What effect does increasing the internal volume on a sealed box have with the sub performance? If the specs on a sub call for 0.875 cubic ft. sealed, then how will the performance be affected if the sub is used in a sealed 1.25 cubic ft. box?
I can answer part of this question, anyone let me know if i'm wrong. Incresing the volume past the recommended could effect SQ first of all. A larger volume will also allow the the sub to hit deeper. Polyfil is used inside of a box to "increase" the volume of the enclosure by 10%, without actually making it bigger.
Does this basically mean I would be trading SQ in exchange for more SPL?
Anyone know how far the SQ would drop by using a sealed enclosure that is approximately 0.5 cubic ft. larger than the recommended volume? Would it be a drastic drop off? How big is too big when it comes to increasing the volume for a sealed box?
You can't just make the box any size you want. If the specs call for a .875 cf sealed box, then make it .875 cf. You can make the box a little bigger or smaller, but don't tweek it a ton. Just make sure if you do make the box bigger, your not gonna need as much power. It's not hard to blow a sub in a box that's way too big.
The box size requirement is dependant upon many factors, including the subwoofers suspension, motor strength, cone mass, size, as well as many other factors. A sealed box is simply a specific mass of air that reinforces the subwoofers suspension, a more efficient sub, like those designed for ported boxes, will have low mass cones, a loose suspension, or a very strong motor. These subwoofers will work well in a smaller sealed box. Subwoofers with a tight suspension, weaker motor, or heavier cone need a larger suspension to take advantage of it. If you go too large, you'll end up with good transient response and bandwidth, but you lose mechanical control over the subwoofer. Too small, and the resonant frequency of the system will be high, the sub will have a very peaky response, and will require more power to reach it's excursion capabilities.
What size enclosure would you recommend? The subs are Diamond Audio D612D4s. The manual calls for 0.875 cubic ft. sealed, but a couple people have told me that was incorrect and that a 1.25 cubic ft. sealed box was required. I want a balance of SQ and SPL.
The manual says it requires a 30 Hz subsonic filter for a vented enclosure. The SSF on my amp is locked at 25 Hz, so I'm sort of screwed there. I'm just trying to figure out what I can do to still get decent SPL while keeping SQ.
1.25 is right on the money if you want a .707 Qtc. I'd go 1.25 gross and stuff it with some polyfill to dampen resonance, a little over a pound would do.
"Q" is quality of damping, duration of sustain time. How long the cone flutters, basically. A lot of box designers and speaker manufacturers design their speakers and enclosures so that this resonance occurs at the lowest of their frequency range, so that efficiency is improved. A low Qtc indicates high damping, or an overdamped condition. A high Qtc indicates low damping, an underdamped condition. Thus, as the box gets larger, the Qtc will get low because the box is less resonant (not as peaky of a response at resonance). As it gets smaller, it will become higher because small boxes are more resonant.
The number 2 is very important here. You'll notice that .707 is the inverse of the square root of 2 (which is 1.414). Another important thing to note is that every time you double box volume, the resonant frequency of the system will increase by a factor of 1:1.414 (1.414 being the square root of 2). A .707 Qtc is considered optimal because it is considered to be critically damped, right between 1 and .05, which 1 is underdamped and .5 is overdamped. It is considered the best compromise between frequency response and power handling.