Some of filter questions

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My filter theory is old and rusty but I got the basics about first order, second order, third order hpf and lpf two-way designs. But my recent projects need some additional knowledge.

1. Three way crossover.

I like to buy pre-assembly but this time I also want to have flexibility in case I will go back to two way. I need a simple crossover at 500hz and 3500hz. Can I serial couple 2x 2-way crossover to get the same result as a 3 way connecting the 500Hz hp to the 3500hz input or will it mess with the 3500hz filter and the slopes? If I add a variable resistance authentication to the treble will the crossover frequency go up or down (just trying to avoid LPad) and what kind of overprotection fuse/compression would you recommend for a Eminence APT50 HF driver?

2. Shelving low pass (high frequency shelving authentication).

I have a full range driver that I want to authenticate -6dB starting at 1000Hz (meaning the -6 point at approx 1800hz) and flat from 1800 using this example below - do I absolutely need a R1 or can I just parallel connect a capacitor of the crossover point 1800hz and a resistance of 8 ohm? What would actually be the value of the capacitor in 8ohm system.

Sorry for the bad language, hope you understand my questions.

system7

About 200 years ago, this smug-looking Frenchman called Augustin-Louis Cauchy invented something called function of a complex varaible:
Augustin-Louis Cauchy - Wikipedia

Along with another Frenchman, Jean-Baptiste Joseph Fourier's sine wave analysis of sound, this is pretty much where we are today:
Joseph Fourier - Wikipedia

Three ways are a solution of all this baffling maths. (Er, baffling to most of YOU, that is. I understand it perfectly! There's a little of the smug Cauchy in me too.)

The theory:

The practise:

How a three way works is all three drivers hang together into a coherent whole.

SEAS-3-Way-Classic

A surprising result, but leading to phase alignment between all three drivers.

Lojzek

Why don't you start simply like this.

I have some drivers that I would like you to design a crossover for me. Now write brand and model of these.

edit: and now please a round of applause for Steve's efforts in making this a little more confusing than it should be.

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Cal Weldon

Paid Member

What the fine feathered friends are saying is you are stepping into a kitchen and wish to produce a masterpiece dish, without the right ingredients and not being a chef.

Why don't you start again, with a less ambitious thought process and let the 'boys in the know' help you.

For starters, no to the premade. It does not take into account the variables required to match circuit to drivers. There is no one fits all.

Second, don't begin to think you can take a proper XO and go from 3 way to 2 way.

Third, there is nothing wrong with a variable L-Pad. It gives you level control and keeps the impedance the same for the XO.

Fourth, protection networks can be a plenty, from a simple fuse or light bulb, to a thermistor, or an auto reset circuit breaker and others maybe I'm not familiar with.

I'll let the others take over from here but please keep in mind this site is called diy for a reason. We are here in numbers to help but we always encourage you to do your own research. No one here is getting paid, we're here to enjoy the result of our labours with the assistance of others.

Cheers.

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Lojzek

You think it's fair to advise purchasing parts worth 15 bucks for a price of 50?

system7

If fabricadetabaco is a bit short of the old bunce or readies, I am sure we can advise on economy measures! But remind me not to go for a drink with him, if he gets a bit tardy on putting the old hand in the pocket!

Actually, I amaze myself sometimes.

Put together these three items in some old box:

BETA-10CX - Loudspeakers | Eminence Speaker
APT:50 - Drivers | Eminence Speaker
PXB2:2K5CX - Crossovers | Eminence Speaker

Voila, the old WLM Diva speaker:

6moons audio reviews: WLM Diva Monitor with Diva Control

Go for \$5,500 a pair.

Hello guys, thanks for the response.
I think I need to clarify a bit more.

First of all, forget about the shelving question, ill take that in the full range subforum, its completely unrelated to this project.
Secondly, regarding L-Pad vs resistor I see that using serial authentication only will mess with the crossover, given the formulas for RC and RL circuitry the RC will infact increase the crossover point on a first order HPF however the parallell RL will actually lower the frequency point, so I cannot expect what to get here. Ill avoid it completely and just use a fixed LPad to match the bass driver sensitivity.

Then back to the topic of 3 way crossovers and the project itself.
The APT50 driver is a left over from a previous project.

Some time ago I bought Eminence Beta10CX and APT50 and some crossover parts calculated online only. The project never finished as I struggled with the filter design (some other thread, I gave up).
I should also say that at that time I also bought Beta12CX and ASD1001 with the Eminence 2,5X crossover above mentioned and I'm very happy with that system.

Now I want to use the APT50 leftover driver in a 3-way system with a no-brand 15" driver I have laying around. I have absolutely no information about that 15" so I'm taking a bit of risk here which is why I want to have a variable LPad on the HF. It seems like a standard rugged PA 15" so I'm assuming the sensitivity is 95-98dB. Its labeled 8 ohm. Pictures attached. I have a small bullet horn for the APT as well so I excect close to 105-110dB - a nice 10dB LPAD should be fine.

This is a low cost project using spare parts for the most but I need a cheap 4" midrange as well, and a 3 way crossover as I'm sure the bass driver have ugly mids. Now here is the question. As this project is most likely to fail I want to be able to reuse the crossover in future projects, and that's why I wonder if its possible to use 2x 2-way crossover to achieve 3-way, like we do with active PA 19" crossovers (2way stereo = 3way mono).
See drawing.

Is this possible without messing with the HPF in the 3,5kHz filter? In practicality it will be like having two filters on HF; one 500Hz and one 3,5kHz. Midrange and bass should be OK, especially if its first order I don't see any problems with this. As I dont play very loud I think first order should be OK as long as I have a protection circuit on the HF.

IF the project fails completely I can then use the 3,5kHz filter in my next project (completing the Beta 10CX or something else), or I can use the 500Hz filter in a separate cabinet for sub only (as first intended with the 15" when I bought it).

Disclaimer I am not doing HiFi, all my projects are fun-boxes primarily with some nice bass and treble to be used in the garage, basement or garden.

Hope this makes more sense.

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Oops I see that the RC crossover point will half when resistance double.

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AllenB

Paid Member
Oops I see that the RC crossover point will half when resistance double.
Use a second order filter so you won't have this problem.
500Hz and one 3,5kHz
Yes, it is far enough apart.

So perhaps something like this then.

Filter 1 500Hz:
Capacitors
C1 = 28.13 uF
C2 = 28.13 uF
Inductors
L1 = 3.6 mH
L2 = 3.6 mH

Filter 2 3500Hz:
Capacitors
C3 = 4.02 uF
C4 = 4.02 uF
Inductors
L3 = 0.51 mH
L4 = 0.51 mH

R1 8ohm
R2 4ohm

Will C2, C4, and L2, L4 have any conflict or issues?
Thanks for all help...

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AllenB

Paid Member
Will C2, C4, and L2, L4 have any conflict or issues?
It will be OK.

You already know that using the generic crossovers is not perfect. I see you are using resistors on the tweeter. This is good, you need to work at it starting like this.

system7

I really can't see much difference between this idea and a proper three way crossover. But I would model it in case it has some unexpected surprises, being unconventional.

This is the Eminence PXB2-2k5cx 2.5kHz filter minus the lightbulb protector, which is designed for a horn tweeter:

This is an off-the-shelf Visaton HW 3/130 NG - 8 Ohm:
HW 3/130 NG - 8 Ohm | Visaton

http://boxsim-db.de/kategorie/systeme/drei-wege/

It works very well with the right choice of drivers:

Use Boxsim to see how it looks:

Software | Visaton

These projects are importable to the projekte folder for a quick start:
3 Wege – Boxsim Projektdatenbank

You are better off using real drivers which are often 6 ohm at DC, rather than 8 ohm calculators. The impedance of a bass and a mid driver is highly inductive and this affects things.

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