Files are uploading now, so give it a few minutes and I'll edit this post with a link.
Edit-
http://dl.dropbox.com/u/2033066/lphpboxtest.zip
The final product I built is a high pass and low pass filter in a box. I ended up going with 3rd order, 18db per octave filters. This simply requires 3 caps, 3 inductors, 2 jacks, a box, and a few wires.
Here is how I tested it.
Chain-
Jeff's Rose of Sharyn DIs-> Redeye-> OD820-> Herbert-> Filter Box(only when noted on the files)->Bogner Uberkab-> V30 -> SM57-> SCA A12-> Firestudio
OD820 was set as clean boost only as I always do, with tone control at the middle position.
Herbert was on channel 2. All tone controls were set at full. Gain was at 9 O'clock. Mid Cut was off. Depth and presence were set at max to fully show what the box could handle. Master volume was half way, very loud with this amp. As it ends up, these settings, although weird, sound great on my Herbert with or without my filter box.
Mic was set back about 7 inches from the cone, at the dust cap/cone meeting point. I had it back this far because I wanted to catch more frequency coming off the speaker. Once again, this actually sounded good.
A12 was set to low setting so the opamp wouldn't color the tone too much.
No post processing, just had to play with levels to get it louder.
Files-
Files are labeled so you know what they are. I did 4 total. 2 with backing track(1 with my filter, 1 without) so you get a full mix idea, and 2 without backing track(1 with my filter, and 1 without).
I think they are like the first minute and a half of the song.
Results-
You be the judge of that. In my opinion, it does exactly what it should do with out having to LP/HP after recording. The sweetest thing about this is that it sounds great in the room. You would have to hear it to fully understand, but I can say this- my cab is very bass heavy/boomy in the room normally. I usually have to cut the bass back a bit and I go very easy on the depth control on the amp. With the box in the chain, the low end tightens up nicely, and I can 'do more' with the tone controls and depth/presence. The piercing high end I usually get with the presence control cranked is gone with the box thrown in. I'd have to say that this filter lets you play around with the amp settings a bit more.
Graphs-
For this test I ran a sweep tone through the amp on the same settings as before. Sweep goes from 20hz-20000hz. I used my room measurement mic, placed center mast on the cab, about 4 feet back, to show the full effect of what the box does to the cab. I then recorded the graphs with and without the filter box and overlayed them using the Blue Cat Analyzer. The darker image is the filter box, the lighter image is without the box. (Sorry, its hard to see whats going on, but that's the best I'm going to get it right now).
Ah, now we see what is happening to the signal... Doesn't even really look like what a LP/HP should do! But it sounds great!
Between ~150-700hz a lot is going on. Also a slight amount of reduction at ~100hz.
I was surprised to see very little done with the high end filter, since audibly in the room and on the clips, there is a difference. Its hard to see in my pic, but when zoomed in there is a reduction in high end going on from 9khz through 22khz. I guess this proves that a little goes a long way. And obviously Jeff was right, you can see the speakers cut off greatly at 5khz.
Final verdict? I'm going to use this thing from now on. It's not a do all/end all product, but I like it. I may mess around with the low pass filter, and see if dropping the cut point down to 8khz does any better.
Discuss.
