The Use of Volume Velocity Source in Transfer Measurements

Reverberation rooms are often used for measuring the sound power emitted by sources of sound. At medium and high frequencies, where the modal overlap is high, a fairly simple model based on sums of waves from random directions having random phase relations gives good predictions of the ensemble statistics of measurements in such rooms. Below the Schroeder frequency, the relative variance is much larger, particularly if the source emits a pure-tone. The established theory for this frequency range is based on ensemble statistics of modal sums and requires knowledge of mode shapes and the distribution of modal frequencies. This paper extends the far simpler random wave theory to low frequencies. The two theories are compared, and their predictions are found to compare well with experimental and numerical results.

Section: Resultsmentioning

confidence: 99%

The ensemble variance of pure-tone measurements in reverberation rooms

Jacobsen¹,

Molares²

2010

“…The latter device, described in Ref. 11, consists of a tube driven by a loudspeaker. The sound pressure and the particle velocity were measured at 11ϫ 11 points with a single 1/2 in.…”

Section: Resultsmentioning

confidence: 99%

A sound field separation technique based on measurements with pressure-velocity probes

Zhang

Xinzhao

Jacobsen

2009

It has recently been shown that statistically optimized near field acoustic holography based on measurement with an array of pressure-velocity transducers makes it possible to distinguish between sources on the two sides of the array and thus suppress the influence of a disturbing source [F. Jacobsen and V. Jaud, J. Acoust. Soc. Am. 121, 1550–1558 (2007)]. However, the suggested technique uses a transfer matrix optimized for the source under test and may be expected to perform less well when the disturbing source is not placed symmetrically on the other side of the array, and this will usually be the case. In this letter, a modified method is presented.

“…Three different sources were used, a "monopole" ͑a Brüel & Kjaer ͑B&K͒ 4299 "Volume Velocity Source," which is a tube with a built-in sound intensity probe connected to a B&K 4295 "OmniSource" loudspeaker 14 ͒, a "monopole on a sphere" ͑a device consisting of a hollow rigid sphere with a small hole driven by an internal loudspeaker, developed for calibrating p-u sound intensity probes 15 ͒, and a model of a helicopter gearbox driven by an internal B&K 4809 electrodynamic exciter. The monopole on a sphere and the gearbox are shown in Figs.…”

Section: Resultsmentioning

confidence: 99%

Statistically optimized near field acoustic holography using an array of pressure-velocity probes

Jacobsen

Jaud

2007

Statistically optimized near field acoustic holography (SONAH) differs from conventional near field acoustic holography (NAH) by avoiding spatial Fourier transforms; the processing is done directly in the spatial domain. The main advantage of SONAH compared with NAH is that the usual requirement of a measurement aperture that extends well beyond the source can be relaxed. Both NAH and SONAH are based on the assumption that all sources are on one side of the measurement plane whereas the other side is source free. An extension of the SONAH procedure based on measurement with a double layer array of pressure microphones has been suggested. The double layer technique makes it possible to distinguish between sources on the two sides of the array and thus suppress the influence of extraneous noise coming from the “wrong” side. It has also recently been demonstrated that there are significant advantages in NAH based on an array of acoustic particle velocity transducers (in a single layer) compared with NAH based on an array of pressure microphones. This investigation combines the two ideas and examines SONAH based on an array of pressure-velocity intensity probes through computer simulations as well as experimentally.