Axiom Home Page Forums General Discussion Advice from Axiom Owners vp-150 8 or 6 ohm

You don't need to get a 400 watt amp to drive the M80s.You very well could get one with a lower rating.I would say the benifit of a seperate amp would be so not to be concerned about the amp running out of power on demanding loads.

That's a bit misleading, actually. Calibrating speakers doesn't mean they'll all play at the same level. After all, your surround speakers are rarely playing at the same volume as your mains. All calibrating does is ensure that if each of the speakers are fed a signal of the same amplitude, they will each produce sound of the same level.

In other words, calibrated speaker will sound as loud or soft as they're supposed sound with the material they are asked to reproduce. These levels are all relative to whatever your master volume happens to be set to, of course.

You certainly put into better words than I did.You are correct.

>>If all the speakers will play at the same level where's the benefit of having a 400w amp would i then need a 400w amp for all speakers to hear the benefits?

All good questions. There are a few reasons why having a bigger amp for the mains is a Good Thing :

1. When the DVD soundtracks are being mixed, the mains get most of the signal, followed by center, then surrounds. The center gets most of the dialog, however. What this means is that in a properly calibrated system you will be putting more sound out of the mains and will need relatively more power for those channels.

2. If you go with M80 mains you will have two channels which can't be driven by all receivers & amps. By putting those on a dedicated power amp designed to run all day at 4 ohms you ensure no problems.

3. Most receivers don't have enough power supply capacity to put out full rated power into all channels simultaneously. If you run two channels through a separate power amp that frees up more power supply capacity for the remaining channels.

Steve, regardless of what sort of receiver or separate amp you might use, setting it at a certain impedance(if it has such a setting)doesn't mean that you're "running" it at that impedance. As previous replies have said, the only effect of the lower impedance setting is to reduce the maximum voltage and therefore the maximum power available. You're not "losing" power by leaving the setting at 8 ohms; you're keeping the possibility of outputting maximum power, as long as the receiver/amp can handle it without shutting down. As to whether you actually need the maximum power which the receiver is capable of, that depends on factors such as your distance from the speakers, the size of the listening room, the dynamic range of the recording and your average listening level. It's entirely possible that you're not using all the power that you have now and that a slightly more powerful separate amp would be of no real benefit.

That's right. Best not to think of it as the "4 ohm" switch, but the "stupid government says we have to put this stupid switch on if you're going to run at 4 ohm" switch

So let me see if i have this right. Ohms are determined by the speaker not the reciever.The lower the ohm rating the more voltage required to drive it which equals more heat.So if i have a 4ohm speaker and my reciever is set to 8 ohm the speaker will try to draw the needed voltage which will produce more heat and possible damage my reciever.If i switch my reciever to 6 ohm setting telling it i have more difficult speakers to drive it will reduce the available voltage allowed to the speaker so it wont overheat.So its a saftey feature not a performance feature.kind of like a computer processor that will run at a lower mhz if it gets to hot so it does'nt fry.

I think i get it now i wonder how many people switch it thinking they'll get more power though.

So if i have a 20x25x8 room do you think one seperate amp 400wpc @4ohms for the mains with my yamaha 1400 110wpc@8 ohms will be loud enough? or would i be better served with more powerful amp for all channels?

Steve

Very close. You have the concept right but not all the words.

The lower the ohm rating the more current the speaker will draw for a given volume control setting... but it will play louder as a result. For a given loudness, a bit more power will be wasted in the amplifier with a 4 ohm speaker so it will run a bit hotter.

It is a safety feature not a performance feature. Exactly. Another way to get the same safety is not to play so freakin' loud that the amp is running wide open all the time

You definitely don't need a more powerful amp for all channels with that room size and speakers. A 400 wpc amp for the mains will take you into the "hot damn !!" range. The reality is that you would probably get away without ANY power amp as long as weren't playing loud music all the time -- the receiver will shut down if it starts to overheat -- but a good power amp on the mains will give you an extraordinarily nice system.

Have to go. Return of the Giant Hogweeds just came up on the CD player

Steve, as John said, the possible problem would be that the 4 ohm speaker would draw more current from the amplifier, the amp might start to overheat, and then its protective circuit would shut it off. Getting a little fancy, Ohm' Law states that current equals voltage divided by resistance(I=E/R), so if the voltage stayed the same but the resistance was 4 ohms instead of 8 ohms, theoretically twice as much current would flow, possibly creating an overheating problem. So, the lower impedance switch or setting reduces the maximum voltage(E)so that the lower R doesn't result in as much increased current(I). My suggestion would be to not make any assumptions about the adequacy of your 1400, which is a quite powerful receiver. Keep in mind that speakers of the sort that you'll be using draw about 1 watt at a comfortably loud average listening level. Split-second peaks might draw up to 100 watts or more, depending on several factors. See how things work out before you assume that you need more power.