Achieving Better Sound in Your Auditorium
By: Gene Houck
Most school auditoriums are designed to be multipurpose performance spaces. While a school may be better served by a music hall and a speech theatre, for reasons of economy, they are combined. The large multipurpose performance space is one the most difficult acoustical challenges, even under the best circumstances.
If you are in the planning stages of an auditorium, make sure that you are working with a designer who can do acoustic modeling, preferably utilizing computer modeling with programs such as EASE (Enhanced Acoustic Simulator for Engineers). Visit www.nsca.org to find a sound contractor near you. Most of you reading this, however, are looking for ways to improve an existing building. So, what are some of the things you can do?
First of all, much of the sound we hear in an auditorium is reflected sound. Only a fraction of the sound from a loudspeaker, the “direct sound,” actually hits the target (the ears of the audience). The rest of the sound, the “indirect sound,” continues on, crashing into walls, floor, chairs, beams, roof, windows, and doors. There are ways to improve good reflections and minimize bad ones.
When sound mixing an event, roll off low frequencies. Bass energy is omni-directional and bleeds into everything on stage. Reducing the input and amplification of low frequencies is essential to a good mix. Most mixing consoles will have a high pass filter (actually a low cut filter) on each channel. By engaging this filter in all but a few low end channels (such as a bass guitar, kick drum mic, or cello, for example), you will clean up the sound and intelligibility. Believe it or not, one of the best ways to improve your auditorium sound is unfortunately overlooked more often than not. It is also the easiest and one of the most economical improvements a school can make.
This simple action is improving your microphone knowledge and, in some cases, your microphones. How is this so? The microphone is the first link in your sound signal chain. Bad sound in means bad sound out. While it may be true that a poor quality mic can be the culprit, bad sound, as it relates to a microphone, can also be caused by wrong mic selection, improper handling, and improper placement.
During these economic times, it is of particular importance to make every effort to look for ways to make improvements without making bills. Many audio renovation jobs have been put on hold indefinitely. While some of these projects may be unavoidable, taking a fresh look at your mic locker can give you a jump start to your renovation without the high price of speakers, power amps, and consoles. Some of these items will cost you nothing but a little invested time. Simply improving your microphone selection and placement can have astonishing results in the impact and enjoyment of your next auditorium event.
First, let’s look at the types of microphone that you will need in your school auditorium.
There are two types of microphones commonly utilized today: dynamic and condenser. The choice between a dynamic or condenser mic is typically dictated by the distance to the sound source. A dynamic microphone is commonly used as a wired handheld vocal mic. They can also be effective for miking instruments, as well as “close range” speech. They are rugged and generally less expensive than condenser microphones.
A condenser microphone is better suited for distance miking or capturing a larger area (such as a choral or a dramatic performance) because of their higher sensitivity and output. Condenser microphones require phantom power (provided from the mixing board). They also are a little more delicate and need to be stored properly, keeping them away from moisture.
First of all, before buying more microphones, make sure you know what you already have in your possession. Many schools have never taken an accurate inventory count of their microphones. Have whoever is in charge of your audiovisual department make a complete list of your inventory. Schools that do this valuable exercise almost always are surprised at what they find. They may find that their mics are in worse condition than they thought, but, in some cases, they discover that they already have what they were about to purchase!
To determine if a microphone is a dynamic or condenser, turn off the phantom power at the mixer (there will be a button labeled “phantom” or “48volt”). Make sure that all volume faders are down before doing this. If the mic only works with the phantom power on, it is a condenser. Engaging phantom power will not damage your dynamic microphones.
Now that you know what mics you have, let’s discuss what mics to use where and how to use them.
Public Address or Speech
1. Headset Mic
Headset mics now come in very small and comfortable designs. They have a low profile and can be utilized with wireless systems, as well. With a headset mic, the mic element is nearest to the presenter or sound source of all three solutions mentioned. For that reason, a headset mic has a distinct advantage.
2. Dynamic Mic on a Stand
This is the most common mic used. Although, in most cases, a condenser microphone with its greater sensitivity will bring better results, a dynamic microphone will do fine, but it is extremely important to make sure the speaker is right on the microphone (no more than 2 inches away). If that is unreasonable to expect, use a condenser microphone.
3. Lectern or Podium Microphone
A condenser podium-style mic is effective because it can pick up easier at a greater distance than an inch or two (where a dynamic mic works best). This type of mic is also referred to as a gooseneck mic, since it has a small condenser mic at the end of a flexible gooseneck stand. Set the gain structure or volume with a large enough pick up area so that the speaker can communicate naturally. If using a condenser podium mic, a distance of 1 foot away from the speaker is recommended. This will also minimize the nasty pop or plosives caused by being too close to the microphone.
4. Lapel Mic
This is popular for its low profile, as well as its ability to be used with a wireless system. The most common mistake is to clip the mic too far away from the speaker’s mouth. A distance of one perpendicular hand is recommended.
Often the biggest miking challenge is a choral performance. Here is a place you can save money. The biggest mistake when miking a choral group or choir is in using too many mics. First of all, a condenser mic is the mic of choice. Condenser mics for choirs come in all sizes. A good condenser mic will be able to cover up to 25 people. To avoid feedback issues in choir miking, less is best. Remember, when you double the amount of microphones in a given area, you have a drop in available gain of 3 dB.
You will need to determine whether you are hanging the mics or placing them on the platform. If hanging the mics, there are many manufacturers to choose from. If line of sight issues (such as video screens) prevent you from hanging mics or if your choir is not always in a fixed position, you will need condenser microphones on mic stands. One of the biggest challenges with this is getting the microphones high enough to adequately pick up the higher rows.
Orchestra and Pop/Jazz Bands
For orchestra and band performances, you will have an array of scenarios and many miking challenges to consider. For area miking, such as string and horn sections, condenser microphones can be placed to pick up multiple instrumentalists. For vocalists and close miking of guitar cabinets and drums, you are best served by a solid performing dynamic mic. Having a multipurpose dynamic microphone can be the most used mic in your microphone toolbox.
To Be or Not To Be Wired
When choosing mics, the single largest microphone purchase is most commonly a wireless microphone system. When running multiple wireless systems, this can run into the thousands, even with a “low end” brand or model so, so be judicious when deciding on the use of wireless mics. If freedom of movement is not an issue, consider staying with wired mics. The performance is always optimum, servicing issues are minimal, and you will save a considerable amount of money.
If you make the decision to go wireless, invest in quality. If you can only afford a cheap system, stay wired. A “no name” cheap system will not only be unreliable, but it will produce a poor sound quality.
Lastly, don’t just make a purchase because you have simply heard of a brand. Compare models and brands, and, in the final analysis, trust your ears.
Gene Houck is the national sales manager for Audix Microphones, www.audixusa.com.