Sensitivity?

[mtrycrafts]

My 4 Ohm speakers, which replaced 8 Ohm speakers, play louder at the same volume. However, it is not an apples to apples comparison. The 8ohm speakers were much, much smaller than the 4ohm ones.
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Speaker's physical size is irrelevant. Its sensitivity and impedance that controls the spl output, not counting the amp, of course.

 

[PENG]

Now we are getting somewhere. I look at it like this.

You hook the 8ohm speaker to the 200w amp, 100w at half volume (theoratically).

Now hook the 4ohm speaker to the 200w amp that becomes 350w, so 175w at half volume (theoratically).

Now factor in the sensitivity rating of 89dB for each speaker, and it becomes appearant to me the 4ohm speaker is (theoratically) 75% louder, once again given the amp is 4ohm stable.

Let's say you turn the 200W amp volume up until it develops 100W across that 8 ohm load (you referred to that as "half volume", leave the volume (i.e. the output voltage) exactly where it is and now you replace the 8 ohm load with a 4 ohm load, the current is going to double. Since P=I²R, the power into the 4 ohm load will double, or 200W, not 175W, if the voltage drop at that point is negligible. The question is, whether the voltage drop is linear from 0 to 100% output. If it is, then you are exactly right.

When Mac said, 87dB 4 ohm=84dB 8ohm, I assume he meant in terms of how difficult it is for the amp to drive the load. It is twice as hard for an amp to drive a 4 ohm load because it has to deliver twice as much current at the same volume (voltage). So if the 4 ohm load is 87 dB, that is twice as sensitive as the 84 dB one, it will make it just as easy as the same amp trying to drive that 84 dB 8 ohm speaker as it is to drive the 87 dB 4 ohm speaker. It has nothing to do with which one sounds louder, just which one is easier to drive. I could be wrong, hopefully he will check in eventually and speak for himself.

Buck: impedance is not "simply resistance". Impedance of a component or circuit is the combined effect of resistance, capacitive reactance, and inductive reactance of that component or circuit. The vector sum of all three is know as impedance.

When capacitive and inductive reactance are zero, impedance equals resistance. In the strictest sense it will be difficult to find anything that is purely resistive, inductive, or capacitive but for most practical purposes, resistors are consider to be purely resistive and capacitors are considered to be purely capacitive etc.

 

[mtrycrafts]

Sensitivity isn't an end all. Keep in mind this is 1 watt at 1 meter, or about 3 feet away. Now perform a test at 10 watts at 5 meters, and you'll notice a difference IF the amp isn't stable at 4 ohms. If it is, the speakers will still require more current and crap out sooner compared to driving 8 ohm speakers. It's a matter of distance and volume. Also keep in mind larger drivers are usually more sensitive, all other things equal.

With 1 watt (all receivers can do this into very low loads)
Ex 1: 92dB 4 Ohm speakers = 89dB 8 Ohm speakers
Ex 2: 89dB 4 OHm speakers = 86dB 8 Ohm speakers
Those speakers should have the same output at 1 meter.

I surely hope the amp is stable at 10 watts into 4 ohms; that is not much of a power drain, even at 4 ohms.

I think what is left out is the applied voltage in all this as the sensitivity can be measured differently, at 2.83 V to both speakers or a strict 1 watt in which case the 4 ohm speaker gets only 2.V

 

[Jack Hammer]

Speaker's physical size is irrelevant. Its sensitivity and impedance that controls the spl output, not counting the amp, of course.

I would think (yeah, I really don't know ) that size would matter (trying to avoid jokes about that phrase ).
I went from a single 4" woofer and 1" tweeter @ 8 ohms, to dual 5.25" woofers w/ 1" tweeter @ 4 ohms. It seemed natural to me that the newer speaker would play louder, and it did noticeably. I don't recall anymore the exact difference, but I went from listening to music at -26 to -32 for the same comfort level (didn't measure actual spl's). But it's a very small room (9x20x7 with seating 8' away) and it is not comfortable to listen to music at extremely loud levels.

 

[zumbo]

I somewhat understand all the technical aspects of this. OTOH, I have been seeing 4ohm speakers get a bad rap since I have been here. I usually disagree, but don't post because I don't have a technical answer. But, I have thought long and hard about it up til I decided to post this thread.

There are good reasons to choose 4ohm speakers. I go back to my car audio days of bridging subs. If you use one 4ohm sub, it hits much harder than one 8ohm sub because of less resistance. So, the amp is trying to double it's power. The same goes with home audio. Hook-up a 4ohm speaker, and the amp tries to double it's power. So, to me, that throws the XdB @ 1w 1m out the window.

So, how can 87@4ohm=84@8ohm? It takes half as much to get the 1w from the source to the 4ohm speaker as it takes to get 1w to the 8ohm speaker. So, using any given 4ohm capable amp, there will be more available power for the 4ohm speaker.

Amps are expensive, this just looks like a good way to get more bang for your buck.

 

[j_garcia]

For normal listening it may be true that you are using around 40-50w total (5-10 per channel?). To handle a dynamic peak, you may need 10x that. With 4 Ohm speakers in the same setup, you are using 80-100w to handle the same load with those speaker and to handle the same peaks that would mean something like 800-1000w peak (not exactly, but you get the idea). Does that make sense? Like I mentioned before, that power isn't free. So in fact, you need to have a lot more headroom with 4 Ohm speakers than it might seem, because the demand is much higher of the amp.

Think of it like a 4 cylinder motor having to do a lot more to achieve the same thing an 8 cyl. motor can do without straining.

 

[zumbo]

Well, I have seen a Honda Civic outrun a Ford Mustang!

But, if your statement were true, a 4ohm speaker couldn't be used at all. Amps would clip or go into protection mode every time you cranked them up. That is not the case.

 

[Buckeyefan 1]

Mtry: BUT, one speaker will have 2 watts, the other will have 1 watt applied.
The amps capability into 4 ohm load will determine when that 4 ohm speaker will run out of gas. If the amp doubles in power to a 4 ohm load, they will sound the same in the end at a given volume setting. If less, it will run out of gas before the 8 ohm speaker.

Exactly. Well put. Very few amps can double down in power, thus the reason 8 ohm speakers play louder than 4 ohm, given the same amp at elevated listening levels.

Try this - hook up some old 4 ohm 6x9 car speakers to your home receiver (if you still have some, many of you are probably too young). They never seem get loud.

If one is pressed to purchase 4 ohm speakers, I highly recommend spending some serious cash on a flagship (or top end) receiver, or go the separates route.

 

[j_garcia]

Well, I have seen a Honda Civic outrun a Ford Mustang!

So have I At an auto-x, I saw a Civic turn in a better time than a Viper GTS. One with a good driver, the other with a GREAT driver

But, if your statement were true, a 4ohm speaker couldn't be used at all. Amps would clip or go into protection mode every time you cranked them up. That is not the case.

Depends on the amp. Not ALL will shut down, but some will definitely struggle. You won't have 800w peaks every time you listen to the system either... that's like a worst case scenario.

 

[zumbo]

Exactly. Well put. Very few amps can double down in power, thus the reason 8 ohm speakers play louder than 4 ohm, given the same amp.

Are you 100% certain the 8ohm would be louder? I can see where 6x9's would not get loud. But, a 4ohm home speaker certainly does. I have post another thread to see if we can get someone to do a "real world" test with two similar speakers with different ohm ratings.

 

[Buckeyefan 1]

I surely hope the amp is stable at 10 watts into 4 ohms; that is not much of a power drain, even at 4 ohms.

How about 10 watts average rms watching a movie, or playing Telarc's 2001 A Space Odyssey, with peaks into the 100's?

Sorry for the generalization.

 

[zumbo]

Depends on the amp. Not ALL will shut down, but some will definitely struggle. You won't have 800w peaks every time you listen to the system either... that's like a worst case scenario.

Most seperate amps I have seen can run 4ohm speakers fine. My system will run you out of the room at 0. It's loud as h#!! in the -. No clipping problem. No shut-down problem. Just plenty of power on tap.

 

[zumbo]

And, lets take movies out of the equation. Nothing I have found taxes an amp like a concert dvd.

 

[Buckeyefan 1]

Are you 100% certain the 8ohm would be louder? I can see where 6x9's would not get loud. But, a 4ohm home speaker certainly does. I have post another thread to see if we can get someone to do a "real world" test with two similar speakers with different ohm ratings.

Yes, but at elevated listening levels where the amp source starts to struggle. It wouldn't be an issue at low to average listening levels where the amp isn't taxed. If you bring a 100lb. Krell, or Mackie 1400i amp into the picture, you can toss this thread out the window.

My point is that one will never enjoy the potential of a well made 4 ohm home speaker with an average receiver. If one adds a separate quality power amp (not your $150 Audio Source), it won't be an issue.

 

[zumbo]

Yes, but at elevated listening levels where the amp source starts to struggle. It wouldn't be an issue at low to average listening levels where the amp isn't taxed. If you bring a 100lb. Krell, or Mackie 1400i amp into the picture, you can toss this thread out the window.

My point is that one will never enjoy the potential of a well made 4 ohm home speaker with an average receiver. If one adds a separate quality power amp (not your $150 Audio Source), it won't be an issue.

LOL! I don't have a $150 Audio Source. I have a $1199 42lb Adcom I got on sale for $899 from Onecall.

 

[Buckeyefan 1]

LOL! I don't have a $150 Audio Source. I have a $1199 42lb Adcom I got on sale for $899 from Onecall.

I know you do. That's a killer surround amp - and you got a steal on it.
I was using "your" as a plural. I should have said "yuns."

 

[zumbo]

I know you do. That's a killer surround amp - and you got a steal on it.
I was using "your" as a plural. I should have said "yuns."

OK. But where did that Audio Source come from? I mean, you hurteded my feelings.

You updated that one too fast for me.

 

[highfihoney]

For normal listening it may be true that you are using around 40-50w total (5-10 per channel?). To handle a dynamic peak, you may need 10x that. With 4 Ohm speakers in the same setup, you are using 80-100w to handle the same load with those speaker and to handle the same peaks that would mean something like 800-1000w peak (not exactly, but you get the idea). Does that make sense? Like I mentioned before, that power isn't free. So in fact, you need to have a lot more headroom with 4 Ohm speakers than it might seem, because the demand is much higher of the amp.

good point.

that is exactly what ive found to be true in my systems when i was running 4 ohm gear,at moderate levels i never noticed any negative differences but at performance levels all but the highest current amps would loose steam,also the farther any amp was from doubling down to twice the power the worse performance it gave me in 4 ohms at performance levels.

i dont think your all that far off in your description of dynamic peaks either,ive seen amps go from pushing a steady 500 watts to an instantanious peak of over 4,000 watts in a 2 channel system.

i would think that the issues you brought up about dynamic peaks would have a huge affect on home theater applications where the source is heavily prone to extended dynamic bursts,even though dynamic bursts only last a second they can have a serious affect on performance if the amplifier is not capable of handeling such a burst.

 

[zumbo]

i dont think your all that far off in your description of dynamic peaks either,ive seen amps go from pushing a steady 500 watts to an instantanious peak of over 4,000 watts in a 2 channel system.

From a wall outlet? What size breaker? 4000 watts? You are pulling my leg, right?

This came from askmehelpdesk.com.

A 15 amp circuit can carry only a total of 1440 watts,which is 80% of the 1800 watts found by mulitplying the volts times amps,15 x 120 x 80%= 1440.

A 20 amp circuit can be loaded 1920 watts, 120 x 20 x 80%=1920 watts.

My amp is rated 175 x 5 @4ohm with a max draw of 1680 on a 20A circuit. There shouldn't be a peak problem. And there isn't! Like I said, a concert dvd taxes an amp much more than ANY movie.

 

[highfihoney]

From a wall outlet? What size breaker? 4000 watts? You are pulling my leg, right?

nope,im not pulling your leg one bit.

i have 2 dedicated 20 amp lines for my gear to run on,i had no choice but to have dedicated lines installed for my gear,it seemed like every time i listened to the rig my wife chose the exact same time to use the damn toaster

toasters suck some serious power

if you want to see & hear a drastic dynamic burst put in "edgar winter" & play the song "frankenstien",if you have a way to visually meter your wattage you can see several drastic bursts.