The best example of a reliable low Fs driver is Exodus Audio's (diycable.com) Maelstrom 18" driver DIYCable.com : Intro » Home » Exodus Subwoofers »
17 Hz, 32 mm xmax, 88 dB SPL
And Kevin Haskins tells it like it is, no fudged specs.
Driver sag in mm = 248/[(Fs)^2], i.e. .9 mm for this driver, hardly an issue.
As for the whole issue of low freq efficiency, all efforts using a box are doomed to the same result because even if the driver has 100% electrical to mechanical transduction efficiency, it takes the same amount of energy to compress a given air volume a given amount, and that energy is lost, at least with current technology.
Earl, speaking of transduction efficiency, which would depend only on the motor design and not be a function of Cms or Mms, do you have any idea of what the range is for drivers?
Ah, no I never just "bash", no way
I always try to be straight and fair, and constructive
But I do make mistakes
I thought you were thinking about the latest BMS with very low Fs a big Xmax, genuine sub driver, and a bit rare in pro world, and that one really is that expencive
Im sorry about the B&C, I was mistakenly thinking about the latest Beyma woofers, and those really are that expencive as well, but really not low Fs
Obviously I dont read too good
How about the "old" 21" Beyma
Right now Im looking at a PrecisonDevices 15" neo, looks fine down to 30-35hz in BR, full 97db
Shouldnt take much EQ to make it straight all the way to 30hz
The bigger PD 21" and 24" looks good too, but also expencive
And their very low 0.2 Qts means they need a lot of "help" to get below even 50hz, pure 100db pro woofer, roll off like a stone
Just looked at B&C 21"
Theres one at 500EUR, and two at 649 and 789EUR
Cheapest 21" B&C I could find, multiply by 1.5 and you have it in USD
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Tinitus we are talking about the same driver I think from BMS. The model I was thinking about, the BMS 18N860 is their newest 18" driver, low fs, huge xmax, and the price I was quoted was not that much. I believe Assistance said they could order me one for in the 4-500 range. Beyma's new 21" drivers are listed on US Speakers in the 4-500 range, as is 18 sounds. As has been mentioned, these are commodity products, and the prices shift quickly. I think they have come down a lot lately.
Yeah, I have heard you US guys can get last years Honda VFR800 at something 8.000 USD
Around here it still cost like 30.000USD, or more
You can get the brand new 1200VFR at about 16.000 USD
Around here it will cost 60.000USD
In rest of EU about half as much
Its about you pay less taxes, if any
And its about huge quantities, which can make the prices drop like a stone
Strange
Here the prices are going up, because they are "hungry" and not selling much
At your place its the opposite, because they import in huge numbers, and are getting huge stocks, not selling, prices go down
Totally upside down
Just checked, BMS 18N860 cost 600EUR, or like 1000USD, and shipping could be another 150-200USD
Seems like we have very different terms, I forgot
Forget about it, please go on
Eh, I may afford the B&C 18PS100, which looks ok too
But I need it to be good at 500hz too, but all B&C are peaked, different story
Around here it still cost like 30.000USD, or more
You can get the brand new 1200VFR at about 16.000 USD
Around here it will cost 60.000USD
In rest of EU about half as much
Its about you pay less taxes, if any
And its about huge quantities, which can make the prices drop like a stone
Strange
Here the prices are going up, because they are "hungry" and not selling much
At your place its the opposite, because they import in huge numbers, and are getting huge stocks, not selling, prices go down
Totally upside down
Just checked, BMS 18N860 cost 600EUR, or like 1000USD, and shipping could be another 150-200USD
Seems like we have very different terms, I forgot
Forget about it, please go on
Eh, I may afford the B&C 18PS100, which looks ok too
But I need it to be good at 500hz too, but all B&C are peaked, different story
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Noah that driver, even though it has a much lower FS, performs quite similarly, in my models, to the BMS and B&C drivers. The prices are all similar as well. Conversely, there is a disadvantage to the driver above 50hz, but since none of them would likely be used by us above that range, to me at least, it just seems like a toss up.
This is absolutely the case and why I say that bass extension has to come at the sake of efficiency unless you use more drivers. And if you are going to use more drivers then spread them out. This is precisely how I came up with the idea of multiple subs, It solves a couple of problems at the same time.
Whatever - these threads always wander. Its not a problem. I sell subs so its pertinent to understand why I do what I do.
I was trying to get drivers for my kits sent directly from the EU. I found out how much markup is normal there and it was a crime. These kinds of markups would never survive in the US. Its the system there that has a stranglehold on the distribution and rips off the customer as a result.
Related to that, I've come to another conclusion that I believe you reached a while. Namely, bass extension between a ported vs sealed box, in room, at these really low frequencies, seems to be pretty similar. however, ported boxes seem to cause more "smoothness" problems in that I often find a bit of a peak around the tuning frequency in my room response. It seems like your better off using a sealed alignment or 4th order alignment since in room bass response will be similar, but integration will be easier. It's less of an issue if you aren't integrating to another speaker, such as the ULF sub, but it seems to be a major issue for the main speakers and broad band subs. I am guessing this is why you did what you did.
My only exception to this at all is if you make a ported box with a very low tuning and enclosure size that would net, if sealed, like a .7 qts for the design. This gives a far more gradual roll off for the sub, akin to sealed, but does offer that excursion control at the port tuning frequency. You called that a leaky box though, I guess it probably is, but I was pretty excited when i realized that benefit.
In the ULF range, it seems, as you mentioned, that lots of subs is the best option if you need more bass down there, well that or larger diameter drivers, but a 21" driver is really big. Your talking about an enclosure that's probably at least 25" wide and will need a good 10 cubic feet of internal volume. I think multiple 18's or even 15's would be easier to hide. What I'm wondering is, based on your comments before, if only talking in the sub 50hz range, would multiple subs be best stacked or is there still benefit in that range to spreading the subs around? I thought you had indicated once that the primary benefit was in the area of greatest modal density, which is above that 50hz range, right?
My only exception to this at all is if you make a ported box with a very low tuning and enclosure size that would net, if sealed, like a .7 qts for the design. This gives a far more gradual roll off for the sub, akin to sealed, but does offer that excursion control at the port tuning frequency. You called that a leaky box though, I guess it probably is, but I was pretty excited when i realized that benefit.
In the ULF range, it seems, as you mentioned, that lots of subs is the best option if you need more bass down there, well that or larger diameter drivers, but a 21" driver is really big. Your talking about an enclosure that's probably at least 25" wide and will need a good 10 cubic feet of internal volume. I think multiple 18's or even 15's would be easier to hide. What I'm wondering is, based on your comments before, if only talking in the sub 50hz range, would multiple subs be best stacked or is there still benefit in that range to spreading the subs around? I thought you had indicated once that the primary benefit was in the area of greatest modal density, which is above that 50hz range, right?
Matt
A complex subject, but basically yes, I agree with you you are saying. There really are three regions in a room and they all act differently: 1) below the lowest mode 2) the modal region 3) above the modal region. We, or I, have almost never talked about the first region above, because its even less defined than 2) which is less defined than 3). By this I mean that all rooms act basically the same in region 3), all rooms differ in region 2), but there are significant similarities that make a single "approach" - like multiple subs - work, but region 1) has almost no generalities since a failrly open leaky room will act nothing like a closed sealed room - yours versus mine - so nothing "general" can be said about it.
There is no doubt that below and near region 1 IB works the best - if you can get away with it. I find that is virtually never the case. A ported box would be fine here IF there weren't any other sources at or below its tuning since the tuning of a ported sub gets all messed up with overlaping sources. Thats why I use monopoles wherever there are overlaping sources.
But basically I've never been a big region 1) guy myself. I have it in my room so maybe thats why I don't worry about it, but suffice it to say, in a leaky room its going to be a nightmare to do well.
There's an important difference - w/32 mm xmax the Mael has about 2X the output at VLF, w/only 1 driver and one box.
Takes 2X the power to do it of course.
Changing the topic, a question about diffraction - is it beneficial to radius all of a box's edges, or just the four on the front baffle?
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Secondary diffraction does happen, but they are an order of magnitude less that the front baffle, so its a question of significance and I don't know the answer to that. Clearly it will depend on how low the other types of diffraction are. For example, I see people put diffracting objects close to the speakers all the time. Is a rear box diffraction going to matter in this case, I doubt it. But in my setup the area near the loudspeakers is completely clear of any secondary diffraction objects. Could it matter in that case - maybe.
The front ALWAYS matters.
Its more like 4X, right. Twice the excursion means about 1/2 the efficiency so thats 2X, then to get the cone to move twice as far thats another 2X. Thats why I am not a big fan of high excursion -its a power hog. The manufactures love it because most of them make amps too!!
Well is the Exodus driver p-p or one way? If it's p-p then it's double, if it's one way, then they are about the same. It is never clear to me what these small boutique manufacturers are claiming.
To the point though, the Maelstrom does not produce twice the output, far from it. It takes 4x the power, and so by the time it's in that same output region it's already at it's power limit. I mean, we are talking very low frequencies at very high levels in either case. I don't agree though that the Maelstrom would produce more than a db or two more down there. A simulation of the two, with the BMS at it's excursion limit, and the Maelstrom at it's power limit, they are within about 2db's of each other. They are consuming around the same power below 50hz. They are also around the same excursion.
To the point though, the Maelstrom does not produce twice the output, far from it. It takes 4x the power, and so by the time it's in that same output region it's already at it's power limit. I mean, we are talking very low frequencies at very high levels in either case. I don't agree though that the Maelstrom would produce more than a db or two more down there. A simulation of the two, with the BMS at it's excursion limit, and the Maelstrom at it's power limit, they are within about 2db's of each other. They are consuming around the same power below 50hz. They are also around the same excursion.
sorry, to clarify, since my comment contradicts itself. The BMS driver was consuming less power across the board, but it was a few 100 watts different, when both were being fed 1000's at their peak in the frequency. They both have a peak at 38hz and a lesser one at 15hz were power consumption rose quite drastically.
My mistake, it does take 4X the power to get 2X the excursion, but that's to be expected for 6 dB more output.
And that's the same as needed by a pair of B&C's or whatever in the same size box, at VLF.
The Mael's xmax is 32 mm one-way, 64 mm pk-pk.
Earl, thanks for your thoughts on diffraction.
And that's the same as needed by a pair of B&C's or whatever in the same size box, at VLF.
The Mael's xmax is 32 mm one-way, 64 mm pk-pk.
Earl, thanks for your thoughts on diffraction.
Depending on what you meant that might still be wrong. Its 6 dB more input power for 3 dB more acoustic power, 6 dB more SPL. Thats exactly my point. As you try and go lower and lower in frequency the growth of required input power goes up faster than the acoustical output power resulting in a run away situation that Matt is quite correct in pointing out. The only way to get 3 dB more acoustical power with 3 dB more electrical power is to use two sources - hence back to why I use multiple subs and not one mega sub.
Could also just get one of these for 30hz and down 
Thigpen Rotary Subwoofer
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Thigpen Rotary Subwoofer
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