Allen,
Yes the entire length of the horn does load the air column but the initial opening of the phase plug does set the initial load onto the diaphragm. There are designs with much lower ratio of diaphragm to slot size initial opening but these will have much lower total power efficiency. The horn will set the bandwidth but the initial opening will set the overall max efficiency.
Yes the entire length of the horn does load the air column but the initial opening of the phase plug does set the initial load onto the diaphragm. There are designs with much lower ratio of diaphragm to slot size initial opening but these will have much lower total power efficiency. The horn will set the bandwidth but the initial opening will set the overall max efficiency.
A horn/waveguide has a characteristic impedance, but this is modified by the diaphragm to phase plug aperture ratio. If this ratio is 10:1 then the impedance seen by the diaphragm is 10 x greater than the actual impedance of the waveguide. So basically this is the dominate form of the increased loading and hence the greater efficiency of a compression driver. This why putting a direct radiator behind a waveguide does not really raise its output all that much, and in fact not at all at higher frequencies.
I am familiar with this kind of driver, but the long route to the exit aperture is a negative IMO. A DE500 is a fraction of that length and the aperture is basically right at the end of the phase plug.
That's actually a very old technology, dating back to the 20' or 30's.
Take a look at the patents that Alexander Voishvillo filed for JBL ; he made some changes to this phase plug design at JBL.
Patent US8280091 - Dual compression drivers and phasing plugs for compression drivers - Google Patents
Allen,
You need to look at the properties of rarefaction, this is a factor in the compression of the air between the diaphragm and the phase plug. it is not simply a compression wave that you have to consider. The volume of air between the diaphragm and the surface of the phase plug is actually very small and this factor is often overlooked in how a compression driver functions.
You need to look at the properties of rarefaction, this is a factor in the compression of the air between the diaphragm and the phase plug. it is not simply a compression wave that you have to consider. The volume of air between the diaphragm and the surface of the phase plug is actually very small and this factor is often overlooked in how a compression driver functions.
Hi natehansen66,
May be reading this would give you more idea 'where to go':
http://www.diyaudio.com/forums/mult...ompression-driver-evaluation.html#post3014199
https://soundforums.net/threads/4329-High-Frequency-Compression-Driver-Evaluation
regards
ivica
Be careful here, because Art's test and my tests arrive at different conclusions. In further looking into this Art's test went to much higher SPL's that my test would allow, so at the extreme of SPL things might be different. But My test would be completely valid in a home situation as one would never achieve the SPL levels that Art tested. Art's would be more useful for sound reinforcement - completely consistent with the two different fields that we work in.
Ok, so rarefaction is not just a negative pressure magnitude? I guess I was assuming symmetry in linearity, at least at low levels. Maybe this effect is defeated when a throat chamber is unavoidable or used intentionally.
Rarefaction is the negative (relative to ambient) pressure in a sound wave. It takes a very high SPL to get significant nonlinearity in air. It is mostly low order and so not very audible, except that it also grows with distance travel if the pressures remain high. Thus a rapid expansion is a good idea, but for the most part this kind of nonlinearity is inaudible in home situations.
Speaking only of the OS/tweeter I've noticed none of that. It takes a few friends and a few beers to get the bacon frying (only had to learn the once) but there was no indication of anything before then. My woofers were sounding a bit warmed up though.
I can see how yours could do double duty in a club.
I can see how yours could do double duty in a club.
gedlee:
I'm also prone to think like badman, that this type of comp drivers will shoot a more "controlled wavefront" into the wavequide/horn than a "pancake" drivers since the built-in horn and the throat diameter controls the directivity of the high freqs. Drivers with short horn in them are less affected by certain irregularitiies in the wavequide.
I'm also prone to think like badman, that this type of comp drivers will shoot a more "controlled wavefront" into the wavequide/horn than a "pancake" drivers since the built-in horn and the throat diameter controls the directivity of the high freqs. Drivers with short horn in them are less affected by certain irregularitiies in the wavequide.
Legis - if that is what Badman is saying then I respectfully disagree. The wave front at the mouth (which determines the devices directivity) is controlled by the waveguide not by the compression driver. In a properly designed waveguide there is no HF beaming. In my experience using all of the different "types" of drivers, the shorter the throat in the compression driver the better, although admittedly this is a secondary effect since the waveguide itself dominates the directivity control.
I think that concepts like "shoot a more 'controlled wavefront'" are not really very scientific and may lead to erroneous conclusions.
I think that concepts like "shoot a more 'controlled wavefront'" are not really very scientific and may lead to erroneous conclusions.
Drivers like that JBL and others like it are dominated in design by the simple fact they use an Alnico magnet and this forces the length of the throat to be longer than can be made with a ceramic or Neo magnet motor.
I disagree here with Earl in that the very top octave up to 20Khz will be very influenced by that long narrow throat and no matter how fast you open the horn after that throat you are not going to have a wide dispersion at the highest frequencies. I just think that Early doesn't consider the very highest frequencies as of much concern, both in power response and in our hearing response. Earl can answer for himself, but that has always been a consideration and why I prefer the shorter pancake compression drivers if the very top end of the audio range is a consideration where you wanted a wider dispersion pattern. The exit angle will be greater in the pancake drivers than what was just shown, no way around that factor. I would consider that long conic throat section as a separate horn section directing the highest frequencies in a very narrow angle.
I disagree here with Earl in that the very top octave up to 20Khz will be very influenced by that long narrow throat and no matter how fast you open the horn after that throat you are not going to have a wide dispersion at the highest frequencies. I just think that Early doesn't consider the very highest frequencies as of much concern, both in power response and in our hearing response. Earl can answer for himself, but that has always been a consideration and why I prefer the shorter pancake compression drivers if the very top end of the audio range is a consideration where you wanted a wider dispersion pattern. The exit angle will be greater in the pancake drivers than what was just shown, no way around that factor. I would consider that long conic throat section as a separate horn section directing the highest frequencies in a very narrow angle.
Yes the driver's inherent horn controls the dispersion at high frequencies. The small horn in the 2440/2441/2445/2446/2450 drivers control the directivity somewhat down to ~3-4kHz. The built-in horn is 15deg conical and ~5-6cm long, but varies somewhat between early and later models.
This short built-in horn is partly the reason why this kind of driver behave quite good in 2-way synergy horns where there are larger injection ports near the throat. The compression driver does not "see" the injection ports at higher frequencies (as much) since the wavefront is controlled (radiated narrower) because of the built-in horn. High frequency wavefront has not opened up or "bloomed" yet completely when it reaches the injection ports.
Pancake drivers radiate hf wider. It's preferable in OS/conical and other CD-type waveguides, but might not be as preferable in synergy horns.
Guys, you have it incorrect. The theory says that there should not be beaming and my data shows that as well. Of course this is only true if you use a precisely correct OS contour with a well handled mouth. Any other approach and there will likely be beaming.
Just look at the data shown on my website. There is a small increase in DI above 10 kHz, but nothing substantial.
If the waveguide contour follows directly from the driver contour without any slope changes then there is no "radiation" from the driver itself, it is all controlled by the waveguide. Even the slightest change at this point will cause diffraction and quite possibly narrowing. You simply cannot state that "Pancake drivers radiate hf wider." because there is no radiation in all cases. You are refereeing to specific examples like a synergy horn, which does not follow the laws that I am describing.
"High frequency wavefront has not opened up or "bloomed" yet completely" - this is not a scientific statement, but is not actually correct as I would interpret it. The diffraction at the end of a compression river will happen immediately and will splay to the sides and imping on the "injection ports".
This is not true if the waveguide is a continuation of the "horn" in the driver exit.
Just look at the data shown on my website. There is a small increase in DI above 10 kHz, but nothing substantial.
If the waveguide contour follows directly from the driver contour without any slope changes then there is no "radiation" from the driver itself, it is all controlled by the waveguide. Even the slightest change at this point will cause diffraction and quite possibly narrowing. You simply cannot state that "Pancake drivers radiate hf wider." because there is no radiation in all cases. You are refereeing to specific examples like a synergy horn, which does not follow the laws that I am describing.
"High frequency wavefront has not opened up or "bloomed" yet completely" - this is not a scientific statement, but is not actually correct as I would interpret it. The diffraction at the end of a compression river will happen immediately and will splay to the sides and imping on the "injection ports".
This is not true if the waveguide is a continuation of the "horn" in the driver exit.
I have thought the whole narrowing radiation pattern of tractrix/expo etc. horns is because of the same phenomenom I was talking about. In expo the start of the horn, which is long and wide enough to direct high frequencies (say first 5cm), opens up very narrowly, thus high frequencies are directed like a lazer. The middle point of the horn, which is long enough (say 15cm) to direct mid-highs, opens up wider, thus mid-highs are radiated wider etc.