Budget Infinite Baffle in Australia

[broughd]

I have been looking for drivers available locally that would be suitable for an infinite baffle subwoofer. It is very expensive to ship drivers (especially bass drivers!!!) to Australia so I want to use locally available ones.

I have found a couple of candidates:

Jaycar 10 inch

8ohm
87db 1w1m
fs=31
qms = 2.898
qes = 1.057
qts = .775
vas = 115 liters

the frequency response graph shows a smooth 10db hump from about 40hz to 100hz, peaking at 60hz. It looks like an approximately 9db/octave rolloff under 60hz.



Jaycar 12 inch

8ohm
89db 1w1m
fs=32hz
qms = 4
qes = 2.32
qts = 1.46
vas = 166 liter

The provided frequency response graph for the 12 is quite flat under 600hz.

The 10" is AU$24ea and the 12" is AU$32ea, for 10 or more.

I don't think either would have much in the way of xmx, but with 16 or 32 of them I expect this wouldn't be too much of a problem?

I am probably leaning towards the 10" as the Qts looks about right at 0.775, but I don't know how the hump in the frequency response is going to affect the results, looks easy to EQ out though.
@ $24ea 32 is going to cost ~$770 so would be cost effective.

Am I right is thinking that the results are not going to be ideal with a woofer with Qts of 1.46?
If Qts was lower I would be inclined use the 12. I am wondering if the 12 is using the same magnet as the 10? It is a very cheap woofer so wouldn't surprise me.

I have read that it is not recommended use drivers smaller than 12" for IB but I would have thought it is ok if enough drivers are used?

Driver frequency response attached.

cheers , DB:

[Moondog55]

The new catalogue has lost that 12inch paper cone, and the 10 inch needs a big box and runs out of steam very early, try Soundlabs
http://www.soundlabsgroup.com.au/p/V.../W+300+-+8+Ohm
or
http://www.soundlabsgroup.com.au/p/V.../W+250+-+8+Ohm
Although I've not tried either as yet
regards Ted

[broughd]

Hi Ted, thanks for your comments!

Sounds like you have some experience with this driver, what did you use it for? I put a couple of the 10" in as cheap replacements in some old hifi speakers and they didn't sound too bad...

The 12" is still listed on the jaycar website so I would expect they still have some but with Qts of 1.46 I don't think I will use them....

I am looking at an infinite baffle sub so the 10" will have a 'big enough' box...

The woofers mentioned look better quality but I am not sure the extra cost is worth it for me as I need 16-32 of them!. They are 2.5 - 3 times the price, but I doubt if they have 3 times the xmax...

I wouldn't have thought the low power handleing would be an issue as an IB driver will generally reach XMAX at quite low power levels.

32 10" drivers should move some air, and the cost of drivers is around AU$770 If that is not enough, perhaps 64

cheers

DB

[GM]

Ideally you want an IB response that mirrors the room's gain curve, which in theory grows at 12 dB/octave below the 1st axial mode or ~565 ft divided by the longest room dim, but this assumes a sealed golden ratio room sufficiently rigid/damped to contain the gain. Obviously, this requires measuring the actual room gain so you can come up with something close enough, then EQ it the rest of the way.

Big, open rooms like mine though have essentially no room gain in the audible BW, so (ultra) low Fs drivers with a Qts up to ~1.42 (depending on boundary loading) can work fine if XO'd well above their mass corner (~2*Fs/Qts). To get such drivers requires mass loading typical spec inexpensive drivers and using more of them to make up for the reduced efficiency.

GM

[broughd]

Thanks for your reply GM

Mass loading drivers sounds like a lot of work... I am interested, what is the FS of your mass loaded drivers?

Do you think the 12" would be ok as is in an IB given that it has Qts of 1.46 and fs of 32hz? I was under the impression with the higher qts drivers I am not going to get the ultra low bass below fs as the motors aren't strong enough to control the cone much below fs? This is the reason I was thinking of the 10".

Also, does the high QTS result in a noticeably slower sound?

Given the choice, for a normal size room (say 350sq feet) would you pick the 10 or 12 for IB (or would that 'depend'...)?

Do you know of any spreadsheets etc to simulate an IB?

BTW the bass horn is not dead yet, I am just looking at all possibilities...

cheers, DB

[GM]

You're welcome!

Well, it is a bit of work in that you have to calc the weight required, then cut wood discs to bond to the drivers, but if you have a spreadsheet and router or jigsaw with a circle cutting attachment it's not too bad.

I don't have an IB....yet. Hopefully in the next couple of years. Anyway, decades ago me and a neighbor I had at the time built a false wall (~300 ft^3 IIRC) IB with two 2' x 8' removable baffles in his basement and we commenced experimenting to find the best in-room response. Bottom line, the lower the Fs, the better.

Not having a clue about your room's acoustics, I can't speculate much, though a 32 Hz Fs combined with such a high Qts wouldn't be my first ten choices. Now if it had a ~14 Hz Fs.......... At ~32 Hz a Qts between 0.4 - 0.6 usually works well depending on room loading.

How 'fast' the woofer sounds is mostly a function of the 80 Hz-up mains since this is where the majority of the LF's harmonics are, though obviously they have to blend well. Regardless, you can stretch felt over the back of a driver and reduce its effective Qts if it should sound 'boomy' in-room.

Where multiple driver array(s) are going to be used, I want the smallest that has the specs I can make work for the app since they will begin beaming at a higher frequency, ergo will be harder to locate by ear.

Any sealed box program that allows you to adjust rear box Vb will do IB.

GM

[Moondog55]

While I have not used that driver myself, i have heard it works OK as an OB woofer but I imagine it would need at least an even dozen for any sort of power handling.
Doping the paper cone with half and half water and PVA glue a few times mould probably stiffen it up a little and add a little mass, probably no more than a few grams tho.

[ThomasW]

Might want to save up and by the Tempest-X drivers from DIYcable that will be available from a supplier in Oz.

I'd email Kevin at DIY cable for information.

[Collo]

I've done a writeup on using the Tempest-X in aussie IB's
http://www.subwoofer-builder.com/ib-tempest.htm

Includes WinISD analysis, costings and links to local suppliers of drivers and amps.

Go for it....

[broughd]

Originally posted by ThomasW
Might want to save up and by the Tempest-X drivers from DIYcable that will be available from a supplier in Oz.

I'd email Kevin at DIY cable for information.

Originally posted by Collo
I've done a writeup on using the Tempest-X in aussie IB's
http://www.subwoofer-builder.com/ib-tempest.htm

Includes WinISD analysis, costings and links to local suppliers of drivers and amps.

Go for it....

Thanks guys for the tip! These do look like excellent IB drivers, I am sure the 12" Shiva-X Subwoofer with 27mm xmax is going to kill any cheap 12" woofer, but it is also roughly 8x the price, can one of these compete with 8 cheaper 12" woofers? perhaps in displacement, certainly not in efficiency.

Perhaps someone can comment on the pros and cons of using multiple 'wimpy' woofers rather than one big strong one... I would expect to get lower distortion because the drivers will be running at much lower excursion, and at much lower amplifier power due to higher efficiency and shared load.

The bottom line is that for about the same money I could get two of these or 16 cheaper 12" units.

cheers DB