Discussion in 'Audio Hardware' started by Henry J, Apr 27, 2021.
There is truth in this very simple analogy from tekton's designer. You should give this a listen.
When I saw him clip in the 4 ohm resistor, I shut it off.
None really. Harder on amplifier. With that said, you get more power (and generally more SPL) per Volt of amplifier signal. So if you buy beefy amps, you get more power output before clipping.
Wont a well designed amplifier put out the same energy at all loads thus keeping the freq response as the speaker was intended to have?
Many amps (majority) have a minimum impedance of 4 ohms in their specs, for a reason. Impedance matters with most amps.
As mentioned, speaker sensitivity is more relevant. An amp is a voltage gain driver, theoretically it puts out the same V at different loads. So 1/2 the load, double the I (I = V/R)and double the power (P = I V). Most won't do that because the power SUPPLY can't supply enough I (charge/sec). But moot, a speaker Z may vary from 4 to 12.
imo amp output Z is critical, it determines how well the amp 'couples' or controls the speaker drivers.
It does 'work' harder
Work = Power x time, lol
More power, same playing time = more work
The ohm rating doesn't matter in itself since speakers vary with frequency.
Generally, 4ohm speakers tend to be less sensitive and they typically aren't good with tube amps or especially SET amplifiers. Tubes and SETs while they tend to sound the best dislike varying impedance which gives them more trouble and because they often do not have all that much power may not meet the needs of a speaker playing loud with bass where the impedance drops. Tube/SET amps do not double into lower impedance loads. And some amplifiers like the older Sugden A21a also don't. 4ohm that is stable is not particularly hard to drive. Most tube amps come with a 4 ohm tap. It's if the speaker drops to 2 ohms where tube amps (and many SS amps) would struggle.
I’m not sure what you mean by “...the same energy at all loads”.
This quote needs to go on a T-shirt.
Does impedance really matter if ... if one listens at moderate levels only. For most speakers, it’s only kicking out a mere 6-8w.
An amp’s output voltage operates in a designed range. It varies depending on the input voltage provided by the external/internal preamp. An audio amp is typically a voltage amplifier meant to increase input voltage by a specified ratio. The higher the input voltage from a preamp stage, the higher the amp’s output voltage up to its rated maximum beyond which clipping occurs. Speakers are an impedance load that call for varying amounts of current. Current delivery to the speakers depends on the quality of the amp’s power supply. Voltage gain (by the power amp) depends only on the ratio of the amp’s step-up transformer for preamp input signals.
A power amp’s nominal output impedance can popularly be stated in two ways. The most common one is an impedance (in ohms): e.g., 0.007 ohms at a given frequency (50Hz) and output voltage (e.g., 2.8VRMS) like the PS Audio S300 power amp. The other way of stating an amp’s output impedance is: nominal speaker impedance (e.g., 8 ohms) divided by the amp’s output impedance (e.g., 0.007 ohms) which equals 1143 (almost meaninglessly termed the “damping factor”). Damping factor is almost uselessly meaningless because both speaker impedance and amp output impedance vary with frequency. For example, if the amp is still running output at 0.007 ohms (or lower, as is quite possible with the S300 amp) but the speaker impedance while reproducing some music has dropped to 5.2 ohms, then the so-called damping factor at that moment is not 1143 but rather 742. If the speaker impedance at any given moment of music playing drops to 4.5 ohms (for example), then the damping factor drops still more. If the speaker impedance swings up to 12 ohms in some parts of the music, the damping factor becomes 1714.
What about an amp that has an output impedance of 0.1 ohms? With the same speakers, the damping factor during any given listening session could vary (using the speaker impedance shift examples above) from 80 to 52 to 45.
So the audiophiles relying on some sort of impression that higher damping factor is better to their ears or lower damping factor is better to their ears have hung their listening impression on a meaningless number that varies constantly with the music. The high damping factor that they thought was important is actually not a factor or an amp specification at all. It’s just a marketing way of restating an amp’s nominal output impedance.
Maybe I’ve misunderstood your question?
I'm someway i have yet to fully comprehend, this makes sense.
But, this can be a misleading figure, when it comes to rating a 4-Ohm speaker.
Allow me to add to the confusion (or maybe clarify a few points.
First, the reason that there are 4-Ohm speakers in the first place is that they are designed to operate with more power.
A speaker is different in nature than an amplifier, which is primarily a voltage amplifying device, as explained earlier.
A speaker is a physical device that uses motion to turn electrical energy into mechanical energy. In other words, a speaker has to vibrate a cone into move air and produce sound. Moving things that have mass in the physical world takes effort.
Take a car that has run out of gas. Two people moving that car will move it more efficiently than a single person doing all the work.
Water is a good analogy to electricity. Take a garden hose. The force behind the water, would be the voltage, while the amount of water coming out, would be the current.
A small stream could have fast moving water, but would be easy to cross. A river moving at the same stream would generate enough force to push you downstream. When we talk about speakers, you need energy in the form of current to move the cone.
When we talk about speaker measurements, speaker sensitivity had generally been rated by feeding 1-Watt of power to the speaker. Power is the voltage times the current. 1-Volt at 1-Amp is equal to 1-Watt. 10-Volts at 1-Amp is equal to 10-Watts. The same way that 1-Volt at 10-Amps is still equal to 10-Watts.
Now days, it is more common to state efficiency of an 8-Ohm speaker in terms of Volts rather than one Watt, even though they have essentially the same meaning.
Ohms Law will tell us that one Watt of power into an 8-Ohm load will yield 2.83 Volts. 2.83 is the square root of 8.
If we decrease the resistance in the circuit by half (4-Ohms instead of 8-Ohms), Ohms law states that the current will double. If we were to keep the voltage the same 2.83 Volts, the total power being delivered to the speaker would no longer be 1-Watt, it would now be 2-Watts.
Thus, the voltage that is used to measure the sensitivity is important and can often be misleading. If a 4-Ohm speaker's sensitivity is rated at 90-dB. and the manufacturer states that it is using 2.83-Volts as a reference, the manufacturer is feeding the speaker 2-Watts of power. If you fed the same 4-Ohm speaker with the same 1-Watt as you did with the 8-Ohm speaker, its true sensitivity would be 3-dB. less, or 87-dB.
The true way of making an equal comparison would to use the same 1-Watt of power. Ohms Law would state that 1-Watt of power into a 4-Ohm load, would measure at 2-Volts.
The manufacturers who would be truthful would state the sensitivity of their 4-Ohm speaker, as measured by 2-Volts (or 1-Watt).
Now, you would be comparing apples to apples.
BTW... The reason that it is 2-Volts, is that 2 is the square root of 4 (Ohms), just like 2.83 is the square root of 8 (Ohms).
So, while this might not be perfectly clear imediately, at least you are now aware of why you see 2.83-Volts, used when referencing the sensitivity of an 8-Ohm speaker...
It does. Not all loads stay the same with frequency. Try a 4 ohm reactive load which dips to 2.7 ohms. And see how much smoke gets emitted with too low power or how many transistors and associated component parts get destroyed doing that.
Also, one point is that quite a few low sensitivity speakers, say 88db that are 4 or 6 ohms seem to have a lower frequency response. My 6 ohm Mirage OMD 28’s go down to 17 hz, at 10 dB down. And they really do. That’s why I don’t need a sub. But they’re difficult to drive, I put my New Rotel A14 amp into production mode shutting it down driving the 28’s loud.
On the other hand, my Emotiva amp drives them like their butter. So there is a trade off. Most of the 8 ohm speakers I’ve owned hit the bottom at about 40 hz. And that is good for most people, and their easy to drive. But they don’t sound like my 28’s, which are just incredible sounding. Shacking the walls when I want them to.
Emotiva amps are known for their ability to deliver massive amounts of current into 4-Ohm loads. They are particularly excellent at driving 4-Ohm speakers to high SPL's.
Interesting. I recently read in another thread that impedance is more important than sensitivity. Where do you get your information to support that claim? Just curious which is correct.
They’re both important.
Thank You for that Info SaG. Makes sense because the 'Synergy' with the Emotiva, you can tell it how the speakers 'Mate' / Resonated/ Connect to the room. The Rotel, that never happened. I kept turning up the bass trying to get to that place but it just didn't happen.
Very impressed with the Emotiva, and again, it's a UPA 200, their cheapest amp at like $299 like 10 years ago.
They and as they are both different, one has nothing to do with the other.
What determines the impedance of a driver? Is it mainly mass and cabinet interactions?
Impedance does not or should not have any effect on a speaker's overall sound quality. Speakers with a lower nominal impedance are designed to handle more current and tendency to being able play louder, as a result.
Sensitivity is important because a speaker with higher sensitivity can be played with a lower power amp. This has a few benefits. The first is opening up a wider field when it comes to amp selection.
All other factors being equal, this would allow someone to use a smaller and possibly a less expensive amp.
Even with a more powerful amp, a high sensitivity speaker may not be as demanding on an amplifier, leaving more power reserves available that would result in better micro-dynamics.
Also it can open up the option to use lower powered class "A" type amps, which may be better sounding.
High sensitivity speakers, like horn loaded designs can be more dynamic and life like.
I think it’s quite obvious that you should be matching the amplification capabilities with the electrical requirements of the speakers system in question. The speakers and environment dictate the driving requirements not the other way around. You can buy amps that can cover most domestic speaker system requirements up front but generally they ain’t gonna be anywhere near cheap.
I run 4 ohm Legacy Signatures on the 4 ohm tap from my tube amp (Rogue Stereo 100). I had some initial concern that there wouldn't be enough juice to drive them, but no worries. They sing. Perhaps the high sensitivity (~92 db) offsets the low nominal impedance.
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