[SOLVED] Can i use an 8 ohm receiver for 6 ohm speakers?

[lordtristan28]

Hi!

Looking to buy a pair of these floorstanding speakers for a cheaper home theater setup, (https://www.amazon.ca/gp/product/B00O8YLL8E/ref=ewc_pr_img_1?smid=A3DWYIK6Y9EEQB&psc=1)

They are rated for 145watts max at 6 omhs, well i cannot for the life of me find a under 300$ reciver that runs 6 ohms, all of them seem to be 8.

I was looking at this one (https://www.amazon.ca/Yamaha-Natura...ild=1&keywords=receiver&qid=1619306439&sr=8-5)
and it said in the manual that plugging any speakers that are under 8 ohms may cause overheating!

What should i do?

 

[kanewolf]

Hi!

Looking to buy a pair of these floorstanding speakers for a cheaper home theater setup, (https://www.amazon.ca/gp/product/B00O8YLL8E/ref=ewc_pr_img_1?smid=A3DWYIK6Y9EEQB&psc=1)

They are rated for 145watts max at 6 omhs, well i cannot for the life of me find a under 300$ reciver that runs 6 ohms, all of them seem to be 8.

I was looking at this one (https://www.amazon.ca/Yamaha-Natura...ild=1&keywords=receiver&qid=1619306439&sr=8-5)
and it said in the manual that plugging any speakers that are under 8 ohms may cause overheating!

What should i do?

The owner's manual -- https://usa.yamaha.com/files/download/other_assets/2/794512/web_VEX7420_R-S202_om_UA_En_A0.pdf in the specifications page shows 6 ohm power levels. I don't believe using 6 ohm speakers will damage that receiver. Four of them, instead of two, maybe.
The owner's manual says "Excessively low" can cause overheating. But also shows power output for multiple lower impedance levels "Dynamic power per channel (8 Ω/6 Ω/4 Ω/2 Ω, IHF)" .
How loud you run the speakers will impact the amount of heat generated.

 

[RoadBlaster]

Most 8 ohm speakers are down around 6.8ohms

Use a 2 ohm resister in series with + outputs if you are not sure & want to be on the safe side ?

I use resisters on my dual coiled subs to make them 4 ohms instead of 2 ohms so I can use 2 amps to drive 1 X 12" sub safely.

 

[BFG-9000]

Some of my amps have wattmeters on them and I can say I just about never exceed 1 watt on any of them, so overheating to the point of thermal shutdown seems unlikely unless you are in the habit of blasting music as loud as it can go. Most larger speakers have around 90dB/1 watt efficiency (those are rated 88dB) so how is your hearing?

Perhaps more importantly, using lower resistance speakers makes it harder for the amp to control bass--it sounds looser instead of tighter from the reduced Damping Factor (if you want the math look up Thiele/Small parameters)

 

[RoadBlaster]

What some of you are also forgetting is when an amp jumps from 8 ohms to 4 ohms for example, you are doubling the current needed to power the amps themselves so if the manual says it would cause overheating then it has already been calculated to work at 8 ohms only with transformers only able to supply 8 ohms current.

So overheating would be the transformers & nothing to do with thieles parameters regardless of how loud or low the volume is the current is greater along with signal to noise ratio.

 

[BFG-9000]

What some of you are also forgetting is when an amp jumps from 8 ohms to 4 ohms for example, you are doubling the current needed to power the amps themselves so if the manual says it would cause overheating then it has already been calculated to work at 8 ohms only with transformers only able to supply 8 ohms current.

So overheating would be the transformers & nothing to do with thieles parameters regardless of how loud or low the volume is the current is greater along with signal to noise ratio.

You know that rated wattage doubling when halving the resistance is a sign of a good amp. This is clearly not one of those as it's rated 125w @ 8ohms and only 180w @ 2ohms IHF*, so is obviously designed for sensible volume levels around 1w like I suggested--where overheating would be very unlikely. OSHA says 85dB causes hearing loss and 1w is already over that with these speakers so how loud do they need to be?

If some people don't understand how to use a volume knob and have to set it at 11, then yes, they would sadly be doomed to listen to nothing but distortion with low-resistance speakers because the speaker resistance changes the usable range of the volume knob.

I expect most people would notice how floppy the bass sounds, even at 1 watt, if using much lower resistance speakers than an amp is rated for, and that's what the formulas describe. You don't need any math at all to know clipping an amp until it overheats sounds bad.

*IHF is a dynamic power standard using 20 millisecond test tones at a single frequency still used by other countries. By 1974 the then common Peak Music Power Output (PMPO) ratings got so ridiculous (like a relay! For a millisecond until it blew up!) that the FTC mandated Rule 46 CFR 432 that required specifying the frequency range and THD so this amp is rated in the US at 100w @ 8ohms RMS @ 0.2% THD. Notably the same amp is rated 115w @ 4ohms @ 0.7% THD for Europe at a single frequency (1KHz) but continuous unlike IHF. So 4ohms is safe but likely much worse THD over the full frequency range, which could be expected because the power did not double to 200w

 

[RoadBlaster]

You know that rated wattage doubling when halving the resistance is a sign of a good amp. This is clearly not one of those as it's rated 125w @ 8ohms and only 180w @ 2ohms IHF*, so is obviously designed for sensible volume levels around 1w like I suggested--where overheating would be very unlikely. OSHA says 85dB causes hearing loss and 1w is already over that with these speakers so how loud do they need to be?

If some people don't understand how to use a volume knob and have to set it at 11, then yes, they would sadly be doomed to listen to nothing but distortion with low-resistance speakers because the speaker resistance changes the usable range of the volume knob.

I expect most people would notice how floppy the bass sounds, even at 1 watt, if using much lower resistance speakers than an amp is rated for, and that's what the formulas describe. You don't need any math at all to know clipping an amp until it overheats sounds bad.

*IHF is a dynamic power standard using 20 millisecond test tones at a single frequency still used by other countries. By 1974 the then common Peak Music Power Output (PMPO) ratings got so ridiculous (like a relay! For a millisecond until it blew up!) that the FTC mandated Rule 46 CFR 432 that required specifying the frequency range and THD so this amp is rated in the US at 100w @ 8ohms RMS @ 0.2% THD. Notably the same amp is rated 115w @ 4ohms @ 0.7% THD for Europe at a single frequency (1KHz) but continuous unlike IHF. So 4ohms is safe but likely much worse THD over the full frequency range, which could be expected because the power did not double to 200w

Back in the 1990's I built alot of the Maplins UK amp projects & my favourite was the Mosfet one using J50 & SK135 Mosfets, now a day I build all my own Pre Amp & active crossovers & all my volume knobs are actually resister arrays as input sound is from Pc so Up & down volume is set there, my latest 3 way Active Crossover is a 5.1 Channel version with lot of wiring to do for the volume switches.
For my bass I use C Bins with 12" Dual Coil T-Rex cones 7 get a really deep bass from them which matches the music source, so there is not much bass in the recording thats what you get.
Also with bridge mode amps the power supply needed is X4 the current needed for 1 amp, so in the end you can pick the amp up because it has a massive 1KV toroidal in there, lol.