Copyright © 2014 AudiologyOnline - All Rights Reserved



 

In-Ear Monitors: Tips of the Trade

In-Ear Monitors: Tips of the Trade

Keith Gordon

October 13, 2008

Until recently, hard wired in-ear monitor (IEM) systems were mainly used by top touring acts;however, new, lower-cost wireless and hard-wired IEM systems are making the technology available to a broader range of performers and audio engineers. Do you have musician patients? Are you getting calls from musicians who are considering making the switch to IEMs and want to discuss it with you?

It is no secret that exposure to high sound levels from conventional stage monitors may cause irreversible damage to the inner ear, resulting in permanent hearing loss and tinnitus. Personal monitoring devices, although miniature in size compared to stage monitors, are capable of producing harmful levels of up to 130 dBA at the eardrum. However, with proper use and guidance from a well-informed audiologist, personal monitoring devices can allow performers to hear the full dynamic range of music while protecting their ears from permanent hearing damage.

Advantages of IEMs

Hearing protection

There are a number of advantages to IEMs over traditional floor monitors, or wedges. The first advantage is the hearing protection that can be gained by isolating the performer from loud stage volumes. This potentially allows for monitoring at lower volumes while still being able to hear accurately;however, the onus remains on the performer for keeping the volume down. This isolation also translates into both better pitch and reduced vocal fatigue, the latter of which can become a major concern on longer tours or with performers who do long shows or perform frequently.

Improved sound in the audio signal path

The next benefit of IEMs is improved sound everywhere in the audio signal path. There is greater accuracy having only those instruments one wishes to hear in the monitor mix without anything unwanted bleeding in from adjacent monitors or instruments. This eliminates volume wars where everyone on the stage turns up their monitors to hear themselves over everyone else's monitor.

Absence of feedback

Furthermore, with no acoustical connection between microphones and monitors, feedback becomes a thing of the past. The audience will also enjoy the absence of feedback. In addition, with no wedges blasting onstage and bleeding out into the room, the sound technician has better control of the audience mix instead of being forced into compromises, such as turning the public address system (PA) louder just to arise above the stage volume.

Cost Savings

Finally, for touring performers, IEMs save money compared to expensive wedges and amplifiers, especially when elements such as labor for setup and teardown, weight and space on trucks, extra cabling, and large road cases are factored in.

Disadvantages of IEMs

Isolation from audience

It is not all rosy in IEM land. The major complaint concerning IEMs is that the same isolation from external sound that provides hearing protection also removes the connection to the outside world, such as audience noise, and upsets the traditional feel of being onstage. This can be partially addressed through ambient microphones that allow performers to hear some room sound. A good monitor engineer will also fade these room microphones in and out between songs so that more audience noise is audible between songs when the cheering is most desirable.

Isolation from conversation

Another limitation of IEMs is that the isolation they create impedes conversation;therefore, one is forced to take IEMs in and out repeatedly, which can lead to ear irritation. Custom models do retain their shape and survive this regimen better than universal plugs that employ foam;however, there is no easy solution for overcoming the isolation issue. The only possible options are an expensive Sensaphonics unit requiring dedicated earpieces with built-in microphones and an innovative Westone unit employing external microphones and DSP that is compatible with most custom IEMs, including Westone, Starkey Labs, Future Sonics, and Ultimate Ears.

Occlusion

The next disadvantage of IEMs is occlusion, the unnatural low frequency sound of our own voice caused by bone conduction that we are all familiar with when we plug our ears and speak. Normally, the sound energy escapes our open ear canal, but with an IEM in the way, it gets reflected back to the eardrum. Although pulling the IEM partially out of the ear canal may alleviate occlusion, it also breaks the seal, destroying bass response and eliminating the majority of hearing protection. Destroying the bass response will also lead the performer to turn their IEM much louder to compensate for the loss of bottom end, so this is not a recommended solution for occlusion. Realistically the only method for dealing with occlusion is to have the impressions taken as deeply as possible, thus minimizing the space between the IEM and the eardrum. It is also important to counsel your musician patients to take the time to acclimatize themselves to wearing IEMs in rehearsals before they move to playing live shows with them.

Lack of bass

The final complaint with IEMs is the lack of physical bass energy. This complaint is heard especially from musicians who rely on low frequencies such as drummers and bassists. Those musicians who really need bottom end are strongly encouraged to try the Future Sonics Atrio series as they produce the strongest bottom end of any IEM on the market. Professional musicians may also wish to upgrade to the custom-fitted Future Sonics Ear Monitor that employs the same driver (speaker) technology.

For seated performers, a butt kicker or shaker can be attached to the stool to supplement the bottom end. There are also floor panels for standing musicians that provide the same effect, but these are rare. They are mostly in houses of worship where the stages are large, the equipment remains set up permanently, budgets are reasonable, and most importantly, keeping the volume low is of tantamount importance. In clubs or on small stages, the instrument amplifiers are kept close to the performer, or a floor wedge or subwoofer is used with just the kick drum and bass guitar fed into it to add bottom end energy.

One v. Two IEMs

To overcome some of the limitations of IEMs, such as isolation from the audience, some performers will wear just one IEM. This is not a recommended solution, and it is important that performers wear an IEM in each ear, for many reasons. Our body's natural hearing protection mechanism, the tympanic reflex, works with both ears together. Its effectiveness is diminished when one ear is protected, because it leaves the open ear more vulnerable to loud sounds. There is also a stereophonic boost (approximately 6 dB) in perceived volume when two earphones are used together. You can try this yourself with a set of earphones and an MP3 player. Start by listening to just one earphone then putting in the second without turning up the volume. The perceived volume of the first earphone will seem to increase when the second earphone is added. Therefore the converse of this, using one IEM, means the volume must be 6 dB louder to get the same perceived volume, thus exposing the IEM ear to unnecessarily excessive volume. It also halves the listening time before the onset of hearing damage.

Pros v. Cons - Summary

The benefits of IEMs outweigh the downsides for most performers. This is particularly true once a performer has had some experience with them and has taken the time to become acclimatized to wearing them, which is the case with any new instrument as well.

Selecting and Fitting IEMs

IEMs come in two flavors, custom fit (e.g., Future Sonics Ear Monitors) and universal/generic ear bud-style (e.g., Future Sonics Atrios). Most performers start with lower-priced universals to try IEMs and get used to them prior to committing to more expensive custom-fitted models. This is due to the major price difference between customs and generics (custom, $799 vs. generic, $199).

Listening evaluation

When having patients evaluate IEMs, ask them to bring in what they are currently using, even if it is just a set of iPod headphones. First, have the patient compare only two models at a time and choose the favorite between the two. Then, have the patient compare that favorite to the next comparison model and again choose the favorite between those two. It is necessary to compare only two at a time because the ear has a short memory for preferences. Please note that you should also use this technique when comparing other pieces of musical or audio equipment involving listening.

When selecting source material for comparison, remember live instruments have greater transient responses than pre-recorded material such as CDs or MP3s. This is because pre-recorded material gets compressed in the mixing and mastering stages. Therefore, if possible, try and use real instruments or attend a band rehearsal. If this is not feasible, find a test or evaluation CD with uncompressed instrument tracks. Failing that, have the musician bring a rough mix of his or her own recordings without any compression or a recording from a live show.

Begin the listening evaluation at lower volumes before gradually turning up the levels as the comparisons progress. This is because patients' ears will not be able to readjust quickly after exposure to louder volumes that induce the tympanic reflex. Most importantly for making valid comparisons is to ensure the volume is the same for each IEM being compared. This is not simply making sure the volume control on the CD player has not moved. Every IEM has a different design with different impedances and sensitivities and thus will output a different acoustical volume for the same electrical input from the amplifier. Therefore, it is necessary to match the perceived volumes between the two IEMs as closely as possible. The reason behind this relates to how our brains interpret louder sounds as better sounding, which can alter the validity of our IEM comparisons.

Fit

In addition to sound quality, fit is another important consideration. Your patients may be wearing their IEMs for hours a day, and for many days of the week between performing and MP3 player listening.

With universal IEMs, fit is primarily a factor of tip material (foam, rubber, plastic) and size, both of which affect comfort and seal. Find what feels most comfortable, yet still provides a tight seal, for your patient. This is important for both isolation from stage volume and bass response. Remember how our ears perceive increases in low frequencies as an increase in overall volume, especially the bottom two musical octaves (20-40 Hz and 40-80 Hz). The benefit of this is that rather than turn up the overall volume, your musician patients can simply boost the bottom end a little.

One benefit to custom-fit IEMs is comfort, because they are molded to the individual musician's ear from an impression made of the ear, which also typically results in greater isolation than universals, up to 25 dB SPL. Customs come in durable hard acrylic, comfortable silicone, and my preference, a hybrid, where the outer portion is hard and the ear tip (canal portion) is softer. The hybrid combines the durability of the acrylic for protecting the electronics while still providing comfort with a softer tip that resides in the sensitive ear canal. With custom IEMs, the fit mainly corresponds to the quality of the ear impressions. It is important for your patients to choose a reputable manufacturer who will rework the fit should it not be perfect the first time. The major manufacturers are Westone Labs, Future Sonics, Ultimate Ears, and Sensaphonics.

Ear impressions

Most of the major custom IEM manufacturers make the following recommendations for taking IEM impressions, some of which may differ from typical hearing aid impressions. First, use a 2" bite block to keep the patient's mouth open while the impression material sets. This is because jaw movement slightly alters the shape of the ear canal. With IEMs, you need to maintain a good seal when your jaw moves into a wide-open position while singing or speaking. Next, it is also beneficial to have the impressions taken as deeply as comfort allows, preferably to the second bend in the ear canal. This increases the hearing protection by adding mass between the external stage volume and the eardrum and minimizes the occlusion effect by reducing the air volume between the IEM tip and the eardrum.

Warranty

Finally, in fitting IEMs it is important to consider physical robustness and warranty. IEMs are professional gear that get used and abused out on the road. One of the often-overlooked benefits of custom IEMs is that the majority of the quality versions have replaceable cables. Frankly, given the investment required, it is best to always encourage your patients to stay with a reputable brand that features replaceable cables on their custom-fit products.

Case Example

Recently at the National Association of Music Merchandisers (NAMM) Convention I had a couple of musicians ask me why they could not get any more gain out of their lead vocalist's IEM system. The minute they added the keyboards to her vocal mix, the IEM system compressed the vocals and caused the "limit" lights to activate on the transmitter and receiver belt pack. As I continued to ask questions with the intention of digging down to the true root of the problem, I eventually determined her IEMs fit so poorly that they fell out constantly. This indicated the "limiter" issue was really a case of her having a terrible seal at her ears. The poor seal meant she had a tremendous amount of loud, external stage noise to overcome, forcing her to turn the IEM system up very loud. To make matters worse, a good portion of the sound her IEM system was managing to create was escaping her ear canal and leaking out due to a bad seal. Lastly, she was receiving very little low frequency content in her mix, because a proper, tight seal is necessary for good bass reproduction.

What can be learned from this example?

First, a good fit is the major starting point for any IEM. Without good fit you are fighting a losing battle for quality sound right from the start. In this example, the poor fit was the root of the problem, causing the IEMs to fall out. In addition, a poor seal can create many of the same problems as poor fit. In the example above, the musician's IEM system was being driven considerably harder than it needed to be because of a poor seal, and clipping (turning on the system limiter) the input stage of the transmitter unit before it sent the wireless signal to the belt pack. Manufacturers must build in these protection circuits on their wireless equipment to ensure that the transmitter portion does not emit frequencies outside of its specified range and compromise other wireless devices operating in the area. Be sure to instruct all of your musician patients in the proper sizing of ear tips and ensure they know how to insert them properly to get a proper seal.

The proper acoustic seal at the ear is also the reason why musicians should not wear their IEMs "loosely" with an intentionally broken seal so that they can hear the outside world better. Instead, they should use audience microphones hung over or aimed at the crowd or ambience microphones placed somewhere onstage away from major noise sources as a regular part of their monitor mix. These ambience microphones are controlled by the band's monitor engineer who turns the microphones up between songs so performers can hear the audience while keeping their IEMs properly sealed.

I learned a trick for wireless IEM users that you can share with your patients, from Mike Prowda, monitor engineer for both Nine Inch Nails and David Bowie. Mike likes to use an external dual-function compressor and limiter before the wireless transmission stage. As mentioned in the example, wireless systems have fairly narrow bandwidths in which each channel operates;therefore, it is best to try and exploit every last part of the dynamic range that is available before going to the wireless transmitter. To accomplish this, it is important to aggressively compress and limit the input signal from the instruments before the wireless stage to utilize all the available signal bandwidth while still keeping it from exceeding the capacity of the wireless transmitter and thus overloading.

This is similar to the approach radio stations take with their transmissions, using multi-band compressors and limiters to deal with different frequencies separately so that the overall energy level is controlled while not making the music sound overly squashed. At the time, Mike was using Aphex Dominators, though there are similar units that can also handle this multi-band compression approach. For those of you without access to advanced tools such as this, try experimenting with whatever compression you do have before the wireless stage to see if you can find improvement.

Always recommend binaural

The importance of the psycho-acoustic effect of using two IEMs versus one is worth mentioning again, as it is critical to the successful use of IEMs. When IEMs are used in both ears, the "stereophonic" effect (a stereo mix is not required, just both ears being used) is known as binaural summation, which yields a perceived 6 db increase in volume without any change in the actual output level of the IEMs' speaker volume. This means if the left and right IEM are each outputting 90 dB SPL on their own and both IEMs are inserted, the brain sums the left and right together and the musician hears what is equivalent to 96 db SPL. The bonus here is that this 6 dB boost is "free" in that it comes without the potential hearing damage associated with those extra 6 dB SPL.

Always encourage your clients to use both IEMs and not just one, like you'll see so many performers do on TV. It makes me cringe to think of how much louder they are blasting that IEM to get the same volume that could be accomplished simply by wearing two IEMs. Even worse, if they are also using traditional floor wedge-style monitor speakers in an attempt to get the "best of both worlds," they will be blasting their open ears, too.

Summary

It is safe to say that personal monitoring is here to stay. Audiologists and hearing professionals are equipped with the tools and expertise to direct musicians and sound engineers in the safe selection, fitting and use of these devices, and to implement effective strategies for prevention of hearing loss. Professionals are advised to take time to investigate before committing to a specific product. After all, your patients will only ever have one set of ears.

Keith Gordon is Director of Marketing and Sales at VitaSound Audio Inc. (www.vitasound.com). He is a veteran audio engineer who mixed monitors for over a decade before overseeing development of a DSP-based hardware/software IEM system in conjunction with Westone Laboratories. He can be contacted at keithgordonca@gmail.com For more information about VitaSound, visit the VitaSound web channel on Audiology Online.


keith gordon

Keith Gordon

Director of Marketing & Sales, VitaSound Audio, Inc.