Help with Bi-Amping and Ohms...

[DogZilla]

OK, I'm a NOOB, sorry...I have a Denon AVR-2808CI (110 Watts per ch) and am awaiting the arrival of my Monitor Audio Silver 5.1 system. All the MA speakers are rated at 6 Ohms; the fronts are RS6's (Sensitivity (1W@1M): 91 dB; Nominal Impedance: 6 Ohms; Power Handling (RMS): 120 W; Recm'd Amp (RMS): 40 - 120 W). The outputs on the back of the Denon are listed as 6 Ohms, except when using A + B (bi-amping) for the fronts, which says 8 Ohms. I asked Denon about this and the reply was that bi-amping 6 Ohm speakers may cause the unit to shut-down and/or damage it. I know the Denon guy must practice CYA in case an issue arises from advise he has given, so I was hoping to get another opinion or two, with a bit more objectivity. I don't plan on balls out cranking them, as I live in a townhouse. Does this Ohm issue really matter, I mean, in this particular scenario?

 

[fmw]

No, the "ohm issue" won't matter in your situation. Neither will the biamplification in the first place.

 

[DogZilla]

Thanks; care to elaborate?

 

[TLS Guy]

Thanks; care to elaborate?

We went through this last week and the week before. There is is no benefit to to wasting an amp powering a tweeter. The result is likely a worse outcome.

Just connect your speakers normally, enjoy them, and forget you ever heard of passive biamping.

 

[DogZilla]

I should have listened....I thought I'd really be doing something by hooking my speakers up like that. I really did....and I thought that maybe if I cut the volume up some more it would make a difference, but then my reciever started to shut down, I guess. It started smoking. By the time I saw the flames coming out of it, they were starting to catch on the curtains. I should never have set that receiver in the window like that; the sun probably heated it up all day while I was at work already. I can't believe it. I should never have tried this. Now the whole unit is full of Class 3 fire extinguisher crud, as well....not to mention what it did to the carpet and wall and even on the ceiling. I rue the day I ever heard of bi-amping. The whole place stinks and its freezing because I still have the windows open. I guess I can forget the warranty, too. Why didn't I listen? I should have listened. Now I have no system and no more budget. I guess it could have been worse (although I don't know how). Do you think if I get it cleaned out and dry it can be repaired? Any experience on this type of thing? Any input would be appreciated.

 

[TLS Guy]

I should have listened....I thought I'd really be doing something by hooking my speakers up like that. I really did....and I thought that maybe if I cut the volume up some more it would make a difference, but then my reciever started to shut down, I guess. It started smoking. By the time I saw the flames coming out of it, they were starting to catch on the curtains. I should never have set that receiver in the window like that; the sun probably heated it up all day while I was at work already. I can't believe it. I should never have tried this. Now the whole unit is full of Class 3 fire extinguisher crud, as well....not to mention what it did to the carpet and wall and even on the ceiling. I rue the day I ever heard of bi-amping. The whole place stinks and its freezing because I still have the windows open. I guess I can forget the warranty, too. Why didn't I listen? I should have listened. Now I have no system and no more budget. I guess it could have been worse (although I don't know how). Do you think if I get it cleaned out and dry it can be repaired? Any experience on this type of thing? Any input would be appreciated.

I'm afraid that unit is toast. It can not be repaired. However, a unit should NOT self destruct like that. More evidence of the modern race to the bottom. At the worst a fuse should have blown and a few power transistors bitten the dust, but a house fire? No way.

The problem is that unit is junk to start with and a defective design. Misguided consumer demand for low price points and the declining dollar are driving price well below what is prudent. In my view the units currently marketed and touted on these forums should cost a factor of two or three times what they do.

I'm going to give a piece of advice to anybody reading this thread. If a unit with a power amp can not provide double the power when going from an eight ohm load to a four ohm load, do not buy it. Wait! Save your money and buy something better.

Junk is the most expensive equipment you will EVER buy. When I was a teenager and a poor medical student, I saved and sacrificed to buy good equipment. Some of that equipment is a half century old and still providing pleasure and good service in my system. That is cost effective equipment.

 

[OttoMatic]

TLS Guy's post is right on. But...... I have a feeling that there might not really have been a fire.

 

[PENG]

I'm going to give a piece of advice to anybody reading this thread. If a unit with a power amp can not provide double the power when going from an eight ohm load to a four ohm load, do not buy it. Wait! Save your money and buy something better.

Coming from an expert like you, you have got to be kidding! If not, you should review some basic electrical principles.

Jokes aside, if I want you to buy an amp that can do 100W into 8 ohms under a specified condition and 150W into 4 ohms under the same condition I will then simply rate my amp super conservatively for 75W into 8 ohms and properly for 150W into 4 ohms. I am not saying Krell or Boulder do that but not I suspect very few people can afford their amps.

 

[PENG]

OK, I'm a NOOB, sorry...I have a Denon AVR-2808CI (110 Watts per ch) and am awaiting the arrival of my Monitor Audio Silver 5.1 system. All the MA speakers are rated at 6 Ohms; the fronts are RS6's (Sensitivity (1W@1M): 91 dB; Nominal Impedance: 6 Ohms; Power Handling (RMS): 120 W; Recm'd Amp (RMS): 40 - 120 W). The outputs on the back of the Denon are listed as 6 Ohms, except when using A + B (bi-amping) for the fronts, which says 8 Ohms.

I know this is a little late but if I understood correctly, using A+B is not biamping. If you remove the jumper straps at the speakers terminals and connect the LF driver(s) to terminal A, the HF driver (and the MF in some cases) to terminal B, you are just biwiring and everything should be fine. If that's what you did, your unit probably failed due to other things.

If your speakers are not biwirable, that is they have only one set of terminals; and if you connect (I believe this is not what you did) a pair of speaker to each of the A and B terminals, then the front channels of your amp would see the loads as 3 ohms instead of 6 ohms and will therefore shutdown sooner than you think.

 

[TLS Guy]

Coming from an expert like you, you have got to be kidding! If not, you should review some basic electrical principles.

Jokes aside, if I want you to buy an amp that can do 100W into 8 ohms under a specified condition and 150W into 4 ohms under the same condition I will then simply rate my amp super conservatively for 75W into 8 ohms and properly for 150W into 4 ohms. I am not saying Krell or Boulder do that but not I suspect very few people can afford their amps.

What I'm getting at is that if an amp does not do that, then some under rated component is limiting current. That equals stress and potential for failure. There are enough cost effective high current devices around, that there is no reason for this not to be the rule.

Speaker impedances are dropping. Honestly in a properly designed narrow fronted speaker with small bass mids, impedance pretty much has to drop into the four ohm range. This should not stress the amp, and any well designed modern amp should drive the load without pushing the devices to current limit. That spec. is the best indication a customer has that he is buying a product that has reserve to drive a huge number of speakers around today without risking the chance of undue stress and failure in his amp sections.

 

[PENG]

What I'm getting at is that if an amp does not do that, then some under rated component is limiting current. That equals stress and potential for failure. There are enough cost effective high current devices around, that there is no reason for this not to be the rule.

Good morning TLS, I agree something is limiting current, but that is always the case and you know there are many reasons. Take a look of a typical transformer's equivalent circuit that either refer all the fix and variable losses to the primary or secondary winding and you will see things that limit current and how the fix loss components (e.g. core losses) that are affected mostly by voltage only. Bottom line is, you can get close to double down but to show 100% double down I believe some manufacturers just play with figures one way or another.

My main point is, if people follow that line of advice you gave seriously, they won't be buying any amps from Adcom, Bryston, Emotiva NAD, Outlaw, Parasound, Rotel and many other reputable manufacturers.

 

[TLS Guy]

Good morning TLS, I agree something is limiting current, but that is always the case and you know there are many reasons. Take a look of a typical transformer's equivalent circuit that either refer all the fix and variable losses to the primary or secondary winding and you will see things that limit current and how the fix loss components (e.g. core losses) that are affected mostly by voltage only. Bottom line is, you can get close to double down but to show 100% double down I believe most manufacturer just play with figures one way or another.

My main point is, if people follow that line of advice you gave seriously, they won't be buying any amps from Adcom, Bryston, Emotiva NAD, Outlaw, Parasound, Rotel and many other reputable manufacturers.

Close is good enough. However not being able to drive loads lower than 6 ohms is nowhere near good enough, for current speaker offerings.