The axial response shows some big improvement in performance (note the changes at 280/1800Hz) from the new construction- clearly the walls were REALLY singing along, causing 6+dB notches like those, no surprise that the wall resonance would contribute to the spectral content (viewed as distortion by the analyzer)
well after looking through the links POOH posted maybe there is light at the end of the tunnel. interestingly enough (perhaps it's only marketing speak) JBL's touting a reduction in harmonic and intermodulation distortion alongside increased spl.(something manufacturer's aren't supposed to care about because it's inaudible?)
the Community m200 peaks my interest on the simple fact that it's not a metal diaphragm and likewise for JBL's CMCD. now if higher frequencies could be reached without resorting to metallic diaphragm's that would be something.
i wish i was in a better position to explore material choices for diaphragms in compression drivers as i've always felt that the move to titanium/metallic diaphragms in the pursuit of higher frequencies brought with it performance compromises that at least for me where not a net benefit.
thus far the only thing i think that i can (from a DIY standpoint) experiment with is EnAble treatments to see if significant changes can be made with positive results.
the Community m200 peaks my interest on the simple fact that it's not a metal diaphragm and likewise for JBL's CMCD. now if higher frequencies could be reached without resorting to metallic diaphragm's that would be something.
i wish i was in a better position to explore material choices for diaphragms in compression drivers as i've always felt that the move to titanium/metallic diaphragms in the pursuit of higher frequencies brought with it performance compromises that at least for me where not a net benefit.
thus far the only thing i think that i can (from a DIY standpoint) experiment with is EnAble treatments to see if significant changes can be made with positive results.
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I need to document it, but I found good results in damping the embossed diaphragm in selenium D2500Ti. I like the idea of embossed phragms (though durability apparently suffers) to distribute breakup.
I should order some 16 ohm phragms (the system doesn't need the sensitivity of 8 ohms) and run some before and afters. I believe JBL used "aquaplas" damping of metal phragms in some models, I used PVA glue and talc.
Since the suspensions are pretty stiff generally and there's efficiency to spare, seems a good solution. A little drop in Fs is not a bad thing for most drivers either.
I should order some 16 ohm phragms (the system doesn't need the sensitivity of 8 ohms) and run some before and afters. I believe JBL used "aquaplas" damping of metal phragms in some models, I used PVA glue and talc.
Since the suspensions are pretty stiff generally and there's efficiency to spare, seems a good solution. A little drop in Fs is not a bad thing for most drivers either.
Turk,
1) Reducing the compression ratio does reduce harmonic distortion, but results in a band pass reduction of high frequencies- the band pass is good for a midrange device, as it reduces upper harmonics. Larger diaphragms have to move less distance for the same SPL, obviously reducing IM.
Limiting the frequency range and designing for the specific range certainly can reduce distortion, but the center to center distance between separate horns degrades off axis response compared to a single driver covering a wide range. Loading multiple drivers to one horn eliminates that problem, but ultimately is limited in SPL to what the HF driver is capable of at low distortion, which is far less than mid and LF output. Combining the output of multiple HF drivers increases SPL potential, but the "plumbing" combiners also increase NLD.
2) High frequencies can be reached with plastics, but the diaphragm (or annular ring) area must be small because of the lower strength to weight ratio compared to metals. Small diaphragms can't put out as much clean SPL as larger diaphragms. Too large, and the diaphragm HF output is primarily breakup modes, raising HD. The "catch 22s" of compression driver design all result in a variety of compromises.
3) The EnAble treatments have not shown any measurable before and after improvement in frequency response (only subjective claims), much less improvement in distortion. Adding weight (in the form of dots) to a HF diaphragm reduces the strength to weight ratio, reducing HF output and transient response.
thanks Weltersys (Art) for the good objective summary.
perhaps dots aren't the way to go but if a thin film of material with damping properties could be applied (without adding to much additional mass)in an appropriate pattern rather then embossing a diaphragm (which seems to weaken the structural integrity) control or reduction of breakup modes might be possible and if nothing else change the sonic signature of a diaphragm material type i've never been particularly fond of.
badman please let me know any results or observations from your experiment!
perhaps dots aren't the way to go but if a thin film of material with damping properties could be applied (without adding to much additional mass)in an appropriate pattern rather then embossing a diaphragm (which seems to weaken the structural integrity) control or reduction of breakup modes might be possible and if nothing else change the sonic signature of a diaphragm material type i've never been particularly fond of.
badman please let me know any results or observations from your experiment!
Turk,
No, they are designed for straight, rather than offset horn mounting. Although the output/distortion of the M200 is impressive for a 2" exit driver, it's output/distortion can be exceeded by standard cone drivers costing far less on an offset (Synergy) type horn.
You mention "the sonic signature of a diaphragm material type i've never been particularly fond of ".
Were you able to hear a difference between the four different diaphragm materials in the recordings in my compression driver tests?
Once equalized, I couldn't tell the drivers apart, but the Klippel (and hearing) tests clearly show that my ears are no longer "golden" compared to a good many 🙁.
Art
You know who has good ears? Eldam identified all 7 drivers correctly on one of the Blind Subjective threads. He commented a lot on sound signature of paper vs aluminum vs fiberglass. These are all open cone type drivers in a FAST configuration - but still impressive.
as i've been unsuccessful in running the klippel test on my 'puter system (freezes and refuses to do any thing forcing me to power down) i guess the shade of gold of my ears is to be determined.
i was able to clearly hear differences but to say i could i.d. a particular type by sonic signature through the playback/monitoring chain involved no. i do feel that in a direct/live circumstance yes. i recently did a gig on a rig that had 3 "cheap" replacement diaphragms amongst 8 horns. at first the crew tried to play it like nothing was wrong but after insisting they check for possible connection faults the tech crew for the rig confirmed my "findings" although with one i had the location wrong.
so what makes these drivers unsuitable for offset mounting?
i was able to clearly hear differences but to say i could i.d. a particular type by sonic signature through the playback/monitoring chain involved no. i do feel that in a direct/live circumstance yes. i recently did a gig on a rig that had 3 "cheap" replacement diaphragms amongst 8 horns. at first the crew tried to play it like nothing was wrong but after insisting they check for possible connection faults the tech crew for the rig confirmed my "findings" although with one i had the location wrong.
so what makes these drivers unsuitable for offset mounting?
Just the physical arrangement. The phase plug was designed to work with an axial throat. The PDF from JBL has pictures.
Yes - for sure. Having heard wooden horns with sand filled walls, I can attest to that. You don't seem to "hear them" at all. There is currently some discussion on the thin metal walls of Altec multi-cell horns in another thread.
Thanks for your experiments and your posted data.
For an offset mounted midrange, it also needs to be small bodied enough or have its output off-center so that the port can get close enough to the tweeter. Big midrange CDs would put the port way too far out.
May I ask why you think an analyzer would mistake a change of level on a fundamental with other spectral components?
I guess we are still wondering if other spectral components can be generated by horn wall motion.
ok i should have done a little more contemplation and research before i asked that last question.
the devil is in the details.
the devil is in the details.
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Of course horns are audible according to the programme material.
Just tap the inside or outside of a horn with a finger nail in various spots to understand the signature sound of that horn/flare.
Once music is playing those signature resonances/timing variations will be audible.
A sonically dead/correctly damped horn is mandatory.
Dan.
Just tap the inside or outside of a horn with a finger nail in various spots to understand the signature sound of that horn/flare.
Once music is playing those signature resonances/timing variations will be audible.
A sonically dead/correctly damped horn is mandatory.
Dan.
xrk971,
The reduction in the low frequency range of your horn when the cardboard/foam core was doubled suggest it was functioning as a "drone cone" below Fc when only a single thickness was used.
Although foam and cardboard are useful for low volume trials of horn designs, they are not nearly rigid and damped enough to withstand the vibrations produced with typical horn drivers capable of throat SPL in the 160 dB range. At those levels, cardboard quickly starts to de-laminate and buzz like a kazoo, and rapidly looses its structural integrity. While testing throat SPL, the old foam B&K 4004 windscreen started to disintegrate after only a few seconds, had to clean debris out of the horn throat.
Even with strong materials like aluminum or fiberglass, thin sections will "ping" or "quack", resonances continue after the stimulating frequencies stop, just like the ringing of a bell.
Art
If enough vibration of the horn walls occurs then the sound radiation would go chaotic and generate all kinds of tones more a kin to noise than anything else - like "buzzing". This can be picked up by an analyzer as a random generation of HD products since there will always be some presence of a 2nd or 3rd harmonic in the noise background. Stop the "buzzing" and the distortion goes down.
There is a reason why bells are made from metal and not wood !
I'm not a material engineer, but I believe to know that in the metal transmit the sound more faster than air (8x > with aluminium ?)! Like the water is 10 x faster than air !
I always heard here the old audiophiles saying "enough with metal horns... we have always the cathedrals" and as some said above. Did you remember the Le Dauphin horns, sand damped ! I surmise many audiophiles in all the world used by "instinct" such methods ! as also mass-spring-mass ! I assume it should be something to tame the lowest energy of a Synergy !
I'm not a material engineer, but I believe to know that in the metal transmit the sound more faster than air (8x > with aluminium ?)! Like the water is 10 x faster than air !
I always heard here the old audiophiles saying "enough with metal horns... we have always the cathedrals" and as some said above. Did you remember the Le Dauphin horns, sand damped ! I surmise many audiophiles in all the world used by "instinct" such methods ! as also mass-spring-mass ! I assume it should be something to tame the lowest energy of a Synergy !
bending mode waves are slow enough for audio concern - "rings like a bell" ring a bell?
in thin shells fabricated of metal too - its only compression waves that are fast in metal
mass production has been developed very far in metals with lots of tools, infrastructure support for fabricating out of metal - so at high volume it can be cheap
horn/waveguide walls don't really need to be metal for the acoustic performance
in thin shells fabricated of metal too - its only compression waves that are fast in metal
mass production has been developed very far in metals with lots of tools, infrastructure support for fabricating out of metal - so at high volume it can be cheap
horn/waveguide walls don't really need to be metal for the acoustic performance
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