Understanding this crossover system

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Bumpy

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Understanding this crossover system
« on: 30 Nov 2018, 08:08 am »
Hi
I have been directed here by the Open Baffle forum to resolve this question.

I have a 3 way speaker which is using a crossover as in the diagram and recommended for the Lampizator Endorphin P17

Now I may need to make changes to it as I am experimenting with substitute drivers. I am not gifted at electronics but eager to learn, so somewhere on the Net where I can substitute in values would be good.

Could someone explain what crossovers I have here. As far as I can gather the tweeter has a first order Butterworth but that is the limit of what I know :(

Thanks




David Ellis

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Re: Understanding this crossover system
« Reply #1 on: 30 Nov 2018, 03:28 pm »
Hmmmm,

Mr. Bumpy, this is a massive "can of worms".

I suppose my summary is, don't mess with it unless you can MEASURE your results.  Changing drivers and changing values will almost surely make matters worse.  Fortunately, the cost of measurement equipment has declined.  Here is a fair primer on measurment:

https://www.audioxpress.com/article/testing-loudspeakers-which-measurements-matter-part-1

It is marginally possible to obtain tolerable sound or even acceptable sound when tuning a speaker by ear, but the most optimal results will always be obtained with MEASUREMENT and listening.  Using on & off axis gated and in room responses combined with listening to music in your room is a very process oriented project.  Additionally, a simple 2 way will be much easier than a 3 way due to the low frequency crossover room reflections and the difficulty in measuring these frequencies.

In general the function of crossover components as I consider them:

Capacitors - stop low frequency and pass high frequency.  A larger capacitor will pass lower frequencies.  A smaller capacitor will only pass higher frequencies.

Inductors - stop high frequency and pass low frequency.  A larger inductor will pass less high frequency.  A smaller inductor will pass more high frequency.

Additionally phase shift occurs across these components and is dependent on impedance, frequency and component value.  This is a starting primer for inductance phase shift:

https://www.allaboutcircuits.com/textbook/alternating-current/chpt-3/ac-inductor-circuits/

In my opinion, the traditional mathematical models created by Mr. Linkwitz and others were groundbreaking in their time.  However, for today's designer, the idiosyncrasies present in ALL loudspeaker drivers and the ability to measure and create a custom crossover for these drivers will vastly surpass a mathematically applied model.

Designing loudspeaker crossover circuits can be super fun, but there IS a learning curve - pun intended  :D .

Sincerely,

Dave

Bumpy

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Re: Understanding this crossover system
« Reply #2 on: 30 Nov 2018, 04:23 pm »
Thanks so much for taking the trouble to answer.

Capacitors - stop low frequency and pass high frequency.  A larger capacitor will pass lower frequencies.  A smaller capacitor will only pass higher frequencies.

Inductors - stop high frequency and pass low frequency.  A larger inductor will pass less high frequency.  A smaller inductor will pass more high frequency.


Even this is a great starting point in the understanding.

I know its not ideal to tune by ear, but I have found that open baffles seem to be much more forgiving of imperfections in this area than closed box. If all else fails I have the starting point faithfully recorded. I am an analytical scientist by profession so well understand the consequences of experimentation.

Do the low pass and mid range crossovers go by a particular name (in the same way the tweeter crossover is called a 1st order Butterworth for example) so I can Google and continue my learning? All I have gleaned so far is that they are LC filters, but I guess that's pretty obvious. :)

Bumpy

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Re: Understanding this crossover system
« Reply #3 on: 30 Nov 2018, 07:11 pm »

I suppose my summary is, don't mess with it unless you can MEASURE your results. 

Dave

Whilst I await other responses to my initial posting my mind turns to the question "Is there a modestly costly way that the one time DIYer can make measurements" - I am thinking microphone, computer and some appropriate software. Any relevant articles for the beginner would be great

David Ellis

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Re: Understanding this crossover system
« Reply #4 on: 1 Dec 2018, 01:32 am »
My first loudspeaker measurement setup many years ago was LspLab.  It was a "complete" system for about $300, and also a "complete" headache.  I spend perhaps 200 hours trying to use the software.  Initially, my problems were rooted in sound card conflicts.  Then I built a sand-alone computer.  The setup worked okay for a while, then I cooked the impedance bridge.  I am not sure how, but isolating the cooked impedance bridge was NOT easy.  Sheldon Stokes helped me along the way.  Eventually, I gave up and purchased Clio Lite.  It worked sooooo much easier and better.  Yes, it was "real", money, but it was also real software with refinement and soooo much easier to use.  And, no headaches!

I am aware that Sound Easy really ain't so easy.  There are a myriad of products. 

My guess is this end of the hobby is better nowdays.  My "entry" into measurement was about 15 years ago.  I have been happy with my measurement jig and haven't looked at the current products.  My guess is this mic and some software might be decent:

https://www.minidsp.com/products/acoustic-measurement/umik-1

Bumpy

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Re: Understanding this crossover system
« Reply #5 on: 1 Dec 2018, 08:02 am »
Thanks again David very useful. The main thing I cant understand is how to you manage to get sound out of the drivers to measure. Is it a special CD track playing all frequencies at once (white noise) or does the computer software somehow send the signal?

David Ellis

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Re: Understanding this crossover system
« Reply #6 on: 1 Dec 2018, 02:13 pm »
Quote
Thanks again David very useful. The main thing I cant understand is how to you manage to get sound out of the drivers to measure. Is it a special CD track playing all frequencies at once (white noise) or does the computer software somehow send the signal?

Darn good question!

I went looking online for a good example and didn't find one with full pictures and video .  This is the closest:

https://www.minidsp.com/applications/acoustic-measurements/umik-1-setup-with-rew  

From the above webpage:

Quote
Connect an audio output from your computer to your sound system. With most computers, you can use the line out or headphone output with a suitable cable. It is advisable to connect into your system at the preamp inputs, so that the preamp volume control can be used to manage the signal level from the computer.

You want to get to a gated response for the most accuracy initially. This will be limited on the lower end of the frequency by the proximity to room reflections.  In my basement I was able to get to a low frequency of about 273hz for a "normal" measurment.  For woofer measurements, I had to use a ground plane measurement to accomplish the crossover between the woofer and midrange at about 300hz.

There is a good illustration of a gated measurement on this page:

https://www.minidsp.com/applications/acoustic-measurements/loudspeaker-measurements

Hmmmmm, another element of this measuring and understanding the T/S parameters, and .... there is variability in the measurement processes used by manufacturers too.  And, the T/S parameters of your current drivers.  Swapping drivers in a 3-way speaker and hoping to get ideal results is an EXTREMELY complex project if you are hoping to get it done right. 

One positive thought.... It is NOT necessary to be a school trained engineer to do this stuff.  Simple mathematical algebra will be the limit of math necessary - and this doesn't happen very often.  The smart guys did the math in the software packages and this is done well and done right  :D .  This was good for me since I gave-up on math at Calculus 3  :D .

I... do recommend you find a simple 2 way speaker to play with before the 3-way.   This hobby really is SUPER fun, but I foresee that most folks would become discouraged and surrender if they started with a 3-way speaker.


mboxler

Re: Understanding this crossover system
« Reply #7 on: 1 Dec 2018, 02:39 pm »
Is part of your question why, in the case of the tweeter, a 4 uf capacitor was used with what I believe is a 5 ohm driver?

Mike

Bumpy

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Re: Understanding this crossover system
« Reply #8 on: 1 Dec 2018, 02:39 pm »
I... do recommend you find a simple 2 way speaker to play with before the 3-way.   This hobby really is SUPER fun, but I foresee that most folks would become discouraged and surrender if they started with a 3-way speaker.

Thanks again David, all good stuff. I only have one set of (3 way) Hi Fi speakers and life's too short for diversions. Like I said earlier, if I don't like it when I arrive I can always go back. Nothing I do will be irreversible. :)

Bumpy

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Re: Understanding this crossover system
« Reply #9 on: 1 Dec 2018, 02:42 pm »
Thanks again David, all good stuff. I only have one set of (3 way) Hi Fi speakers and life's too short for diversions. Like I said earlier, if I don't like it when I arrive I can always go back. Nothing I do will be irreversible. :)

Not really Mike.

I just need help in understanding all the crossovers so I can approach changes of capacitors, inductors etc from a position of knowledge. I have found stuff on the tweeter, but need stuff on the other two crossovers.

mboxler

Re: Understanding this crossover system
« Reply #10 on: 1 Dec 2018, 03:08 pm »
Not really Mike.

I just need help in understanding all the crossovers so I can approach changes of capacitors, inductors etc from a position of knowledge. I have found stuff on the tweeter, but need stuff on the other two crossovers.

So you are aware that if the tweeter is changed from 5 ohm to 8 ohm, the capacitor would need to be changed to 2.5 uf if you want the crossover frequency to remain at 8000 hz (electrically)?

 

Bumpy

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Re: Understanding this crossover system
« Reply #11 on: 1 Dec 2018, 05:16 pm »
So you are aware that if the tweeter is changed from 5 ohm to 8 ohm, the capacitor would need to be changed to 2.5 uf if you want the crossover frequency to remain at 8000 hz (electrically)?

I am indeed. I have been able to read a lot about the crossover on the tweeter because I know what it is and I have found calculators to help me find values.

If only I had the same for the mid range and bass crossovers - That's where I need help as I have no idea what the components do or how to adjust them to change frequencies.

Mike B.

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Re: Understanding this crossover system
« Reply #12 on: 1 Dec 2018, 06:11 pm »
What the designer tries to do is crossover with a three way driver setup


Caps, coils and resistors are his/her electrical tools. The driver specs and box are physical characteristics. Your example appears to be a first order midrange and tweeter electrical layout. The woofer a second order electrical layout.



Bumpy

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Re: Understanding this crossover system
« Reply #13 on: 1 Dec 2018, 08:21 pm »
Thanks Mike. I think things are a bit clearer.

In the mid range 1st order crossover am I right in assuming the capacitor value adjusts the low frequency transition and the inductor adjusts the high frequency transmission or is it more complex, with interactions between the two?

mboxler

Re: Understanding this crossover system
« Reply #14 on: 2 Dec 2018, 03:14 am »
Thanks Mike. I think things are a bit clearer.

In the mid range 1st order crossover am I right in assuming the capacitor value adjusts the low frequency transition and the inductor adjusts the high frequency transmission or is it more complex, with interactions between the two?

A capacitor alone creates a high pass filter...voltage across the driver increases as frequency increases.  An inductor alone creates a low pass filter...voltage across the driver decreases as frequency increases.  When a capacitor and an inductor are in series with the driver, the two act as a capacitor as frequency increases until a certain frequency is reached, at which point the two act as an inductor.  This gives you a band pass filter.

Given a .39mh inductor and a 80uf capacitor, the frequency when the circuit goes from capacitive to inductive is around 900hz.
« Last Edit: 2 Dec 2018, 05:00 am by mboxler »

S Clark

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Re: Understanding this crossover system
« Reply #15 on: 2 Dec 2018, 05:32 pm »
What the designer tries to do is crossover with a three way driver setup


Caps, coils and resistors are his/her electrical tools. The driver specs and box are physical characteristics. Your example appears to be a first order midrange and tweeter electrical layout. The woofer a second order electrical layout.
If only it were this easy.  Anyone with a modeling program and some data could design a crossover for three drivers with flat responses.  But even if you had such drivers, the nightmare of a threeway design is keeping phase from creating cancellations... and I mean huge Grand Canyon type valleys.  When you start changing drivers, or cap/coil values, unpredictable things start to happen. 

It really depends on your goals.  If you are after the best sound, send it Danny Richie and pay him to design a crossover.  If you insist on trying to build your own three way crossover with  limited experience don't expect professional results. 
I've probably designed >30 crossovers with a Clio system, and I'm not terrible with 2 ways.  I wouldn't try a three way on anything other than a learning project. 
Regardless, you can upgrade parts easily, and pick them up from Jeff at very reasonable prices.

Bumpy

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Re: Understanding this crossover system
« Reply #16 on: 3 Dec 2018, 09:10 am »
If only it were this easy.  Anyone with a modeling program and some data could design a crossover for three drivers with flat responses.  But even if you had such drivers, the nightmare of a threeway design is keeping phase from creating cancellations... and I mean huge Grand Canyon type valleys.  When you start changing drivers, or cap/coil values, unpredictable things start to happen. 

It really depends on your goals.  If you are after the best sound, send it Danny Richie and pay him to design a crossover.  If you insist on trying to build your own three way crossover with  limited experience don't expect professional results. 
I've probably designed >30 crossovers with a Clio system, and I'm not terrible with 2 ways.  I wouldn't try a three way on anything other than a learning project. 
Regardless, you can upgrade parts easily, and pick them up from Jeff at very reasonable prices.

Thanks I would love to send them to Jeff, but they weigh about 100 lbs each and I am in the UK :(.

You may have missed it, but I am not designing a crossover system from scratch. I have existing open baffles which play perfectly across the frequencies. I am tweaking by substitution and am aware of all the pitfalls. All I want to know here, is what the components actually do in the attached crossover diaphragm.

Bumpy

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Re: Understanding this crossover system
« Reply #17 on: 3 Dec 2018, 09:13 am »
A capacitor alone creates a high pass filter...voltage across the driver increases as frequency increases.  An inductor alone creates a low pass filter...voltage across the driver decreases as frequency increases.  When a capacitor and an inductor are in series with the driver, the two act as a capacitor as frequency increases until a certain frequency is reached, at which point the two act as an inductor.  This gives you a band pass filter.

Given a .39mh inductor and a 80uf capacitor, the frequency when the circuit goes from capacitive to inductive is around 900hz.

That's perfect thanks.

Now to understand the low pass crossover.

I will make a guess. The inductor itself is low pass and the capacitor is there to bypass the driver of any high frequencies.
« Last Edit: 3 Dec 2018, 01:02 pm by Bumpy »

HAL

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Re: Understanding this crossover system
« Reply #18 on: 3 Dec 2018, 03:36 pm »
The low pass filter is actually a 2 pole filter in the case of this crossover for the woofer.  Both the inductor and capacitor form the filter for the driver.  This gives a 12dB/Octave low pass style filter, if it is setup as a Butterworth alignment.

The response of the filter depends on the load impedance that the woofer presents to the network.  The woofer is not a simple resistive, inductive or capacitive load, so it cannot be modeled that way for the circuit frequency response. 




S Clark

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Re: Understanding this crossover system
« Reply #19 on: 3 Dec 2018, 03:41 pm »
Yes, inductors (chokes) filter out high frequencies and allow low frequencies to pass through.  Factors affecting their performance include their value in milli Henrys, the gauge of the wire, and the iimpedance of the system to which they are attached.  They can affect phase as well. 
And you are correct about the capacitor in the woofer circuit.  It allows high frequencies to bypass the woofer.