[xsk3l3t0rx]

my setup before i go any further:
 
nuforce dda-100 (using usb input from computer running ubuntu 14.04 LTS)
klipsch rb-51 II reference series bookshelf speakers
C&E 14AWG speaker wire
 
link for speaker details: http://www.klipsch.com/rb-51-ii-bookshelf-speakers-pair/details
link for amplifier details: https://www.nuforce.com/index.php?option=com_k2&view=item&layout=item&id=306&Itemid=370/index.php#specifications
 
issues: so this amp is awesome, absolutely no problems whatsoever running 2x rb-51 II's at its rated 50wpc. this amp rules. however, i noticed that on the specs page it mentions that it can run at 50wpc @ 8ohms (the speakers are 8ohm), OR 75wpc @ 4ohms. i would like to know if it would be safe to buy two more rb-51 II's and wire them in parallel...
 
the rb-51's are rated at 75W and are 8ohms, so by running them in parallel, the amp would see 4ohms of resistance correct? would this be safe for the amp/speakers or both? i understand that it wouldnt be true quadrophonic sound, and i didnt buy a 2-channel amp for surround sound, nor do i listen to music mixed for it. i simply want two more speakers, plain and simple.
 
*also, would it be more safe if the speakers were run at 75W@4ohms, than at 50W@8ohms? because i feel like i'm underpowering the speakers with only 50W, but that is just an EE question and not a listening question, as it stands, i love this setup.. thanks for any help you can give, and i apologize if this was posted in the wrong category (i dont THINK it is).

 

[PleasantSounds]

You can do that and nothing should go up in smoke if you wire it carefully, but I wouldn't consider this a good solution for what you're trying to achieve.
 
The thing to worry about is how the two sets of speakers will interplay with each other in your room. Usually it's hard enough to get the acoustics of one pair working well, let alone two simultaneously.
 
Consider also that by adding a 2nd pair, when the amp outputs 75W per channel, each speaker would be handling only 35W - so in effect you'd be underpowering them to a higer degree.
 
Another issue is that usually the harmonic distortions of the amp output are higher at 4 ohm than at 8. This is negligible as long as the volume levels are fairly low, but your intent is to max out the amp so this could become noticeable. 
 
Regarding your 2nd question: the amp is rated to run with 4 ohm load, but it will work harder doing so. If you want to know which is "safer", I'd point at 8 ohm, although neither is too much for the amp.
 
Rather than adding another pair of 8 ohm speakers, I'd replace the existing ones with 4 ohm ones, if you really need more power. 

 

[ProtegeManiac]

  my setup before i go any further:
 
nuforce dda-100 (using usb input from computer running ubuntu 14.04 LTS)
klipsch rb-51 II reference series bookshelf speakers
C&E 14AWG speaker wire
 
link for speaker details: http://www.klipsch.com/rb-51-ii-bookshelf-speakers-pair/details
link for amplifier details: https://www.nuforce.com/index.php?option=com_k2&view=item&layout=item&id=306&Itemid=370/index.php#specifications
 
issues: so this amp is awesome, absolutely no problems whatsoever running 2x rb-51 II's at its rated 50wpc. this amp rules. however, i noticed that on the specs page it mentions that it can run at 50wpc @ 8ohms (the speakers are 8ohm), OR 75wpc @ 4ohms. i would like to know if it would be safe to buy two more rb-51 II's and wire them in parallel...
 
the rb-51's are rated at 75W and are 8ohms, so by running them in parallel, the amp would see 4ohms of resistance correct? would this be safe for the amp/speakers or both? i understand that it wouldnt be true quadrophonic sound, and i didnt buy a 2-channel amp for surround sound, nor do i listen to music mixed for it. i simply want two more speakers, plain and simple.
 
*also, would it be more safe if the speakers were run at 75W@4ohms, than at 50W@8ohms? because i feel like i'm underpowering the speakers with only 50W, but that is just an EE question and not a listening question, as it stands, i love this setup.. thanks for any help you can give, and i apologize if this was posted in the wrong category (i dont THINK it is).

 

The amp will put out 75watts RMS at 4ohms, but each speaker will only get 37.5watts maximum RMS. So you will spend more, add two more speakers, and "underpower" each of them even more. That's like buying gear with an auto-shut off feature when no signal is detected to save electricity, when it needs 5mins standby to assume that you're done listening, when if you manually shut it down yourself then it wouldn't have wasted 5mins idling.

 

In any case "underpowering" isn't really a thing unless you hear a lot of distortion. The reality is that amps are rated at a certain level of distortion, not the maximum continuous output, and sometimes that isn't even stated. So while as an extreme example a cheap HT receiver may be rated at "160watts @ 8ohm, 2khz, one channel driven" (out of seven channels), that might be at 1% distortion too; actual output may actually be 45watts @ 8ohm, 2khz, all (seven) channels driven, 0.001%THD. With your NuForce, it's entirely possible that it can do more than 75watts at 8ohm but with much more distortion. At the same time, what makes you think the speakers are underdriven? Just the power ratings on the amp? If your ears give up on the SPLs before you hear audible distortion on the amplifier like out of control woofers for example (if not outright screwed up sound) then the distortion isn't audible to you. Even then you'd have to compare with another amp at the same SPL if it's not actually just the woofer hitting its max excursion. I doubt you'd have that problem given the efficiency of those speakers.

 

In practice, putting 37.5w into each speaker at 4ohms likely will just make the distortion worse - as it is it's making 0.07% at 15watts out of each channel already. Not to mention that now you have four speakers - how do you plan on setting this up? This will just screw up imaging. To avoid that, you can stack them in a mirrored MTTTM set-up like Dynaudio's Contour and Statement Series, but there's still one problem: the Dyns have cabinets designed specifically to do that while you're stacking two cabinets on each other. How do you ensure that the ones on top don't fall off nor suffer from vibrations, playing upside down and all and not properly mounted on speakers stands?

In short: don't bother. You don't actually have any problems with your audio system, but you do have something wrong in your system - we call that "upgraditis" in some forums. Formal medical name that encompasses all symptoms of all similar and related diseases are compiled as SARS, or severe audio replacement syndrome. You should just sit back and enjoy that system, or if you really must give in, do it right get a new amp or new speaker altogether.

 

[xsk3l3t0rx]

The amp will put out 75watts RMS at 4ohms, but each speaker will only get 37.5watts maximum RMS. So you will spend more, add two more speakers, and "underpower" each of them even more. That's like buying gear with an auto-shut off feature when no signal is detected to save electricity, when it needs 5mins standby to assume that you're done listening, when if you manually shut it down yourself then it wouldn't have wasted 5mins idling.

In any case "underpowering" isn't really a thing unless you hear a lot of distortion. The reality is that amps are rated at a certain level of distortion, not the maximum continuous output, and sometimes that isn't even stated. So while as an extreme example a cheap HT receiver may be rated at "160watts @ 8ohm, 2khz, one channel driven" (out of seven channels), that might be at 1% distortion too; actual output may actually be 45watts @ 8ohm, 2khz, all (seven) channels driven, 0.001%THD. With your NuForce, it's entirely possible that it can do more than 75watts at 8ohm but with much more distortion. At the same time, what makes you think the speakers are underdriven? Just the power ratings on the amp? If your ears give up on the SPLs before you hear audible distortion on the amplifier like out of control woofers for example (if not outright screwed up sound) then the distortion isn't audible to you. Even then you'd have to compare with another amp at the same SPL if it's not actually just the woofer hitting its max excursion. I doubt you'd have that problem given the efficiency of those speakers.

In practice, putting 37.5w into each speaker at 4ohms likely will just make the distortion worse - as it is it's making 0.07% at 15watts out of each channel already. Not to mention that now you have four speakers - how do you plan on setting this up? This will just screw up imaging. To avoid that, you can stack them in a mirrored MTTTM set-up like Dynaudio's Contour and Statement Series, but there's still one problem: the Dyns have cabinets designed specifically to do that while you're stacking two cabinets on each other. How do you ensure that the ones on top don't fall off nor suffer from vibrations, playing upside down and all and not properly mounted on speakers stands?


In short: don't bother. You don't actually have any problems with your audio system, but you do have something wrong in your system - we call that "upgraditis" in some forums. Formal medical name that encompasses all symptoms of all similar and related diseases are compiled as SARS, or severe audio replacement syndrome. You should just sit back and enjoy that system, or if you really must give in, do it right get a new amp or new speaker altogether.

that was an excellent post. ifi had to be dead honest, you're probably right. i play guitar too and we call it GAS (gear acquisition syndrome). i do enjoy this setup, and im gonna keep enjoying it just the way it is. thanks for all your help. not only did u guys save meba bunch of money by buying more speakerd, you helped me understand how some specs work and their effects. take care