chris1973 wrote:
tomp wrote:
chris1973 wrote:
So, I'm not sure about what the engineers say about this:
My information defines fc as the box resonance, and f3 as the low end rolloff.
From this I would assume that if fc is above f3, it is a competing signal with the bandwidth of information the driver is supposed to be faithfully reproducing in a flat manner, hence detrimental to the performance of the system.
However, if fc is belowb f3, the resonance is producing gain in a place where you are losing gain from the natural rolloff of the system, and therefore might be beneficial in extending the low end response of the system altogether.
Chris
CHris:
What is Fc? I have never seen that in a list of TS parameters. Thanks.
Fc is box resonance as defined by Vance Dickason in the LDC. it's Qtc x fs over Qts
Thanks Chris. Hope your Thanksgiving went well. I'm still trying to digest all the goodies we had.
The term Fc is interesting. I'm still away for the holiday so I don't have access to my SDC but looking it up on the web I see several definitions for Fc, Fb, and even an Fcb. We could combine those with Fs and come up with Fcbs. That way we could watch it all on TV.
I'm including an interesting chart of terms I found. There is another parameter that may trump all the others that I saw on that chart, SAF. Seriously, I try to separate the various factors out so that I can make the unavoidable compromises that are necessary. Mixing resonant frequency and Q might tell you what the output is at any given frequency but by separating them you can tell what the "qualitative" effect of those two parameters are. For example, if you have a small box with a resulting higher Q and higher Fb (or Fc if you chose that semantic) although the bass will not go as low, it may seem to have more bass because of the bump. That is a common ploy used in small montors to create an image of more bass. Is it real low bass? No, but it might be satisfying. If you have an idea of what all the individual parameters are and how they are affected by box size you can make better decisions.
Now to really get folks pissed off at me. In my not so humble opinion, with the drivers that are available today you are really putting yourself at a disadvantage by relying totally on passive box alignments. Even if you want to stay with passive crossovers you can still smooth out the low bass respose and possible extend it if you have sufficient linear volume displacment in the driver and also sufficient amplifier power. I'm including an example of that process in my main system. With EQ, at my listening position which is 11 feet from the subs, the response is flat to 10 Hz. Since the 4 DVC 15 drivers have so much linear volume displacement, the distortion barely exceeds 5% at the higest point. This measurement was taken with only half of the subs working for a comparison with the single 18" Ultimax kit I was testing for the magazine. In reality it represents a measured 106 dB at that level.
The best part of this discussion is that we seem to have gotten the creative juices flowing and that is always a good thing. Now back to digesting food rather than audio information.