Hurting my head- when you connect tweeters to front speakers- what's happening?

[azneinstein]

Alright, excuse this uber-noob question but I'm trying understand the electrical fault aspects of this. I understand loads and impedance- but how "bad" is it when you connect tweeters (with cap) directly to the +/- to your front car speakers. Not separates, but me adding a tweeter to my coaxials.

So when you do that, you're effectively putting: 4ohm tweeter+4ohm speaker in parallel creating a 2 ohm load? (tapping tweeter cables directly to front speakers' cable +/-)

Is it because the tweeter doesn't require much power? Since this is all powered through a headunit, wouldn't this cause it to die because of the lower resistance load at 2 ohm? (doesn't the amp see a 2 ohm load regardless?)

Does that mean that an amplifier, rated at 4ohms CAN go to 2 ohms as long as you're not pushing it causing it to overheat/overwork?

Trying to understand this part and can't find anything on it or explain this part, or say why it's okay, just thought that the ohm load would be the most important, and I can understand if we were in series and caused it to be a 8ohm which just reduces the output power of the headunit.

Finally, is this bad? This is something car audio does for years, it's not the best but for most, it works and definitely bring better highs. And fidelity-wise, how bad is it?

Thanks. - Ken

[Cal Weldon]

Hi Ken,

It maybe not a good idea but overloading an amp often takes more power than a tweeter takes so loading it down to 2 ohms in the upper frequencies might not trip your protection. That's more likely to happen in the bass area. Hopefully others with more knowledge than I will chime in with more info.

[AEIOU]

Yes, the overall impedance will drop to 2 ohms. But, the additional tweeter has a high pass crossover (capacitor) so the impedance drop will only occur in the frequency range covered by the tweeter. The impedance will still remain at 4 ohms below the tweeters crossover frequency.
Is it bad for your amp? It depends on how well your amp can handle 2 ohm loads at higher frequencies.

[azneinstein]

Cal, AEIOU- Thanks for the info. So to my understanding...

I knew that high freq requires much less power (duh) but I didn't make the correlation that the tweeter's spectrum was the only part that would receive the 2-ohm load, I had the assumption that the overall load would dictate mainly the amount of power- so the woofer would also get 2ohms stressing the Headunit or creative a high high enough load.

I understand what we're doing now, 4 ohm load only on the woofer spectrum, and 2 ohm on the tweeter part.

When do you or a speaker builder have to finally account for the tweeter's impedance?

(off topic) If I was building a 2-way 8-ohm bookshelf, would it be better then to:
Woofer (8 ohm) + Tweeter (whatever ohm I want) in series
Woofer (4 ohm) + Tweeter (4 ohm) in parallel to achieve a 8 ohm overall impedance (but now I'm assuming that the entire woofer will get the 4 ohm load, overloading the 8-ohm amplifier based on the above understanding)

[AEIOU]

If you use an 8 ohm woofer and a 4 ohm tweeter with a crossover then the impedance will be 8 ohms in the frequency range covered by the woofer (bass) and the impedance will be 4 in the frequency range (treble) of the tweeter.
Don't concern yourself so much with impedance, no need to math woofer and tweeter impedances. What you need to concern yourself with is woofer and tweeter SPL/sensitivity. The should match or at least the tweeter should have greater SPL/sensitivity because a tweeter is easier to attenuate.

[Cal Weldon]

Originally Posted by azneinstein

Woofer (8 ohm) + Tweeter (whatever ohm I want) in series

Until you have a better understanding of this game, best to stay away from series crossovers (I am guessing this is what you mean) An 8 ohm woofer and whatever ohm tweeter in parallel will give you an 8 ohm load. The largest demand on your amp is the bass as you know so that's the important area to focus on. Not to say the tweeter's not important but as far as your amp is concerned, it is less.

Woofer (4 ohm) + Tweeter (4 ohm) in parallel to achieve a 8 ohm overall impedance

No, if the two drivers were the same that would give you a 2 ohm load. Since they are each covering a different part of the spectrum their impedances are separate so a woofer and tweeter both 4 ohm gives you a 4 ohm load.

[AEIOU]

You never wire a woofer and tweeter in series with each other, without a crossover. Whatever current is flowing through the woofer is going to go through the tweeter too. However, who would hook up a tweeter without using a crossover?
Series wiring without a crossover adds impedances, parallel wiring without a crossover divides impedances, regardless if they are woofers, tweeters or woofers and tweeters.
4 ohm tweeters are sometimes too loud/bright and often require some attenuation. A simple series resistor with the tweeter will attenuate the tweeter while at the same time increasing the impedance to the amplifier.

Originally Posted by azneinstein

Cal, AEIOU- Thanks for the info. So to my understanding...

I knew that high freq requires much less power (duh) but I didn't make the correlation that the tweeter's spectrum was the only part that would receive the 2-ohm load, I had the assumption that the overall load would dictate mainly the amount of power- so the woofer would also get 2ohms stressing the Headunit or creative a high high enough load.

I understand what we're doing now, 4 ohm load only on the woofer spectrum, and 2 ohm on the tweeter part.

When do you or a speaker builder have to finally account for the tweeter's impedance?

(off topic) If I was building a 2-way 8-ohm bookshelf, would it be better then to:
Woofer (8 ohm) + Tweeter (whatever ohm I want) in series
Woofer (4 ohm) + Tweeter (4 ohm) in parallel to achieve a 8 ohm overall impedance (but now I'm assuming that the entire woofer will get the 4 ohm load, overloading the 8-ohm amplifier based on the above understanding)

[Jamii]

you guys are forgetting about impedance rise of the speaker.... a driver coil is effectively an inductor (measured in mH), so depending on inductance as Frequency rises, the impedance of the speaker will rise... your coax might be up around 12ohms @ 10khz.... I wouldn't worry about it. It's the sensitivity (SPL/1W), and appropriate x-over point you need to worry about...

more information...
http://www.churchsoundcheck.com/imp1.html

[AEIOU]

No, I didn't forget it at all, I'm quite familiar with inductive reactance.
No need to overly complicate an explanation to someone who has difficulty understanding loudspeaker impedance to begin with.
If you want laboratory grade accuracy, you cannot approximate the impedance, you need to sweep (measure) the impedance.
Impedance numbers such as 4 or 8 ohms are only generalizations. Also as I'm sure you already know, the rising impedance due to voice coil inductance can be compensated for with a Zobel.

Originally Posted by Jamii

you guys are forgetting about impedance rise of the speaker.... a driver coil is effectively an inductor (measured in mH), so depending on inductance as Frequency rises, the impedance of the speaker will rise... your coax might be up around 12ohms @ 10khz.... I wouldn't worry about it. It's the sensitivity (SPL/1W), and appropriate x-over point you need to worry about...

more information...
Loudspeaker Impedance

[Jamii]

I agree, must draw a line in the sand somewhere! But sometimes it takes just a bit of extra information for the concept to *click* make sense... that was my experience learning electronics as a trade, anyhow.

Also, as far as my experience goes with 1st order crossovers, they work well - as long as you match the tweeter to the woofer (or coax, in your case).

There is a bit more to it than that, finding a suitable tweeter and x-over point, but i can't find the words to easily explain it right now.

Cheers!