meekster said:
I have a gut feeling that the 40 Hz - 18 kHz specs are -10 dB points. If someone has the opportunity to do response measurements, please post the test conditions and methodology along with the results.
I was thinking of trying to do some rough measurements when Scooper and I finally do our long-delayed cab mini-shootout. We'd be comparing the Schroeder 1210, the Acme Low B2, and the EA CXL 112.
If transportation factors allow, I will try to also bring my old Eden D210-XLT. We may be doing it in a rented rehearsal space so there may be another cab or two on hand.
Given that I don't have anything much in the way of proper test equipment, I was thinking of doing what I can with what I have. While there are a lot of problematic factors, this should give us a level playing field with the various cabs and at least quantify some of the differences between them.
EQUIPMENT AVAILABLE
* Sennheiser 421 dynamic mic (best mic i have I'm afraid... I also have a Shure SM-57 and an MXL V-57 which is a super-cheap large-diaphragm condensor)
* mackie 1202 mixer (for mic preamp)
* iRiver HP120 recorder/player (can record 16/44.1/stereo WAV files, uncompressed)
* Panasonic portable CD player
* my home computer
PROPOSED METHODOLOGY
======================
PREPARATION
* burn a CD containing a swept sine wave. I can generate this easily enough. Probably just sweep from 20 Hz to 20 KHz, but with what duration?
SETUP
* pick a spot for cab placement that seems to sound pretty good in the room.
* pick a spot for mic placement maybe 2-3 feet in front of the cab. This is tricky... we want it close enough to minimize room coloration and ambient noise, but far enough to minimize mic proximity effect and allow the cab's sound to "develop". Probably just pick something that subjectively sounds good, then
* connect CD player to power amp and connect to the cab. Disable all EQ on the CD player. Adjust power amp and CD player volume to get a decent level in the room. (start with the loudest cab.)
* adjust preamp and recorder levels.
RECORDING:
for each cabinet, do the following:
* place cab in exactly the same spot, maybe up off the floor
* plug in cab to the power amp
* set cab tweeter control (if any) to "neutral" position
* leave the mic in the same spot, adjust ONLY the height so it is on-axis for the center of the cab front.
* do NOT adjust any levels! We want a good relative comparison of the cabs. Note that this poses an apparent disadvantage for 8-ohm cabs vs. 4-ohm cabs, but without better test equipment I don't see any other way we can be remotely fair.
* start recording
* verbally announce which cab we're recording
* play back the sweep on the CD player
* stop recording
ANALYSIS
* load the WAV files from the iRiver into my computer
* from each wave file, generate one or more images showing frequency vs. amplitude and anything else that seems interesting.
* Harmonic distortion analysis? Not sure what I could use for this, or if it will tell us anything meaningful in these conditions.
* Post the resulting images on TalkBass.
* Hide
There are a lot of less-than-ideal factors in the above:
- the mic is not really flat
- the room will likely be very colored
Taken together, this means we won't get "real" frequency response plots,
just relative comparisons between the cabs.
Other issues:
- we may have real problems with ambient noise
- the Mackie doesn't have the best preamps
- the iRiver doesn't have the world's best converters (it has an optical input but I don't have any other converters to plug into it).
... although I expect the latter two factors to be relatively insignificant given all the above.
Suggestions on improving the plan would be welcome. Suggestions involving purchase of new equipment will be ignored
