Beyond the Ariel

[thoriated]

Also, the remaining HF impedance peak after the charcoal was introduced was at a very high 110hz, considering the approximately 31hz minimum, which suggests that the activated charcoal was having a larger influence under 100hz on modifying the box air volume characteristics.

Incidentally, the KEF White Paper indicated that coconut shell charcoal was more effective in this application than charcoal derived from coal because of the higher incidence of very fine micropores with a diameter under 10 Angstrom in the coconut shell charcoal.

[mige0]

Originally posted by thoriated


Can you elaborate on your experiences with activated charcoal?

Some ten years ago some people experimented with liquids that vaporise at room temperature – both with some strange mixtures and also what was commonly used in freezers then.

I didn't try this, but set up an experiment which basically follows the same idea of liquidisation at in-stroke of the membrane and vaporisation at the out-stroke of the membrane – in an attempt of keeping the pressure inside a cabinet basically constant to mimic infinite enclosed volume.

Or - seen from an other point of view = absolute absorption of the backwards radiated energy of the diaphragm.

My set up was
1. a speaker that resists humidity (Dynaudio 21W54 with the magnet structure towards the front)
2. a perforated chiller/ heat exchanger at the back of the speaker with a small sealed volume in between
3. a second sealed volume behind the perforated heat exchanger that best is described as a steam boiler

Basic principle:
the steam generated in the second sealed chamber is cooled down in the chiller (think of something like the motor chiller / radiator in cars) when trying to enter the first volume.
If the chiller is efficient enough, no steam reaches the first chamber hence no pressurisation of the first chamber by the steam.

On the other hand no air reaches the second chamber as well – kind of separation with no compliance is (should be) happening in the heat exchanger.

Proof of concept was, if any difference in speaker/box compliance could be measured when the steam boiler is in action or not.

Bottom line:
measurements have proven my brilliant idea wrong

Maybe just a fault in calculating the necessary steam volume production – haven't investigated any deeper.

- at least - its a good story to tell


Michael

[augerpro]

thoriated> do you have some impedance and nearfield SPL plots you can post?

[thoriated]

Hi -

I didn't take SPL measurements, relying heavily on Basta for modeling in that regard, but I have some measurements of the bass xover impedance and response from 30 hz to 500hz (the nominal xover frequency) for the actual xover, box and driver used with the activated charcoal. This is for the 2220A LF driver only - the HF unit was not connected, but is expected to have an insignificant effect on loading and response below 300hz.

• f Zin db
  30 12.66 -1.1
  50 18.03 +0.1
  70 18.40 0
  100 18.49 0
  150 16.75 -3.5
  200 18.20 -5.2
  300 19.44 -5.2
  500 26.75 -5.5
  
  

Since the above measurements were taken, an xover component value was adjusted slightly (a resistor from 82 to 100 ohms) due to listening tests, and these measurements were not repeated, but the expected change in response would be a lift of up to 1db at 150 - 200hz, and a drop of up to 1db at 500hz compared to the values above. The response shaping above 100hz is largely to correct for expected baffle step, which should start shelving down, according to modeling, just below 500hz. Therefore the overall effective LF response is a quasi-first order that transitions to a 3rd order elliptical rolloff immediately above 500hz (not shown here) with a null at about 1.7khz.

This is a ported system with only a moderate amount of fiberglass fill (about 20% by volume) used in addition to the activated charcoal. The -1db drop in response at 30hz is due to series 600uF input polypropylene capacitance. The measured DCR of the 2220A used here is 6.0 ohms.

[Truetone]

425 horns all done. Cartons made. Will start boxing up and posting next week. Thanks for your patience.

martin

[mige0]

Hi Lynn

if you don't get around with the mid-bass units you already have, I'd warmly recommend you to try the Jantzen JA8008 designed by Troels Gravesen.

A surprisingly homogenous unit with great tonal musicality and extraordinary wide projection for its size.

But – you'll have to allow for some break in time until this speaker comes out of its pampers and spreads its wings.

I'm pretty sure this baby almost exactly meets your taste and preferences for the current project.

Anyone who'd like to give it a try - ask friendly Mrs. Iwona Jantzen for more stable packing material (and technique) as my quartet needed a week or two to recover from surround flattening due to sub-optimal package.

No permanent damage left over though – just an unnecessary annoyance.

Michael

[JoMoCo]

Recent picture smuggled out of GPA skunk works...

[Lynn Olson]

A rather frightening application for the 288's! Looks a NASA or military test setup - maybe to emulate the SPL's of a rocket launch. Some of the early rocket motor failures were due to extreme sound pressures destroying components like turbopumps and piping. It's an extreme environment any way you think of it - liquid hydrogen and oxygen, near-plasma temperatures coming out of supersonic exhausts, and SPL's sufficient to destroy many materials in a matter of seconds. The Huntsville NASA team had their hands full designing the Saturn engines.

Many thanks for the suggestions about pearlite and activated carbon. These are absorbers I would never have thought of - only at DIYAudio would I have seen anything like that. They might come in very handy for getting a few dB of broadband attenuation for the backwave of the dipole.

As mentioned in earlier posts, I'm not in love with the dipole pattern for its own sake. The reason is much more mundane and grubby; I just want to reduce cabinet coloration as much as possible, without going down the path of a Linkwitz-style heavily-equalized pure-dipole system. I'm going to explore a variant of the Gary Pimm quasi-cardioid, using a modest amount of broadband absorber for the backwave. Even 3~6 dB of backwave absorption reduces the magnitude of the baffle peak, extends the LF substantially, and decreases the magnitude of the diffraction coming off the edge of the baffle.

I've listened to Gary's system at some length, and the sound he is getting out of the Eminence Beta 8's and the Fountek ribbon tweeter is astounding. These are hardly exotic drivers, but the results (and measurements) speak for themselves. My approach will be less box (he's using heavily damped 5-sided boxes open at the rear), less backwave attenuation, and more conventional subwoofers.

[chrismercurio]

Lynn,

Can you post or point to a picture? Maybe I should still try to build that Auditorium 23 SoloVox knock off for the 604 and see what happens (sonically).

Regards,

Chris

[angeloitacare]

Lynn

i know you are concerned about natural tone, and want to avoid coloration as much as possible.
I have bought and tried recently a pair of Audax Medomex 6" papercone drivers.These are predecessors of the Audax PR170M0. These have not the clarity, and are not as much revealing and dinamic as Lecleach/S2 horns. I have tried the S2/LeCleach, crossing at 500hz/1000hz/2500hz , 6db slope, and midbass accordingly. Crossing at 1000hz, i got the best results. When it comes to play music specially with voices, the Audax sounds far more natural / neutral / coloration free.
It is however not as much revealing and dinamic. Since i do listen more instrumental / jazz etc. , i prefere horns. But the Audax PR170M0 has 99db/wm. I guess in a short wave guide, it might be a interesting compromise. It certainly will be much more tonally accurate and close to the original event, than any solution with a horn in the midrange channel. I think it would also be a great match with your RAAL's. My observation does correlate with others, like Magnetar and Aleks :

http://www.audiovoice-acoustics.com/...read.php?t=672

I'm weaning off JBL compression drivers. IOW the Audax pair even when ran up high is still distinctly superior in smoothness and tone over the 2440's I am used to and also has the dynamic/presence character I like.

Aleks made a comment about the PHL 1120, which is very similar to the Audax PR170M0 :

Ever tried PHL? Its Phillipe Lessage, ex Audax head-designer that opened his own company. He has a few amazing midrange spekers like 1120, for example. I used them and they are phenomenal.

Angelo