Noob Question: What's the preferred method of attenuating a tweeter to the woofer? - diyAudio
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Old 18th May 2015, 02:00 AM   #1
ReDress is offline ReDress  Canada
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Default Noob Question: What's the preferred method of attenuating a tweeter to the woofer?

Hey, guys

I have a 6 ohm tweeter and an 8 ohm woofer and was curious as to what was you preferred method of attenuating the tweeter to match the woofer?

(Side note: I did a search but didn't quite understand all that was said, as such putting it into simple laymans terms would be greatly appreciated)
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Old 18th May 2015, 02:24 AM   #2
rayma is offline rayma  United States
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Originally Posted by ReDress View Post
I have a 6 ohm tweeter and an 8 ohm woofer and was curious as to what was you preferred method of attenuating the tweeter to match the woofer?
An L-pad. It's two variable resistors connected together, with about the same total impedance as the driver.
When you adjust the knob, one resistor goes up, while the other resistor goes down.
It connects between the crossover and the driver. You can also use two resistors of the right values instead.
Variable L-pad: Shavano Music Online - Using L-Pads
Fixed resistors: L-Pad Driver Attenuation Circuit) Designer / Calculator Help

Last edited by rayma; 18th May 2015 at 02:30 AM.
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Old 18th May 2015, 04:03 AM   #3
hongrn is offline hongrn  United States
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You attenuate a tweeter's sensitivity so it matches that of a woofer, so that their sound pressure level, expressed in decibels, are the same, regardless of their impedance (ohms). The impedance of the individual drivers, along with the desired attenuation in decibels are used to figure out the values of the resistors in the L-pad. In other words, you need to figure out the difference in sensitivity of the drivers, and how much padding down you need to do.
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Old 18th May 2015, 05:13 AM   #4
ReDress is offline ReDress  Canada
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So if I'm to understand you correctly, so long as the spl levels of the two drivers match up, the impedance between the two don't (hypothetically) matter? The reason I ask of this is because the drivers I'm looking at are of different impedances, however, they have the same levels is spl. At that point, do the differences in impedances still matter?

(Thanks for the continued help in advance guys, it's appreciated)
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Old 18th May 2015, 05:24 AM   #5
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At this point it becomes a little more technical ! As the impedance Z has an imaginary part then there's the amplifier, constant voltage type which tries to keep up with the request of current. The critical band is the bass region where the max phase rotation before breakdown is 35 ( plus and minus), referred to solid state devices and to the lowest Z accepted, often not under 4 Ω

Last edited by picowallspeaker; 18th May 2015 at 05:26 AM.
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Old 18th May 2015, 10:14 AM   #6
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Quote:
So if I'm to understand you correctly, so long as the spl levels of the two drivers match up, the impedance between the two don't (hypothetically) matter?
Yes

Quote:
The reason I ask of this is because the drivers I'm looking at are of different impedances, however, they have the same levels is spl. At that point, do the differences in impedances still matter?
You can match drivers with different impedance, you still need to check the final impedance (drivers + crossover) over the full audio band, and decide if it is an easy load for the amp or not.

A word of caution on drivers with the same sensitivity (same SPL number). For a tweeter the SPL you see on the spec is the SPL you will get. For a midwoofer this is not true because of the baffle step effect: depending on the baffle width, there is a frequency where gradually the output decreases as the frequency goes down, up to a 6dB of loss. This is because as the frequency lowers, the wave length increases and at a certain point the baffle is "tiny" compared to the wave length and the wave wraps around the cabinet, and only half of the output is in front of the speaker as the other half is behind. In order to get a balanced SPL from bass to mid you need to account for this loss (partially or totally), and set the total SPL to a value in between (depending on the speaker location one can apply a total baffle step compensation, i.e. 6dB, or a smaller value, e.g. 3-4dB).
All this talk to say that if you have say a tweeter and a woofer both rated at 90dB, once installed in a box with an appropriate filter, the SPL of the woofer will be 84-87dB, and won't match the tweeter anymore, so at the end you have to attenuate also the tweeter.

Apart the l-pad, you can attenuate a tweeter also by using a single appropriate resistor in front of the tweeter filter.

Ralf
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Old 18th May 2015, 04:22 PM   #7
jReave is offline jReave  Canada
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There are 3 standard ways to pad a driver, 2 of which have already been mentioned:

1. L-pad which maintains the shape of the driver's FR

2. series resistance before the filter which tends to give an upward tilt to the response

3. series resistance after the filter which tends to give a downward tilt to the response

Numbers 2 and 3 will also result in increases to the impedance which can frequently be a useful goal; are perhaps a little easier to adjust when fine-tuning (changing 1 value instead of 2); and can also be combined together to achieve the desired response target.
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Old 18th May 2015, 04:28 PM   #8
rayma is offline rayma  United States
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Quote:
Originally Posted by ReDress View Post
the drivers I'm looking at are of different impedances, however, they have the same levels is spl.
At that point, do the differences in impedances still matter?
Most crossovers have the filter sections for each driver all in parallel, driven by a voltage source (the amplifier).
Each section is then electrically independent, and the driver impedance does not affect the other filter sections.
You could disconnect entirely one of the filter sections, and the others would not be affected electrically at all.

Last edited by rayma; 18th May 2015 at 04:35 PM.
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Old 20th May 2015, 09:31 PM   #9
ReDress is offline ReDress  Canada
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Perhaps as an extension of my question - if the two drivers are of the same impedance, yet have different degrees of spl sensitivities, how would one be able to match them so as to have them attenuated to the same level (ex: a tweeter and woofer of the same impedance, yet the woofer has higher spl levels, how would they be attenuated and matched to the same level) Or does this not matter as long as the impedances are the same?

Thanks in advance for the continued help guys. Much love
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Old 20th May 2015, 11:19 PM   #10
AllenB is offline AllenB  Australia
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If the tweeter wants less power then it needs less current and that equates to a higher impedance. You can arrange it (using a series and a parallel resistor, an L-pad) so that you have 8 ohms and lower tweeter level but in this case you'll pass more current than you need, the extra current is deliberately wasted.

It's a choice, and the amp will respond the way it responds, which will typically be no different. Most amps present a low source impedance and will be fine either way.
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