| 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: |
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| 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 :cool:
cheers
DB |
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| 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 |
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| 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 |
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| 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 |
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| 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. |
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| 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. |
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| broughd |
| quote: | 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. |
| quote: | 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 |
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| broughd |
| quote: | Originally posted by 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 |
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 |
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| ThomasW |
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.. |
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| broughd |
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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| pkm |
| Have you considered car audio woofers?Often they have higher Qts which is what you want,for example repco lately have 12" Fusion subwoofers for $69.95 in NZ. |
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| broughd |
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 |
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| ThomasW |
If possible reconfigure the room because a square is a terrible shape from an acoustic standpoint.
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... |
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| broughd |
| quote: | Originally posted by ThomasW
If possible reconfigure the room because a square is a terrible shape from an acoustic standpoint.
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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?
| quote: |
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 |
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| broughd |
| quote: | Originally posted by ThomasW
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 |
| quote: | Originally posted by ThomasW
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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| ThomasW |
| quote: | Originally posted by broughd
[B]
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| quote: | | 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....
| quote: | | 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
| quote: | | 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... |
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| Brett |
| quote: | Originally posted by broughd
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. |
Hebels. Cheaper and easier. |
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| broughd |
| quote: | Originally posted by Brett
Hebels. Cheaper and easier. |
Concrete boxes? There will already be several good size boxes for the mains so I am not sure we want any more... I think we have basically decided on an IB. The IB shouldn't cost too much, 16 * $35 = $560 (or 32 = $1120)
In terms of construction cost, the owner is a professional builder, so building manifolds or strengthened walls etc would not be too hard, and the extra materials aren't expensive in the context of building a house...
Thanks for the idea but I can't do everything, think I'll stick with the IB...
cheers, DB |
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| broughd |
| quote: | Originally posted by ThomasW
You still have a square room. You really want a golden mean rectangle
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Thanks for the advice, we may be able to change the room dimensions...
| quote: | Originally posted by ThomasW
Sounds very impractical....
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Well - I'll take that to mean that you think it would work but that it isn't something that you would do... It is actually a (home) bar so a solid wood wall covered in speakers would in my opinion be a nice feature.
| quote: | Originally posted by ThomasW
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
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Again, thanks for the advice, I'll check that out.
| quote: | Originally posted by ThomasW
Seems like I already answered that question... |
Please don't shoot me down here I'm just trying to learn something...
You obviously know a lot more on this subject than I do... as you say, one way of looking at the effect of a LT circuit is that it modifies the driver Qts and Fs.
Another way of looking at it is that it is an EQ circuit that applies a gain pattern to the input signal tailored that a specific driver.
You said that as the drivers are low Qts they will need EQ to bring up the bottom end.
If I find an EQ circuit that happens to provide the gain pattern that I need then why should I not use it?
As I said, you know more about this than I do so perhaps the only reason is that it is hard to get a LT circuit right and a simple EQ is easier.
cheers, DB |
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| Brett |
| quote: | Originally posted by broughd
Concrete boxes? |
I thought you were talking about reinforcing the gyprock walls, which is why I suggested the Hebels. |
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| ThomasW |
In the 9 yrs we've been running the IB forum several hundred people have built IBs, to date none have felt the need for an LT circuit.
Once you get your IB operational, run a set of measured frequency response plots, then you can decide whether or not you need an LT circuit. |
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| broughd |
| quote: | Originally posted by ThomasW
In the 9 yrs we've been running the IB forum several hundred people have built IBs, to date none have felt the need for an LT circuit.
Once you get your IB operational, run a set of measured frequency response plots, then you can decide whether or not you need an LT circuit. |
Fair enough... thanks for your patience... |
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| broughd |
I've just been evaluating one of the jarcar 10" drivers. Fed 9v (close to 5w I think) sine wave at 20hz it goes to 8mm peak to peak. This is probably a bit over its xmax although I'm not sure.
There seems to be a little distortion and suspension noise, although not too much - I don't think I would be enough to be annoying as I can hardly hear it at 3m or so, I don't really know how much noise to expect when treating a driver this way although the noise coming from this seems reasonable... also I think some of it is coming from the back but that wouldn't be audible in an IB.
There seemed to be some minor rattles and squeaks up above 60hz or so, perhaps the spider resonates a bit at certain frequencies??? For the record it sounds quite respectable in a sealed box.
I am leaning toward the conclusion that it would be suitable for an IB system provided lots are used; thoughts ???
cheers, DB :) |
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| paulspencer |
Firstly about drivers. There is more to consider than cost and output! If you buy a lot of cheap and nasty drivers rather than a few good value quality drivers, you can easily end up with something impressive looking, loud yet quite a bit less impressive in terms of SQ.
I recall the first time I listened to Jaycar subs. They had their JV60 kit on display with the Vifa P17 in a vented box. Listening to them vs the bass from any of their subs, it was clear that none of them were close to musical. The Vifa kit was good, but the subs they had, all of them were terrible in comparison, a big step backwards. This was around 2004, back then I couldn't imagine wanting that sound, and I'm fussier now. Some of those 12" drivers were worth $300, just slightly less than you would pay now for a Tempest. The beauty of the Jaycar drivers is that you can evaluate them easily. However, unless they have changed dramatically, I wouldn't use any of them. I did build a 10" sub for my parents, built for $150 including amp. It was just to add some bass to their TV.
The point I'm getting to is that you must first start with decent drivers. Cheap and nasty drivers won't suddenly become better when used in large numbers. They will always be limited by their inherent weaknesses which will persist no matter how many of them are used. Yes you will get an incremental improvement by reducing the load to each one, but you will find that a decent driver will sound better. Even fed with lots of power and moving at xmax, a decent driver will get a better result than a pile of dodgy drivers barely even moving.
If you are talking about the best performance for a given amount, then it may make more sense to chose a number of decent drivers over a large and very expensive uber driver. However, I'd suggest starting with drivers which have a certain level of quality. If budget is restrictive, then start with less of them, and add on later. I think this makes sense for two reasons:
1. You won't be held back by their SQ
2. You have a more logical upgrade path - no need to sell drivers
I'd suggest as a minimum you look at drivers like Peerless SLS or XLS which are very good value here. Both work well with a fairly high crossover point, easily 80 Hz. The XLS is tending to be overlooked these days, being an older driver and not so impressive now with its xmax of only 12mm. However, if you look at the measurements, it's distortion in the 40-80Hz range is very low. Within its limits it has excellent performance, it appears to still be more articulate than most of the new drivers.
Many sub drivers won't do it, and if you try to cross around 80 Hz the sound is awful.
The new Tempest X drivers also look very good.
Regarding construction, timber framed plasterboard walls are good for taming room modes - they tend to absorb the bass. They are also good for letting the bass get through! Are the studs already in place? Hardwood is a pest to work with. If you have an old house with F8 OBHW it makes life so much more difficult! The timber gets dry and hard, unseasoned when originally built, but now very different. Pine is so much easier!
If you can influence the construction, then it makes sense to do a few things like sealing up any gaps and trying to at least get two a skin either side of the stud which is continuous - no holes or openings. Easier said than done. Then acoustic insulation and ideally more than one layer of plasterboard, joined with liquid nails which remains flexible and gives you some bass damping.
I did this with my home theatre reno, and I was surprised to notice two things:
1. Much less bass gets out - I don't have to worry about neighbours
2. Much more bass stays in - dramatic increase in impact |
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| lazenna |
| Just wondering are you the paulspencer with the open baffle mains.If you are,are you still using them? |
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| broughd |
Hi Paul !
Thanks for your comments, I think you have made a number of good points.
I did some sims, and for 32 of the 10" s above had about the same max output as two 15" tempests and about the same cost. The main difference was in efficiency, so > 10x amp power is required!
Your comments about distortion levels make sense to me, I think I can live with the lower efficiency. Fewer drivers make for an easier install too. I'll check out the peerless drivers you mentioned when I get the time... who sells them here?
It would be quite funny if the neighbors complained because the house is in the middle of a 100acre block in the bush... we'll do our best though!!!
Construction of the room in question has not yet started, I'll pass on your suggestions regarding construction. I assume the techniques would work just as well with cement sheet?
What about cement sheet with wood panels installed over it?
The system will be used 2/3 for music and 1/3 for HT. How many of the Tempest 15s would I need (2, 4 etc), is there a simple driver displacement / room size rule of thumb to work this out?
cheers, DB |
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| jol50 |
I've had great luck with low priced drivers in cars IB, though HT is not exactly the same. The Fs/Qts is important because that is in essence your enclosure tuning, in a way. I'm of the school that you tune the subs to your use and then EQ if you have to, not the other way around as is common today. I used to use pyramid originals, but have not since there were upgraded. Quality seems to be higher at lower excursions IMHO, so moving more air (larger/more drivers) helps but I'm not sure about as many as you are thinking. Your gains diminish after about 4 I think, what I usually run in a car.
Right now I am using an infinity 300wrms sub in a car IB, it seems to work well. With about 100wrms each it is powerful and overpowers the high side of the system so much I rarely turn them up. Even if I do I get maybe half of xmax. They do say in the manual half of rms ratings for IB use. But I am considering changing out to the cheaper drivers, they will be much lighter (4 of these is really heavy in car), and with more efficiency I am thinking I will not lose that much db, and I can run a smaller amp to boot. If you need huge output then cheap driver may not work for you. But in my experience the gains of high power and HD driver is not that much with IB as with enclosures...you still run out of xmax with IB.
Most HT go with 15s even 18s that I have read about, larger tends to give you free efficiency and lower Fs that helps you. In a car you get cabin gain that lowers your curve so 10s and 12s work better than in a house. If you have a wall of subs that big, you need to anchor it to concrete or something that is why manifolds work nice. I just model a huge sealed box to show IB in software. Anything that dampens will help the wall, such as drywall, concrete, MDF, even filling the wall with sand...think heavy. A manifold will cancel the physical movement more and cause less mounting issues. |
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| kesa32 |
broughd , 4x 15" tempests should do the trick nicely, as paul has stated the qaulity will be there , also they'll take a lot more abuse than cheap drivers ( ib's need to be able to handle big transiets in a ht ) , you can power these with a behringer ep2500 for about $680 and you'll have a sub that will be very gutsy for a room that size :D
cheers ken |
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