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Multi-Way Conventional loudspeakers with crossovers

Lpad v single resistor
Lpad v single resistor
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Old 18th September 2013, 10:34 PM   #21
Wavewhipper is offline Wavewhipper  United States
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I did some testing over a few weeks, fixed L-Pads made from 2 watt resistors, and at levels so loud I can't hear anyone talk, or myself, they did not even get warm on the midrange and tweeter. Just find an L-Pad calculator online, and find the values for example, -2, -3, -4 db. They are about $.50 each, so $1 for each db step.

Please be sure the 2 watt resistors do not get hot at your listening levels, please. I would not want to hear of anyone's speakers catching fire. Then, it is fixed and will not crackle or able to be messed with.
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Old 19th September 2013, 01:07 AM   #22
BlueWizard is offline BlueWizard  United States
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10 watt resistor are cheap, about $1 each, and they are easy to come by.

Better to have an not need than to need and not have (sufficient powered resistors that is).

Steve/bluewizard
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Old 19th September 2013, 05:45 AM   #23
AllenB is offline AllenB  Australia
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1 Watt resistors can be used with some efficient tweeters/super tweeters.. but unless sure, I'd agree with Steve.

There can be a negligible improvement in using some types of resistor and many good ones come in about a 1W package, however the improvement isn't worth compromising the required values. Ie: I may have only 3r3 of a good resistor and try to use that value when possible. It's normally better to use components of different/lesser quality to make another value when needed.

Sometimes L-pads aren't as critical to the absolute values used. The impedance can end up a little higher or lower than 8 ohms most of the time, as long as it has been flattened a little and you have the right L and C. I'll sometimes tweak the two resistors to suit some value of inductor I have to use.
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Old 19th September 2013, 06:31 AM   #24
BlueWizard is offline BlueWizard  United States
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If we use an assumed 8 ohms and we seek -2dB, -3dB, & -4dB, here are the values I get -

-2dB -
Rs = 1.6454 ohms
Rp = 30.8969 ohms

-3dB -
Rs = 2.3364
Rp = 19.3822

-4dB -
Rs = 2.9523
Rp = 13.6777

Off the top of my head, I would use these values assuming they are available -

-2dB -

Rs = 2x 3.3 ohm in parallel for 1.65 ohms total
Rp = 1x 10 ohms + 1x 20 ohm in series for 30 ohms

-3dB -
Rs = 2x 5 ohm in parallel for 2.5 ohms
Rp = 1x 20 ohm

-4dB -
Rs = 1x 3 ohm
Rp = 1x 8.2 ohm + 1x 5 ohm in series, or 1x 10 ohms + 1x 4 ohm in series for 13.2 ohms to 14 ohms total

I think this might be what AllenB is getting at, you use a combination of standard values in series parallel combinations to come reasonably close to the calculated value.

Prices for 10 watt 5% are about $0.65 each. Cheap enough.

Actually there are probably resistor values that would work better but Parts Express doesn't list them in order of size, so exact values are hard to track down.

I think, matching left speaker/right speaker attenuation is more important than precise attenuation. If the attenuation is -1.9dB or -2.1dB, is less important than both side being the same.

Just a thought.

Steve/bluewizard

Last edited by BlueWizard; 19th September 2013 at 06:33 AM.
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Old 19th September 2013, 07:58 AM   #25
AllenB is offline AllenB  Australia
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I tend to find that component tolerances of 10% can be ok while first prototyping a crossover, enough of what's important is still coming through, such as whether speaker issues are being rolled off or reduced in level (eg: making up values from odd resistors). Being precise with values won't fix the acoustic problems, but it's more important later.

Last edited by AllenB; 19th September 2013 at 08:01 AM.
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Old 19th September 2013, 12:18 PM   #26
Wavewhipper is offline Wavewhipper  United States
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I have my 6db starter xover going well but once in awhile I get a surprise "honk" in vocals. I need to mic the system, or just hold on till I find a good deal on an LR-2.
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Old 19th September 2013, 02:22 PM   #27
AllenB is offline AllenB  Australia
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I've run a comparison where: the upper grey trace is a plain 6dB slope, the red trace is an 8 ohm parallel and 4 ohm series L-pad with a 10uF capacitor using the shown impedance.

The green trace is from reducing the parallel resistor to 2.5 ohms. The series resistor needed to be reduced to 1.5 ohms and the capacitor went to 25uF.
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Old 30th September 2013, 04:54 PM   #28
midrange is offline midrange  United Kingdom
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Lpad v single resistor
Just to summarise my understanding.
A series resistor changes the impedance seen by the amp. This effects the frequency response of the tweeter.
An Lpad flattens the impedance. This does not effect the frequency response.

A follow up question if I may. Theoretically, if there was a choice of 2 identical tweeters, with differing sensitivities, and one needed an Lpad and the other needed no attenuation, would it be advantageous to use one instead of the other?
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Old 30th September 2013, 06:32 PM   #29
BlueWizard is offline BlueWizard  United States
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"...if there was a choice of 2 identical tweeters, with differing sensitivities, and one needed an Lpad and the other needed no attenuation, would it be advantageous to use one instead of the other? ..."

If it were only as simply as that. Treble can be piercing. That is, it can sound louder even at the same measured level.

So, as an example, if you have a woofer with a Sensitivity of 89dB and a Tweeter with a Sensitivity of 89dB, that is no guarantee that the tweeter will not still need a bit of attenuation. Though, it will be very little.

To the extent that it is possible the two part L-Pad is impedance stable which is an advantage to the Tweeter crossover, as you design it either for the actual tweeter impedance at the crossover point, or you design it to the generic rated tweeter impedance.

However, if you use a Series only resistor, then you have to design to that resistor plus the impedance of the tweeter at the crossover. And, neither the attenuation or the impedance is as constant as with an L-Pad.

That said, there are many speaker crossover design that use a Series Resistor. But that is typically done by people who know what they are doing and who are specifically trying to achieve the effect that a series resistor will give them.

But, in my opinion, for some one designing a basic crossover, and need control fixed impedance attenuation, the simplest solution is a common L-Pad. Resistors are cheap, buy a bunch of them to cover a range of attenuation, ultimately choose the one that works best for you.

In my opinion, there is a time and place for a Series Resistor, and that time and place are in the hands of an experience crossover designer.

But then that ...is... just my opinion.

Steve/bluewizard
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Old 30th September 2013, 07:35 PM   #30
midrange is offline midrange  United Kingdom
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Lpad v single resistor
Actually my question assumed that the RIGHT level of output from the tweeter (by measurement,or listening). I am not assuming a design by numbers.
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