Well, the original objective was to cover the range from 18 to 180hz. We wanted something capable and imposing both visually and auditorily, but we couldn't afford to spend too much money. So I tried to substitute quantity for quality. I used cheaper drivers that couldn't handle as much power, built the enclosures from particle board, etc... There were 64 cabinets in all (32 bass), and yes... my plan did work pretty well other than the fact that the bass drivers came in spec'd wrong.
If I had to do it again today, I'd probably take a similar approach, using floor underlayment as the cabinet material, etc. I would probably try to select moderately priced bass drivers that would hold up well under near max travel conditions for hours at a time with a free air resonance of around 25hz.
Before, whenever I blew out one the original drivers, I started replacing them with LF Peavy Scorpions. The peavys were tough, but there again, they didn't go quite low enough. You guys probably know of something better than the peavys, but I'll leave that up to you.
If I had to do it again today, I'd probably take a similar approach, using floor underlayment as the cabinet material, etc. I would probably try to select moderately priced bass drivers that would hold up well under near max travel conditions for hours at a time with a free air resonance of around 25hz.
Before, whenever I blew out one the original drivers, I started replacing them with LF Peavy Scorpions. The peavys were tough, but there again, they didn't go quite low enough. You guys probably know of something better than the peavys, but I'll leave that up to you.
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18-180 is very wide bandwidth and really not suited to any scoop, tapped, or line loaded topology as there will be a audible group delay peak in the upper pass band. There is no free lunch, you are in direct radiator territory. Relatively high performance 30-80 Hz would be a reasonable expectation.
I think we crossed over the original (4x12") bins at 60hz, because that was about as low as our full range cabinets would go. That worked out well, especially after we switched from simple vented direct radiator boxes, to Cerwin Vega (15") full range copies that had a better port design and a short conical horn.
The 4560s I like to use as bass fill-ins will go from 40-180 with ease. I suppose I couold relocate the driver into the upper horn mouth, getting it into a safer location, add another foot to the horn entry using the newly available area, and aim for 18-50hz. I could then stack them on their sides underneath the JBL cabs, using them only as true subs.
DemoMan,
Something like the DSL DTS-10 tapped horn, with a response of 15-70 Hz -3dB would do what you want using relatively inexpensive drivers. The DTS-10 style sub can have the exit on various sides to fit with different stacks. You could also easily re-fold it to fit the 4560 footprint.
Art
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Yes, I can see that. The design looks very similar to mine, other than being a real TH. Worse thing about it, is it looks rather mundane. I don't think I'd have to change it's dimensions much really. The size of channel stack I'm looking at would have two 4560s side by side, for the bass end. And, aren't they about 30" wide? The bass and sub-bass stacked together would need to be around 4' to 5' vertically.
I already have 4560s, but If I really felt like spending the money, I'd build and use two 4550s stacked, and then put the sub-bass bins on the sides. I guarantee you'd feel the kick drum, with that setup.
Still, I'd like to see how my own sub design holds up against these others.
Moving slightly off topic momentarily, but:
These look like one-offs to me. Anyone here recognize these as a standard cabinet from any manufacturer? They look to be loaded with 8"s? To my mind, they should be very sensitive & and cover a very wide range if wired and crossed appropriately.
https://www.flickr.com/photos/122644358@N03/17716227516/in/album-72157652290896090/
These look like one-offs to me. Anyone here recognize these as a standard cabinet from any manufacturer? They look to be loaded with 8"s? To my mind, they should be very sensitive & and cover a very wide range if wired and crossed appropriately.
https://www.flickr.com/photos/122644358@N03/17716227516/in/album-72157652290896090/
As Dan mentioned JBL 2226 drivers are 15", you can also tell the size by comparing them to the JBL 2350 horns above which are about 32" wide.
The cabinets appear to be quad home brew variants of the JBL 4550 cabinet, which has about the same dimensions but uses only two drivers.
Doubling the drivers would insure the 3/4" deep ports would be "blown out" at high drive levels, and the side by side placement guarantees plenty of destructive off axis cancellation (horrible comb filtering) in the usual 500-800 crossover region popular with the 2350/15" combos.
Art
Lol... yeah, they have something on there that looks more like a bumper sticker than a manufacturer's label (to me). Nothing I'd recognize.
Okay, I see in your magnification: "Double WOOfers"
I know those are big cabinets... we used to build them. Still it's hard to believe you can get four 15s in there, and yet have that much area left over.
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Ah... yes. Something to compare with. That's where accumlated knowledge comes in handy. I'm not very knowledgeable regarding JBL HF horns. Mostly what I know, is that they are VERY expensive!
Yes I know they are a modified 4550 design. We used to build them, and they are easily recognizable. I suppose it's just an optical illusion, but I thought the drivers were smaller, and was thinking that with four 12s or 8s in the same box one might be able to get on up into the higher frequencies. You can eliminate the phase cancellation, by blocking the hf on two of the drivers when they enter that territory, and then again limit one of the remaining two, at the next higher point of concern. Then of course by using the smaller drivers, the port (and box volume) problem, would take care of it's self.
However... Loaded as seen, with the 15s, and with ports something like the Altec 816, I'll bet that would make a very impressive bass cabinet, say from 50 to 250hz. Mmm... and I like the way it looks...
I think it says: "made for JBL audiophiles" "JBL 4550"
I see the little JBL "!" in there also. Hard to believe that was a JBL sanctioned product though. The picture was from Japan, BTW.
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U'mm, after thinking more on what you've said there; Maybe you know something I don't, but since the factory design already included two drivers, what did they really have to lose by adding two more? The side by sides, are the same distance apart as the above and below. And there is only maybe another 2" between the diagonals.
If I were building these, I would have added another vertical 'phase plug' (if you will) to help even the pressure... but to my mind those four 15s should actually function as one approximately 30" driver... up until the frequency approaches phase interference.
Personally, I don't see why this would be very far below the problem frequency one would encounter with only two 15". Perhaps you could enlighten me?
Yeah, but with that one box you could cheerfully annihilate lots of cheaper boxes at once.
We've already passed the point where a good 15" cab can take on an old-school 2x18" ported design and hold its own.
Are you sure you want to go to 18Hz?
If so, I'd probably buy a whole lot of car subs (eg, JBL GTO1214), put each into a ~60-70L ported box and tune to 18Hz.
Throw a great big pile of power at it and you're all set.
With 20 of those drivers, you could do 128dB from 18Hz up, using around 6kW total. 60L each tuned to 18Hz. Could be really cool.
Chris
The vertical placement of two drivers maintains horizontal dispersion while (in general) reducing vertical dispersion, so off axis horizontal response is (in general) the same as a single driver. Off axis vertical response will be choppy, but normally the cabinet can be situated so the listeners are on axis, while normally listeners are located left to right across the horizontal axis.
Destructive interference occurs when the point sources are more than 1/4 wavelength apart.
Placing the two 15" drivers side by side results in two point sources twice as wide as the single, dropping the frequency where phase interference occurs by an octave.
What I hear you saying, is that when using only two drivers... phase interference is confined to the one axis wherein the drivers are actually doubled in width?
Even so, according to my previous calculation, phase cancellation would not become a serious concern below 5-600hz? Further... would not a better phase plug, mitigate most of the issue?
Just thinking out loud... The reason I am pursuing this line of thought, is that this seems a better solution to achieving the per channel 50-250hz SPL levels I need, vs the 4x4560s or 2x4550s, that I was previously considering.
Nice suggestion... Originally, I had (as my subwoofers) 2'x3'x4' cabinets with four 12s similar to what you are suggesting mounted in the sides, and a port in the front. That worked okay, but then I got ambitious and modified the cabinets further. I moved the drivers to the face, and built a horn-shaped 1/4 wavelength port inside. Afterward I could tell a BIG difference, and that setup seemed to work very well!
Maybe someone will get around to running a sim on the drawing I posted, soon. And then we can see just what sort of levels we are actually talking about here.
Incidentally... back in the day, I had considered building a sort of horn design which you guys would probably call a TH, whereby I would have four 12s lined up in the mouth of a 8' long rectangular tube, w/ only one divider forming the horn inside. Doesn't give you a lot of control over the horn shape, but it's a cheap and easy way to build a 14' folded horn if it would actually work as I envisioned. The main reason I decided against it, was not enough mouth area unless you could locate it in a corner. ...which we usually did not have available to us at a gig.
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1)More or less ;^). Vertical problems are less apparent than horizontal.
2)More like below 400 Hz, which is below the cutoff of the 2350 horn depicted.
3)That solution would work OK below 250 Hz, but an offset driver approach (drivers "V" loaded into a more narrow throat) would provide a higher compression ratio, more efficient.
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