For all you electrical experts out there, help me clarify a question I have regard Ohms and speaker loads.

I read this statement when reading about speakers recently.

"When the electricity passes into the speaker, some of it is 'resisted.' The ohms rating of the speaker is how much is resisted, and an indication of how much energy it takes to drive it - the higher the ohms rating, the more difficult it is to drive."

For some reason I was thinking the LOWER the Ohm rating the more difficult a speaker is to drive (i.e a 4 Ohm speaker is more difficult to drive than an 8 Ohm speaker.....2 Ohms more difficult than 4 etc..) I thought this was the reason so many amps are rated for a load 4 ohms and above. I've never seen a warning for driving a speaker rated for greater than 8 Ohms. So I assumed the higher the number, the less resistance. Sort of an inverse relationship. I also recognize that the rating on a speaker is more like an average....it can be higher or lower depending on the frequency. Thanks for your input.

The description is not accurate. They should have said that more voltage is required for a higher impedance to achieve a given wattage. It is not necessairly "harder" to drive a lower impedance speaker - it's more a matter of the amplifier being designed to handle very low impedances such as 2 to 4 ohms.

The less the resistance the higher the current the speaker draws

an ohm is a measure of resistance, so naturally a higher number would indicate more resistance...

"It is not necessairly "harder" to drive a lower impedance speaker - it's more a matter of the amplifier being designed to handle very low impedances such as 2 to 4 ohms."-SH (ill leave the misspelling in for what its worth... hate to agree with you so soon after the last times.)

soundhound had a stereo magazine behind his spelling book in school!

"It is not necessairly "harder" to drive a lower impedance speaker - it's more a matter of the amplifier being designed to handle very low impedances such as 2 to 4 ohms"

Thanks guys. One more question. Why do most amplifier manufacturers warn only against using their amps on loads less than 4 ohms? Why would they not also warn against using the amp at higher impedances like 16 ohms or more? Obviously, there are not very many 16 ohm home speakers available (if any), but there are also few speakers rated for 2 ohms and less, so why the warning? Wouldn't a higher impedance (16 vs. 4) be more potentially damaging to an amp?
16 ohm loads might be possible if drivers were wired in certain configurations. Example: A subwoofer cabinet with two 8 ohm woofers. If you had a mono amplifier that was not rated for loads under 4 ohms, you might wire the woofers in series to achieve a 16 (approx.) ohm load. Probably a bad example, but just trying to better understand.

Thanks,
Steve

Consider that the lower the impedance the closer you are getting to a short which would be 0 ohms. Audio amps need something to work against and low impedance can let them "overwork" them selves causing excessive heat, distortion and other nasties. If the amp can run at 0 ohms it's a welder

Thanks Keta, that analogy makes perfect sense. For some reason, I think my 755 would make a pretty good welder...but I'm not willing to try!

i caught this in a description of b&w speakers,just somebody elses opinion i guess


Sensitivity combined with impedance indicates how much amplifier power is required for the loudspeaker to play at satisfying volume levels. When comparing this spec to low impedance (4 ohm) designs, you must add 3 dB to the figure, since 4 ohm loads draw twice the current from the amplifier, providing the illusion of greater sensitivity, while placing more stress on the amplifier?s power supply. The moderate sensitivity of the Pearl indicates that small amplifiers can achieve realistic levels in all but the largest rooms.

System impedance indicates whether the speaker presents a "hard" or "easy" load on the amplifier. True 8ohm speakers are less amplifier and cable sensitive, and partner well with a broader range of amplifiers, including tube designs.

Today's home theater amplifiers are nowhere as robust as the stereo amplifiers of 20 years ago - the presence of the "6 ohm" switch is a result of this. A good stereo amplifier of that period would have no problem whatsoever driving a 4 ohm load all day long. "Hard" and "Easy" are relative terms - 4 ohms is hard for most home thater amps, but easy for a more robust one, depending on how they're designed.

soundhound - Are you thinking primarily of home theater receivers here as compared to older amps, integrated amps, and receivers? I'd certainly agree when it comes to the typical receiver power amp section, as the "4 ohm" or "6 ohm" switches you mention attest to. On the other hand, I've been under the impression that separate power amps from companies like Outlaw, ATI, Rotel, Anthem, etc. are built robustly enough to handle lower impedance loads without issue.

the great GONK questions the great SOUNDHOUND this should be enough for us all to sit back and LEARN!

not being sarcastic i really appreciate BOTH of your experience above and beyond!

look forward to ALL feedback!

btw, just killed my monitor asw-210 amp....HEARTBREAKER!

I was referring to seperate power amps and receivers. Any amplifier that has the "4 ohm" switch is not robust enough to drive that impedance without the reduction in rail voltages that the switch provides, whether seperate or receiver. This is done for cost reasons mostly, as it would be impractical and costly to make a multi-channel power amplifier with the transistor complement, heavy heatsinking, and large power supply of the more robust stereo amps of 20 years ago. Many of those could drive 2 ohms without complaint.

Home theater amps that have the switch can sometimes drive a 4 ohm load, but the switch limits the power output to levels that won't overload the amp.

what does that switch do, throw a 4 ohm load in series with the output to "stabilize" the ouput?

No. It typically reduces the power supply voltages that feed the output stages of the amp by use of a power transformer with two secondary windings. It essentially transforms the amplifier into a lesser powered one. An "ideal" amplifier that is capable of outputting 200 watts into 8 ohms will output 400 watts into 4 ohms. Many older stereo amps came close to that ideal. The Altec solid state professional amps that I have will do that easily, and they will do almost 800 watts into 2 ohms.

I'm not singling out any particular manufacturer of home theater amps - almost all of them make use of this switch.

Could part of the issue be manufacturers trying to push more out of the 8 ohm value than they used to? Say they made an amp like the example, but instead tried to get up to 250 or 300 watts @ 8 ohms instead of 200. Then they're still kind of limited to the 400 or barely over at 4 ohms.

painttoad, you probably already see this, but it would be better to use the amp's value at the 4 ohm load instead of just doubling the 8 ohm value for the reasons we are discussing now.

i may be going off on a different subject kinda,

i deal more with car than home so i never actually go by the power rating so to speak,speakers are continuously(did i spell that right curegeorg?haha!) variable, i understand that so the wattage at the impedance never comes in at a constant level.(as i believe)but...

i have b&w 601's,passive biamped.if this is an 8 ohm(nom) speaker does that mean each section will be 16 ohms,am i driving my amp half power(load)?
60wpc x 6(at 8 ohms) even though i still push full bandwidth all the way to the speaker x-over, have i reduced the load at all? it sounds better,has better dynamics,doesn't get as hot as it used to.
i thought i knew about audio but i surely never meant to confuse myself(others of course) but never me!

It's still an 8 ohm speaker.

No - due to cost and heat constraints, the power ability must be reduced into 4-6 ohms. Additionally, some manufacturers now are not as honest about their ratings as they once were when most everybody held to rigid FTC rules on stating power output.

Ditto.

Car, home, boat, they're all variable, but just ust the nominal value listed. It's close enough for practical purposes and just easier that way. I believe the amp itself can respond to different frequencies with different power amounts. There isn't much constant, but we can do well enough despite that.

now i am confused.how can that be?

8 ohm with a parallel jumper between them
looks like 2 16 ohm loads to me (or some kind of equivalent)

They are an 8 ohm load because they are not really "in parallel" - they are divided by the crossover network so that each driver only handles part of the bandwidth. Outside of that driver's bandpass, it's essentially no or little load on the amplifier - the other driver takes over. A very loose description.

so, the way you describe it,they are not really separate?i figured with separate inputs it would be a low pass,and a high pass with no interaction between them, can u understand what i'm thinkin'?

They are separate but cover different ranges of the audio spectrum, with a bit of overlap at the crossover region. To go deeper would involve more writing than I have time for right now, so I would suggest you do a Google search on crossover networks.

A very loose description. [/QB][/QUOTE]

i think i liked it better,it's gonna get serious now,isn't it?

thanks SH.

Certainly can't argue with that. The "low impedance" switch has been a staple of receiver power section design for quite a while, and you've written a good summary of the drawbacks involved in that approach. I've even seen some receiver designs that omit the low impedance "4 ohm" switch and simply rate the amps for speaker loads of 6 ohms or higher. (This is something that I noticed when looking at Denon's site this morning - the rear panel of every receiver in their line, from the $400 AVR-1705 up through the $6000 AVR-5805, lists the allowable speaker impedances as 6-16 ohms. I don't know how much factor of safety they have for loads under 6 ohms, but it is indicative of the lighter design approach you're talking about.) It also makes sense that some of the compromises in transistors, power supplies, and heat sinks carry over to separate power amps that pack five or more channels into one chassis. There still seem to be some fairly robust multichannel amp designs available on the market, although I don't know if many of them include the degree of engineering "oomph" found in the amps you're thinking of.

It reminds me of when a friend of mine bought a pair of Martin Logan's a couple years ago. He bought a two-channel Classe amp at the same time, but the speakers came first and his Yamaha receiver couldn't handle the Aeons (a 4 ohm load that could dip below 2 ohms at times), so he had to wait several days after getting the Aeon's before he could listen to them.

i searched around and couldn't find much of exactly what i was looking for but i did find this(i added the quotes)this came from a passive bi-amp statement.

Unlike bi-wiring, """the load to each amplifier is different from that using a single amplifier full range.""" The voltage demands on each amplifier remain the same (each is still fed a full-range input and gives a full-range output), but the current demands are reduced. This of itself can improve the amplifier’s ability to deliver the signal to the speaker.

Be careful when bi-amping that the gain and polarity of each amplifier are the same, otherwise you will compromise the frequency response of the system.

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Bowers & Wilkins home audio and home cinema speakers 2003

am i gonna get sued?

and i have my tweeter gain backed off a bit