2-Way Cornscala Re Driver Positioning?

[kvsound]

Hi All,

First post here but long time reader of this forum - many thanks for an endless supply of great information! I'm about to start building my third pair of Cornscalas and this time, I'll be building the 2-way version in a Cornwall sized box. I'll be using a pair of Crites woofers and Faital drivers with a pair of Dave's Elliptrac 400 horns and the crossover will be ALK's AP12-500.

Because of only 2 drivers being used, there is a good degree of flexibility in terms of moving up or down, the woofer and horn on the motorboard. So my question is: Does driver position matter, or just go with what looks good?

Also, does cabinet material have any effect on the sound? I'm thinking of using either MDF or Ply or maybe even a sandwich panel of MDF inside and Ply on the outside.

Thanks,

John

[moray james]

Welcome to the forum now as an official poster. Sounds like you have been busy already with your other projects so you are a vetran project builder. Position does matter though many simply go with what the factory chose for driver height. You want your horn to be close to ear level at your listening position. Some feel that woofers should be close to the floor boundry but I believe that your woofer should be in close proximity to your horn and your reflex vent wil be closer to the floor for reinforcement. You can experiment with your exixting designs by putting them up on temporary risers to find the height which provides the best quality of sound. A good rule of thumb is to have the tweeter at about 38 inches off the floor. With your two way design you may need to experiment to find the best height.

As for building material I have found that a laminate of 5/8 inch birch ply and 1/2 inch or 5/8 inch MDF make a well damped strong panel for a large cabinet such as you are building, use a compliant adhesive to laminate the panels so you will achieve some additional damping. Use lots of braces and stiffening. To obtain optimum structural rigidity a brace should be at least 2 1/2 times as wide as it is thick so 2x4 material will work well. Stiffern the top panel sides and back and tie the front to back and the sides together.Provide a hanger or cross brace to support your horn driver. Use a couple of dividers in the reflex vent to tie it to the cabinet bottom and keep it rigid. Brace around the woofer and place a good cross brade between the woofer and the horn. Your cabinet will as a result be a little larger but the lack of vibration will pay off in cleaner sound. A totally unbraced and non stiffered cabinet is going to flex enough that the cabinet walls will radiate more acoustical output than the drivers do and that is all distorted sound comming off the cabinet.If you can feel it vibrate you can hear it. Many will tell you that the manufacturer did not do this and it is not necessary to achieve good results which is true, but you are building your own to achiece exceptional results. If you don't want to go to the bother you might consider a used cabinet and add a little extra stiffening as that will save you a lot of money and time. This kind of upgrade can make a significant improvement over a stock cabinet and I am sure many here could confirm this. That being the case you can imagine what a really well built rigid cabinet will do for your speakers. Take a look at any of the old speaker design books by A. Cohen with DIY designs for Altec JBL and Bozak. Those cabinet were built like tanks. Many used 2x4 frames and braces some with double wall sand filled panels. Good luck have fun and please post on your build as many will be interested to see what and how you do, Best regards Moray James.

[Don Richard]

The separation between your drivers depends on the polar patterns of the two drivers at the crossover point. You want to match the polars for best results:

[moray james]

Don: is there a way for the average DIY'er to figure out how to do this without having to resort to polar responce measurements? Best regards Moray James.

[Don Richard]

You would at least need polar data for the crossover frequency area - there were some on the forum here when the horn he wants to use was developed. Then use driver spacing to set the lobe null angles to the top horn polar angle. Here are more formulas:

[moray james]

Thank you Don. Best regards Moray James.

[kvsound]

Thanks Moray for some great ideas! I'm gonna have a lot of fun with this upcoming build and do some experimenting before the final build. I'll build myself a cheap mdf test box first ala Bob Crites and experiment with different internal volumes and port configurations as well as driver heights. Trial and error and my ears will tell me when the right sound has arrived! I can build these things but an engineer I'm not!

Presently, I have at hand a pair of 3-way Selenium Cornscalas which I've built for my dad which will be my reference point. These have the D405 mid and HM4750 horn with the woofer in a Cornwall sized enclosure and the D220 tweeter in its own top enclosure. When my ALK crossovers arrive next week, I'll try these with the Faital Pro's at the end of the HM4750 Selenium horn which is gonna be a very interesting comparison with the 3-way. I'll then build the test box and bring Dave's oval horn into the picture! I'll post my observations as I move along this very interesting path.

To complete my set-up, I've just taken delivery of a pair of GR-Research 12" sub drivers and a Rythmik Servo plate amp for a dual driver sub build. I might even spring for a pair of dual driver subs eventually. I think I'm gonna end up with some seriously great sound at the end of all this - fun times ahead!

Cheers,

John