T15 Ohm Setting

Technolust

Polkians,

I went to BB looking to pick up a set of speakers to build a surround sound last Christmas season for around $150. Saw they had a sale on these T15's for $50 a set so naturally I bought all three sets they had and built the surrround sound in one day instead 3 months!!! Yippee for me, now I don't have a complaint at all with these speakers; honestly I prob don't push them that hard either.

My question is I have an Onkyo TX-NR787 receiver I picked up on sale as well a few weeks ago and it only has 4 Ohm or 6 Ohm setting. How do I know what Ohm to set this as if my T15 are 8 Ohm?

Can someone please explain what Ohm's mean?

Thanks a bunch!!!

-Technolust

mhardy6647

Ohms is a measurement of the "impedance" of the speaker as it presents itself as a "load" to the amplifier. The lower the number, the closer the speaker is to being a short circuit to the amplifier. Practically speaking, the lower the impedance (Ohms) value, the more current the amplifier will be called to deliver to the speakers (all else being equal).

Semi-technical aside. The interrelationships between voltage, current, resistance/impedance and power are governed by a set of simple, interrelated equations, all based on a principle called "Ohm's Law". Resistance and impedance are related but not identical properties; for speakers and music, impedance is the parameter represented by the number of Ohms.

As to which setting you should use -- I have no clue. 6 is closer to 8 than is 4, so I would think "6" would be the better choice, but I'll defer to someone with more experience with receivers like yours to answer more definitively.

Another semi-technical aside. The "impedance" of a speaker varies as a function of the
frequency of the signal being fed to it. In other words, the impedance presented by the speaker to the amp in the bass frequencies (say, at 50 Hz) will almost certainly be different than that presented in the midrange (say 400 Hz) or the treble (say 8,000 Hz). That "8 ohm" impedance is a nominal value and doesn't actually even say much about
the "impedance curve" (impedance as a function of frequency) of your speakers. Again, practically speaking, 6 is probably "close enough for Government work".

I hope this is helpful and not overly confusing!

mhardy6647

The basic equation of Ohm's Law relates voltage (usually abbreviated "E"), current ("I") and resistance or impedance ("R").

E = I x R

Power ("P") is intimately related to these parameters, too.

P = E x I (which is also equal to I^2 x R)

Here are a bunch of algebraic manipulations of those two basic equations that can be used to calculate one parameter given two others




The usual analogy for understanding Ohm's law is to think of a garden hose hooked to a faucet with a given amount of water pressure.
Water pressure is like "E"
The flow rate is like "I"
The size (cross-sectional area) of the hose is like "R"

rpf65

Nominal impedance of the T15 speaker is 8 ohms. Use the 6 ohm setting.

Technolust

Mhardy6647,

Thank you so much for all the info that certainly helps clarify things for sure. However, it does get a little confusing when adding the frequency. The pie chart on the other hand is like all the buttons on the calculator you never push but I do remember E = I X R from high school so that was helpful. So essentially what it is saying is that an 8 Ohm speaker has a higher resistance than a 4 Ohm where the 4 Ohm speaker will allow more Voltage & Wattage to pass through.

This would make sense because it feels like the sound is more clear/less muffled on the 4 Ohm setting than the 6 Ohm setting.

Technolust

rpf65,

This leaves me to a question for you. Since using the 6 Ohm setting, the sound coming from the speakers is muffled compared to the 4 Ohm setting. So if I set it to the 4 Ohm setting will this hurt the speakers or the receiver since I like the sound better at that setting?

Also note that I rarely ever bring the volume up past 60 dBs.

Thoughts?

rpf65 wrote: »

Nominal impedance of the T15 speaker is 8 ohms. Use the 6 ohm setting.

mlistens03

Technolust wrote: »

rpf65,

This leaves me to a question for you. Since using the 6 Ohm setting, the sound coming from the speakers is muffled compared to the 4 Ohm setting. So if I set it to the 4 Ohm setting will this hurt the speakers or the receiver since I like the sound better at that setting?

Also note that I rarely ever bring the volume up past 60 dBs.

Thoughts?

rpf65 wrote: »

Nominal impedance of the T15 speaker is 8 ohms. Use the 6 ohm setting.

At those volumes you’ll probably be okay whichever way you go.
I don’t know much about your specific receiver, but AFAIK, a lot of receivers use the impedance switch to choke the power supply, and keep the amplifier from pushing more voltage/current than it can handle, in order to keep it from overheating, and then cooking itself. So, if I’m correct, you should, in theory, not have as much extra power (or headroom) in the four ohm mode.

rpf65

Technolust wrote: »

rpf65,

This leaves me to a question for you. Since using the 6 Ohm setting, the sound coming from the speakers is muffled compared to the 4 Ohm setting. So if I set it to the 4 Ohm setting will this hurt the speakers or the receiver since I like the sound better at that setting?

Also note that I rarely ever bring the volume up past 60 dBs.

Thoughts?

rpf65 wrote: »

Nominal impedance of the T15 speaker is 8 ohms. Use the 6 ohm setting.

Manufacturers offer the difference impedance settings so that the source can better match the load. The lower the nominal impedance the speaker, the harder it is to drive. Many AVR’s and speakers have been damaged or completely destroyed by trying to drive 4 ohm nominal impedance speakers. Really should use a high current amp to drive 4 ohm speakers, but that’s another topic.

The 4 ohm setting will lower the voltage supplied to the amplifier in your AVR. This is to further protect the amp section and power supply from damage caused by overheating. Both your AVR and speakers should be fine weather you select the 4 or 6 ohm setting on your AVR, when using 8 ohm nominal impedance speakers.

tonyb

The short answer is....set them to the 6 ohm setting and forget about it.

Technolust

Thank you two for the help and guidance. I have an Onkyo TX-NR787 receiver and I have changed the impedance to 6. I also spoke with both Polk support and Onkyo support, both stated to set the impedance to 6 OHMs as well. Talking to Onkyo, we discovered I had the wrong crossover settings and changed the center channel to 100Hz and increased the volume to the surround and back speakers which fixed the muffling sound.

After the changes the sound is far better my question if you know it is are Dolby Atmos speakers are actually necessary/worth getting?

Thoughts?

mlistens03

I think that Atmos is worth it, but I think with your setup, I’d go towards better main and center channel speakers before Atmos. Others may feel differently.

tonyp063

I would explore the subwoofer part of the setup before I went anywhere else.