How does OHM and sensitivity effect performance?

[PhilV91]

I'm planning to get an Onkyo TX-SR706 and i would like to know if the speaker is rated at 4 ohms verses 8 ohms what effect will this have on performance? Also the sensitivity like 86db versus 92db what effect does that have? Most speakers ive seen fall into one of these two types.

 

[Adam]

A higher sensitivity means that the speaker will play louder for a given power input. In other words, a speaker with a sensitivity of 92dB will play louder with the Onkyo 706 than would a speaker with a sensitivity of 86dB.

The lower the impedance (ohms), the more current the amp has to supply. I'll check to see if the 706 can handle a 4 ohm load.

 

[Adam]

As an update (and something that you may have already known), the 706 can handle speakers rated at 4 ohms.

 

[PhilV91]

As an update (and something that you may have already known), the 706 can handle speakers rated at 4 ohms.

I didnt know thanks. But If i have 2 speakers say rated 150 watts one has 4 ohms and the other has 8 ohms and the Onkyo i believe is rated 100 watts x7 what effect will this have? Are you saying the 4 ohm will cut the rating in half to 50 watts?

 

[Adam]

I didnt know thanks. But If i have 2 speakers say rated 150 watts one has 4 ohms and the other has 8 ohms and the Onkyo i believe is rated 100 watts x7 what effect will this have? Are you saying the 4 ohm will cut the rating in half to 50 watts?

No, the 4-ohm speakers won't cut the rating in half. In fact, the power output will be higher for the lower impedance speakers.

The specs don't give the continuous power output for various impedances, but as a matter of comparison, they do give the power output at 1 kHz with one channel driven: 8 ohms = 125 W, 6 ohms = 160 W.

 

[PhilV91]

so if your looking at 2 speakers and all other things being equal you would get the 4 ohm over the 8 ohm?

 

[Adam]

so if your looking at 2 speakers and all other things being equal you would get the 4 ohm over the 8 ohm?

Here's where my knowledge breaks down, so I hope others chime in. While the power output of the amp goes up for lower impedances, I don't know if that necessarily equates to it being any louder.

I'm more of a fan of "average" impedance speakers (i.e. 6-8 ohms) because more electronics are designed to handle them than are designed to handle the 4-ohm speakers. As one example of many, the Onkyo 506 (which costs under $200) isn't rated for speakers that are below 6 ohms. Because the lower impedance speakers draw more current, amps need to be designed to handle that - and the lower priced receivers that I've looked into aren't.

 

[PhilV91]

I also heard the Onkyos run kind of hot so im guessing since the 4 ohms draw more current that means they would make the Onkyo run even hotter than the 8 ohm correct?

 

[Adam]

I also heard the Onkyos run kind of hot so im guessing since the 4 ohms draw more current that means they would make the Onkyo run even hotter than the 8 ohm correct?

That's a good question. I don't know the answer to that, but I would suspect that it wouldn't be very noticeable. The amount of power that you'd normally use to power your speakers (if you're like most people) wouldn't be very high - less than one watt per speaker. I have the impression that those units can run hot whether you are powering the speakers or not. I was at Circuit City about a year ago and felt an Onkyo 805 that was in their show room. It was on, but it wasn't powering anything - and it was very hot to the touch. That doesn't mean that the 706 is that way, but rather an example of a unit running hot when not playing through the speakers.

 

[Alex2507]

so if your looking at 2 speakers and all other things being equal you would get the 4 ohm over the 8 ohm?

I think the take away message here is that with speakers nothing is ever equal. Picking the speaker that you like the best is critical. I believe the way it works is that with a 4 ohm speaker the power supply portion of the amplifier must provide double the wattage to the amp. With the inconsistencies in the way speaker impedance and amplifier output is rated you would be much more out of the 'clipping' range with an 8 ohm speaker. Even an 8 ohm speaker will spend much of it's life close to 4 ohms.

Having said all that I understand that you have to turn things up really loud (dangerously loud) before you run the risk of clipping a modern receiver. Classical music is suppose to be tough on them.

Any idea which speakers you are interested in? They all behave differently regardless of their ratings. I wouldn't worry about the Onkyo heat issue. They have been blaring tunes for quite some time and I don't expect that to change. I've yet to hear of one failing due to heat.

 

[PhilV91]

My budget is 1k im looking at many different ones but here are some. TSC TSAT 2000, Mirage nanosat, Polk RM95, Pure Acoustics Dream Tower, and Im conidering Aperion Intimus 4T or Definitive Pro 800 but i really dont want to spend that much im trying justify spending that much.

 

[Alex2507]

TSC has popped up in conversation a lot recently and in a good way.

This is the speaker you mentioned:

http://www.thespeakercompany.com/TSAT-2000-Satellite-Speaker-Single-P60.aspx

That whole 3-1/2 woofer thing with a frequency response of 120Hz doesn't give me the warm fuzzies but your needs may require that size. I don't want to just start barking about Infinity Primus 362's like a trained monkey ... too late.

Seriously, now that you've provided a budget and a few options a discussion can begin about speakers. How many do you need? 5.1? 7.1? Is the sub included in the budget?

 

[pzaur]

My father in-law's Onkyo runs very hot. It used to shut off periodically during use until my brother in-law convinced him that the door on the entertainment center was restricting air flow causing it to over heat. There haven't been any issues since the change.

It still runs hot and doesn't shut off.

-pat

 

[TLS Guy]

I didnt know thanks. But If i have 2 speakers say rated 150 watts one has 4 ohms and the other has 8 ohms and the Onkyo i believe is rated 100 watts x7 what effect will this have? Are you saying the 4 ohm will cut the rating in half to 50 watts?

Unless the amps in the receiver can maintain output voltage as the impedance drops the power delivered will be halved. All of the cheaper receivers and even the moderately priced ones, actually can only deliver half their rated power into four ohms and are stressed.

Most speakers today, even if rated at 8 ohms are actually four ohm, especially if they are diffraction compensated, which good speakers are. However, if the amp provides half its rated power, that is only a 3db reduction in spl. The difficulty comes in that speakers are reactive loads, and voltage and current are out of phase to varying degrees. This is hardly ever specified. So some speakers are known to be power hogs and require the amp to provide more current and power to the speaker than you would think from the impedance curve alone. This is particularly true of the B & W 800 series and many of the Dynaudios. These speakers require mega amps.

I can personally attest to the fact that the B & W 800 series require huge amps, and are quite unsuitable to power from any receiver I'm aware of. Unless they are driven by very good powerful amps, they are very underwhelming. I think this is true of the whole B & W range to some degree.

For this reason I'm not as keen on receivers as many others on the forums, though I understand their convenience.

 

[Davemcc]

Impedance varies with frequency. It's not a constant. That's why it's referred to in the specs as nominal impedance. Manufacturers simply pick a number that they think will best reflect a speakers performance. An 8 ohm nominal speaker may dip into the 4 ohm range at some frequencies. To find out how a speaker really performs, you would have to look at a graph of impedance by frequency.

 

[Rickster71]

so if your looking at 2 speakers and all other things being equal you would get the 4 ohm over the 8 ohm?

Since you put it that way; I'd take the 8ohm.
My opinion is that; even though a speaker isn't a static load.
An 8 ohm speaker won't dip down into 4ohm or lower territory, as much at a nominal 4ohm speaker would.

These were just on sale, with a $50 off coupon for Audioholic members.
I got two pairs.

http://www.thespeakercompany.com/TSBL-65-2-way-Bookshelf-Speaker-Pair-P46C6.aspx
Even at regular price, they are a great speaker.
Try them. If you don't like them TSC pays shipping both ways

 

[Pyrrho]

I'm planning to get an Onkyo TX-SR706 and i would like to know if the speaker is rated at 4 ohms verses 8 ohms what effect will this have on performance? Also the sensitivity like 86db versus 92db what effect does that have? Most speakers ive seen fall into one of these two types.

I recommend that you select your speakers first, and then decide if the amplifier you are thinking about can handle them. Speakers make more difference in the quality of the sound than anything else, so you should put your efforts into selecting the best ones you can afford. I recommend going out and listening to as many different models and types in your price range as you can stand to listen to, and then pick the ones you like best.

As others have said, the impedance and the sensitivity of the speaker have to do with how difficult a load it is for the amplifier, and how loud it will play at a given power input. Neither have anything whatsoever to do with sound quality of the speaker. In other words, since you have not yet purchased the amplifier, you should pretty much ignore those specifications and select the speakers you like best. If it turns out that the speakers you want are low impedance or have a low sensitivity, then you will need to consider whether or not you can afford the amplification necessary for them. In my case, I ended up with speakers that are an easy 8 ohms, of normal efficiency, and they can be used with pretty much any amplifier made. Had I preferred something with a low impedance or terribly inefficient, then I would have had to spend more money on the amplification to deal with them.