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Old 1st February 2012, 06:07 AM   #121
system7 is offline system7  United Kingdom
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You can tell I am warming to this theme! Here's a mighty pretty loudspeaker, the Gale GS401A, that made everybody's jaws drop when playing Led Zeppelin's awesome Black Dog at 70's HiFi shows...

Click the image to open in full size.

This baby had punch like an Acoustic Research unit and slam and presence like a PA speaker and detail like a Quad electrostatic, and I was left plain wondering what magic stuff was hiding behind those grilles that sounded so GOOD! I'm gonna tell you...

Firstly, the bad: it was a hideous 4 ohm load for amplifiers and had a reputation for frying them.

The good: two AR derived foamed 8" paper units wired in parallel as in PA applications, with a simple AR type inductor for an overall second order rolloff to take care of the bass up to 500Hz.

Next was a 4" foamed paper Peerless midrange in a simple sealed plastic tube that went up to 5KHz. The midrange was a particular strength, and considered better than the dull and peaky KEF B110 5" bextrene midrange used in BBC type monitors. Secret sauce? Probably the resistive padding used on the drive unit and after the second order midrange filters. Early models had 4X 10R wirewound padding the midrange and flattening impedance.

From 5KHz, re-enter the excellent mylar domed Celestion HF2000 unit on a third order crossover. Often considered better than the KEF T27. Third order protects the tweeter from LF well, and acoustically matches a second order from the midrange. A lot to like there, and some ideas that found there way into the very fine and lively Wharfedale E70. You can read its history here.
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File Type: jpg Gale_GS401_drivers.JPG (27.8 KB, 482 views)
File Type: jpg Gale_GS401a_crossover.jpg (621.5 KB, 483 views)
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Old 1st February 2012, 08:06 AM   #122
AllenB is offline AllenB  Australia
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You know, when I first heard a pair of those Gales I was also bustling to get the grilles off for a butcher's. They weren't perfect but as you say, they had magic.
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Old 4th February 2012, 09:49 AM   #123
system7 is offline system7  United Kingdom
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The 1970's BBC LS3/5A has legendary status in small monitors. This one was designed to work in small BBC broadcast vans. Astonishingly real reproduction of voices is its strength. Surprising bass for a small box too. Naturally efficiency is not its strength, which applies to all small boxes.

Click the image to open in full size.

The old 5" KEF B110 8 ohm bass/mid and T27 tweeter are not that exciting by modern standards IMO, but commendably neutral when equalised carefully. The BBC did a lovely job of equalising in the crossover, and building a very neutral cabinet out of 12mm light birchwood ply with carefully considered damping.

The small drivers, crossing over at 3KHz (think wavelength around 5") give good dispersion, baffle step correction is applied via L1/R1 to rolloff the frequency response above 500Hz which accounts for the impressive bass, near 6dB applied here, and a little LCR trap around 1 kHz to tame a peak in the B110 output. The T27 gets little special treatment beyond a third order crossover and a Zobel network (R4/C6) to level impedance. The autotransformer doesn't do anything special beyond giving variable attenuation and can be treated as a simple inductor, in fact later versions used an inductor and resistors. I expect the overall response follows the usual BBC pattern of declining slightly (ca. -2dB) with increasing frequency, which is very unfatigueing to listen to.

Overall, very nice. I heard the Chartwell LS3/5A version of these, and found it hard to believe how so small a box could make such a big and clear sound!
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File Type: jpg BBC_LS3_5A.JPG (27.2 KB, 424 views)
File Type: jpg BBC_LS3_5A_XO.JPG (45.0 KB, 161 views)

Last edited by system7; 4th February 2012 at 10:05 AM. Reason: Clarified a couple of things.
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Old 6th March 2012, 02:48 AM   #124
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One world reknown tube amp designer uses the Kef B110 in a t-line with the Hiquphon OW1 for testing her designs.

Thought I better post the link before another controversy gets started.

transmission line speakers at KE Engineering - YouTube
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Old 6th March 2012, 11:33 AM   #125
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Quote:
Originally Posted by system7 View Post
You can tell I am warming to this theme! Here's a mighty pretty loudspeaker, the Gale GS401A, that made everybody's jaws drop when playing Led Zeppelin's awesome Black Dog at 70's HiFi shows...

Firstly, the bad: it was a hideous 4 ohm load for amplifiers and had a reputation for frying them.
Is that the real crossover? No wonder amplifiers fried. 7uf directly across the amplifier terminals!

They did make a cool looking turntable, though.

David S.

(Appears to be a drawing error.)

Last edited by speaker dave; 6th March 2012 at 11:37 AM.
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Old 6th March 2012, 01:58 PM   #126
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A friend of mine had the boring version with the standard cabinet, nicely made but never could understand why when he could have had *chrome*. He kept blowing the output stages on his Amcron power amps with them :-)

That turntable was beautiful, cost a fortune too I seem to remember, wonder if anyone has one...

All the best
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Old 2nd April 2012, 11:05 AM   #127
system7 is offline system7  United Kingdom
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Time we looked at a transmission line as popularised by IMF in its huge 1/4 wave monitors, which has the optimal resistive bass damping according to its adherents...

This is the 1970's B&W DM2A, which is the (then) fashionable 8" bextrene bass, Celestion HF1300 tweeter and Coles 4001 supertweeter in a 1/8 wavelength line. In fact the HF1300 had its origins as a horn compression driver. 3rd. order butterworth filtering was also the BBC standard in those days. Nice impedance at the price of a slight SPL bump at crossover.

Click the image to open in full size.

Much to like there. The offset drivers (this is the RHS cabinet) are designed to reduce diffraction problems, and the inverted tweeters should be more time-delay coherent. I had a listen to these, and can't fault them. The bass excursion was quite impressive.

Much the same drivers were used in the reflex-loaded Spendor BC1, which was a legend for lack of colouration:

Click the image to open in full size.

Spendor BC1
Attached Images
File Type: jpg B&W_DM2A_diagram.JPG (78.8 KB, 72 views)
File Type: jpg B&W_DM2A_loudspeaker.JPG (24.8 KB, 66 views)
File Type: jpg Spendor_BC1_Troels_Gravesen.JPG (33.5 KB, 35 views)
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Old 2nd April 2012, 05:42 PM   #128
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Some of those older t-lines had smaller cabinet volume relative to driver Sd. My Fried t-lines for a 10" have 4.75 cu.ft. line volume in approximately a 10.5' line length. The anti resonant frequecnies exiting line terminus give the illusion of a much larger cone radiating area to the listener.
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File Type: jpg speakers 006.jpg (656.9 KB, 72 views)
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Old 2nd April 2012, 06:12 PM   #129
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Ah, now you're talking! The B&W DM2/2a's are my all time favourite speaker. I've got and use 2 pairs on 2 systems and after all the speakers I've had over the years these are the ones I always return to, so much so I've given up :-)
Similar to the Spendor BC1's in many ways (not really surprising given almost the same driver line up and complex crossover) they have *much* deeper tighter bass.
I know a lot of people say they are 70's style boomy but I think they'll find that's entirely to room placement due to that eighth wave loading (I know there is argument if there's even such a thing but that's what B&W called it and it's fine by me, it's only a name!)
If you have them the usual 12-18" from the wall they will indeed boom, they should either be a *long* way away (more then 3') or ideally and counter intuitively a lot closer (less then 10") this brings down the upper bass and makes them tight, firm & able to reproduce anything.. the stands should also be a lot lower then you'd think (again less then 10")
My living room pair in a room 15'X24' with the speakers firing lengthwise down the room are about 4" from the rear wall and on home made 9" stands, in my much smaller 10'x12' study about 3" away but on 18" stands, those are used nearfield :-) Driven by a stock Quad 606mk1 and a rebuilt but unmodded Quad 303 respectively.
Of course there's way better out there but I've not found any that give me as much actual all round musical pleasure..
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Old 3rd April 2012, 03:14 AM   #130
Mr. dB is offline Mr. dB  United States
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Quote:
Originally Posted by system7 View Post
In fact the HF1300 had its origins as a horn compression driver.
I thought the HF1300 had its origin as the "Presence Unit" tweeter for the GEC metal cone speaker?
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