| 12Pi is a 4 ohm speaker? [message #59439] |
Sun, 21 June 2009 09:02  |
MArz
Messages: 4
Registered: June 2009
Location: India
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Esquire |
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Dear Wayne,
I am a newbie and therefore please excuse the confusion that i am in. Your site mentions the 12Pi subwoofer as being 4 ohms.. But arent you using 2 LAB 12 drivers which are rated at 6 ohms each?? so wouldnt that give a resultant impedance of 3 ohms if they are in parallel and 12 if they are in series???
Also your design is a push pull design .. does this mean that the while one speaker is connected IN phase the other is connected OUT of phase to get the push pull effect???
Also i wanted to build a pair of these to try out for my band so i really would appreciateif you could let me have the plans...V2? if possible pleeesssseee??
I earlier built a pair of the LAb horns but when i use them one per side while i do get copious quantities of BASS i tend to destroy them if i drive them too hard. I had connected the speakers in teh LAB horn in parallel first but after 2 successive blow outs i them connected them in series and now they are fine albeit at lower levels...
you have also mentioned that the Pi 12s are rated at 1600W RMS? Again the LAB 12s are only 400W drivers... is the increased power rating because of teh heat sink device???
Sorry to sound sooo confused but i am...
Awaiting your response eagerly...
Regards
MArz.
Sometimes You gotta say "What The Fuck"!
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| Re: 12Pi info [message #59441 is a reply to message #59439] |
Sun, 21 June 2009 09:43  |
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Wayne Parham
Messages: 18787
Registered: January 2001
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Illuminati (33rd Degree) |
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I'll send plans in a separate E-Mail.
The impedance is raised due to horn loading. But impedance isn't a flat line, and you're right, minimum is closer to 3Ω.
About power handling, the LAB12 is a good driver, but it won't even handle 400 watts indefinitely. Put a 40Hz sine wave into it at 400 watts and it will blow in less than 2 hours. Then again, music content has a much higher crest factor and isn't as hard on the drivers.
Still, the 12π uses a cooling plug which raises the power handling ability over double what the stock driver allows. We don't actually use the LAB12 anymore, we have an OEM version made that fits the cooling plug. When the cooling plug is installed, each PI-12 woofer will handle over 800 watts continuously, even if the signal has a low crest factor like a sine wave.
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| Re: 12Pi Push-Pull Drive [message #59457 is a reply to message #59454] |
Mon, 22 June 2009 10:16 |
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Wayne Parham
Messages: 18787
Registered: January 2001
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Illuminati (33rd Degree) |
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The push-pull drive wires the drivers electrically out-of-phase, so cone motion is forward on one and backward on the other. They are then positioned in the horn so each provides positive pressure. In other words, the cone that is reverse-connected is also physically installed backwards.
You can see this in the plans - One driver is oriented so the front chamber and throat opening are on the front side, and the other has the throat on the back side. The wiring diagram shows the electrical reversal too.
This is done to reduce even harmonics. It works very well, as seen in the measurements. It just sounds cleaner and tighter. What is also very noticable is the absense of output below horn cutoff. It is very quiet below cutoff. Every other horn I measured, you could really hear a lot of sound even when the sweep was well below cutoff. The fundamental was very low, but distortion was loud. The harmonics were presented to the horn and amplified by it. Not so with push-pull drive, it's dead quiet, clean. This is one of the real eye openers, or maybe I should say ear openers. It is an easy-to-identify proof that the concept is working. Measurements are very useful, but this is something you can immediately tell even without a measurement system.
The 12π hornsub with its push-pull drive reduces harmonic distortion by a significant and audible amount. At the lowest frequencies, the second harmonic is well inside the passband, so this is very important. Some might say 2nd harmonics aren't too objectionable, and I wouldn't argue but I would say it is better that they didn't exist. The front chamber and horn folds produce a low-pass filter function which tends to reduce third harmonics. Most of them are outside the passband. Fourth harmonics are canceled by push-pull drive and are even further outside the passband, as are all higher harmonics. So this design is as free from distortion as you can possibly get. I know of no other basshorn subwoofer that is as clean as the 12π hornsub.
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| Re: 12Pi is a 4 ohm speaker? [message #59742 is a reply to message #59615] |
Sat, 04 July 2009 12:35 |
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Wayne Parham
Messages: 18787
Registered: January 2001
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Illuminati (33rd Degree) |
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You can mount castor wheels and handles wherever is convenient for you. We placed them where they are most convenient for loading and unloading a freight truck with a ramp. The wheels fit nicely on the ramp, between the two side edge guards. You can rock the basshorn back onto its castor wheels and push it like a hand truck.
As for panel fitment, we actually cut our on a CNC machine and use dados for every panel. This makes assembly a lot easier, and ensures a perfect fit. Our flat pack kits come this way too.
The plans we send out do not show dados for two reasons. One is to protect our investment in design time and CAD, CAM and CNC programming. We make flat pack kits available for those that want them. The other reason is if you're planning to cut out the parts yourself with a table saw and hand tools, you probably won't be cutting dadoes anyway.
If you buy flat pack kits from us, the plans aren't used as a cutting guide, only for identification of parts and where they go. If you want CNC cut parts, you should buy from us rather than trying to duplicate the CAD drawings and CNC programming. I've worked with outside shops that tried to do their own CAD and CNC from the non-dado plans, and they inevitably get some dimensions wrong somewhere. It becomes frustrating for both them and me.
On the other hand, if you're planning to try and cut out your own parts and build using a table saw and hand tools, you probably won't take the time to cut dados. Instead, carefully measure and draw lines on panels to indicate where things go, then use PL adhesive and wood screws for assembly. The screws apply clamping pressure while the PL adhesive dries. At least, that's how I built the prototype. Worked for me.
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