What are benefits of adding HF driver 7khz up?

[weltersys]

Originally Posted by speaker dave

But this is what's odd about Art's experiment. He has two horns, two drivers and the signal mixing some distance in front of the horns. It isn't under extreme pressure conditions in the throats, its at 100dB or less, some distance out from the horns.

I'm not sure why his mixing products are as loud as they are.

David

I stand corrected regarding my previous statement that the SPL at a compression driver’s diaphragm level would be higher than the throat.
The highest level would be at the narrowest point of the throat.
In the driver I measured recently, the screen (as close as the mic can get) is not at the apex of the phase plug, so there still would be some level increase closer to the diaphragm than at what I referred to as the throat.

The throat screen SPL in my 104 dB test would have been very close to 129.7 dB, using the test attached below as a benchmark.
I used a 1.4" exit driver for the test to lessen the effect the microphone displacement in the throat would have, the smaller diaphragm 1" exit drivers at 104 dB may be about 3dB louder at their throats to achieve similar level.

In a shallow horn as in your Avatar, similar, or higher, throat peak SPL would occur at 3 meters even at what some might call "moderate" listening levels.

Beranek's book “Acoustics” describes the nonlinear distortion mechanism:
"If the horn were simply a long cylindrical pipe, the distortion would increase the farther the wave progressed..."

Doubling the distance would double second harmonic distortion in a pipe.
The nonlinear distortion increases linearly with distance traveled in the tube, or the length of the horn.

"in the case of an exponential horn, the amplitude of the fundamental decreases as the wave travels away from the throat, so that the second-harmonic distortion does not increase linearly with distance."

If my (copy of John Meyer’s) interpretation of Beranek is correct, in a long, narrow horn like the Maltese, even though it has a more rapid expansion than an exponential horn of the same length, while SPL is falling at roughly the inverse distance law, the nonlinear (air) distortion increases with distance.

The distance from the horn throat to the microphone in my VHF test was 48.5 inches (26 inches inside the horn, 22.5” from horn mouth to microphone), many times the distance in Pano’s test, allowing much more distance for air-nonlinearity to take place, thus increasing the relative level of the audible IM tone.

Art

[gedlee]

Originally Posted by weltersys

For those of us that for various reasons require high SPL at high frequencies, the subject has more than a passing interest.

If air nonlinearity is a factor then we are in different worlds because in a home setting this could never be a factor. Now in a large venue or concert, yes this may be a factor, but there are lots of much more important ones.

I'm sorry, I just get fixated on those things that really matter. Its just a querk of mine.

[speaker dave]

I have no doubt that the pressure in the throat would be much higher than external to the horn, but didn't you say that the to-be-mixed HF signals came from two separate drivers on two separate horns? This would mean that you might get harmonic distortion of the individual tones (high pressure in the throat), but the IM could only occur in the lower SPL environment outside the horn.

I can't say whether these things matter or not, but I am technically curious and eager to learn.

David S.

[Pano]

Originally Posted by gedlee

But, to me, its all just an academic discussion with no outcome that has any real significance.... niether of which is very interesting for audio.

Originally Posted by gedlee

I'm sorry, I just get fixated on those things that really matter. Its just a querk of mine.

Oh, beautiful dismissal!
(Just FWIW, some people do need high SPLs. Some people do need substantial HF - E.G. for long throws in dry air. Yeah, that's audio, too.)

I can't say whether these things matter or not, but I am technically curious and eager to learn.

What Dave, no blinkers?

[weltersys]

Originally Posted by speaker dave

I have no doubt that the pressure in the throat would be much higher than external to the horn, but didn't you say that the to-be-mixed HF signals came from two separate drivers on two separate horns? This would mean that you might get harmonic distortion of the individual tones (high pressure in the throat), but the IM could only occur in the lower SPL environment outside the horn.

I can't say whether these things matter or not, but I am technically curious and eager to learn.

David S.

It is a very curious fact that the IM generated in a single horn with twice the power used in the stereo horns produces no audible IM component, while the stereo horn set up does.
My explanation in #251 is as good as I can get with my present knowledge, which at this point in time is empirical data from my own tests, and some limited information on the subject gained from the internet and various audio texts and articles read over several decades.

There seems to be no lack of AES papers containing contradictory complicated formulas explaining the phenomenon, but little data backing up how those formulas were derived.

At any rate, I satisfied my initial goal of testing whether beat frequency IM tones from stereo high frequency drivers are audible, as it turns out, they are.

My goal did not include the "why", if anyone reading can provide a better explanation than in #251, I'm all ears .

Art