Someone explain ohm ratings to me?

[slider33]

I just bought a Toshiba HD-A1 and of course, as you all know, I now "have" to upgrade my receiver to take advantage of TrueHD. Heck, to be honest I am still using two channel. Anyway, I am looking for an entry level receiver and have been looking at something like the Pio VSX-516/816 or a few different Yamahas. Now, my speakers are 6 ohms, 60 watt max (100 watt center). I will be upgrading these shortly but in the meantime I need to use them. The Pio receivers look like they are 8 ohm only, and some of the Yamahas can do both. Will an 8 ohm receiver drive my speakers ok? Would I be better off going to a little better receiver that can do 6 ohms (HK 140 or Panny XR57) even though it may have less wattage? (HK is only 45w I believe).

Thanks a lot.

[ekb]

I'm sure the Pioneer will be able to handle 6 ohms. It's not black and white. At 4 ohms and loud volumes the Pio might be in trouble. But at 6 ohms and reasonable volumes you should be OK.

The HK tend to be rated more honestly. The lower wattage doesn't mean that it's less than other receivers. Most other companies stretch the truth.

Ed

[slider33]

Thank you. I can't have my system very loud anyway because I live in an apartment, but I am looking for a nice 5.1 (7.1 capable) setup to work with my new A1. I have narrowed it down to a few receivers but I'll start another thread to ask about those.

[cadbury8]

If you will be looking into upgrading your speakers and you are getting a receiver that matches the speakers that you have now then i would just make sure the receiver has pre amp outs so you can hook up an amp. The reason i mention this is you could end up in a trick bag if you find speakers you like that will require more power.

[slider33]

[QUOTE=cadbury8]If you will be looking into upgrading your speakers and you are getting a receiver that matches the speakers that you have now then i would just make sure the receiver has pre amp outs so you can hook up an amp. The reason i mention this is you could end up in a trick bag if you find speakers you like that will require more power.[/QUOTE]

Thanks for the heads up. I doubt this will be a problem because I live in an apartment and will probably just be getting decent satellites for the rear and bookshelfs for the front. Obviously a sub and center to match. No floor standing for me.

[Sdiver2489]

[QUOTE=slider33]Thanks for the heads up. I doubt this will be a problem because I live in an apartment and will probably just be getting decent satellites for the rear and bookshelfs for the front. Obviously a sub and center to match. No floor standing for me.[/QUOTE]

FYI there are plenty of 4 ohm bookshelfs out there

[slider33]

[QUOTE=Sdiver2489]FYI there are plenty of 4 ohm bookshelfs out there[/QUOTE]

Fair enough, but I won't buy them :D

lol

[swest]

[QUOTE=slider33]I just bought a Toshiba HD-A1 and of course, as you all know, I now "have" to upgrade my receiver to take advantage of TrueHD. Heck, to be honest I am still using two channel. Anyway, I am looking for an entry level receiver and have been looking at something like the Pio VSX-516/816 or a few different Yamahas. Now, my speakers are 6 ohms, 60 watt max (100 watt center). I will be upgrading these shortly but in the meantime I need to use them. The Pio receivers look like they are 8 ohm only, and some of the Yamahas can do both. Will an 8 ohm receiver drive my speakers ok? Would I be better off going to a little better receiver that can do 6 ohms (HK 140 or Panny XR57) even though it may have less wattage? (HK is only 45w I believe).

Thanks a lot.[/QUOTE]
Your title is 'Someone explain ohm ratings to me?'. The answer to that is that it's all about 'current'. You know, Ohm's Law. In this case the relevant form is E=IR (Voltage = Current * Resistance). In the case of alternating current, the Resistance translates into Impedance, which is how speakers are rated.

So, for a given Voltage level (say, 28.3 volts) delivered to the speakers, a 6 ohm speaker (at a given frequency) will draw more Current than an 8 ohm speaker (at the same frequency) =>

28.3v = 4.7a * 6ohms
and

28.3v = 3.5a * 8ohms
i.e. the 6ohm speaker draws 4.7amp vs 3.5amps for the 8ohm speaker.

The calculations for power dissipation are also bound up with Ohm's Law (E^2/R=P), so in the above case, the 6ohm load is dissipating 134 watts, while the 8ohm load is dissipating 100 watts. This makes the amplifier run hotter with the 6ohm speaker, and, if it's not designed for it, will make it shut down or even fail prematurely. So we say that a 6 ohm speaker is a more difficult 'load' than an 8 ohm speaker.

The good news is that, in 5.1 or 7.1 Home Theater applications, a preponderance of the energy, by frequency, being delivered to the speakers is being delivered to a standalone unit: the Subwoofer. And its program is delivered from the receiver at line-level, so the receiver is isolated from issues of power for that range of the spectrum.

Now, I don't know the actual breakdown by percentile, but the energy being dissipated for that portion of the audio spectrum below 80 hz is probably the same order of magnitude as the energy being dissipated for the audio spectrum above 80 hz (experts should chime in here.) So that, as long as the amps in the receiver are only being asked to reproduce frequencies above 80hz, you probably will never run into trouble with reasonable loads (i.e. speakers of 4ohm ratings and above).

As it turns out, the VSX-816 has switchable impedances, and allows for 6ohm loads in its design. And, although I'm usually a Yamaha kinda guy, at least when it comes to receivers, the Pioneer VSX-816 is quite a piece of gear for <$300...

Good luck.

[slider33]

Wow thanks a lot for the very informative post. I am happy to hear the 816 has switchable impedances, I didn't think it did. I think I have decided to go with this one as the options you get for the dollar is great.

[swest]

[QUOTE=swest]...The good news is that, in 5.1 or 7.1 Home Theater applications, a preponderance of the energy, by frequency, being delivered to the speakers is being delivered to a standalone unit: the Subwoofer. And its program is delivered from the receiver at line-level, so the receiver is isolated from issues of power for that range of the spectrum...[/QUOTE]
Sorry, this paragraph makes the assumption that you have used the unit's bass management to set all your speakers to Small...

"And you know what happens when you make an assumption, you make an ass out of you and umption." Thank you, Samuel L. Jackson, for that pithy quotable.

[slider33]

[QUOTE=swest]Sorry, this paragraph makes the assumption that you have used the unit's bass management to set all your speakers to Small...

"And you know what happens when you make an assumption, you make an ass out of you and umption." Thank you, Samuel L. Jackson, for that pithy quotable.[/QUOTE]

I always liked "when you assume, you make an ASS of U and ME"

:D

[swest]

[QUOTE=swest]...Now, I don't know the actual breakdown by percentile, but the energy being dissipated for that portion of the audio spectrum below 80 hz is probably the same order of magnitude as the energy being dissipated for the audio spectrum above 80 hz (experts should chime in here.) So that, as long as the amps in the receiver are only being asked to reproduce frequencies above 80hz, you probably will never run into trouble with reasonable loads (i.e. speakers of 4ohm ratings and above)...[/QUOTE]
Well, the experts haven't gotten to us yet, so I'll have a go at it...

While the above statement is not entirely incorrect, the whole truth is not quite what I thought it was, and I should have realized it.

If you look at the Pink Noise power distribution (which is logarithmic, like we hear), you see that power is equal in frequency ranges that are proportional, so that the frequency range from 20hz to 80hz has the same power as the frequency range from 80hz to 320hz... If you use that particular proportion (20hz to 80hz) to break down the entire audio spectrum, you get something like:

20-80hz
80-320hz
320-1280hz
1280-5120hz
5120-20480hz
so that one-fifth (1/5) of the total power dissipation of the entire audio spectrum takes place in the sub-80hz range, again, assuming uniform frequency distribution at equal volume (pink noise).

So, if one uses a strict interpretation of 'order of magnitude', then 25% is still within the ballpark...

This result is still a good thing, though. And I would certainly stand by the conclusion for 6ohm speakers... Drawing the same conclusion for the 4ohm case might be a little iffy.

Experts?

p.s. Of course, in the foregoing discussion the definition of sub-80hz is limited, and rather abitrarily so, down to 20hz even though we all know that there are soundtracks with content even below that...