[apl175]

After much thought, I've decided to see if I can replace the factory PA-300 amp in my car with something a bit more responsive. A number of posts here have stated this is a good start, rather than replacing the speakers first (I have the Premium sound system).

I know that the existing speakers are 8 ohm, per this website:
http://vccs.volvocars.se/acces...7.htm

but i know that nearly all automotive amps are 4 or 2 ohms. What part am I missing? Can I use a 4 ohm amp to drive the 8 ohm factory speakers?

Is the total impedance actually less than 8 ohms, because multiple speakers are attached to each channel?

Thanks
2005 V70 2.5T

 

[MrTippy]

Re: 8 ohm speakers - 4 ohm amp? (apl175)

Yes, the speakers are wired in parallel so the resultant impedance is, I'm guessing, around 4 ohms.

You'll have no problem using an amp that is rated for 4 ohm speakers--and it would work for 8 ohms speakers, too, the output would just be correspondingly lower.

The PA-300 is servicable. You would probably be more satisfied with the effects of a good equalizer or digital sound processor first, e.g. in going from the the HU-613/803 to the HU-650/850, Volvo attenuated the bass response substantially.

 

[LloydDobler]

Just for reference, what you never want to do us use lower ohm speakers on an amp that isn't rated for it. It'll drive too much current. If the amp (or head unit) has overcurrent protection, it'll just shut off with no damage. If it doesn't, it'll kill the output transistors.

But yeah, the Volvo 8 ohm speakers are wired in parallel to give a 4 ohm load on each channel, as far as I know.

When it comes time to do the speakers, do NOT install 4 ohm speakers in your rear doors unless you disconnect the 8 ohm speakers way back in the rear pillars (assuming you have them), as the resulting load will be 2.6 ohms.

 

[SiCkEsTC30]

You shouldnt run different ohm amp and speakers. 8ohm speaker requires less current than a 4ohm speaker. So if you really want a 4ohm amp get 4ohm speakers also. But if you run the 8ohm speakers with the 4ohm amp you need to run them in parallel. This is how to calculate parallel wiring.

Resistance = (Speaker A x Speaker B) / (Speaker A + Speaker B)
Resistance = (8 Ohms x 8 Ohms) / (8 Ohms + 8 Ohms)
Resistance = 64 / 16
Resistance = 4 Ohms

 

[Jexx]

Re: (SiCkEsTC30)

Quote, originally posted by SiCkEsTC30 »

You shouldnt run different ohm amp and speakers. 8ohm speaker requires less current than a 4ohm speaker. So if you really want a 4ohm amp get 4ohm speakers also. But if you run the 8ohm speakers with the 4ohm amp you need to run them in parallel.

For sake of clarity.

Of course it is desirable to run speakers at the same impedance as the amp, but you CAN run higher ohm speakers with a low impedance amp (i.e. 8ohm speaker with a 4ohm amp), as Mr. Tippy suggested. Of course, the downside is that the amp won't put out as much power. It won't hurt anything to do so. Sometimes this is even done on purpose to limit the amplifier's power output and not blow the speaker.

But, you cannot run speakers with a lower resistance than the amp (i.e. 2ohm speakers with a 4ohm amp). The amp will shut down, or, more likely honestly, will fry something in the power supply.

While the formula provided works, parallel resistance can be calculated far easier: divide the single speaker resistance by 2. Thus:

8/2=4 ohms.

 

[LloydDobler]

Re: (Jexx)

Quote, originally posted by Jexx »

While the formula provided works, parallel resistance can be calculated far easier: divide the single speaker resistance by 2. Thus: 8/2=4 ohms.

That only works if the speakers are the same ohm rating. Be sure to use the formula for non-matching speaker impedance because it goes non-intuitive really quickly.

 

[Jexx]

Re: (LloydDobler)

Quote, originally posted by LloydDobler »

That only works if the speakers are the same ohm rating. Be sure to use the formula for non-matching speaker impedance because it goes non-intuitive really quickly.

Well yeah, but that's pretty rare in car audio.

 

[Boogs]

Re: 8 ohm speakers - 4 ohm amp? (apl175)

I replaced the front door speakers in my 850 turbo wagon and I noticed that the dash midranges were 8-ohm whereas the doors were 4-ohm. If they are wired in parallel the load would probably be around 6-ohms. I'll put an ohm meter on and verify this, however I'm planning on replacing the lousy 2" paper woofers with actual tweeters. I can barely stand the stock system in the wagon especially coming from the Monsoon system in my GTI.

Where is the stock amp located?