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Old 29th September 2007, 02:44 PM   #1
pjanda1 is offline pjanda1  United States
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Default Radio Shack 40-1285D 6" FR

I found a pair of these NIB in my travels yesterday. I can't find any reference to them after searching various places. They look nice: smooth black cone and whizzer, black cloth half-role cloth surround a 9.8 oz magnet, big spider, tons of Xmech. I'll post pics when I get home if anyone is interested. In the meantime, does anybody have any idea what the specs are? I haven't got a way to measure them, and the look deserving of a nice home.

pj
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Old 29th September 2007, 07:24 PM   #2
GM is online now GM  United States
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Greets!

These are my second best fave later RS driver with the 40-1297 being numero uno. I designed/built a prototype ML-TQWT that within the limits of its relatively high Fs, whizzer cone, etc., impressed the @#$% out of me with just the $0.98 tweak and a 3/4" thick polyfil sheet filter/grill. Didn't even need any BSC with the 'pancake' design (wide baffle) I used. WRT HF, my hearing by then was rolled off enough that a super tweeter would have been nice, but was plenty good enough for mono HT/TV. Bet it will pound pretty good in a standard height BIB.

RS specs are typically all over the map depending on build date, so these specs may only be a situation of better than nothing:

Fs = 64Hz
Qms = 4.00
Qes = 0.62
Qts = 0.5368
BL = 5.53 N/A
Vas = 0.88 ft^3
Re = 6.96 ohms
Le = 0.8 mH
Sens = 92.3 dB/W/m
Xmax = 1mm assumed
dia = 5.21"
Sd = 21.376"^2
Pd = 14W

GM
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Old 29th September 2007, 10:21 PM   #3
pjanda1 is offline pjanda1  United States
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Were these in production for long? I assume they were introduced not long before RS stopped selling such things. Do they compare to the earlier models? They're a little more handsome, IMHO.

I was thinking of a BIB also, but I'm also curious to try something new. I was wondering about a Metronome. GM: do you still have the specs for the ML-TQWT you built?

pj
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Old 29th September 2007, 11:50 PM   #4
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Don't know, for the most part I was away from speaker building between '89 and '96 and didn't get involved with RS drivers again until 2k when I first became aware of these. The 'D' implies a long run though.

They don't compare particularly well to the '60s - '70s AlNiCo units I mostly used if that's what you mean.

Did some more digging around and there's Thailand and Taiwan made rev 'D' units with the former rolled off above 10 kHz enough that a super tweeter is mandatory while the latter is good to 20 kHz, which is what mine are.

I built the 29" long version, but don't recall how long the final straight taper was, though probably 2" since it was floor coupled. Regardless, I designed it to either sit on the floor so that the mouth was floor coupled and tilted back if run full range or with a gapped baseplate if stand mounted and XO'd to a sub system since it was planned for an inexpensive HT system that became stillborn when RS decided to get out of DIY speaker building and the ~ equivalent car audio drivers were way too expensive.

GM
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Old 1st October 2007, 05:51 PM   #5
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Mine are the Thai versions. I was comparing their whizzers to my Hemps, and thinking that as they looked lighter, smaller, and awfully stiff (with the curve) that they should extend plenty high. But, as always, you were right. I played 10K, 12K and 15K test tones through them. 10K was strong, 12K slightly less so, and 15K nonexistant. I have a pair of RS super tweeters that seemed destined for use with them.

If your specs are even ballpark (given that they were taken from drivers with a high variability and a different manufacture), they seem to need a large BIB. With your formula, I get a Vb of 8.147 cu ft. My ScottMoose dimensioned Hemp BIB's are 8.6ish. If it weren't for the considerably higher Fs of the 40-1285D's (my BIB's are L=150.5"), they'd probably work allright.

I just noticed that the boxes even say "Acoutic Suspension." Was there a time when people were looking for acoustic suspension fullrange drivers? Interesting.

pj
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Old 1st October 2007, 07:41 PM   #6
GM is online now GM  United States
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Don't know about worldwide, but there was a time in the USA that 'AS' drivers was what most folks wanted and AFAIK still do in high SQ apps. Anyway, it has a pretty stiff suspension, so if it was me I'd give them a tryout in the BIBs just to see.
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Old 2nd October 2007, 01:37 AM   #7
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I got to thinkin' about the Qts, and lookin' at a pair of Ikea boxes. The result is below. The backs are open, with the exception of little corners for stability. Bass is pretty strong to 80hz. They sound pretty nice. They are fresh out of the box, so I won't judge much. Compared the the Hemps, the midrange isn't is warm and they sound smaller with less distinct images. I hear some peaks, but there are fewer problems than I'd expect. I didn't think I'd much notice that they don't extend past 12K, but instruments with high overtones (piano, violin, cymbals) sound considerably less real than on the hemps. I guess that upper half octave or so (I think I can only hear to 16K) really does make a difference.

I think I'm going to take 'em down to the basement for some breakin' in.

pj
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Old 2nd October 2007, 01:39 AM   #8
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