Bought a woofer, need help finding suitable enclosure

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Hello everyone :)

I bought today an 8" driver from Skytronic to complement the bass response of my system (tube amp powered, KT88 ultra-linear single-ended, so around 8W per channel).
My room isn't very big, something like 8sq.m.
I have a hybrid 2W amp for different types of music and just because I built it :p, and I was thinking about using it (paralleled channles) to power the woofer.

The thing is: I usually run sealed enclosures for subs, but putting the T/S parameter of this driver on AJ sealed designer, I get negative box volumes!
This is why I come here asking for help, to find an enclosure design suitable for this particular driver.

TL subs have caught my attention after reading some posts here, and with a Fs of 53Hz, I get a 1/4 wave pipe lenght of 1.60m, which isn't very long.

I'm at your mercy :D

Thank you for your help in advance ;)

Woofer:

http://www.skytronic.co.uk/product/product.php?s=902.195

Driver model 902.208, T/S parameters on the same page as pdf.
 
The woofer has quite high Fs, so hasn't much potential to go deep, and has very high Qts meaning no way in a vented box and will require a large sealed box (relative to Vas) and still have some peaking. This driver is designed for open baffle use.

As for your results with the sealed box and TL design softwares, I can only think you have entered something wrongly or done something wrongly with those softwares.
 

GM

Member
Joined 2003
Greets!

OK, you're starting with a fairly high Qts, but I imagine the amp is going to raise it even higher, so ideally need to know its output impedance (or DF) for best results. Also what XO point/slope you're planning on using. A BIB pipe horn is simple to build and yields considerable gain down to ~30 Hz (a plus with only 4 W), so combined with some room gain down at least into the 20s before the driver runs out of ~linear travel, but would probably be way too big for such a modest size room.

Anyway, with the additional info hopefully we can come up with something worth the effort and still fit in the room somehow.

GM
 
Ok, here's the schematic of my amp. I'm running each channel on 4Ohm speakers at the moment.

http://www.diyaudio.com/forums/attachment.php?postid=904666&stamp=1146400950

I have a 12dB crossover cutting at 3000Hz waiting for a home. Should I get/build a different one?

I hope I gave the needed information, sorry if I missed something.

Thank you :)

EDIT: Just in case, I bought a 7W TDA2003 amp kit from velleman (K4001)
 

GM

Member
Joined 2003
Greets!

For sub duty, the Sony would be the choice since it has more power and an insignificant output impedance, as does the Velleman, so you can use it too if the sub has enough acoustic efficiency gain. Wanting to use a 3 kHz XO is definitely way too high for a sub though, so you're going to have to choose one based on where your mains roll off.

GM
 
Greets!

'Best' is in the 'eye of the beholder', so don't have a clue what will be 'best' for you, but if you can lay a BIB style pipe horn down on the floor up against the sound wall (wall behind the mains) or stood up in a corner, then short of a compression horn it will yield the most gain/tuning flexibility:

L = 169"
folded height = 84.5"
Sm = 201.618"^2
depth = 16.886"
width = 11.94"
zdriver = 46.203"
a-b-c = 8.443"

See http://www.zillaspeak.com/bib.asp for a layout sketch.

If you're feeling adventurous, mount the driver on the internal baffle to make a tapped horn first and if you don't like how it performs you can seal off the hole and baffle mount it.

If this is too big, Exolinear's end loaded Omega 1/4 WL Reflex will yield a modest gain to a lower F3, Fb than a traditional TL or sealed alignment in a relatively small bulk:

L = 94.75"
CSA = 90.63"^2
vent = 9.063"^2 x 0.75" long

Driver at one end, vent at the other, simple enough. If you decide to build this one and place the driver and vent on a side, then it ideally needs to be a bit longer at 100.445".

.........and if you still prefer a traditional TL, then his end loaded Alpha:

L = 59.68"
CSA = 61.63"

All dims i.d. and approximate. CSA = cross sectional area. Add stuffing as required to any of these. Obviously, as size shrinks, so goes the LF gain BW, though if corner loaded and your room's construction is rigid enough, then either of the pipe horns will serve only to reduce potential distortion. Worth it IMO, but if there's not space available.........

GM
 
Arg! I just noticed I made an error WRT Omega's driver placement, total length. :(

GM

Revised:

If this is too big, Exolinear's Omega 1/4 WL Reflex will yield a modest gain to a lower F3, Fb than a traditional TL or sealed alignment in a relatively small bulk:

L = 94.75"
CSA = 90.63"^2
zdriver = 19.9"
vent = 9.063"^2 x 0.75" long

Driver down 19.9" from one end, vent at the other, simple enough. If the vent is on the side, then add 1/2 the vent's height to the total length.
 
Some updates.

PVC pipe: 1,50m long and i.d. of 18,5cms.

I tried the sub with my 3 amps: the small hybrid, my KT88 and the Sony.

My guess: with a full-range driver there, I could fill the entire room without a problem on one single channel :D
One thing though: without the XO, sometimes the sound is, well, tubey, like speaking thru the pvc pipe :p

The sony definitelly has the power to drive it properly. I mounted it upright between to small 30cms high speakers. I don't need muchtop shake the room, even sitting on my old, very used, flufy chairs I could feel the bass on my... body :D
I tried it on a fixed location, around 70cms from a corner. I could hear some rom ressonace at certain frquencies, but the bass was extremelly good! I found it very even throught the bass range.
I then layed it down on the floor, just in front of me. The bass was everywhere, though I could discern the open end of the tube due to a apparent slightly louder volume.

But this is cool, one cheapo pvc pipe and you have one heluva subwoofer! Very nice experiment! :D
 
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