As part of my PA system, I've used some sealed 18" subs for a while. I quite like them for certain things, but they take a lot of power and they don't go as loud as a cone that big would suggest.
Here's a link to the previous subs: https://www.diyaudio.com/community/threads/fun-in-a-theatre-3x-faital-18xl1800.386725/#post-7034321
More recently, I've been playing around in Hornresp, and realised this:
For a start, I modelled a Faital Pro 12RS1066 in a 28L PR enclosure using Hornresp. It looks like it's possible to use 2x PRs tuned to 40Hz (300g added per PR) and a 4th order HPF at 35Hz just about keeps PR and main driver excursion in check. Result: >120dB output at/above 40Hz while (just about) keeping within rated Xmax.
I chose the 12RS1066 because I have a couple of them sitting around here not-doing-anything, and thought it might be fun to put them to work. Link: https://faitalpro.com/en/products/LF_Loudspeakers/product_details/index.php?id=201050125
I plan on using a small front baffle to hold the Faital driver, and then mount the PRs on opposite sides of the enclosure for force cancellation. Obviously the PRs and driver will take up some cabinet volume, but I'm still expecting an incredibly compact subwoofer.
I'm attaching the Hornresp file, for if anyone wants to play around.
Before I drop the cash on a pair of PRs to test, can anyone see any problems with this?
Thanks,
Chris
Here's a link to the previous subs: https://www.diyaudio.com/community/threads/fun-in-a-theatre-3x-faital-18xl1800.386725/#post-7034321
More recently, I've been playing around in Hornresp, and realised this:
- While having the option for the 18"s to hit 20Hz can be fun, it's rarely useful in a PA system.
- 12" PA sub drivers are sometimes made with the same motor as a 15" or 18" driver, which means they have a lot of motor force for the size of the cone, and could therefore produce decent LF output in a small box
- The problem with small boxes is that it's difficult to fit a bass-reflex port in there, especially if we're chasing output density.
- Passive radiators can help in low/medium-power applications, but when a subwoofer is expected to receive ~kilowatt power levels for hours at a time, heatsinking becomes an issue.
- Dayton Audio make some 12" PRs which have aluminium cones, which should help enormously with heat exchange: RSS315-PR: https://doc.soundimports.nl/pdf/brands/Dayton Audio/RSS315-PR/pdf_dayton audio_RSS315-PR_1.pdf
For a start, I modelled a Faital Pro 12RS1066 in a 28L PR enclosure using Hornresp. It looks like it's possible to use 2x PRs tuned to 40Hz (300g added per PR) and a 4th order HPF at 35Hz just about keeps PR and main driver excursion in check. Result: >120dB output at/above 40Hz while (just about) keeping within rated Xmax.
I chose the 12RS1066 because I have a couple of them sitting around here not-doing-anything, and thought it might be fun to put them to work. Link: https://faitalpro.com/en/products/LF_Loudspeakers/product_details/index.php?id=201050125
I plan on using a small front baffle to hold the Faital driver, and then mount the PRs on opposite sides of the enclosure for force cancellation. Obviously the PRs and driver will take up some cabinet volume, but I'm still expecting an incredibly compact subwoofer.
I'm attaching the Hornresp file, for if anyone wants to play around.
Before I drop the cash on a pair of PRs to test, can anyone see any problems with this?
Thanks,
Chris
Per the chart, looks like 0.2% eff./40 Hz/28 L = (112+(10log(0.2))) = ~95 dBSPL/W
120/95 = +25 dB dynamic headroom
10^(25/10) = ~316 W + driver power rating, so certainly doable with modern high Xmax (sub) woofers, PRs as proven by modern low B organ speakers (SR-1 BASS CABINET).
120/95 = +25 dB dynamic headroom
10^(25/10) = ~316 W + driver power rating, so certainly doable with modern high Xmax (sub) woofers, PRs as proven by modern low B organ speakers (SR-1 BASS CABINET).
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The only problem is the PR rated Xmax is actually Xmech, it will make nasty sounds when it hits the suspension limit.
If you haven't had heat problems with the driver sealed, with the increased level the PR provides it won't be using as much power for the SPL .
If your running close to the PR limit, you might want to go with the SLAPs PRs ~50mm Xlim.
How do you plan to transport it / them?
If you have driver on front, and the PRs on the sides, then it can't lay down without potentially sagging a suspension. More of an issue for the PRs (with the added weight) than the driver, IDK if you worry about that sort of thing maybe depends on how much transportation they see. Perhaps the idea will be to transport them standing up. If you do driver on front, PR on each side, and terminals on the back, then there might be no flat surface to lay it down on or push flat to a wall. I've done this to myself with my home sub, but it doesn't need to travel.
You might consider Driver + PR on front, terminals + PR on back, then you have a flat side to lay it on and no drivers will sag. Or even in use, orientation could be either way, high or low. Maybe that's what you meant, I'm not sure from what you wrote.
In mine I included a brace to directly connect every mounting screw in each PR to its mirror in the other PR with big old wood screws, I felt like that was a good bit of construction.
I bet it turns into a neat solution, interested to hear how it works for you.
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I tried that with B&C speakers 12TBX100, and it was not satisfactory. Not many drivers have more Xmax, and if they do, 3dB is not going to do much. This is interesting case for car audio subs, that go to 22-25-30-32mm.
Why is the limit 28l? At first sight it seems arbitrary. There should be no issue with carrying more than double sized box. I would believe that B&C speakers 18DS,115 could work in such box volume.
Why is the limit 28l? At first sight it seems arbitrary. There should be no issue with carrying more than double sized box. I would believe that B&C speakers 18DS,115 could work in such box volume.
Good point on the Xmech. With a HPF in place and leaving it as 90v input, I've got the PRs hitting around 21mm of one-way excursion, but I'm starting to doubt whether they'll be linear there. Perhaps a pair of the 15" version would be better. If nothing else, it's more heatsink area.
These will be powered by a Powersoft T602, which is capable of a little over 100Vrms, so there is a possibility of the PRs making some bad sounds.
Haven't tested the 12RS1066 sealed. The previously-mentioned sealed boxes use the Faital 18XL1800, which has a lot of Xmax (rated 20mm), but lacks the motor force to perform in a small ported box. They're intended for big ported boxes tuned low.
I suppose, if heat buildup is really an issue, I could mount the 12RS1066 magnet-out.
I was only planning on 2x PRs, so that'd be left/right side with the driver on the front. That still leaves the top/bottom/back for handles/feet/connectors.
Internal bracing will be tricky - there won't be much space inside, but I'll see what can be done to keep the cabinet as strong as possible.
Chris
I'm curious about your 12TBX100 project. Did you also use 2x PRs? What was the problem?
I'm not fixed at 28L, but it seems to be a "happy place" for the Faital 12". If I make the internal volume much bigger, the frequency response gets peaky at 40Hz, or I can tune lower and be flat down to the mid-30Hz range - the problem there is that the main driver runs out of Xmax.
If I go smaller, even more power is required, and it will be difficult to fit everything inside the cabinet. NB - 30cm cube is 27L.
Chris
Well either it was tined high, played nice and kicked like a horse, but not much bass, or it played fairly low, but not loud enough. The driver didn't have enough displacement volume to pull it all out at once. Either higher Xmax driver is needed or larger one. Everything elsw was fine.
It may seem a stupid comment, but why does the port have to be inside the speaker box, why not fold it on the outside and the box dimensions can remain fixed while playing with an external port length.
The cone and the PR are out of phase for most of the range - so no cancelation happening. For small enclosures the back is the best location nevertheless and even required if more subs have to be clustered.
Because a folded port has higher losses and having the port on the outside still makes the sub bigger.
ICG, I'll be using 2x PRs, and those will be mounted opposite each other.
For what it's worth, when I'm not using the 18"s, I have a Void 600w 12" driver in a 40Hz ported box. It's pretty good, but I'd like to build something even smaller that will match it for output and LF extension.
Also, it's difficult to get a port big enough to avoid serious losses, while avoiding undesired quarter-wave behaviour. In the end, you usually end up modelling it as a transmission line.
Passive radiators allow the user to get rid of the port, which ought to save cabinet volume.
Chris
Fair enough, thanks!
For what it's worth, when I'm not using the 18"s, I have a Void 600w 12" driver in a 40Hz ported box. It's pretty good, but I'd like to build something even smaller that will match it for output and LF extension.
This is for a portable PA system.
Also, it's difficult to get a port big enough to avoid serious losses, while avoiding undesired quarter-wave behaviour. In the end, you usually end up modelling it as a transmission line.
Passive radiators allow the user to get rid of the port, which ought to save cabinet volume.
Chris
I always wondered about the KEF Cadenza and later 104s I had with the B139 passive radiator while they used a port on the Concerto.
Couple of screenshots attached. First is the Maximum SPL graph for one of my current subwoofers. The amplifier voltage is with the T602 bridged (6KW@4ohm), so I can only really run two of these cabs before I need another amplifier. The net cabinet volume is around 100L, and they're very much excursion-limited - indicated by the red part of the graph.
2nd screenshot shows the Max.SPL graph in light grey against the simulated 12RS1066+2xPR receiving 90v input.
The 18" wins above and below 40Hz, but we're talking 100L of air volume vs 28L. The 12" box barely needs EQ, while the 18" has the sloping-down response that would be expected from a sealed box.
In all, I think this could be a kick-*** little box. One would probably be enough for small shows, but the Powersoft T602 could (just about) run a total of 8x 12RS1066, which would put out some pretty serious SPL: 136dB@40Hz, from 224L of cabinet volume. A bigger amp (the T602 falls down a little: 2.5KW/ch@4ohm, but only 3KW/ch@2ohm) would get me to 138dB.
The TH118 simulates at 143dB for four cabinets (at a little past Xmax), each one a little over 300L. One TH118 would be around 131dB, while a set of four of these 12"s would match that SPL while using 112L of cabinet volume.
Comparing to known-good designs, it looks like this idea is packing a lot of output into a very small box. I think it's worth building a prototype and doing some testing.
Decision:
To physically fit the 15" PRs, a larger cabinet is required, which results in a 2dB peak at 40Hz, or I can push for a little more LF extension.
The 12" PRs will hit Xmech if the Powersoft T602 hits maximum output at 37Hz exactly. This isn't likely to happen with normal music, but I do have a neat little trick I can pull here: the T602 has an excursion limiter, which could be used for a couple of dB of gain reduction (that really is all that's needed) in the (unlikely) event that a 37Hz sine tone comes along at full power. I think we might be on to a winner.
Chris
2nd screenshot shows the Max.SPL graph in light grey against the simulated 12RS1066+2xPR receiving 90v input.
The 18" wins above and below 40Hz, but we're talking 100L of air volume vs 28L. The 12" box barely needs EQ, while the 18" has the sloping-down response that would be expected from a sealed box.
In all, I think this could be a kick-*** little box. One would probably be enough for small shows, but the Powersoft T602 could (just about) run a total of 8x 12RS1066, which would put out some pretty serious SPL: 136dB@40Hz, from 224L of cabinet volume. A bigger amp (the T602 falls down a little: 2.5KW/ch@4ohm, but only 3KW/ch@2ohm) would get me to 138dB.
The TH118 simulates at 143dB for four cabinets (at a little past Xmax), each one a little over 300L. One TH118 would be around 131dB, while a set of four of these 12"s would match that SPL while using 112L of cabinet volume.
Comparing to known-good designs, it looks like this idea is packing a lot of output into a very small box. I think it's worth building a prototype and doing some testing.
Decision:
To physically fit the 15" PRs, a larger cabinet is required, which results in a 2dB peak at 40Hz, or I can push for a little more LF extension.
The 12" PRs will hit Xmech if the Powersoft T602 hits maximum output at 37Hz exactly. This isn't likely to happen with normal music, but I do have a neat little trick I can pull here: the T602 has an excursion limiter, which could be used for a couple of dB of gain reduction (that really is all that's needed) in the (unlikely) event that a 37Hz sine tone comes along at full power. I think we might be on to a winner.
Chris
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Hi Chris. Hope you've well. Have you ever tried a Linkwitz transform.? Probably silly question and maybe wholly unsuitable for your application. !
I've just laid out a PCB to try one at home. Small (15 to 25 litres) sealed 8" long excursion. Different than your ideas here granted. I just pondered if you'd tried an LT?!
I've just laid out a PCB to try one at home. Small (15 to 25 litres) sealed 8" long excursion. Different than your ideas here granted. I just pondered if you'd tried an LT?!
While a LT would allow deep bass from a small enclosure, it would be severely limited in maximum output. There are no passive radiators to aid in volume displacement.
Also check out the Ciare 12.00SW. Similar TSP but with more xmax. It is however an old design and there is no mention of shorting rings.
Hey Jim,
Yep, I have. The thing to bear in mind is that an LT is just a fancy EQ curve that's been given a name. IMO, in the day and age of DSP, not especially useful any more: it's better to use parametric EQs to flatten the room + sub as a system. I might have a spare Behringer DEQ2496 around here somewhere if you'd like to play with it - shoot me a PM.
All,
I hadn't modelled other drivers because I happen to have some 12RS1066 around here. It's a good point, though: I should make sure they're the best for the application. The Eton driver claims a LOT of Xmax, but the 2x2ohm voice coils might pose a problem with using multiple subs in parallel for a PA application. I'll model it in Hornresp and see what's what.
Thanks for the discussion so far!
Chris
For sure!
Even if you find the 12RS1066 isn't the "best" for the application, doesn't look like you could get much more LF output density without increasing PR displacement.
I'd think power compression on the 12RS1066 would probably keep it from bottoming out the PRs if sustained 37Hz tones are hit, but you should be able to keep all that under control with the T602 limiters.
The car audio type drivers with more Xmax may have more LF (given more power), but probably won't perform as well up top with the heavy MMS and inductance losses. I'd be more concerned about Pmax up high than low.
Cheers,
Art