First "build" - please design a new cabinet for my sub

[loftarasa]

Hi guys, I need your help with my sub, which I bought used, cause it's not going loud enough, low enough.

The sub is currently a 16" cubed, 2.3 cu ft sealed box, using a Peerless 835017 XXLS 12" and a Hypex DS4 plate amp.

It does OK for like indie, acoustic and classical, but I need to hear more of "the drop" for dance music - it currently kind of wimps out around 40-45hz (estimate).

Use is 100% for music, and I listen to a lot of house and drum'n'bass, kind of loud! :T

I'm realistic about the limitations of a 12" sub, but would be happy to be able to go down loud to, hmm, say 30hz?

I think the most economical thing for me to do is to keep the sub and amp, but build a new ported cabinet, and that's where I need your help!

Would really love some input on cabinet modelling/design, bracing, dampening, any other construction tips for this driver.

This would be my first "build" (I have a friend who can help with the woodworking). I don't know anything about WinISD, etc, so hope to get some tips from you guys.

Particulars:
My amp (Harman Kardon 990) has a built in active crossover and sub outs, which I usually set around 60/70hz.
My room has bass traps in the corners and my listening distance is about 4-5 meters away in a medium sized room.

[fbov]

First off, welcome to HTGuide. You've asked a very common question, which may explain the lack of responses. That, and the fact that you've included links to the answers you seek!

For "input on cabinet modelling/design," look at the Peerless link.
"You can use a 2.5 cubic foot box with a 3" diameter vent by 13" long for an F3 of 30Hz. If using a plate amp with a built in boost, it should go to the lower 20's."

It may seem that you're all set; 2.3 cu ft is close enough to 2.5 to just port your current box... except it's 2.3cu ft OUTSIDE displacement. We want the interior volume, so subtract 2x the panel thickness and recalculate. Internal dimensions matter... and bracing, damping, etc. are well covered in any sub thread, and will be here, too.

So let's back up. This looks like a good driver, the amp is no slouch. But your application is infrasonic, below 30Hz. I know what you mean by the "drop" and comparing subs, I don't get the drop I like it without extension to 10Hz. That rules out all but the largest horns, and points toward an LLT (large, low tuned) alignment for vented, or a boosted sealed approach, perhaps with multiple subs in both cases.

So... what are your actual room dimensions. Dimensions determine room standing wave modes, and modes determine the onset of room gain, which is the secret to infrasonic extension. An LLT is large, and tuned so low that it has a falling response, but reaches very low frequencies. The combination of very low extension and a falling output, called an extended bass shelf (EBS) matches up with room gain to yield a net response that's nearly flat to single digits.

You mention WinISD. I learned Unibox (Excel-based). In both cases, you'll find that the Madisound data sheet has all the parameters you need to model the driver in box. I've attached an FR plot of a simulation I did for someone else, using a pro driver, but illustrative of the EBS concept in a driver that's not intended to dig deep.

And if this gets interesting, you can expect a lot of input... just keep your focus on your goals as everyone tends to suggest their favorite or their choice, which may not match your application.

Have fun,
Frank

[loftarasa]

WinISD wants a massive box and vent!

Frank, thank you very much for your detailed response to my noobish post ;x( , and also explaining I'd need a much more complex project to get "the drop" from my dance music. Had no idea it's at 10hz! :E

I'm going to soldier on and build a new ported box to optimize what I have.

I read several WinISD tutorials and subwoofer build threads, it's coming together in my head, though I have some new and hopefully better questions.

First, I input the driver parameters from the Peerless datasheet, WinISD wants me to have a massive box (4.3 cu ft!) and 4" vent (12") long!!

Also, the width, height and depth dimensions it gave me seem dumb, basically suggesting a monkey coffin 33" high. That's a big no for my living room :M

If I overwrite the desired volume to 3.3 cu ft, the response plot looks ok. Is it fine to then calculate more equal cabinet dimensions (e.g. 18" x 18" x 18")?

Further, if I tweak the tuning frequency anywhere much away from 22hz (the Fs of the driver), the plot starts to go skewiff quickly.

I'm only concerned about that for the length of the port needed, and if I need to model that better somehow. Does it make much difference?

When I conformed to Madisound's recommendations for a 2.5 cu ft ported box with 3" x 9" vent, it seemed like it moves the F3 quite a bit higher than the driver is capable of.

Thanks for any more help.

[fbov]

Since you seem concerned over port length, I modeled your Peerless driver two ways, the only difference being 2x port length.

I started with your WinISD optimum, 120 liters with a 10cm x 30cm port. You'll notice there's a slight peak at ~30Hz, which is not bad for most applications, and will give you both a lot of extension, and a really good kick in the gut due to that peak. (Make the port shorter for an even larger peak.)

I then doubled port length. The result is an extended bass shelf alignment. Note that the box tuning is lower (17 vs. 23Hz), F3 is 6 Hz higher, but F10 is now below 15Hz, and you have 10dB more output at 10Hz. The driver is now real close to Xmax at 25Hz and 120W... the only issue is that you've lost ~3dB of output at 30Hz.

Now we get back to your room - how big? What kind of room gain can we expect? I use a sealed sub, an amp with a little boost, and in a 22x15x8' room, I'm fairly flat to 10Hz. In effect, my sealed sub + boost results in a response that's similar to the EBS simulation for your sub. Room gain makes up the difference, enough so that I can hear the opening note of Also Sprach Zarathustra...

Bottomline? Port length sensitivity is nothing to worry about. We moved it 12 in. with only good things happening. In fact, you may want to try shorter ports, to see what kind of response profile (flat, peaked, rolled-off) maximizes the drop you're looking for - maybe 10Hz is my preference, but not yours!

I will note that I tried your 3.3 cu ft, and the driver is just not as happy as it is at 4.3 cu ft.... EBS needs a large box to work properly, and in fact, has an extreme known as the LLT.

http://www.hometheatershack.com/forums/diy-subwoofers-general-discussion/1820-llt-explained.html

HAve fun,
Frank

[loftarasa]

Thanks again, Frank. A bigger box it will be then, and the port length doesn't matter too much, so don't sweat it, got it.

My room is like 15' x 18' x 10' and I sit about 6-7' away from my speakers which are about 1m in from the back wall and 2m in from the sides, about 6' apart.

My last question - do I have to conform with WinISD's prescribed width/height/depth dimensions or does only the volume matter and it's OK to make more of a cube shape?

Thanks.

[PMazz]

Any shape is OK as long as the port has room to breathe. Give it a ports width away from a wall and you're good to go.