Monkey see, monkey do... two RL-P18s for me too!

**Mongrel714** · **10-09-07, 06:43 PM**

Quote:

Bradley wrote:

You mean wrap the port with whatever I line the box with? Seems like people are using fibreglass mostly, or in some cases foam sheets. Would something visco-elastic like Dynamat work well?

I'm not to sure about the dynamat, that is mostly for deadning troublesome vibrating panels, you need something like fiberglass, I used some 1" thick "batting" I picked up at an upholstery shop, better than fiberglass and no itching.

**Bradley** · **10-09-07, 10:35 PM**

Yeah, I didn't think so. I was just wondering since I have a bunch of dynamat-like material somewhere in my garage, new in the box.

**Bradley** · **10-10-07, 03:37 AM**

Totally out of control over here! Not done and not really happy with the braces. But here's what I've got "sketched up" so far:

Again, this is just a rough draft and work in progress. However, if I'm lucky the port will terminate in that third brace. Both ends are going to get the mondo 1.5" radius flare.

**Bradley** · **10-10-07, 07:44 PM**

Here's the latest draft.

I think the only thing left to do is add some donut support rings for the port tube. I'm not going to bother trying to model the flares or rounded edges.

The smaller holes, or "swiss cheese", aren't really necessary. I'm just a little worried about coming in at 17.0 cubic feet (or higher) as planned. I'll need to add up the volume of all the bracing and port tube once the "ink" has dried on the design.

**Bradley** · **10-11-07, 03:15 PM**

Came up shy on the net volume inside the box, so I've had to make revisions. The side-to-side braces in the middle (just behind the driver) were retarded anyway, so I got rid of them.

By the way, I ditched the VB script in favor of an Excel spreadsheet to calcuate the volume using surface area measures taken from the Google Sketchup drawing. All the files I'm using are on my web server if anyone wants to check them out, including the Sketchup drawing.

http://s16v.com/subwoofer

Bradley

**Sonnie** · **10-11-07, 03:34 PM**

I like that sketching program... nice...

**thxgoon** · **10-11-07, 08:14 PM**

Ya those sketches look sweet! Does Sketchup calculate the volume?

Edit: Nevermind just read the last line of your post

**SteveCallas** · **10-12-07, 12:30 AM**

I'd have to believe window braces are the most efficient use of bracing if trying to minimize displaced volume. Braces with holes cut in them aren't efficient uses of space and add a lot of unnecessary work.

Not having at least 8" of clearance from the port opening is definitely a problem you should concern yourself with, as it can result in early onset of compression. How much clearance will you have as it is designed now?

**Bradley** · **10-12-07, 12:35 PM**

Quote:

SteveCallas wrote:

I'd have to believe window braces are the most efficient use of bracing if trying to minimize displaced volume. Braces with holes cut in them aren't efficient uses of space and add a lot of unnecessary work.

Do you have a link or pic of what you would consider ideal/optimized window bracing? If I understand you correctly, I could draw up another model and compare the two. Either way, the large (and thin) port tube needs to be supported by the braces and that requires a significant amount of material.

Quote:

SteveCallas wrote:

Not having at least 8" of clearance from the port opening is definitely a problem you should concern yourself with, as it can result in early onset of compression. How much clearance will you have as it is designed now?

The outer edge of the port tune is 5 inches from the interior rear wall. It's about the same distance from the back of the driver. There is 11.5 inches of space from the end of the port tube to the side wall that it "points" at.

On the whole, there is a lot of space around the end of the port tube. However, if you think I should move it closer to the driver and/or center it in the box (front-to-back), I will consider that.

Thanks.

Bradley

**Bradley** · **10-12-07, 01:11 PM**

Steve,

I thought about for a while and finally came to the conclusion... CIRCLES RULE! Here's my latest design.

**Bradley** · **10-12-07, 04:13 PM**

The brace pictured below is within 1% of the volume of the "rib" style brace used in the current box design. The "border" of the brace is 2 inches wide. Also note the port tube has been moved 2 inches toward the front of the cabinet, closer to center.

If I add 2" wide horizontal supports from the circle to the edges, it would consume about 10% more space than the large-circle "rib" style brace currently employed. That would probably make for a stronger brace but I'm not sure it is worth the space penalty. Perhaps reducing the border or "stick" width to 1.75" would hit the right balance.

**Blaser** · **10-12-07, 05:53 PM**

I have to agree that when tuning so low, a single 8" port/driver is more than sufficient on real program material. dual 6" ports will only add complexity in the design/construction while there will be no noticeable benefit. I have hit 125 db from a single driver at WOW and did not notice any bad thing from the port...

I would only advise to use the most power you can. I am powering my drivers with dual 2000 W RMS (4.5% THD) amps, and I really feel that these drivers are rated a very conservative 1000 W.

Congratulations for this project in advance...

**Bradley** · **10-12-07, 08:47 PM**

Thanks, Blaser.

Having spent many, many hours already on the design with a single 8" port, I really don't think dual six inch ports would be much more difficult. The two smaller ports would actually integrate better into the rear half of the enclosure space, remaining almost one port diameter away from any of the walls and the driver.

My only concern with using more power would be cone excursion, possibly bottoming out the driver, especially with the 14.5 Hz tune. I'm going to start out with 500-600 watts mostly because that's what the amplifiers I already have sitting here will do.

Hoping to finish up the design tonight and start cutting MDF tomorrow!

**SteveCallas** · **10-12-07, 09:50 PM**

Yes, move the port closer to the driver so that you can have 8" clearance from the side wall.

**thxgoon** · **10-12-07, 10:02 PM**

Quote:

Bradley wrote:

My only concern with using more power would be cone excursion, possibly bottoming out the driver, especially with the 14.5 Hz tune. I'm going to start out with 500-600 watts mostly because that's what the amplifiers I already have sitting here will do.

Be carefull if you're using less power than the drivers are rated to handle. Running a clipped signal into the drivers will burn them up very fast.

**Bradley** · **10-12-07, 10:30 PM**

Steve: Come on... you know post #35 was funny.

thxgoon: I hear ya. I will dial it in carefully and keep an eye on the clipping indicators.

**Bradley** · **10-13-07, 03:37 AM**

Latest update: window-style braces added, port moved 2" toward the center of the box.

(It's hard to tell but I actually modeled the 1.5" radius flare on the port, hence the three MDF rings on each end. Thanks to Collo for the tutorial on doing roundovers in Sketchup!)

Almost there... almost there... almost...

**Rodny Alvarez** · **10-13-07, 11:04 AM**

Looking good!!!

That thing its going to be HEAVY!!

**Bradley** · **10-13-07, 01:39 PM**

Not compared to Scott's.

But yeah, I am guessing well over 200 pounds for each box with the driver installed.

**Mongrel714** · **10-13-07, 09:06 PM**

That last design looks great, we have a winner!!, I thought #35 was funny too.

**SteveCallas** · **10-14-07, 12:13 AM**

Agreed, last design looks the best so far. Ideally you'd be able to give the port opening more clearance still - once it's done and closed up it's very difficult to change things Initially upon seeing post #35, I thought you went ahead and made that.

**Bradley** · **10-14-07, 01:53 AM**

Quote:

SteveCallas wrote:

Initially upon seeing post #35, I thought you went ahead and made that.

Geez... you must think I'm a total moron.

I'll see if I can move the port one more inch toward the driver. Starting to get cramped in that area around the center brace and driver. What I'm doing right now is modeling up a rough outline of the driver itself so I can see how it fits.

**SteveCallas** · **10-14-07, 02:48 AM**

Quote:

Geez... you must think I'm a total moron.

Not at all.

**Bradley** · **10-14-07, 03:38 AM**

OK, here is the latest modification to the center bracket with silhouette of a RL-P18 driver to show relative placement/fit. Port tube is now a full 8 inches from rear wall.

Anyone see any problems with this?

**SteveCallas** · **10-14-07, 05:45 AM**

Oh boy, now you're really gonna hate me. The vent on the back of the driver should ideally have clearance equal to its diameter as well

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