Bass/Treble System

[Mukhalled]

hi,

I had already seen the lables of the speakers and calculated the impedance of them. The tweeters 8ohms each, 3-way speakers 4ohms each and the woofer 6ohms. if we calculate the one side without the woofer it will be 2,67ohms impedance, but the woofer is connected to both sides so how shall I do?

 

[Mukhalled]

Can't I measure impedance with ohmeter? ( with ohmeter I meant true RMS) isn't it the same thing? i may chose wrong word

 

[audioguru2]

Hi Mukhalled,
A multimeter measures DC voltage and current, AC voltage and current, and DC ohms. The AC voltage might be measured in "true RMS".
To measure impedance you need a signal generator with a known output resistance that feeds different frequencies to the load to be measured. You measure the voltage across the load with an AC voltage meter and record the voltage divider action of the resistance of the generator with the impedance of the load. Then Ohm's Law calculates the load's impedance for each single frequency.

Now we know the truth of the impedance for each speaker. The calculation of the amount of impedance for each channel is simple. Your amp is definitely overloaded!

Usually woofers (actually called sub-woofers) are driven with a higher power amplifier. Your woofer has an impedance higher than the 3-way speakers, and it is only one, so if you power it from a 2nd identical amp, its power will be much lower than the 3-way speakers.
The total power of your 3-way speakers is 28W when the car battery is 13.2V. The power of your woofer would be only about 11W. The system would sound awesome if the woofer had a 100W amp. ;D

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[Mukhalled]

Thanks, Audioguru (my teacher  ;D) for the clear explanation.

So my amplifier is overloaded now  :-\, what can i do to not overload it (to make the impedance suitable, in other words 4ohms)? But the problem is that I'm a little bit stubborn  ;D, I wanna keep those five speakers ( 2 tweeters, 2 3-way speakers and 1 sub-woofer).  ???

I need your help
*Are you electronics engineer sir?

 

[audioguru2]

Hi Mukhalled,
I'm glad you understand. I remember when you built the amp and complained about its distortion when you turned up the volume. The overloaded amp was complaining back to you!

If you add resistors in series with the speakers to increase their total impedance to the amp's 4 ohm rating, then the toal power of 14W for each channel will be divided into the resistors reducing the level of the speakers, and then the speakers won't have damping from the amp.

Instead of adding a 2nd amp only for the tweeters and a 3rd more powerful amp for the sub-woofer, you could disconnect the tweeters on the 3-way speakers and your existing amp would drive the 3-ways and tweeters without overload. You could also add a capacitor in series with the 3-ways to reduce their bass, then the sub-woofer can be connected like now without overload.

My new car came with an awesome sound system. They claim 228W! The rear speakers are 2 ohms each (i've never seen 2 ohm speakers before) and are probably about 20W each. The front speakers are probably 4 ohms and are 14W each. The tweeters are probably 8 ohms like yours and are 4W each. Then the remaining 152W is given to the 10" sub-woofer.

I used to be an audio electronics engineer and actually got paid well to do things I love to do. Now I am a retired old bum, chatting on the web and getting paid occasionally for some consulting. ;D

 

[Mukhalled]

Okay, I thank you again Audioguru for the support and I might ask many many times again in the future  ;D. I'll do what you recommended and i'm sure it will work better because i trust you  .

I also wanna thank Staigen & Alun  ;D

Best wishes,
Mukhalled