德國全音篇之 葵花寶典 (三)

20 十二月

續葵花寶典 (二)。
There are other brand names. Fostex 8 inchers need their (backloaded)horns, too; same story, same disease. From an enthusiast’s point of view you’ll have to note they come with ceramic magnets.The good thing is they are available and cheaper than Lowther. But for direct radiating you can’t count on them. Supravox 8 inchers, working fine on small fiat baffles, don’t exist any longer. Siemens, producing 8 inch full rangers in the eighties, closed down their department of electroacoustics. The French Triangle T 17 FLV608(as used by Gordon Rankin, see SP 9), somewhere between 5 and 6inches,goes down to less than 85dB(!)below 1kHz [3].Nice, but not matching to our needs ,sorry!

Direct radiating can be tested easily, I strongly recommend to give each speaker a first run on a small flat baffle, any piece of plywood about 3O to 45 inches will do. Mount your speaker out of centre, don’t use any frequency correction, no notch filtering, no damping, nothing, just hear them. If the sound isn’t too bright and pleases you, you found the right one. I checked Supravox., they are ok, Lowthers not.

Old radio speakers worked their whole life under these conditions. The box you look at has an open backside and in matters of acoustics acts as a flat baffle. This principle causes unavoidable losses of bass power below 200Hz,This is one reason for the bass correcting knob you End on the frontside. (Other reasons are to fit them to the acoustic signature of the room and -last not least – to the taste of the user.) The speakers had to have high sensitivity all the way, especially between 100Hz to 1kHz, otherwise the flea power of SE tube radios would never have driven them to any sufficient sound. But those 3 to 5W worked and did the job amazingly well. So here they are, the speakers we’re searching for.

文中間中有些英文怪怪地,不過武林劍譜通常係咁。

當中提及的 test method,其實同speaker 的 Q 有關,Lowther  如此test,一定 冇低音,要Lowther 出低音又唔用妥妥妥協的 backloaded horn,可以在放大器上串電阻,使output mode  變成半voltage driven 半current driven。這是最簡單的方法,provided that 電阻的放大器power 輸出仍然足夠。旺記用此法好久矣。否則就要把放大器改成 current mode ,懂 diy 的也不是難事。有興趣者可往 http://sound.westhost.com/project56.htm 參考。

 

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