What to do with these drivers?

[PeteMcK]

Couldn’t help myself, I bought four 6” CW2108 on special at Jaycar for AUD12 ea; now just have to figure out what to do with them.
WINISD gives me 95L tuned to 35Hz for a pair, or a more sensible 24L going isobarik. However, I recently found a 2M length of 30Cm stormwater pipe, so I’m thinking TL?

Specs are: Fs:49Hz Sd: 127Cm^2 Vas:15.2L Qts: .558 Re: 7.3 ohms

Any ideas, no matter how left of field, appreciated...
Cheers,
Pete McK

 

[GM]

Well, if it's made of plastic so you can cut it, then you could step it up a bit by sliding a divider board in it to get the path-length long enough to push Fp down into the 20s and if you load it with a pair of isobarically loaded pairs in a tapped horn configuration and corner load it, then you theoretically have a minimum ~103.5 dB/W/m eff. ~30 - 180 Hz in your modest size pipe. All this of course assumes the specs are reasonably accurate.

GM

 

[PeteMcK]

Hi GM,
Yep, it's plastic, I was thinking of cutting it in two to make a pair, and use a divider as you suggest. What's 'tapped horn configuration'? - sorry, haven't been following that thread.

I don't know how accurate the specs are, haven't measured yet, but the drivers aren't broken in yet, my past experience with Jaycar drivers is that results are reasonable using published specs...

thanks for the input
Pete McK

 

[sreten]

Hi,

The specs indicate sealed and AV type use, i.e. add a subwoofer.

It is an extremely poor idea for the boxes to exceed driver Vas
for budget (and many expensive) drivers, supension linearity is
the major cause of distortion below 100Hz, the air in a box is far
more linear (up to a certain pressure) than driver suspension.

You are pointlessly chasing your tail with boxes (normal or isobaric)
where volume = ~ 3 times the effective driver Vas, said box with
suitably correct drivers would go far lower / louder ... whatever.

I'd suggest a well stuffed box with a target of 8L to 10L effective
volume per driver, Qtc = 0.9 to 0.95, which should combine well
An AV 80Hz filter, or a hifi first order bass filter.

Left field ? open baffle + stereo subs, somewhat like the Nao mini ......

/sreten.

 

[AndrewT]

probably worth checking the T/S parameters and inputting the data in Hornresp as a TH.

 

[PeteMcK]

Andrew, Hornresp is a program I haven't tried yet, this will give me the impetus to give it a go.

Sreten, Points well made, however, I've tried the bigger brother of this driver (Bigger magnet & lower Fs) and it worked well in a BR ~2.5 x Vas; & I've already got drivers I can only use for mids.
I'm aware of the distortion < Fs problem, but I don't play that loud, and most infrasound isn't music, so I'm not sure that distortion is that important for this kind of sound... I'm not expecting super hifi from these, just bought them because they were cheap


I think I've refined my design goals (however unrealistic...) - likely use is HT, and I want small, narrow boxes. So I will probably go isobarik (never tried this before), using these drivers to get from mid 30s to 150 or higher for BSC (so 2.5 or 3.5 way, using a bunch of odd drivers I have lying around)... Just have to figure out how to make a 'clamshell' look elegant.

I'll save the stormwater pipe TL for better drivers later. Feel free to try & change my mind...

Thanks for the responses
Pete McK

 

[GM]

What's 'tapped horn configuration'?

Greets!

You're welcome! It's a 6th order bandpass that's taken to its logical extreme, morphing from two separate air chambers and vents to one big tapered 'vent' folded at least once to load both the front and rear of the driver: http://www.cowanaudio.com/images/30hzth1.jpg Of course you can do more complex foldings like any LF horn: http://img179.imageshack.us/img179/125/2008018we8.jpg

Anyway, here's the Hornresp data for you to play with, which BTW the driver specs are the same for a single driver or dual isobaric pairs wired in series/parallel in case you wanted to build four to spread around the room. The horn specs aren't exact since I just 'ballparked' it 'close enough' to make sure it was viable, though in retrospect I'm not sure the drivers will fit on the throat side. Regardless, ideally you would make these out of wood and build a stereo pair with just one isobaric pair each to keep size as small as practical with a very small footprint if stood up in the corners.

GM

 

[sreten]

.... and it worked well in a BR ~ 2.5 x Vas ....

Pete McK

Hi,

Whilst this is always possible my point is this is not good practice.
It is what I call a non-optimum box, where the trade-offs regarding
sensitivity, box size and bass extension are nowhere near optimised.

Particularly limited in comparison is the driver size for the box and by
implication Vd*, volume displacement, cone area x excursion, which
is what you need the lower you want go, with bass boost if needed.

You say it worked well, I do not think so compared to what is possible.
But then again square pegs in round holes is fun trying I suppose ...

/sreten.

* a perusal of the loudness curves for bass should convince
you extension can be meaningless without SPL capability = Vd.

An externally hosted image should be here but it was not working when we last tested it.

10dB extra SPL capability At 30Hz can equal ~ 20dB apparent capability.
This is why the extreme bass balance of a system is so finicky.

 

[PeteMcK]

GM, thanks for the data, but it sounds a little complex for my limited woodworking skills, & due to a dodgy shoulder I'll probably have to limit my activities for a while

Sreten, I take your point. Just out of interest, what would you call optimum for other driver I mentioned above? (It's always good to get someone else's perspective on things). Specs are Fs 39Hz, Vas 20L, Qt .433, Re 6.9. I'm using pairs in a 54L box tuned to 33Hz. (actually, now I think about it, as a pair that's only 1.35 x Vas, maybe not so bad?)

Cheers,
Pete McK

 

[sreten]

Hi,

Acccording to the specs for a pair in a box :
Vented 40L/33Hz to 50L/30Hz.

54L is fine .....

/sreten.

 

[Pano]

10dB extra SPL capability At 30Hz can equal ~ 20dB apparent capability.

Good point, sreten!

Thanks for pointing it out so , um, graphically.