What Is Phantom Power?

May25

Condenser Microphones and DI Boxes that have active circuitry in them require electricity in order to function. Some Condenser Mics and Active DI Boxes have slots to insert batteries. But, no one wants to have to constantly replace batteries.

Phantom Power to the rescue!

The phantom power button on a Soundcraft EFX8 soundboard.

Phantom Power is DC Voltage (just like battery electricity) that is sent from a phantom power supply through an XLR cable to the Mic or DI Box at the other end.

48V Phantom Power Buttons

Phantom Power Supplies can be stand alone units, but are most commonly built into soundboards. On smaller and lower end mixers, there will be one phantom power button or switch. Once enabled Phantom Power will be sent to all XLR channels. On larger and higher end mixing boards, each channel will have it’s own Phantom Power button or switch. Generally stand alone preamps, used in recording studios, will have a phantom power button or switch.

Behringer Phantom Power Supply

The amount of voltage generally supplied is 48 volts. However, many condenser mics and DIs don’t require a full 48v. Some only require 9, 12 or 24 volts and have built in transformers to reduce the voltage and not damage the mic or DI box.

Most times it will be labeled as “48v” instead of “Phantom Power”. (same thing)

Phantom Power on the Avalon vt373sp

Virtually all modern mics and DI boxes that do not require phantom power (dynamic mics & passive DI boxes) will not have any issues if sent 48v. They simply will not use it. However, some vintage equipment (notably vintage ribbon microphones) can be severely damage if sent phantom power.

If you have the option, it’s best to only enable phantom power to the microphones that need it.

As well, if enabling phantom power, it’s a good idea to mute the channel(s) that will be affected before enabling it. Enabling phantom power can produce a loud pop sound. Once enabled (after the pop) it should not produce any other unwanted sound. If it does, your microphone or cable may be wired improperly.

Phantom power travels through the XLR cable on pins 2 & 3. Audio also travels through the XLR on pins 2 & 3. They do not affect one another. As long as the audio signal is balanced, phantom power does not affect the audio. You should not even know that it’s there! Hence the name, Phantom Power. Sneaky Sneaky!

Difference Between Speaker Cable & Instrument Cable?

May19

Is there a difference between Instrument Cable and Speaker Cable?

YES!!

Instrument Cable vs Speaker Cable

Instrument Cable

Instrument cable (commonly referred to as Patch Cable, 1/4″ Cable or Guitar Cable) is designed to carry a instrument level signal or line level signal over fairly short distances.

Instrument cables have 2 wires in them. One wire carries the signal. The other is a ground wire.

The signal wire is usually somewhere between 18 gauge to 22 gauge. (quite thin)

The ground wire is either twisted or braided around the signal wire in order to shield the signal wire from waves in the air that add unwanted noise to the signal. See Electromagnetic interference / radio-frequency interference (RFI) on Wikipedia for more information on this.

The longer an instrument cable, the more susceptible they are to picking up interference. So, if you have a 100′ instrument cable, it will very likely be noisy. (no matter how good the shield is) For this reason, instrument cables should be no longer than 25′. The shorter the better.

Speaker Cable

Speaker cable is designed to carry an amplified signal over short or long distances.

Speaker cables have 2 wires in them. They are both the same thickness and type of wire. One wire is positive, the other is negative. There is no shielding on speaker cables. Shielding is not needed because the signal traveling through speaker cable is amplified. The strength of the signal is way higher than line level. Radio interference does not affect the signal because it is too quiet to be heard in comparison to the amplified signal traveling through the cable.

The gauge of the wires in the speaker cable vary depending on how powerful the signal traveling through them will be and the length of the cable. The higher the amount of power needing to go through the cable, the thicker it should be. As well, the longer the cable is, the thicker it should be.

Speaker cables should be treated with the same respect as AC power cables. In fact, they are pretty much the same thing. If you have an extension cord with no ground, you can cut the ends off of it, and you will have a perfectly fine speaker wire. (a 2 conductor copper cable)

Can I use one in place of the other?

Both instrument and speaker cables may have 1/4″ connectors on them. They can be hard to tell apart, but are very different and should not be mixed and matched. If you aren’t sure if you are dealing with an instrument cable or a speaker cable, unscrew the connector and have a look at the wires.

What happens if I use a speaker cable for my guitar?

You will have a very noisy signal because speaker cable is not shielded.

What happens if I use an instrument cable in between my amp and my speaker?

You can damage your amp. (Think about a powerful water pump hooked up to a tiny hose.)
You could also melt the cable and potentially start a fire. Instrument cables are not high enough gauge to carry an amplified signal.

The low cut button. What does it do?

Mar21

Low Cut Button

When the low cut button on soundboard is pushed in, it engages a ‘Low Cut Filter‘ on that channel. (same as ‘High Pass Filter‘)

It’s called a low cut filter because it cuts out all of the low sound below a certain frequency.
It’s called a high pass filter because it only allows the sound above a certain frequency to pass through. Both the same thing.

High Pass Filter on Avalon vt-737sp

On the majority of soundboards that ‘certain frequency’ is fixed, hence only having one button for it. On most boards the low cut is at 75hz, 80hz or 100 hz. On some higher end consoles and studio gear, you are given a knob to control what frequency the low cut is at. Some even let you control how gradual or steep the cut is.

Why should I use low cut?

By using low cut appropriately you can achieve a cleaner mix, get more headroom out of your PA and reduce the chance of low feedback.

Low cut is, in my opinion, probably the most under-used feature on audio equipment. It is VERY valuable to have a low cut and can make the different between a clean mix and a muddy one.

Different sound sources produce different sounds with different ranges. (frequencies)

A Bass Amp can produce low bass all the way up to treble
A Guitar Amp produces mainly mids.
A Trumpet produces mids and treble.
Voices very, but generally produce sound from low mids to treble.

If you want a more in-depth look at what frequencies are produced from different sources, I recommend the following link.
Frequency Chart
(an interactive frequency chart)

Unless the sound source for your channel is producing fundamental bass sound, you should engage your low cut. Doing so will eliminate the amplification of unwanted low sound.

This unwanted sound can be:

Microphone handling or floor rumble (from bumping the mic or stepping on the floor that the mic stand is sitting on)
The popping of “P’s” and “B’s” from a voice
Unwanted electrical hum (60hz)
Other nearby sound sources (the bass amp on stage or the pounding subs that are less than 20′ away from your mic)

Low Cut on Soundcraft GB4

When mixing live, the question shouldn’t be, “Which channels should I turn the low cut on for?“.

It should be, “Which channels should I take the low cut off for?“.

My answer at most gigs would be:

Kick Drum
Floor Tom
Bass Guitar
Some Synths (depending on the sound)
Sample (depending on the sound – if there are bass drops, you definitely need it off)
Some Keyboards (depending on instrumentation)

Another plus to using low cut properly is, that when you reduce the amount of unwanted bass going through your PA, you will increase your headroom. This is because it is more work for your power amps to amplify bass. So again, cutting out the unwanted bass, will allow you to get more volume out of your sound system. Not to mention it will sound less muddy.

Low Cut on a Mackie Onyx 1640 Mixer

Mic Preamps: What do they do?

Mar9

Why do I need a microphone preamp?

The output volume of a microphone is very low. Most times, it’s too low to work with at all.

If you have a mic plugged straight into a Mixer or Audio Interface without a preamp, there will not be enough signal. This will result in no sound at all or extremely quiet and poor quality sound.

Modern day Mixers, Audio Interfaces and Audio Processing Units (compressors, EQs, FX, ect) are designed to accept a signal of +4dBu. The volume of typical microphone signal is -65dBu to -40dBu.

This is why a microphone preamp (mic pre) is needed.

Mackie DL1608 Preamps

Does it matter which microphone preamp I get?

Microphone preamps are controlled by just one gain knob and that’s it. Very simple! If all they do is increase the volume, it doesn’t really matter which one you get, right? …… Wrong.

Because mic pres boost the signal so much, they can really affect the sound. Similar to how the sound from different microphones vary.

A mic pre can color the sound to make it sound warmer, shimmery, fatter, brighter, darker, brittle, muddy, dirty or just plain bad.

They can also keep the sound very clean, transparent, neutral & accurate.

API 512c Preamp

Types of microphone preamps:

Solid State Preamps are small and maintenance free. The nicer ones can sound incredibly accurate and transparent. Generally they sound more neutral than a tube preamp. Solid State pres maintain a very consistent sound a low volumes and high volumes. However, if you push them to the point of distorting, the distortion they produce sounds very bad. (this is called clipping)

Tube Preamps have glass tubes in them. Over time tubes may fail and need to be replaced . Many people try putting in different types of tubes to get different tones from their preamp. Tube preamps are larger, they produce more heat and they require more electricity than solid state pres. Tube preamps generally add color to the sound. They have the potential to make things sound very pleasing. As you turn up a tube preamp, the sound changes. The harder you push it, the more dirty the sound gets. The distortion a tube preamp produces is musical and generally warm sounding. So, you don’t have to worry as much about clipping your tube pre. In fact, many people purposefully make their tube preamps distort to achieve certain sounds.

On the vast majority of soundboards (mixing consoles) these days, each channel is equipped with a solid state preamp. The microphone signal runs through the preamp before going through the rest of the board. (EQ, Aux Outs, Fader) Many audio recording interfaces come with solid-state preamps built in. I’ve also recently seen a couple of recording interfaces that had tube preamps in them. (solid state pres are much more common though)

Avalon Vt-737sp

Many standalone preamps include additional features like:

Signal Indicator Lights or VU Meter
Clip Indicator Light
Phantom Power
Pad
Low Cut
Phase Reverse
Unbalanced Instrument Input
Equalizer
Compressor
Impedance Selector

When it comes to microphone preamps, you get what you pay for! Don’t expect to get an outstanding studio quality pre for $100.

The Speed of Sound: How fast is it?

Mar4

Question: What is the speed of sound?

Simple Answer:

1127 feet/second
343 meters/second
768 miles/hour
1236 kilometers/hour

Full Answer:

Sound is a wave. It needs to travel through something in order to move. The speed to which it travels greatly varies depending on what substance it is traveling through. The denser the substance is, the faster the sound wave can travel through it.

Sound travels 1127 feet/second through Air.
Sound travels 3041 feet/second through Helium.
Sound travels 4862 feet/second through Water.
Sound travels 21063 feet/second through Aluminum.
Sound travels 39400 feet/second through Diamond.

All of the above speeds are assuming that the temperature is 20°C (68°F).

In solids, the density of the material (not the temperature) affects the speed that sound travels through it. More solid substances like aluminum conduct sound faster than air.

Temperature affects the density of liquids and gases. The colder they are, the closer together the molecules become to one another. Because of this, one would think that as temperature in liquids and gases rise, the speed of sound through them would fall. However, this is not the case.

Sound travels 4603 feet/second through Water at 0°C (32°F).
Sound travels 4862 feet/second through Water at 20°C (68°F).
Sound travels 5006 feet/second through Water at 40°C (104°F).
Sound travels 5092 feet/second through Water at 60°C (140°F).

Speed of Sound vs Temperature in Dry Air

When we look at the speed of sound through gases and liquids at different temperatures, something interesting happens! When the temperature is increased, the speed that sound travels through it increases too. This is because in gases and liquids, higher temperatures cause the molecules to move faster (and have more energy). Therefore, they can vibrate faster and sound waves can travel more quickly through them.

Sound travels 1009 feet/second through Air at -40°C (-40°F).
Sound travels 1048 feet/second through Air at -20°C (-4°F).
Sound travels 1087 feet/second through Air at 0°C (32°F).
Sound travels 1127 feet/second through Air at 20°C (68°F).
Sound travels 1166 feet/second through Air at 40°C (104°F).

Humidity in the air has a very little, yet measurable effect on sound speed.

Air pressure is often stated as a contributing factor to sound speed through air, however this is incorrect. Air density on the other hand is a contributing factor. The lower the air density the slower the sound travel will be. Although altitude has no effect on sound speed through air, it does correlate with air density and temperature which do. As you go up in altitude/elevation, the air density and the temperature drop.

INTERESTING FACTS:

In a vacuum where there is zero air density, there is no sound at all! This is because there is nothing for the sound waves to travel through.
Volume does not affect the speed of sound.
Frequency (Pitch: Bass, Mid, Treble) does not affect the speed of sound.

If you’re looking for more information about the speed of sound and how it’s affected by things, Wikipedia has some more great information.

Real Time Audio

Professional Audio Blog

Tag Archives: Answers

What Is Phantom Power?

Difference Between Speaker Cable & Instrument Cable?

The low cut button. What does it do?

Mic Preamps: What do they do?

The Speed of Sound: How fast is it?