Shure M615as Schematic

PINK NOISE GENERATOR

Output Level (Level control at 10)

AUX LEVEL	HI-Z	MIC	LEVEL	LO-Z MIC LEVEL
- 1 dBV (890 mV)	-29	dBV	(35 mV)	-49 dBV (3.5 mV)

Spectrum

Equal energy per octave pink noise, flat % I dB, 32 Hz to 16 kHz

lmpedance

OUTPUT		DESIGNED FOR USE WITH	ACTUAL
Lo-Imp.
Mic Level		25to 600-ohm microphone	110 ohms
		circuits	balanced
Hi-Imp.
Mic	Level	33-kilohm microphone circuits	2.3 kilohms
			unbalanced
Aux	Level	High-impedance (10 kilohms	1.5 kilohms
		or more) unbalanced aux	unbalanced
		circuits

ANALYZER

Sensitivity

(Pink noise levels to turn off LO LEDs; INPUT LEVEL control fully clockwise)

INPUT	15 dB	INPUT VOLTAGE	SOUND
	ATTENUATOR		PRESSURE USING
			ES615 MICROPHONE
Lo-Imp. Mic.	Out	-117 dBV (1.4 pV)	45	dB SPL
	In	-102 dBV (8 pV)	60	dB SPL
Hi-Imp. Mic.	Out	-92 dBV (25 pV)		-
	In	-77 dBV (0.14 mV)		-
AUX	-	-62 dBV (0.79 mV)		-

FlatlES615 Switch

In ES615 position, complements low-frequency rolloff characteristic of ES615 Microphone (see Figure 1)

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-10

-20

2 0 50 100 500 FREQUENCY IN HERTZ

ES615/M615 SYSTEM LOW

FREQUENCY RESPONSE

FIGURE 1

Above 1 kHz Switch

FLAT: Used for near-field measurements; produces flat resultant frequency response.

ROLLOFF: Used for reverberant and far-field measurements; produces resultant frequency response rolled off at 3 dB per octave above 1 kHz (see Figure 2)

ABOVE 1 kHz ROLLOFF

FREQUENCY RESPONSE

FIGURE 2

Mic Overload

(Pink noise levels to turn on MIC OVERLOAD LED)

INPUT	15 d~	INPUT VOLTAGE		SOUND
	ATTENUATOR			PRESSURE USING
				~ ~ 6 MICROPHONE1 5
LO-imp. Mic.	out	-40	~ B (10V mv)	122	d~ SPL
	In	-25	dBV (56 mV)	137	dB SPL
Hi-Imp. Mic.	Out	-17	dBV (0.14V)		-
	In	-2 dBV (0.79V)			-

lnput Overload

(Pink noise aux input level to turn on INPUT OVERLOAD LED; INPUT LEVEL control fully clockwise)

-25 dBV (56 mV)

HiILo Envelope

2 to 12 dB+I-(	to k	6 dB), adjustable
Aux Output Voltage Gain
INPUT		GAIN
		-
Lo-Imp. Mic		+54	dB**
Hi-Imp. Mic		+31	dB**
AUX		- 4	dB

'* lnput attenuator out

Impedance

INPUT	DESIGNED FOR USE WITH	ACTUAL
	-
Lo-Imp. Mic.	25to 600-ohm microphones	950 ohms balanced
Hi-Imp. Mic.	33-kilohm microphones	140 kilohms unbalanced
Aux	100-ohm to 10 kilohms high	42 kilohms unbalanced
	level sources
OUTPUT	DESIGNED FOR USE WITH	ACTUAL
Aux	High-impedance (10 kilohms	4.7 kilohms unbalanced
	or more) unbalanced aux	(with MIC input in use)
	circuits

Operating Voltage

M615: 108-132 Vac, 50/60 Hz, 5W

M615-2E: 90-125 or 180-250 Vac, 50/60 Hz, 5W

Temperature Range

Operating: -7" to 57°C (20" to 135°F) Storage: -29" to 71°C (-20" to 160°F)

Dimensions

See Figure 3

SETUP AND OPERATION

In the following setup and operation procedures, the objective is to produce a smooth acoustical frequency response in the audience listening area. This condition is indicated by both LO and HI LEDs being off. However, due to the nature of random noise, a signal near threshold will cause flickering of the LED, rather than a positive on-off indication. It is generally sufficient if one or several LEDs are blinking, but not off completely.

The time required to allow the analyzer to respond to a change and sample sufficient noise to give an accurate indication depends on the octave band observed and the amount of change made. The low-frequency octave bands require more time to stabilize, and major changes in equalization require more time to provide LED indications. Up to 20 seconds may be required for large lowfrequency changes, while 1 second is sufficient for midand high-frequency changes. Note that when the M615 is turned on, at least one minute is required for the circuits to stabilize and provide proper LED indications.

ANALYZER CHECKOUT

The M615 Analyzer may be checked for proper function prior to use as follows:

1.Connect the line cord to a 108-132 Vac (M615), or 90-125 or 180-250 Vac (M615-2E), 50160 Hz power source. (Select the proper operating voltage using the VOLTAGE SELECTOR switch.)

2.Connect the supplied test/interconnecting cable between the pink noise generator AUX LEVEL output and the analyzer AUX INPUT.

3.Set the ABOVE 1 kHz switch to FLAT, the HIILO ENVELOPE control to 2, and the PINK NOISE LEVEL control to approximately 5.

4.Turn on the ONIOFF switch and allow the unit to stabilize for one minute.

5.Slowly adjust the INPUT LEVEL control until all LEDs are off. Note that the low-frequency LEDs (below 500 Hz) will respond more slowly to INPUT LEVEL control adjustment.

This check indicates that the M615 is operating satisfactorily and is ready for use.

While the M615 is factory-calibrated for AUX LEVEL output to AUX INPUT checkout as described above, a similar checkout using the MICROPHONE LEVEL output to MICROPHONE INPUT may be performed. To account for normal slight variations in response between the auxiliary and microphone connections, set the HIILO ENVELOPE control to 3 for this checkout.

1.Connect the testlinterconnecting cable supplied with the ES615 Analyzer Microphone or a similar cable with male and female professional three-pin connectors between the pink noise generator MICROPHONE LEVEL output and the analyzer MICROPHONE INPUT.

2.Set the 15 dB ATTENUATOR switch to OUT, the FLAT/ES615 switch to FLAT, and both IMPEDANCE switches to either HI or LO.

3.Perform the checkout procedure as described above.

If one or more LEDs remain on, an adjustment may be performed (by qualified service personnel only) as described in the Calibration: Rectifier Level section.

EQUALIZATION: GENERAL

While the final measure of any equalization effort is a subjective judgement of the quality of the sound delivered to the audience, acoustic measurement instrumentation such as the M615AS Equalization Analyzer System can be of considerable assistance in more efficient and consistent equalization procedures.

The M615AS consists of a pink noise generator (equal energy per octave), an equalization analyzer and an omnidirectional analyzer microphone with a flat response compatible with the analyzer. The analyzer indicates the relative signal amplitude of each octave band for the complete audio spectrum.

In general, equalization analyzer equipment is used to allow equalizer adjustment by measuring sound system performance instead of by subjective evaluation. Connection, setup and operation of the equalizer remains the same. Recommendations regarding various equalization objectives are also generally applicable.

Analyzer equipment usually is used first to establish the desired house curve, which is the sound system response characteristic preferred for that particular application. For playback equalization the analyzer microphone is located in the main audience area and connected to the equalization analyzer input. The noise generator is connected to the audio console or mixer input and the volume adjusted to provide a sound level at least 10 dB above the room ambient noise level. In such an arrangement the analyzer is placed in close proximity to the equalizer so that, as equalizer adjustments are made, the results are easily observed. Adjustment for a flat response in the audience area of a large room will usually result in an overly bright sound. Common practice is to adjust for 3 dB per octave rolloff of the high frequencies starting at about 1 kHz for rever- berant-field equalization. Frequency response is then checked in other locations in the audience area and, if necessary, the equalizer is readjusted slightly to improve the average response for the entire audience area. Final equalization adjustments are based on listening tests using typical program material.

Home entertainment system equalization using instrumentatioy is similar to playback equalization, except that an amHifier (or amplifier portion of a receiver) is used insteyl of a mixer, the analyzer microphone is placed in the ,desired listening location instead of the main audi- e w e area and the system is equalized flat for near-field eqdalization.

Equatization of a sound reinforcement system using instrumentation is the same as for playback equalization. The sound system is equalized initially to produce the desired house curve with all microphones turned off. The individual microphone volume controls are then increased equally (assuming microphones have similar characteristics) or to the approximate use settings, below the feedback threshold. The mixer master gain control is then increased slowly while observing the equalization analyzer. As the feedback threshold is approached, the analyzer will show a prominent increase in amplitude of the frequency band where feedback is about to, or does, occur. This band is then suppressed using the appropriate equalizer filter control. This process is repeated until the major feedback tendencies have been sup-

pressed and a reasonable sound volume level can be produced. A talk or other performance test of each open microphone is then conducted and the quality of the sound produced is sampled by listening in various locations throughout the audience area. Additional equalization adjustments are made based on the listening evaluation, while taking care to avoid any significant reduction in the feedback threshold previously achieved.

Equalization of a stage monitor system using analyzer equipment is similar to playback or house system equalization except that measurements and evaluation are confined to the performer'sstage area. The pink noise generator is connected to the mixer input and the audio console or mixer volume adjusted to provide an output from the monitor speakers at least 10 dB above the ambient noise level. A person is placed in front of the lead performer's microphone (to simulate performance conditions) and the analyzer microphone is placed next to the person at ear level to sample the sound field in that area. The analyzer microphone output is viewed on the equalization analyzer and initial response adjustments, such as low-frequency rolloff, are made. The audio console or mixer volume control for the performer's microphone is then set to a stable point slightly below the feedback threshold. The monitor master gain control is gradually increased until an obvious increase in amplitude in a particular frequency band is noted on the equalization analyzer. This is the onset of feedback and the appropriate equalizer filter control is used to reduce the system response in this area. This process is continued until satisfactory gain before feedback and the desired response is achieved. A voice test of each performer microphone position is made to determine if an adequate feedback threshold is attainable. Final adjustment of the equalizer and/or individual channel tone controls (if available) is made to improve quality or intelligibility of the sound presented to the performers.

OPERATION

This section contains basic instructions for connecting and operating the M615AS Equalization Analyzer System. It should be noted that individual room acoustics, equipment characteristics, and increasing operator proficiency will all contribute to the development of equalization analysis techniques which may differ somewhat from the guidelines described here.

Connections

Interconnect the units of the sound system as for normal operation. Connect the M615 pink noise generator output to the input of the console, m i ~ e r ,preamplifier (either microphone, or aux level using the supplied test/ interconnecting cable), amplifier or receiver, and, if the M615 microphone-level output is used, set the MICROPHONE IMPEDANCE switch as required. Connect the ES615 Analyzer Microphone to the M615 microphone input. Set the FLAT/ES615 switch to ES615 and the microphone input IMPEDANCE switch to LO. If a flat-response equalization microphone rather than the ES615 is to be used, set the FLAT/ES615 switch to FLAT and the IMPEDANCE switch as required.

Sound Reinforcement Systems

1. Place the speakers of the sound reinforcement sys-

tem in listening area locations to provide optimum audience coverage. Maximum coverage in many installations is obtained with the speakers on each side of the sound source and as far forward as possible. Assuming a single speaker to either side of the sound source, the speakers should be positioned so that an imaginary line from the center of each speaker runs to the back row of the audience area. For "clustered" speaker installations covering a wide area, each speaker should be positioned so that its angle of coverage slightly overlaps that of the speaker next to it as their sound output enters the audience area. The pink noise generator output of the M615 may be used (at low system power levels) to provide an audible signal source for speaker placement checkout. A listening test of the audience area may be made for dead zones, frequency response variations, or other symptoms of improper coverage. Avoid listening to speaker pattern overlap areas, as these are apt to be erratic.

2.Set the front-panel ABOVE 1 kHz switch as required. A system equalized using the ROLLOFF position provides a smooth 3 dB per octave rolloff starting at 1 kHz, which usually results in the most pleasing audience reaction. Research has shown that a perfectly flat frequency response curve generally yields an overly bright sound that is made more natural by using this gradual high-frequency rolloff. The FLAT position is normally used only for near-field equalization particularly in small or acoustically "dead" rooms, or for electrical equalization of preamplifiers, tape recorders, and amplifiers.

3.Set the 15 dB ATTENUATOR switch to OUT, the HI/ LO ENVELOPE control to 12, and the PlNK NOISE LEVEL control to 0. Place the ES615 or other equalization microphone on a microphone stand at a seated listening height, approximately on-axis to one of the speakers and mid-way between the speaker and the rear of the audience area. Turn on all units in the system and allow one minute warmup time. Starting at 0, turn the INPUT LEVEL control slowly up until the first LO LED goes out or flickers. Note the INPUT LEVEL control setting and reduce it by approximately 3. This assures that the input sensitivity is low enough to prevent the ambient noise level from affecting equalization results. If the MIC input is being used and the initial INPUT LEVEL control setting is 4 or less, the 15 dB ATTENUATOR switch should be set to IN and the process repeated. If the INPUT OVERLOAD LED comes on during adjustment of the INPUT LEVEL control, the control setting is too high and must be reduced for proper LO LED indications. IMPORTANT: The equalization procedure requires a stable ambient noise level. Extraneous noise such as construction, rehearsal, or loud conversation will interfere with measurements and adjustments.

4.Slowly increase the PlNK NOISE LEVEL control until one to three HI LEDs go on. Most LO LEDs will go out; those remaining on at either end of the spectrum indicate the bandwidth limits of the sound reinforcement system. It is important to note that any attempts to equalize at these bandwidth limits must be done judiciously. Excessive boosting of these frequencies

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