What do you guys think about this design?

[Brian Steeves]

Ok I have been playing around with Adire's LspCad program modeling my Tempest. Here is a design I came up with for your thoughts.
8.83 cuft./250 liters
Tuned to 18.6 hz
one 8" port 38" long
F3 is roughly 19hz

My main concern is driver excursion at high power levels.
Also looking at the spl in room/box chart shows a large amount of room gain peaking at 26 hz.

Any thoughts or ideas?

If I knew how to capture the plots for the sims. I would post them. Anyone know how?




She said,"you're gonna put that thing WHERE!"

[ThomasW]

Brian

Email me the "box" file and I'll check it out. The w/e is slowly beginning to slow down.

You can't cut and paste an image/graphic into a post like you can text.

There is a "SnapShot" tool in LspCAD you can combine 4 different graphs and then do a "save as".

To put the graph/image/plot inside a post, it must be uploaded to a website as a gif or jpg file. Then you link to the file with the standard image commands.




theAudioWorx
Klone-Audio

[KennyG]

Brian, I'm no expert, but I took a quick look, changed a couple things, and here's what I came up with.
Using your 250l box vol, 20.3 port dia and 96cm port length...here are the things I changed; in "Box" pull down change Qa to 7 and "fill" to 50%...in "Room & Cabinet" pulldown change "Summation Factor" to 3 db (cause Dan Wiggins seems to like that one!) Now look at your in room response...I get +/- 1db from 21 to >75hz, an F3 of 16.5hz, that looks pretty flat.
However, like I said, I'm new at this too, Thomas and Jon can guide you better, but hey, this is more food for thought! KennyG

[Brian Steeves]

Yeah,
I had some questions about changing the Ql and Qa values. I didn't know if I needed to or not. As far a fill goes I will more than likely line the tube wall with a poly-batting material. Not sure how much fill this will equal.




She said,"you're gonna put that thing WHERE!"

[KennyG]

Brian, the fill goes in the box, not the vent, if you stuff the vent you are slowing down the sound waves in the vent, and I don't think you want to do that, the more experienced builders can tell you what that does, I can only make educated guesses. (and none of them are good)
THe manuel tells us that for a 50% fill a value of 7 is correct for Qa

[ThomasW]

Brian

Got the file, then added Kenny's ideas. Between the two of you I think you've go a "keeper"

This looks quite good.

I'll putter around with it for a while. If I find anything that makes a significant difference. I'll let you know.




theAudioWorx
Klone-Audio

[Brian Steeves]

Kenny,

I was talking about lining the walls of the sono-"tube".

Thomas,

So you like this design better than I originally posted here..?
http://www.htguide.com/CFBoards/index.cfm?fuseaction=Threads.viewthread&CFB=1&Tid= 5582&DoOnePage=Yes&RequestTimeout=500

You had concerns about it acting too much like a sealed sub above 45hz, remember?




She said,"you're gonna put that thing WHERE!"

[ThomasW]

Brian

The "like a sealed box" is Jon's statement, but understand he's the REAL engineer, I'm just following along

The difference in the 2 designs is for all intents and purposes trivial. There's a 10% "fudge factor" for ported designs. So 240L vs 250L, Fb 16.5Hz vs Fb 17Hz aren't audible.

It's REALLY important to understand that just because something in a "sim", models better, doesn't necessarily mean the in-room performance will be better. Now of course we model for the best performance, but when it reaches the point of "splitting hairs" then it's time wasted.

Here a quote from a post I made on HTF. Perhaps it will help with understand how the "process" works. This was in response to several questions about "stuffing/lining" boxes.

OK here are my "suggestions" based on experience/listening. Not modeling. I'll list them from good to better to best IMHO So pricing is $-$$$$
1)fiberglass:
2)polyfill:
3)Acousta-stuff:, this is a "crimped" fiber poly/dacron
4)continuous fiber Fortrel:, I don't have a source for this anymore
5)long fiber wool: Yep the real stuff, right off the sheep, but long fiber only. It's pricey
6)high wool content custom "gasket" material: note, this is only for lining the walls of cabinets. I use this on the walls of all my ported designs. And I use it to line the walls of sealed designs, then "stuff" the box, with long fiber wool. This product is quite expensive $6.00/sq ft in 3/8-1/2" thicknesses. It's only available from custom gasket mfgr. They are listed in the yellow pages in most BIG cities. Some will sell it by the running foot. It comes in many different "recipes", so chose the one that contains the highest wool content 80-90%

Hank,

Acousta-stuff is pretty much priced the same as long fiber wool, so I'd choose wool $10+/lb. Either of these is especially good for for mid/woofer application. Wool is a not good choice where people have a problem with "wool moths". In Denver they aren't an issue, too cold, too dry.

I don't fixate much on damping materials for "dedicated" subs. I use polyfill,(actually "bonded polyester batting") It's easier to get a consistant, even layer compared to loose poly. I hate working with "glass".

The more esoteric ($$$$) damping products I use for woofer/mid-woofer/midrange enclosures, not subs.

Chris

I haven't sat down and measured absorption coefficients/frequency of these materials. I'm sure someone has. The 250Hz info is from our mutual pal Greg M. With all(except the gasket material), the "thicker the better" but there is a point of diminishing returns.

Here's how I "tune" a box. Build to best modeled specs. Then measure performance. Adjust volume, port etc, as necessary. Then by "ear" I add damping until the bass stops getting "tighter" and the only change is a drop in efficiency. At that point I drop back to the previous measured amount of damping. I do this by weight and usually it's ounces(or fractions of an ounce for mid/woofer -mids) for a final "tune". Now this is just my method, so the usual disclaimers, and YMMV

theAudioWorx
Klone-Audio

[JonMarsh]

Brian,


It looks like you've got a good design here, as long as the SPL capabilities in the range above the port tuning meet your requirements. There have been some posts on some forums with people being dissappointed in acoustic power handling; it's just one of those tradeoffs. Model the cone excursion predicted for the maximum outputs you want from 20 Hz on up; if everything looks OK, then you should be fine. I don't use LSP CAD, so can't comment directly on specific setup and plot results.I use Sound Easy from Bodzio, and BoxPro, haven't got my own Tempest's yet, but will be modelling them soon. Another point to consider is room location for the listening position and the woofer. You can set that up by ear, but if you want to do some what-if's, RPG Acoustics has an excellent package for analyzing the room response of simple and complex systems (5.1, multiple woofers, etc), and optimizing the speaker and listening position. Have a good Sunday, and have fun building your sub.


Regards,


Jon




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