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High Efficiency Speaker Asylum Need speakers that can rock with just one watt? You found da place. |
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High Efficiency Speaker Asylum Need speakers that can rock with just one watt? You found da place. |
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In Reply to: Re: Oris 150 posted by Hermit on January 20, 2001 at 14:53:57:
Hi John!You wrote:
> > I'm waiting for 40Hz J-horn plans from Bruce
> > but I'm tempted to try one of Wayne's whilst
> > I'm waiting. Any suggestions Wayne?Thanks for asking!
If you have corners, try a pair of the seven Pi cornerhorns with JBL 2226's and JBL 2426's. Use a 2370 horn in front of it. If you don't have corners - or if your listening area is very large - then do the ten Pi folded horns with the same motors. Both are wonderfully simple designs. Easy to build; Even easier to service.
Suitable HF "second sources" are the Peavey CH-3 horn and the Eminence 2001 HF motor. I'm also considering the Eminence H290 horn. It looks to be functionally equivalent, but I haven't tried one.
As you probably know, the Peavey unit is a two piece design, and some would say that two piece horns are trouble. I've never noticed vibration noise from them and I run 'em at full power pretty often. But if worried, one can always glue the two pieces together. The price is certainly right.
With the Eminence motor, I'm not happy with the top octave unless it is compensated. But both these HF motor/horn combinations are more efficient than the LF section - so you have some attenuation that can be removed in the top octave for compensation.
I put 50 ohm resistors in series with the HF motors in these systems, and then run a 0.47uF capacitor as a bypass. Put it in parallel to remove attenuation of the top octave. The JBL's don't need as much, so I put a 10 ohm resistor in series with the 0.47uF bypass.
Personally, I like a 1st order LF network and a 3rd order HF network. The upper rolloff slope of the 2226 is about 20dB/octave, so an 18dB/octave HF network complements it well. And the 1st order device I like is actually a 0.75mH coil - so it isn't performing any "crossover." It's just "shaving" those two little peaks at 1200 and 1600 on the 2226. The coil attenuates a little under 2dB at 1200 and is only removing 3dB at 1700. After that, the woofer's "done," so the coil is just providing compensation - it doesn't appreciably affect woofer rolloff, as a "normal crossover" would.
These are all figures for the JBL "H" and Eminence - 8 ohm units.
Honestly, as I've told some of my new friends who've asked - This is "splitting hairs." The improvements from a crossover like this are maybe a decibel or two more linearity between 1Khz and 2Khz as opposed to a "garden variety" unit such as the Eminence "1K6" crossover. So the latter may be a better approach because it's "a phone call away."
But either way - I'm a big proponent of that simple little 0.47uF and 50 ohm resistor thing. It's a cheap way to gain a half octave. A "must do" scenareo for this kind of loudspeaker, in my opinion. Of course, you can also do the same thing with active components - but it's not like you need a monster capacitor or anything to do the compensation at "the powered end." Half a microfarad is a little-bitty thing, even at 200 volts breakdown voltage.
Alternately - If neither the JBL or the Eminence parts are a good option for you, you can certainly select other motors and run the " PiAlign " program to calculate cabinet size. I'm guessing that you may be British, and I expect that JBL parts may be a bit "pricey" there. Good quality motors, suitable for other horn designs, will perform well in these cabinets as well.
About the only combination that should be avoided is the folded horn with woofers that resonate much below 40Hz and that also have Vas * Qts less than 60 liters (2 cubic feet). They would have horn cutoff higher than woofer rolloff, which would create an annoying peak.
Sorry, but I've never done these designs in metric units. Most everything else I do is metric, but when I made these designs, few people on "this side of the pond" did much work in metric units. You'll just have to keep your conversion factors handy. All my friends overseas think we Americans are quite crazy. I don't think they attribute this to our measurements system, but I'm sure they consider it to be part of the proof. [grin]
If you're serious, let me know and I'll send you some plans. You can get general plans and the program that gives specific dimensions on the www.PiSpeakers.com website, but it's more of a description of the design than it is an actual blueprint. The schematic for the crossover isn't there except in general terms, and "cabinet-shop-ready" artwork isn't posted.
Another thing that isn't listed on either document is panel bracing. I discuss it with cabinet makers here, and I know that you guys know to do it too. But just as a reminder - Bracing is obviously important on the longer panels of the folded horn. We use 3/4" x 2" braces - routed to a rounded shape - to brace the panel at the mouth and to enhance rigidity. You can see this on the flyers and on the photograph at the website.
The areas behind the sloped panels are filled with expansion foam, which is shown on the plans. But be careful of expansion foam bought at a local supply store and supplied in aerosol cans. This stuff hardens in relatively short period of time - which is nice - but it doesn't give it time to expand in a homogenous state - which is not nice. This stuff can easily burst a panel, even when you've calculated the expansion and put 1/10th the volume required to expand to fill. That means it has left some voids in some places, without supporting the panel, and yet in other places it hasn't filled at all.
There's more than enough information on the website to put 'em together, but I do give the cabinet shop a more "carpenter friendly" set of plans. They're not really interested in all this technical mumbo-jumbo. So just let me know if you're interested. Please write directly from the website, so I can return mail with the information you request.
Wayne
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Follow Ups
- Pi Speakers - Wayne_Parham 01/20/0123:23:54 01/20/01 (2)
- Re: Pi Speakers - Hermit 05:10:34 01/21/01 (1)
- Eminence Horn Plans - Wayne_Parham 13:36:06 01/21/01 (0)
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