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Old 31st March 2010, 10:11 AM   #1
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Default Unknown speaker - where do I begin?

I have a pair of so-claimed full-range speakers for wich I would like to build a cabinet.
First idea was to re-create the original cabinet but since I cannot find anyone who has one and who is willing to disassemble it, I'm kind of stuck.
The original cabinet was a corner speaker cabinet wich was open at the back, but had some sort of waveguide (is that what it's called?) inside.
It also had an additional tweeter.

The speakers themselves are AFAIK made by goodman. (for a local company called Artec) Someone told me the magnets are Alnico.
They are twin-cone, 12/15" and rated at 25/100 Watts
Measured impedance is 8 ohm
They have the code "7/79" printed on, wich looks to me as the manufacturing date.

Now, where do I begin to create or find a new cabinet for these speakers?
I should probably begin with measuring the specifications, but wich ones do I need?



Thanks in advance, a speaker building noob.
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Old 1st April 2010, 06:26 AM   #2
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Yes, you'll need a tweeter to match them.

Let's try to guess at some of the parameters.
I'm thinking efficiency will be high, (>90dB), because amplifiers at that time didn't have too much power. Following that, power handling will be fairly low, by today's standards. Think no more than 100W. I'd also expect resonance to be quite high: 60Hz+.
Usually, speakers of that era like large ported boxes. I know my dad's old PA drivers are of similar age, and, when modelled, they take a silly-large box.
HTH
Chris
PS - it'd make a lovely guitar speaker.
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Old 1st April 2010, 06:32 AM   #3
freddi is offline freddi  United States
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I'd make one open baffle first, mount and listen - I've got RCF 12" fullrange with ~same cone, whizzer and dustcap

Last edited by freddi; 1st April 2010 at 06:39 AM.
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Old 1st April 2010, 06:38 AM   #4
ratza is offline ratza  Romania
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Quote:
Originally Posted by hidnplayr View Post
Now, where do I begin to create or find a new cabinet for these speakers?
I should probably begin with measuring the specifications, but wich ones do I need?
You need the Thiele-Small parameters of the speaker.
Measuring Loudspeaker Driver Parameters
The Subwoofer DIY Page - Measurements

You can decide if you need a tweeter or not just by playing some music on the speakers and see if they go up enough to fit your needs.
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Old 1st April 2010, 01:20 PM   #5
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Do you have a picture or diagram of the original cabnets? If they had some
type of waveguide and opened into the back and intended to be corner mounted
that could be a back loaded horn. If they were in a horn they probably will not
work well on an open baffel.
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Old 1st April 2010, 06:00 PM   #6
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Thanks for all the info guys,
I'll create one open baffle just to test the sound , and it will come in handy to measure the resonance frequency, right?
Does it matter how far above the ground the speaker is positioned in such a cabinet?

I dont have a diagram of the original cabinets, else I would have probably just made those Attached is a simple drawing i made, of what i remember seeing from such a speaker without disassembling it

The back loaded horn theory sounds right to me, will any of the measurements be able to verify this speaker is intended for such a cabinet?
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Old 1st April 2010, 06:32 PM   #7
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Goodmans were good 'middle class' products (for the most part) as I remember them in the 1970's. Their really astonishing 'speakers were the litle ones... or so it seemed at the time, before the LS3/5a! Yours would probably be earlier in date than those I knew, though.

I'm not sure whether these help, but there are some drive units & cabinet designs in the 1963 catalogue (try the lower parts of pages 6,7 &8):

http://pagesperso-orange.fr/rififi/G...963-page01.jpg
http://pagesperso-orange.fr/rififi/G...963-page02.jpg
http://pagesperso-orange.fr/rififi/G...963-page03.jpg
http://pagesperso-orange.fr/rififi/G...963-page04.jpg
http://pagesperso-orange.fr/rififi/G...963-page06.jpg
http://pagesperso-orange.fr/rififi/G...963-page07.jpg
http://pagesperso-orange.fr/rififi/G...963-page08.jpg
http://pagesperso-orange.fr/rififi/G...963-page09.jpg
http://pagesperso-orange.fr/rififi/G...963-page10.jpg
http://pagesperso-orange.fr/rififi/G...963-page11.jpg
http://pagesperso-orange.fr/rififi/G...963-page12.jpg
http://pagesperso-orange.fr/rififi/G...963-page13.jpg
http://pagesperso-orange.fr/rififi/G...963-page14.jpg
http://pagesperso-orange.fr/rififi/G...963-page15.jpg
http://pagesperso-orange.fr/rififi/G...963-page16.jpg
http://pagesperso-orange.fr/rififi/G...963-page17.jpg
http://pagesperso-orange.fr/rififi/G...963-page18.jpg
http://pagesperso-orange.fr/rififi/G...963-page19.jpg

Also, cabinet design in the U.K.from the 1950's onwards, at least as far as the early 1970's was heavily influenced by a book by Gilbert Briggs - alas, I do not have a copy, but I remember my father reading it & thinking about a brick-built corner horn shown therein: my mother thought differently!

Adam K, London,
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Old 1st April 2010, 06:37 PM   #8
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As a rule of thumb if it's intended for horn loading the QTS will be rather low
typicaly .2 to .3 where as for an open baffel look for a QTS of .7 to 1.3
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Old 1st April 2010, 08:42 PM   #9
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Here are the results from a quick measuring session.
(The speaker was hanging from a wire, between the legs of a chair, probably not an ideal situation)

I have no idea however what these Q values mean in real life.
According to a website, the Qts indicates that this speaker will work well in a sealed enclosure, correct?


Thanks for the links to the catalogue, rilydriver, interesting lecture!
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Old 5th April 2011, 03:09 PM   #10
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I have found the original cabinets!
If anyone ever finds a similar pair of speakers, I'll be happy to answer your questions
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