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Multi-Way Conventional loudspeakers with crossovers

Lpad v single resistor
Lpad v single resistor
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Old 13th September 2013, 05:57 PM   #11
BlueWizard is offline BlueWizard  United States
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AllenB,

When is an error not an error?

Answer: When it works.

But in the general sense you are right, and that is what I tired to convey. Since the crossover doesn't have a constant (or near constant) load, it has be designed accordingly. It has to be design to the series resistor PLUS the nominal impedance of the Tweeter.

It will give you uneven attenuation because the resistor ratio will keep shifting. But again, I've seen designs that seem to produce good results, both DIY and commercial, that use a single resistor.

I personally wouldn't do it when the impedance stable L-Pad option is available. But it must work for some people some of the time, or people wouldn't use a single series resistor.

So, while I slightly bristle at your use of the word ERROR, I can't actually say you are wrong in the general sense.

If we use the 4dB attenuation in my example above. The average ratio of the Series section to the Parallel section is 5.2 to 3, or 1.73:1. If we use the nominal impedance of the Dayton Tweeter (8 ohms), then the series resistor needs to be 1.73 times that or 13.9 ohms. That makes a combined impedance of (13.8 + 8) 21.8 ohm.

I would assume you would have to design the tweeter section of the crossover to accommodate a 21.8 ohm load. Also, if you find you need a different attenuation, and therefore a different Series Resistor, then you need to consider how much that change is going to throw off your Crossover, and you might need to redesign the crossover. Seems like a lot of unnecessary complexity, when you have a impedance stable option available.

Personally, I would just go with the impedance stable L-Pad.

But then, that's just me.

Steve/bluewizard

Last edited by BlueWizard; 13th September 2013 at 06:01 PM.
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Old 14th September 2013, 01:04 PM   #12
AllenB is offline AllenB  Australia
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I used 'error' to simply mean that it is causing something extraneous. It can help to see it this way.. some errors can be fixed by way of a compromise and some will need to be corrected independently.

This particular problem comes down to convenience and component count. Errors are not a bad thing, but they still need identifying. There is also the element of finding an efficient way to succeed.

In what way would you say that an L-pad is stable?
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Old 14th September 2013, 06:16 PM   #13
Wavewhipper is offline Wavewhipper  United States
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Just by theory it would seem that higher frequencies would be attenuated more than lower ones. As F increases the tweeter becomes higher in impedance and shift the emf balance towards the resistor. It could be used as a tool if you wish to attenuate AND darken the tweeter, maybe take some of the piercing effect out.

Actual component configuration can alter basic theory.
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Old 14th September 2013, 06:49 PM   #14
ivanlukic is offline ivanlukic  Serbia
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I am building K&T CT235 loudspeaker (Eminence Beta 10CX woofer + Eminence APT50 supertweeter). The crossover uses series resistor for the tweeter. It has one advantage over L-pad that the combined impedance is much higher than with L-pad. The compression horn drivers have some peculiarities and prefer high damping factor amplifiers. With valve amps the new higher impedance of the tweeter will produce the same effect as having higher damping factor amp. Besides, it seems that with higher impedance driver lower value crossover elements can be used that are cheaper and less bulky.

In some cases series resistor is a good trick.
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Old 14th September 2013, 07:04 PM   #15
BlueWizard is offline BlueWizard  United States
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Quote:
Originally Posted by AllenB View Post
I used 'error' to simply mean that it is causing something extraneous. ...

In what way would you say that an L-pad is stable?

Allen, keep in mind I actually didn't disagree with you, I just thought the statement needed a little more context, which you have now explained very nicely.

An L-Pad (by itself) provides a stable purely resistive load to the crossover and to the amp within the bounds of normal realistic operating temperatures.

The only unstable, or inconsistent, element is the tweeter itself which is not fixed at a nominal 8 ohms but changes from say about 6 ohms up to about 12 ohms.

However, the presence of the L-Pad and more specifically the parallel resistor will soften those impedance swings. So to the degree that it is possible, the L-Pad helps present a consistent impedance to the crossover and amp.

The whole purpose of the L-Pad is to give you the attenuation you need while at the same time, to the extent possible, maintaining a consistent impedance as seen by the crossover.

So the combination is not absolutely stable, but it is more stable, or perhaps more consistent.

Seems a small point though. Again, I never said you were wrong.

Steve/bluewizard
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Old 15th September 2013, 02:15 AM   #16
AllenB is offline AllenB  Australia
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Steve, we're on the same page

Quote:
Originally Posted by Wavewhipper
Just by theory it would seem that higher frequencies would be attenuated more than lower ones. As F increases the tweeter becomes higher in impedance and shift the emf balance towards the resistor.
The higher the tweeter impedance at some point, the lower the attenuation will be. Series resistance causes the frequency response to take on a shape that resembles the impedance curve itself.

With regards to L-pads, the tweeter will begin to appear as a pure resistance at some point but this will be at a high level of attenuation. At typical levels the impedance will be somewhere between that of the tweeter itself, and the resistance.

If you imagine an L-pad and tweeter connected directly to an amp it can be shown that the series resistor and the parallel resistor are both in parallel with the tweeter. In order for the impedance to appear closer to resistive, at least one of these resistors needs to be small compared to the tweeter. So if that is the intention, the L-pad is preferred.
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Old 15th September 2013, 12:30 PM   #17
Wavewhipper is offline Wavewhipper  United States
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I came back and caught that. I was in a big fuzz for a few days over a 3 way crossover and got it backwards. After 30 years ? Yep, I am so ashamed I somehow did not see the correct EMF, Q, and bandwidth.

Well, at least with an L pad, the bandwidth stays more constant over L-pad settings.

Last edited by Wavewhipper; 15th September 2013 at 01:00 PM.
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Old 15th September 2013, 12:35 PM   #18
ODougbo is offline ODougbo  United States
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My friends and I had a simple cap and inexpensive lpad that we used for 2-ways for years, they sounded great, many of them still going (made approx 50).

As far as "series" resistor, I thought these sounded better than others, The Madisound Speaker Store
The eagle brand was also good, hard to find them now.
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Old 17th September 2013, 09:31 AM   #19
ODougbo is offline ODougbo  United States
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What I've always thought would be a good idea (if it could be done) is to use an Lpad (mechanical) and find correct high level.
Than transfer that to an lpad circuit, have no idea if that would work, sounds possible.
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Old 17th September 2013, 10:18 AM   #20
Jay is offline Jay  Indonesia
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I use L-pad only when the attenuation needed is too much. This is in combination with a series resistance but at the input of the crossover, not next to the tweeter.

All of this approach is based on listening. Technically, it is very simple. But when listening is concerned, that is what I want.
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