Hi there, it seems that this is now down to a two way discussion, and nobody else wants to add their own tuppence worth. I had hoped that a few more people with more advanced knowledge than myself might givesome help. I know I'm fairly ignorant as far as theory goes, and a little basic knowledge will always lead the uninitiated into making hugely exagerated errors when dealing with the more advanced subjects. But I'm gradually stumbling along and there does seem to be some light at the end of the tunnel.
I have a solid background in engineering, and when considering using a new piece of equipment, a good look at the spec. sheet is the first step on from quantifying what is actually needed to do the job. When I read that something has a certain parameter, I get extremely frustrated when the equipment does not seem to match the given figures. Itappears to the beginner, that for most specifications with regard to horns, there is a certain laissez-faire regarding physical rules, and one has to take a trip into virtual reality to finally get to the point where the design figures have been originated from. I guess that at some points along the theory trail, the rules are open to a bit of interpretation, and that it depends on how the designer has interpretedand applied those rules. For a beginner revisiting an original design, and trying to make sense of the final figures, it's a bit like doing the times crossword for the first time. If you aren't familiar with the setters personal take on things, a lot of the clues make no sense at all. It is only after familiarisation with how they work that you finally get the true meaning. I see! said the blind man. Or at least I hope I do!. I suppose the clues were there all the time, but I was too busy looking inside the box (literally) to see the bigger picture (again a bit of irony!). The trip into virtual reality was also literally true, as well as apocalyptic.
So I guess it's apologies all round, and can someoneplease follow me through my reasoning so thatI may rest a bit easier. At least I could then offer up a better opinion as regards to some other topics.
So, I think what I am proposing is a general set of rules for everyone to apply to their own sims, so that when posting some comparisons, everyone is playing at the same level. Does this make sense?. Does everyone agree that there is a need for a set of ground rules?.
I will put forward my own version and ask for comments, suggestions, and ammendments where it is deemed necessary.
Basics.
To bring everything down to the same level, and to ignore theidiosynchratic nature of environment, all plots should be made in half space.Anything else is an artificially enhanced environment, and would be open to too many different interpretations. I'm forgetting free space,so if you are doing some high-flying, then apply as appropriate.
Use 1w/1 meter for sensitivity.This will give everybody an idea of how efficient it is.
Next would be a plot at the highest diphragm displacement that thexmax of the driverwill allow, or ifxmax is not exceeded, a plot at the RMS rating of the driver.
Horn parameters.
First, the compression chamber. Hornresp has a flatrepresentation of the diaphragm.
For most drivers this already poses a question. There is a volume of air in front of the diaphragm that is not accounted for. Also, there will normally be a baffle that has a cutout for the cone, if rear mounted, that also adds volume. If one is presented with a problem like the WSX and the rather complex compression chamber, there needs to be a general 'rule of thumb' that can be applied so that this may be represented as accurately as possible.
Sohow does Hornresp deal with themodelwhen you enter a smaller chamber area than the SD of the driver?.Would it be more accurate to assume that the chamber is all at the same area as the SD of the driver, sum up theenclosed volume of the whole chamber including the volume in front of the diaphragm and baffle, and then use the smallest area of the exit into the horn as the throat area?. In the case of the WSX, this might mis-represent the actual distance of the diaphragm from the throat of the horn, but should we concentrate on the compression/volume side of things, or do we ignore the reference to area of the chamber on axis to the horn?. Comments please. Bear inmindthathave been discussing low frequency bass, and should we apply some different rules for higher frequencies?. If so, whatdo you propose?.
A theoretical horn can be modelled easily enough. Producing a modelof an existing (folded) horn without the original design parameters is a completely different kettle of worms. Most of the time, if a manufacturers plot is available, use it. How do you know it is accurate? and what happens if you want to find out how it behaves with a different driver?. Well these are the questions that have prompted this section in the first place. If we can all agree to a set of rules for this, then we can all share and add to a database of designs that we can use for comparisons tonew designs, without any controversy. If anyone has a measured plot usingreasonably accurate measuring equipment that disagrees with published figures, then please get them posted. But also make sure that the measuring environment is correctly noted!. It can give others an idea of performance under certain conditions.
Plotting the horn segments.
Most horns are made up of flat sided plywood, and do not curve. The horn is built up of flat sided sections and so resemble morea series of conical segments, thanslightly curved exponential segments. What is a more accurate representation?.Is it acceptable to plot a series of conical segments as a single hypex or exponential horn, and if so, to what degree of accuracy do we have to work to?.Comments please gentlemen.
Throat to end of first section, and subsequent sections. S1-S2 etc.
I would normally work along the central axis of the horn, and if going round a fold , look for the narrowest radial restriction. After finding all the narrow points, I would then compare each in progression from throat to mouth. If a narrower restriction is foundfurther down the horn path than a preceeding one, therestriction further down will takepriority in deciding the end of the first section. Each subsequent section then has to be derived from the next narrowest restriction further down that takes priority over preceeding restrictions.
A lot of horns will provide more restrictions than we have available sections to enter.
This would suggest that an Hyperbolic curve is more appropriate to simulate this horn.
The actual length of the path of the horn around the folds. ?. If we were to assume a rotational transfer of the volume of air going around the fold, thenwe would have to assume that some of the air must travel a lot further and faster than the rest, all the way around the outside of fold, while some remains on the inside and slows down. Just measuring the outside length of a hornaround the folds etc. is not the correct method.A lot of people have a misconception about this, and I suppose at first glance this may be a natural assumption to make. The volumetric transfer is more linear,the airacts more like a liquid, albeita liquid that is compressable, hence propagation delay equal to the path length.
However, if youimagine a ball inside the horn at the start of the fold. The balls' diametercan expand to suit the radialwidth of the hornat any givenangle.If we take away any outside influences like gravity, friction etc, and then imagine that the ball can movealong without rotating,then have theball in contact with the inner, or the outer surface and slip it along all the way round. Every part of that ball will travel exactly the same distance.The centre of the ball willdescribe the path length of the horn. Simple. But, in the real world, surface friction, eddies,turbulance etc. will detract from the overall efficiency, and most horns will have voids where the outside surface is not a perfectly expandingcurve that matches the inner surface. It seems that for all intents and purposesthese are ignored, and provided the volumes of thevoids are not excessive, will not have much effect on the horn?.This would then require that theenclosed volume of the fold has a radial cross-sectional area, at any given angle, equal to (or slightly greater than) the projected linear expansion rate of thehorn flare, and does not pose any restrictions to this. Does anyone care to commentso far?. Would anyone like to comment on void volumes that would appear to be excessive in some horns, and would imply that some form of correction should be made?: and if so, how is the correction applied ?.Do these voids add some delay on the path, and should a correction to the length of the horn path be made in proportion to the volume ofthe void?.What is everyone's opinion?.
After deciding the path, as enclosed inside the box, let's consider the virtual reality bit.
Projecting outside the box. For an axially symmetrical hornthere would be no real need for forward projection, would there?. If hornresp is giventwice aslarge amouth area, does it automaticallyproject a curved forward wavefront proportional to the area?. If there is a projection to be added in the front of a flat faced assymetrical horn, like a bass bin, does it assume that the forward projection has already been included in the horn length?. If two assymetrical bass bins are put together, so that the horn is symmetrical about the central axis, doesHornresp then automatically add what some manufacturers would claim as their correct projected horn length?. I have made my own assumptions on these questions and I would be interested to find outwhat other people assume when preparing sims for evaluation.
We need to come to a concensus of opinion, and lay down a few rules for evaluation purposes, so that we can all be confident about other peoples' figures. New guys can get a comprehensive guideon how to prepare their presentations for evaluation on the forum. Those of you who are sitting there and saying this is all elementary and saying what the
This email address is being protected from spambots. You need JavaScript enabled to view it. is this all about- it should never be posted in the first place: all I have to say to you is, when was the last time you learnt anything new?. If the answer is a long time ago, then you can tell me now when the world is going to end.
Come on guys,this forum needs some good input from all of you to liftit above the current level. There are very few people contributingand willing to discuss fresh ideas. Even if you don't know much on the subject, any opinion is worthwhile.I think it is a comment on the effectiveness of this forum, that there have only been two contributions to the advanced section of the forum. Doesn't anyone want to discuss any ideas (however fanciful) they might have?.
I hope some more will come from this diatribe, even complete repudiation would be an improvement.
I will also put up some new models for a few horns that will supercede previous models posted that might have been (almost certainly, I hear you say)in error.
Apologies, I seem to have gone off on a rant.
Any input will be gratefully recieved.