Receiver Capable of Handling 4 Ohms - Page 2

Amazon has one 9040 available now.

Factory rated at 87 db/watt/meter, tho I suspect it is somewhat lower, and they are in a room 18' x 28' with a cathedral ceiling that tapers from 8' to 13.5'.

Crown 602s now power them, they never shut down, never get hot.

As for the 4 ohm setting, deliberately restricting power output by some 40% just somehow seems wrong to me, even if it worked.

I think he's saying that the 4 ohm setting on receivers limits power (by lowering supply voltage.)

It limits heat by limiting current by limiting voltage. I have seen some benchmarks with a 4 ohm switch activated where power is limited by quite a bit.

Some people suggest not using a 4 ohm setting for this reason. Same logic holds for a 6 ohm switch.

MichaelJHuman wrote: It limits heat by limiting current by limiting voltage.

Exactly, if the 4 ohm option in "speaker setup" is selected, in my system, in my room, maximum volume is restricted to the point that realistic levels for, say, Star Trek or T2 are not possible.

Not me -- no corpse here.

I think the bottom line on an AVR might be that if it has a switch for 4u or 6u speakers, it probably can't handle 4u speakers very well.

There is an element of truth to that, usually meaning that the heat-sinks and ventilation become an issue before performance.

Speaking about Yamaha, in particular, they only include the switch in order to meet the temperatures in their initial specifications. If your unit has good ventilation, there is no issue.

To be precise, any amplifier which does not provide exactly TWICE the output power at 4-ohms that it does at 8-ohms has some design limitation ... probably the power supply or the ventilation.

That does not mean that it cannot perform well at a reduced output level or higher temperatures.

The short answer is no.

You can achieve THX standard loudness with 80+W/ch and speakers that are 86+dBSPL efficient.

*Most* AVRs and HT speakers meet those requirements!

I don't come up with those numbers. Assume speakers with 90 dB sensitivity. Assume 2 meters average listening distance to speakers. 6 dB loss for 2 meters of distance. I figure you need 128 Watts to hit 105 dB.

Of course, you don't that continuously. But I have my doubts that many receivers can supply the needed power.

I am not sure most receivers can manage 80 Watts / channel. Take your average $500 receiver with a 400 Watt power consumption rating. I figure maybe they can do 25x7 Watts continuous at 1% THD. Maybe they can hit peaks of 60x7 Watts. On loud action scenes in movies, I suspect they simply can't provide sufficient power.

Of course it would be great to have facts. For example, to see where peaks on each channel are occuring, how close together they are, how much power the filter caps can supply for these peaks, etc. I know of no source for this info. I imagine THX has a pretty good idea. If they are honest, maybe there's some hope, because some pretty midrange models have managed select certification. I would like to see what sensitivity speakers you are supposed to pair your receiver with, and at what listening distances, because that makes a big difference in terms of how much power is needed.

My Yamaha RX-Z7 does not sound good at reference level, and it's 2nd to Yamaha's top of the line. I will accept the argument that some company's models produce more power, but I still have my doubts that most receivers perform well at reference level.

Also, I think your powered sub needs to keep up, or you really can't claim the ability to play at reference level.

If I am right, the good news is a slight reduction in SPL gets you to power levels most receivers should be able to handle. So what if you can only hit 100 dB peaks. I think that's sufficient for many people.

I feel that owners of the Onkyo 805/875/876/906 would disagree with this. I don't have 4 ohm speakers to test with but I feel that my 876 would do it with no problems. Maybe I'm too biased, but the Yamaha 2600 before it doesn't have the power this thing has, and I doubt very seriously that any of Yamaha's new offerings would come close to it. JMHO. Nothing more.

1) You need an amp to make a speaker play I assume you mean adding an external amp; I think I can state, factually, that you will get better sound IF your receiver did not supply enough power for your needs, and the external amp DOES supply sufficient power.
2) See (1)
3) See (1)
4) Just to repeat, AVRs have amps. The #1 reason to add more amps is for more power

For fair disclosure, there are people who feel that power is not the only factor. They feel some amps sound better than others. This is debated endlessly. Sticking to know facts, if you can't push your volume level to your desired SPL without clipping, you would need more power. IMO, that's the bottom line. Any other factors are debateable.

Not all receivers have pre-amp outs to power external amp(s). It's better to have them and not need them than to. . . .

In the Onkyo line, pre-amp outs are in the 7NN and above models.

Are you aware that the THX specifications are based upon an amplifier's output voltage capability into a 3.2 Ohm load..

I would further add that the majority of price-point AVRs whose SRP < $999 do not meet the THX criteria for THX Select..
And have no chance to meet the criteria for THX Ultra.

Just my $0.01...

MCode, have you ever heard what sensitivity THX assumes for speakers?

The 4 Ohm switch limits the power supply voltage, which in turns limits the maximum available current. If the output stage is driven beyond its voltage/current capabilities the amplifier's output devices or power block IC will self-destruct and breakdown.

Regarding temperature, this does enter into the consideration but here the AVR has built-in thermal sensors for protection. Again, adequate free air space clearance is required, a minmum of 4" for Left/Right sides and top.

NO consumer AVR will double its power output into 4 Ohms from 8 Ohms, especially if its SRP is $1499 or less. This requires a perfect world and power supply design which doesn't exist in our price-point world.

Just my $0.01..

Keep in mind..
For THX, their assumption is that the user will assemble a complete system made up of THX certified components including processor, power amplifiers, subwoofer and loudspeakers. Then this THX system of pre-matched THX components will deliver a minimum SPL level within a defined room volume.

The actual sensitivity specification for a THX certified loudspeaker will vary significantly depending upon the drivers being used. I think some of the JBL Synthesis and Klipsch Ultra 2 loudspeakers had a sensitivity specification of around 95dB (1W @ 1M). Again the crucial factor is that when these THX certified loudspeakers are used within a full THX certified system it must deliver the minimum defined SPL level.

Thats why the THX amplifier criteria is quite stringent especially for THX Ultra 2, I recall the amplifier had to be capable of outputting at least 40V (peak voltage) into a 3.2 Ohm load with at least 4 channels being driven @ 1kHz. Additionally the amplifier had to deliver @ least 18 Amps when driven in a 2.2 Ohm load.

Just my $0.01..

"THX standard reference level" (85dBc with 20dB headroom) has NOTHING to do with volts, amps, watts, impedance, sensitivity, wire gauge, weight or the size of your hammer.

It is simply a marketing term which references the standard monitoring loudness level established within the movie and studio industry (defined in SMPTE RP 200-2002 “Relative and Absolute Sound Pressure Levels for Motion Picture Sound Systems”).

And if you want this sound in your Home Theater it has to meet those specs does it not. I'm not saying there is not AVR's out there that will not meet those specs, because there are. The CE's that pay for that right will meet those specs. So I believe it is more than a marketing term. This isn't Bose marketing hype is it? Correct me if I'm wrong. I'm always willing to learn more about this hobby.

Yes. The reference loudness spec is 85dBc with 20dB of headroom. <=== Note: you did not see the term "THX" in that spec, did you?
"THX" is simply a marketing scheme.

*IF* YOU PAY money to THX and your product meets their various specifications, you can display the THX logo on your product.

There are many, many systems out there that meet the reference loudness "85dBc with 20dB of headroom" specification that do not pay THX for the use of their logo.

Just because a system does not have "THX" on the front panel, does NOT mean it cannot meet the industry spec!!

And all of this you posted is what I said in my post. As I said I believe it is more than marketing hype. Would you say the offerings from Yamaha this year would meet those specs? No, I doubt it. The Yamaha 2600 did. Do you think that the Denon 3310 would meet those specs? If you do then you should read test reports on its performance with all channels driven and especially with any 4 ohm speakers in the mix. I realize there are many AVR's or receivers that would pass THX certification, but realize that before you turn over your hard earned money for one of these, I'd find a reputable test report on it before I purchased it. THX "certification" at least narrows the field. JMHO. Your opinion is different and thats okay too.

I am not sure anyone is disagreeing now. Seems like semantics. The bottom, line, IMO, is that to meet 105 dB peak SPL on every speaker, as needed, while playing a movie is not easy. I suspect it's even harded to meet 115 dB from your sub, especially since subs have to move a lot of air, and require a lot of power to do it.

I contend it's not important either. Who cares. As long as your system meets your own SPL needs, which I contend are likely lower than 105 dB peaks for many people, you are good to go.

You can save a lot of money by ignoring the people with vested interest in you spending money

*ANY* AVR matched with an appropriate loudspeaker system can meet the "THX" reference loudness specification!! There is no magic.

I own a set of speakers that produce 100dBSPL/1W/1m.

They can produce the "THX" average reference level with an amplifier power of 0.0316W and the peak reference level with an amplifier power of 3.16W. (At 100W they will produce 119dBSPL)

Do you get it yet??

To have a home theater system to deliver that specification does take volts, amps, impedance, sensitivity, and wire guage..

No need for a hammer unless you are wall mounting some speakers..

Just my $0.01..

I didn't know an iPod was THX certified..

Just my $0.01..

I must have been reading too fast. Was there some evidence mentioned telling us about how easy it is to get 105dB peak? What sort of speakers and amplifiers or receiver you must have? Why do you say it's not easy?