I have built to sub boxes and they are only around .5 cubic feet. What will be the result of that? It is a sealed (air tight) box. The subs are getting plenty of power. I'm just wondering if they will blow or not hit as hard or just not play as low?
TIA
BSZ

BTW: The sub wants .88 cubic feet

 

Im not sure about this, but I think if the box is too small, it won't hit as hard. It will still hit, just not as much as it could. If its too big, it makes your bass sound sloppy. Its probably not even a big enough difference that you would want to rebuild the entire ox, so I wouldn't sweat it too much. On the other hand, you have cut the volume down by about 43% of the desired volume, so if you want it perfect ( I know I would), you might want to build another, or explore different options.

 

I'm a little rusty on this, but here goes. If the enclosure is sealed, not ported or leaky, the closer to exact volume the better. This can be calculated based on the specifications of the speaker - btw - this goes for all speakers not just subs. I take it that the mfg provided the 0.88 cf to you. Ideally the volume creates a dampening effect on the movement of the speaker. If the volume is too small, it will dampen it too much. This will cause loss of frequency and introduce distortion. It will also reduce how fast the speaker can move - this also has many effects on performance. Note that if the walls of the enclosure flex - are not rigid - this compromises performance as well as the volume changes dynamically.

All speakers benefit from having the proper type and size of enclosure - usually mfg tells you what the desired type of enclosure is for the speaker. Note: most tweeters are self enclosed and hence are taken care of by the mfg in the design and mfg of the speaker.

 

Thanks for the input. The boxes are constructed of .75 MDF so that is not flexing. The box was actually assembled pretty tight, but I sealed all joints before and after assembly so I dont think there is any air leak. The contors of the stock sub location are insaine. I guess it will be back to the drawing board because I have too much time in it all ready to only do it half a$$. BTW, if anyone has any ideas or better drawings, I would really appreciate the help. One last thing, no external boxes. I know it would be easier, but I need what little space I have in the trunk (uses term loosely)

Thanks,
BSZ

 

I used to build boxes all the time.
Ok, here is the reality of the situation:
If you box is to small (why does this sounds semi-dirty?) .. anyway, if your box is too small you need to run higher wattage to the speaker. The small size of the box makes it harder for the speaker to move. As the speaker moves, the pressure difference inside the box is increased due to the small size of the box. If you are running a small amp, the reduced box size will cause additional strain on the amplifiers as well. Finally, if the speaker is not a high quality one with a very stiff cone, the small box will cause additional distortion due to increased cone distortion from the higher pressures. In summary, the system becomes much less efficient.

All in all, if you have good speakers, and a tough amp, you will be fine.

 

Actually sealed boxes are more forgiving in terms of too big or too small, on the otherhand a ported box has to be dead on or it will sound like crap. That is why it is easier for a begginer (not calling you a beginner btw) to make a sealed box because you can be a little off in your calculations and the sealed box will be more forgiving.
With that being said, why don' t you just rebuild the box to the correct specs if you know it isn't correct?

 

Your box will basically be MUCH less efficient and play no where near its potential. It should still be punchy as hell though

 

Don't forget, most manufacturers require you to add the displacement of the sub's motor structure and basket to the airspace required. For example: The JL 10w7 is recommended to have about 1.25 ft^3. It displaces .9 ft^3, meaning, a box for a 10W7 should be 1.34 ft^3 inside volume.

A good rule of thumb is about +/- 15% from the recommended volume+sub displacement. Smaller requires more power and loses low end extension (the -3 dB point is raised). Larger boxes allow more low end extension but can sound sloppy due to insufficient cone damping. You are most likely to be over 50% off. See if you can milk a bit more airspace out of it.

 

my box is also a bit too small and i was wondering if the fiber fill stuff actually works?

thanks
Rajiv

 

The fiber fill stuff does help, but it won't make up a huge difference.

 

Having the box in there as a guide really helps to see more potential space. I think I've got it to just shy of 1400 square inches. Thats right at .81 cubic feet. That along with some poly fill and I think I'm going to be A O K!! The only PITA is I have to build 2 boxes. Thats the price of fame I guess. Question. How much poly fill do I put in there? Do I stuff it full or just gently lay it in there?

The subs are pretty high quality. PolkMOMO MM124 subs and each one is getting a PolkMOMO C300.2 when bridged produces 550RMS of reasonably clean power.

Once I get thes boxes built, I will slap up the plains for all to see.
Wish me luck cause I'm going to need it.

Jeff
BSZ

 

Stuff it full, you trying to trick the speaker so to speak so it thinks the box is bigger because the poly fil slows down frequency\air\sound. Btw, I didn't notice a difference at all in the last box I built when I did that, sounded the same with or without it.

 

What I gather from previous replies:
-Manufacturer recommended box size is obviously ideal
-Smaller boxes are more "punchy" but a lot more work on the sub due to increase in pressure, can become distorted, and are overall not recommended
-Larger boxes decrease pressure, can also become distorted, are less punchy, may increase the volume, but are overall not recommended

My question is, what if you keep the same overall box volume but greatly change the shape? For example to save trunk space you replace a 2ft x 2ft x 2ft box with a 2ft x 1ft x 4ft box.

Or what if you make it not even rectangular? Maybe have it "U" or "L" shaped to fit in a specific space?

 

nice 1st post
thread you are replying to is 13 years old

 

It's a topical addition to the thread and deserves a response; it's better than adding another thread to the thousands already out there.

Sunday Driver: As long as the square footage of empty space is equal to the recommended area, you should be fine. I'd fill the space with subwoofer batting to keep the air from moving around too much in the box.

 

The air inside acts as a spring or cushion that helps push the woofer back out after the amp uses power to force it in. So the speaker really doesn't care about the shape just the volume. Smaller box = more pressure as there is less space to compress. Now with that said I've found having a really skinny box where a flat surface is very close and parallel to woofer is not ideal as the sound waves inside the box bounce directly back. Of course it really depends on how well the box is built and braced, if its solid construction the shape shouldn't matter.

As for fiberfill this old article sums it up nicely:
http://www.glasswolf.net/papers/polyfill.html
Like anything there is a point where you can go too far. Then the fiberfill starts taking up too much space and makes things worst.

In general if your box has less airspace then it will be louder but not as deep and also require more power. So I've always measured the available air space first, then purchased a sub that is recommended for that given volume. Sometimes this means dropping down to a smaller sub, because in the end I'd rather have an 8" that sounds good vs a 10" that sounds like crap. Today we have slim fit subs and wattage is cheap so there is less compromise. When I first got into car audio in the mid 80s you really had to get creative with box building due to the equipment limitations. This is what put the original Kicker Solobarics on the map - they required like 1/2 the airspace of a normally woofer so all of sudden you could fit subs anywhere.

 

I'm looking to install an alpine 12" that requires .85 cubit feet of air space, but the box I have is only .74 cubit feet of airspace. Will this make a big difference in sound quality or put too much strain on my amp? I'm running a 500 watt Kicker amp with a Alpine 12" type s