My turn...A7 restore...

[aditya]

Its really nice to see your posts again GM. I had started to miss them.....thanks.

[aditya]

.....Technically I haven't really attempted to crank them since I lowered the crossover point so....
But I will say this. they are very transparent sounding with it at 1000. almost Martin Logany.

Sorry for Hijacking your thread AA.

With the present xover configuration (with the 1.5mH for LF & 10 mfd in the HF rail), it is in reality crossing over at around 1280 to 1340 Hz, not 1000 Hz.

Sorry AA.....pls don't mind

[gearfreak]

Ok, weather's cold and I've got some 1.5" MDF (or HDF?) that I've been playing with.

GM, can you clarify something for me?

... I got down to 35hz or so with 1" full width.
<snip>
Next I am moving onto sealing it, and using ~3" length (to be adjustable during testing) of 3" dia PVC.
The impedance graph suggests to me that this is the next logical step (for me).
(i.e. the lower freq impedance bump is larger than the higher hump... )

Hmm ~28"^2 vent area x 5/8", so you need to start with a 6" dia. pipe..........

...by this, are we attempting to match the area alone, or also the volume represented?

Area alone:

Slot:
~28" x 1" = 28"^2

Round: (6" dia. pvc)
3 * 3 * 3.14 = 28.26"^2


So yes, agreed if matching the area.

But maybe we're also/instead talking about volume... as what I am seeing is that I am getting similar results (down to low 30's) with 2 x 3" ports.

Vol:

Slot: (5/8" = .625")
~28" * 1" * .625" = 17.5"^3

Round (2 ports): (3" dia. pvc)
(((1.5 * 1.5 * 3.14) * 1.5")) * 2 ports = ~21.2"^3

Round (3 ports): (3" dia. pvc)
(((1.5 * 1.5 * 3.14) * 1.5")) * 3 ports = ~31.8"^3


The 3 port option was similar, but not quite as good as the 2 port option. I will have to post the impedance sweeps.



To that end, I had a concept earlier of how to read the impedance sweep, (first peak larger = ___________ , second peak larger = ____________ ), but I've now forgotten and can't relocate the source info.

Anyone have a description of what to expect in a BR in this sense? e.g. (first peak larger = need more port length)
My assumed goal is to get the two impedance peaks to arrive at a like level.

[Alien_Shore]

To that end, I had a concept earlier of how to read the impedance sweep, (first peak larger = ___________ , second peak larger = ____________ ), but I've now forgotten and can't relocate the source info.

Anyone have a description of what to expect in a BR in this sense? e.g. (first peak larger = need more port length)
My assumed goal is to get the two impedance peaks to arrive at a like level.

As GM informed me, if the target tuning is Fs, then the old saying is true: "first hump bigger = port too large, second hump bigger = port too small". But apparently if you aren't tuning for Fs, then that doesn't hold true and you'll need a consultation with the GM guru.

[cradeldorf]

Also should the port never exceed the piston Dia? which is 122 sq in.

[gearfreak]

As GM informed me

Thanks! Ahh. So perhaps that's how I ended up thinking I needed a 3", but longer, single port.

[voice of the theater]

Great to hear that you seem to be in the "home stretch" with your restoration. Please post some pics when you're done and let us know what drivers you end up using/how they sound/etc......

[gearfreak]

Me? Hah. no restoration. Just continuous tinkering. :-)

[analog addict]

Sorry for Hijacking your thread AA.

No worries. I've been trying to talk Dennis Had into taking these on to play with the crossovers. Dennis can make a pile of junk drivers sound wonderful, and it's all in the crossover. I can only wonder what he could do with high quality drivers.....

[cradeldorf]

Me? Hah. no restoration. Just continuous tinkering. :-)

I know the feeling, I just can't seem to ever be happy with the sound. :/