Budget Infinite Baffle in Australia

broughd

Member
2007-10-11 12:05 pm
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:
 

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broughd

Member
2007-10-11 12:05 pm
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 :cool:

cheers

DB
 
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

Member
2007-10-11 12:05 pm
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
 
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
 

broughd

Member
2007-10-11 12:05 pm
ThomasW said:
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 said:
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
 

broughd

Member
2007-10-11 12:05 pm
GM said:
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



I found another driver that looks possibly suitable, it is a 12" paper cone and the specs are:

Specifications
• Nominal impedance:8 ohms
• Power nominal: 225WRMS
• Frequency response: 28Hz - 550Hz
• Qms: 1.642
• Qes: 0.445
• Qts: 0.35
• Vas: 57.615 litres
• Fs: 33.172Hz

The Qts is a bit low but this is an IB candidate right?

The design I am working on uses 16 of these and a linkwitz transform which seems to produce a reasonable looking result. From 80-40hz it is flat, 40-20hz down 3db and 20-10hz down another 9db which is probably close to what I am after.

At 20wrms excursion is 4mm at 20hz and output at 20hz is 111db so I think the drivers will cope - I won't be using it at 111db very often!.

Is it worth pursuing the driver modifications (adding weights) or is this unnecessary if I am already using an equalization circuit?

cheers, DB
 
The low Qts means it's overdamped so it will take more EQ to lift the bottom end.

IMO adding mass to lower the Fs is unnecessary because you can use EQ and the effects of room-gain to boost the lowest frequencies.

The primarly benefit of using an LT is to lower the Qtc and the system Fs. With this system you certainly don't need or want a lower Qtc.

You haven't posted any information about the room and where you intend to place this IB. Is it really practical to use 18 drivers? A manifold would be 1/2 again as big as Collo's..
 

broughd

Member
2007-10-11 12:05 pm
Thanks for your reply!

I have attached an image depicting the approximate layout of the room and possible mounting arrangement of the IB drivers.

The room will be approximately 6m square, with a sloping ceiling. Construction is hardwood floor joists with hardwood floor, hardwood studs with pine paneling for the ceiling (with insulation behind), hardwood stud walls covered in cement sheet. It is not built you but I will try to convince the owner (my father in law) to make the wall for the IB more solid than the others, perhaps by doubling up on studs.

There is plenty of space behind the wall because it is just the roof space of a workshop.

As you can see there is plenty of space to mount lots of drivers, even without a manifold. Some people say that it is good to use a manifold even if not required for space reasons because the vibrations cancel out and stop the wall from vibrating.

I think heaps of drivers all mounted on the same wall would look really cool though... :D

cheers DB
 

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broughd

Member
2007-10-11 12:05 pm
Hi !

One thing with car audio woofers, its just my opinion, but they always have ugly graphics so I'd have to put them somewhere where I couldn't see them... I much prefer the look of plain cardboard...!

Seriously, thats probably a good idea, especially as the car subwoofer drivers should really have more xmax than a cheap hifi woofer.

The low qts of the hifi woofer probably isn't too much of a problem though if I can just eq the bottom end to correct it, especially because when using many drivers the system efficiency is relatively high (100db/w/1m or so) so the amplifier shouldn't run out of voltage too quickly. Unless I can get a really good deal I would be paying double or more for the car subs. Jaycar had a 15" car sub with qts of 0.5, fs of 25hz and xmax of 15mm - perfect! its a shame they don't sell them anymore :(

Anyway, I'll keep an eye out for anything suitable!

cheers, DB
 

broughd

Member
2007-10-11 12:05 pm
ThomasW said:
If possible reconfigure the room because a square is a terrible shape from an acoustic standpoint.


I don't have exact measurements but think it is actually going to be slightly rectangular... and the roof is sloped, that has to count for something... I'll mention that though, there is in fact plenty of scope to extend the room further out, construction hasn't started yet - in a couple of months I think.

The other possibility is making the short walls under the sloping roof relatively acoustically transparent, at least to the bass. That would help right?



If you go with the low cost 12"s I'd put them in 2 manifolds because the pressure exerted on a wall by arrays is tremendous. Any wall flex means output is being canceled...

Point taken, the more I think about it, it will be somewhat impractical to make the wall heavy/stiff enough to stop it flexing.

Theoretically do you think making the wall of 4 inch thick hardwood (i.e. build whole wall by laminating 4x2s) with external bracing be stiff and heavy enough? I would be surprised if it wasn't good enough and it wouldn't be completely impractical.

Would two manifolds or one big one be better? There would be increased efficiency by putting all drivers together right? Would that lead to more pronounced nodes though ?


cheers, DB
 

broughd

Member
2007-10-11 12:05 pm
ThomasW said:
The low Qts means it's overdamped so it will take more EQ to lift the bottom end.

IMO adding mass to lower the Fs is unnecessary because you can use EQ and the effects of room-gain to boost the lowest frequencies.

The primarly benefit of using an LT is to lower the Qtc and the system Fs. With this system you certainly don't need or want a lower Qtc.

You haven't posted any information about the room and where you intend to place this IB. Is it really practical to use 18 drivers? A manifold would be 1/2 again as big as Collo's..


Hi!

I have attached some frequency response plots from WinISD.

The first is without the LT, the second with.

It appears to me that in this case the LT changes the response to be basically what I am looking for. In this case why shouldn't I use it? Would I be better off with a normal equalization circuit?

cheers DB
 

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broughd

Member
2007-10-11 12:05 pm
ThomasW said:
The low Qts means it's overdamped so it will take more EQ to lift the bottom end.

IMO adding mass to lower the Fs is unnecessary because you can use EQ and the effects of room-gain to boost the lowest frequencies.

The primarly benefit of using an LT is to lower the Qtc and the system Fs. With this system you certainly don't need or want a lower Qtc.

You haven't posted any information about the room and where you intend to place this IB. Is it really practical to use 18 drivers? A manifold would be 1/2 again as big as Collo's..


Hi!

I have attached some frequency response plots from WinISD.

The first is without the LT, the second with.

It appears to me that in this case the LT changes the response to be basically what I am looking for. In this case why shouldn't I use it? Would I be better off with a normal equalization circuit?

cheers DB
 

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broughd said:



I don't have exact measurements but think it is actually going to be slightly rectangular... and the roof is sloped, that has to count for something... I'll mention that though, there is in fact plenty of scope to extend the room further out, construction hasn't started yet - in a couple of months I think.

The other possibility is making the short walls under the sloping roof relatively acoustically transparent, at least to the bass. That would help right?


You still have a square room. You really want a golden mean rectangle
do you think making the wall of 4 inch thick hardwood (i.e. build whole wall by laminating 4x2s) with external bracing be stiff and heavy enough? I would be surprised if it wasn't good enough and it wouldn't be completely impractical.

Sounds very impractical....

two manifolds or one big one be better? There would be increased efficiency by putting all drivers together right? Would that lead to more pronounced nodes though ?

There's a reason the IB FAQ page recommends using test boxes to determine optimal placement. If your room remains fundamentally a square, you'll have a mess regardless of how many manifolds you use

It appears to me that in this case the LT changes the response to be basically what I am looking for. In this case why shouldn't I use it? Would I be better off with a normal equalization circuit?

Seems like I already answered that question...