Why do mfg make 4 ohm speakers (1 Viewer)

[alan halvorson]

I hope no one comes across the old Apogee Scintilla planar speaker. Nominal impedance of 1 ohm and never went above 2 ohms. In its day, only a handful of amplifiers (mainly Krell) could drive it satisfactorily.

 

[Rajeev_s]

If higher ohms mean higher impedance - resistive + reactance(inductive and/or capacitive). Then higher ohms must need better amps to drive it (Ohms law). So why does lower ohms mean more power is needed to drive it. This has baffled me ?
Chu Gai, you could possibly chime in.

 

[Chu Gai]

It simply means that for a specific voltage, more current will be required.
E=I*R therefor

I=E/R

If 2 volts were called for at say 8 ohms that would require...I=2/8 or 0.25 amps.

If that same volts were called for at 4 ohms that would require...I=2/4 or 0.5 amps.

If the amp or receiver can't deliver 2 volts at 0.5 amps there will be issues.

As far as I'm concerned, the people making these difficult speaker loads (not the 4 ohms, but some of the electrostatics, etc.) ought to provide an amp that can drive them. That's my $0.02.

As to why there are 4 ohm speakers, I'd imagine it had to do with something like the manufacturer coming up with a specific design...say a vented box...then saying something like I want X spl at such and such a frequency and then backcalculting what kind of drivers had the correct Thiel-Small parameters. Then they start looking. Drastically oversimplified upon my part but it just may be that's the way things worked out when they set certain goals.

 

[Doug_H]

I have seen this in several posts recently and any receiver that has a physical switch on the cack is a sure sign you do not want to drive 4 ohm speakers with it.

I am sure someone can explain this better than I can but I believe the reason for the switch is that the receivers power supply is not capable of handling a 4 ohm load so they restrict the power level when the switch is used.

A good way to guage an amps ability to handle a 4 ohm load cleanly is to look ate ratings into 8 and 4. The rating should double from 8 to 4. Soo if you have 100 watts into 8 you should have 200 into 4.

Many receivers can handle a a 4 ohm load but may not do so cleanly and most often will not give you the dynamics and detail a speaker is capable of.

 

[Rajeev_s]

Duh, I feel dumb. Why didnt I think about it ?
Anyway thanks for clarifying. :rolleyes

 

[Dave-Z]

I think one of the most critical pieces of data to look at in terms of 4 ohm vs 6 or 8 ohm speakers is the distortion rating of the signal when driving speakers of different levels.

In most cases, where amps/receivers are designed for 8 ohm loads, you will see a very large, exponential(not linear), increase in distortion.

For example, let's look at Denon's AVR-3803 THD(distortion)rating and focus on the increase when going just from 8 to 6 ohms: (Also, keep in mind, this is a Good! receiver... not great, but good)

Below is basically telling you what to expect when driving Denon's 110w front channels into an 8 ohm speaker, and the increase in both power and distortion due to the lack of impedance when facing 6 ohms:

- System Call
110 W + 110 W (8 ohms, 20Hz - 20kHz, 0.05 % THD)
150 W + 150 W (6 ohms, 1 kHz, 0.7 % THD)
(also notice at 6 ohms it's just rated at the 1kHz point, not full spectrum)

Just moving impedance 2 ohms, the level of distortion didn't just increase a little, or double, but increased by a factor of 3.5. That is, 3.5 times worse. Following this progression, this same receiver would have a THD, distortion level, of 8.4% at 4 ohms. That's big time folks.

Now to put this in even greater perspective, maximum acceptable level of THD is .1%. Beyond that, it becomes more and more noticable to the listener.


Let's now look at a an example of a receiver specifically designed to drive a 4 ohm load, NAD T773:

Power Output Stereo Mode 145W (21.6dbW)
Simultaneous Continuous Output Power into 4/8 Ohms *
7 x 110W (20.4dBW)

(*Min. power per channel, 20Hz - 20kHz with no more than 0.08% THD rated distortion.)

Not an apples to apples comparison, as the above spec is the 2 front channels from the Denon while enhanced stereo output from the NAD, but it's close, Washington -vs- Granny apples.

The NAD, which markets directly to just the beginning cusp higher end consumers and components, emphasizes the clarity of it's signal and the stability as well. You can see that it's rated across full spectrum, 20Hz-20kHz, with a THD no higher than .08%. You'll also notice that they don't increase the over-all power rating, i.e. 110w to 150w with the Denon, while the NAD states only 110w for both.

This is serious power regulation, and you pay a premium for it. Most times you'll see NAD at an equal power rating as H/K, Denon, Pioneer... with a higher pricetag and less bells and whistles, but what you get out of that is a cleaner signal across the board.

How important that is in the over-all scheme of things is totally up to the individual and his/her components. If you've got 8 ohm speakers, I don't see any major reason or necessity to spend more on a NAD, aside from personal preference, when you can get a receiver much cheaper that performs either just as well, or even better, for your needs, and may also include more features to play with.

However, if I were planning on driving 4 ohm(as I do), or even 6 ohm speakers, I would make this an absolute priority above all else, that the signal driving my speakers is crystal clear, or else why did I spend all that money on them in the first place, when I could have gotten cheaper 8 ohm speakers and they would sound better than the more expensive 4ohm. (~Caveat~ ohm rating is not an across the board indicator of the quality of the speakers, so I don't suggest thinking that any 4 ohm speaker is better than a 6 or 8ohm speaker, just a trend I've noticed)

Don't know how well this helped, just know it was important info to me when choosing a receiver or pre/pro.

 

[Philip>L]

This is only true of an ideal amplifier and unfortunately does not, or does so seldomly or for too high of a price in practical amplifiers.

 

[Chu Gai]

Sometimes it's not even an issue Rajeev with your equipment. Consider a situation where you've got reasonably efficient speakers in a not too big room and the speakers aren't too far from your sitting position. Well if you don't crank it up to levels that are going to leave you deaf, then even if that receiver is only rated at 8 ohms, it may still yet have sufficient power to do it's thing with a set of 4 ohm speakers. It's one of those real YMMV situations because it's so highly listener/room/speaker dependent and gets further complicated by the fact that lower end receivers don't necessarily put out 5x100 continuous watts. So if you're looking for a system find your speakers first. If they're 4 ohms so be it. There's something out there that with a bit of carefull shopping and patience will drive them adequately.

 

[John Royster]

Why do manufactuers make 4 ohm speakers?

Because generally the design goals are "sound good and have a great crossover no matter what the nominal impedance winds up being. Don't let impedance be a design limiting factor."

That's my take.