1. What is a pre-compensation load? Is it the same as the R2 on a L-Pad (R1/R2)?

2. Is it possible to have a pre-compensation without the main R1 attenuation? Or is it just a reactance adjustment for the motor? (in some PA speakers I have no R1 and a R2=16.5 Ohms in shunt with the motor / X-over C=3.3uF series and I=0.72mH shunt / What x-over freq. is this and how to find if HF/Motor is of 8 Ohm impedance?)

3. Are the designs you show for L-Pads correct, since they do not show the same connections as for other (standard) L-Pads? As an example from pag.60 a 12dB attenuation R1=25, R2=16, C1=0.47 and from pag.63 a 14dB attenuation R1=30, R2=14, C1=0.33.
I am used to see R2 in shunt with the Motor and "after" R1. As an example from another site: http://www.lalena.com/audio/calculator/lpad/
For an LPad (Driver Attenuation Circuit) with Att=-12 db and Z=8 Ohms => Resistors
R1 = 5.99 Ohms
R2 = 2.68 Ohms
Or for an LPad with Att=-14 db and Z=8 Ohms => Resistors
R1 = 6.4 Ohms
R2 = 1.99 Ohms

How can your design deliver 10.8 Ohm in the HF/Motor side on the first case and 10.2 Ohms on the HF/Motor side of the X-over for the second case? Is this right? Are the BIG resistor values you use better -- as in table of page 23 -- than say the small values for 'other' L-Pads as in Lalena.com. What is the difference, are they of the same effect after all?

Congratulations and Happy New Year.
da Bastos

First, I would like to ask you what are the advantages of using the compensation circuit on the “right side” of R2 instead of the ones on the left side like the L-Pads from lalena.com and others. They seem to deliver less wattage to the speaker trough the process and to “burn more energy to the air”, if I have my two pages of numbers right and not taking in consideration reactances from the capacitor for the break frequency and the one´s from the main circuit.

Example
LPad – Driver Attenuation Circuit for –2.4 dB
R1=1.93 Ohm, R2=25.14 Ohm, Speaker=8 Ohm
For a Total of 300Watts: R1=72.4 Watt, R2=172.7 W, Speaker-54.9 W
With and after compensation on R1: R2=227.6 W, Speaker-72.4 W

With your Compensation+precompensation Circuit for –2.4 dB
R1=2.5 Ohm, R2=34 Ohm, Speaker=8 Ohm (Attenuators from page 23 of your Paper)
For a Total of 300Watts: R1=16.8 Watt, R2=229.2 W, Speaker-54 W
With and after compensation on R1: R2=243 W, Speaker-57 W

I just happened to find a site to - Calculate the resonant frequency of a capacitor and inductor - http://www.mhsoft.nl/Mysystem/Reactance.asp - that I was asking for in my first question to you. Do you think this is good/right for Hi-Fi filter calculation. Does a resistor, like the one’s on attenuations, change this (the resonant frequency) or not? I am learning on how to work w/ SPICE. Is there a website for Speaker File Spice Databases? Thanks again.

Best Regards
da Bastos

Hi. It his a pleasure to be able to ask you a question and having you ‘in person’ to answer to them. First I am learning how to work with Spice software and what a difference from 20 years ago with/when my only book (that) was >PHILIPS Building Hi-Fi Speaker Systems. Thanks to all of you guys from Berkeley. I am making such great improvements that I feel pity that I am only an unemployed architect and not a technologist engineer to find a job in this area. It seems that now everybody has a position open for engineers. At least I have time for what I like and what I can do…

Second I wanted to take in consideration that how more times I read your paper ‘Speaker motors and passive crossover filters’ there is something that doesn’t add up. Since my first question that I couldn’t find an answer.

1. On page 33 you show:

R1 3 1 5.5
R12 1 0 3.7

If the speaker is 1 – 0 your R1 should be 3 – 0 (not 3 – 1) and R12 3 – 1 and not 1 – 0. (Or Spice is right and the drawing is wrong?)

2. Again on page 35 you show:
!
L2 5 6 0.6mH
C2 5 3 16Uf
!
R1 3 1 5.5
R12 1 0 3.7
C1 3 1 5uF

If the speaker is 1 – 0, R1=> 3 – 0, R12=> should be 3 – 1 (from C2-1.st order?) and not 1 – 0. (Or the drawing is not right…)

What is confusing me is that the Pre-compensation can be connected to 1 (Motor-Speaker) or to 3 (C2 from 1.st order x-over).

Again on page 37 and page 52:

! series/parallel compensation
R1 3 1 25
R12 1 0 16
C1 3 1 0.47uF

If you noticed R1 IS OK, C1 IS OK AND R2 IS WRONG AGAIN.
Should it be R2 1 – 0 ? Or R2 3 – 0 ? With L1 from 2nd order x-over. All connections from Spice seem to be right and the x-overs drawings wrong.

If L1 is 1 – 0 (page 51) then, when you introduce a !series parallel compensation on the circuit (from page 52) 1 becomes, then, 3 from C2 (C2 => 5 – 3), C1 =>3 – 1 AND R1=> 3 – 1 (Speaker 1 – 0).

R2 is then 1 – 0 (parallel with the speaker 1 – 0). But the drawing is not showing that. What it’s showing is R2 (from)3 –(to)0 (in series with C2 (of 2nd order x-over) .

Thanks again Mr. Wayne and thank you for your time.

Best Regards

From da Bastos