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Multi-Way Conventional loudspeakers with crossovers

First project - Will this crossover design work?
First project - Will this crossover design work?
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Old 15th March 2020, 11:52 AM   #11
Douglas Blake is offline Douglas Blake  Canada
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Quote:
Originally Posted by Mygyth View Post
I was under the impression that the impedence graph should be as close to flat as possible?
You will almost always have a rise in impedance at the woofer's resonant frequency and sometimes at crossover points. Rising impedance is generally NOT a problem.

The time to worry is when you get deep dips in impedance, below your target. Those can become an amp-killer.
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Old 15th March 2020, 01:00 PM   #12
Pharos is offline Pharos  United Kingdom
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"I was under the impression that the impedence graph should be as close to flat as possible?".


I don't understand the purpose of the CR network across the woofer at all, but I agree with AllenB that it will be a S/C at audio frequencies.


That network although the same in structure, does not look like a Zobel netork.


In any case I have very strong reservations about the need for a Zobel network.
It is argued that one is necessary in order to present a relatively constant Z to the amplifier, but it only really matters if the Z dips to low values placing high current demands on it. What does it matter if the Z goes up to 750 ohms at 1KHz for eg? That will help the amplifier.


I have used just an L in series with my mid/woofer, to flatten its FR characteristic. I don't care that it has a very high Z above the Xover, this serves to lower the load and hence stress on the amplifier.


The loading of the 3.8 ohm resistor will only cause a higher current to be drawn from the power amp; what advantage does that have?
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Old 15th March 2020, 02:15 PM   #13
system7 is offline system7  United Kingdom
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That Eekel's Mini suggestion was a serious one:

Eekels' Mini

But is rather sophisticated.

An off-the-shelf crossover is this one:

Click the image to open in full size.

HW 2/70 NG - 8 Ohm | Visaton

Add a couple of attenuating resistors for tweeter level and it looks quite good for a 4 ohm bass IMO. You can design for flat impedance, but this is something that mostly interests the SET (single ended triode) valve enthusiasts.

Cheaper regular HiFi voltage feedback amplifiers dislike low impedance at high phase angle. Typically reflex designs at 4 ohms. They run out of current. High impedance bothers them not at all.
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Last edited by system7; 15th March 2020 at 02:31 PM.
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Old 15th March 2020, 05:31 PM   #14
Douglas Blake is offline Douglas Blake  Canada
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Quote:
Originally Posted by Pharos View Post
.
The loading of the 3.8 ohm resistor will only cause a higher current to be drawn from the power amp; what advantage does that have?
Basically any current passing through a crossover that does not go through a voice coil is wasted energy... something to be avoided if you want efficient speakers.
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Old 15th March 2020, 07:01 PM   #15
Pharos is offline Pharos  United Kingdom
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Exactly Douglas, to be avoided in any case.

System7, I still have in the loft, a crossover of that form made in 'about '67 in my apprenticeship; I didn't think that they were still used, let alone advocated.
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Old 16th March 2020, 01:19 AM   #16
Mygyth is offline Mygyth
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Thanks for the clarrification on the impedence graph guys. Helps heaps to know i dont have to be so precious about that.

@System7 Thanks for the reccomendation. I took a look, and put that crossover diagram into XSim (Image 1). Obviously it was less than ideal for my drivers at the given values, but after some tweaking, i think i have it looking ok (Image 2). Is that functionally going to any better than the other setup I had? (Image 3). Should i just go for the cheaper setup at this point?

@Pharos, You clearly know alot about what your talking about and i appreciate your input. However, I really dont know alot about what im talking about. Can you please clarify what you mean in simpler terms? I can't see a 3.8 Ohm resistor anywhere on my schematic.

@AllenB Is there a good amplifier you could reccomend me, or perhaps a guide on how to choose one? Again, I really dont know alot about this, but im happy to invest the time required to learn.

Thanks again guys.
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Old 16th March 2020, 02:31 AM   #17
system7 is offline system7  United Kingdom
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Unless you have bought the woofers already, I think the 8 ohm version of this paper cone will just be easier: TCP115-8 4" Treated Paper Cone Midbass Woofer 8 Ohm

Your 4 ohm driver is not a polycone according to Dayton Audio:
TCP115-4 4" Poly Cone Midbass Woofer 4 Ohm

From what I see of the tweeter, it needs quite a high crossover, around 3kHz:
Dayton Audio ND28F-6 1-1/8" Soft Dome Neodymium Tweeter

So smaller values like 4.7uF and 0.2mH ought to do the right things. The tweeter has quite a sharp impedance peak around 1kHz, so a 10R resistor in parallel with it will be no bad thing.

The bass filter is usually just a coil and capacitor. Simple as that.

I am a bit mystified by the downward slope on the bass driver, and I wonder how Dayton have measured it. Always a headache with imported files to know how hey were measured. In a box or on a big baffle?

The bass breaks up a bit above 5kHz, so hope for the best.
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Old 16th March 2020, 03:33 AM   #18
AllenB is offline AllenB  Australia
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First project - Will this crossover design work?
Quote:
Originally Posted by Mygyth View Post
@AllenB Is there a good amplifier you could reccomend me, or perhaps a guide on how to choose one? Again, I really dont know alot about this, but im happy to invest the time required to learn.
If I told you all my amplifier biases I'd be here all day. There's one thing you should know first.. as amplifiers of different types get closer to perfect performance, they begin to sound the same as each other. It's important to remember this so you don't accidentally aim for the moon. Just stick with solid performance.

Are you interested in accuracy or do you want something with special distortion features. Are you buying or building, if building have you done it before?

Some would suggest a class A amplifier for efficient speakers or low level listening. Have you an opinion?
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Old 16th March 2020, 08:05 AM   #19
Mygyth is offline Mygyth
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@system7 Thanks, just subbed in that woofer. Looks like i can get a decent crossover quite a bit cheaper (Image 1). Also should have a minimum of ~8.4Ohms impedence. Which, since i gather higher impedence is better makes this a significant upgrade on my last setup?

@AllenB I dont think i need any distortion features? This is for my garage/workshed, so it doesnt need to be crazy, and I am on a budget, so going somthing with solid performance, should be good.

In terms of building or buying an amp, I dont know whats involved in building one. Given im already pretty far out of my comfort zone with this project, Im probably just as happy to buy one provided the price is right. How difficult is it to build one?
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Old 16th March 2020, 02:57 PM   #20
Douglas Blake is offline Douglas Blake  Canada
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Quote:
Originally Posted by Mygyth View Post
Which, since i gather higher impedence is better makes this a significant upgrade on my last setup?
Sorry to but in again ... but higher doesn't mean better. It is a little easier on the amplifier because it draws less current, but that's about the only advantage.

"Better" generally comes from carefully matching drivers and box designs. In theory, the right drivers in the right box don't need a complex crossover. Sometimes it can be as simple as a single capacitor to keep bass energy out of the tweeter.

The crossover does play a role, of course, but mostly it's there to correct for our compromises.

What I meant by my previous post is that if you are doing a design and you get a real low dip in impedance someplace on the response curve, it could overheat and damage the amplifier... That is if you are designing for 8 ohms and at some point the impedance dips to 1 ohm, even while the rest is still at 8 or 10 ohms, your amp is at risk.

The opposite... that characteristic rise to 20 ohms or so at woofer resonance is not harmful. It's just hard to look at.
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