I am going to get JMLabs-Focal front floor standing speakers which are rated at 6 ohms if I am not mistaken (might be 4 ohms). I have older JBL book shelf speakers rated at 8 ohm. I would like to use JBL for surrounds. I know its not ideal situation, but I dont want to spend money on surround speakers right now, as I already have JBL bookshelf from older set-up and I will be using stereo set-up most of the time anyway.
Does it pose any risk if I have two fronts 4/6ohm speakers and surround JBL 8 ohm impedance ?
All of them will be hooked up with NAD T775. Do I need to make some adjustment in receiver setting or it will just pick up everything fine ? Thanks.
Are you going to be driving the speakers pairs from front/rear outputs? If the speakers are driven by separate amplifiers, then you should be OK if the new speakers are not a four Ohm load.
Worst case scenario is the receiver is taxed a little more by the 4 ohm speaker, and might make the unit run hot and potentially shut down.
There are settings in some receivers, Yamaha comes to mind, that allow for matching the ohm of the speaker. Although it is sometimes 6 or 8.
The ONLY thing this does is lower the requirements needed to shut down the amp when too much is asked of it, and/or it gets too hot. It is a protection feature, and does not change the performance of the amps.
If you really want to allow the NAD, as well as the new speakers, to perform optimally. Use the "Pre-outs" and pick up a decent, used 2 channel amplifier that will be more stable in lower ohms.
Maybe a s/h Adcom or Rotel could fit the bill.
Then the NAD and be used to power the center, surrounds, and do the Dolby processing etc.... Im sure it would run much cooler, and the dedicated amp for the fronts might deliver better 2 channel preformance than using two of the seven amps in the NAD.
"The ONLY thing this does is lower the requirements needed to shut down the amp when too much is asked of it, and/or it gets too hot. It is a protection feature, and does not change the performance of the amps."
Well, yes, it does affect the performance of the amplifier. The switch is used to limit current delivery to the speakers. When you have a speaker that requires high current and the amplifier is forced to limit the current available to drive the speaker properly, that does change the performance of the amplifier and the system.
Currently, plan is to drive all of them with one receiver , NAD if possible. It will take some time for my setup to hook up at my new place, but it seems I need to be careful in general.
I have seen NAD hooked up to Jmlabs at dealer, so I don't think load from JMlabs are problem for NAD. It was just mixing 8ohm speakers in the setup which I wasn't sure about.
Are you planning to drive these speakers with a stereo two channels receiver or with a HT surround sound receiver? Giving me a only model number implies I should know all models of all manufacturers. I don't. Tell me what you intend to use and I can better answer your question.
nad t775 is 7.1 surround receiver. So all these speakers will be hooked up as surround. Jmlabs, lower ohm rating, as fronts and jbl as rear. Overall 4.0 setup as I don't have sub and center channel speakers as of now.
Each amplifier channel in a surround amplifier sees only the single speaker connected to that single channel. Unless the amplifier manufacturer specifically warns against low impedance loads you can use any reasonable speaker with their amplifier. The problem with four Ohm loads is two fold. They do not remain four Ohms over their entire frequency range sometimes dipping down in impedance to dangerously low points and they are often coupled with demanding crossovers which together with the driver's impedance require large amounts of current from the amplifier. Read a few of the posts in this section to find more information on what problems exist with low impedance loads. If at all possible, I would always recommend the highest impedance loudspeakers you can find that suit your taste. It simply makes life easier for your amplifier.
If you are not confident the speakers you have chosen will perform well with the NAD, I would honestly suggest you choose another speaker. If this is the speaker you really want to own, take care with the volume levels for the first few days and monitor the temperature of the receiver as you gradfually increase the volume level for sustained periods. If the amplifier begins to run hot, you either need to provide better ventilation to the receiver or think about other speakers.
Another option would be to pick up a power amp for the fronts and leave the recievers amp to drive the rears only. That's an option for the future...or now if you can afford it. You can genrally pick up a good amp pretty inexpensively at Audiogon.
FWIW Kothrush, I powered in my HT, 6ohm fronts, with 8ohm center and rears just fine with my T763 with absolutely no problems. Adding a power amp to the 6ohm fronts did help open up the sound stage quit a bit. The new T775 IMO is a great AVR. It should have problems with what you want to do. The Focal speakers are normally 6ohm, but of course probably dip lower than that at times.
"FWIW Kothrush, I powered in my HT, 6ohm fronts, with 8ohm center and rears just fine with my T763 with absolutely no problems."
Just to make things clear, FWIW, all six Ohm speakers are not the same. Speakers have a wandering impedance "curve" and what one manufacturer might call a six Ohm speaker could be considered a four Ohm load by another manufacturer. The nominal or stated impedance of any speaker is not even a good guess as to how dangerous or difficult it will be for the amplifier as a load. If all speakers were merely a resistive laod it would be much easier to guess which speaker would work well with any amplifier. All speakers are reactive loads however and therefore will present unusual circumstances with each amplifier.
In all likelyhood the six Ohm speakers will be fine with a NAD amplifier. But being a bit careful at first is, IMO, still good advice.
FWIW--I just purchased a "set" of Focal Chorus speakers (L-C-R)...according to the accompanied literature, all of the 700 and 800 series are 8 ohms nominal impedence. AND, they sound absolutely FANTASTIC!!! Many thanks to those on this board who passed along advice!
Kothrush, the NAD is more than powerful enough to drive the speakers, it won't even strain. The Focals are generally very easy to drive and the NAD will switch gears to adapt to a 4 ohm load if necessary anyway. The power section in the T775 is up there with many separate power amp. We drive much harder to drive speakers with that receiver all the time. It's really not a problem at all. I've never even shut down an NAD receiver in 15+ years selling them.
i don't know if "wandering" is the right word for the impedance of speakers.... but they certainly have different resistance at different frequencies.... at 80 hz, they may present a 4 ohm load, at 2k, 40 ohm...
i have never had a problem with amplifiers shutting off under lower loads... even cheap amps... but then, i very rarely exceed 95 db of output.... but- i have had more problems matching levels because of different speakers... (both of the same, and different resistance).... an amp will want to put out more power to a lesser load... but then again, not all 4 ohm drivers are more efficient, and may actually sound softer than really efficient 8 ohm... likewise, you may have 2 pr of 8 ohm speakers, with wildly different efficiencies (or simply better/worse speaker placement)...