The disappearance of the traditional amplifier

As Chad mentions it is cheaper - it is easier to build a higher performance amp with limited bandwidth powering one driver than the same quality performance with very large bandwidth driving several drivers as well as a lossy passive crossover. Usually when something is both cheaper and better in performance it tends to win out in the market place. I suspect active speakers will win out eventually if not for performance but more likely because of lower cost for similar performance.

vibration-prone space will be deleterious to the ultimate sound from the speaker.

It certainly would if you used tubes. In that case you can still go active but they would need to be 'outboard' amps dedicated to each driver (this would still make the design active and is actually how active speakers started)

It is always nice to see a good discussion on pros and cons. There is definitely
more than one way to skin a cat. I tend to agree with Kirkus about the older
generation Genelecs but I happen to like their active newer 8050 and 8020 small
monitors. In fact, I'd be happy with a great many many speaker designs both
active and passive, horn or panel etc. - so it is not like it is ever as clear as
"night and day". In many cases, it is all a matter of combining as
many small incremental improvements as possible - soffit mounting is one,
room acoustic treatments is another, and going active speakers is just one more
increment (similar to tri-amping) etc. etc.

For example, if you prefer Tube power amplifiers then the incremental benefit of
active speakers may be outweighed by the loss of that tube sound...

Here are some photos of field coils.

It seems to me that the best-sounding speakers are the ones that pay give proper attention to power response, which is indeed rare.

Dr. Floyd Toole devotes quite a lot of time to this important aspect in his new book: Sound Reproduction: The Acoustics and Psychoacoustics of Loudspeakers and Rooms. ATC have been preaching about even power response for about 30 years. Careful attention to driver size and use of waveguides can create a smooth continuous off axis response which means the speaker will sound consistent in almost any room and from any position in the room. Ignoring the off axis response or power response can create an exciting and impressive speaker due to the nasty discontinuities like this huge hole or "scoop" in the mid range - this can make the speakers seem artificially "revealing" or amazing but will make it very difficult to setup as the user will really struggle to find a good placement which creates a balanced sound from primary and reflected energy as well as a good stereo image.

The result according to Duke is that sound pressure levels up to 112 dB are reproduced with less than 1 dB of power compression.

Although this thread seem to be digressing there have been many excellent comments.

Duke's claims are extrodinarily good. Most people would be surprised how effortless undistorted and uncompressed sound can be - even at what would seem to be very high SPL's (provided a good recording of course).

Sadly most speakers do not come with anything like high quality pro type drivers but at least they usually come with nice cabinets and great veneers...

But the "waveguide" designs in the Genelec monitors bear very little resemblence to a true constant-directivity spherical or bi-radial "waveguide" horn, in both the theory and the way they behave.

Good Discussion. Yes but....horns are different in that they use a compression chamber. For horns the exact mathematics and expansion design become critical, however, for a normal non-compression driver a simple conical expansion often has teh best performance and is enough to control dispersion such that a smooth power response is achieved.

See this

and see K&H O500C - click on the "measurements" link in thr right hand corner for directivity plot. This is an example of an impressive response that is extremely smooth and wide both on and off axis and illustrates the use of the "waveguide".

Kirkus,

Thanks - you make some really interesting points. I'd like to point out that a lot of the discussion depends on what "driver" you have to begin with. Let me explain.

To me the TWO main ideas of the short open waveguide are as described by K_ilpo_p....

1) it allows a driver to have greater sensitivity (better SPL and lower distortion) at the low end of its passband
2) it can narrow the low end of the passband radiation pattern - which enables one to match the higher frequency driver radiation pattern to that of the lower driver - for a smooth transition at crossover. Note that this type waveguide cannot help with the high end of the passband radiation pattern because that narrows anyway as the wavelengths become smaller than diaphragm.

Without digging into physics it seems clear that only a CONE shape will maintain uniform spherical wavefronts therefore if you have a dome driver (such as a dome tweeter or the midrange in the K&H O500) then you pretty much start with a spherical wave and therefore a cone waveguide is the simple answer to control dispersion (no bending of the wave is needed as in the case of a horn which has to be bent from a plane wave in to a spherical wave).

Here is some more interesting reading.

But they're not constant-directivity (which was my
main point), and since as it does indeed very much depend on what
"driver" you have to begin with . . . these behave fundamentally
very much like a standard direct-radiating driver.

I agree absolutely. "Constant-directivity" is indeed a term that
applies to compression horns rather than 'short open conical
waveguide". And the constant directivity in a speaker using short
conical waveguides is achieved primarily by limiting the drivers to covering
frequencies with wavelengths larger than the diaphragm diameter (this means
a three way in most cases rather than a more protypical two way
"CD" horn). The waveguide simply narrows the wide dome
dispersion so as to integrate the dome with the driver covering the lower
frequencies below the crossover.

After all, if a dome behaved as a point source, then
simply screwing it into a baffle of appropriate size would produce absolutely
perfect directivity characteristics.

In general this is true - a dome works very well as a point source...this is why
they are so popular as the standard tweeter in the majority of speakers (used
within a limited bandwidth of course as they do start to become directive
somewhere above about 8 to 12 Khz and also suffer from breakup like any
regular cone at even higher frequencies and, of course, they rapidly drop in
SPL output as you go low in frequency and exceed excursion limits - however
there is not much "music" above 12 Khz anyway and they make
awesome cheap tweeters )

Large domes for covering lower frequencies also have a nice dispersion and
sound great but they have proved much less successful than the ubiquitous
dome tweeter - mainly because they are expensive to build properly (you
need a very large voice coil/motor and rocking can be an issue due to lack of
lateral support/alignment for the motion ( so some designs resort to having
two spiders) - all factors that make large domes extremely expensive
compared to a regular cone so few designers use them (awesome but way too
expensive).

Vertical mounting of course doesn't eliminate the crossover-related off-axis lobing, but it places it entirely on the vertical axis . . . and the vertical-axis listening position in the control room varies far less than the horizontal.

Kirkus,

Good point. I agree tha this is an interesting discussion. Thx to you and to Kilopop and others.

However I woudl add that your point above is even more a problem for passive designs.

I would add that the advantage of Active speakers is that you can make a much sharper and phase compensated crossover filter precisely because it is active. This should reduce lobing. From what I know the 1038's allow the HF/MF combined unit to be rotated inside the cabinet for horizontal placement and this should ensure that any remaining lobing remains in the vertical axis where it is less significant.

the low-mid transition is that of a horizontally-placed design.

Yes but at 410 Hz (the crossover) the wavelength is about 2.7 feet (30 inches)! Given the drivers are only about 12 inches apart the lobing should not be apparent except at extreme angles (well above 60 degrees).

I wonder if you are hearing the effect of soffit mount - this has a significant impact on lower mids and mid bass compared to free standing (you no longer have comb filtering from reflections off the wall behind the speaker so that bass becomes solid, more tangible, more directional and less diffuse)

But 400Hz does lie in a region below where most types of room treatment are effective, and yet above the region where a "control-room-sized" (whatever that is) room is exhibiting primarily modal behavior.

Agreed - the frequencies between 60 and about 500 Hz are the principle reasons to soffit mount speakers. You can avoid the inevitable suckouts that occur with certain lower mid and mid bass frequencies. The suckouts are often not that huge (6 to 9 db) but they are harmonically related and are therefore usually quite audible. If you heard a certain unusual mid bass thickness in the vocals then it might be the affect of the soffit mounted Genelec's versus what you are use to hearing all the time from free standing near field speakers.