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Old 4th May 2007, 09:03 PM   #1
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Default Bought a woofer, need help finding suitable enclosure

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

Thank you for your help in advance

Woofer:

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

Driver model 902.208, T/S parameters on the same page as pdf.
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Old 4th May 2007, 10:08 PM   #2
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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.
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Old 5th May 2007, 07:15 AM   #3
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Default Re: Bought a woofer, need help finding suitable enclosure

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
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Old 5th May 2007, 08:22 AM   #4
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Ok, here's the schematic of my amp. I'm running each channel on 4Ohm speakers at the moment.

http://www.diyaudio.com/forums/attac...amp=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)
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Old 5th May 2007, 03:02 PM   #5
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i was snooping around my garage and uncovered this amp of mine:

http://www.sony.co.uk/view/ShowProdu...ICA+Amplifiers

I can use it at home, just need a big battery
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Old 5th May 2007, 06:39 PM   #6
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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
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Old 5th May 2007, 08:39 PM   #7
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The sony has a fixed XO at 80Hz, so I might try that (my loudspeakers go to aprox. 50~60Hz on the spec sheet, and I believe they go to about that frequency from my listening).

So, what do you reckon will be my best choice for an enclosure?

Thanks
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Old 6th May 2007, 11:16 PM   #8
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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
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Old 7th May 2007, 12:12 PM   #9
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Cheers GM!

Thank you for your input and options you have opened up to me

I guess I'll try that TL first, PVC pipe is cheap

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Old 7th May 2007, 07:58 PM   #10
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Greets!

You're welcome! Let us know how they do.

GM
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