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Some EAW horns have none? correct?they have 'stiff suspension'
How 'stiff' is stiff?
my 2226 wants a huge basshorn rear chamber volume,why not only front load it? i know il have a lack of subsonic loadingsWhat about the Fc and midbass?/???
How to model? what can i expect.? no reactance anulling possible...severe lack of response ?? even in midbass??
Cheers!
Follow Ups:
HiIt is both the "high pass" nature of the horn's radiation resistance AND the reactance's acting on the radiator mobility that sets the low cutoff performance of a given horn.
While the radiation resistance is related to the size and expansion of the horn, the reactance that is acting here is the sum of both the suspension spring force and enclosure spring force (in parallel) which sets the total compliance or reactance.
In this light, one can see that if the driver suspension is made increasingly stiff, the compliance eventually reaches the same point it would have previously with a sealed back volume.
Bassmaxx has several horn loaded systems which have an open back and the old Scoop or "J" bins which were popular in the 70's did as well.
Any back loaded horn system which has both a direct radiation and horn loading is an acoustically identical situation in this regard.There are several reasons one could argue that suggest this is not the "best" way to go.
So far as measured coherence, one finds the direct radiation is "ahead" of the horn radiation by a time corresponding to the horn path length difference.
This "pre echo" signal may even sound good in some situations however it would be hard to argue that spreading any signal out in time to any degree makes it more faithful to the original.
Also, this double path is like a transmission line in that there is a defined bandwidth where cancellation does not occur and past that the system interferes with it self.
If that system is large as in Pro-sound, the multiple sources also cause interesting polar patterns and radiation lobes.
So far as distortion, the air spring one has in a sealed and ridged back volume is more linear than a driver's suspension (at the same excursion), especially if one is dealing with a driver that is made to be "beaten on".
A much better approach (I think) is to use a high compliance driver in a sealed box like in the LAB sub or any of our stuff at work.Several subwoofer shoot-outs have been held by members of the Live Audio Board, two things stood out.
First, the B.M and Lab horns smoked all the other subs tested.
Direct radiator systems had WAY more distortion than the horns at a given level and that was quite audible as well as measured.
Second, that the Lab sub with it's 2 12's, produced a little more sound with a little less distortion and a flatter response than the B.M with it's exotic Aura and / or McCauley 18 inch driver..
This seemed odd to many as the displacement of the 2, 12's is less than the 18's used.
The difference is that the 2, 12's had an acoustic impedance which asked for a greater compression ratio and so for a given displacement produce more acoustic power and by having the impedance's and reactances more closely matched, gave a response which was flatter deeper, and on average more efficient.
Hope this helpsTom
If the horn is long enough and has a high length to cross-section ratio the air column of the horn is so stiff that reactance annuling has little effect, pushing the Fb up by only a small percentage, and conversely performance above the Fc is not significantly different with the rear chamber being left open. However, without the stiffening of a sealed rear chamber there is the problem of the driver being unloaded below Fc, so care has to be taken or serious overexcursion can result. As for EAW I'm not aware of them using any boxes without rear chambers.
As for EAW I'm not aware of them using any boxes without rear chambers.
oh perhaps i confused them with BASSMAXX..
Ive found that the horn required for the jbl to reach 30hz with some wobble,is ~700L about the same as one WITH a rear chamber :-P
it looks like it wont be of any use,as i simply must have 30-35hz ,because i have 40hz already with my miniature basshorn.
a 40hz horn for the jbl would be worth it ,if small enough -300L....
CHeers!
to get the kind of SPL they claim from two cabinets that large isn't really all that impressive.
Im not a salesman of bassmaxx,i just want to front load,no Vrc on my jbl2226 in a tiny 30hz horn :-)as u can see in the reply to GM it sorta works,id use a subsonic filter...but its too huge-the throat area = sd so the horn is fat from the start,and just gets fatter!
lab12 is the anwer it seems
:-)
440$ NZ for the lab12 ugh!Cheers
Mike.e
How about the Altec A7 (825/828) cabinets are front loaded and rear reflex.
Ron
hey Mike -think Bassmaxx used both Aura and an Eminence at one time with success so guess was a long scoop - dunno 'bout EAW - not seen info -
re:Bassmaxx approach - oughta be something in the archives under tomservo's and djk's comments
fwiw seems like bassmaxx slope on graph in sub-shootout appeared shallower - not sure what happend to distortion , etc. - might be subjective thing and how mates up with room
John Sheerin can explain (if has time)
Search! thats an idea! ugh completely didnt think.!4am brain not going
Cheers!
In Reply to: Re: Whats the low-frequency slope of BASSMAXX One's? posted by freddyi on August 24, 2003 at 11:41:27:
> what T-S might the open back case "like"?
One example would be:
30Hz-200Hz
Sd:800cm^2
Re:6ohms
Athroat:160cm^2Qes:0.72
Qms:12.5
Vas:16.8L
Fs:77.5Hz
Bl:18.6Tm
Mms:224gmSystem efficiency of ~44%
John
:-O is that the woofer specs they use!!
crazy! high Fs tiny vas high Qts!!!!!!!!!!my jbl isnt quite like that :-P
Fs=40
Qts=0.33
Vas=175L
xmax=7.6mmCheers!
What's your performance goals? Any driver can be effectively used open back over some BW.GM
30hz-90hz120db etc...HIFI usage for music...
While the required flare rate is 6.6Hz to keep the system balanced, you can't have an Fc below Fs, so based on published specs, 40Hz is it.GM
And the reason is that once you mate the driver to the horn the horn air mass will push the Fs down. The drop can be as much as an octave.
This doesn't alter your choice of flare rate to achieve a certain Fc but does affect your choice of driver to mate with the horn.
Not so with an open back, i.e. backhorn. Even if you make Fc < Fs, dipole cancellation will negate it.GM
Any horn loading, whether it be on the front or rear wave, will lower Fs, the amount depending on the mass and impedance of the air column involved. In the case of a fairly short scoop style of horn the Fs might not go down more than 10% or so but go down it will. Part of the trick of designing horns is being able to anticipate how much the Fs will drop for proper driver matching to a particular horn.
