audio-talk

Yes. That's a very coarse scale there !
But good work, Ant.

manipulating the graphs to see what the bottom end is doing, with the filtering turned off



can clearly see where it hits resonance at about 40hz or so with hump in the response and the hole on the response at around 260hz. I knew that hole was there, abit higher up than I expected, and the dip at about 850 hz which I can't say I have really noticed. not sure why that graph doesn't fit the page properly either

overlay of the left and right speakers with a 1/12 filter, looks like I need a balance control!

Saw some eminence beta 15a drivers the other day.
Wonder what they'd be like grafted into the cabs.

Twin 15" drivers per cab is quite appealing

You'll probably find the peaking in the midbass increase somewhat because it's now sharing the available volume with another driver that has its own Vas (volume compliance), so the effective system Qtc will increase. That isn't to say 'it won't work' / 'sound good' -it might. One of those imponderables that tends to be difficult to assess in advance since the drivers are dissimilar.

If you want a rough & ready way of assessing what the alignment may be like, you can fake up a 'compound' set of T/S values since the data is available for both units.

Compound spec.:
cSd = Sd of both drivers added together
cVas = Vas of both drivers added together
cRe = Parallel resistance value of the two drivers Re values (use Re, not the nominal which is meaningless)
cFs = Mean of the two Fs values
cQes = Mean of the two Qe values
cQms = Mean of the two Qm values
cQts = (Qes * Qms)/(Qes+Qms) using the mean values for Qe and Qm taken above

That's sufficient to use with any simple box modeller; just enter in whatever your box volume is & you'll get an approximate idea of what will go on in the bass end under anechoic conditions. Rough and ready only, as noted, but gives some general hints.

Done a little bit of fiddling with these today.
Read something that scott wrote in the thread for the 12" ones about the vent stuffing and part of it clicked into place with something that was bothering me.
There is a peak at resonance and a corresponding dip above that which was annoying me, and which was a little confusing as the vent 'should' flatten the impedance peak and resonant peak somewhat and it wasnt doing much. You can see it in the traces clearly.
Scott wrote that if the vent damping is too restrictive that it can appear practically impermeable and negate the point of the vent.
The vent damping was 2 parts, a thick layer of fairly dense wool felt and a thin layer of heavily compressed wool felt so ive taken the thin layer out. Its opened them out quite considerably and the peak appears so far to be less noticable. Still there, but not as intrusive. The dip above the peak seems to the main beneficiary because it seems to have mostly gone.
Ill have to get the laptop, mic and other gubbins out to see what it looks like. There also seems to be better decay on bass drums, more texture if you will.
I think i can hear the box abit more, some panel resonance that was probably in the region of the dip before.
Imaging seems a bit better, probably because there is more vent output and the vent is on the top.
I think the vents could do with being a little more restricted, but i havent got anything suitable to try it.
At least the vents are easily accessible

Did abit more fiddling with these over the last few days.
There was something not quite right which was getting on my nerves and i was abit lost as to what it was. So i went back to how they were a couple of months ago by putting the monster xp speaker cable back in after cutting out the chunk of cable that had damaged insulation. Shortened one cable by nearly 2 feet but it just about reaches, and put the vent stuffing back how it was.

Listened to it and it was back where it had been, so i then took the very compressed wool felt back out, listened again, and put in a sheet of dacron wadding about 10 mil thick under the uncompressed wool felt, then added a piece of cloth between the wool felt and the top metal mesh that keeps it in.
Much better balance. So the highly compressed stuff was too restrictive, the straight uncompressed not restrictive enough, and the additional dacron layer with the loose weave cloth seems to be just about right.

There seems to be a definite sweet spot, getting the correct amount of vent restriction seems to be more important than the vent size. I think what its doing is providing just enough damping at the driver resonance to keep the driver just about under control, like tweaking the rebound on a shock to reduce the tendency to bounce again and make the car/bike settle in a controlled way. If that makes any sense

Spoke to fane about getting another pair of the 15-300tc drivers and they have discontinued them.....
Bugger.
According to the chap at fane there simply wasnt enough demand to have them made so it made sense to drop them. The 12 on the other hand has plenty of demand.
Neither uk distributor has them either so unless i can find some second hand the second pair i had been asked to look at building isnt happening.
Balls