Yes, increase. Why not? Say I have a 2245 in a 10' cab and it's flat to 26hz. adding the second 2245 effectively increases the cab size x 2. So now does it not have the potential to take advantage and lower it's effective -3db point? Or is this wishful thinking?
I tried a few things not that long ago. covid created time and ability to mess around and make stuff out if junk with no lumber available initially.. strange coincidebce to a way To have fun but it was kind of??
If i use isobaric as a set of TS parameters and constructed a nice ‘flat ‘ response TL (MLTL)for it, then cabinet ‘A’ it was(is Still ) If i then remove one of the drivers and leave a single motored Sd, i get a very rising rate and upper frequency biased response(in the subwoofer region this could be a sloppy silly attempt to help an inductance issue at higher freq, but that's so sloppy the botyonm so damped out and peaky at top IMO its not even a consideration, so ‘A’ goes back to a nice Sd with 2x motor. Isobaric.. flat, low end heavy MLTL.. but,
if i make cab ‘B’ a flat response cabinet for a 2Sd pair version of the same driver. (Previously i had in fact as w transflex mltl) And i remove one driver(in SIM to observe changes but similar cabinets), the entire mid band between peaked ends is missing. its then horribly worsened if i isobaric that with one Sd, 2x motor.. so 2Sd it remains, and did....
If i make a 1Sd single motor TL with a nice flat response, i can then put 2 isobaric pairs in it (if they somehow fit) and the response shape will only change in one way. seen as an overall SPL dB gain, slightly shifted to the lower end, if scrutinizing. After correcting for excursion/input power, maybe 4.5dB? i have a umm6 /dats/etc and a hobbiest level of ‘testing’ at best.. but i managed to get Isobaric TS parameters and build a few versions of ‘junk’ test boxes using drivers i had previously disliked because of a lack in motorforce to push compound TL type enclosure air masses and not fizzle out with an already handicapped by inductance motor... the boxes were not ‘sized to much differentky overall 130-160 liters? I have sims sonewhere.. but the aproach was interstingly more and more length as vent less as chamber (or tapered equivalent as TL —-> MLTL goes).
If i use isobaric as a set of TS parameters and constructed a nice ‘flat ‘ response TL (MLTL)for it, then cabinet ‘A’ it was(is Still ) If i then remove one of the drivers and leave a single motored Sd, i get a very rising rate and upper frequency biased response(in the subwoofer region this could be a sloppy silly attempt to help an inductance issue at higher freq, but that's so sloppy the botyonm so damped out and peaky at top IMO its not even a consideration, so ‘A’ goes back to a nice Sd with 2x motor. Isobaric.. flat, low end heavy MLTL.. but,
if i make cab ‘B’ a flat response cabinet for a 2Sd pair version of the same driver. (Previously i had in fact as w transflex mltl) And i remove one driver(in SIM to observe changes but similar cabinets), the entire mid band between peaked ends is missing. its then horribly worsened if i isobaric that with one Sd, 2x motor.. so 2Sd it remains, and did....
If i make a 1Sd single motor TL with a nice flat response, i can then put 2 isobaric pairs in it (if they somehow fit) and the response shape will only change in one way. seen as an overall SPL dB gain, slightly shifted to the lower end, if scrutinizing. After correcting for excursion/input power, maybe 4.5dB? i have a umm6 /dats/etc and a hobbiest level of ‘testing’ at best.. but i managed to get Isobaric TS parameters and build a few versions of ‘junk’ test boxes using drivers i had previously disliked because of a lack in motorforce to push compound TL type enclosure air masses and not fizzle out with an already handicapped by inductance motor... the boxes were not ‘sized to much differentky overall 130-160 liters? I have sims sonewhere.. but the aproach was interstingly more and more length as vent less as chamber (or tapered equivalent as TL —-> MLTL goes).
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It will remain unless you stack a lot of cabs that the baffle step slides down, but 26Hz is low already.
The SPL goes up +3dB from double power and +3dB from greater area =+6dB total
The SPL goes up +3dB from double power and +3dB from greater area =+6dB total
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But it's the same as starting with a 20' cab with one motor. I should be able to get that down to 20hz easily, no?
@discopete
I think in general terms you're right.
For a given F3 adding a second driver to form a constant pressure pair roughly doubles the driver stiffness and power required whilst reducing the Vas (or halving the cabinet volume). That was the consensus I remember from a (I think) Speaker Builder discussion many years ago that was dubbed "No Free Lunch". For a given volume, F3 should drop.
If you had the extra driver you could get a rough idea by attaching it in a face-to-face configuration with the installed driver and connecting so that they both move together.
For an actual implementation you'd want to T/S the thing.
I think in general terms you're right.
For a given F3 adding a second driver to form a constant pressure pair roughly doubles the driver stiffness and power required whilst reducing the Vas (or halving the cabinet volume). That was the consensus I remember from a (I think) Speaker Builder discussion many years ago that was dubbed "No Free Lunch". For a given volume, F3 should drop.
If you had the extra driver you could get a rough idea by attaching it in a face-to-face configuration with the installed driver and connecting so that they both move together.
For an actual implementation you'd want to T/S the thing.
On paper its rediculous to intentionally buy two drivers to build a box for unless its an isobaric box and isobaric solutions to a problem nothing bogger in another way or smaller in another wont handle. size is a convenient excuse, but theres more reasons and they dont get any credit until you want them to. i think if you erase the ideas of comparing and just use your type of approach its very best! i dont really understand the particulars in your case so i just threw mine at you in case it sparked a similar idea/solution? If you shrink size its going to be skewed to a volume/length in qw functions or its not involving the length that matters and it can scale (somewhat??) i hope im not confusing lol 😀 i know I've confused myself a lot!!
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Isobarik effectively uses a 2nd driver to halve the net volume of the box (+ overhead).
If the driver you use will work in a volume that is 2x as big, yes you can use isobarik to reduce the real size of the box.
It is worth noting that large volume reflexes often have a pretty ugly alignment, extention sadrificing quality.
dave
If the driver you use will work in a volume that is 2x as big, yes you can use isobarik to reduce the real size of the box.
It is worth noting that large volume reflexes often have a pretty ugly alignment, extention sadrificing quality.
dave
Im guilty of this last part then, as MLTL is the basic architecture in the isobaric i have.
I think you need to download WinISD or similar and play with some models to see what physics does, not random thoughts. 2 18's would certainly provide "enough" bottom end with very short excursion so pretty low distortion. Of course, two boxes allows more flexibility in placement, even if huge.
Is 10' a bit small for that JBL? Stuffed? What is your Qtc?
The SUB18 is about 10. Vas for the 2245 is something like 25. With eq a 10' box will yield a -3db point of something like 26hz. These are models I've seen. So what is possible with a 25' cab? Add a second isobaric 2245 to a 10' cab to find out, no?
I simmed the 2245H and above about 275 litres the alignmnet starts venturing into territory i do not like. And 225 litres (8 ft3 gives almost the same response (F10 about mid 20s. Note that F3 has been shown to be meaningles sto humans (Toole).
This for a box with a high R high aspect ratio slot vent.
That means one could get away with about 115 litres net + overhesd (box panels, bracing, isobarik coupling chamber, vent).5 ft
25 3 (or 50 or 12.5) yields some pretty ugly alignments.
dave
This for a box with a high R high aspect ratio slot vent.
That means one could get away with about 115 litres net + overhesd (box panels, bracing, isobarik coupling chamber, vent).5 ft
25 3 (or 50 or 12.5) yields some pretty ugly alignments.
dave
There are several very nice looking eq'd curves in 9-10' net boxes over at LH. Are you saying the same box in isobaric will go off on a tangent if attempts are made to extend the response?
Isobaric is to reduce cabinet size, not lower F3. If your cabinet is way too small, then it can extend response back to close what a correct cabinet would do.
Again DOWNLOAD WinISD. Load in your driver parameters ( or anyone for education) and play with the alignments to get an understanding how it works. A little knowledge is dangerous, but too little is too dangerous.
As Planet10 suggests, for a sub, the roll-off and F3 are not as significant as some think as room gain comes to play. As I am not a bass freak, I filter 20 Hz 4th order HP on my subs anyway. For my current build, there is no difference for in-situ use between a 5 foot QB3 and a the 2 foot total BP-4 I am building even though the graphs show a 20 Hz difference in F3 but my displacement is almost half through the band allowing both lower distortion and more peak overhead.
Again DOWNLOAD WinISD. Load in your driver parameters ( or anyone for education) and play with the alignments to get an understanding how it works. A little knowledge is dangerous, but too little is too dangerous.
As Planet10 suggests, for a sub, the roll-off and F3 are not as significant as some think as room gain comes to play. As I am not a bass freak, I filter 20 Hz 4th order HP on my subs anyway. For my current build, there is no difference for in-situ use between a 5 foot QB3 and a the 2 foot total BP-4 I am building even though the graphs show a 20 Hz difference in F3 but my displacement is almost half through the band allowing both lower distortion and more peak overhead.
Did not do the sim, just JBL recommendations. But they are famous for boom so your data is more informative.
It can do that. But only if the s=ituation is that the box you have is too small and making it isobarik can almost double the net volume leading to an alignment that goes lower without increasing the size of the box.
dave
So this is my point exactly. Too small in this context is purely subjective, no? If you simply take full advantage of Vas, why would the outcome be detrimental?
A slight dB skew for displacement(amount of air molecules involved in the process)? other wise MASS got loaded into a mechnical and the response of mms shows a slight skew to a mass loaded TL bass extension
as well. And its just the shuffle of the same energy on and out, to reveal an arguemebt that is IMPOSSIbke to loose or win, if you include heat in the ‘wanted’ section instead of the byproducts of wasted resources which makes $$ of it matter too, the driver or the electric bill to run another amp or lesser ohm load at the one already in use(and heat is the again, the wasted resource)...
But ‘fun’ is a reason if we want to measure it.
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Correct, you can use isobaric to either shrink a cab or tune it ~ a 1/2 octave [~0.707x = 3 dB] lower, so in my time/place the lack of high power [Xmax] to go low was the prime reason for isobaric [5ft^3 was a 'bookshelf' speaker], though rarely used since there was precious little usable content below 60-100 Hz depending on the playback medium and in my case limited its use to a 120 Hz/2nd order, the only SS XO I knew/know how to make.
GM
Yes, but the PO's box is already too large so it would not help his situation.
"too small" is if the Q is higher than .7 or so. Not subjective. Physics. OK, I'll give you .8 for acceptable ripple.
If one really wants to lower the F3 of a driver via cabinet alignment, a BP-6 can do it, but with an 18 inch JBL, only use I think of is for talking to elephants or submarines.
If lower F3 is your only goal, look into a Linkwitz Transform.
"too small" is if the Q is higher than .7 or so. Not subjective. Physics. OK, I'll give you .8 for acceptable ripple.
If one really wants to lower the F3 of a driver via cabinet alignment, a BP-6 can do it, but with an 18 inch JBL, only use I think of is for talking to elephants or submarines.
If lower F3 is your only goal, look into a Linkwitz Transform.