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In Reply to: Chicago Horn Club meet - sub vs sub - how did it go? posted by freddyi on March 25, 2007 at 07:22:09:
I was going to start a separate thread,but since it is being discussed here,I might as well put the info here.I built the tapped horn last weekend,based on the plans for the 30 hz horn William Cowan has on his website,but extended it to 90",and used the LAB12 genII driver,as a start,to see what these things will do. I was not expecting it to work anywhere near as well as it does on the first try.
For shear output,the LAB is the winner,(I'm talking about stupid loud,knocking things off of shelves,pissing off the neighbors,and getting a visit from the police)but for any normal use,that is really not a factor.
The tapped horn wins hands down for low freq extension,plus it is much easier to build,and can be used standing in a corner,laying down along a wall,or mounted under the floor,through a wall,or in a ceiling.
The subs are crossed over at 90 hz,LFE output from the Yamaha DSP-A1 HT amp,and powered by a Carver TFM-42 amp,one channel for each sub,with level adjusted for the difference in efficiency.
Except for music with really deep bass content,the difference in sound is pretty small,with the LABhorns being slightly tighter.
I'm not ready to haul the LABs out to the curb just yet,but for anyone who doesn't have room for the LABs,the decision would be a no brainer...
Follow Ups:
in aural presentation vs LAB?what's happening on excursion and how did you brace the divider?
does it tie with gussets to front and rear wall? - is there much flex or cabinet reaction on strong passages? does it sounds "taut"? (- realize you may still be tweaking xover & level)
I glued 1" dowels between the center baffle and the front and rear panels,about 12" apart.Seems ok,but would be better to have more.Since this was an experiment,one side panel was left unglued,just screwed with a gasket of duct tape,so it could be easily taken apart.It takes most of 2 sheets of ply/MDF to make 1 cabinet,with enough left to use for bracing.I will probably add more bracing eventually.
As it is,there is some vibration of the panels,(no audible)but with it in the garage,there is far more vibration of the garage wall than the box,so it is not a real concern at this time.
Cone excursion is surprising low,a bit difficult to see with the magnet facing out,and the opening down in the corner.I will try to come up with a more accurate method than sticking my finger against the cone,and use sine waves for a better point of reference.
wouldn't test excursion with sine - too chancey - I smoked a pretty big voice-coil accidently with 90 watt rated amp when a transform was left onhow does one kluge-simulate TH with McBean?
here's a quick and maybe not well-described sim of yours just from rear-load perspective - indicates some power dip around 32 which may not be in effect with TH - might be kinda ballpark--?
quick BLH sim
power dip
Don,It appears that your driver is facing the inside of the horn but Bob C's is in the other direction. Is there a reason for this? Have you taken any measurements?
Thanks,
Don
On the Cowan Main Page select "Tapped Horns".
The LAB12 driver is 6 3/4" deep,plus it needs some clearance for the vent,so it won't fit the other way.:-( I would have mounted it facing forward if it did,but don't think it really makes any difference performance wise.In room response measurements are always suspect because of standing waves,but is reasonably flat to 25 hz,and down a few db at 20.
those look like a very easy weekend project. Looks like three or four sheet of 3/4 MDF and a couple drivers and away you go. Cheers.
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