How to change the ohms on my receiver

[guitarplyrstevo]

I currently have an Onkyo TX-SR574. On the Onkyo website, it said that the amp is rated at 80 watts per channel at 8 ohms, and 100 watts per channel at 6 ohms. How do I change the ohms of my amp from 8 to 6? Also will this harm my amp or speakers in any way? Speakers are rated at 8 ohms

 

[MDS]

I suspect that you are thinking that if you could somehow change to 6 Ohms you get more power and it would thus be louder, no? No.

Voltage, current, and resistance are all related. When the resistance goes down, the current goes up because the voltage is constant (in the case of the receiver). If you were to use 6 Ohm speakers, the current requirement would be greater but if the speakers have the same sensitivity as 8 Ohm speakers, the resulting SPL will be the same. The receiver is just working harder to produce it.

Regardless you can't 'change the ohms' on the receiver. Some receivers have a switch to set for 6 or 8 Ohm operation but all it does is lower the max voltage so that the current requirement is lower, lessening the demand on the receiver's power supply.

 

[guitarplyrstevo]

I suspect that you are thinking that if you could somehow change to 6 Ohms you get more power and it would thus be louder, no? No.

Voltage, current, and resistance are all related. When the resistance goes down, the current goes up because the voltage is constant (in the case of the receiver). If you were to use 6 Ohm speakers, the current requirement would be greater but if the speakers have the same sensitivity as 8 Ohm speakers, the resulting SPL will be the same. The receiver is just working harder to produce it.

Regardless you can't 'change the ohms' on the receiver. Some receivers have a switch to set for 6 or 8 Ohm operation but all it does is lower the max voltage so that the current requirement is lower, lessening the demand on the receiver's power supply.

So then why does the Onkyo TX-SR875 have an option on the configuration menu to change it from 4 to 6 to 8 to 16?

 

[MDS]

So then why does the Onkyo TX-SR875 have an option on the configuration menu to change it from 4 to 6 to 8 to 16?

To reduce the available voltage so as to limit the current that will be drawn. When you reduce the voltage you reduce the current and hence the power but it lessens the demands on the power supply. There is an article on this site about those kinds of switches.

 

[Rickster71]

So then why does the Onkyo TX-SR875 have an option on the configuration menu to change it from 4 to 6 to 8 to 16?

It's to accommodate people with 4, 6, 8, or 16 ohm speakers.

 

[Midcow2]

That is only to protect the AVR ...

So then why does the Onkyo TX-SR875 have an option on the configuration menu to change it from 4 to 6 to 8 to 16?

Most receivers that have a switch for other than 8 ohms (typically speaker average impedance) have some sort of internal resistance to PROTECT the AVR. When you switch to one of the lesser ohmages on the AVR you are in effect adding a resistance (impedance) in series with your speakers thus reducing your effective power.

The main purpose of different ohm settings is to limit the current (Ameprage) and protect the AVR from overload. Power= I (current) * V(voltage) and I= V/R. So if you half the resistance the current doubles.

Most newer AVRs have protective circuitry to prevent overlaod; but it is not prudent to always depend on that. And typically the protection is to compeltley power off the AVR.

Most newer, substantial (90RMS-125RMS) AVRs can handle 4 ohm speakers. Older receivers or lower power receivers can handle 4 ohms sometimes at lower volumes. At higher volumes they can trip the protective overload circuitry

If your lower powered ACR has preouts then you can easily add a 2-channel Power amp to drive the front 4 ohm speakers.

With a lower powered AVR, if you have 4 ohm speakers and no-preouts you are limited to (1) run lower volume, (2) buy new speakers or (3) upgrade AVR.

Remember resistance is when the votage and current are in phase. When they are out of phase you get either an inductive component or a capacitive component and the resistance becomes impedance. Also, the most important thing to remember is that the impedance of a speakers varies with the frequency; it is not a single number but a range. Most AVRs are designed with a 8 ohm average load in mind. Some have a 6 ohm setting which reduces the power by typically adding a 2 ohm internal protective resistor. A 4 ohm setting is rarer and i personally have never hear of a 16 ohm setting and not sure what a 16 ohm setting would accomplish.

The Onkyo TX-SR875 is a very good substantial AVR with 140W RMS per channel into 8 ohms. It should be able to handle just about any speakers you throw at it. I would leave the setting at 8 ohms. The only issue I have heard at all negative about Onkyo is that they sometimes runs hot. If you are going to drive the 875 pretty hard I would make sure you had the recommended air clearance and then you will be fine.

Good Luck!

 

[Davemcc]

How do I change the ohms of my amp from 8 to 6?

The simplest answer to this question is change the speakers to 6 ohm speakers.

 

[guitarplyrstevo]

Thank you for all your help.

So bottom line, matching the ohms with the speaker is ideal? Lowering it wont produce more power, it will just force you to run at lower volumes because of the amp working harder right?

 

[Midcow2]

No lowering ohms increase load on AVR and does produce more power.

Thank you for all your help.

So bottom line, matching the ohms with the speaker is ideal? Lowering it wont produce more power, it will just force you to run at lower volumes because of the amp working harder right?

Your AVR is rated at 80RMS into 8 ohms and 100RMS into 6 ohms.

Here is why, usually votage is fairly constant. and Power = V*I = V^2/R

80 RMS = V^2/ 8 then V=~25.3

assuming fairly constant voltage the power increase if you lower the speaker load to 6 ohms (25.3)^2/6=~ 106 RMS.

Your current also increases from 25.3/8=3.17 amperes to 25.3/6=4.22

Most AVRs have protective circuitry to prevent current overload. Larger, newer more robust AVRs can handle 4 or 5 ohm speakers.

If you are having sound problems or running out of power you can (1) get 8 ohm speakers or (2) get a more powerful AVR.

Setting your AVR to a 6 ohm or 4 ohm setting is an attempt to try and maintain the current level and protect the AVR, not necessarily to provide louder sound.

Also you need to realize that power and sound are logrithmic A doubling in power only porduces a 30% increase in sound. Going from 80 to 100 is actually only a 10% increase .

 

[Iamedgeman]

I have been researching why the Onkyo receiver only offers 4 or 6 ohm on the receiver when the specs on the receiver state that it can support 4, 6, 8 or 16 ohm. Very frustrating when you go into the speaker menu and you can not select 8 ohm for your speakers.

After hours of looking online, I finally looked in the manual. Found the answer. Looks like the receiver will only offer 4 or 6 ohm.

Here is what the manual states:
Set the impedance (Ω) of the connected speakers.
"4ohms": When any of the connected speakers
have 4 Ω or more to less than 6 Ω impedance
"6ohms": When the connected speakers all have
6 Ω or more impedance.
• For impedance, check the indications on the
back of the speakers or their instruction manual.

So, since I have 8 ohm speakers, the system should default to 6 ohm (and above) under the speaker menu selection.

 

[highfigh]

I currently have an Onkyo TX-SR574. On the Onkyo website, it said that the amp is rated at 80 watts per channel at 8 ohms, and 100 watts per channel at 6 ohms. How do I change the ohms of my amp from 8 to 6? Also will this harm my amp or speakers in any way? Speakers are rated at 8 ohms

The impedance switch was discussed here a couple of years ago- it's there to prevent problems that shouldn't occur in the first place, due to designing things to hit a price point, rather than performance goals.

Power is a calculated value, based on the voltage and resistance of the speaker. The power supply can provide a certain amount of output, but if the speakers demand more, it may not be able to deliver. This switch limits the power supply's output, so it doesn't fail.

Even if you could select the output, adding 20W would barely be audible.

In light of your screen name, this would also apply to your guitar amp if it's solid state, but not exactly the same if you use tubes. Tube amps use an output transformer to couple the amp to the speakers and it has a rating, just like these amps but the effect of using the "wrong" speakers is somewhat different with tubes. You can use speakers that are one step to either side of "correct", but it's not good to go farther than that, so an amp rated for 8 Ohms can be used with 4, 8 or 16 Ohm speakers, but don't connect it to a Tweed Bassman cabinet that has original/similar speakers in its original wiring configuration- that will present a 2 Ohm load and your amp will NOT like that, at all- especially if you really crank it.

Some guitar amps have an impedance selector (Marshall, mostly) and this is only supposed to be changed when the amp is turned off- it changes the output transformer's connection, to allow the setting to match the speaker. McIntosh audio amplifiers have connections for the same reason.