Axiom Home Page Forums General Discussion Technical Questions two speakers running in parallel

Because of localization of of the centre sound, I am going to try and run two VP100s in parallel - one above and one below the screen. Would i need to set my receiver to 4 ohms in the speaker coonfiguration?

thanks in advance!

Ian

No, because setting your receiver to 4 Ohms limits the available power. What receiver are you using?

From Audioholics

What Doesn't Matter?
Impedance Selector Switches
This so called feature, used by some manufacturers, is designed to prevent overheating of the receiver or damage to its output transistors because of excessive current flow. The manufacturer accomplishes this in one of 2 ways: 1) Stepping down rail voltage supplied to the power amp or 2) feeding half the signal strength to a voltage divider of power resistors. Both of these methods severely limit dynamics and current capability of the power amp. This results in an audible decrease in bass capability and dynamics transient sound because the 4 ohm setting effectively increases the receiver's output impedance. Unfortunately many manufacturers put these features on their products to ease customer concerns with driving low impedance loads and for safety reasons when getting UL approvals. Note: In order to meet UL requirements, a receiver cannot be rated down to 4 ohms without having this switch onboard. Receivers without this switch are usually rated down to 6 ohms. In most cases, well designed receivers can easily handle 4 ohm loads safely and efficiently. It is highly recommend to keep the impedance switch set to 8 ohms regardless of your speakers impedance and make sure your receiver has plenty of ventilation.

I have the Onkyo TX-NR905. The manual states to select 4 ohms if the impedance of any speaker is 4 ohms or more but less than 6.

It was my unbderstanding that connecting the speakers in parallel drops the ohms in half. So i was just wondering if i have to compensate for this or use the native ohm rating of the speakers.

Thanks!

Ian, that's correct that connecting two speakers of equal impedance in parallel has the effect of reducing the net impedance to one-half the previous value. As the Audioholics article explained, setting the receiver to a lower impedance value is simply a safety type of feature required by various regulations to help prevent overheating; it in no way optimizes the receiver for the lower impedance. By reducing the maximum voltage that the receiver power supply can deliver, the maximum current and power are likewise reduced, following Ohm's Law. So, although the chance of overheating is reduced, so is the maximum performance possible. Therefore directions in manuals to do this should be disregarded and the impedance setting left at the higher value.

Thanks for the advice. I will leave it at 8 ohms to keep max performance of the speakers.

Ian

Ian, you shouldn't have any problem driving 4 Ohm speakers with that receiver.

I think it's about high time we start lobbying receiver manufacturers to begin including two center channel speaker outputs on their units. There seems to be a real trend here to go with two centers, one above and one below the screen, and I'll betcha there'll be more next year, and the year after that! And it's just about time that the receiver dudes start steppin' up to the plate! Yeah!

Maybe the manufacturers(listening; guys?)can even dedicate an unused rear channel to be switchable to front duty on some new digital amps currently in development.

I'd like to add another center below my 65" Mits too. But since it's a RPCRT I don't have room to add another M3 just below the screen. There is about an inch and a half indentation down there and I may be able to carefully snuggle in a W3 without too much surgery to the TV, maybe.

I would love for recievers to be able to assign the amps to outputs. Right now I am not using my rear amps for 7.1, I could easily use one of them to drive one of my centre channels...this is a feature that should be a MUST in my opinion.

I used to run a VP150/VP100 pair in parallel with superb results on the center channel perception at the sitting point (clarity, imaging, etc). At the current setup at my father´s, they are still running like that for multi-channel audio (no video setup).

Talking about the trend on the two centers, I have seen that post several times on this forum. For those with the size and adequate spacing, the results from running above and below the TV sets has been awesome.

For projection screens, there is several members that mentioned many times centers composed of a pair of mains (M3´s for example, even a setup with 5 M80´s), but the deal is the same, driving a pair of speakers as centers.

I havent seen yet any manufacturer that goes into the double-center option, but that is an idea to see in the future releases.

AAS