Ohms

[jgstudios]

Occasionally I see 6 ohm speakers that I like. THere is a pair that I'm very interested in purchasing. From previous posts I found out that my current Polk Rti a9 speakers are rated "nominally" for 8 ohms. These have actually been measured closer to 6.34 ohms or something like that, and I've read that this kind of nebulous rating is a common occurrence for many speakers brands. It causes confusion for someone new, wishing to spend hard earned money on this gear. Most of the power amps I see show wattage specs for 4 and 8 ohm speakers. One amp in particular that I'm looking to purchase very soon to connect to the Polks specs out with ratings for 800 watts into 4 ohms and 550 watts into 8 ohms. What would the math for the wattage come out to with 6 ohms rated speakers? What setting should I set the amp to if I were to connect 6 ohm speakers, what about my Polks are they 6 ohm or 8 ohm? I'm not even sure if that amp has specific settings that I can change. My current Pioneer AVR does have settings for 4 and 8 ohm speakers, but not for 6 ohms. Just out of curiosity, is there a calculation for wattage that I can use with other amplifiers against a given set of speakers if the rating is not listed for a specific speaker ohm rating?

More Info: OK, to answer some requests from posters. The Amp will be the Emotiva XPA-DR2. I realize that the Polk specs for 500 Watts is peak power, but MANY posters on various forums stated that more power would bring these speakers to life and I figured that having plenty of overhead would give me room to grow with more gear in the next year or two. I'm mainly getting this Amp for future growth, not just for the Polks. My Polks are the first of future possible purchases, so I have yet to decide exactly what the future holds. That Ohm measurement that I referred to was me trying to remember the info from the link below, so that information I listed was dead wrong, sorry about that. Perhaps you guys can interpret this for me and give me correct info that a newb can understand. Looks like it was 4.49 Ohms at 67 Hz. But I'm not really sure what that means as far as it's true specs. I shoulda just kept my mouth shut on that. My current Model AVR is Pioneer Elite VSX 33. So from what I've read below I don't need the 500 watts for these speakers, but maybe I can save some money and get a lesser powered 200 Watt amp and still plan for future gear changes. I will be using the Pioneeer AVR pre-outs into the new Amp. I will be getting a new pre-amp sometime this year. I will be getting more speakers this year, and into the future. But I am pretty happy with the Polks so far paired with a 12" sub. I'm getting the Bass I like, and it's also working well as a 2.1 system for movies/TV. I will be fleshing out the surround sound into a 5.1 environment. But my gears are turning on outfitting other rooms in my house with more stuff. Dedicated music stereo system, maybe wireless, not sure yet. That's the fun of this so far. Learning, getting advice and researching. That's alot of fun to me. The listening enjoyment is the cherry on top. Thanks. to all for your advice. JG

https://www.soundandvision.com/content/polk-rti-a9-speaker-system-ht-labs-measures

 

[Verdinut]

First, except for some ribbon and possibly some electrostatic speakers, the impedance of speakers varies from one frequency to another. The 6.34 figure you stated cannot represent a realistic specification for a speaker system.

What is the amplifier you are interested in purchasing? Some solid state amplifiers and many receivers have an impedance switch and it should always be fixed to the 8 ohm position. If you use a 4 ohm speaker and set the switch to 4 ohms, the power output of your amplifier will be reduced and here at AH, we don't recommend to proceed that way:

https://www.audioholics.com/audio-amplifier/impedance-selector-switch-1

The output of an amp for a 6 ohm load will vary depending on its power supply and design. There is no easily calculation as such to obtain the exact figure. If the manufacturer specifies an output rating for 4 ohms, then there should be no problem with driving a 6 ohm speaker.

 

[ski2xblack]

There is no easily calculation as such to obtain the exact figure.

Well, yes, but it's safe to conclude that into 6 ohms it will produce >550w and <800w...which will still be beyond adequate for all but the most ridiculous of domestic rigs, and certainly more than enough to flog his polks into submission.

With those sort of power numbers it's probably a pro amp, so it's doubtful that it has a supply limiting impedance selector switch a la the typical AVR.

Hey, OP, help us help you. What specific amp are you looking to purchase soon? What model is your current Pioneer AVR? What convinces you that you need to add external amplification? (Take this little test that Gene and friends came up with and it will help you determine the answer.)

 

[lovinthehd]

Many speakers can vary quite a bit from their nominal rating and can be measured by frequency and represented in a chart like this for a speaker I own that's nominally 8 ohm (an Ascend Sierra 1)

 

[Swerd]

Occasionally I see 6 ohm speakers that I like. There is a pair that I'm very interested in purchasing. From previous posts I found out that my current Polk Rti a9 speakers are rated "nominally" for 8 ohms. These have actually been measured closer to 6.34 ohms or something like that, and I've read that this kind of nebulous rating is a common occurrence for many speakers brands. It causes confusion for someone new, wishing to spend hard earned money on this gear.

Verdinut, lovinthehd, and ski2xblack are correct. Impedance in loudspeakers is not a constant value, it varies with the frequency. For example, the Polk RTi A1 as measured by SoundStage Network:

It's impedance goes a tiny bit lower than 4 ohms, around 200 Hz. For much of the audio range, it's impedance is above that. For the purposes of choosing an amp, impedance values lower than 4 ohms can pose a problem for some amps, but higher impedances pose no problem. Definitions of "nominal impedance" can vary, but as you can see, an impedance curve tells you more than a single number.

Most of the power amps I see show wattage specs for 4 and 8 ohm speakers. One amp in particular that I'm looking to purchase very soon to connect to the Polks specs out with ratings for 800 watts into 4 ohms and 550 watts into 8 ohms.

Sound and Vision's HT Lab measures the ATi A9 speaker's sensitivity as 90.5 dB (500 Hz to 2 kHz). Measured 1 meter away, 1 watt (2.83 volts) produces sound that is 90.5 dB – that's quite loud. Polk rates this speaker as nominally 8 ohms. By those numbers, this speaker should not be hard to drive. If you plan on using a 550 watt amp at 8 ohms, it will be loafing while driving these speakers. It might be more amp than you need. For less money, even a 200-250 watt/channel amp would be loafing.

What would the math for the wattage come out to with 6 ohms rated speakers? What setting should I set the amp to if I were to connect 6 ohm speakers, what about my Polks are they 6 ohm or 8 ohm? I'm not even sure if that amp has specific settings that I can change. My current Pioneer AVR does have settings for 4 and 8 ohm speakers, but not for 6 ohms. Just out of curiosity, is there a calculation for wattage that I can use with other amplifiers against a given set of speakers if the rating is not listed for a specific speaker ohm rating?

Many AVRs, such as your Pioneer, have impedance switches that actually limit the output of the AVR's amp section so it won't overheat or fail. Most or all stand-alone amps do not have those switches, and should be stable (they won't go into oscillation, overheat, or fail) at lower impedances.

Because speaker impedance varies with the frequency, it's pointless to worry about calculating the wattage they might draw. With the right lab test equipment you could measure it, but any effort at calculating would be only a rough estimation. Don't worry about it.

 

[markw]

Is this them? Why do you think you need all those watts?

https://www.crutchfield.com/p_107RTIA9C/Polk-Audio-RTi-A9-Cherry.html

Let's look at this logically.

First, they are speced for a sensitivity of 90 db. So one watt will be quite loud.

Second, they say they can handle 50 - 500 watts. Translated, that meant that an amp that produced 50 clean watts will sound purty durn good with them.

That 500 watt figure? That's the maximum power they MIGHT survive for very, very short periods of time. Look at that 500 watt figure like tire speed ratings. Just because you put on "V" series tires, rated for 149 mph, that doesn't mean you must drive 149 mph to get good performance.

Oh, that 6.34 ohm rating you say you measured on your speakers? Dollars to donuts you slapped an ohmmeter on it to get that reading. That's not an "impedance", that's a DC resistance.

Big difference. DC resistance is stable. Impedance is not

As others have already pointed out, impedance varies from very low to very high depending on what frequency is being reproduced. Also, please note many manufacturers qualify that number with the word "nominal", which means it varies and is pretty much an educated guess.

 

[jgstudios]

Well, yes, but it's safe to conclude that into 6 ohms it will produce >550w and <800w...which will still be beyond adequate for all but the most ridiculous of domestic rigs, and certainly more than enough to flog his polks into submission.

With those sort of power numbers it's probably a pro amp, so it's doubtful that it has a supply limiting impedance selector switch a la the typical AVR.

Hey, OP, help us help you. What specific amp are you looking to purchase soon? What model is your current Pioneer AVR? What convinces you that you need to add external amplification? (Take this little test that Gene and friends came up with and it will help you determine the answer.)

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Thanks ski2xblack, I did amend my original post with more info. Please check it and let me know what you think. JG

 

[GrimSurfer]

Watt's all this about ohms? (Sorry... Couldn't resist)

 

[markw]

Watt's all this about ohms? (Sorry... Couldn't resist)

View attachment 28658

Jeez, guy. Try to stay current, will ya?

 

[GrimSurfer]

It's hard... My teachers always said that I lacked the capacitance for science!

 

[lovinthehd]

It's hard... My teachers always said that I lacked the capacitance for science!

Where's the cringe smiley?

 

[GrimSurfer]

My old English teacher is looking for it ATT because of my diction!

 

[lovinthehd]

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Thanks ski2xblack, I did amend my original post with more info. Please check it and let me know what you think. JG

FWIW just easier if you add information as the conversation goes on rather than amending your original post which then can make the next few answers look odd.

Polk forums are famous for their fanboys and the speakers-are-hungry and you need the most massive amp possible without regard to actual use sort of nonsense. Amp needs are related mostly to your actual use as well as the speakers involved...how loud do you want to go with what allowance for headroom and at what distances are you from the speakers? I'd suggest you get a feel for the relationships of power/use by playing around with an spl calculator like this http://myhometheater.homestead.com/splcalculator.html

Generally I'd say just use your avr until you run out of gas, and if it's not the speakers themselves running out of gas (they're not limitless at the upper end) then maybe an external amp might be in order....

 

[markw]

Simply adding more power is not an end all and be all solution. n fact, at some point it actually does more harm than good, and I'm not talking about smoking the speakers.

OP, meet "thermal compression"

http://www.ajaudio.co.uk/Loudspeaker thermal compression.htm

 

[jgstudios]

OK All this info is good. I feel a bit more at-ease. So, I've always heard since my youger days in the 70s and throughout the years that using a power amp will expand the headroom of the system, in particular to the speakers, which will drive them more easily and povide more dynamics. My interpretation of that is I will hear more detail from the speakers. Also, they will be given the power they need without taxing the amp. Prior to purchasing my polks, my AVR never felt warm with my old speakers. Now with the Polks, I have to turn the volume up higher and the AVR is noticeably warmer; not hot, but it's certainly pretty warm. It's certainly pushing more juice out to the speakers to get the same amount of volume that I'm used to hearing. As I approach 0 my brain starts to think about clipping, but I'm currently going to around -18 or -15 Db on the volume knob to get to a nice volume level for my ears. It's possible that as I get more adjusted to the new speakers I will be inching my way toward louder volumes and getting closer to 0. How bad is that? Now, with the power amp, I"d be using the AVR pre-outs, thereby bypassing the AVR amplifier, wouldnt' that prevent any risk of shortening the life of my AVR and give the job of powering the speakers to the external power amp? Is that correct? I'm hoping also, that this could provide some noticeable difference in the quality of the speaker sound? Am I thinking about this correctly?

 

[markw]

Well, apparently what we offer here doesn't sufficiently answer your questions. Maybe some of those "MANY posters on various forums ""can give you a satisfactory answer.

But, here's a hint: If you aren't satisfied with the sound with what you currently have, perhaps you should reconsider your speaker choice. More power won't change the character of a speaker and, just because others like a speaker doesn't mean you will, no matter how many people rave about it.

 

[ski2xblack]

Please check it and let me know what you think.

Ok, it's one of the new EMO amps. Looks good on paper, should have zero issues with the load your polks present, and has more power than you would likely reasonably use. In terms of dbW, it will get ~6.6db louder than your Pioneer before running out of gas. That's a significant difference. And it can deliver power in excess of your polk's rated max, so there's that.

Generally speaking, you don't want to clip your amp, ever, so too much power is just enough. But as Markw just pointed out, there are finite limits to the brute force approach. So before your splurge on watts you may or may not use, you should still take that "do I need an amp" quiz that I linked to in my first post, and also mess around with that peak spl calculator that lovin linked. That should give you a more concrete idea if you need 500w, or could get by with a less powerful, less expensive amp, or skip it entirely and allocate those funds to something else (for the cost of the Emo you could get a pair or three of serious quality subs, which would provide a far more tangible improvement than adding watts you may or may not even need).

 

[jgstudios]

OK, guys, thanks for all the info. It's much appreciated I will study your advice. If I spoke out of turn, I didn't mean to offend. I will bow out from this post.

 

[davidscott]

Damn I thought this was a thread about OHM speakers.

 

[markw]