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Picked these up over on AK BarterTown. Arrived today and everything is in awesome, like new shape. Removed one of the rear covers from the 909-8A drivers and it has the Pascalite diaphragm in it, 6.3 ohm. Other driver looks like it has never been opened as well, measures 6.3 ohm as well. SN 433 and 437.
To use these for hifi, I assume remove loading cap and install felt like I did when I converted 808 to 802's?
How does the MR994A compare to the 811 and 511 horn?
Thanks
BillWojo
On paper, not a fair comparison to the 811 and a clear winner over the 511 due to no throat distortion in comparison, ditto much better WRT frequency and especially, polar [power] response. Still a diffraction horn though, so a [big] step down from a pure [large] waveguide.
GM
Thanks GM. What about converting the drivers over to hifi use? Am I on the right track?
Thanks
BillWojo
Caveat- I have limited experience with ferrite small format Altecs.
What I do have suggests very little, if any, reward in removing the loading caps.
I had exactly one discussion about this with Bill at GPA, who seemed to agree.
The ferrite is a whole different animal, and doesn't necessarily respond like the Alnico units.
Might be worth checking with Bill to make sure I walked away from the discussion with the proper understanding of his opinion.
"step down from a pure [large] waveguide."Quote:
Originally Posted by GM
What, specifically, are these? I'm guessing: 805, 1005, 311.
You're welcome!Quote:
Originally Posted by BillWojo
IME and apparently Jeff's plus some others I no longer have links to, especially WRT the Mantrays since they load a bit lower than the 511: Altec Compression Driver Rear Loading Caps
http://www.lansingheritage.org/image...-16a/page2.jpg
GM
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Same here..........Quote:
Originally Posted by Old Guy
Hmm, AFAIK, all same 'family' of drivers have 'close enough' Plane Wave Tube [PWT] measurements, so various horn loading's will be similar even though the two basic types of motors [AlNiCo Vs Ferrite] have distinctly different construction designs to make them 'close enough' in performance plus combined with Jeff's measurements I'm thinking you may have had a bit of a 'failure to communicate' with Bill, with the caveat of what is each individual's definition of 'high power'.
Note too Jeff's posting Altec's [and some others] switch to a 3/2 XO to maximize/optimize this HIFI specific variant due primarily to account for the fact that point source drivers have a ~90 deg input lag, hence most 2nd order XO apps need to have the HF wired in reverse phase Vs a compression driver's ~0 deg input lag and combined 180 deg lag between point sources, so this in itself makes it worthwhile for us relatively few folks that are more sensitive to phase shifts < ~ 1400 Hz. By ~2 kHz though, most folks can hear it fine, though usually don't quite know why they can't get their DIY speaker's mids/HF XO 'right', hence the rule-of-thumb suggestions to 'swap the HF leads' or '[re] check each stages' polarity', etc..
GM
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While all horns are technically waveguides [WG], 'pure' ones are conical, i.e. not compression loaded, so must acoustically be 1.0 WL long to load to Fp, ergo for a 1 kHz Fp = ~13543" [34400 cm]/1000 Hz = ~27"/34.4 cm] axial length.Quote:
Originally Posted by lokie
Unfortunately, when the compression driver has a small, round built-in HF WG, an incredibly accurate, acoustically long for the BW adapter is required to minimize reduced HF response, increased distortion, negating much of the WG's seemingly effortless large point source presentation.
GM
...when you decide you are hooked on CD and want to experiment further, I can probably dig up some HP1240's to lend you.
You'd need a 2" 4 bolt throat adapter.
The 909-series, as I recall, didn't come with loading caps on the diaphragms. Then again, they might have. Been a while....
The OEM version of the 909-8A has no rear cover and just a loading cap. It is labelled a 027534.
Now, we just need to know if that was by the engineers' design, or the marketing department's bottom line.Quote:
Originally Posted by magnarc