Magico - Wide vs. Narrow

Imo, all else being equal, the edge diffraction of a wide cabinet is more likely to degrade image precision because its false azimuth cues arrive at a worse time.  But imo cabinet shape matters more than cabinet width. 

It is not clear to me that baffle width has a major effect on perception of the acoustic space on the recording, but if it does, I think the advantage would lie with the wide baffle. 

Duke

@mark200mph wrote:

"The wings on the infinity had rear firing tweeters and they did that as well on the genesis 200 model.my new fr 30 has a rear firing tweeter."

Ime a well-integrated rear-firing tweeter can contribute to "being able hear the recording space". 

Incidentally, the superb Snell Type A-III mentioned by @erik_squires also had a rear-firing tweeter, if I recall correctly.

@erik_squires , imo the width of the Snell Type A helps the rear-firing tweeter to work well even when the speaker is up against the wall, assuming the wall is not absorptive.

Imo rear-firing tweeters need some reflection path length, but not nearly as much as a fullrange dipole because the rear-firing tweeter’s output is limited to short wavelengths. As the wavelengths get shorter, the reflection path length we can get away with also becomes shorter.

The sheer width of the Type A’s cabinet gives us good path length for the rear-firing tweeter, and the geometry becomes that of a slot all around the tweeter which tends to direct its output up and to the sides. So the rear-firing tweeter’s output arrives late enough that it doesn’t degrade the clarity, but it does improve the spectral balance of the reflection field, which (among other things) contributes to "being able to hear the recorded space", in my opinion.

I don’t think there was anything about Peter Snell’s Type A that wasn’t incredibly well thought-out.

Duke

@tomic601 said, "A rear firing tweeter... is 100% distortion..."

I disagree.

Implemented correctly, one beneficial thing a rear-firing tweeter does is this: It corrects the spectral balance of the reflection field.

Duke

rear-firing tweeter advocate

Quoting @tomic601 (replying to my post that rear-firing tweeters can correct the spectral balance of the reflection field) :

"While destroying the timing information that the ear brain is much more sensitive to. "

There are conditions under which a rear-firing tweeter can can be detrimental. Imo we do not want the output of the rear-firing tweeters to arrive too early nor be too loud, and we want its power response to be correct for the application. These characteristics are perceptually intertwined. Hence the "implemented correctly" stipulation in my previous post.

@tomic601’s follow-up post:

"my decision references are unamplified acoustic instruments in reverberant spaces captured w simple microphones, so the temporal data is in the recording."

Imo effectively presenting "the temporal data in the recording" is precisely the scenario in which a correctly-implemented rear-firing tweeter is most beneficial.

You see, in the playback room there is a "competition" between two sets of spatial cues: The venue spatial cues on the recording, and the "small room signature" inherent to the playback room. It is desirable for the venue spatial cues on the recording to be perceptually dominant if the goal is a "you are there" presentation.

Painting with broad strokes, the ear judges the size of an acoustic space by three characteristics: The time delay between the first-arrival sound and the first reflections; the temporal "center of gravity" of the reflections; and the decay of the reverberation tails.

It is in the effective presentation of the reverberation tails on the recording that a well-implemented rear-firing tweeter is most beneficial. Briefly, the in-room reflections act as "carriers" which deliver the reverberation tails on the recording from all around.

The ear looks at the spectral balance of incoming sounds to judge whether they are reflections or new sounds, and the overtones are especially critical to the ear making this determination. If the overtones are not loud enough for the ear to correctly identify the reflections as such when delivered by the in-room reflection field, that energy ceases to be "signal" and becomes "noise". But if the overtones are still loud enough, the ear will hear the reverberation tails arriving from all around as they decay, delivered by the spectrally-correct in-room reflections. This spectrally-correct delivery of the reverberation tails by the in-room reflections effectively presents the natural decay characteristics of the reverberation tails on the recording, which in turn are a significant contributor to a "you are there" playback experience.

And a well-implemented rear-firing tweeter corrects the spectral balance of the reflection field, restoring its typically-too-weak overtone levels, without introducing other problems. 

That being said, this is a complex topic and this post is an incomplete look at just one aspect of it.

Imo and ime.

Duke

@erik_squires wrote: "That’s an interesting POV. I would have thought that the slot [the area between back of a speaker with a rear-firing tweeter and the well immediately behind it] would act like a severe low pass filter."

Sorry I over looked responding to this earlier.

I manufacture a bass guitar speaker cabinet which uses a 3" cone unit for the top end. It’s gently highpassed around 1.5 kHz or so. Behind the cone is a wide, shallow isolation chamber which extends laterally the full width of the cabinet, with generous openings on the top and sides. So, it’s a slot of sorts. The openings allow enough of the 3" cone’s backwave energy to escape out the top and sides that the bass player can clearly hear his overtones even if he is virtually atop the cab, and I’ve gotten feedback that the other musicians can better hear what the bass player is doing as well.

I’m sure there are some losses in the slot behind the 3" cone, but it’s still making a worthwhile contribution, so I don’t think the net effect is a particularly severe lowpass filter.

Duke