the 4 ohm rating

Bigjoe, funny you ask that question at this time, as I am headed down a similar path of questioning. So far in my search I've found a list of reasons against high impeadance. The topper may be that the mainstream consumer doesn't care and making high impeadance drivers is far costlier.

Looking forward to learning more from others about this.

Six of one and half a dozen the other. The greater proportion of 4 ohm drivers reflects the fact that most drivers (these days) are 4 ohms.

Some of the best speakers ever, such as the original QUADs and the Apogee Scintilla, have had impedence graphs that were all over the page. Looks like a snake that had been hit with a Tazer. We are talking impedences much lower than 4 ohms.

Sorry for the long response:

Many speaker designers feel that speakers are 'voltage driven' and thus design speakers around that idea. This allows for a speaker to have dual woofers (in parallel for 4 ohms) and thus the amp will produce twice as much power so that the woofers will be driven hard enough to keep up with the high frequency units of the speaker. A good example of this sort of design is the B&W 802. The concept of 'voltage driven' speakers also allows for the amplifier to compensate for driver or cabinet resonance by responding to the resultant impedance bumps.

Now, not all amplifiers are capable of this 'voltage paradigm', but any amplifier that is will be seen to produce a constant voltage into any load. A good example of an amplifier of this sort might be a transistor amp that makes 100 watts into 8 ohms, but is 200 into 4 ohms. Sometimes it is interesting to point out that such amps will only make 50 watts into 16 ohms.

*So*, with the above two examples used together flat frequency response will be the likely result.

However, not all speakers comply with the 'voltage paradigm' nor do all amplifiers. Examples of speakers that are not on the voltage paradigm are horns, ESLs and planar magnetic speakers (ex.: Maggies). These types of speakers are on a 'power paradigm' where flat frequency response from the speaker is obtained by flat power response from the amp, regardless of the impedance of the load. This is often because the impedance of the speaker is not as closely related to built-in resonances. The high impedance of an ESL at low frequencies is a good example- this impedance has nothing to do with resonance in the speaker.

The kind of amplifiers that are on the power paradigm are: most tube amplifiers (tube amplifiers with very high feedback being the exception) and low or zero feedback transistor amplifiers.

This is a major reason why you have to be careful about matching amps to speakers.

Now back to your question about 4 ohm speakers: 4 ohm drivers are not any more likely to get damaged, and tube amplifiers for the most part are not likely to put any more power into a 4 ohm speaker then they would do into 8.

A couple of good reasons to think carefully about a 4 ohm speaker: speaker cables are a lot harder to build for 4 ohm setups. Also, most tube amplifiers will produce more power and lower distortion (regardless of design) when driving an 8 ohm speaker.

If you have a transistor amplifier there is no real reason to avoid 4 ohm speakers unless the amp is not really rated for the load. Yes, the amp is working harder but if properly designed this is not a problem for the amp, although it will produce more heat.

So if you plan to use tubes, you might want to think twice about 4 ohm speakers, but if using transistors it might be the other way around. Either way you want to be careful, not so much for the damage issue, which I think is a red herring, but more for the reason that your investment in the amplifier is best served with a speaker (all other things being equal) that is properly matched to it.

There was a great speaker,discontinued a few years ago.It had all the characteristics found in all the "HOT TO TROT" stuff being sold today,even by the same mfgr!It was the Avalon Ascent Series 2.Not too big.Gorgeous to behold and listen to.The load was 6 ohms.Never dropping below 5.5(according to the literature),and 88 db sensitivity.This design,compared to the more recent stuff had the following features.You be the judge as to it's worth!175 lb cabinet.Massive external crossover for each channel(55 lbs ea.)Sealed box design with a Q of .5(supposedly ideal bass"definition" characteristics).Gorgeous veneers as well.The downside was that the "really deep bass"(below 35 hz)was not there.Not many speakers can do this either,as in really accurate.This could easily be remedied with a killer sub(like a REL).Don't kid yourself,if you are thinking that it could not compare to the Ceramic/Diamond stuff of today.That design (the Ascent) was,admittedly,an all out design.The driver compliment was a Nomex- Kevlar woofer/Highly modified Aluminum hybrid(with magnesium)midrange/and a Highly modded titanium tweeter.I have heard this design on many occassions.I admit it's mine,but,it absolutely is a bargain ,when it shows up used.I'm a fanatic in terms of "Performance" and NOT marketing.This product is an easy load on an amp,and when set up according to the manual (200 pgs of informative reading)I cannot see myself parting with it as long as I live in my current home.Anyone seeing a pair used should,at least,try to give an audition.Asside from being built to a quite literal "HEIRLOOM STANDARD" they surpass,IMO,the vast majority of the "Really Shiney" stuff being "Marketed to Death" today!Oh yes, and remember,that CONSTANT IMPEDENCE makes a difference!My amp sure runs cool!!