Some questions about a tweeter's power dissipation

[TheSoundNoob]

Greetings!

I got a bit confused while working on crossovers for a Project of mine, here's the situation:

In short, I'm planning to build some kind of diy portable speaker using four Dayton Audio DS175-8 woofers (two per side of the speaker for stereo) and two Dayton Audio ND25FW-4 tweeters (one per side, or that was the plan anyway) and use a car stereo headunit for amplification.

I modeled up a crossover in Xsim and all was going well until i checked the component power dissipation graph, which said that the tweeter would dissipate a lot more power than the woofers would in the system (There should be an attachment to this post with a Picture of what i mean).

This got me confused,
Is this normal?
The tweeter itself only has a power handling of 20 wrms, will this damage it?
This doesn't mean the tweeter will be louder, right?

I apologize if this question is a bit stupid, I'm really new to designing crossovers….

 

[Galu]

What happens if you take out the resistors?

 

[DanHat]

I do not understand the 10 ohms to ground in the tweeter circuit. That will sink some significant current. It seems to me you would need either a resistor or an lpad in series with the tweeter if you need to attenuate it. I do not see the need of resistors in series with the woofers. It seems that would just waste power and increase the effective qts of the woofers. That could possibly causing a boomy bass issue depending on the enclosure design.

 

[Jack Hidley]

The series resistor with the woofer is to create the shelved response in the low pass filter. In this case, since you need a system with a low resistance to get enough power transfer from the amplifier, you would be better off to drop them to the DCR of the inductor and add in a series resistor with the shunt capacitor to drop the Q of the low pass filter.

The resistor in parallel with the tweeters shouldn't be there. Make it a series resistor. It isn't going to make a lot of difference. It is dissipating 20W of power, but over 8khz, where there is no signal.

 

[DanHat]

As I understand it a shelf filter is a resistor in parallel with an inductor not in series with an inductor.

 

[Jack Hidley]

Dan,

The resistor can be in series or parallel. It will change the shape of the shelf response depending on where it is placed. When in series it makes more of a broad cut from Fcb*2 to just before the roll off of the LP filter.

 

[Galu]

I'm really new to designing crossovers….

In its simplest form, the crossover would contain no resistors.

Before adding resistors, be clear on how they are used to attenuate and to shape frequency response.

I have attached an illustration to show you what a bass shelving filter does, but will leave it to the experts to show you how to include one in your crossover!

 

[TheSoundNoob]

Alright, first off I'd like to thank you all for such fast and informative replies. You folks really do know what you're doing for sure!

It's definetely a good thing i decided to post here, because otherwise I would most likely have done something real foolish. I decided to follow Galu's advice and just ditch all the resistors in the circuit, given my lack of experience in the field. To be honest the frequency response looks fine without them, at least for a budget oriented portable system it should be fine. Also the car stereo I'll be using supposedly has a built in EQ so i could make some corrections there.

Massive thanks to everyone who replied though, very helpful!
I guess i learned from my mistake before even making it!

Cheers

 

[Galu]

Thanks for the feedback. As a beginner, you've made a good decision.

Don't hesitate to return when you're ready to take bigger steps.