New Sub

[boostinsteve]

Hey guys,
I am in the process of building my new sub. I finshed the structure of it w/out any of the bracing. I got curious to how it sounds, and went ahead and hooked it up. To my surprise, it actually sounds really good. You can definately tell that there is resonance through the enclosure due to a loack of bracing, but I will address that my next day off.

Specs:
15" titanic sub
500 watt bash amp
6.1 ft3 enclosure with a 1"x22.5" vent tuned to 20.1Hz.
I plan to brace the hell out of it, but ran out of time this weekend due to paperwork for work.
I will get some pics up when I get the chance as well.

[johnnyrichards]

Re: New Sub

Should be a monster, but you might catch a little flak for the port dimension ratio. A lot of people don't want to see anything past the 8:1 range.

[philiparcario]

Re: New Sub

that tiny 1 inch port draws my interest. I figure it is noisy(chuffing),
but if he faces it towards a wall it may work out for him.

Sometimes placement can over ride calculators many would say that sub needs a 5 inch port to prevent chuffing.

[Brent_S]

Re: New Sub

that tiny 1 inch port draws my interest. I figure it is noisy(chuffing),
but if he faces it towards a wall it may work out for him.

Sometimes placement can over ride calculators many would say that sub needs a 5 inch port to prevent chuffing.

Pretty sure he's got a slot port with a dimension missing from the post. A 4"x17" round port tunes 6 ft^3 to ~17Hz. So a 1" round port would have to be considerably shorter than 17"...definitlye couldn't be 22.5".

To Johnny's point, I've seen that 1:8 recommendation, too...the claim being the box becomes more of a sealed aperiodic with an extreme ratio. However, I'm running a 1"x16"x?" (HxWxL) on a pair of 315HFs, 3.5 ft^3/20Hz tune each, with no apparent problems. I haven't actually done any measurements to confirm the tuning frequency, but in room measurements show essentially flat response to 10Hz with Audyssey's help. Output limits don't seem to be a problem so far...was outside Saturday while my son was watching "Percy Jackson" with a friend...MV at -15dB below Reference was rattling the siding/coach lights/gutters even though the theater room is an internal room and completely wrapped in R-13|R-19...that blu-ray disc has some well recorded and extremely hot LFE. :-)

-Brent

[anunnaki]

Re: New Sub

I target staying around the 1:11 or less. They tend to get a little noisy when that is exceeded.

I would highly suggest a different vent. This configuration will have a vent velocity exceeding 17m/s at just 27hz with a peak of 33m/s at 18hz. I design my sub enclosure not to exceed 17m/s at anywhere in the bandwidth so as to keep the system completely free of any vent compression.

A 3.0" x 16" vent in this enclosure volume would do the trick though it will need to be 44.42" in length.

If you can bump the enclosure volume to 7.5ft^3 and tune to 20hz with a 3.25" 16" X 40.56" vent it will offer a bit flatter response and offer a bit more extension.

[killersoundz]

Re: New Sub

I target staying around the 1:11 or less. They tend to get a little noisy when that is exceeded.

I would highly suggest a different vent. This configuration will have a vent velocity exceeding 17m/s at just 27hz with a peak of 33m/s at 18hz. I design my sub enclosure not to exceed 17m/s at anywhere in the bandwidth so as to keep the system completely free of any vent compression.

A 3.0" x 16" vent in this enclosure volume would do the trick though it will need to be 44.42" in length.

If you can bump the enclosure volume to 7.5ft^3 and tune to 20hz with a 3.25" 16" X 40.56" vent it will offer a bit flatter response and offer a bit more extension.

Vent compression? Never heard that term before.

[anunnaki]

Re: New Sub

Essentially the air acts compressed because the velocity is too high. Think of how on some vented speakers you can feel air many feet from the speaker. This is causing audible noise that is not part of the fundamental source, coloring the sound. This also limits output, though not significantly, unless the driver in question is substantially "under vented".

Some reasons why people get into DIY are to eliminate many of the compromises that commercial companies allow or "live with" in their products. For others it is increased value and/or satisfaction in their own work.

When simple things such as vent velocity are well within the designer's control, why allow it if it is something that could be a potential issue later.

The design I recommended earlier was with a simulated 500 watts of input power. Should one decide to use the full 800 watts rms that driver can handle, vent velocity increases to about 21m/s. Livable but still too high if it were for myself. If this were my sub and I knew I may increase power at some point, I would go with a vent of 4.0" x 16" x 50.65".

This way I would know that I would not have a compromised design when it came to clean output. For me it is piece of mind, for others it may be viewed as overkill. To each their own, but that is the fun of it!

[killersoundz]

Re: New Sub

I'm with you I just never heard it referred to as that.

On the other hand though I've heard you want to avoid a port that is too large as well. Makes sense to me, if the port is grossly over sized it could cause the speaker to unload from the enclosure entirely.

Bass box pro cuts the vent velocity off at around 34m/s. I actually think keeping the velocity just under that at full modeled power is fine, especially if you put rounded inner edges on the ports or use flared port ends.

[boostinsteve]

Re: New Sub

After doing some runs with it, there seems to be no real port chuffing, but at the same time I really haven't turned it up real loud yet. The depth is really nice. I did notice the velocity coming out of the port is a little high, but for now will be fine. The thought is rolling around in my head of changing the port configuration to 2 5" ports though. I will keep you guys posted. There is one funny thing about high port velocity, Everytime it hits, my dog gets up and goes to investigate what just blew that air at him. Hilarious.