The way you mount a speaker driver (or enclose it) will have a significant impact on how it sounds. This is due to the nature of how speakers and soundwaves work. There are some common mistakes people make with mounts and enclosures – from selecting the wrong materials to overtightening the screws. This is all explained below. But first, it’s important to understand why what’s around a speaker matters a lot.
The speaker driver rapidly moves the cone back and forth in a pistonic motion. When it does this, it pumps out soundwaves both forward (a frontwave) and backward (a backwave). You don’t want the frontwave and backwave interfering with each other. This can cause wave cancellation. You want to isolate them and that’s what a speaker enclosure helps with. If the frontwave and backwave do mix, it may cause you to lose some of the amplitude of the waves (this is how noise-canceling speakers work).
Baffles and Enclosures
You also have to consider how the frontwave will be impacted by the baffle (the surface around the front of the speaker). If the distance from the center of the speaker to the edge of the baffle is larger than the wavelength of the sound, then sound at that frequency will bounce off the baffle and be heard louder than it was intended. This increased output of higher frequency sounds is called the baffle step response.
Putting a speaker driver in a box or another speaker enclosure can prevent a lot of the interference because the backwave gets trapped inside. For example, when a speaker is put into a car door, the door acts as the enclosure and traps the backwave inside so only the frontwave enters the car for people to hear.
Common Speaker Enclosure Mistakes
If you are trying to enclose (or mount) your own speaker driver or install a speaker into another finished product, here are the common mistakes to avoid.
Not isolating the backwave from the frontwave. Make sure whatever egress there is behind the cone for the backwave that it’s far enough away to prevent wave cancellation with the frontwave.
Putting the speaker grill (or cover) too close to the speaker cone. If there isn’t enough space for the cone to move freely back and forth it can rub and buzz against the grill.
Creating an open space cavity in front of the speaker. That space will act as a megaphone and adversely impact the frequency response of the speaker.
Using the wrong material for the gaskets for mounting. Whether a speaker driver is front- or rear-mounted, it must have a gasket that creates a full seal. Rubber or foam rubber work well because they compress just enough to seal with most surfaces. Something that’s too hard (like metal) could create unwanted vibrations or not compress to form a full seal. A gasket material that is too soft could compress too much and not end up acting as a gasket at all.
Over tightening the screws. Most people think tighter is better with screws. With speakers, that extra torquing as you mount it could deform the speaker basket. That could, in extreme cases, cause the voice coil to rub.
Loudspeaker manufacturers are experts on speaker mounting and enclosures. The high-tech testing tools they have at their disposal is a big advantage in determining how to get the best sound possible in the finished application. Manufacturers can give advice both on installing their off-the-shelf products and the custom-built speakers they offer. Their knowledge should cover everything from material selection, to correct torque settings, to handling limited space issues, and they can help you get your speakers to perform the best they can for their intended purpose.