more classic approach seems the norm for such rooms today. The large number of loudspeakers needed usually means bass-managed smaller loudspeakers will be used, and thus multiple subwoofers can be employed at the lowest frequencies. The basics of attenuating first-order reflections and positioning loudspeakers away from nearby walls to avoid boundary effects still hold.

Additional Information:

Footnotes:

¹Large rooms, such as concert halls or lecture halls, usually have a much lower Schroeder frequency and modes are not as important a factor.

²The term “room modes” is used in the literature since these frequencies are acoustic eigenmodes of the room. They exist axially between parallel walls, tangentially across four surfaces, and obliquely across all six surfaces.

³Due to frequency/time duality, the room response shown is actually smoother than if the measurements were conducted over a longer period instead of the 10-second sweep that was used.

⁴R. Walker, "Optimum Dimension Ratios for Small Rooms," Paper 4191, (1996 May), Audio Engineering Society Convention Paper.

⁵ EBU, Tech. 3276 2nd, Listening Conditions for the Assessment of Sound Programme Material: Monophonic and Two–channel Stereophonic, 1998, European Broadcasting Union, Grand–Saconnex (Geneva) Switzerland. Available from: https://tech.ebu.ch/docs/tech/tech3276.pdf.

⁶ ITU-R, Rec BS.1116-3, Methods for the Subjective Assessment of Small Impairments in Audio Systems, 2015, Intern. Telecom Union, Geneva, Switzerland. Available from: https://www.itu.int/rec/R-REC-BS.1116/en.

⁷See ch. 13.3.2 of Toole, Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms.