calculating ohm demand on amp with parallel connections

[mike c]

I already know that 3 8ohm speakers in parallel has a 2.6ohm demand on an amp with the simple formula 8 divided by 3.

but what formula do I use when I want to know:

16ohm + 8ohm = ?

 

[j_garcia]

The real question is, what exactly are you trying to do?

You can visualize the result as a single imaginary speaker (Figure 2B), whose impedance is represented by Zt. Zt stands for the equivalent-load impedance, while Za and Zb represent the impedances of speakers A and B, respectively.

Equation 4: Speakers in Parallel
Zt = (Za x Zb) / (Za + Zb)

According to this formula, a 16 + 8 would yield a 5.3 Ohm load.

Gotta be careful when combining speakers because you have to look at the demand on the amp - you do increase the theoretical output of the amp with a lower impedance, but that power isn't free: the amp still has a max limit and more speakers draw more current leaving you with less operating headroom. Impedance also varies with frequency.

 

[mike c]

you remember the pipe in music project I was planning awhile back ...

I got 6 pairs of speakers on a 6 channel amp capable of 4 ohms. if my math is right, I don't even need impedance matching VC's.

anyway, my thought was, would the sound be affected by impedance matching VC's ... 8 ohm to 16 ohm, I was thinking of using non impedance matching VC's for my other 3 VC's (I already have 3 IMVC's) so it would present the 5.3 ohm load on the amp.

do you have the formula for more than a pair of speakers?

thanks btw

 

[j_garcia]

I'm not sure what you're asking in the second part? OK, 6 channels, 6 pairs of speakers - you are fine without IMVCs. If the speakers are being driven by individual channels, then you don't have to worry about the total impedance, as that is per channel only.

 

[PENG]

In case you want to know how to calculate the equivalent impedance of more than 2 speakers, the more general forumla is:

1/Zeq=1/Z1+1/Z2+1/Z3+.......+1/Zn (Req=equivalent impedance)

Formula is one thing, but please be reminded that in your example of 16 and 8 in parallel, if the 16 could dip frequently down to 8 and the 8 down to 4, then in the worst case scenario, the amp will see 8 and 4 in parallel, giving an equivalent of 2.66 ohms (see formula in j Garcia's post) if they dip to their minimum at the same time. Not likely but be aware that it could happen.

 

[mike c]

I was wondering if I had made a mistake in buying IMVC's when my amp could handle the 6 pairs (which are all 8 ohms)

thanks PENG for the multiple ohm load formula

my question would be ... for a pair of speakers that are naturally 8ohms, if we were to use an IMVC that would let the amp see it as 16ohms ... would that affect SQ?

 

[PENG]

I was wondering if I had made a mistake in buying IMVC's when my amp could handle the 6 pairs (which are all 8 ohms)

thanks PENG for the multiple ohm load formula

my question would be ... for a pair of speakers that are naturally 8ohms, if we were to use an IMVC that would let the amp see it as 16ohms ... would that affect SQ?

Depending on the particular design, it may affect SQ, but not sure how audible it is.

 

[dave1490]

I already know that 3 8ohm speakers in parallel has a 2.6ohm demand on an amp with the simple formula 8 divided by 3.

but what formula do I use when I want to know:

16ohm + 8ohm = ?

check out this site give,s the math for different ohmage and wattage.for Series/Parallel Wiring.



http://www.termpro.com/articles/spkrz.html

 

[mike c]

thanks PENG and dave1490

 

[jcPanny]

House speakers

Regardless of whether you need the impdance matching feature, use VCs so that you can adjust the volume or turn the music off in each room. Otherwise you will have a single volume control on the pre-pro or amp for all of the speaker.

Just wire 2 speakers in parallel to each amp channel if they are all 8 ohm speakers and the amp can handle 4 ohms. Series and parallel combinations will complicate wiring and cause different speakers to receiver different amounts of power from the amp.

 

[mike c]

but I was thinking of ordinary VC's for the rooms (non IM)... but I agree, better safe than sorry.

 

[annunaki]

One key thing to remember...

Electricty follows the path of least resistance. A 16 ohm load and 8 ohm load should not be used in parallel on the same channel. The 8 ohm load will get a disproportionate amount of the power as opposed to the 16 ohm load.

 

[mike c]

i didn't know that ... it would seem most hobbies/fields have the same concept.

my koi hobby (I design our own filtration systems) says water follows the path of least resistance ...
designing exhaust systems in our basement also proves that air follows the path of least resistance ...

 

[Tomorrow]

Guys,

Thanks for all the good information and tips in this thread. I've been wondering about it..........