One of our main tool for loudspeaker R&D is our own anechoic chamber. This ensures an extremely accurate adjustment and painstaking speaker design, which – without anechoic chamber – could not be achieved to this degree and not without compromise.
Usually the lowest operative sound pressure level for a loudspeaker occurs around frequencies below 300Hz. The average sound pressure level of the high and mid-frequencies should be adjusted to conform to this frequency range. In a conventional room it is impossible to place speaker and measuring microphone at a sufficient distance to any wall in order to avoid acoustic reflection in close proximity to the test-setup: Only the frequency range measured before the first significant acoustic reflection coming from a wall can be meaningfully evaluated. Thus, due to inherent so-called windowing, frequencies below 300 Hz cannot be mapped. It forces the developer to approximate the zone of indecision by either combining diverse measuring methods (near field measurements of all single sound sources and windowed measurements) or by using simulations. This approach is only able to deliver a roughly estimated result.
The developers working at EVE Audio GmbH have the means to execute highly accurate measurements down to 70Hz, which ensure clean and balanced calibrations. Another advantage of a large anechoic chamber lies in the capability to measure large speakers comprehensively. Multi-way systems in particular, featuring widely spaced single sound sources (speaker drivers), can only be precisely calibrated using microphones at distances of > 2m - as well as angled measurements of various angles and distances which are essential to any serious speaker design. EVE Audio's anechoic chamber, built as a room-within-a-room construction, offers the advantage of high absorption of exterior noise. This has a positive side effect when testing and optimizing amplifiers and ensures a high signal to noise ratio (almost inaudible background noise from active speakers). Any sound engineer, sitting close to a near-field studio monitor, appreciates this on a daily basis. Undesired resonances as well as flow noise or clattering can be easily identified and eliminated. Without the use of an anechoic chamber these are a lot less audible and might be concealed by exterior noise.
Anechoic chamber in the former BRF/RFZ building (Central Bureau of Radio and Television).
Dimensions: 9.25m x 8.25m x 8.55m
Operating volume: 6.7m x 5.7m x 6.1m
Solid sandstone double-shell masonry construction, 20cm gap
Low cutoff-frequency fu = 70Hz
Free-field deviation up to 45Hz < 6dB
Maximum test distance to test object = 3m
Length of the sound absorbing wedges - app. 1.2m