jessie.dazzle wrote:

… I do not fully understand the relationship between output impedance and diaphragm control; also I don't know what you mean by "negative impedance". Your mid-bass drivers have 15 Ohm coils; from what you write, I assume you are driving them from 15 or 16 Ohm taps. Correct?

Bud wrote:

The next time you are at live music, listen specifically to this "dark side" of the live sounds. Then listen again to your system. I think it is the key to a whole new level of reality in out favorite illusion.

rickmcinnis wrote:

Having tried many types of coils nothing was as transparent as the NORTH CREEK 8 gauge air core coils. I do not think you will be happy with the JANTZEN or any other using a metal core. They are much cheaper than the NORTH CREEK and look better. I, too, have used this combo approach to get a crossover curve and found it works well when one wants to avoid more amplification stages to get a sharper slope.

Rick, thanks for the opinion.  I generally would agree: nothing beats air core coils. There are a few “howevers” of to look at the subject a bit deeper.

If we are use a very low crossover frequency then the air core become huge, really, a true barrel of copper. The inductance of could and driver, combined with capacitance of the cables and HUGE air coil create a perfect resonating detector. Combined with a driver high sensitivity one might pick radio stations and all imaginable noises right in this detector. So, to do the things properly as 10mH air core 8ga coil will be 15” in diameter and near 60 points in mass. Now, to shield this coil you would need ½ inch steel. The problem is that if you locate such a sarcophagus too close to the coil then the core will talk with it and you have no air core anymore. So you need to locate the shield no closer than let say 5-7” from the end of the coil. So, we are taking about a table size enclosure for a single coil. Do not forget that that I gave an example of 10mH air core 8ga coil but in my case I would need 30mH – I will not be able to lift up such a coil. Alternatively the shield might be done with co-netic like alloys that have 800 times more shielding capacity. Prepare to pay for the shield much more then you paid for the coil. That all combined with the fact that such a coil can’t effectively filter and the inductance of driver’s VC will crew up file in the driver’s peaks.

Do not forget that even 8ga coil the DCR of the coil is large as it has a LOT of wire, 10H of the air core will have .4R. The toroid coil with metal core will have literally a few turns of wire and will have DCR of .02R. You get purity or air core but you lose dumping as you have too high DCR. Also, I am pretty confident that all air-core advantage exist only at HF, at lower frequency it is very questionable.

How I know all it? I when over it, not once and it made me to feel OK with metal core for LF. In my case the main roll off will be by line-level filter but I can wire more curves in my amp. I need one very soft first order and I think line level will do fine for now. It possible to add a filer in plate voltage but it would require to change my amp that it a bit complex without it.Rgs, Romy the caT

Romy the Cat wrote:

Last night Levine and BSO played a phenomenal Mahler 5, truly great play.  I had some issues with BSO sound and I probably will bring it up to them. Tonight I decided to listen the M5 broadcast for the first time and I realized that my bass is gone. I mean it became not as interesting as I remember it was 3-4 days ago when I was listening it last time attentively. I have no time to look into it now but something is not right….

As I predicted the Vitavox drivers, as they start working after years of sitting in the box, got softer and the resonance frequency dropped. Sine I recognized that my midbass lost its quality very aggressively I anticipated that the resonance dropped in 20s. I was wrong. Measuring resonance not I got 37.2Hz. That is very interesting as I did not expect the sound go so week with juts 5Hz off the mark.

I decided to move resonance back to 42Hz stopping it to work with open back chamber. Here I had another surprise – the driver was practically did not response to the presence of the back chamber cover. Before it moved resonance for 12Hz but now the driver was so soft that presence of the back chamber lid it recognized as almost open air! Funny but now I need to displace the back chamber again.

I took dense, non-compressible foam and fill ~ 30% and then 50% of the space in the back chamber with back chamber sealed from outside.  The resonance went to 38.6Hz. Not a lot I figured. However, the Sound got surprisingly better. Paying more with it I was able to drive the resonance to 39.4Hz and this is how I finally closed the back chamber for now. The sound is nothing like the last week, the sound is very good but it become good only if I set resonance over 38Hz -38.5Hz. I have no explanation for this phenomena and I did not expect that the 1-2Hz will do such a huge difference. I was thinking and thinking about it and then I got bored from it. If for whatever reason my horn and my driver want to have resonance over then I will give it to them and let them choke from their sick pleasure.

Anyhow, I have my midbass back and get some idea how my driver behaves as it ages. The moral of this story is that if you use vintage drivers with paper suspension in your horns and if you demand high level of operation and performance then let your vintage drivers to burn-in a lot and only then lock the operation of your horn.

el`Ol wrote:

Romy, are you going to verify the decision of using fragile vintage drivers? E.g. by trying JBL midbass drivers? They would be closer to the design philosophy of the Fane Studio 8M. http://www.jblpro.com/components/maxout.htm#2020H

Romy the Cat wrote:

I changed the new flash at my site to “Ok, the midbass horn project is successfully over. Over 3 months, over 400 posts, over 180 pictures… all publicly available…” The project started physically on July 16, 2010, ended on October 28, 2010. The preparation for the project took much longer - I would say that it was the last 8 years… The cost of materials in my rough estimate is around $5000. I will not disclose the cost of labor, it is a lot but frankly it is still lower then I initially expect. During the project… The major fuckup was just one - the difficulties with accessing of the right size of back chamber. The major worry - the upper positioning of the midbass would too much localize the midbass direction.  The major success – an existence of a properly made, 42Hz midbass horn that is in time-aligned but invisible and doesn’t ruin the room décor. The major discovery - if horn has no reflections then it linearizes driver impedance. The major coincidence – the efficiency of midbass horns driven by Milq’s bass channel is identical to the Macondo’s MF reference efficiency. The major funny story – me telling to a person who inquired what I was building, informing him the I am building a “God’s Voice machine” Now is the most interesting question: was it worth it? I do not know. I pretty much wasted a summer on this project but from another point of view EVERYTHING that we do is waste of time in one way of another. This midbass horn is something that I wanted, so I got it and I guess it made it worth and valuable to me. Would I do it again? I do not know. I did it because THIS listening room did inspire me to have this THIS type of horn. If I move out of this room then I would need to get another inspiration. I am thankful that I did this project in my mid 40s it would be much more difficult for me to do it in 10 or 20 years… I kept the whole project open and available for public, sharing my success and failures, blinders and brilliance, stupidity and cleverness. If nothing else, then I feel that my project extends knowledge base about midbass horns and create opportunity for the installations of others to sound better. So, in the way the torch of the horn-loading idea is still lit and now is passed to whoever have interest in it.

I forgot to drops a few thanks to the folks who helped me with my midbass project.

The biggest thank you goes to Sergey Konovlev – my carpenter who reconstructed the attic, measured the spaces, developed AutoCAD plans, constructed horns, lifted them up, installed them, built supports and followed up with finishing the walls. He also, was a sole listener of my bitching and my assessment that he does something wrong.  In the end of the project before hosting the horns, when we were guessing if the horn will fit the narrow hole inside with less than an inch clearing I decided to make the process interesting and promised $1000 bonus if the horns fit. I will tell you that you never saw a Jew boy who was so happy to give away $1000 as I was after the horns did fit perfectly.

I would like to thanks Pablo Cheline, my local guy, who moved the horns around and helped with insulation work. A thank you goes to Bruce Edgar with whom I consulted a few times during the project and from whos experience I took some inspirations. A thanks goes also to Jeffrey Jackson who it the beginning of the projects consulted me about the materials, glues and assembling techniques. And of course the special thank goes to John Hasquin with whom I consulted during initial planning stage. Despite that John was not engaged while the project was in progress but his upperbass horn very much save the midbass, not to mention that I always have a warm feeling about John’s judgments.

There is something that is not visible besides all those posts, picture and public thought – the level of anxiety that the project brought in my regularly quite habitual life. The last crumple days before the raise the horns I got it a bit personal and was in way very psychotic.   The last 3-4 days I did not go anything besides working on the horns and did not think about anything else beside “what else my horns need”. The very last night before the hoisting the horns I did not sleep and I cough myself at 4AM on the morning waling across my listening room, patting the horns and telling them that “everything will be all right”.  Despite of that binding experience and certifiable behavior I have no particular feeling about the midbass horn now. They are in the wall, they do what they need to do and they do not bother me. I think that this type of “out sight -out of mind” approach works very good for loudspeakers….

 Paul, what are you talking about? I use from my 6C33C no more then 1-2W. The 6C33C at LF might give 20 W but it is load over to 600R. I load it to near 2500R (11.83:1 transformer with 15R driver) – you figure out your how much power and gain I burn in the transformer. I do not want to have more line gain; in fact I would like to have less line gain but instead to add some gain via transformer. It is sad that I do not have tabs on it.  What I do not know is why adding current help to get rid of clipping if the tube runs at voltage deficiency. Anyhow, I need to find a good balance between the losses in transformer and attenuation in my line level.  I do not want to lose the idle mode of my 6C33C operation as it sound very good for bass. I might go for 1500R loading but with fast core:

http://www.intactaudio.com/forum/viewtopic.php?t=1085

but there are some other consideration that I have in my mind. I do feel that I a bit idle the 633C too aggressively but it might be why my hyperbolic horn does not sound “hyperbolic bass” but rather as “tratrix bass”. You never know where you will find and where you will be lose….