Newbie questions - impedance and old speakers

[Soma]

hi board i have some questions i hope some of you can answer or direct me to the answers for.

my current setup is:
- onkyo receiver (http://www.onkyo-intl.com/products/av_components/av_receivers/tx-sr600/index.html)
- Mission M73i front floor standings (http://www.mission.co.uk/archive/m70i/loudspeaker_m73i-spec.htm)

and im about to add a 100w 4 ohm sub. i dont really understand impedance can someone explain it? the front speakers are 8ohm but the sub is 4 ohm will this affect anything? do they need to be the same impedance to work properly? ive searched on impedance but there is nothing about mixing speakers with different impedance.

also before i got the mission speakers i ran these (http://5oma.50megs.com/images/onkyo.jpg) old speakers on my amp. would running such old speakers with crappy speaker wire have affected my amp at all, or only damaged the speakers? i never had the amp up too loud or anything was just wondering.

im a ht newbie so go easy please. thank you.

[markw]

Is this a passive (non-powered) sub?

4 ohm speakers running singly might not pose a problem but when paired with other speakers, there might be problems.

By running a 4 ohm unit in parallel with other speakers you run the risk of having the overall impedance fall well below the 4 ohm level. (somewhere around 2.66 ohms). Now, if your amp can handle this then you're fine but few can.

You are best off geting a plate amp to drive that sub, or even a powered sub to begin with.

Check out partsexpress or madisound for these. Wire won't make a bit of difference here.

[Soma]

sorry i should have mentioned the sub is active (powered). does that mean it should make a difference and i can run a 4ohm sub with 8 ohm fronts?

[F1]

sorry i should have mentioned the sub is active (powered). does that mean it should make a difference and i can run a 4ohm sub with 8 ohm fronts?

Then it doesn't matter as the sub is powered by its own amp and it only draw insignificant current from the receiver. Your setup should be fine.

[Soma]

thanks for the comment I went and brought the sub and it has made a very noticeable difference and im very happy

one thing I do notice though is when i turn my amp off the sub makes a loudish "boom" noise.. what could cause this?