Stephens Trusonic 80fr

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Thanks GM
Can you clarify for me since I am new at this, would this cab design be an empty rectangle volume inside? Ive seen some MLTL designs but they have a dividing tapered part inside.
Like a simple bass reflex? 60" x 10" x 15"
What is "vent 33.1875"^2/6.5 dia." ?
If u can explain I would really appreciate it . I want to try and build it.

You're welcome!

Correct except ~155/10 = 15.5" or 155/15 = 10.33" ;)

Wider is better, but ideally the cab needs to be ~1.5x the driver's depth when there's a large driver offset like this one has.

A simple baffle thickness reflex vent that can be round, square, rectangular in shape, though best not to exceed a 9:1 ratio [ < ~1.92" x 17.281"] if rectangular since the vent's friction might cause some audible noise.

GM
 
regarding Karlson, if making a K12, I would keep a cutout for a 12" speaker and use an adapter ring or plate just in case sometime in the future a 10 or 12 might be employed.

Karlson 12 was tuned in the low 60 Hertz range - I would expect it to have more "hit" than the lower tuned Karlsonator 8 but less LF extension as a tradeoff. (- don't have a Karlsonator 8 for reference but do have Karlsonator12 and a 6 prototype)

1954 Karlson Twelve aka "Karlsonette" as the eight inch model had not yet appeared. It featured an adjustable lowpass gap via a movable wood bar on the back panel.
http://i.imgur.com/ZMGQve3.png

1956 Style Karlson Twelve (appeared as a DIY article in July 1958 Popular Mechanics magazine) and featured a 6-slit distributed port.
https://public.bn1301.livefilestore...39j/transductor-bo.jpg?psid=1&rdrts=165109659

1960's kit version of Karlson 12 brought back the full width rear lowpass shelf and sold apparently with a blank port board and instructions on porting for various drivers of its day. Its been seen with a 12 hole distributed port and loaded with Tannoy Red and EV SP12

Panel thickness is 3/4" - GregB was working from Karlson's sketch in the brochure
http://i.imgur.com/1pSgd4r.png

loaded with EV - -rear view - maybe these holes had less drag than the narrlow slits
http://i.imgur.com/ip5l9A0.jpg

GregB's Karlsonator 8 is tuned about a half octave lower than K12
https://lh3.googleusercontent.com/Z...TpCeXGMjqMobia902qaluMwa4q-OGg=w2048-h1609-no
 
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Electro Voice Topas mod

Hi

A pair of 80fr's 16 ohm unit was sitting on a shelf for a decade, when last week, i bought a pair of electro voice Topas loudspeakers. They are 2 way speaker with an additional 10'' passive membran. (made at the end of the 80's or beginning of the 90's in Switzerland, where EV had a small factory)

The 8'' mid-range unit of the Topas were not orignal and the sound was awful. So i swap the mid-range driver for an 80fr. As the orginal x-over in the topas was at about 1.4 kHz, meaning the tweeter-unit could go quite low, I chose a 5.9 uF paper-in-oil cap for first-order cross-over at around 5kHZ. The 80fr is directly coupled.

As the EV Topas was very!!!!!! cheaply made, I rework the internal damping.

The sound is way better than expected. No mid-rangy feeling anymore. Still a glourious midrange and a very fast mid-bass. The passive radiotor does a good job in extending the bass.

One speaker is finished, the other nearly finished. But as i test the sound only in mono, I already happy. As soon as the other one is ready as well, i'll upload some pictures.

Cheers

Martin
 

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If that is a Stephens it has had the surround replaced...

Question for Stephens enthusiasts. Some darn fool* spread a black gooey substance on the large fabric accordion surround of my wonderful 150w (purchased around 1968, but half time since in storage). That raised the resonance by 20 Hz or so.

I can find no replacements for the cone or surround on the web. But there are dealers on the web who offer to replace surrounds.

Anybody have a suggestion for who or how for getting a Stephens surround surgically replaced?

Failing to find a method to bring my 150w back from the near-dead, I suppose I should be willing to find a worthy new DIY owner.

Thanks.

Ben
*to help others who might be temped, it was "liquid electric tape"... I guessed it looked like the stuff Parts Express sells.... but I guessed wrong
 
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People do things like putting generic foam surrounds on Lowther PM6A drivers, and then they enjoy the music even though the authenticity has been sullied. So a surround is essential but it is not at the top of the list of the bits influencing the performance of the speaker. Oh and I have ruined a few drivers with stuff from the hardware store...
 
Put them in an OB and add low and high frequency augmentation - just so you can admire the crackle black finish on the frame and magnet. These things are beautiful to look at and don't deserve to be hidden away in a box that sounds bad. JMO...

GM recommendation of MLTL seems to be like a good one, but don't be put off from OB so easily.

Quite easy to add a sub amp, like Parts-Express has, with built in XO, so it's easy to dial in. Adding a tweeter on top with a simple cap, and shape the OB to your liking.

That could be fun too!
 
Up and running...

Finished the mod of the second speaker.

The quickly replaced my main stereo set in the living room. Exeptional sound. Seamless transition from the 80fr's to the tweeters. Suprisingly deep and well defined bass.

Just awful sound. No vintage feeling, pure hifi!

The pictures shows them together with my Pioneer last generation plasma and an old (1972) Pioneer SM-3000 power amp (and headphone adapter).

Cheers Martin
 

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