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WE had talked about the naturalness of the Advents and many of their contemporaries, versus the brightness of the newer,flatter response speakers. At that time, I commented that after a 24 days of live music on a trip, I came home and found my modified Polk RTi28's to be too bright and went back to my Double Advents.I'm never one to leave well enough alone, so I dragged the Polks back out and tried a trick from Henry Kloss. I used a double layer of grill fabric over the tweeter on the Polks to attenuate the highs. The second layer being cut from some old Advent beige fabric I had saved. The results were that the sharp edges and "brittleness" were removed from the sound, but none of the clarity; and the overall sound was much more natural and lifelike. More similar to the Double Advents, but a bit more open sounding. Female vocals and strings, in particular, lost the hard edge, and vocal sibilents were less noticeable and less "spitty". The system is active biamped with a pair of Advents used as the bass drivers below 160 Hz. I'll evaluate this set up for a week or two and see if it "sticks". I'll also evaluate non-polar electrolytic caps versus the Solens that are in the Polks right now.
But so far, it's a good argument for the slightly rolled off top end we had talked about a while back. I think Kloss and others knew what they were about, and their musical perceptions were correct.
Jerry
Follow Ups:
By adding the fabric, you padded the output of the tweeter by some X amount. Not the same as rolling off the response though it may also occur depending on the absorbtion rate of the material across the frequency response range. Back in the caveman days, it was not unheard of to do the opposite of removing the grills to bring up the tweeter, especially in AR, EPI, etc. The Advent was an exception and if I remember right 1 of the 1st speakers where the grill was an integral part of the actual speaker design.
Brian,If you look at the transmission characteristics of various fabrics, you'll see very little absorption at 1-3 kHz, and quite significant amounts at 10 kHz and above. Playing around with a graphic equalizer indicates that the extra fabric rolls off the high end starting at around 4-5 kHz and increasing smoothly to around -3 dB at 15 kHz. It's a fairly subtle effect and not noticeable on a lot of instruments.
As I indicated in my posting, I'll be trying other solutions; but the extra fabric layer does seem to work the way I want.
Like the Advent grill, the Polk grill works on diffraction effects by being a smooth transition from the tweeter mount to the beveled edges of the box. The Polk fabric is really transparent and is mainly cosmetic.
Jerry
Sometimes adding a zobel or a just a 10-30 ohm wire wound resistor across the tweeter terminals helps tame it. It has helped in a few of my own projects and does not effect the overall performance, only tame that shrill sound.charles
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