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Why Won’t My Mic Work?

we've provided a few signposts that will help you with the sometimes-frustrating journey of determining the microphone input specifications of a given device.

February, 07 2012 |

The eight-member team of Shure's Applications Engineering Group gets a lot of questions. They come every day from customers all over the world through a variety of channels - email, phone and via the interface on the company's Find An Answer (FAQ) database. It's Apps' mission to problem-solve.

According to Apps chief Michael Pettersen, one recurring question is: "Will my microphone (wired or wireless) model 'X' work with my whatchamacallit?" Or "Why doesn't my Shure mic work as expected with my new i-Thingamabob?" While we'd love to have the microphone input specifications of every device in the world that needs a microphone, it's just an impossible task. Instead, we've provided a few signposts that will help your navigate this sometimes-frustrating journey.

To select the proper microphone, it is essential to have specifications for the microphone input of your device. Typically, these specifications will be provided in the Owner's Manual, most of which (for current or recent products) are online and free.

Vital Microphone Input Specification #1

Called 'Input Sensitivity' or 'Nominal Input Level', this specification indicates how strong of a signal the microphone must supply to satisfy the microphone input of the device. This specification might be given in millivolts (mV), or volts (V), or in a minus dB form (-dBV, -dBm, -dBu, -dBs).

In the Shure product line, there is a wide variation of microphone signal levels available depending on the model. If a microphone is selected whose signal level is too low for the device, the audio will be noisy and low in level. If a microphone is selected whose signal level is too great for the device, the audio will be distorted and unintelligible. Proper matching of the microphone's signal level to the device's required input level is imperative.

Vital Microphone Input Specification #2

Called 'input impedance' or 'actual input impedance', this specification is important as it determines the proper impedance range of the chosen microphone. This specification will be given in ohms. Contrary to popular audio mythology, the impedance of a microphone does not need to exactly match the input impedance of the device.

In the Shure product line, there are different impedances available depending on the microphone model. If a microphone is selected whose impedance is lower than, or equal to, the device's input impedance, the microphone will work as long as it provides the proper signal level - see #1 above. If a microphone is selected whose impedance is greater than the device's input impedance, the microphone will not deliver its full signal level to the device and the audio will be noisy and low in level.

Vital Microphone Input Specification #3a, #3b, And #3c

The final requirements are:

a) The type of microphone input connector on the device
b) How many connection points are inside the connector
c) What is the function of each connection point

This specification will be the name of the connector, such as: XLR female, 3.5 mm mini-phone jack, TRS 1/4 inch female phone jack, screw terminals, TINI QG connector.

Each of these connectors has at least two connection points and most have three (or more) connection points. Common circuit functions include: ground, audio send, audio return, and DC bias. It is imperative that the circuit function of each connection point be known so that the proper microphone wiring can be determined.

In the Shure product line, there are different wiring schemes available depending on the microphone model. If the microphone connections are not properly matched to the device's input connector, there may be no audio, or funny sounding audio, or the microphone might be damaged if there is an unexpected voltage appearing on the device's connection points.

And finally, just because two connectors mate does not mean that each is wired the same.

Lab Test

Now that we knew what we were looking for, we set out to determine how easy or difficult it might be to find this information. We put it to the test by thinking about which kinds of devices you might want to connect to your microphone and settled on BeachTek's DXA-SLR, a camera adapter that's tripod bushing-mounted and used to power two condenser mics.

The challenge: Answer these questions with available resources online or contact the manufacturer. And if we contacted the manufacturer, how long would we wait to get a response? Here's what we discovered:

Input sensitivity
In this case, it relates to the camera device (rather than the adapter)

LO Gain: -51dBu
HI Gain: -36dBu

Input Impedance
According to our BeachTek expert: "If you look at the specs of most mics, they usually indicate a minimum input impedance of 1k ohm. Virtually all of today's audio equipment has an input impedance much higher than that."

Type of connector

Balanced XLR (2)
Unbalanced mini-jack (1)
RCA inputs (2) - for playback monitoring

Number of connection points

3 pin for XLR

Function of each connection point
On XLR connectors, these are standard:

Pin 1 - Ground pin
Pins 2 & 3 – Signal carrying

BeachTek on condenser microphones: "These mics have much higher sensitivity than dynamic mics but require power to operate. They will either have a built-in battery or be powered by an external power source called phantom power – normally 48 volts. Phantom power can come from a mixer, camera or our DXA-SLR adapter - it sends 48 volts down the XLR cable on pins 2 and 3 to power the mic."

We were able to find most of the information we were looking for by checking out the operating instructions for the DXA-SLR we found online. Remaining answers were provided by BeachTek's CEO, Harry Kaufmann, who picked up the phone and called us back within an hour or two of our email message. According to Harry, "In this case, we're manufacturing the adapter, so customers have to be especially careful to match the mic's characteristics to the device's, which in this case is a camera." And just like Shure, he said, "We get calls, too. There's almost nothing more important than educating our customers."

CONCLUSION

So there you have it. There are many variables that affect whether a particular microphone (wired or wireless) will work properly with a particular device. Still stumped? If online resources or the printed materials that came with your device don't include the specifications indicated here, get in touch with the manufacturer. Not all will have the real time 'talk to a real human being' technical support that Shure offers, but most will offer some level of customer service.

Davida Rochman

A Shure associate since 1979, Davida Rochman graduated with a degree in Speech Communications and never imagined that her first post-college job would result in a lifelong career that had her marketing microphones rather than speaking into them. Today, Davida is a Corporate Public Relations Manager, responsible for public relations activities, sponsorships, and donation programs that intersect with Shure at the corporate and industry level.