BDS spreadsheet questions

[weinstro]

Hi,

I'm trying to follow the FRD consortium toolset to design a set of MTM's, and had some questions on the BDS spreadsheet:

1. For my MTM config, I have the mid-woofs (drivers #1, #3) centered and mounted equal distances from the top and bottom edge. Why is the chart "distance delayed via baffled edge" different for the two mid-woofs? The baffle layout is completely symmetrical.

2. Under the options for "Next Type", what does wMTMw do? How do I use it? Seems like I might want to use this feature, although I don't have the "w" 's.

3. I've cleared the flags for drivers #4 and #5. However, the chart "distance delayed via baffled edge" still calculates a response for drivers #4 and #5. Should I care?

4. Chart "Driver Group Sum Response and Radiation Gain" -- I get no chart here, on the bottom of the worksheet. Is there something I should be doing? Should I care?

5. What does a good baffle response curve look like? How about a fantastic one?

6. What does a bad baffle response curve look like? Other than mine, of course.

7. Different loudspeaker altogether - for a soffit mounted application, where the baffle really is something like 10 feet by 10 feet, can I skip BDS in the crossover design process?

Thanks!

[weinstro]

OK, I've read the manual and managed to answer my own questions in the original post. Trying a few simulations from BDS to FRC, I've come to realize that the baffle dimensions and tweeter location can be designed to compliment the driver's frequency response, to result in a flatter overall response. This has led to two follow-up questions:

1. The subject of my modeling has several dips and peaks in the response. I'd like to model this driver's off axis response. Is this as simple as doing an SPL trace of the manufacturer's response curve at 30 degrees, and then modeling the same on a baffle with BDS @ at the same angle?

2. My driver has a dip 5 dB deep centered at 10kHz, with a Q = 6. Is there something I can do to the baffle to design in a diffraction peak at this point to offset the dip somewhat? Maybe a concentric ring or raised ridge....

[Ron E]

1.
The BDS has a directivity model already in place and IIRC you can model the off axis response. Baffle related peaks and dips are less obvious somewhat off axis.

2.
I would not try to correct for a sharp dip in any way, it probably goes away off axis anyway. Do you listen with your head in a vice?