Need help using "Edge" to design Baffle Step Correction Circuit please.

[G]

Hi all,

I'm usually lurking and posting over in the DIY Tubes area but I need a little help. I have a pair of FE206Es in BR cabinets that I built about a year ago and I would like to design a baffle step correction circuit for them. I have downloaded the "Edge" program but I'm having a little trouble understanding everything I'm looking at. Can someone hold my hand and walk me through this first design? Any help is appreciated.

 

[Svante]

There is some help at the home page on available from the help menu. Do you have a more specific question?

 

[G]

Well where do I start? I put in the dimensions for the baffle 289 x 800 mm. I then chose circular for the driver shape. I used 200 mm for the driver dimensions but I'm not sure that is correct as the membrane itself is only 175 mm across. I placed the microphone about 2.5 mters away because tha is how far away my listening position is from the face of the speakers. I then hit the "apply!" button and then asked the program to suggest "F1 and F2". It "suggested" that R1 should be 10K, R2 should be 10K, L be 6813 mH and C be .068 uF. Somehow I don't think these figures are right. That is why I'm asking for help. I'm not sure what I did wrong but I certainly did something wrong and I have no idea what it was. I built the BR cabinet according to the plans suggested by the Fostex engineers at the bottom of the PDF for the back loaded horn plans.

 

[Svante]

Ah OK, you have two choices of compensation circuit, 1 or 2. You select the value of R1, in the active case (usually circuit 2) you typically enter a relatively high value for R1 (eg 10k), and then you should use R2=10K and C=68nF. If you want to use a passive circuit, circuit 1 is typically used, and the speaker is modelled as a resistor=R1 (which may be a bit optimistic, actually). So if you enter 6 ohms for R1, Edge tells you to use L=4 mH and R2 of 6 ohms.

The sillily high value for L originates in that Edge calculated it based on a loudspeker impedance of 10000 ohms, which of course is crazy.

 

[G]

Ah OK, you have two choices of compensation circuit, 1 or 2. You select the value of R1, in the active case (usually circuit 2) you typically enter a relatively high value for R1 (eg 10k), and then you should use R2=10K and C=68nF. If you want to use a passive circuit, circuit 1 is typically used, and the speaker is modelled as a resistor=R1 (which may be a bit optimistic, actually). So if you enter 6 ohms for R1, Edge tells you to use L=4 mH and R2 of 6 ohms.

The sillily high value for L originates in that Edge calculated it based on a loudspeker impedance of 10000 ohms, which of course is crazy.

I see where I made the mistake now. Thanks. I do have a few more questions if you have time. Do I use the dimensions of the speaker membrane itself or do I just consider a FE206E to be a "8 inch speaker"? Also, I have all of the corners on my cabinets rounded using a router. Do I just enter the dimensions of the parts of the baffle that are flat or do I use the absolute outside dimensions? Thanks for your time Svante.

 

[Svante]

I'd take it halfway through the suspension, the same way as you do when you calculate the effective piston area. So for an 8" speaker it would be less than 8", maybe 6-7". You could actually calculate the effective diameter from Sd if you wish: d=2*sqrt(Sd/pi)