Thanks for the follow up.
First of all an RCA connection is a one way connection. The interesting thing is that the Velodyne only corrects if the other subs are connected, so the reason it is kicked back to life is from vibration from the other subs. It sounds as if there is a loose connection or dry solder joint. I think the use of the high outputs from the other subs is akin to thumping the TV to bring back the picture.
Now I have had a closer look at your graph especially the Eq settings.
I notice that form 63 to 100 Hz there is a 6 db increase on your settings, I doubt that is the room.
I think this is due to your mains cutting off too soon. With those settings your sub is not 12 db down until 200 Hz, and not 24 db down until 400 Hz!
So you are using your sub for a good deal of the diffraction compensation of your mains, whether you realized it or not. I suspect that this may be happening more often than I thought and consuming the power, since subs by their nature are so inefficient.
That reinforces my view that Lucas Labs are misguided in advising speakers be set to small most often. I think any speaker with reasonably robust drivers and an F3 below 60 Hz should be set to large, and the sub just used to fill the roll off of the mains in particular. Your mains should be much better suited to reproduce the frequencies above 60 Hz than your sub.
I'm going to answer the question raised by "TheFactor" here, as it is on topic.
As most of you likely know my big system does not have a sub in the sense that most of you understand a sub.
These speakers contain two transmission lines, with the longer winding round the back of the smaller.
The smaller line with the MTM driver arrangement has a calculated and measured F3 of 44 Hz. The line is allowed to roll of acoustically there is no electrical cut off to the drivers, so it is analogous to a large setting of mains.
Since the baffle is narrow and swept back there is a step response.
The lower line has a calculated F3 of 27 Hz with second order roll off. The measured F3 because of room gain, I suspect, is 22 Hz
So the lower 10 inch drivers are fed from different amps. The upper driver has not only bass duty but also provides the diffraction compensation for the MTM drivers.
The lower driver is cut off second order above 80 Hz to prevent comb filtering issues.
The amps driving the lower drivers gets a lot less warm than the the amp that also has to provide the diffraction loss. In view of where the power distribution curve actually is, this should not be surprising.
The center channel is a line with a calculated F3 of 47 Hz, measured it is around 43 Hz. Diffraction compensation is active. The speaker plays full range and is allowed to cut off acoustically.
The surrounds are sealed units with an F3 calculated and measured at 53 Hz. Since they are sealed roll off is second order. They are allowed to roll off acoustically.
The rear speakers have a bass response that a lot of subs would envy.
They are again dual lines, biamped. The F3 is 35 Hz second order, so there is good output to 25 Hz. They of course are not rolled off. They really get to show off their stuff in some of the multichannel SACDs I have.
The question of sub setting on my other system, was explained in a recent thread, so I will copy it here: -
Those subs were made for a purpose. Being isobarik and coupled cavity, they are very inefficient.
I built them to splice to the speakers that are now my surrounds, that I used to use on location recording. They are sealed with an F3 of 53 Hz. Band pass subs have a second order roll off high and low pass acoustically.
Also in a band pass sub, the designer has precise control of Q. So I could extend the bass, without, making it at all boomy
The current speakers use the venerable KEF B 139s on a ported enclosure. I know these driver s very well after thirty plus years using them. I can really mask the fact the enclosures are ported, and they have an alignment that is first order stating at about 100 Hz, so -3db is 53 Hz, but they are still only 6 db down at 30 Hz, at they point they roll off at 24 db per octave.
So the subs have practically nothing to do. I have customized a Crown VFX 2 to splice the curves. So now the combined curves roll off at 12 db per octave with a 3 db point of 27 Hz.
So if you play the subs alone, you only occasionally hear them on music.
However on tone sweeps you can hear the difference markedly, and also on music that has low bass content. Even though the are highly inefficient, they are called on to produce so little sound the Quad 405 2 driving them barely gets warm.
I would not recommend these subs for a home theater situation.
The other thing is that coupled cavity designs have higher distortion and time delay issues than conventionally ported subs. In fact the distortion and time delay issues are so high with third and fourth order coupled cavity alignments, that I won't use them. Apparently Dr Omar Bose disagrees as he lives these higher order alignments for his bass modules.
So in summary, these subs were designed and built for a very specific purpose, and for general use I would expect people to be quite disappointed with them. However in the manor I use them, it guilds the lily nicely in that very nice sounding system in that space. That is the beauty of DIY.
It was a foul rainy cold afternoon on Saturday, and my wife and I listened to music all afternoon by the fire, ending our listening with two hours of Prairie Home Companion. A really warm fuzzy pleasant afternoon.
