Building an enclosure this weekend

[bmccord]

Hello all. I am finally building my enclosure for my 10" Dayton Titanic this weekend. Basically, it is a .85 ft^3 box within another box concealing the port system. I want a big as possible port as to minimize any port noise. I designed the box in WinISD or whatever that program is called and came up with 2 - 3" ports at 44" long. Therefore, I just made a pho-box to hide the extra long port in atempt to maintain the lowest tune and lowest vent "mach". Do you think 3" is too big of a diameter? My other option is 2.5" diameter, but I think 3" will be fine. Oh yeah, the ports are just going to be PVC pipe with radiused pipe ends...

Here is the design thus far. Feel free to add your $.02

 

[WmAx]

3" is fine. But you may end up with some port chuffing at low frequency test tones at high amplitudes, due to the small edges of the pipe combined with the air velocity. You could drasticly reduce the chance of this by using the special flare ends sold on speaker DIY sites, or you could make some flare ends on a wood lathe. You could even do better than the small edges of the pipe by terminating the pipe to the back of a 3/4" board and using a roundover router bit to get a radius at least bigger than the radius possible on just the pipe wall end. Note: the chuffing is not likely to be audible with actual music and movie program material. Test tones make it much easier to hear such artifacts.


-Chris

 

[bmccord]

my thoughts exactly, i figured I would get a little with PVC, but I dont have much else to work with that doesn't cost an arm and a leg. I was going to round the pvc inlet and outlet ends to almost nothing and with 3", I was hoping there would be very little. It may be audible at a 25 Hz tone but in a movie or music, I would thing it would be far from noticable. Who knows... I hope this thing works out. The way it is layed out is supposedly tuned to 26 Hz so we'll see. Thanks.

Brett

 

[j_garcia]

It seems like you have room, why not larger diameter ports that aren't as long?

I don't understand your bracing? Is the driver in another enclosure or will that bracing be routed out so the driver is open to the whole volume?

 

[WmAx]

It seems like you have room, why not larger diameter ports that aren't as long?

If you increase port diameter, you have to increase the length to get the same tuning frequency as the smaller diamater port.

-Chris

 

[bmccord]

The sub is in the small box all by itself. However, it has a perpindicular brace within the small box because the top and bottom side is 19" long. The outer box does nothing but enclose the port system. It doesn't even need to be there and the sub would repond the same, just for looks. As for the port Diameter, according to the software, the larger the Dia, the longer the ports would have to be, as when I set it to 2.5" dia, the overall length was reduced by almost 10".

Brett

 

[j_garcia]

I've never designed a ported sub only sealed, so not familiar with the fact that larger diameter would need a longer tube. Interesting...seems like it would be the other way around. Anyway, how did you arrive at the 26Hz tune? Is there a "best" tune for that driver in a given box? That seems like a LOT of port length to arrive at a 26Hz tune. Definitely look at flaring the ports somehow, as I have at least read a little about port types (slot loading, port, transmission line, etc...) and it showed the ideal port has a strange, non-linear shape that is flared on both the inlet and outlet and compresses in diameter toward the middle of the length. It said that flared ends on a standard port will definitely help with port turbulence though.

 

[jonnythan]

40 inches seems awfully long.

Post some screenshots from WinISD.

edit: Just saw that the sub box is .85cf. It looks like you have a much larger box around that...

I don't get what you're trying to do. If you simply got rid of the inner box and made a 2cf box, you could probably get by with a single 4" flared port and avoid a lot of complication, right? Plus you'd get better low end..

 

[j_garcia]

The larger box is just to house the ports due to their length. Seems to have a nice look to it, but also looks like an overly complex design. Why are there TWO ports that long? I agree with jonnythan, if you're already building a larger box, why not just USE that volume?

 

[bmccord]

Well, not sure really. I just saw in the driver specs for the Dayton 10" Titanic that the optimum ported volume is .70 ft^3 and WinISD came up with .85 so I just stuck with it. Then came the porting. I wanted 2 - 3" ports so that port huffing would be at minimum. Then, per WinISD to use 2 - 3" ports, it said they need to be lik 43" long or something of that nature. Obviosly a larger box will net lower Hz but if I eliminate the smaller box, will it hurt the efficiancy of the system? ...not that 3 miles of porting helps or anything. The hole idea is to get as much beefyness out of this sub as humanly possible. Size is of no matter within reason. Thanks for all the help. I have not built a box in almost 10 years and kind of excited to do it again.

Brett

 

[annunaki]

With that driver, I would do a 1.25 ft^3 enclosure tuned to 27hz with a single 4" port (flared on both ends) 33.61" long. One could also do a 1.25 ft^3 enclosure with a 1.5" x 8-1/3" square vent (rounded on both ends) 33.61" long. The curve is not quite as linear (inaudibly) as the other enclosure (.85 ft^3), but will extend you deeper. Not to mention it would be much easier to construct. Either configuration (round or square port) would give you an anechoic F3 of 24.5hz. In room, this could be pushed down to 20hz or below!

 

[bmccord]

So you are saying a 1.25 ft^3 enclosue with a 4" dia port that is 34" long in a similar configuration would be better? I am not a fan of square ports. Not sure why, just had bad luck with them. Thanks.

Brett

 

[bmccord]

Does anyone know what the proper way to set up a slot vent? If I can make one that doesn't make any strange noises, I will just go with that...

 

[annunaki]

The biggest things to remember with slot vents is to make sure that there is an adequate opening, and round your edges. The more bends in the slot vent the more chance for noise as well. The advantage to slots vents is they brace the enclosure as well as vent it.

If you are afraid of using slot vents, simply go with the 4" port or dual 3" ports. You shouldn't have any noise issues using and aeroport. If you wanted you could still use two 3" ports, however, they would be 39.09" long. Doing two 3" ports figuring their displacement and the woofer's (.06?) you will need to make a 1.64 ft^3 enclosure, gross.

 

[annunaki]

I suggested a 4" port before because the length would be a little less, though you would give up some port area to dual 3" ports. Using an aeroport surely would help to alleviate any noise issues.

 

[MacManNM]

The 4" port is not going to be big enough. You need to use 2 3" or larger ports, if you dont, it's going to chuff like crazy.

 

[bmccord]

Indeed. The box the sub is currently in has a 4" port and watching War of the Worlds was rather dissapointing due to all the port noise. It was pretty rediculous at -15 dB levels. so....thats why I was thinking 2 - 3" ports. I did not know that you add the port volume into the box volume. i figured since it was hollow, it was part of the acoustic volume. I am taking the driver volume into consideration though and the amp doesn't matter due to it being in the secondary enclosure.

Thanks all.

Brett

 

[bmccord]

Also, what is aeroport?

 

[MacManNM]

Well If I were you, I wouldn't build a vented enclosure at all for that unit. I would build a sealed enclosure and use a linkiwitz transform circuit. This will increase the power requirements for the unit but will give you a nice response down to 20hz. If you really want a vented enclosure you are going to need at least 3-3" ports to keep the noise down. If you build ~4 ft^3 box and have 3-35" ports the response isn't too bad. But with room gain you might have some problems. the other thing you can do is decrease the port length to 22" and build a passive notch filter in the unit to flatten the response out.

 

[WmAx]

Well If I were you, I wouldn't build a vented enclosure at all for that unit. I would build a sealed enclosure and use a linkiwitz transform circuit. This will increase the power requirements for the unit but will give you a nice response down to 20hz. .

It should be noted for the original poster that a sealed box will substantially reduce the maximum output level at lower frequencies, and increase non-linear distortion, especially with use of a Linkwitz Transform circuit.

-Chris