The om series of microphones offer some amazing advantages over competing mics. Superior gain before feedback, excellent background noise rejection and smooth frequency response help these mics to excel in live reinforcement applications. Additionally, the feedback stability of the these mics allows considerably more freedom to equalize for the sound you wish to achieve, rather than equalizing purely to fight feedback. Like any vocal microphone, constant abuse and saliva begins to take its toll in sound quality over time. Here are some simple steps to get your om series mics cleaned, matched and performing at original factory specs.
These tips are not endorsed by Audix, they are based on our experience with using and maintaining om series mics. Some of the tips listed may void your warranty with Audix, so if your mics don't sound right you may want to send them back to the factory. They have a $45.00 "fix everything wrong with the mic" policy that is awsome.
This is based on the om6 and om7, there may be some variations, namely capsule depth to the other om mics, but it should generally apply to all of them.
The four main things that effect the sound of an otherwise functioning om are:
If you are trying to match up a set of om's, capsule depth is critical. So first measure the distance shown in the picture below to assure that all your om's are exactly the same depth. Note: Audix warns that twisting or touching the capsule voids your warranty so proceed at your own risk. To change the depth, grip the capsule and rotate it inside the housing. Clockwise will lower it and counter clockwise will raise it.
The om's capsules are much closer to the grill than SM58's and most other vocal mics. In the photo below I have arranged an om7 and 58 to show the difference. The grill shape is different on the two mics and the photo accounts for that. As you can see the om is about 3/8" closer than the 58 capsule.
That simple little dome shaped black foam inside the grill can make a tremendous difference in the sound. An om7 with the proper capsule depth has about 1/4" between the grill and edge of the capsule. Some older om's were shipped with various thickness' of grill foam. Thin being good and thick being bad. With thick foam, the capsule actually touches the foam and saliva accumulates around the capsule forming a small chamber that cause the mics to "bark" and sound really dull and boomy. Get rid of thick foam and put in the newer thin foam! You can contact Daniella at Rat Sound (805-278-2826) or contact Audix to purchase the newer 'correct' foam.
Match your foam. Make sure that the foam is of the same type/thickness in all your mics.
Clean the foam occasionally, I know its gross but washing with warm water, and drying it out will make a nice difference.
Clean and dry the metal grill. Use your best friend's toothbrush to really get in there and get the muck out. Warm water and some mouthwash will give the mic a nice fresh smell.
Over time saliva will leave a residue (muck) on the fine nylon mesh on top of the capsule. You can now void your warranty (Audix will still completely overhaul your mic for $45 if you screw up), by removing the Audix serial # tape and gently removing the screen mesh disc. The disk may be glued but your fingernail should be adequate to pry if off. Do not mess with the white venting tape below. Carefully wash the discs in warm water and then with the same tape, replace it after it has dried. Do not worry about regluing. This should work 2 or three times before you need to replace the tape if you are careful. If you do need to replace the tape, do not use electrical, masking or gaff. Try the numbering tape used to label cables, available at electronic stores. Make sure it is the same width, 3/8".
The venting tape. It looks white and kind of fibrous, do not mess with it. There are ports behind the diaphragm and this tape restricts airflow and greatly effects the low frequency response of the mic. If it damaged, your best bet is to get the mic repaired by the factory and brought back to original spec.
Mic Build Variations
There have been some changes over the years in the design of the om7's and other older om mics.
Tall round Vs short round grills. Older om's were shipped with a shorter round grill, less oblong. They also had a different capsule depth, you can try and match these to the new ones but it may be best just to get those dinosaurs rebuilt.
Thicker venting tape. You may notice some mics have two layers of venting tape. The thicker the tape the less low frequencies. The current om7s use a single layer. Two layers is not bad and actually has some advantages, the main thing here that all your mics are the same.
The flat top. Audix makes a flat top grill that fits the om series mics. In some applications the flat top offers several advantages. It keeps the artist lips farther from the capsule resulting in less proximity effect.
Advantages of the flat top:
Disadvantages of the flat top:
Undentable grill. A few years ago Audix switched over to a spring steel grill. It is very hard to dent and the mic will bounce right back up when dropped face down on concrete. If you do not have them, get them. We are considering purchasing and stocking them so if your interested, let me know and I will have Rat make them available
OK, I hope this is informative and helpful. Feel free to post comments on the message board and I will try respond and update this as need be.