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How do you figure the impedance for each side?
Car speakers are usually 4 ohms each. Therefore at high frequencies each side has a 3-way and a tweeter in parallel, resulting in 2 ohms.
Adding the woofer lowers the resulting impedance at low frequencies the same.

The TDA1554 IC is designed to power no less than 4 ohms for each side, so it is overloaded at both low and high frequencies.

You need to add a separate amp to power the tweeters and you should add a 3rd more powerful amp for the woofer. I have never seen a woofer connected to both channels like you have, but I guess it will work allright. This connection does not give you separate control of woofer and tweeter levels but maybe resistors can be added to the tweeters to attenuate them.

The tweeters should have capacitors in series with them to keep low frequencies out of them. The woofer should have an inductor in series with it because woofers play medium frequencies strangely. Try it without an inductor and if you don't like the sound, an inductor can be added later. The inductance of the woofer prevents it from being in parallel with the tweeters so the amp isn't overloaded.
The system will end up looking like this:

post-1706-14279142481095_thumb.png

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Hi

Mukhalled, how did you measured the impedance of the speakers?

Audioguru, dont you think the amp #2 is going to be slant loaded by the subwoofer speaker? There is speakers with 2 voicecoils, specially made for this purpose.

The right way to do it, i belive, is to use one amp for the subwoofer and an active filter and a summing amp before that.

//Staigen

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Hi Mukhalled,
If the 3-way speakers and the tweeters are all 4 ohms each, then each amplifier has a 3-way speaker in parallel with a tweeter and has a 2 ohm load at high frequencies. Therefore the amp is overloaded.
You probably measured the DC resistance, but the capacitor in series with the tweeter prevented you from measuring it.

If your woofer is also 4 ohms then the amps are also overloaded at low frequencies.
Since the woofer is connected between different amps then you can't measure its resistance in parallel with a 3-way speaker.

Your amp is overloaded and will fail! :o
I use Microsoft Paint to copy, paste and sketch schematics.

Hi Staigen,
I think Mukhalled discovered a cool way to power his woofer in mono. Then he doesn't need to replace it with a dual voice-coil one. The amps for the tweeters won't even notice its odd wiring. If he needs more power for it then he'll need a separate amp for it. ;D

post-1706-1427914248121_thumb.gif

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Hi again,
It was hard to draw schematic circuit so i took the one that Audioguru did before and made some changes on it  ;D.
When I measured the impedance like it shows in the attachment, I disconnected the amplifier and it was not 4 ohms but i added some resistors in parallel, then it became 4 ohms  8). This was the right side. I measured the left side and did the same thing to get 4 ohms.
*(There is a filter connected to the bass speaker to get low frecuencies)

post-3826-14279142481373_thumb.png

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Hi Mukhalled,
Don't do that!
By adding 4 ohms to the amp now its load impedance is 1.33 ohms.

Hi Staigen,
Mukhalled previously sketched the speaker system that shows each channel with a 2 ohm load at high frequencies, and a 2 ohm load at low frequencies, with the heating brilliantly divided between the amps for low frequencies.

The amps attempted to drive peak currents of at least 5A though the speakers but the absolute max peak current rating of the TDA1554 IC is only (!) 4A.

Amps don't have a massive current capability like the mains where you can keep connecting stuff in parallel with it. Now Mukhalled added even more stuff as a load for his amp.

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Mukhalled,
You can't measure impedance with an ohmeter, just measure resistance. You can't measure the resistance of the tweeters because they have a capacitor in series with them. You can't measure the resistance of a channel including the woofer because the woofer is connected between different amps.
The 3-way speakers also have a cap in series with their mid-range and tweeter parts so you can't measure the resistance of them, just the woofer part of them.

A 4 ohm speaker has a resistance of about 3.5 ohms plus the resistance of your meter's probes.

Please show a sketch of the amp, speakers and the resistors you added. ;D

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Hey Mukhalled, you must use AC to measure the impedance. In this case you also must use several freqs to get a usable measurement, say at 100 Hz, 200 Hz, 400 Hz, 800 Hz and so on, but i would not do it that way, i would have used 3 or 5 amps, one for the subwofer and the others for the other speakers.

//Staigen

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You could measure the resistance by connecting to a signal generator and measureing the voltage drop (use a true RMS meter or oscillosope) at differant frequencies when the speakers are connected to it, if you know the internal resistance of the signal generator then it's quite easy to calculate the impedance connected accross it.

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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?

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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

post-1706-14279142482342_thumb.png

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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?

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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

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