I can't at the moment find the QTS for the driver I'm using, but judging by the size of the magnet and using my addled memory I believe it is quite low. Since I have plenty of power on tap for the woofers it still develops more than enough spl... the window screens in the whole house buzz.....
Good thing about H- and U-frames is that they effectively raise driver Qts by (as I understand it from the article) adding the mass of the air within the frames to the moving mass of the cone. So the beta will be more effective than you think.
I've been thinking to myself, if the subs are going to be separately powered anyway, why bother with a high efficiency PA driver in the first place? I was looking at this:
Dayton IB385-8 15" Infinite Baffle Subwoofer
Even with the low Qts of about .6, it should do well on OB because the Fs is so low. the equation I heard is Fs/Qts = OB rolloff point. so 22/.6 = 36hz, which is low enough for me. If you can suffer the lower output of an H-frame then the bass will get even deeper, and these woofers have the healthy x-max to deal with it.
I've been thinking to myself, if the subs are going to be separately powered anyway, why bother with a high efficiency PA driver in the first place? I was looking at this:
Dayton IB385-8 15" Infinite Baffle Subwoofer
Even with the low Qts of about .6, it should do well on OB because the Fs is so low. the equation I heard is Fs/Qts = OB rolloff point. so 22/.6 = 36hz, which is low enough for me. If you can suffer the lower output of an H-frame then the bass will get even deeper, and these woofers have the healthy x-max to deal with it.
My sons ob (b20 + piezo up top) uses $20 jamos I bought from pe on closeout. They have qts of .85, a larger mag and appear more robustly built than the alphas. They produce so much bass and may sound better overall. Having simmed ob its clear higher qts remains flatter and extends deeper. I think nelson uses betas on ob with a simple circuit and prefers them to the alphas.
In fact, nelson made it clear that he's prejudiced against trying the alphas, and probably won't ever compare them to the betas. (His words, as I can recall: "the beta comes with a magnet.
" Then later, "if I tried [the alphas], I might be surprised. " cool smilies added for the full NP effect.)Overall, I'm willing to agree with folks who argue that lower Qts is better for transient response, but if you're going to go that route, it seems like you have to accept low efficiency as the tradeoff.
In simplest theory, each driver's VC center would be offset to the rear based on how much delay each XO introduces: Lenard Audio - Education - X-overs. Time Alignment.
GM
GM
Hey guys, stop me if I'm crazy. But could this work?
I know I already pointed out the website with the different phase plugs for a lowther. An exponential phase plug that obscures nearly the whole driver provides the smoothest on- and off-axis responses by far.
Soooo.....What about using a 10" or 12" waveguide for a phase plug?
Some positives: the threaded insert means that the waveguide should stick to the magnet with no extra help. It looks as though it should fit in place of the 12LTA's dustcap. And it might just be possible to fit a tweeter inside the horn itself.
Of course, I have no idea how this would affect the 12LTA's sound, but if the lowther is any example, the result could be effective!
I know I already pointed out the website with the different phase plugs for a lowther. An exponential phase plug that obscures nearly the whole driver provides the smoothest on- and off-axis responses by far.
Soooo.....What about using a 10" or 12" waveguide for a phase plug?
An externally hosted image should be here but it was not working when we last tested it.
Some positives: the threaded insert means that the waveguide should stick to the magnet with no extra help. It looks as though it should fit in place of the 12LTA's dustcap. And it might just be possible to fit a tweeter inside the horn itself.
Of course, I have no idea how this would affect the 12LTA's sound, but if the lowther is any example, the result could be effective!
How do you plan to deal with the wavefront during rarefaction? FWIW, the best overall performing phase plug I ever made was created using a large light bulb similar to this one: http://www.buylighting.com/v/vspfiles/photos/B248005-1.jpg
GM
GM
I'm not entirely sure how to answer that question, GM. I'm not yet entirely sure of what relationship rarefaction has with such a phase plug or why it should be affected. All I am going on is the seemingly remarkable result shown on this page, in comparison with more conventional phase plugs:
Audioprogress
What I see is a much smoother and more linear on-axis plot, along with off-axis plots that are much more consistent than with any other style of phase plug. It might have even been you who posted this in the first place. Anyway, how do you suppose this example deals with rarefaction, or does it?
Anyway, from now on you can all refer to my new signature in such discussions :
Audioprogress
What I see is a much smoother and more linear on-axis plot, along with off-axis plots that are much more consistent than with any other style of phase plug. It might have even been you who posted this in the first place. Anyway, how do you suppose this example deals with rarefaction, or does it?
Anyway, from now on you can all refer to my new signature in such discussions
:
LOL about your sig Chaz... personally, i don't mind cutting off a dustcap and replacing with a phase plug of sorts but it cracks me up to spend $1000 per driver only to cut it up and start placing light bulbs and tree branches in the center to improve the sound.
Cutting up a $20 Pioneer B20 or even a $60 12lta is one thing but i never felt like cutting up an expensive Fostex or TB. Perhaps they could benefit from some tweeking but i leave them stock.
Chaz, what direction are you leaning? Will you go the AN route or the 12lta route? I think either will prove fruitful.
Zilla
Cutting up a $20 Pioneer B20 or even a $60 12lta is one thing but i never felt like cutting up an expensive Fostex or TB. Perhaps they could benefit from some tweeking but i leave them stock.
Chaz, what direction are you leaning? Will you go the AN route or the 12lta route? I think either will prove fruitful.
Zilla
You know what I think I'll do? For gits and shiggles I think I'll buy a pair of GRS 8" fullrangers and put them on an OB with sub support, and then try fitting an 8" waveguide phase plug just so see what happens. Then I'll experiment with a helper tweeter in the waveguide for a cheap coax. After that, if an 8" driver on OB is an obvious improvement over my 5" TBs, I'll probably go with the LTA to start with. I teach music and summertime is pretty lean since folks are off on vacations; all the expensive projects will have to wait at least until the fall.
I've posted it periodically, but wasn't the first.
You proposed using a WG, but it will work similar to a huge, rigid whizzer if not capped off/filled, so asked what you planned to experiment with to make it a a proper phase plug.
GM
Ah, see, that's what I needed to know. So it does need to be capped and/or filled? I'm sure there are several workable options for that, but the first thing that comes to mind is handi-foam. I'm curious, what does its acting like a whizzer have to do with rarefaction? I only ask because in all my reading this is the first time I'm seeing the concept discussed.
Yes, if attached to the pole piece.
'Rarefaction' as in the sound wave pulse [diaphragm] moving inward.
Right, where the WLs are small enough to ‘fit’ in the horn it will act as a frequency dependent time/phase delayed one same as a whizzer, so for it to act more like a phase plug it needs to be spaced away from the diaphragm somewhat:
GM
Attachments
FWIW, I bought the GRS driver and the waveguide "phase plugs." I'm going to try slapping them in an open baffle with my sealed sub for low end (although this will not be permitted by SWMBO in the long or even short term). Depending on my experience with this larger driver, I may keep riding this train into to BETA 12LTA territory.
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