I know what the problem is, but I don't know how to fix it. Should I tape a record or something on the grill in front of the speaker to prevent it pointing directly at me?
Eddie Van Halen used to tape housing insulation infront of his cabs in the beginning days of van halen in small club gigs. He said this would filter out a lot of the harsh high frequencies. I wouldnt ever do it on my cab, but you could give it a shot.
Framus Cobra
Marshall JCM 900
peavey 5150

Mesa 4x12
i m assuming its closed back, otherwise you wouldnt get that effect.

all i can say is stand NOT in front of the amp...if you cut the treble you risk making the sound mudy when you re anywhere else other than the front of the amp.
Quote by Horlicks

A well placed piece of gaffa tape does the same thing at a fraction of the cost...

and you can change the shape and size to find the best combination.
Quote by Dave_Mc
how do those marshall handles compare tonewise to, say, mesa handles?

Owns a Blackheart Little Giant...
The amp is open back. The problem is that when I put a piece of cardboard or something in front of it, it blocks out the lows and the mids as well.

I need something, because at gigs I like to face the amp towards the crowd, but they always hear this harsh, ice-pick sound.

The Weber Blocker sounds good, as well as the FlapJack. I'll try and make one.
Put a piece of tape, small, on the grill right over the cone.
I don't give a shit if you listen to me or not