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What are the benefits of 4 ohm speakers?

Discussion in 'Audio Hardware' started by Henry J, Apr 27, 2021.

  1. regore beltomes

    regore beltomes Forum Resident

    Location:
    Helenville, WI
    A 4 ohm speaker will give higher SPL at a given voltage but at twice the current. I=E/R where R is the speaker impedance.
    E is the voltage supplied by the amp which is fixed. Therefore when impedance is halved current is doubled.
     
  2. tumbleweed

    tumbleweed Intermittent audiophile

    Location:
    Colorado foothills
    SandAndGlass likes this.
  3. SandAndGlass

    SandAndGlass Twilight Forum Resident

    Insurance is good. Very few Class A/B amps will go below 4-Ohms. Most amps that will are class "D".
     
    Khorn likes this.
  4. thetakeout

    thetakeout Active Member

    Location:
    Texas
    Sorry if this has already been posted. This is one man's opinion on the op's question. I have no dog in this hunt. My speakers are 12 ohms and 8 ohms.

     
  5. SandAndGlass

    SandAndGlass Twilight Forum Resident

    Here are some key points from the article:

    "NAD amplifiers and receivers. Thus we can rate our receivers with a difficult 4-Ohm load, with ALL channels driven simultaneously, over the FULL frequency bandwidth (20Hz - 20kHz), and at rated distortion. This is the Full-Disclosure rating method on which all our amplifier and receiver specs are based, and it's a far cry from the FTC's minimal requirement of using an 8 Ohm load, any channel (singular), at an easy 1 kHz frequency, with no distortion specified!"

    First, when any company measures the power of an amplifier, they don't use a speaker, they use a pure resistive load. This is so there is no reactance to effect the amplifiers performance (this is fine).

    Today, an amplifier may have several channels, such as amplifiers used for home theater surround sound. It is one thing to measure an amps performance with only one or two channels, instead of with all channels operating at a time.

    If you had an amplifier that was rated at 100-Watts per-channel and it had 5-channels, then it would need to to have a power supply that could deliver 500-Watts, so each channel could operate at full power. This is rarely done. In the case of a stereo amplifier, they will typically state rated power "with both channels driven".

    Stated power without a distortion limit means nothing. Some might list power at distortion limit at 1-Watt, some at 0.5-Watts or even lower.

    They might state the amplifiers power with a 1-kHz. test tone. Others will use a frequency sweep from 20-cycles to 20,000-cycles.

    These are commonly used variables in testing.
     
  6. Doug Sclar

    Doug Sclar Forum Legend

    Location:
    The OC
    Ah, but there are some advantages. It can pull more power for a lower voltage amp with high current capacity.

    For example, Altec made a 1 ohm speaker for car audio back in the day when the 12v power supply voltage was all one could reasonably get from a car amplifier. By using 1 ohm speakers one could get a lot more power from those 12 volts than they could using 8 ohm speakers. Of course with that type of load you will need lower resistance in your speaker wiring or you'll end up wasting power heating the wire.

    There are also cases where a cabinet will have two 4 ohm speakers wired in series to essentially create an 8 ohm load. Were one to do that with 8 ohm speakers, the load would be around 16 ohms which may not pull enough current from the amp to get the volume one wants. Were they hooked up in parallel the load would most likely dip below 4 ohms at times and that would make them hard to drive with some amps. So in that case 4 ohm speakers would seem to be a good choice.
     
    VinylSoul likes this.
  7. rischa

    rischa Where'd Dizzy go?

    Location:
    Madison, WI
    Thank you -- what I was trying to ask is if a 4 Ohm tap could be faked. That is, could 8 Ohm taps be run through some sort of protection circuit and labeled as 4 Ohm connections, even though they don't actually connect to a transformer that is rated for 4 Ohms. This is probably a stupid question, I realize, but I swear I read that some manufacturers do this to save money.
     
  8. Helom

    Helom Forum member

    Location:
    U.S.
    Some amps get close to such ideals but none truly manage this feat.
     
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  9. SandAndGlass

    SandAndGlass Twilight Forum Resident

    That is what they do with SS amps that cannot really drive 4-Ohm speakers. what it does is kick in a protection circuit to limit the power.

    You can run 4-Ohm speakers with any SS amp, you just can't play them at higher volumes which draws too much current.

    Tube amps have no reason for doing this. The amp delivers so much power. The transformer taps simply determine how that power is delivered.
     
    rischa likes this.
  10. rischa

    rischa Where'd Dizzy go?

    Location:
    Madison, WI
    Ok, I must have read that in reference to SS amps. Thanks for elaborating.
     
    SandAndGlass likes this.
  11. Alluxity actually uses the term “close to” when discussing the different power/impedance ratings.
     
  12. SandAndGlass

    SandAndGlass Twilight Forum Resident

    That's odd, I never heard that one before?

    You'd think that they would just go ahead and measure it and be done?

    [​IMG]

    The Emotiva XPA-2, 250-Watt 72-lb. SS power amplifier, is located on the bottom shelf below the TV, on the right side.

    Note that this 250-Watt amp (into 8-Ohms) has a huge power supply and weighs 72-pounds! It is a class A/B design and can drive a 4-Ohm load, but even with all of that heft, the output is rated at 400-Watts into 4-Ohms. Even still, that is a lot of power!

    The Polk LSiM towers are not particularly efficient tower speaker's at 88-dB. They do take a good bit of power to drive properly.

    They are 8-Ohm speaker's and I have had them pretty well maxed out in stereo and HT, and the Emotiva amp just sits there and pumps the power out.

    You would gave to have an outrageous power supply in order to deliver 1000-Watts into a 4-Ohm load!
     
  13. I can’t remember where I read the “close to” thing but the amp is a very compact unit that weighs 68lbs. I would think power output is probably as listed. Of course I haven’t seen it yet. I can’t wait to get these units already and plug them in. I guess now I have to concentrate on new speaker cables.
     
    SandAndGlass likes this.
  14. head_unit

    head_unit Forum Resident

    Location:
    Los Angeles CA USA
    Well, the end user can benefit-for instance the ELAC speakers have a lot of bass for their size (at the expense of a "power hungry" reputation.
    ...out of the amp. But most amps really can't do that:
    Having tested a lot of amps, and read a ton of tests, this is rarer than a unicorn at the end of the rainbow. Almost every amp rated to double power really does not. What you find is the higher impedance is underrated to give the appearance of "doubling power." For instance, 100W@8Ω/200W@8Ω if actually measured will be something like 130-140W@8Ω and 100W@4Ω: NOT a doubling like a perfect theoretical amplifier. I've only ever seen 3-1/2 amplifiers that truly double power at the clipping point: PS Audio Stellar 700 & 1200, with the S300 coming close, and some $80,000ish thing Stereophile tested.

    Amps are tested with resistors due to practicalities, but speakers are not resistors by a long shot. The moral of the story is that even if the speakers are 8 ohms, the better comparison is the 4 or better yet 2 ohm ratings. And if you think you're going to push difficult 4 ohm speakers like our Focal 936 with a receiver, don't think you're going to reproduce Motorhead live! (RIP Lemmy & co :(). OR ya need a bigger amp, at least 300W@4Ω or more.

    The flip side is if you can accept large speakers they *may* be more efficient and won't need as much power.
     
    SandAndGlass likes this.
  15. I’ll tend to trust respected manufacturers specifications.
     
  16. Helom

    Helom Forum member

    Location:
    U.S.
    Hard to know which ones to trust. Yamaha overrates the power of most of their AVR amps (as most AVR manufacturers do), while they underrate the power of their integrateds. Cary is a very well respected brand but some of their tube amps fall short of spec by an by huge margin - 10s of watts, which is unacceptable when talking tube amps under 60WPC.

    FWIU, no amplifier truly doubles power into 4 ohms at the same distortion figure of its 8ohm RMS spec, as it would essentially require a 100% efficiency. A handful of watts is close enough, but some amplifiers can manage that with a lightweight switching power supply.
     
    SandAndGlass and Khorn like this.
  17. PTgraphics

    PTgraphics Senior Member

    I have Martin Logan Theos speakers as my stereo setup. I am still looking for a decent integrated or power amp to power them so I can finally hear what they really sound like. I have used old amps or as of now a AVR because I have no real amp any longer. These 4 ohm speakers dip down to 2 ohm. My room is small so lots of low volume listening. It’s interesting in looking for something to power these with that not many double the watts into 4 ohm, some a lot less to doubling. For my 4 ohm speakers I’m told current is just as important as watts.
     
  18. With the amp I’m getting being relatively new as far as I’m aware none of the major mags have done a review that includes full test measurement results. I’m sure one will show up. Subjective reviews are great and can maybe mean more for our audiophile objectives but some basic measurements should be mandatory including power output into different loads
     
    head_unit likes this.
  19. SandAndGlass

    SandAndGlass Twilight Forum Resident

    Most amps that are designed to operate with different loads already do that. But by far the majority of home audio amps are AV receiver's and work with ordinary 8-Ohm speakers. Amps that work with 4-Ohm speaker's do state their 4-Ohm power operation.

    I do understand your desire for a powerful amp, even though K-Horns have a high sensitivity rating. It still takes a lot of power to deliver deep powerful bass.

    What I am curious about is why you are that concerned with your amps ability to operate and produce a lot of power down into the 2-Ohm range?
     
    head_unit likes this.
  20. I’m not at all. It’s just that I’m in the middle of getting new amplification and the ohms subject showed up here. I have total confidence in the capability of the amp. And again, I wanna have an amp that’s capable of driving any speaker I may be forced to go to due to circumstances such as moving. Either I pay now or maybe I end up paying a lot more later.
     
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  21. motorstereo

    motorstereo Forum Resident

    Location:
    Ct.
    I wish I'd taken a pic of the specs printed in the top plate of my old Mcintosh mc2500's. 1000wpc into a 1/2 ohm was one. In a pinch I'm guessing it could double as an arc welder as a half ohm is pretty close to a dead short
     
    head_unit and trd like this.
  22. SandAndGlass

    SandAndGlass Twilight Forum Resident

    Sounds pretty much like a dead short to me!

    Looking at my quote, it should have read:

    "You would gave to have an outrageous power supply in order to deliver 1000-Watts into a 2-Ohm load!"
     
    motorstereo likes this.

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