Help Needed : Passive Line Level Baffle Compansation Circuit

[mertol]

Hi All;

Warning : There could be dump questions ahead!!!

I am trying to add baffle compensation to my diy active speakers with passive line level XO.

I am planning to (almost build the circuit) implement the circuit defined

Baffle Step Compensation

I have a question about how the Vr is actually wired.
Is it standard voltage dividing mode , where pin 2 is out, pin 3 is in and pin 1 is connected to R1 , or is it connected as a variable resistor either pin 1 or pin 3 is not used at all.

I am asking this as some where in the explanation about formulas only 1/2 of the Vr is used.

This could be a very dump question but if anyone can help I'd appreciate

PS: I will be using a generic 10k pot for the tests but I already ordered 2x 10k stepped attenuates , I assume it's OK to use stepped ones instead of the standard carbon pots.

Mertol

[PeteMcK]

if you connect it as a variable resistor, your 2nd option, you'd be changing the frequency of the turnover point (& you could change both freq & level if you made the bottom resistor variable)

[CharlieLaub]

Originally Posted by mertol

I am asking this as some where in the explanation about formulas only 1/2 of the Vr is used.
Mertol

The reason is suggest in the first response. The formula is only correct for one value of Vr, but since it is a pot and the typical baffle step is 3dB, the author (Rod Elliot) chose to use the value of Vr at the midway point to calculate what size capacitor is needed. Thus the formula uses 0.5*Vr.

This is also the reason why R1 is there, not just to make the max step 6dB, but also because if there was no R1, as Vr approaches zero, the middle frequency of the step would start to be very unilke what it is when Vr is in its maximum position. For this reason, you would not want to use this for say a large step compensation, for instance to boost the 6dB fall off for an open baffle speaker, without recalculating the value of the capacitor needed for the exact value of Vr that will be used (and then it should just be a fixed resistor).

For an accurate value of C, but only if you know what fixed baffle step dB gain you will use, just insert that value in place of Vr/2 in the equation.

-Charlie

[speakerdoctor]

You could also try the line level BSC circuitry described here:
Advent experiment - mod - much better sound IMO - The Classic Speaker Pages Discussion Forums

there are a lot of posts, but scroll thru them quickly and you'll eventually find some good infomation.

[mertol]

Thanks a lot, I built the BSC (for one channel) and listened it briefly, anything more than 3db seems to take to much air from the music. And I seem to prefer -2 db baffle step, however test speaker was close to the real wall (btw it's a sealed cabin) , around 25 cm

One last question.

As seen below I have an extended baffle to host the woofer. Which width should I use, the inner baffle (20cm) or the outer baffle (16 cm) , both have slightly rounded edges.

[planet10]

Paul Joppa's PLLBSC

dave

[PeteMcK]

re:'anything more than 3db seems to take to much air from the music' -yes, that's what I found, so I prefer to add a woofer as above. C1 in the link fron Planet 10 may solve that problem though

re:'Which width should I use' - the widest, 20cm which gives you a baffle step freq of 575 Hz

[mertol]

Thanks a lot , I finished the XO including the bsc and a switch with Bsc on/off functionality. Comparing to my other bookshelf speaker Jamo concert 8's, even with the BSC there is almost one full octave of bass with the concert 8's.

I think that's quite normal as the 6.5 inch seas excel and the port combined has to has far more extension in the bass department , than my home brew sealed 4.5 incher.

At some songs you can bare understand the difference while at some others it's almost like 1/2 of the music is not there.

I now think the first comments were correct as I seem to need the bass between 40-90hz. If I can find a reasonable woofer (around 90db) that can go down to 40-50hz in a sealed cabin I will build speaker stand with an active woofer to complement...

PS: My homebrew speaker seems to be sounding a little bit sharper (not necessary a good thing) and has far better imaging than the concert 8's right now. Perhaps I can smooth it down a little bit with going to a 12db octave XO and lowering the XO point very slightly to 2.7khz...