The more I read forum posts the more I realise how little I know. Part of it is some of the terminology and some of the abbreviations (why is abbreviated such a long word?). Anyhow, i am building these two back horns, and expect to use the JX92 drivers, but I don't expect the bass to go very low, theoretically 42 Hz, but I think that is optimistic. So to solve that I figure that a bass woofer is needed, but how do we define what is called sub bass. At what frequency does ordinary bass become sub bass? Come to that at what frequency does bass become midrange. Is there a specification somewhere or just a matter of opinions. Hence the second question what is the best frequency to crossover, from the horn to the sub bass or bass woofer?
I go to great trouble not to be completely mis-understood
Hi Richard. I second your opening lines, but then isn't that why we are all here - to share our different learnings !
As far as I am aware, low bass is 20 to 40Hz, mid bass 40 to 80Hz, and so on all the way up to the high treble range of 5 to 10kHz. Sub-bass is a loose term normally relating to a separate low freqency driver/cabinet being used to augment the bass of a less fully specified system.
Thus a sub-bass does not have any specifically set crossover frequency - they are often separately 'plate amp' self powered and their controls empirically adjusted in situ to augment the response of a main system.
So if you use a 'sub-bass', it will be adjusted to match whatever you build.
Hi guys - I've had trouble with small direct radiator drivers to subs having enough upper bass impact - examples in larger room were JBL 6.6.5" 2-way to Contrabombarde; another 6.5" AR to 170l bandpass boxes and Linauem (sp?) 2-way 5" to 10" in T-line and control 1 JBL to summed BP6 bandpass but I like drums with high peaks. The T-line wehn run up to ~100hZ got boomfy on bass guitar. Freddy
Most sub-bass systems have greater output at 100Hz than 30Hz, and a 100Hz crossover will not resolve this. The 'sub' needs to be low pass filtered with a lower turnover than the frequencies it is required to operate up to. Often a 50Hz roll-off is necessary just to flatten its stand-alone in-room response.
A T-line 'sub' is likely to need even more filtering to reduce the first peak of augmented output.
Really a sub is a lot of equipment for the frequency range it covers, but then it does make such a difference.
Hi Graham - on that rough 2'x4' OB I used 50Hz on the 21" woofer and 100Hz on Beta 12CX to get semi acceptable results. Theres a short line laying around which gives the following ourdoors response with a woofer having ~19hz fs and 0.46 qts. I wonder how to make the 3"ID vent less compressive? - it has a 3" opening. Box is ~44"x21"x 11.5" with one diagonal forming the line. Two of these might be ok indoors (?) is it any better than a reflex?
in contrast a longer line outdoors with Eclipse W1038R (Qts ~0.3, fs ~20) This box = 48"x18"x12" both cabinets ~same size 6CF vs 6.15CF
Last edited by karlsonkab (2006-09-13 16:48:39)
My thoughts on the K-Killer - good for PA but not home audio.
Both curves are too efficient circa 35Hz; they indicate too great a phase change and this will upset bass reproduction up to 100Hz.
Violet and blue on the tapered line show out of phase cancellation between driver and front opening. Green - smooth response, no boost, no dip.
I suspect the tapered line is restricting driver motion because it is acting as a compression chamber behind the driver. When the line is full area behind the driver and tapering towards the far end, the action is resistive - phase linear - and allows a low Fs driver to maintain better output right down to the pipe controlled cut-off, which can be lower than driver Fs.
(Green had exit blocked) - will you use Sd for the 12" Monacor's line and will it have one or more folds? does pipe line aspect matter? how much taper is "right"?
my wimpy polycone 12" wouldn't do PA go up in smoke
Last edited by karlsonkab (2006-09-13 17:23:44)
I have to use driver chassis size at the cabinet mounting point but down to Sd by 12" and then tapered. I am keeping the first fold at cabinet depth away from the driver so that cone output is not attempting to pressurise across the closed end of a pipe.
I don't know what taper is "right", it is bound to be different according to Qts etc.
A 'wimpy' polycone should be okay on a damped folded pipe because the loading is due mainly to moving air mass (as with a baffle) and not a cone-flexing sealed enclosure air-spring or a delayed enclosure/pipe/vent energised back pressure.
Last edited by Graham Maynard (2006-09-14 02:47:05)