bridged rotels

[mike c]

I would like to balance the power going to the LCR speakers

the Rotel RB-03 has a rating of 70w x 2 (20-20 .03% 8ohms)
and they say it is bridgeable to 150w x 1 (20-20 1% 4ohms)

the Rotel RB 1070 has a rating of 120w x 2 (20-20 .03% 8ohms)
and they say it is bridgeable to 330w x 1 (20-20 1% 4ohms)

so what is the bridged output in 8ohms?

why put the 4 ohm rating when it says in the manual to only use 8 ohm and above for the speakers.

(im just trying to learn, I know you guys said I get the 1075. just future proofing the purchase too - in case I get the audiophile bug)

[Kevin D]

Bridging is equivalent to halving the ohm load. Those amps can handle 4ohm loads in stereo mode, but only 8ohm loads in bridged mono. It seems like the manuals be mixing specs and causing confusion.

The distortion figures should be correct for those loads hooked up. Hook 8ohm speakers up and get .03%, hook 4ohm speakers up and get 1%. This is in stereo mode. In bridged mode an 8ohm speaker will produce 1% distortion, and if you could safely run a 4ohm load you could expect over 3% distortion.

If that didn't make sense, they are listing distortion figures for speaker loads. For bridged applications on an 8ohm load, the distortion will be equivalent to a 4ohm load.

This is why bridging is usually not recommended, your getting more power at the expense of distortion.

Kevin D.

[mike c]

so for example if I bridged two RB1070s for the 8ohm left and right channels. they are actually getting 330w @ 8ohms? or should the wattage be a lot lower in terms of 8ohms?

[bleeding ears]

mike, I too wondered about this 4 ohm V's 8 ohm thing with amps and the simplest explanation I got was this-.

When bridged an amp sees only half the impeadance of the speakers.

Eg Using 8 ohm speakers and bridging the amp reduces the ohms to 4.

This is one disadvantage of using 4 ohm speakers, a bridged amp would see 2ohms which is not good for most amps.

Also as Kevin said, the distortion rises when using bridged mode.

Apparently bridging an amp is not the best way to go, but if you have 8 ohm speakers you can do it.

Whether you notice or hear the higher distortion is another point again.

Apparently distortion levels are not detectable until they get to a fairly high level.

I am not sure what level that point is exactly, perhaps Kevin or someone else can help out here.

the bottom line is if you like the sound when an amp is bridged go for it!
You sure do get a lot of watts from a bridged 1070 amp for the money.

However if you are like many here and are constantly analyising and listening for where they can improve their setup, then you too will probably be wondering what it would sound like if only I had.......? LOL

If you are going to constantly seek better as many here do, you may ?be better off doing it the best way the first time and going for an unbridged setup.

The only problem is it costs. :lol:

Pete

[Kevin D]

so for example if I bridged two RB1070s for the 8ohm left and right channels. they are actually getting 330w @ 8ohms? or should the wattage be a lot lower in terms of 8ohms?

Yup, bridged you will get 330watts on an 8ohm speaker. Like Pete said though, get a 300x2 amp if you think you will hear the distortion (whether you actually do or not).

Car stereo DBL competitions use ohms law all the time. An amp rated at 50watts (12volts, 8ohm load) might be able to produce 1000 watts or more (14volts, .5ohm load, incredible high distortion)! It takes a special amp to handle .5 ohms, but you can see where it goes.

Kevin D.

[bleeding ears]

One or two more points to consider.

If you have 4 ohm speakers the 1075 amp will put out approx 5 x 200 watts.

Mind you watts is not everything.

Sound quality is probably the priority, so once you have sufficient power for your speakers any extra power may just enable you to increase the volume a few decibels.

eg with a 4 ohm speaker of say 90 db efficiency using the 1075 (200 watts from amp) you should get approx 112db max volume

alternatively with an 8 ohm speaker of say 94 db efficiency using the 1075 (120 watts from amp) you should get approx 115db max volume

The rule here is - you get about 3 db extra volume each time you double the wattage going to the speaker.

So getting the right combination of speaker ohms and efficiency may be just as effective as getting a vey high powered amp.

Let your ears be the judge.

Pete