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Hi all,
I've got equipment coming in the next day or so to start taking response measurements of my Edgarhorns. They are already full of sand so moving them outside is not really an option.
Can I move the mic into the midbass horn and negate enough of the room interactions? If not, do I just go with what I get for readings or is there a way to compensate for the room?
equipment
Behringer ECM8000 mic
Rolls MP13 preamp
trueRTA software
TIA,
Dan
Follow Ups:
Dan
In addition to the comments by Fred and John, you can seperate the room and speaker responses to a certain reasonable degree of accuracy. If the test signal used by the RTA is swept, then you can measure what the horn is doing with a close measurement with the test mic in the horn mouth. With a steady state signal like pink noise however, room resonances will begin to dominate. At any rate, compare the response of the horn with the test mic in the mouth (with ideally a test tone which sweeps over a 1/3 octave for instance, ala the Stereophile Test Disc) with the response you get at your listening position (the test signal could then be pink noise, steady state, which would tend to energize the room resonances). This should identify which artifacts are particular to the room, and which are specific to the horn. If you do the horn measurment first, don't get hung up on minor (a couple of dB) variations from flat. When you see what the room is adding, you should see that this is the least of your problems.
Good luck
Paul
I'm not real familiar with true rta, but usually with an RTA you play noise and it shows you the response. It will be influenced by the room depending on any windowing that is applied, but I would just assume it will be influenced by the room if you're measuring low frequencies. Btw, you can get a simple, free RTA program off the web. It's called jDFT, I think. You should be able to find it through google. I've used it to measure spectrums of various things where I couldn't run a dual channel setup - my lawn mower exhaust, a simple car stereo install, etc. Then you just need a cd with pink noise or something similar. I personally don't like RTA's much and use Speaker Workshop if I have a choice (or anything similar - dual channel measurement), but it is a bit more complicated to setup and run.
I'm usually in the same boat with horns - can't / don't want to move them outside. Besides, with the typical undersized midbass horn, the loading might change anyway depending on placement. I'll typically ignore room effects to some extent and just get an idea of the tonal balance in the room. Now if you have some funky case where the direct sound and the reverb are vastly different, this may not work for you, but it's never been too big a problem for me. It helps if you can smooth the response either in the program or mentally. Don't start trying to eq every little peak and dip.
I'd put the mic where you plan on putting your head for starters. Measurements in the horn will not necessarily translate to the response outside the horn, so I would not do that unless you are doing some other kind of measurement.
Another advantage of something like Speaker Workshop is that you could also measure impedance and then tweak your passive crossover design on the computer before building and experimenting, if that's what you're wanting to do. Just fyi.
-- perhaps one thing is that RTA won't tell much with regards to "quality" - you can lay mic on the floor for sub, maybe 1-2M on-axis for midbassSystem 100 midbass w. 250Hz cone-drive tractrix
System 100 midbass outdoors with two different type driver (btw - the low sine distortion on the graph was with K43 type - 2220H had higher H2) 2220's rise to peaking around 2K can be seen
Hi freddyi,
I suppose the first thing I'm looking for is to try to get a feeling for what the midbass is doing as the impedance begins to swing up.
Do you think the room interactions will make much of a difference?
dunno - probably to some degree - in a little room I cna't get graph without some suckout - whats your midbass's driver?
Yeah, I guess I'll just have to try it and see what it looks like. The driver is an EVM Pro-15B.
I suppose if push came to shove I could rig up a sled and rope slings like the piano movers. Then I'd just have to bribe my son into stopping by to lend a hand. ;)
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