Bracing and Fill in small box?

[Eric J]

Hi.

I've just completed the bulk of my first DIY woofer. I used the Dayton 8" DVC and the Dayton 70 watt plate amp. Box was built using 3/4" MDF with a volume of .508 cf.
My question is regarding stuffing and bracing. I've noticed that this tiny little system weighs more than many of the entry level commercial subs I've looked at. Do you recommend any internal bracing on an enclosure of this size?


Second, the fill called for is "normal". Can anybody elaborate on this? Is there a formula for fill amount based on volume?

According to PE, the Qtc is .707 and the F3 is 54.06 hz.

Thanks in advance for the recommendations.





It's being used in a very modest HT setup. I did test it with some music today and it added a lot of depth. As for HT, I had trouble finding a good DVD with lots of LFE in it.

I have pics which I'll try to get up within the next day or two.

Thanks in advance for the help.

[BobEllis]

You're probably OK without bracing, although generally you'll want to keep unsupported lengths under 7" or so. A simple 1x2 cross brace is plenty in a small cabinet like that. Yep, most (all) entry level subs are WAY underbuilt and usually perform poorly.

Normal stuffing is in the vicinity of .5 lb/cubic foot. It won't hurt you much if you are a bit over or under.

Unfortunately, you were correct in calling this a woofer. An F3 of 54 Hz isn't subwoofer territory. You're probably getting usable response into the mid 40s if your room is fairly small. You won't hear much LFE with that unless its harmonics. Sure, it you are using small mains, you'd expect to get the results that you did - a nice improvement.

A subwoofer is needed to get the impact of the LFE in a lot of movies. By that I mean usable response into or below the 20s. The only way to get there is with lots of cone area and lots of excursion capability. A 12" is about the minimum to get a real subwoofer. Most here go with 15" or 18" and often in multiples. Once you hear a real sub, you won't want to be without one.

[servicetech]

A larger ported box will get the woofer to play quite a bit deeper. With a 1.5 cu ft ported box you can get into the low 30's. Inexpensive subwoofers tend to like large ported boxes. For $19 plus the amp and box, it's quite a bit cheaper than a commercially made sub 8)

[Eric J]

Thanks for the responses.

Now I know why most folks on here go with such large drivers. It was a fun and educational little project and the sub does get down lower than my 2 way mains. After knowing a little more and having the confidence to build another one, I'll feel better spending my money on a bigger and better driver and amp.

BobEllis, thanks for the fill equation. After I take the system apart and put a finish on the cabinet, I'll stuff it with a little poly. I might go ahead and give it a simple brace too. Certainly won't hurt anything.

Servicetech, I appreciate the suggestion of a ported box. I initially was leaning towards the ported enclosure of 1.21 cf. This had an F3 of 33 hz. After I bought my partial sheet of MDF, I realized I didn't get enough. I was a bit scared of the port for my first attempt.

[servicetech]

In the future buy MDF in full sheets if you have a way to transport it. Partial sheets are almost as expensive as full sheets and it's not like you won't use the rest of the MDF for some future project

Don't be scared of the ported box. With today's software you can simply plug in the speaker parameters and get decent results. It's not like the old days where you had to calculate everything manually with a scientific calculator.