Need help picking driver (1 Viewer)

[JasonS]

I am thinking of building a sub, but I'm not sure which driver to get. I want to use the amp in my current sub for the time being, but may pick up the 250 watter from PE someday. My current amp is 125 watts, so I need something that will work well with either wattage. I have confirmed with the manufacturer there is not boosting or cutting going on. PE currently has a decent sale going on, along with free shipping. I am willing to build a fairly large box. What are your suggestions?

 

[Brent_S]

Can you put a little more definition to "fairly large"...for some, 6 ft^3 internal is cosidered small? How about a budget?

The Quattro15 or the DVC15 (on sale for $99) in 6 ft^3 net, tuned to 20hz are probably your best bang for the buck with only 125 or even 250 watts on tap. The DVC15 gives you the most potential with more power handling and excursion.

For a little more money, the Reference Series 15"ers should get you a little better sound quality, but output and frequency extension pretty much stay the same for a given box size, although the RS15-HO has a nice curve even in a 4 ft^3 box, but output is reduced accordingly.

-Brent

 

[JasonS]

Thanks. I'm my room, I have the sofa facing the tv, then a loveseat against the wall at a 90 degree angle. The sub sits in the corner of the loveseat and sofa. There is still open room behind the sofa. I think they are each around 3' deep, so I'd say I could fit a 2.5' cube back there. Is my math right in that being 15 cubes? Maybe that 6 cube would be about right.

 

[Brent_S]

30"x30"x30" external would be a touch over 13 ft^3 gross internal volume, assuming .75" thick walls. The net seen by the driver and used by simulation software is gross - volume of driver/port/amp/bracing/lost Rolex/anything else inside the cabinet.

If you're willing to go larger than 6 ft^3 net, the RS15-HiFi is also a contender. Either the DVC15 or RS15-HiFi in 10-12 ft^3 tuned to 15 hz look pretty nice and make good use of only 125/250 watts. The RS15HF will give you a little flatter response across the passband which can also be interpreted as the DVC15 having more output above 40hz. When you move up to the 250 watt amp, the RS will just exceed linear Xmax, but will still be within Xsus.

www.linearteam.org Download WinISD Pro Alpha and you can experiment with potential alignements to see the size/output/power tradeoffs of different alignments and drivers.

-Brent

 

[JasonS]

Okay, I ordered the dvc last night. I'll download Winisd and see what it says. Any idea if the dvc prefers side-firing or down-firing?

 

[Brent_S]

The DVC15 is considered acceptable for down firing (3% sag), but down firing isn't really "preferred" by any driver that I'm aware of. It's used for convenience, aesthetics, necessity, and occasionally the boundary loading is part of the alignment's design. For a driver to truly "prefer" down firing, I would think it needs to be designed with the suspension offset by the gravity sag factor so that the coil was at zero excursion when installed. Lots of DIY and commercial designs do it with success, but my personal opinion is to not unless I absolutely have to.

-Brent

 

[JasonS]

Okay, I got my DVC15 today(it's big!), and have a few questions about WinISD. I've found a patch for winisd with dayton drivers, and it's suggesting a 7.803 cube box with a 4" port 6.73" long tuning it to 21.24Hz. How does that sound?

 

[Brent_S]

WinISD's recommendation is certainly acceptable. Remember, WinISD's recommendation is just based on the developers' view of an optimum alignment, there's nothing authoritative about it, but it's usually a good starting point. You can play with the box volume, tuning, port diameter, etc. to see how these change the response curve, SPL levels, and power handling.

You might want to try re-entering your own DVC15 using PE's specs and Dumax testing results. See the help file for what parameters and what order to enter. My WinISD Pro Alpha default recommendation for the DVC15 using my parameters is 8.347 ft^3 tuned to 20.96 hz. Not terribly different than what you got, but some.

My current DVC15 build (#@%@ paint won't finish outgassing) is about 5.9 ft^3 net, tuned to 17hz. I'll have about 400 watts on tap.

Comparing my 5.9, your 7.8, and my WinISD rec of 8.3. The bigger boxes are about -4db @ 20hz where my 5.9 is -7db. As a result, the bigger boxes have a flatter passband. However, in terms of output, my 400 watts in a smaller box only gives up about 1db of output in the 20-30hz range compared to the large boxes with 250 watts. Above 35hz, I have more output. Output is related to displacement. The bigger boxes need less power down low to move the driver the same distance so you can get the same output with less power. Since it sounds like you're sitting nearfield, I don't think output's going to be a problem with any of these alignments, even with "only" 125 watts.

10 ft^3 box tuned to 20hz looks even better. Keep going bigger until 250 watts reaches Xmax at some frequency or you just aren't willing to put something that big in your house.

My build is incredibly easy using precut MDF "shelving" from Home Depot . Comes in .75x16"x48" precut panels for $5 each. Requires minimal woodworking, only cutting required was to create a 16"x17.5" top/bottom for the box and some bracing. External dimesions end up at 16x17.5x49.5 + legs...3" in my case. Down fired the port, full length 4" Precision Port. This about as big a box as I would accept and I have a dedicated theater room. YMMV.

-Brent

 

[JasonS]

Thanks. I like how the 10 cube looks, but that may be a little tight. My sub is right next to my seating position, next to and facing the wall. The room how another 10' or so behind me, that my kids play in. Since I'm firing into the wall, how much space should I leave? I could potentially go 35"(depth of couch) x 24"(end-table-ish height) 25"(this leaves 10" between the driver and wall. Is this enough?

 

[Brent_S]

10" to the wall should be plenty. Think about it this way...most downfiring designs usually leave 2" - 4" gaps from the driver to the floor or base plate. Firing into a wall is no different. When built, you may want to experiement with the distance to see if the boundary loading makes any difference for you.

If possible, I'd suggest trying to use cabinet dimensions that allow you to experiment with driver orientation in that corner. You might enjoy the tactile enhancement of facing the driver towards your primary seating position. Or, you may find firing towards the open play area at the back of the room sounds better.

35x24x25 external gives about 10.2 ft^3 gross internal volume, assuming .75" thick material. I'd figure on ending up with something in the 9 ft^3 range after bracing/driver/port.

-Brent

 

[JasonS]

Thanks for your help. I'll try to keep in mind the possibility of firing it different directions.

What kind of bracing will I need? Do you have pics of what you've done?

 

[Brent_S]

You're quite welcome. We learn by helping each other.

My bracing is 1"x.75"x9.5" ribs spaced about 10" apart. If you look around at other DIY projects, you'll see examples of much more elaborate bracing. On the other hand, if you look at the Velodyne DD-18 review on Audioholics, you'll see that Velo uses no internal bracing with 1" thick walls. You really can't do too much bracing as long as you leave the appropriate air volume. I aim for keeping the unsupported panel width to around 10-12".

Bracing #1:


Bracing #2:



Shots of Rustoleum Hammered Metal Finish.
Front:




Shiny:



In the front shot, you can see a bit of the insulation I've placed right behind the driver to kill reflections. Not sure how audible the effect will be in use, but it certainly killed the echo/reverb when I talked/hummed into the driver opening. Also applied the same to the top panel, opposite the internal port opening. Insulation is just R-19 that I ripped to half thickness. Would have used the full R-19 thickness, but it touched the port flare at the bottom of the driver opening.

-Brent

 

[JasonS]

Okay, I've been recommendd a few projects based on the tempest, and one is a 194l box tuned to 18.8. I'm a little confused on porting this project. The test says it uses an FP3 3" flared port kit, but the diagrams call for a 6.25" cutout for a 4" flared port. Which is it?

Also, if I enter 2, 4" ports into the project in WinISD, it suggests a length of 25.19". If I enter 2, 3" ports, I get 15.8". This is in a 194 liter box tuned to 18.8

 

[Robert_J]

That error in the PDF has been there since day one. Use the 3" port kits and cut the appropriate sized hole for them.

-Robert

 

[JasonS]

I know I sound cheap, but $40 for a couple of tubes sounds expensive. Any alternatives?

 

[Robert_J]

You can use the PSP-Ports, PE flared ports or build your own. If you don't use flared ports, you will have port chuffing at high volumes.

-Robert

 

[Brent_S]

A 4" PSP requires a 6.25" cutout...diameter of the inner flare. 194 l tuned to 18.8 hz only needs a 4"x11" straight port or a 4"x12" PSP.

With only a 250 watt amp, you're unlikely to have a port noise problem, even with a straight pvc port. Going with the 4" PSP should cover you up the excursion limited power handling of the DVC15.

-Brent

 

[JasonS]

So, where can Ilearn more about port noises, the causes of it, and how to avoid it? By the way, I'm starting out with only 125 watts. I'll probably move up to the 250 watter someday, but don't know when.

 

[Robert_J]

Look at the Port Flaring Experiments on subwoofer dot com.

-Robert

 

[JasonS]

Thanks, I'll have a look. Also, I was expecting the sub to come with some kind of gasket to put between it and the box, which it didn't. Is this another item I can find at Home Depot? I'm planning on going there over lunch for T-nuts.