Impedance Matching for Drivers

[jmascreen]

Hi,

I want to match the impedance for the following drivers. The motto is to build a 3 WAY FS with mostly first or second order crossover.

Drivers

Tweeter - TL25SN 6 ohms
Mid - M13NH 4 ohms
Woofer - SB25NP 8 ohms

All the drivers are from peerless India.

Regards
Justin

 

[pranavkumar]

Hi,

It depends what net impedance do you want.
A crossover includes mainly two sections :
1. Filter Section, which filters out the low frequencies from the signal for the tweeter for eg. This filtering depends on the impedance of the driver.
2. Attenuator circuit, which is a voltage divider circuit using two resistors in series, and the output taken across one of the resistor.

There are many calculators available online for calculating the L&C values for the filter and the resistor values for the attenuator circuit.
The attenuator circuit can be designed in such a way so as to give you a net impedance as required by you.

from the drivers that you have chosen, i think you should go ahead with a net 8ohm unit.
making it a six or a four ohm unit would require you to use resistors in parallel to your driver, hence dissipating a lot of the amps power as heat instead of sound energy.

Hope this helps !

 

[jmascreen]

Pranav,

I want's the net output as 8 ohms. Can you provide some more in depth details like how to find the components and calculate there values

 

[pranavkumar]

hi !

To know the component values and everything, you would first need to find the crossover frequencies, in your case.. as it is a 3 way design, you would need TWO crossover frequencies... one for the Woofer-Mid filter and the other for the mid-Tweeter filter.
Here is a link to an online crossover:
ERSE - Crossover Calculator - Second Order 3 Way

Incase you do not know what Linkwitz, bessel and butterworth filters are... choose a butterworth for a relatively flat frequency response for the pass band.

Here is a link to the Attenuator circuit, also called : L-Pad Attenuation.
ERSE - Crossover Calculator - L-Pad Attenuation

you can put in impedance values with crossover frequencies to find the L and C Values and also the resistor values incase you plan to use a L-pad.

Ready made crossovers are also available at this website :
www.diyaudiocart.com
This is an indian site, so shipping and everything would be reasonable.

Although i'm not aware of the crossover design which is available at the online store. But if it suits your configuration, buy it... it will surely save you the trouble of winding inductors and finding capacitors.

Hope this helps.

 

[jmascreen]

Thanks Pranav for explaining me the details.

Is this the formula to find the cutoff frequency

f(hz) = (344/2/D) * 10 raise 3. Where D is the diameter of cone ?

 

[spirovious]

You can read some guidelines here-
Introduction to designing crossovers without measurement - diyAudio
http://techtalk.parts-express.com/showthread.php?219617-The-Speaker-Building-Bible

 

[pranavkumar]

Hi,

i'm not aware of this formula..
although for a first order crossover, the crossover frequency can be found by the below stated formulla:
f(hz) = 1/(2*pi*R*C) for a high pass filter where the capacitor is in series.
and
f(hz) = R/(2*pi*L) , for a low pass, where the inductor (L) is in series .
R in both cases is the impedance of the speaker.

For the mid range : you will have to use two filters in cascaded configuration i.e. the high pass followed by a low pass to have a band pass.
where did you get that formula from ?

Thanks Pranav for explaining me the details.

Is this the formula to find the cutoff frequency

f(hz) = (344/2/D) * 10 raise 3. Where D is the diameter of cone ?

 

[jmascreen]

Pranav
I got the above formula from Passive Crossover Networks. Its under the THE SPEAKER DISPERSION chapter.

 

[pranavkumar]

Hi,

i'm unaware of what the person is trying to say. i will read up more on this and get back to you.

BTW, do you plan to make the crossover yourself ?

 

[jmascreen]

used the x-over pro 6 with 2nd order all pass.. the parts values are as

C1 = 23.84 ?F, Polypropylene, 0.00323 ohms
C2 = 82.6 ?F, Polypropylene, 0.0016 ohms
C3 = 5.804 ?F, Polypropylene, 0.00663 ohms
C4 = 45.69 ?F, Polypropylene, 0.00245 ohms
L1 = 0.118 mH, Air Core (#16), 0.264 ohms
L2 = 4.481 mH, Air Core (#16), 0.756 ohms
L3 = 0.369 mH, Air Core (#16), 0.292 ohms
L4 = 6.16 mH, Air Core (#16), 0.914 ohms
R1 = 0.879 ohms

I will try to use the one available with diyaudiocart, but currently its out of stock. If I get soon I will use that else I will try to pull something like ur PCB

 

[pranavkumar]

oh great, now that you have your values, i will obviously have to ask you, Where did you get X-Over software ? (PM Me please)

The values look fine, but getting a 82.6uF Polyprop cap is next to impossible here in india. you would probably have to use a combination of a few or a electrolytic which is not recommended.

I hand wound the inductors with 18swg copper wire also known as bell wire. try and find plastic transformer cores to wind your inductors on, its easier that way !

keep posting pictures as you start building
cheers !

used the x-over pro 6 with 2nd order all pass.. the parts values are as

C1 = 23.84 ?F, Polypropylene, 0.00323 ohms
C2 = 82.6 ?F, Polypropylene, 0.0016 ohms
C3 = 5.804 ?F, Polypropylene, 0.00663 ohms
C4 = 45.69 ?F, Polypropylene, 0.00245 ohms
L1 = 0.118 mH, Air Core (#16), 0.264 ohms
L2 = 4.481 mH, Air Core (#16), 0.756 ohms
L3 = 0.369 mH, Air Core (#16), 0.292 ohms
L4 = 6.16 mH, Air Core (#16), 0.914 ohms
R1 = 0.879 ohms

I will try to use the one available with diyaudiocart, but currently its out of stock. If I get soon I will use that else I will try to pull something like ur PCB

 

[jmascreen]

Even I feel its impossible to get these items. So what I am thinking is to get the standard stuffs like Crossover Design Chart and Inductance vs. Frequency Calculator(Low-pass) and pull up

 

[navin advani]

used the x-over pro 6 with 2nd order all pass.. the parts values are as

C1 = 23.84 ?F, Polypropylene, 0.00323 ohms
C2 = 82.6 ?F, Polypropylene, 0.0016 ohms
C3 = 5.804 ?F, Polypropylene, 0.00663 ohms
C4 = 45.69 ?F, Polypropylene, 0.00245 ohms
L1 = 0.118 mH, Air Core (#16), 0.264 ohms
L2 = 4.481 mH, Air Core (#16), 0.756 ohms
L3 = 0.369 mH, Air Core (#16), 0.292 ohms
L4 = 6.16 mH, Air Core (#16), 0.914 ohms
R1 = 0.879 ohms

I will try to use the one available with diyaudiocart, but currently its out of stock. If I get soon I will use that else I will try to pull something like ur PCB

Does the software you are using compute insertion loss? Insertion loss is the energy consumed by the crossover.

a 5-6mh Air core inductor is going to be pretty large even with 16 SWG. I do not see a schematic so I hve to ask, are these inductors in parallel with the driver concerned? if so why not get a ferrite core inductor for L2 and L4? having said that I suspect L2 would be a series inductor and L4 (and C2) might be part of a notch filter. If there indeed is a nothc flter it would a good idea to listen to the loudspeaker without and without this notch filter in circuit. Also if C2 is part of a ntoch filter or in parallel to the driver it can be a 68uf electrolytic mated to a 10uf polyester (it will be pretty close to 80uf).

BTW do yo have a reactance bridge to measure the inductors and capacitors?