Need help with baffle step compensation

[brianpowers27]

I have a ported MTM center channel that I designed with a 30" wide x 7.5" tall baffle. I set the speaker on top of the TV which is about 3" away from the back wall.

Could someone walk me through the process to create a BSC filter?

[dthomas]

I have a ported MTM center channel that I designed with a 30" wide x 7.5" tall baffle. I set the speaker on top of the TV which is about 3" away from the back wall.

Could someone walk me through the process to create a BSC filter?

If you have the speaker setting 3" from a back wall you really should not need baffle step compensation as your baffle will appear nearly infinite.

Why do you want BSC does it not have enough bass? Also it would help to know the drivers/crossovers and any measurments/sims you did on the speaker.

[brianpowers27]

I am sorry. I meant to say that I am 3' not 3" from the wall. I do not have any measurement tools (yet)

I have two polk audio 5.25 mid woofs and an unknown 1" dome tweeter. I have an old 3.5khz 12db octave crossover with a 10uf cap and a 8.7 ohm resistor for the woofer zobel.

[Dirk]

In calculating this, do not consider the size of the speaker's baffle. Consider the size of the speaker's baffle PLUS the size of the face of the TV. It acts as an extension if it's nearby.

[brianpowers27]

Let's say that the face of the tv is 25" tall. This would yield 32.5" of height. What would we expect as a baffle loss?

[curt_c]

I modeled your baffle in The Edge which you can down load from Tolvan Data.

Interpolating the resultant curve suggests the following values as starting points for your BSC compensation circuit:

for 2 8-ohm drivers wired in parallel:
L= 2 mH R= 2 to 3 ohms

For 2 4 ohm drivers wired n series:
L= 4 mH R= 4 to 6 ohms

The resistor would be paralleled across the inductor and this circuit would be connected in series with the + lead of the speaker input terminal.

Of course these values are just initial values, as the actual speaker load and response, as well as room loading will affect the final result. Some adjustments to the values will likely be necessary.

C

[brianpowers27]

Which dimension would you base the baffle on, since it is in a horizontal orientation? Since these are large inductance values, would you consider using another type of inductor other than air-core?

[curt_c]

Which dimension would you base the baffle on, since it is in a horizontal orientation? Since these are large inductance values, would you consider using another type of inductor other than air-core?

These will be fine:

http://www.partsexpress.com/18-gauge...-inductors.cfm

If I understand your question correctly: Diffraction programs use all the edges to determine the diffraction/baffle step. Consequently, they are more accurate than calculators that just use the baffle width.

C

[brianpowers27]

Would this situation change if the speakers was decoupled by means of spikes our isolation foam from the TV?

[Dirk]

Not enough to deviate from the standard values. The inch or two additional distance is peanuts.