AudioCircle
Industry Circles => Sonic Craft => Topic started by: Bumpy on 30 Nov 2018, 08:08 am
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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
(https://www.audiocircle.com/image.php?id=187441)
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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 (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/ (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
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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. :)
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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
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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 (https://www.minidsp.com/products/acoustic-measurement/umik-1)
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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?
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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 (https://www.minidsp.com/applications/acoustic-measurements/umik-1-setup-with-rew)
From the above webpage:
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 (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.
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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
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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. :)
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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.
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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)?
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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.
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What the designer tries to do is crossover with a three way driver setup
(https://img.bhs4.com/39/7/397c22cd7425b35561b7be8ec096bfc1cde18deb_large.jpg)
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.
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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?
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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.
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What the designer tries to do is crossover with a three way driver setup
(https://img.bhs4.com/39/7/397c22cd7425b35561b7be8ec096bfc1cde18deb_large.jpg)
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.
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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.
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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.
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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.
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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.
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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.
That's somewhat correct. As frequency rises, the impedance of the capacitor decreases. Without taking into account phase shift, think of the capacitor as a variable resistor in parallel with a 8 ohm resistor (the driver). As frequency rises, the resistance of the variable resistor decreases.
At 292 hz, a 68 uf capacitor has an impedance of 8 ohms. So, if we treat it as an 8 ohm resistor in parallel with another 8 ohm resistor, you get the equivalent of a 4 ohm resistor. At 877 hz, the impedance of the capacitor is 2.66 ohms. This in parallel with the 8 ohm driver is 2 ohms.
Given a fixed inductor value, the voltage drop across the inductor will increase and the voltage drop across the parallel capacitor/driver will decrease as the signal frequency increases. The voltage changes occur twice as fast as they would without the capacitor.
The same voltage will always pass thru the capacitor and the driver at ALL frequencies.
In reality, the impedance of a 8 ohm resistor in parallel with a 68 uf capacitor at 292 hz is 5.66 ohms with a -44.9 degree phase shift.
Here's a calculator you may find fun to play with
https://keisan.casio.com/exec/system/1258032649
Here's some "light" reading on complex AC circuits.
http://www.bcae1.com/compleximpedance.htm
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Thanks guys for taking such trouble to help me out. I think so far I have much better understanding of these particular crossovers. Hopefully no more questions for a while :) :thumb:
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Bumpy,
My apologies for the late reply. Initially, I was going to recommend another circle as my focus is less on the design side, and more on the flavor of the ingredients. However, it appears that you more or less received what you were after. Even though, there is a steeper curve...
While most of the information here is vague, some slightly incorrect, and a tad misleading, it does represent what you are up against. One thing that was touched on in part, but not completely fleshed out is the phase rotation. None of those reactive components completely block the signal. The tweeter does not stop playing below the upper XO point, nor does the mid stop above it. So we have two drivers playing the same information at a fixed distance from each other. That means they will create both peaks (coupling), and dips (cancellation). These can be minimized by rotating phase. Inductors, and capacitors rotate phase in opposite directions. They rotate almost 90 degrees as they move in and out of full reactance. So, the cap on the tweeter has to work with the inductor on the mid. The cap on the mid has to work with the inductor on the woofer. Electrically, the cap on the woofer even finds itself in series with the mid an octave or two above and below the lower XO point.
The best advice I can give at this point is this. During your listening tests, stick with the same brand/series of cap and coil. It is OK to use a different cap on the tweeter from what you are using on the woofer, but keep that tweeter cap the same brand and type as you change values. Do not bypass caps, but stacking similar values to achieve a custom value is OK. Burn new parts in before you do your listening test. When you have arrived at your final values (and/or topology), you will be ready to select the specific parts that possess strengths for your subjective and unique requirements.
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Thanks Jeff valuable info there. :thumb:
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Bumpy,
Do not bypass caps,
I come back to this thread time and again to refresh my understanding, but this one sentence stands out. Can you explain why one should not use bypass caps. Its often recommended elsewhere?
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I'll make a completely non-scientific guess at Jeff's assertion.
Adding a bypass capacitor of .1uf can be good, bad, or just wierd. The sound will change depending upon the "marraige" between the primary and bypass capacitor AND, the placement in the crossover circuit. Something that works behind the tweeter may not work in a notch filter behind the woofer and the subjective impact might be VERY different. Adding bypass capacitors during TESTING would really change the listening experience resulting from the amplitude and phase of the curve. Hopefully this make sense.
I am a huge fan of bypass capacitors, but adding them during initial testing introduces another variable that would make the testing more difficult.
My 2c.
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That makes a lot of sense :)
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I have returned to this topic as it has proven extremely valuable and my speakers
now sound just 10% short of perfect. Thanks so far.
(https://www.audiocircle.com/image.php?id=223343)
(https://www.audiocircle.com/image.php?id=187441)
My last focus is on the midrange driver which is a Supravox alnico T215 RTF 64. I find the driver performs great at its lower frequencies and doesn't need a filter there, so I removed the series capacitor.
I am therefore left with single quality inductor in series. Over extended listening there is a very slight raggedness to the upper frequencies of the Supravox so I would like to lower this low pass filter frequency a little.
Here are my questions
1. With just a single series inductor what type of filter is this (first or second order, Butterworth? etc)
2. If I add a parallel capacitor to it, what type of filter do I get and presumably the low pass frequency is lowered.
Thanks
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"I find the driver performs great at its lower frequencies and doesn't need a filter there"
How did you determine this? By ear? By measurement? Removing the cap means the mid will reach well down into the woofer range and result in superposition addition (and cancellation when out of phase).
1. Remove the cap and you have a first order on the top range of mid and nothing on the bottom. The overlap with the woofer will be unpredictable.
2. Put the cap parallel and you have next to nothing on the mid. The inductor passes lows, the cap will pass highs and the mid will see the sum of both- or play sort of a screwed up full signal.
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"I find the driver performs great at its lower frequencies and doesn't need a filter there"
How did you determine this? By ear? By measurement? Removing the cap means the mid will reach well down into the woofer range and result in superposition addition (and cancellation when out of phase).
1. Remove the cap and you have a first order on the top range of mid and nothing on the bottom. The overlap with the woofer will be unpredictable.
2. Put the cap parallel and you have next to nothing on the mid. The inductor passes lows, the cap will pass highs and the mid will see the sum of both- or play sort of a screwed up full signal.
Some complex stuff there so I'll try and unravel it in stages
"I find the driver performs great at its lower frequencies and doesn't need a filter there"
How did you determine this? By ear? By measurement? Removing the cap means the mid will reach well down into the woofer range and result in superposition addition (and cancellation when out of phase)."
I have tried using microphone measurement techniques but have found, with open baffles, that they don't offer much value in defining what's happening. I'm not sure why this is, but put it down to the increased dependence on the rear wave compared to conventional boxes.
So I do prolonged listening tests often over a number of weeks. The way I have wired my speakers allows me to listen to each driver one at a time in perfect isolation. The midrange extends down nicely without drama and certainly no apparent excessive movement of the cones at low frequency - in fact no movement at all! When played together with the bass driver there in no evidence of cancellation or addition. Phase has been set at the best sonic overlap (generally better base performance). It should be noted that the base drivers are of good quality (vintage Altec 416) and contribute beautifully to the base regions, unlike the Eminence Alphas that are often recommended and which did not match the quality of the Supravox.
I tried also with the capacitor in place and SQ suffered.
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"I find the driver performs great at its lower frequencies and doesn't need a filter there"
How did you determine this? By ear? By measurement? Removing the cap means the mid will reach well down into the woofer range and result in superposition addition (and cancellation when out of phase).
1. Remove the cap and you have a first order on the top range of mid and nothing on the bottom. The overlap with the woofer will be unpredictable.
2. Put the cap parallel and you have next to nothing on the mid. The inductor passes lows, the cap will pass highs and the mid will see the sum of both- or play sort of a screwed up full signal.
1. Remove the cap and you have a first order on the top range of mid and nothing on the bottom.
OK that confirms what I thought, that the top frequencies will have a be first order (6dB) roll off with just the inductor. Given that the driver will have an impedance is this what the call an LR filter?
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"I find the driver performs great at its lower frequencies and doesn't need a filter there"
How did you determine this? By ear? By measurement? Removing the cap means the mid will reach well down into the woofer range and result in superposition addition (and cancellation when out of phase).
1. Remove the cap and you have a first order on the top range of mid and nothing on the bottom. The overlap with the woofer will be unpredictable.
2. Put the cap parallel and you have next to nothing on the mid. The inductor passes lows, the cap will pass highs and the mid will see the sum of both- or play sort of a screwed up full signal.
2. Put the cap parallel and you have next to nothing on the mid. The inductor passes lows, the cap will pass highs and the mid will see the sum of both- or play sort of a screwed up full signal.
I'm sorry, but I'm struggling with this. The filter is the same orientation as the low pass on the bass driver albeit with different values ie inductor in series and capacitor in parallel with the driver. Its probable that I did not make it clear where the capacitor was going.
BTW thanks so much for your help.
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On the woofer, the second order crossover has an inductor in series and a cap that bypasses. The inductor blocks high frequencies going to the woofer. The bypass cap passes high frequencies and blocks low frequencies, letting the highs pass the woofer. The textbook effect is a 6 dB reduction in highs by filtering by the inductor and another 6 dB reduction by letting highs bypass at a chosen crossover point.
If you put both in parallel to each other and in series to the mid, one will block lows and pass highs and the other will block highs and pass lows... kinda cancelling the effect of each other--- obviously depending on values chosen as to which frequencies are affected. As designed, with a cap and coil in series, they work together to allow the passage of a mid range frequency (high treble blocked by coil, low bass blocked by cap). But I may be misreading what you are proposing....
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given that the driver will have an impedance is this what the call an LR filter?
Yes, L for inductance, R for resistance.
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On the woofer, the second order crossover has an inductor in series and a cap that bypasses. The inductor blocks high frequencies going to the woofer. The bypass cap passes high frequencies and blocks low frequencies, letting the highs pass the woofer. The textbook effect is a 6 dB reduction in highs by filtering by the inductor and another 6 dB reduction by letting highs bypass at a chosen crossover point.
If you put both in parallel to each other and in series to the mid, one will block lows and pass highs and the other will block highs and pass lows... kinda cancelling the effect of each other--- obviously depending on values chosen as to which frequencies are affected. As designed, with a cap and coil in series, they work together to allow the passage of a mid range frequency (high treble blocked by coil, low bass blocked by cap). But I may be misreading what you are proposing....
I think you may be. :)
The inductor is in series as now (6dB reduction of highs) and the capacitor would be parallel to the driver and therefore bypass it (further 6dB reduction of highs). Is this a Butterworth second order (12db) low pass?
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Yes, not sure how Butterworth is defined, but it is a traditional second order, 12dB filter.
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Thanks again
I'll try some calculations and see what I come up with
The single inductor of 0.39mH and the 8 ohm driver gives a low pass of about 3200Hz.
With the added cap I would like to bring that to about 2000Hz, (and from 6db to 12dB slope) but the calculators I have found suggest that the inductor is not in the required range, so I may have to start over with both components - it gets a bit expensive experimenting with quality components :(
I have tinnitus and I think it is triggered by 'distortions' at about 4000 Hz so there is an added reason to pursue this.
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If available, check the impedence of the driver at the crossover frequency. It may not be 8 ohms.
See in the graph below, the impedance changes as frequency changes. This is a mid made by Peerless/Tympani, a respected driver.
(https://audioxpress.com/assets/upload/images/1/20181216144722_Figure1-TymphanyPeerlessPMT-40N25AL01-04.jpg)
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Here is the impedance curve for the Supravox driver
http://rutcho.com/speaker_drivers/supravox_t215_rtf_64/images/supravox_t215_rtf_64_z.png
There will be a small tweak to my calculation for the slightly raised impedance at about 3KHz
What are the consequences of allowing the driver to be open to very low frequencies. Obviously this will present a higher impedance, but how will that manifest itself?
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I tried also with the capacitor in place and SQ suffered.
This almost always occurs in the mid. It is a critical position. While it can, and will, degrade mid performance, many times the alternative is worse as it is necessary to control the response of the mid. If you are able to omit it, consider yourself lucky.
Given that the driver will have an impedance is this what the call an LR filter?
It would not be called a LR here. By definition, impedance is frequency dependent reactance, not DCR.
Is this a Butterworth second order (12db) low pass?
Butterworth describes the characteristics of the rolloff (Q=.707). Does your rolloff approximate this Q?
I'll try some calculations and see what I come up with. The single inductor of 0.39mH and the 8 ohm driver gives a low pass of about 3200Hz. With the added cap I would like to bring that to about 2000Hz, (and from 6db to 12dB slope) but the calculators I have found suggest that the inductor is not in the required range, so I may have to start over with both components - it gets a bit expensive experimenting with quality components :( I have tinnitus and I think it is triggered by 'distortions' at about 4000 Hz so there is an added reason to pursue this.
When switching from a single pole to a two pole mid LP, you should also consider the tweeter cap value. The issue that you site, is it better, worse, or the same when the tweeter is connected?
With this fly by the seat of the pants design approach, you should not be using expensive parts. However, as mentioned before, they do need to stay the same for each position as you adjust values. While it may not sound wonderful as a whole, the best sounding topology with cheap parts will also sound the best with better parts. I would recommend using film everywhere, and air core inductors.
What are the consequences of allowing the driver to be open to very low frequencies. Obviously this will present a higher impedance, but how will that manifest itself?
The higher imp results in rolling the driver off (woofer).
If the boost or cancellation is not detrimental to the response, you only concern is excessive cone excursion (mid).
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I've spent a happy afternoon using REW with UMIK-1 to investigate things.
I found it beneficial to reverse polarity on the bass driver alone to integrate it better with the midrange driver. I achieved this by reversing the wiring on the rear terminals. BUT the inductors are now on the negative wire rather than the positive. IS this OK?
Also my inductors have red and black output wires, Are they truly directional and if I have now reversed polarity should they be reversed as well?
I appreciate this is all pretty standard stuff to many of you, but please bare with me.
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I'm not sure I'm helping at all as you do not answer... I deleted my suggestions on reversing the mid or woofer because I did not want to lead you...in this infinite monkey :icon_lol:
The inductor is not polarized, but the OD would tend to be input if used in series. It will be fine connected to the negative input, but you may consider moving it to the other leg if you end up with a shunt cap in the bandpass (mid).
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Thanks again Jeff. Believe me I do read and appreciate all the replies made here and I try my best to apply them. :))
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When switching from a single pole to a two pole mid LP, you should also consider the tweeter cap value. The issue that you site, is it better, worse, or the same when the tweeter is connected?
Having Tinnitus (years of riding a noisy Harley) is a real challenge. Firstly one can have no idea what specific frequency triggers it, though in my case high frequencies are suspected. Secondly its also a phycological response so just concentrating hard to analyse sound triggers it, and sometimes just remembering you have tinnitus triggers it!
Nonetheless I have the option of four suitable tweeters namely Siemens, Grundig (small and big) and Saba Greencones. All are vintage paper cone, alnico magnets so both tonally and in sensitivity they are well matched to the other two drivers.
My choice ATM is the Saba Greencone it is the smoothest and less likely to trigger the Tinnitus.
(https://www.audiocircle.com/image.php?id=223763)
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Completely understood. Even before we consider that many other people also suffer tinnitus (about 20% of adults including me), or that I've been engaged in audio for more than 40 years (professionally for over 30 years). The part I'm missing is, "is it better, worse, or the same when the tweeter is connected" You mentioned somewhere in this thread that it was easy to connect each driver separately in the current setup.
Now, you are looking at a different tweeter before further fleshing out the XO? I'd would have assumed you would have selected the best candidate before starting...
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[quote author=Jeff link=topic=161048.msg1855466#msg1855466 date=1619293022
Now, you are looking at a different tweeter before further fleshing out the XO? I'd would have assumed you would have selected the best candidate before starting...
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Correct, I had all these tweeters in place during my early evaluation and each was listened to for extended periods as single drivers. The Siemens (biggest magnet) was the most dynamic and full of life, and the Saba was the smoothest overall (smallest magnet) and showed up best as a flat response on REW. I do realise that magnet size does not always correlate with 'performance' and that these vintage driers extend nowhere near the upper reaches of modern tweeters. But they are open backed, which of course is a bonus for OBs :)
I had originally chosen the Siemens for its sense of realism, but it demonstrates that interactions with the mid range and crossovers also have a big bearing in overall SQ.
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I want to add a second inductor to lower the upper crossover point of the midrange low pass filter.
I will buy the same same brand of inductor to match that already fitted i.e. Jantzen Cross Coil, Copper foil Inductor 47mm width, 12AWG.
Just to confirm that the two inductors are wired in series.