Axiom Home Page Forums General Discussion Home Theater Center Channel Options

I currently have an M3/VP150/QS8/M3 setup (lexicon logic 7 based processor... running 7.1). I am debating going to two center channel speakers for two reasons:

1. I run a front projector so I have a lot of room up there.
2. I want to put my tube amp front and center (it is a big beast) for aesthetic reasons.

Given this, what would be the effect of:
1. going from the VP150 to two VP100's
2. going from the VP150 to two M3's
3. in either of the above, wiring the two speakers in series and plugging them into my Anthem MCA 5 (it should be able to take the load... I think ;-)

Any comments/suggestions are welcome... and thanks! Note I was debating selling it all and going to a totem dreamcatcher system, but I would have a very hard time parting with the QS8's... simply a great side surround speaker!

Why not just add another VP150? If you hook them in series the load becomes 8 ohms, and your amp will not have any problems with running them.

My reasons for not getting a second VP150 are:

o cost (though with selling used... it may work out the same)
o size (may be a little too overwhelming)
o amp load. I thought it would be going down to a 4 ohm load (or thereabouts)... I do not see how more drivers could be easier to drive.

Thanks!

The resistance doubles when you connect them in series not divides. so two 4 ohm speakers look to your amp like one 8 ohm speaker. In the case of the VP 150 which is 6 ohms the load would be 12ohms, Simple rule is Less Resistance=More Current, the higher ohm load is easier for your amp to drive. You can refer to the post in technical questions by fhw for more details on resistance vs load.

Regards
John.

Quick lesson on resitive loads from an EE:

When adding resistors in series, the total resistance adds sequentially. If R1 is 6 Ohms (as is the case for the VP150, not 4 as suggested above) and R2 is 6 Ohms, the two in series (+ of one connected to - of the other and the + of the first connected to your receiver's + with the minus of the other connected to the - of the receiver) add to 12 Ohms. I don't know enough about receiver fault tollerances to know whether or not that would be high enough to trigger a protection circuit and turn off the unit, but it would half your power output.

Adding resistors in parallel is basically the inverse. If RT is the total resistance, it looks like this:

1/RT = 1/(R1 + R2 + R3 + ... + RN)

If all the loads are the same value, that works out to dividing the that value by the number of loads. In the case of the VP150, that means a 3 Ohm load which again might trigger some sort of fault circuit, I don't know. It would also effectively double the power draw from your amp, minus whatever voodoo they've employed.

Bottom line, call your amp manufacturer and find out if it has any goofy circuit or if this could be damaging.

Gentlemen... thank you very much for the education... I am a slow student however and have a couple of more questions ;-)

John... I read your bit in the technical questions area. Is it simply the case that the 12ohm load is simply too "wide open" for some amps and I could have trouble driving it... or does this go into the realm of safety. I have always assumed the higher you go the less you worry...

My other question is on sound quality... in a front projection system would two VP150's actually give a realistic effect or would it sound like everyone talking on screen is 8 feet wide?

Thanks again... I will do more reading to understand things better.

You are correct that the higher you go the safer you are but this has its practical limits as well. Suffice to say that your amp should not have any problems with a 12 ohm load. As Semi correctly states that the power will be cut in half but you should hardly notice this as ½ the power does not mean half the volume. For example going from 100 watts down to 50 watts would result in a 3-decibel loss of volume at rated power so it is not really significant.

As to the other question about every one being 8 feet wide. There are so many other factors that will come into play here it is hard to quantify this in a simple statement. If the 2 VP150’s are strung across together I don not think it will be an issue, you could also make a small stand and double stack them if this is an issue. It would take some experimentation to see how best to place them. I have 3 VP150’s 1 is being used for center channel the other 2 are being used for rear effects, on the weekend I will try moving one to the center channel and see how it works.

The other thing to consider if you are concerned about the load there are device you can buy that will allow you to run the extra speaker on the center channel without changing the load.

Regards
John

Here's another note of encouragement for using two VP150's, however, it's not very significant.

I believe the impedence of a VP150 is not actually 6 ohms, it's 5.5 ohms. Therefore it's closer to 11 than 12.

OK. Patch sold me.

:P

Anthem MCA 50 5 x 180w @ 8ohm
Power Output
(Continuous RMS, 20 Hz - 20 kHz, <1.0% THD, AC line voltage held constant at full load)
Impedence(Ohm)------------- 8 --------- 4 --------- 2
# of channels driven ------- 1 -- all ---- 1 -- all ---- 1 - all
Watt -------------------- 225 - 180 -- 370 - 265 -- 535 - 340
Frequency Response
20 Hz - 20 kHz (-0.15 db); 5 Hz - 100 kHz (-2 db)

I think you amp should be good enough to drive a light bulb.
I'm planning to get a MCA 50 myself.