HELP: 8 ohm speakers on a 4 ohm amp?

solidus

Standard Member
I am about to buy an LG wireless universal speaker kit to make my rear surround speakers wireless (G4TV review). I currently have a 5.1 set of 8 ohm 100w Energy Take Classics. The LG gear is said to work with 4 ohm 100w speakers. Will I run into any trouble if I do this hook-up?

One more thing. I wanted to get a Yamaha VX863 receiver rated at 105w/channel with these 100w Energy speakers. Was that stupid? Wait, it gets worse. The store I went to only had the HTR6180 model, which I thought was 100% identical to the VX. I got home and realized that the HTR is actually rated at 120W/ch. I will be blowing those 100W Energy speakers pretty quick, won't I? I don't actually intend to run the amp at 100% volume, being in a condo and all, but it's still not a good idea, right?

I got a killer deal on the speakers and would still love to keep them if possible with this receiver. I noticed that the volume display goes from -80db to +16db on it. Can I just find out at what setting will it be delivering 100w/ch? I saw that the 5.1 Yamaha HTR-6030 100w/ch unit was only going up to +10db. So if I make sure I won't go over 10db, will I be fine?
 

andy1249

Distinguished Member
8 ohm speakers on a 4 ohm amp should present no problems ,

As for the amp wattage , all amps exaggerate this figure by a very large degree , the 120W rating for your amp was probably for 1 channel driven , in all likelihood your amp will deliver a lot less with 2 or all channels driven , which is how you will use it most of the time. So your speakers will probably be well able to handle the amps power.
 

solidus

Standard Member
Thanks Andy. One thing that worries me is that when I started looking in the receiver's book (yeah, I know!) it says the following:

Built-in 7-channel power amplifier

Minimum RMS output power:
(1 kHz, 0.7% THD, 8 ohm)
Front: 120 W + 120 W
Center: 120 W
Surround 120 W + 120 W
Surround back: 120 W + 120 W

Dynamic Power (IHF)
Front L/R, 8/6/4/2 ohm 140/175/205/250 W

If I add all the minimum RMS together, that's 840 W total power on paper. Now let's just say they overstated it by 10%, so the unit will do say 750 W but I will only use a 5.1 setup for now, would that result in a closer to spec (120W/ch) situation than with a 7.1 setup?
 

solidus

Standard Member
Looked a little more in the book, and they say it has a 400 W/500 VA power supply that includes use of 2 AC outlets on the back for 100 W total.

Hmm...Is it safe to assume that 400 W is the absolute maximum for all channels at any one time (not even counting power consumption of processors, etc)? Hypothetically speaking, could there be a moment while say watching a movie with the receiver cranked up to 100%, when the fronts would end up using 110 W each and the rears use say 30 W each? That would be at almost 400 W total power, yet my front speakers would probably go bye-bye, right? Using a 2 ch mode would just be asking for trouble I'm sure.
 

Andy98765

Distinguished Member
Well a few things to note.
I think getting a wireless kit for the rear will end up in dissappointment, the rear speakers will only be rated at the output of the wireless kit not the AV amp, the 120watts will not travel over the airwaves?.
As for 120watts per channel, maybe 1 or 2 channels driven, but not all. The yamaha web site seems to be down at the moment but if you look up the power consumption of the AV amp I bet it does not even reach 500watts. You would need a Cambridge audio or Arcam AV amp to have higher power consumption than the rated output and they spec along the lines of 100 watts per channel 5 channels ALL driven and have a power consumption much higher than the output.
Going back to the wireless kit, what is its rating? I bet its power comes from a powertop adapter, you still need to run wires at the rear and hide the kit (one to each speaker and a power source.
Do yourself a favour and wire your rear speakers directly to the Av amp.
There are many ways to hide cables, it really is not that hard.
 

solidus

Standard Member
Haha, great to have so many helpful Andys around! I just thought wireless would be awesome to avoid having to take up baseboards, etc to hide those damn wires. I might be moving soon so don't want to through the trouble and can't stand looking at wires.

I found 2 user reviews of this kit saying that it's pretty good (links Review 1 on BeachAudio Review 2 on Amazon). I wanted the KEF system first before I found out about the price. Once I saw it's min. $500, it's out of question.

Here are the specs of the LG wireless amp:

Power consumption . . . . .50 W
Reception Output . . . . . .2.4GHz
Amplifier . . . . . . . . . . .155W + 155W (Rated Output Power: 130W, 4Ω, THD 10 %)

Hmmm... 50 W in, 130 W out (or 310 W?)... So my theory on the power supply's total wattage being the max speaker output power is iffy. I guess that's why they are called amplifiers lol...

Btw, that 10% THD is way too high, right?
 

Andy98765

Distinguished Member
Anything over 2% is TOO high
50 watts power comsumption would be the sort I would expect for a 15watts per channel amp (real world).
I really wish companies would stop inflating figures and give the consumer realistic real world outputs. This is along the lines of PC speakers quoting 1000's of watts with a 12 watt plugtop adapter.
Look at micro trunking for installing cables. http://www.tlc-direct.co.uk/Main_In...Dline_White_Index/Dline_16_8_White/index.html and they are in different colours.
It is the same as all-in-one systems they quote 1200watts output with a 200watt power consumption leading people to believe that their all-in-one is far more powerful than say a Cambridge Av amp that quotes 500watts output with 850watts power consumption.
I know which one I would get if I wanted.
A, Quality
B, Sound FAR more powerful than ANY all-in-one.
 

andy1249

Distinguished Member
Now let's just say they overstated it by 10%,

Believe me , its usually a lot more than that , take the Onkyo 605 as a recent example ( a purchasing mistake of mine , but thats another story ...)

It was widely advertised as 7 x 90W , in some publications even 120W , in reality it was more like 45W.

Try 50% less for a more realistic figure when it comes to that particular amp.
 

Gadgetcity

Active Member
Btw, that 10% THD is way too high, right?

You can pump 120W into 100W speakers for a little while if it is a clean audio signal. Audio from music and film is very bursty so the average power will be much smaller than the 120W peaks anyway.

Distortion is the killer (flat topped audio or speaker cone full travel). If you drive a heavily distorted large signal into the speaker then you are more likely to do some damage. You can hear the distortion and turn the volume down before it does any damage.

To kill a speaker you normally need LOADS of power to tear the thing or over power/distort it for a reasonable time which builds up heat which causes damage.

I doubt you could stand 120RMS from each speaker for long in the average sized room, and there is little chance that your amp could deliver anywhere near this anyway (unless you inject a 1kHz continuous tone :eek:).

To answer your original question, 8 ohm speaker on a 4 ohm amp is fine. It is the over way round that can cause problems as the speakers can take more current than the amp expects.
 

solidus

Standard Member
Thanks :thumbsup:, I am now good with 8 ohm spkr 4 ohm amp question. So the other way is the problem. Thanks to you all I am also much more at ease with my receiver/speaker package. I'll be keeping this combination if these Energy speakers sound good. Audioholics as well as actual users seem to rate it high and have positive things to say about it (links: Amazon .com, FutureShop). I tested one of their sets at the store, and seemed allright. I was so worried about the wattage difference though that I haven't hooked them up yet.

Andy9, thanks for the link. I'll see how that can work for me.

Andy1, before my purchase I was also considering the Onkyo 605 and 705 receivers (along with some Denons like the 788) but read that they might heat up more than the Yamahas so decided to go with the later. The features are quite close for each. Now that you're saying your Onkyo 605 seems like it's delivering half of it's rating, I am glad this one is rated 120 W. The only thing that sort of bothers me is knowing that the 1080p HDMI signal is not straight-thru and I will lose BTB/WTW colors. I probably won't notice those though...
 

The latest video from AVForums

Star Wars Andor, Woman King, more Star Trek 4K, Rings of Power & the latest TV, movies & 4K releases
Subscribe to our YouTube channel
Support AVForums with Patreon

Top Bottom