Q1. How much clearance is required between the bottom endcap and the floor plate?
The quick answer...
gap = nominal diameter / 4 for most drivers orgap = nominal diameter / 3 for high excursion drivers
Consider this drawing....
The principle applied....
Air movement generated by the driver shouldn't encounter any reduction in the CSA through which it has to flowThe maths....
The smallest area is represented by the green cylinder, and has a total area of:gap * circumference = gap * pi * (nominal diameter)
This must equal the Sd of the driver, or in our example, pi * (nominal dia / 2)^2
So ...
gap * pi * (nominal diameter) = pi * (nominal dia / 2)^2
dividing both sides by pi...
gap * (nominal diameter) = (nominal diameter^2) / 4
dividing both sides by nominal diameter...
gap = (nominal diameter) / 4
More accuracy could be obtained by calculating effective diameter from Sd, and factoring in the height of the surround vs driver rebate depth, but this method is going to be fairly close. If you have a driver with a large Xmax, you would build a bit of leeway in by dividing by 3 instead of 4
Sonosub.exe v1.03 currently divides by 5, meaning it's check is not rigorous enough. This will be fixed in the next release.
This would give you.....(all sizes in inches)
| Driver nominal diameter | Clearance for normal driver | Clearance for high-excursion driver |
| 10 | 2.5 | 4.0 |
| 12 | 3.0 | 4.0 |
| 15 | 3.8 | 5.0 |
| 18 | 4.5 | 6.0 |
Q2. How much clearance is required for the port?
The distance between the port intake and the back of the driver must be no smaller than the internal diameter of the unflared portion of the port. The same clearance is required between the top endcap and top cover plate (when used). Sonosub.exe issues a warning if either of these clearances is too smallQ3. Do I need flared ports?
Yes you do. Flared ports allow a higher airspeed before audible turbulence occurs.
See the section on port flares for help with calculating flare requirements
Most sono builders use a roundover bit in the router to flare the port exit in the top endcap.
Making a flare for the port intake is described in the donut ring walk-through
Q4. How much of a problem are the resonances?
In a normal box, a driver-to-rear-wall resonance that occurs in the working frequency range, can be troublesome, adding a peak of up to 6dB. Frequency peaks in a sonosub are not as strong because the reflecting surface of the top endcap is fairly small. Adding some closed-cell foam damping material to the endcaps is good practice. See the Speaker Stuffing page for some more information about damping.The port resonance can't be lessened with damping materials, but it's frequency is nearly always at the top end of the operating range of the sub. Problems here can usually be addressed by lowering the crossover frequency.
Q5. When does re-calculation take place?
When entering data in metric mode, validation and recalculation occurs as you type.When entering imperial data, you need to indicate when you have completed the field. As you type, the foreground color of the field changes to red, indicating that the data has not yet been validated. Pressing "enter" or clicking on another field validates the data. If the format is correct, the foreground color is changed back to black and the results are calculated, otherwiswe an error message is presented.
