question about sub box design

[h0bo4life]

hey I've been trolling here for a while and I believe I am posting in the right section ....


just had a couple questions. I am building a subwoofer for home theater in a sealed box using the dayton rss315ht-4(300 watts rms) driver and the 240 watt dayton amp. first off, I know that the amp is underpowered for the woofer. What kinds of problems might that cause??? would I get clipping??? should this matching of amp and loudspeaker be fine as long as it isn't at high volumes?

my second question and the real reason for my post is that I am wondering about box shapes for subwoofers. Most of them seem to be cubes rather than golden ratio. Why is that? Should I make mine a cube or shoot for varied dimensions to fight standing waves?

It would be most convenient for me to do a taller sub with a smaller footprint and if there is no advantage to making a box that is like 16x16x16 I would rather do 14x18x20 or something. THanks for any input guys!

[mike c]

as long as you meet the enclosure volume requirements, and fit the driver and amp in the process ... there's no set RULE to go for a cube size. that's the benefit of DIY, build your enclosure with exactly the size you want.

but i must warn you, the standing waves are mostly resolved by non-parallel walls. a cube or rectangular box both have parallel walls.

[h0bo4life]

that sort of answers my question about box shape...i guess I am still wondering if their is some advantage to going with a cube since that is what everyone else seems to do.

as far as my amp and subwoofer matching should i be concerned that it is underpowered or is this an ok set up???

[mike c]

if I had to guess ... it'd be because:

aesthetics - balanced look
low center of gravity - the height is about the same as the footprint, less chance of tipping over

i don't know about the amp power ... the experts here will get to that

[mrstampe]

As I've begun to pick up the subwoofer building craft, these are a few of the points I have learned...

1) Sealed subwoofer enclosures generally allow for simpler construction, greater driver damping, "tighter" bass response, a higher tuned frequency, poorer power efficiency. This design seems to be favored in music applications and when space is limited for placement of your sub.

2) Ported enclosures trade driver damping and build simplicity for significantly lower tuning, higher efficiency. The majority of Shacksters favor this design, as it better suited to the Home Theater demands of low frequency response.

3) SW enclosure choice is a personal one that depends on your listening preference, music vs. HT application, driver characteristics, and space availability in your room.

4) Enclosure geometry is pretty diverse as you look over all the designs posted on the HTS. There are lots of cubes, rectangles, tubes, and even one that looks like the Smurfit-Stone building in Chicago!






Since your goal is to use this 12" driver in a home theater setting with a somewhat underpowered amp, you'd get the most out of your RSS315 in a ported enclosure. If you're looking for a smaller footprint to allow for a larger volume, take a look at the many sonosub tube designs all over HTS.

[brent_s]

Hobo, how did you arrive at that "300 watts" limit for power handling?

Assuming your 16x16x16 is external dimensions using .75" material, that's a 1.8 ft^3 enclosure. I'm also assuming the RS315-HF...based on that enclosure size. You're just at rated Xmax at 20hz with 240 watts, without taking the rumble filter into account. Naturally, excursion limited power handling rises with frequency. That 240 watts translates to 97dB@20hz, 103dB@30hz, 106dB@40hz, all 1m groundplane...boundary reinforcement ideally adds 6dB per boundary (wall) and you could/should also get some room gain below the 1/2 wavelength of your longest room dimension.

That's a complicated way of saying you're not really underpowered, IMO. If you need more SPL, you'll need a second sub or a different driver/alignment, not a more powerful amp. Doubling the power into a given driver, assuming it has available excursion to handle the increase, yields a barely noticeable +3dB gain. In your case, you've got a little excursion left with 240 watts, but no where near enough to handle double the power.

If you do try to overdrive the SA240, it has soft clipping, which should simply compress the drive signal if you clip the output. Do this long enough and it will simply shut down when the thermal protection is tripped.

-Brent

[h0bo4life]

thanks for your responses guys!

brent... thanks for putting stuff in plain english for me. The subwoofer just says that it's 300 watts RMS and yes that is the enclosure size.

Mrstampe... most of what you said is stuff I've picked up reading here and there.... however I haven't read much about tube designs. I like that solution cause we are really short on floor space in our living room... Now i just gotta talk the wife into the idea!

at this point I would say I am ready to go ahead and build thanks again for everybody's help.

[cassb]

Hobo, did you finish building your sub with the Dayton 12" driver and Dayton 240W amp? I'm interested in how it sounds -- I'm thinking of the same hardware, just using their 10" model driver instead.

Thanks!
Bryan