AVS Forum banner
Status
Not open for further replies.
1 - 8 of 8 Posts

·
Registered
Joined
·
241 Posts
Discussion Starter · #1 ·
Well... what are they? I always thought it doubled the power of an amp. However in real life it is almost impossible to find a receiver that can handle a 7.1 setup with 4ohm speakers. They also double the distortion. I always thought that having a low ohm speaker was better than an 8 ohm speaker. Was I completely off the mark?
 

·
Registered
Joined
·
1,417 Posts
a 4 ohm speaker requires twice the load which is harder on the amp then a 8 ohm load, so if anything it makes the weaknessess of most amps become more obvious, and in no way increases power at all.


When you listen to material there are sounds that require different ohm loads, and your speakers vary the load with the material, and there was a little agreement that was unofficial in the late 80's that was no speakers would go below 4 ohms, and so that way the amp designers only had to worry about an 8 and 4 ohm load. I remember it actually being 3, but since it is 4 or 2, effectively it was 4. Most everyone seeemed to follow that with teh exception of infinity who was famous for going down to 2 and even 1 ohm loads which would simply pop fuses on most amps. They don't do that any longer but pissed allot of people off back then because their speakers would make amps shut down,


This is one of the reasons that old infinity speakers were always so power hungry. I tended to like that and still own my Kappas because while hard to drive when you get them lit up, they are very nice sounding. I used Infinity 7's and even 5.1's which were the later model that had a port and non all Polypropoline woofers which took a elephant to get the wooferes to just tighten up. Even on my 5.1's I always used 200 wpc or better, and got my best results using a amplifier that could do 250 into 8 and double down close enough to say all the way to 2 ohms, and while the speaker is rated at 150wpc into 8, you never , ever blow them with clean power at 250. If I used a 150wpc mid level multi channel amp, I couldn't get tension on the woofer, but with 250 into 8, and the double down, I get this very tight and more accurate response. It was a tradeoff because while few compared to old Kappa's on performance for price, you also had to go way higher on the amp to get the great performance out of them.


Speakers for 5.1 Kappa's were about 1300 a pair back in 97

3 channel amp to drive mains and matching center 5500 bucks


I had 4 other friends that got the speakers but went about 2k on the amp and they don't even begin to sing.
 

·
Registered
Joined
·
241 Posts
Discussion Starter · #3 ·
I was enlightend to the fact that they do not double the power of an amp a long time ago. Just used it as an example of how little I knew on the subject. The question still is are there any benifits to having 4 ohms instead of 8? Is it just a different speaker design with no added perks and only downsides?
 

·
Registered
Joined
·
720 Posts
With a 4 ohm speaker you WILL drive more power out of an amplifier. The amplifier notices the tougher load and will push out more power; downside causing higher distortion and heat. If you are going to run good separates 4 ohm speakers are nice because you will get all the juice out of the amps that you can.
 

·
Registered
Joined
·
475 Posts
There are no specific benefits. The only reason why 4 ohm speakers tend to be higher end is that the designers can design strictly for sound instead of amplifier requirements. That means if the better design is 4 ohms instead of 8, so be it. They know that it is usually not an issue for the buyer because they can usually afford the amps to drive them.


Conversely, cheaper speakers tend to be 8 ohm since the manufacturers know that they will be driven with cheaper amplifiers which prefer an 8 ohm load. As a result, they must sometimes compromise the design to achieve the 8 ohm impedance.


Of course these are just generalizations. Just becuase one brand is 4 ohms and another is 8 does not necessarily mean the 4 ohms are better. The better speaker is the one that sounds the best to you.
 

·
Registered
Joined
·
1,494 Posts
The reality is that outstanding speakers are available with average impedances ranging from below four ohms to above eight ohms. Any well designed amplifier can handle a four ohm average load. A great many speakers have impedance curves that range around six ohms.


The THX spec for loudspeaker design used to require (and I assume it still does) the curve not to drop below 3.2 ohms and, likewise, amplifiers that were THX certified had to perform into a 3.2 ohm load.


The impedance curve alone does not say much about how easy or dfficult a speaker will be to drive.--it is only a guide. Other issues such as phase angle at specific frequencies, capacitive loading, all play a part in determining just how easily a speaker may be driven.


Charles Wood

Fosgate Audionics

Rockford Home Group
 

·
Registered
Joined
·
3,947 Posts
If I may...


Ohm's Law states that 1 volt can push 1 amp thru 1 ohm. 1 volt can push 2 amps thru 1/2 ohm, and 2 volts can push 2 amps thru the same 1 ohm. So, since power = volts x amps (Watt's Law), power can be increased via either increasing voltage or decreasing impedance. Amp makers choose their power supply voltages to suit their desired power capabilities, and the current capabilities to suit the impedance-handling capabilities.


First of all, a speaker can be built with almost any impedance, without changing its other perameters or overall sound. Lower-impedance speakers are used where the available voltage is low, but current is plentiful, such as car audio applications. Car amps are often 2-ohm capable, because the power supply voltage needn't be high, and current is generally in abundance.


Impedance is, simply put, AC resistance. It is made up of resistance and reactance, reactance being made up of inductance and capacitance. The only reason that impedance is different from resistance is because speakers contain both inductance and capacitance, which is why impedance varies with frequency, and an impedance rating is an average. Any given speaker's impedance can vary as much as twice or half the rating throuought the frequency range.


However, Ohm's Law still applies here, where power vs. impedance is important. Power doubling into half the impedance first assumes that the amp's output voltage is the same with both speakers. For this to happen, the amp's power supply has to have the ability to not run out of current when the demand doubles, and the output devices must be capable of handling the increased load.


Assuming our hypothetical amp can do this, then at a given volume setting, the amp's output voltage, with a given input signal level, will remain the same, so the current will double when the impedance is halved. Understand again that a speaker is not a single impedance at all frequencies, or ever exactly 4 or 8 ohms, but can be anywhere between or above or below.


Of course, an amp's power reserves are not limitless. All amps power actually does halve when the impedance doubles, and can double into half the impedance, but only to the point of the afore-mentioned current starvation. When the power supply runs out of current, the voltage sags, and clippiing and distortion happen sooner.


If you need more volume on a budget power, choose a more-sensitive speaker, which plays louder on a given power. Low-sensitivity speakers require more power to sound good, which is not a problem when the amp is powerful, but mid-line receivers are often compromises in design, and meeting a power rating can be a strain.


So, the simple answer of the benefit of a 4-ohm speaker is more power at a given volume level, but only if the amp is capable of driving the speaker's lower impedance well. 8-ohm speakers are easier to drive, because the current demand is lower. There's no free lunch, and everything is a compromise. The match between amp and speaker is what matters.
 

·
Registered
Joined
·
8,948 Posts
I suspect that in most cases speaker sensitivity will probably make more of a difference as to amp load than speaker impedance. Speakers for HT should always be at least 90 dB or higher IMO, especially if you are using a receiver.


Dsmith
 
1 - 8 of 8 Posts
Status
Not open for further replies.
Top