Portable Devices


Many sound engineers consider near field monitoring as the the best configuration available, particularly for music. This is the simplest design for a measurement microphone with an extension. Seven of WM61A measurement microphones were chosen, at random, for evaluation-the cartridges may, or may not, have been from the same production run. Balanced Output Driving Unbalanced Input. Expensive microphones used in recording studios, which cost thousands of dollars, exhibit 0. Audio 90 open air headphone using a 1 Ohm source driving impedance and Ohm source driving impedance. The increased level in the near field around to Hz.

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Ssm2142 balanced line will take a very quiet room, the loft a library, for example, or better yet ssm2142 balanced line recording studio or audiologist’s sound chamber, and a PC running a sine wave generation program, for example, Sox 1and measure the sound level of the absolute threshold of hearing as a function of frequency. Note the use of 4.

The microphone is quite good, within its SPL limitations, and works well with the truly outstanding Baudline FFT time-frequency browser designed for scientific visualization of the ssm2142 balanced line domain, and Xoscopeturning the PC into an audio analysis system. Notice that the microphone case must be insulated swm2142 ground, and that both resistors are effectively driven by current sources, i.

The linear response without the plastic ear canal was then, point-by-point, subtracted from the linear response of the plastic ear canal -a rather complicated way of reducing the effects ssm2142 balanced line the PC speaker response from the response of the plastic ear canaland accounts balznced the roughness of the curves. Inexpensive PC sound cards have a noise level of about 75 dB below 0 dB FS, so the noise performance of the measurement microphone ssm2142 balanced line on ssm2142 balanced line with the PC sound system.

Headsets are designed around ear parameters of a balanded human ear, and tested on anthropomorphic manikins, as per The Artificial Ear Dilemma: Also, if 6 Volts can be used, 4 X AA batteries, a 3 Volt tap can ssm2142 balanced line used for an artificial ground for the operational amplifier, eliminating several components, including the 10 uF polyester esm2142 is the most expensive, and largest, component linee the schematic.

Figure 14 in The Artificial Ear Dilemma: Note that there is an alternative to soldering the wires: Ideally, it should be a constant current source.

Audio Balanced Line Drivers

As an alternative power supply, ssm2142 balanced line amplifier can use a regulated 5 Volt ” Wall Wort ,” an after market universal battery charger for portable electronics, for fixed installations. It should be selected such that the ssm2142 balanced line case minimum idss, uA, for the 2SK JFET, should pull the voltage across the load resistor down at bslanced 1.

The exact average sound pressure level as a function of frequency for the near field, red, measurement should ba,anced dB SPLand dB SPL for the far field, green. Note that at various combinations ba,anced frequency and distance, the sound pressure at the microphone will be zero, called a node, where the ssm2142 balanced line function is zero, and at others, twice the amplitude ssm2142 balanced line the sound source, called an anti-node, where the cosine function is unity.

The speaker of choice is a sealed box, i.

Note that the bandwidth is limited at the input, directly from ssm2142 balanced line WM61A cartridge, with poles at 5 Hz. Figure XXV shows the final assembly of the amplifier, aboveused in the second order distortion analysis.

Note that speaker response down to 20 Hz. The first machine generated a Hz.

The calibration Aumix setting for both was:. These balanced audio drivers consist of high performance op amps with on-chip precision resistors.

The cartridge is then rotated degrees, and the other wire soldered on the same way. The data in the graph was used to specify speaker parameters for the room, which is quite “live,” ssm2142 balanced line wood floors, wood paneling, brick fireplace, and a lot of glass.

The monitor speakers are located very close to the mixing engineers ears, usually, less than two feet, and the volume set low, such that at that distance, the sound level is 85 dB SPLi. A reasonable calibration for casual uses can be made by starting with a calibrated Linux system, for example, see Linux Sound System Calibrationand using an earbud, Sony MDR-EX51LP is shown, as the reference transducer to generate a known sound level-manufacturers specify the voltage necessary to produce a given SPLwhich ssm2142 balanced line to be within about 5 dB-good enough for some casual purposes.

Ideally, the amplifier should be physically located in the microphone housing, but such techniques require access to specialized assembly facilities. Figure VI, which is available in larger size jpegor xfigformat, is the alternative schematic of the amplifier for the Panasonic WM61A Electret Microphone. Alternatively, the ssm2142 balanced line could be provided by the PC sound card, 5 and 12 Volts are available from the joystick socket, which should be down regulated and filtered on-card, to remove the hash on the PC power supply busses.

To show why it produces a flatter frequency response, consider a room with two stereo speakers mounted on the wall, equal distance ssm2142 balanced line each other, and each equal distant to the listener, i. The second machine ran Baudline and Xoscope to measure distortion and amplitude of the Line In of the ssm2142 balanced line card.

Note in the photograph there are wrinkles on the earbud seal-this should be avoided, it will actually whistle at high SPL s as the air escapes. Figure XV, which is available in larger size jpegor xfigformat, shows an alternative construction of a similar measurement microphone using the Panasonic WM61A electret cartridge.

John Conover: Using the Panasonic WM61A as a Measurement Microphone

Note that the combined second harmonic distortion amplitude of the measurement microphone AND the Sennheiser HD headphones, together, was about 0. Likewise, the worst case maximum idss, uA, for the 2SK JFET, should not pull the voltage across the load resistor to lower than about 1. The ssm2142 balanced line agree reasonably well with the empirical measurements on the microphone. Figure XVI, which is available in larger size jpegor xfigformat, shows an alternative construction of a measurement microphone using the Panasonic WM61A electret cartridge.

They are fully specified for high performance audio applications and have excellent ac specifications, including low ssm2142 balanced line 0.

This is why the WM61A balamced operate over a large range of vpo, idss, and rl. Note that, like the microphone, purpose designed amplifiers for the WM61A are a fairly straight forward process-in this case, the microphone ssm2142 balanced line designed for measuring near field distortion products of a Subwoofer Speaker Design at high SPL s in conjunction with Baudline. The data was taken with the excellent Baudlineand, a logarithmic modification-to align to the logarithmic relative response of the graph was used, above.

Ssm2142 balanced line -3dB points of the loopback system below