My Subwoofer - Is it totally in the woods?

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Hiya and good day everyone :)

I am a newcomer here at DIYa so please bare with me if it's too obvious :clown:. I have just started my first project and I hope you will give some good critique and suggestions before I start the power tools.

I am going to build a subwoofer for my home theater. I have very good sound already and just miss the feeling of that very low bass from 20-65 hz that my B&W (NT 9) speakers can't reproduce convincingly enough.

I have decided to use a Peerless 12" XLS woofer (SWR308-830500) and probably the corresponding 12" slave (830548).

For the box I have come up with a 67 l. (2,37 cft) rectangular design with both driver and PR facing towards the listening position. The beauty will be powered by a 200W ZapPulse 2.2 unit from LC Audio.

I have used UniBox 4.04 and Subwoofer Simulator to calculate the size of the box and the corresponding graphs. Both programs are giving me almost the same result (all specs. within one percent) and to me it looks very nice (remember, I'm new to this stuff). I would be happy if some of you guys could take a critical view at my design and tell me if I'm missing something obvious?

Finally a few stupid questions ;-)

SPL
When looking at the SPL Total, is the graph taking into account the rather steep drop in the drivers frequency response that starts at appr. 100 hz?

Volume
When I look at my 67 l. box design I am not sure if this is before I cover the walls, or after? Should I calculate how much volume the wall-covering-stuff will take up, and add that volume to the 67 l.? Or just make it 67 l. and *then* cover the walls?

Impedance
What does it really mean that there is thse huge peaks and drops in the curve?

Sorry for the long post - I hope you're still with me ;-)

Take care,
Claus
 

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You might want to put the PR on the back to halp balance Newtonian forces...

Because of the looks I would prefer it to face the same way... :ashamed: The weight is estimated to end up close to 55 kg. On top I plan to put my Amp + DVD so I guess it will total around 82 kg :dead:. Should be enough to keep in place I guess? Or...?

...and you might find, once room gain is added in, that the sub has a big bump at the bottom.

This is serious... :bigeyes: I have just used Room Response Calculator v0.6d to calculate my room gain and in the subwoofers intended working area I have just 4dB difference in gain (peaking at 20 hz).

I have done a simulation in UniBox 4.04 and if it does become a problem I can (apparently) just fill the box completely up with damping material which will reduce SPL with 2,5 dB. I guess that should compensate or am I missing something?

The reason I consider this solution is because I'm going to move to a bigger place very soon and get a much bigger (+twice the size) audio room and I think this will reduce room gain.

Best,
Claus
 
frugal-phile™
Joined 2001
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Beeblebrox said:
Because of the looks I would prefer it to face the same way... :ashamed: The weight is estimated to end up close to 55 kg. On top I plan to put my Amp + DVD so I guess it will total around 82 kg :dead:. Should be enough to keep in place I guess? Or...?

With amp & DVD player on top, it is much more important to kill the driver's load on the box before it gets to your amp & DVD player (it's a scary idea putting a DVD player on a sub).

It doesn't matter how much it weighs... you will still have a force applied directly to the box. If you can kill much of that force by putting the PR on the back you are way ahead -- with identical woofers mounted push-push you are probably killing over 90% of that force (number PFTA), with a PR it won't be as large but will still be substantial.

dave
 
DON'T put your DVD-player on the sub.
I use two subs, each with 1 XLS-12 and 2 XLS-10 passive units.

Even if the box looks silent, lay your hand on it, and you'll feel it really isn't.
If you do, why do you actually buy a good quality DVD-player? No DVD-player is made to work perfect if it's shaking!
It's like buying a Porsche GT Turbo and throw diesel in the gas-tank....

Grtz, Joris
 
Dept. of large boxes

Depending on how large a box you can tolerate, have a look at this approach. The 830500 has a very low Qts of 0.2 and you can raise it to 0.5 with several ohm of resistance in series. Google for details. Don't worry, you gain way more than you loose! Now put it in a box of 285 litres and tune it to 14.7 Hz. It should be 1dB down at 14.33 Hz and 3dB down at 13.14 Hz. On paper, anyway.

No prizes for guessing what I want to get next! :smash:
 
As I have a self made XLS10 incl. passive radiator standing next to me, I can confirm that the high mass of the box doesn't mean that it doesn't react on the driver moving its cone.

I've once tried to put a compact stereo on top (for testing). Don't think about doing that.

As for your other questions, Claus:

When looking at the SPL Total, is the graph taking into account the rather steep drop in the drivers frequency response that starts at appr. 100 hz?

You're referring to the plot in the Peerless datasheet? The drop is due to the measurement method Peerless used to aquire the data. The plot in the pdf doesn't have to do with a 67l box with passive radiator ;)

When I look at my 67 l. box design I am not sure if this is before I cover the walls, or after?

Your software calculated the net volume inside the box (it wouldn't make sense for the programm to calculate your gross volume anyway).

What does it really mean that there is thse huge peaks and drops in the curve?

The peaks are the way a loudspeaker "reacts" on voltages at different frequencies.

The fact that there are two peaks (and a drop in between) shows that your software simulated the behaviour of a vented (bass reflex) box. Speaking of equivalencies, the passive radiator acts like a huge port. So everything is pretty normal with the impedance plot so far.

Hope this helps. :D

edit:

There are a couple of good application notes on the peerless website: http://www.d-s-t.com/main/main/engi.htm

When I used to build my XLS10 subwoofer, after doing searches and studies of some discussion forums and web pages I found out that I could have cleared the "non-wooden" issues of the design entirely out of these few documents...

Sebastian.
 
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