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Old 19th May 2016, 05:01 AM   #1
jing is offline jing  Australia
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Default A two way 2nd order series crossover design

Hi Guys,

As a newbie here, I am currently designing a two way series crossover.

I am using HIVI F6 as woofer and TW025m1 as tweeter, the graphes of which show, best and recommend cross over is around 2-2.2K, a bit below the tweeters and perfectly fit F6.

f6-sm.jpg
f6-imp.png
tw025m1.JPG
In this case, I believe a 2nd order would be good, therefore I have come up with an idea like this, which a modified version of LCAudio:

2ndsxo.JPG

This is from a fine tuning using Xsim with initial numbers from online calculators, which is for parallel only but as said parallel and series has the same math. (I am yet to find a sxo calculator.)

The impedances used here are from actual SPLtracing, which, at 2200hz, are 12.9ohms and 8.1ohms for F6 and TW025M1. (I am not a fan of Zobel, because I think it is approximate anyway.)

The simulate result is as following, I believe I have got a very close 2nd order.


fr.JPG

My question is, is this really going to be like this in reality?

Regards,

Jing
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Old 19th May 2016, 05:43 AM   #2
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Hi Jing,

XSim is nearly 100% accurate when measurements were taken from drivers in cabinets.

Otherwise, taking SPL traces is just approximate, especially since you don't have any acoustic distances.

If this is a 2 way, estimate about 1.2 to 1.4" distance. Tune the woofer and set the distance to that, then revisit your crossover. This will give you a better indicator of your complexities.

Zobels are wonderful things, but the online calculators may not be. As important as the frequency effects of Zobel's are the phase shifts that may help you align the drivers. I often bump the cap or resistor to finish tuning that. Zobels can be very useful, don't become snobby about circuits. Sometimes you need them and sometimes you don't, that's all. I usually just use XSim's impedance chart to create an accurate Zobel. Connect the woofer by itself, and adjust the C and R values until the impedance plot after the resonance peak is flat. That's where to start.

Best,


Erik
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Last edited by eriksquires; 19th May 2016 at 05:50 AM.
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Old 19th May 2016, 05:49 AM   #3
jing is offline jing  Australia
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Quote:
Originally Posted by eriksquires View Post
Hi Jing,

XSim is nearly 100% accurate when measurements were taken from drivers in cabinets.

Otherwise, taking SPL traces is just approximate, especially since you don't have any acoustic distances.

If this is a 2 way, estimate about 1.2 to 1.4" distance. Tune the woofer and set the distance to that, then revisit your crossover. This will give you a better indicator of your complexities.

Zobels are wonderful things, but the online calculators may not be. As important as the frequency effects of Zobel's are the phase shifts that may help you align the drivers. I often bump the cap or resistor to finish tuning that.

Best,


Erik
Sorry Erik, I am not quite sure about your reply. SPLtrace is to trace the curve measured by manufacture, and it can be very close if plotted with patience.

Often see people use DC resistance and a Zobel to do the same job but I doubt how much more accurate that can be.

When you talk about distance, do you mean I need measure the frequency response from a distance?

Regards,

Jing
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Old 19th May 2016, 07:23 AM   #4
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Jing,

SPL charts provided by manufacturers are often just a part of their advertising. They won't have told you how the drivers are measured, or whether there has been any smoothing applied to the chart.

Regarding "Often see people use DC resistance and a Zobel to do the same job but I doubt how much more accurate that can be" - I have absolutely no idea what you are talking about. I am fairly sure that very few people will try to design a crossover based on the DC resistance of a driver, and I'm fairly sure (unless you are a mystic) that designing a Zobel (to do what?) based on DC resistance is an impossible exercise.

You seem fixated on a series crossover, instead of a parallel one. Is there any particular reason for this? Both have their own complexities, but in general, the different sections of a parallel crossover are transferable with the driver, while the series crossover is a wholistic design.
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Old 19th May 2016, 07:25 AM   #5
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Hi Jing,

Sorry for the confusion. What I meant was, if you measure things yourself, then XSim is very close. By this I mean that you use a microphone and OmniMic or Room EQ Wizard In this case XSim will be nearly 100% accurate. On the other hand, tracing from a picture, using any of the free tools like SPL Copy or SPLTrace or whatever is worth doing when you are trying to choosing matching drivers but not beyond.

Since the manufacturers usually plot on an infinite baffle, you must measure a woofer in place to get the most accurate bass and slope for it. This way the effects of your speaker box's volume and baffle will be taken into consideration when you design your crossover.

In terms of measuring speaker distances, in most two ways this means that the woofer's signal will arrive a little after the tweeter. You must know exactly what this delay is in order to be able to create a reasonably accurate crossover. This is why just copying SPL and impedance traces won't give you a final answer. Please see my blog post here.

I am no longer sure what you are talking about in terms of a Zobel. The common use is to maintain the driver impedance over a wide range. This makes the low pass circuit consistent. Otherwise the slope of the low pass can get more and more shallow as the driver impedance increases. However, whether or not it makes a difference in any given speaker varies. I've made some speakers with them, and some without. Depends on how soon and how fast the woofer impedance rises.

The Zobel also has phase shifting effects which may be beneficial or destructive, so that matters more than having an absolutely flat impedance curve.

Best,


Erik
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Old 19th May 2016, 08:24 AM   #6
jing is offline jing  Australia
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Quote:
Originally Posted by eriksquires View Post
Hi Jing,

Sorry for the confusion. What I meant was, if you measure things yourself, then XSim is very close. By this I mean that you use a microphone and OmniMic or Room EQ Wizard In this case XSim will be nearly 100% accurate. On the other hand, tracing from a picture, using any of the free tools like SPL Copy or SPLTrace or whatever is worth doing when you are trying to choosing matching drivers but not beyond.

Since the manufacturers usually plot on an infinite baffle, you must measure a woofer in place to get the most accurate bass and slope for it. This way the effects of your speaker box's volume and baffle will be taken into consideration when you design your crossover.

In terms of measuring speaker distances, in most two ways this means that the woofer's signal will arrive a little after the tweeter. You must know exactly what this delay is in order to be able to create a reasonably accurate crossover. This is why just copying SPL and impedance traces won't give you a final answer. Please see my blog post here.

I am no longer sure what you are talking about in terms of a Zobel. The common use is to maintain the driver impedance over a wide range. This makes the low pass circuit consistent. Otherwise the slope of the low pass can get more and more shallow as the driver impedance increases. However, whether or not it makes a difference in any given speaker varies. I've made some speakers with them, and some without. Depends on how soon and how fast the woofer impedance rises.

The Zobel also has phase shifting effects which may be beneficial or destructive, so that matters more than having an absolutely flat impedance curve.

Best,


Erik
Hi Erik,

Thanks for the much elaborated reply.

Look, I am by no means trying to make a pair of perfect sounding speakers. To be honest, judging from the drivers data, what I might get will not be perfect no matter how accurate the math is and how hard I try.

What I am trying to do is to use limited tools and basic methods to make it sound comfortable to a degree that the drivers's nature allows.

I have heard that series xo can have a reasonable flat curve with much tolerance of the components, whereas a parallel xo does the opposite.

Therefore, series is my choice.
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Old 19th May 2016, 08:27 AM   #7
jing is offline jing  Australia
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Quote:
Originally Posted by Cloth Ears View Post
Jing,

SPL charts provided by manufacturers are often just a part of their advertising. They won't have told you how the drivers are measured, or whether there has been any smoothing applied to the chart.

Regarding "Often see people use DC resistance and a Zobel to do the same job but I doubt how much more accurate that can be" - I have absolutely no idea what you are talking about. I am fairly sure that very few people will try to design a crossover based on the DC resistance of a driver, and I'm fairly sure (unless you are a mystic) that designing a Zobel (to do what?) based on DC resistance is an impossible exercise.

You seem fixated on a series crossover, instead of a parallel one. Is there any particular reason for this? Both have their own complexities, but in general, the different sections of a parallel crossover are transferable with the driver, while the series crossover is a wholistic design.
At least you need a constant value to design the Zobel, right? As the impedance is changing, what are you going to use? The one at xo point?

Jing
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Old 19th May 2016, 08:52 AM   #8
AllenB is offline AllenB  Australia
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Quote:
Originally Posted by jing View Post
At least you need a constant value to design the Zobel, right? As the impedance is changing, what are you going to use? The one at xo point?

Jing
Technically, Zobel compensation means bringing the impedance to a consistent and resistive nature and with speakers this usually means one specific thing, ie the top half of a woofer's impedance with the highest practical value as the result, so there are usually fixed formulas for this.

This makes crossover design easier when done by hand.. usually a well crafted crossover won't use these values, but it doesn't matter as there is more than one way to achieve the same result.
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Old 19th May 2016, 08:53 AM   #9
jing is offline jing  Australia
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If this design does not error too much, I am then going to try it out.

Last edited by jing; 19th May 2016 at 08:56 AM.
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Old 19th May 2016, 08:56 AM   #10
AllenB is offline AllenB  Australia
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Quote:
Originally Posted by jing View Post
I have heard that series xo can have a reasonable flat curve with much tolerance of the components, whereas a parallel xo does the opposite.

Therefore, series is my choice.
Parallel is not the opposite, it is more like freestyle design on each driver.

If simplicity is your aim then you have made a reasonable choice. If I were going to do a series design it would include some extra elements in the parallel crossover style. At least the option is there.
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