Eminence is often asked to provide cabinet plans for our woofers. We do not provide drawings with specific cabinet dimensions and details, but we do offer cabinet recommendations in the form of specifications. The reason for doing it this way is because we do not know what size or shape cabinet you need or want to build. For example, if we specify a rectangular box of “A” width x “B” height x “C” depth, someone may not be able to fit the “B” height where the cabinet needs to be installed. Our approach allows the designer/builder the flexibility to build any shape. We provide multiple recommendations for all of our pro audio and bass woofers within their respective pdf files.
Unfortunately, one magic, do it all enclosure for every speaker does not exist. There are trade-offs involved in cabinet design. You must decide how your speaker and cabinet should perform to meet your needs. The main concerns are mechanical power handling (how much power a particular speaker will handle in a specific cabinet), how low the cabinet needs to play, and how much output you will need.
From the Eminence cabinet designs, the box should be built to the Vtotal specification. This is the internal volume of your cabinet with no speaker in it. If the cabinet will have bracing and you want to be precise, be sure to account for the volume of the bracing and add it to the internal cabinet volume. If the change is no more than 10%, it is probably not very crucial to include, as it should not significantly affect the end result. No need to worry about the volume of the speaker and ports! That difference in volume is represented by Vb and has already been calculated. Remember, you’re building to Vtotal.
If you are looking at a ported or vented design (ported and vented have the same meaning), round vents are specified in most of our recommendations. The number of vents to use is given. The diameter of the vent is represented by Dv. The length of the vent is represented by Lv. Some of our recommendations do actually call for a rectangular vent shape. In this case, Hv represents the height of the vent, Wv represents the width, and Lv represents the length (or depth that extends into the cabinet).
In regards to vent placement, Eminence recommends asymmetrical placement around the speaker. Some people may also consider rear porting a cabinet. This is acceptable, but keep in mind that most of the sound around the resonant frequency of the cabinet will be produced by the vent. Thus, a lot of your bass will come from the rear of the cabinet. You need to consider how you will use the cabinet and where it will be placed if you consider rear porting. For example, will a wall block your sound or influence the bass? How do you want the cabinet to project to the audience? You will also see “vent ends = one flush end” in our recommendations. This simply means that every vent should have one flush end with the exterior of the cabinet.
For your knowledge, Fb represents the box tuning frequency. F3 is the –3dB frequency the cabinet can produce. This is considered the lowest audible frequency. It is a point 3dB down from the mid-band piston response. QL basically represents the quality of the box. An ideal QL for a vented enclosure is 7. This assumes the box is well built, free of voids/leaks, and that good materials are used to construct.
Minimal, medium, or heavy are used to describe the amount of acoustic fill to use. This is somewhat of a subjective detail. A good rule of thumb for a sealed enclosure is to use a ½ pound of acoustic material for every cubic foot of internal volume. You can actually stuff the box. A good test to determine if you need more or less is to snap your fingers inside the empty box. If the “snap” rings, you need more fill for a “dead” sounding box (ideal environment for sound reproduction, no reflections). If there is no ringing or reflections heard when you snap your fingers, then you have enough fill. For a vented enclosure, you do want the sound to resonate/ring inside the enclosure. You want to line the walls of the enclosure. We recommend starting with no lining and work your way up one wall at a time to determine what sounds best. If you use too much acoustic material, the bass will sound well defined, but dry. If you use too little, the bass will be loud, but undefined. Do not block the vents. They need a clean air flow to operate correctly.
Located within the header of each recommendation, you will often see “displacement limited” to a specific amount of power. Often, it is well below the power handling published for the speaker. This represents the mechanical power handling of the speaker in that enclosure. Keep in mind that a speaker’s performance will vary from enclosure to enclosure. The bigger the enclosure and the lower the tuning frequency (if ported), the more abusive it is to the speaker. The mechanical power handling is the limit for the speaker and enclosure. Do not confuse this with the speaker’s published power handling.
Another common note located within the headers is to use a high-pass filter set to a specific frequency. This is to prevent over excursion issues. The high-pass filter rolls off the abusive lower frequencies that would harm your speaker. The degree of the roll off is determined by the slope of the filter (steeper slope = greater protection). Ideally, this is done with active controls, like an electronic crossover. A passive filter can certainly be used, but it will be very difficult to find an off-the-shelf product and probably quite expensive to make your own. For bass guitar, the high-pass filter is indeed added protection, but not a necessity. This is more for pro audio applications.