Subwoofer for my Warfdales

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Hi, I'm new to WinISD and loudspeaker design, contemplating my first build, would appreciate your thoughts/comments :
A Skytronic 902-222 in a vented* enc. of (design1) about 8.5cu.ft tuned about 25Hz, 2 ports of 2.5inch dia x 3inch long.
Perhaps a little bit big, and a volume reduction to (design2) 6cu.ft, 29Hz, 2ports 2.5in x 3.3in might fit the domestic a bit better without sacrificing too much,
it would still give a useful addition below 50 Hz to the present setup.

Background story :-
I have a pair of Warfdale black boxes dating from the mid 70s, yes ok I know ! stay with me :) :-
They are nice enough to listen to in a domestic environment (ie no roof shaking disco style emanations!)
but they could do with a bit of extension down the bottom end.
It would be nice to hear a bit more of the lower reaches of classical organ music for example.
So whilst browsing the catalogue of a UK supplier of loudspeakers, and expecting to have to pay lots of ££,
I was surprised to find the above low priced 12inch that, when I plug it in to WinISD, seems to give a quite reasonable extended low freq. response, am I deluding myself or missing something ,,,

They would be driven by their own amp. off an active crossover/pre-amp from the source to the main amp.

PS *the EBP quoted by WinISD v0.43 of 40.8 suggests a Closed Box design but the resulting plot is not very impressive being 3db down at 42Hz already,
compared to about 21Hz for 8.5cu.ft and 26Hz with a bit of lift for the 6cuft design. (both of which seem amazingly low and probably lower than I actually need!)

thanks for reading ,,,

Your boxes are massive for a 12" driver, that comes from trying to vent
a driver that should be used sealed, I cannot find all the specs,
Fs and Qts, Vas is apparently 130L and sensistivity at 91dB / 8ohm
very high for a "subwoofer", another reason big boxes are needed.

Check out the parameters of typical 12" 4 ohm car subs, they work into
1 to 2 cuft boxes typically. Fs around 30Hz, Vas 50L, and Qts usually
a little too high for my liking, 0.6 to 0.7, 0.5 is better for venting.

IMO take a decent 12" car sub, put it in around 40/50L sealed and
add a subwoofer amplifier with optional bass boost at 30Hz or so.
(If building the c/o yourself make this a peaking 2nd order high
pass filter with Q around 2, possibly make Q adjustable.)

Alternatively this package is good value :
WHARFEDALE DIAMOND 9.1 SPEAKERS & SW150 SUBWOOFER 2.1 SPEAKER PACKAGE - available from Superfi UK Visit for details

rgds, sreten.
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..It would be nice to hear a bit more of the lower reaches of classical organ music for example...

Hi, You wont regret if building a T-TQWT with Skytronic 902.222 driver:D



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It sounds like you're setting off in a similar way to I did. I actually bought the driver after being convinced by the sims that it'd go flat out to 30Hz. The box was large, though. Needless to say, I didn't build the large box, and bought one of these pre-made car "sub" boxes. It wasn't very good. Hit you in the chest at 80Hz, but very little below that.

So, I tried again, this time, I did some research into bass from smaller cabinets (for a bedroom system). Came up with 2x8" drivers, 42L sealed, with a Linkwitz Transform circuit to get the bass nice and low.

Anyway, here's a link to a supplier that delivers pretty quick (linked to the page with lots of Visaton woofers - they're not the best, but parameters are available, which is a plus...).
Your Search Results | CPC
Visaton - Lautsprecher und Zubehör, Loudspeakers and Accessories


PS - it'd help if you told us your budget, musical preferences (and at what volume!), what size space are you attempting to fill... What will you drive this with....
Thanks for your thoughts folks, a few in return :

sreten> "that comes from trying to vent
a driver that should be used sealed"
Yes, that is what puzzled me and why I added the PS in my orig. post
about the closed box that WinISD proposed, didnt
look as good, to my untrained eye, as the vented
see my new attachment, in which a closed box of 2cuft is shown

>"IMO take a decent 12" car sub"
any recommendations in this price range ?
I originally started with the idea that I might spend
much more on a single 15" or 18" common to the two
channels, till I saw the 'bargan deal' on those
Skytronics! Looks like on advice I may need to reject
them then ?

richie>"Do you realise how physically huge 6 cu ft box
Yep! In another room I have a pair of 5.6cuft
containing electrostatic mid-top and 15" cone base,
built for me 35y ago and only moved once :-!)
Those are in the main domestic region, this project is
for my hobbies/refuge/retreat room :)

bjorno> "T-TQWT"
errr ? I found TQWT via google but what is the T- bit ?
I fear that my woodworking skills may not be up to
that ! Perhaps for my second project LOL! and those
resonances/comb structure looks a bit fearsome.
I will have to do a lot more reading on that, thanks for
the pointer tho.

Chris : thanks, good questions!, I prepared the above for dialup posting before I saw your post, will get back to you shortly on your questions ,,,,


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Hi Artl,

Could i suggest that you look at the JBL GT5-12" subwoofer, it is only around 10 pounds more then the skytronic, but you get a quality brand, twice the power handling and over twice the Xmax (14mm).

In a 6 cubic foot box the skytronic driver will exceed Xmax with only 100 watt input power, even with a High Pass Filter, the JBL tuned to 22Hz with a HPF at 18Hz and 250 watt input power will give you, 91db @15Hz, 107db @20Hz and 109db @25Hz onwards!:)

You would need two 4" ports to avoid any port noise, compression etc, I can vouch for the quality of the subwoofer i have 12 of them.:devily:

6 cubic feet is pretty big but you will get used to it very quickly, i have dual 15 cubic foot boxes in my room of 3.5m by 4.0m and i don't notice them that much any more.

If you build a 2 cuft box and stuff it well you should be able to get the Q
somewhat lower than 0.9, though you could go a little higher, say 2.5cuft,
(assuming the published Vas is accurate, you can check driver parameter
consistency in WinISDPro, and quite a few other things not in WinISDbeta.)

Room gain is a fickle thing, the box roll-off might work well or add a bass
boost circuit very low, similar to Baffle Step Compensation
but with a much bigger capacitor.

rgds, sreten.
Chris> "but parameters are available, which is a plus...)."
Yes, and a very interesting site, well laid out and a delight for dialup use not overblown and stuffed like most commercial sites these days, also first one that I've seen that includes suggestions/plans for enclosures, a lot of stuff to prowl through. Mind you, my first efforts in the two flavours of WinISDs at duplicating the TIW300 box are not going well in the port dimension department !

>"it'd help if you told us your budget, musical preferences"
Budget is very flex, musical prefs range from classical thro folk and ethnic most of which dont need extended bass but I also like solo church and cathedral organ stuff (Bach and all that) which is nice if you can hear/feel the 32ft and 64ft pipes :) Sound level req. is modest, I dont need to raise the roof nor rattle the floorboards.
>"What will you drive this with.... "
Yet to be decided, initially prob something cheapish from Ritcher till I build some mosfets.(project no2)

Homeboy>"JBL GT5-12" subwoofer, it is only around 10 pounds more"
Not a problem, buget is wide :), thanks for the suggestion to JBL, looks good.
>"i have 12 of them"
eeek! what all at once ? some sort of distributed array ?!
I will have to consult the domestic staff before I widen the budget that far !
I made dual subwoofers over the summer, each are 15 cubic feet gross, with four 12" subs in each, they are tuned to around 21Hz, they only get 400 watt input power, but the bass they produce is awesome.

Also i am building a 14 cubic foot TV stand with 4 of the jbls and i'll tune that to 15Hz for some serious infra sonic bass!

I have a skytronic 8" kevalar sub i got last year and its not bad for the money, their speakers are pretty decent, but i would still go with the JBL.:)
I think it'd be best to drive the subwoofer with something decent from the start, cheaper stuff tends to be underdone in the power supply department. I'd recommend a look through here: 41Hz Audio:Sounds Good to Me! - the stuff they do is reasonably cheap, but can shove out a decent amount of power. I built the amp6-b, and it's pretty damn good. Doesn't show itself up on the end of some Fostex drivers, which usually do well at pointing out everything wrong with a solid state amplifier (admittedly, I tried a cheap class AB thing through them, it was awful). So, the quality should be good, and the power speaks for itself.

In your position, I'd consider two 12" or 10" cabinets, used in stereo... 1x12" per side should be sufficient (though 2x12" per side would be much more impressive). I'd also go sealed, as sealed cabinets tend to be more flexible towards some eq - ported cabinets unload the drivers below port tuning, and if you're looking for *some* output all the way down, having the drivers unload and bottom out if you go too low isn't going to be of much use. Yeah... I'm a sealed cabinet fan.

Homeboy>"even with a High Pass Filter,"
Hmmm, that is going to cause more headscratching as I no longer have access to Zverev ! Any good filter design links ?
>"a HPF at 18Hz"
gosh, that will need some pretty big inductors ??

Chris>"look through here: 41Hz Audio:"
Another good link to add to my growing collection, thanks.
They dont supply transformers for the PSUs, and Maplin dont carry much anymore:(
..bjorno> "T-TQWT"
errr ? I found TQWT via google but what is the T- bit ?
I fear that my woodworking skills may not be up to
that ! Perhaps for my second project LOL! and those
resonances/comb structure looks a bit fearsome.
I will have to do a lot more reading on that, thanks for
the pointer tho,,


T stands for Tapped and as GM wrote:'the specs had TL 'written' all over them', I too agree.
A T-TQWT is IMO a very simple enclosure to work with:
Just a box with an internal divider + an access lid where the terminus is located but if not mounted, turns the T-TQWT into an OD-TL(TQWT) Offset Driver that comes very handy for an in-room smooth FR if the box is placed in a 0.5PI corner where most speakers picks up a lot of boundary gain.

The wavelet picture is misleading because it shows an un-stuffed box: You have to shave off a lot of shown resonances and combs before an interpretation can justify the T-TQWT: See the picture..



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I don't know much about designing HPF's, but if you do it at line level (say between your AVR and amp), you will probably just be using some small resistors and capacitors.

The reckhorn B2 (£50) and the behringer MIC 2200 (£80) both have adjustable high pass filters that go down to around 10-12Hz, and give you a bit of Eq also.
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