Box size vs output

[Cj Kumz]

Let's have three scenarios with the same sub:

1. Sub in recommended box @ rated power.

2. Sub in larger box but being under powered.

3. Sub in smaller box but being over powered.

Question: Will these 3 setups have equal output due to the the fact that all will reach there mechanical limit and move same amount for air??

[Triticum Agricolam]

Making a box smaller or larger doesn't make it louder or quieter over large frequency range, only around the tuning. So you could theoretically have all three boxes have the same output at a certain frequency, but they are all going to have a overall different sound to them.

[Cj Kumz]

Ok so running the sub at rated power would give optimum performance than underpowering compensated with a larger box. Reason I'm asking is I wanna know if its worthwhile to get a big amp when you can just underpower with a cheaper amp and compensate with a large box.

[kingdragon]

It all depends from the enclosure.

To make a large enclosure it can go deeper can have have more volume. Smaller box produces tighter bass.

Now as for the power you better have more power rather than being underpowered as you can kill the sub.

By using ported boxes the hole secret is the tuning frequency. Lower = music , Higher = SPL.

In all ways you must not take it on the edge.....

I wrote down them as simple as I can.

[Cj Kumz]

Thanks for your input. So all in all most important is to make sure we not building boxes that will cause us to pass our mechanical limits.

[Triticum Agricolam]

Thanks for your input. So all in all most important is to make sure we not building boxes that will cause us to pass our mechanical limits.

It is very important to make sure you aren't exceeding the mechanical limits of your sub, but there is a lot more to it than that. Here are some pictures to help illustrate:

This graph is of the output from a FI SSD 15 in various sized boxes all tuned to 33 Hz on 1,000 watts. The green line is a 2 cu ft box, the yellow is a 3.5 cu ft, and the red is a 5 cu ft. FI recommends 3-4 cubic feet.

As you can see, much above tuning the output is pretty much the same, as you get much below tuning the output starts getting closer too, but right at tuning you have pretty significant differences. Please note that this graph is just raw output, these boxes are going to sound much different in a vehicle due to cabin gain, but the graph at least lets you see the differences in output.

When I design and build enclosures for people I'm always looking to get loud, but usually not at a significant expense to sound quality. So when I design, I'm looking to make the box the right size to get the sound that I want, regardless of how it effects power handling. For example I just finished an enclosure for a SSD 15 and it was 2.75 cubes at 32 Hz, which is a little less than what FI recommends. I wanted smooth, even sound that wasn't peaky and that's exactly what I got, though I did sacrifice some potential output capability.

Now lets talk about excursion, here is graph showing the cone excursion from the above three boxes:

As you can see you get increased cone excursion as the enclosure gets larger. The red horizontal line shows where the Xmax is for that SSD 15 driver. Its important to note that Xmax is not the mechanical limit of the sub, its just where it starts to lose cone control and sound quality begins to suffer. Xmax isn't a hard number either, different manufactures have different ways of determining it and will come up with different results for the same sub. Usually the mechanical limit of the sub is significantly more than the Xmax. For example, a Stereo Integrity HT 18 sub, (sister company to Sundown) has an Xmax of 22.5 mm, but a Xmech of 43 mm. Reaching the mechanical limit of the sub can be pretty difficult to do, especially with the subsonic filters we have on today's amp, as long as they are used correctly.

Here is a shot of the cone excursion of the SSD 15 in the 5 cube box:

I've got a subsonic filter set at 25 Hz and I'm putting 2000 watts into it. This is twice the RMS power rating of the sub, but you can see with the subsonic filter in place we don't begin to exceed Xmax until below about 27 Hz and at no point should we get anywhere near to the mechanical limit of the sub.

When it comes to designing enclosures, you have to decide what your priorities are. If you want to get as loud as possible on the least amount of power and aren't concerned with having a peaky box, then build it big. If you are more concerned with sound quality, building it smaller would probably be better.