modeling scoops...

for my benefit as much as anything but useful for anyone interested,

pitfalls & problems etc when designing and simulating for driver selection.


out of interest does anyone know how to keep drivers from running out of xmax, too early is it just by reducing the rear chamber?

(if so then ill have to have a rethink as to this design im working on... though its just for monitor / hifi duty)

www.speakerplans.com/forum/forum_posts.a...74&PID=198509#198509

for people interested mykeys posted input for a hog.


thogh ive been re reading various things and looking at other threads via google and it seems that whilst it can give you a rough idea you might as well not bother modeling to get any idea of actual response, could potentialy teach you how to modify scoop for a specific driver though






Edited by: sKs01

sks01, I have put some links on the 'is this a rear loaded scoop' thread.

RLHs won't be suitable for monitors in my opinion.

check out MJK's MathCAD worksheets at quarter-wave.com - they should be indispensible for your application. The standard for RLH and transmissionmodelling basically - they give results that measurements verify.Bob brines gives a good tutorial on usage on his site.

Also keep in mind that hornresp models any driver as a flat plane radiator - individual driver response is not taken into account (imagine trying to do so...)

cheers ill look into it.

so far ive come up with something that seems to work quite well in hornresp for this aplication. (though ill test the design using mathcad to see if it works as predicted in that) crossover point arround 80Hz and -3db 35Hz though 93db efficiency but then its not a PA aplication so thats not a massive problem.

sorry should've been more specific, design aim for that is for something that looks good more than sounds spot on in terms of accurate sub (not pro production more sat messing with fruity loops)

what ive ended up with is something that looks a lot more like a th than a scoop at the moment anyway, trying to reduce path difference between driver and mouth to move the phase cancellation dip out of the passband. but with a large rear chamber rather than a tight compression chamber. though that design might need to change as its quite tall. (90cm)

hmm for some reason i cant edit the last post, i should've said for people other than deadbeat that thats with a 12" driver not an 18"

sks, can you post the plots or inputs? I'm curious.
Edited by: Deadbeat

this is more or less a thought exercise at the moment as i havnt had any specific size limitaions yet only real size ive been given is a 12" driver...

(horn resp says that the combined response cannot calculate for a driver inside the horn mouth, however ive been playing around looks like it should work as a rough approximation, using the path length to the driver. though i havnt tried it as a th sim yet as im unsure how, it doesnt prompt me when i press caculate...)

driver is eminence definimax 4012



pmax plot suggests it will have that same sort of 40Hz bump as most 18" scoops (due to xmax being eaten up @ 60-70Hz) which was the sort of thing i was after just lower volume

any comments on how this moddel is inaccurate wrong or just downright silly would be appreciated, i shouldve said that though i was orrigianly modelling a miniscoop, it has somewhat turned into a fullsized, that mightve been what you were thinking about deadbeat, in which case i shouldve said earlier.

might well do a th version and a vlp version as well as a reflex so he can see what he fancies best. in terms of output and looks.

damn still cant edit: path difference i've bein using is -175, not sure if its strictly accurate but seems to be what i would expect given that sort of design in terms of output.as effectivley when you make a tapped horn your moving the cancellation area out of the passband by moving the point where the driver and horn actualy sum, yes?
Edited by: sKs01