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Old 05-28-2015, 02:18 PM
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Question Lowering power to the tweeter with affecting other spks

How do I cut power to a tweeter? I have 2 mids and 1 tweet per channel. The tweet is 8 ohm the mids are 8 ohms each wired to 4 ohms, with the amp seeing 2.6 ohms. I was going to build my own HP and lp crossovers for these. Can I add something to the crossover? Thanks
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Old 05-28-2015, 04:11 PM
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Correction of title. I need to cut power to tweeter and not the other speakers.
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Old 05-28-2015, 04:42 PM
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To simply lower the volume of the tweeter in a circuit that includes only the tweeter (like a tweeter being used on it's own channel), you can use a resistor in series. For a reduction of -3dB for example, you would use a resistor of 3.3ohm assuming an 8ohm nominal speaker. The amp would see a total nominal resisitance of 11.3ohm.

This, however, won't work if you've already taken into account an 8ohm nominal load if you've already configured the crossover. By padding the tweeter with a resistor, the rest of the parallel circuit now sees a nominal 11.3ohm load.

To fix this, you need to form a fixed L-pad with a parallel shunt resistor in place. You can go to this website to calculate you values:

L pad calculator - attenuation dB damping impedance decibel loudspeaker speaker voltage divider - sengpielaudio Sengpiel Berlin

To lower the volume of an 8ohm tweeter by -3dB (for example) but keeping the rest of the "upstream" crossover components working as they should, you need to insert a ~2.3ohm resistor in series with the speaker, and a ~19.3ohm resistor in parallel with the tweeter.

I will also note that you have other problems in the way you assume crossovers work. A nominal 8ohm tweeter wired in parallel with two 8ohm mids will not produce anywhere near a 2.3ohm nominal load at any frequency. The lowest dip you would see in impedance would likely be about an octave higher than the fs of the mids (or the fb of the enclosure, assuming a sealed design and not a free-air speaker) after the Q effects taper off and you're left with a more resistive load. It would be safe to assume that around this point the nominal impedance of each driver will be paralleled to produce a final load of around 4ohm. You can model the drivers and get an idea of the impedance minimum (Zmin), or run your own impedance sweeps to know for sure though.
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Old 05-28-2015, 08:27 PM
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I read your info spleclipse about thirty times, it make some sense to me. If I hook up the 2 mids wired together(4 ohms nominal total) with a crossover and the impedance of that(.187 ohms) Separately to the amp from the tweeter(8 ohms nominal) and That crossover being(.38 ohms), will the amp see a parallel circuit? Simply just running separate wires for the mids and separate wires for tweet per channel. Can I just put a 3 ohm resistor in series between the tweeter and the tweeter crossover? Or do I need to do the l- pad?
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Old 05-28-2015, 09:32 PM
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Quote:
Originally Posted by Potsy1 View Post
I read your info spleclipse about thirty times, it make some sense to me. If I hook up the 2 mids wired together(4 ohms nominal total) with a crossover and the impedance of that(.187 ohms) Separately to the amp from the tweeter(8 ohms nominal) and That crossover being(.38 ohms), will the amp see a parallel circuit? Simply just running separate wires for the mids and separate wires for tweet per channel. Can I just put a 3 ohm resistor in series between the tweeter and the tweeter crossover? Or do I need to do the l- pad?
Where are you getting those impedance figures (.187 and .38)?

Crossover points and slopes are correlated to impedance. For some crossovers (such as a simple 1st order HPF), you can put a resistor in series with the capacitor (the only component in a 1st order filter) without a need for a shunt resistor. For higher order or more complex filters, you have to use a shunt resistor to make the tweeter "look" like it's still an 8ohm speaker to the rest of the crossover components even though its impedance is increased to attenuate the volume.

So I guess another question is: can you show me what kind of crossover you're trying to build?
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Old 05-28-2015, 09:53 PM
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I want to build a second order linkwitz-riley. I got them numbers from the inductor specs.
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Old 05-28-2015, 09:59 PM
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Seems like the dictionary would be helpful. Thanks for being patient, I'm new at this.
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Old 05-28-2015, 10:11 PM
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Www.apicsllc.com/apics/misc/filter2.html. I'm looking at the second order
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Old 05-28-2015, 10:32 PM
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You wouldn't include the DCR (direct current resistance) of the inductor in your calculation of impedance the way you did, although it will have an effect. Here's a bit more on the resistance of inductors and signal loss:

The Loudspeaker Crossover Part II: Capacitor & Inductor Issues | Audioholics

The link you posted doesn't work, but there are many websites out there that will provide you with the parts you need for a textbook 2nd order crossover network. Just remember to calculate the parts for the tweeter using the tweeters DCR (8ohm or whatever) and the combined DCR of the mids (which should be around 4ohm). Each "leg" of the crossover (HP and LP) can then be run in parallel from the same speaker lead so everything works from a single channel.
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Old 05-28-2015, 10:55 PM
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This shows diagrams after you enter the impedance and crossover frequency etc...
2-Way Crossover Designer / Calculator
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