Help with New Sub (2 Viewers)

Have decided to try building a sub for my system and am looking for some recomendations. This sub will be used for Home Theater/ HDTV only. The only music we would listen to with this system is the music in the actual broadcast/dvd. The sub is primarily needed for special effects I guess. We really want it to blend in for other aspects of viewing. The one I have now is cheap and really boomy and the wife is constantly complaining, mainly during HDTV viewing. Have tentalivly picked a Quatro in either a 12 or 15 inch. The 15 is on sale now for about the same as the 12. Problem is size needs to be limited somewhat. Not more than an 18X18 inch footprint, but can go vertical a little bit. The box designs on the PE web site show a ported for the 12 at 17x17 and a sealed for the 15 about the same size. Which one would be better for my application? Along the same lines, what amp would work out the best? Was looking at the 240 watt. Other recomendations would be appreciated if something better than the Quatro in the same general price catagory.

Boom is a function of poor box tuning, and or a room placement issue.

With subs, bigger drivers are better.

The 15" Quatro and a 240-250 watt amp are the best low buck deals around.

If you can go taller then 18", you might be able to go ported, if not you should go sealed.

What about the Dayton 12" DVC? I could go ported with that. Would that be better than the sealed Quatro 15?


Mark

With subs it's all about displacment (amount of air moved).

If you want to compare drivers you calculate the Vd (swept volume of air). This is calculated by multiplying the driver's Sd, times the Xmax doubled.

I did that and the 15in Quatro is more than the 12in DVC. I could probably even go up to a 15 in DVC which has the best using the above formula. I worry that the 240 watt amp won't be enough in a sealed system. I would prefer the sealed as it is easier to build and has a smaller size.

I'm cuurently in the finishing stages of a 12"DVC in a 2.8-2.9cuft box tuned to 20hz. Go to the thread in this section titles "My first sonosub" and read all the posts by Brent and Steve. I have a very small room, so I'm looking at acheiveing in the low 100db at 20hz... which should impress the neighbors two doors down.

Decide if you're going front or downfiring and how you're going to construct and mount the port. There are several programs in the internet for port calculation. Go to google and type in "subwoofer port calculator" or "subwoofer box calculator".
http://www.bcae1.com/spboxnew2.htm This website actually has a design helper to give you a visual of box vs. driver comparison. You should also download winISD and play around with it. The latest version does not have any Dayton drivers, so I just picked one that had parameters near the same and used it to model.

In a 3.0cuft box, a 4" port works out to about 26".
Unless you're going to build a box with one dimension being at least a few inches longer than that, you will have to go with an elbow... have you ever seen 4" PVC with an elbow? It's a rather large peice of plastic... I mean big... as in grand... or huge if you prefer. Engineering the port was the most complicated part of my box. You must engineer the port and interior bracing to fit with each other.

For the record, my box is front firing/front ported, made of .75mdf (front panel is 1.50mdf) in dimensions of 20"deep, 18.5"wide, 19"deep. My bracing is extra pieces of MDF in a cross pattern for the side/top/bottom panels, with dowell rods connecting the front and back panel running through the cross. The port is 26" long with single 90degree elbow.

I'm powering it throught a 240watt PE plate amp. I'll finish it tonight and fire it up... write back with a report. Like I said, with room gain, I'm expecting low 100db at 20hz... we'll see.

Thanks. Your project and the advice in that other thread convinced me to go with the Dayton DVC 12. I had totally skipped over taht thread because I didn't want a sonotube sub. I have the winsd program and now need to play with sizes. I hate to put an elbow in if I can help it. Can you put in 2 shorter ports to make up for the 1 long one?

Nope, model the tuning with 1-20" port vs 2-10" ports and you'll see why.

I can probably go as high as 24 in. Any more and the better half will give me some flack. I was just reading Sam's original thread again and it has me thinking about a sealed system using the Dayton HO or HiFi. The dimesions work out and so forth. I'll model in the DVC 15 and see what I get too.

Like Thomas said, two shorter ones don't equal one long one. Using 2 3" ports (if I remember correctly) models out to like 29" a piece in a 3.0cuft box... and again, this is tuned to 20hz. This site is a great little tool for quick calculation of porting.
http://www.ajdesigner.com/phpvent/su...n_length_l.php
Refer on the page to the appropriate k-factor "end correction factor" which for two unflared port ends (which is what you'll probably have) is 0.614.
For a 20hz tuning using a single 4" port
If box size equals, then port length is:
3.0=26"
3.5=21"
4.0=18"
You can see the relation between box size and port length for a specific tuning freq.
You can also tune for a different freq. 20hz is just a good standard that I've seen most guys use to model. It's like a car's 0-60mph... "How loud is your sub at 20hz?" is a standard we can all use as a benchmark. That same 4.0cuft box tuned to 22hz is a 15" port, which would be much easier to fit. If you've got a small room, you might be willing to go with 22hz because you know you'll get some good room gain. Personally, I'd stick with 20hz and just build a box that accomodates a port of that length... or step up to a 4cuft box and the fitting would be easier.
I'm sure you know this, but in general, a bigger box will play louder and deeper. A longer port tunes to deeper freq. You can't run a big sub with small ports because of the tornado of air out the port.
Just foor kicks, a 3.0cuft box using 4 2" ports tuned to 20 hz is 27" for each port... I love the internet.

I'm trying to keep the footprint under 18x18, so maybe a 2 or 2.5 cf box might do it if I tune for 22hz. I don't listen at reference levels so I really don't think it will make that mcuh of a difference. To be honest, a sealed system would still blow away what I got. Brent posted this in the other thread.

This sounds ideal to me and is what I think I'm going to start to plan for. A couple of more questions. How do I determine what volume of space the amp and driver take up? I can figure the volume of the bracing (rather my son the math genius can LOL), but the other parts in the box have me stumped. Also, do these figures account for stuffing the box with fiberfill? I have read that this increases the box size.

Thanks everyone for their help. It looks like I'm getting involved in another expensive hobby that I know my wife will just "love".

I recommend that you tune lower than 22Hz or go sealed.

Why?

Well there's lots of soundtrack info recorded at frequencies like 15Hz. If you try to play 15Hz from a ported sub tuned to 22Hz, you 'unload' the driver, and that = one dead driver.

What happens if you try to play 15hz from a sealed sub?

It tries to play it. The loudness depends on room gain one gets, how big the box is, how much power is available, and how much excursion the driver has...

If the box is small enough, the box itself functions as an acoustical filter, that removes the lower frequencies.

Mark,

an 18"x18"x24" external cabinet would yield you an 16.5x16.5x22.5 internal cabinet, assuming .75" material. That's 3.54 ft^3 gross.

Simple WinISD comparison of max SPL from 240 watts of the alignments being discussed:

dvc12 1.75 sealed = 97.6db@20hz, 103.8@30hz, 109db@50hz

dvc12 3ft tuned 20hz = 104.6@20hz, 108.7@30hz, 110.2@50

Quattro15 3ft sealed = 99.97@20hz, 106.2@30hz, 110.8@50h.

As they say on Sundays..."You make the call"

wbs

Being my first sub and all, I think I'm going to go with the 12" VDC sealed. Talked to the wife tonight and she didn't seem real thrilled with a 24" high cabinet. She's also worried how it will look. Has no trust in my woodworking skills. For now, smaller is better. I can cover the front with a nice grill and the sides are not that visible. I'm going to order the driver and amp tomorrow. I just have to decide on the exact box size. Am I'm to assume that those figures are for a 1.7ft^3 stuffed? I also need to figure out the displacment of the driver and amp. (sa-240)

Thanks all for the help.

WinISD models are without stuffing. With the Q of the 1.75 ft^3 box already at .701, I don't really see a reason to add stuffing to make the box appear larger. Others may disagree. Making the box larger will lower the Q and power handling, but give you a shallower frequency rolloff. It's relatively cheap to experiment once you build the box. Listen without stuffing...add stuffing...does it sound better/worse? Maybe use an SPL meter and some test tones to judge objectively as well.

The driver's displacement is roughly Sd x Xmax..with a sealed design you don't have to be as precise with your calculations. You'll probably want to wait until the SA-240 arrives and measure how much of it will be inside of the enclosure to determine how much volume it consumes...not sure if there's enough info on the PE website to determine in advance.

If woodworking's a challenge, you could order the 2 ft^3 box from PE and be done. Also, the Home Depot near me carries 16"x48"x.75" MDF "shelving". Plan the right cuts and you'll end up with a 16"x17.5"x17.5" (16x14.5x15 internal) cabinet that yields 2.15 ft^3 gross. Throw in the driver, amp, bracing...should be close enough. Find a really good panel saw operator and you've only got to cut holes for the driver & amp yourself.

When the wife's not looking, go ahead and build a ported enclosure. At some suitable date in the future, swap cabinets and let her decide if the performance advantages are worth the decor penalties. At roughly $3 for a sheet of the 16"x48" MDF, it's not a terribly expensive experiment.

Good luck!

wbs

After having slept on it and looking at the posts this morning, I've changed my mind again and decided to go ported. I looked at the models in WinISD and I guess I really want the "performance advantages" of a ported design even if I probably won't notice them. I do know it will be less work for the amp. I am now trying to come up with a box design using the 16x48 mdf shelving. My footprint cannot exceed 19wX20 deep. 19x19 would be perfect. But I can't seem to fit the boards right. I'm drawing a lot of pictures. I'm shooting for 3.3ft^3 box. Then with the bracing and other stuff, I should come in around 3 I hope. I am also debating a 3in or 4in port like Sam was. A 3 inch would allow me to not to use elbows, unless my model is wrong. How bad can the noise get with a 3in port? Would a flared port help?

If you're using the same modeling I am, a 3" port in a 3.0cuft tuned to 20hz works out to 14". Someone mentioned in the other thread that a 3" port would be the smallest you would want to go with and and would be fine 99% of the time. In hindsight, I might have gone with the 3, but after the second trip to home depot, I wasn't going back.

Also, did a test run last night(couldn't help it). I screwed the driver in place with 4 small screws and set it up in the HTR... Holy Ballz!!!! I played a couple of the usuals, Phanton Menace: Podracer Scene, Titan AE: Ice Field... and a few others... but the best scene was War of The Worlds in about the third chapter where the Tripod first starts blasting people and Tom Cruise is running away from it down the street... knocked a silk plant off a shelf in the next room... then the wife made me turn it down. I only had the gain up about 1/3 and at a moderate volume on my Onkyo... I can't wait to get it fully finished and bolted in to really open it up.
It's a monster!

Ya, I have been thinking about this all day. Surfed the net looking for the difference in ported and sealed. While I realize that the ported is more efficiant and gets lower and louder, I just don't need it. Knocking over the plant is a good example why I'd better go with the sealed. LOL While it wouldn't bother me, I'd get thrown out along with the gear. One of the reasons for replacing the sub is to get it better intergrated to the speakers due to complaints that I admit were valid in some situations. It's not a big room, but after reading about the differences, I really think the sealed will create more harmony, if you know what I mean. I will do like Brent suggested and after it's in, I'll experimnet with the ported box. I'd also like a dedicated room where I can play with it. Something to look forward too. At least I I'll have all the parts. I ordered everything today from PE and they should be here tomorrow. I'll get started on the box next week. I'm out of town for the weekend unfortunately.

Thanks for everyones help. I'll probably change my mind again before it's over.

Mark