| Romy the Cat wrote:|
...this interesting point has no practical answer.
First of all in the case of Rakesh horn what N-Set proposed is not necessary. Those 115Hz Hasqiun-style horns that Rakesh emulates are well dumped with own mass and own construction techniques – layers of particles boards with lagers of proper glue are great damping environment. In addition it is juts 100Hz – not too stressful foe the horn of this design. Rgs, Romy
When I obtained the spreadsheet of measurements for my 115Hz, a number of possibilities presented themselves to me, all of which were easily achievable. I could easily use alternating layers of plywood and in fact had set aside some outrageously expensive 'panzer holz' to this end (see http://www.ltlewis.co.uk/), vary thicknesses of different layers and become more anal about the throat driver interface. In the end I did absolutely nothing. I was worried about the thickness and made sure that at the throat area the horn was about 160mm in thickness and this decreases to 70mm at its minimum. Why was I happy to have the thinning at the mouth end? I did not want to give any flat surfaces where the exiting waves would reflect in a uniform fashion. I would say that any modern horn, irrespective of aesthetics considerations, should have this feature.
It is interesting that Romy mentions '115 Hasquin-style horns' that I emulate since I did indeed approach John Hasquin to see if he could undertake this project (he would not) and for advice (which he is very generous with).
John Hasquin wrote the following in response to a query I sent him and it is well worth quoting in full:
"Re: Tractrix with Lecleach
The mouth termination on the Lecleach helps to prevent defraction. This too can be avoided with the tractirx by high passing at slightly above the Fc of the horn. If you have the extra room you can use the Lecleach if you want, I didn't noticed any sound quality differecnes between the two for mid bass use. There is nothing to be gained from using other materials for the back chamber if you make it thick enough. My back chambers are 1.5 inches thick, so they are plenty stong. Using a denser material will only make an already heavy horn heavier. You can use any material you want. I like MDF because it is well dampened when layered and glued together. It is also not as expensive as plywood, or natrual woods. The AK151 should be good up to around 800Hz without too much trouble. They don't quite have the speed and snap that the Fane Studio 8M, but they are can be used. That's a decision you have to make for yourself. "
Horn lore is incremental. I agreed with most of that advice. In fact, the wall thickness of the back chambers of my UB115s are 10cm, i.e. close to 300% as thick as per JH's recommendation, based in part on what I know of the pressure that develops in the back chamber. I discarded the idea of experimenting with the AK151s in that horn based on what JH and a friend of mine in Paris told me about these drivers. I also had a look at Jeffrey Jackson's horns which are based on a slightly different approach to that recommended by JH but still does not use a full Lecleach profile. I was puzzled by this and Jean Michel Le Cléac’h confirmed that the profile is a truncated Le Cleach:
Jean Michel Le Cléac’h wrote:
Hello, The 140Hz horn commercialized by Eleven Horn is for sure a (T=0.707 )Le Cléac’h horn but the mouth is shorten and its roll back is quite small. This has surely been done by Jeffrey Jackson in order to have a smaller width than the complete roll back horn. See attached graph. Best regards from Paris, France
Since as JMLC himself makes clear, his calculations in themselves do not propose a re-evaluation of horn theory, but propose some advantages which mainly result from the minimisation of re-entry at the mouth, I decided to give the UB115s some of the theoretical benefits of the mouth design of a Le Cleach profile, without the concomitant increase in overall diameter of the horns, which I had set at an absolute maximum of 96cm (+ 27.3cm /2, i.e. radius of my 396Hz horns=109.5cm, with my LeCleach rollover, not more than 115cm, or + 21cm/2, i.e. radius of 550Hz horns=106.5cm
| Romy the Cat wrote:|
The answer is that all logic that we use is purely intellectual self-gratification. Sure we can measure the resonances in mouth but we have no mechanism to evaluate how different degree of resonances and different randomness of mass distribution in reality affect Sound.
In addition, in case of 50Hz horn there are zillion OTHER reasons why the horn sound in one way or another. How to subtract from those zillion reasons the contribution of random masses? I do not know the answer.
The problem is complicated further by the fact that the people who built many horn and try different construction methods also not able to say truths because of various reasons. It is just too complex, too expensive to investigate and in most cases not necessary or needed to wide public, therefore not worthy to invest for horn builders.
So, my attitude is following. I build my 42Hz horn and I exposed all my techniques I used. In the very end I do like how it sound but I would not name a single specific technique that I feel is responsible for the sound that I like. Furthermore, if my horn was used in playback differently then I might be less (or more) satisfied with how it sound. So, looking back to my midbass horn project I might call myself an experienced guy (it took 10 year of thinking about that horn) but do I feel that my experience give me option to say definitely about this or that construction techniques as an assurance of proper midbass sound. I do not feel this way and therefore I would argue any certainty in large horn construction.
I have seen a lot in audio. I have seen amazingly sounding bass enclosures made with over-damped and under-damped boxes. I have seen (even owned) insanely expensive enclosure what the microscopic resonances were measured by laser readers and the enclosures still sounded like shit. I have seen the enclosures made from thin horrible wood with firmness of cardboard box and some of them had phenomenally interesting bass. I feel that there are no rules and there are no winning patters. It is very complex to foresee anything in bass resonance and I feel that empirical practicing, observing own very specific results, proper interpretation of results and then to react upon those results is the only way to accomplish Sound of own envision. I am not even mentioning that what a person envisions is a reflection of his various non-audio qualifications, but it is a while deferent subject….
I faced exactly the same dilemna with regard to the construction techniques that would be used in the making of the UB115s. Counter-intuitively I opted to err on the side of doing too little rather than too much. Rather that interweaving different thicknesses of different materials, I decided to educate myself. I am humble enough to know that I may not be able to fault these horns using these specifications and I will be quite happy to live with these as they are. Aesthetically, I actually prefer the look of the mouth as I have designed them. They appear more elegant and refined, somewhat more ethereal for such bulky structures and they avoid the blockiness that I do not find appealing in other tractrix horns that I have seen. I agree with Romy that the beginning of the horns is not right but for very different reasons and my solution will be different, to suit my aesthetic sensibilities.
What lesson is there in my endeavour for those who are about to embark on the journey of building or commissioning someone to build their upper bass horns (from emails I receive I know quite a few people are considering taking the plunge when means, family or real estate allow)? In my opinion, the first thing is that you must get started! The more you think about it, the more you consider the theory and pros and cons of different ideas, the more you will get nowhere as those that I consider the practitioners in the field have such different opinions of what works best. And please please please keep your horns under 1m in diameter! If you have a family and your means are limited - as mine are- forget about horns and just book yourselves a nice holiday somehere nice as these horns are inevitably expensive if you are having them made. There is more gratification in knowing that my littles ones have had a wonderful break in such an amazingly beautiful place as I am now, than having my horn loaded system in operation.
Lastly but not least, Romy's site is a great place for insights in a system that is so far ahead that we might only want to emulate what he has achieved rather than discover our own personal solutions, but do not expect it to be helpful to beginners (which is how I class myself) in a practical manner. Romy's advice above is to approach a master of the art such as Jeffrey Jackson or John Hasquin. My advice is the precise opposite. This is too big a venture to hand over completely to someone who will make all the decisions and balancing of sometimes conflicting priorities for you. Try to do it yourself if you can or get someone to build it who will listen to your needs and your vision and then give it shape.
One very last thing if I may. I am not a hidden marketing agent for Russ Collinson, and I do not get a discount for singing his praise, although I fear Romy might think so, but he has been so exceptionally capable that one would not think that these were the first horns that he has ever built. But it was an amazing journey from the very beginning, from the time when he declined taking on this project, to the discussions that we had about the construction techniques, and it never failed to amaze me how he was open to new ideas, was prepared to look at what other people had done, and select what worked best in his mind, and develop and modify his own tooling where necessary. If you are in the UK or anywhere he can ship to, I would without hesitation say that you should give him some serious consideration.