Introduction
Arai 290 and 480 horns are Hyperbolic Constant Directivity 95° horn so this opening is coherent between 2.5m to 6m listening distance, further you will need a 60° horn. The coherence of a speaker in a personal room is when we are are close to a 50/50 or 60/40 ratio between direct field (what go out of the speaker directly to your hears) and the reverberant field (the direct that touch a wall and go to your hears). More information about this : http://hyperphysics.phy-astr.gsu.edu/hbase/Acoustic/reverb.html In a studio, usually very damped with a RT a lot lower than a personal listening room, the direct field is majoritarian as a pro studio doesn't have the same goal (mastering) than a listening room. As the horn use fins, it maintain an open directivity upper, fins are really important in this design with these opening coverage and allow a Constant Directivity pattern. Each fin create a horn cell by division, each horn cell must be identical, symmetrical and have the same point of origin. Yuichi made Arai horn without fins but mainly for mid-range application as he said, for full range it doesn't make sense, specially for the big A290. Due to her smallest size the A480 is less impacted, but still impacted, to fins removal. The throat adapter is round to square so there is no compression, no pinch are present at the throat. The consequence is that at 0°, in front of the horn, you will need EQ but once you have EQ the off-axis measurement haven't any noticeable accidents. The brain merge direct and reverberant field but know the difference due to timing, because reverberant arrive later, so even if you listen on-axis in a room, you need the better off-axis behavior possible for a room listening. Differences and behavior compared to TAD TH4001The TAD TH4001 is the closest cousin of the Arai 290. The TH4001 barely don't need EQ due to round to rectangle (it's a pinch so a compression) throat adapter but have an audible accident as a resultant. This accident will be off-axis and moving in upper frequencies according to the measurement angle, he will impact reverberant field, not in a very good way. So comparing to the A290 the power response of the TH4001 tightens in high frequencies, the result is that the Arai A290 sound more coherent (as the power response is more coherent) at upper frequency. In a room without acoustics treatment on side walls, in a pro studio environment it will be less (or even not) noticeable. These two horn look the same but by listening side by side in a room they have in fact a different behavior due to the compression on the TH4001. Here is the original design content based of the Arai 290 wrote by Yuichi Arai, I have added some observations in red:This is not a perfect design guide, but gives you some idea to generate the Horn contour. Originally I wanted to build a good Horn speaker. Unfortunately I could not find out good design guide which matches to my willing. So, I made may own calculation system long time ago. However, the Horn system exists still in the high end market today. Which means that there is still some DAY funs in this space. This is the reason why I summarize how to design the horn from my book which was published long time ago. Please refer the idea how to generate the horn design such as A-290 but not to look at details. I have no confidence about the consistency in detail numbers. |