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Old 19th December 2010, 07:10 PM   #1
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Default Stiff Woofer?

I recently acquired a pair of 1964 Jensen TF4s that appear to be in excellent shape. This is a 4-way ported speaker with a 10 inch woofer. With the bass control on the amp set flat, the speaker is definitely deficient in bass. I recapped the pair which didn't help the bass (the woofer is directly across the speaker lines anyway, nothing in series). I've heard that an old surround can get stiff. Could this be the problem? The surround on these woofers does not appear to be foam. The surround is brown colored, I'm guessing it's cloth. Will the bass improve with use?

Bobby Dipole
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Old 19th December 2010, 07:36 PM   #2
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I'm guessing you're using a transistor amp, with very low output impedance...

A speaker that old pre-dates A.N.Thiele's seminal papers which underpin box speaker design today. Your Jensens were very probably engineered around valve (tube) amps with rules of thumb and only cursory measurement. As such, the output Z of the driving amp now typically matters *a lot*.

Basically - if you are using a solid-state amp, the speaker is seeing too much electrical damping it probably was not designed around. It will sound 'thin' as a result. Try adding 1-5 ohms in series with one side of the speaker cable on each speaker, and listen again. Play with this series R until it sounds right - it's cheap and easy to do.

This basic change of paradigm afflicts many classic speaker designs too, hence all the reports of '...you need a valve amp..' for Monitor Golds etc. You don't, it's just hindsight and appropriate maths


PS if you are using a transistor amp do not go mad caning the things to get them to 'loosen up' because 1) it may not happen and 2) their continuous power rating is also probably based around tube amps i.e. only 15-30w or so...
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Old 19th December 2010, 07:56 PM   #3
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Quote:
Originally Posted by martin clark View Post
I'm guessing you're using a transistor amp, with very low output impedance...
I'm using a 1957 Pilot AA-903B amplifier with these speakers. This is a mono tube amplifier. (I'm only using one speaker at a time, of course. They both sound the same.) The Pilot amplifier is also a recent acquisition. With the bass turned up all the way, the speakers sound just about right.

Bobby Dipole
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Old 19th December 2010, 08:23 PM   #4
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Default SWAGs

Quote:
Originally Posted by Bobby Dipole View Post
I'm using a 1957 Pilot AA-903B amplifier with these speakers. This is a mono tube amplifier. (I'm only using one speaker at a time, of course. They both sound the same.) The Pilot amplifier is also a recent acquisition. With the bass turned up all the way, the speakers sound just about right.

Bobby Dipole
Your SWAG is the same as mine. Re-cone the drivers. As compliance decreases [fs] is shifted upwards. This may be true also for the MF and HF drivers as well.

Regards,
WHG
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Old 20th December 2010, 04:58 AM   #5
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Quote:
Originally Posted by Bobby Dipole View Post
I recently acquired a pair of 1964...Will the bass improve with use?
You mean, another 46 years more?

Bass cabinet design was primitive voodoo witch doctor guesswork in those days. Most likely, they just don't have good bass.

Leave the bass up all the way and the heck with it, or get some other speakers.
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Old 23rd December 2010, 09:25 PM   #6
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Default Baloney!

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Originally Posted by head_unit View Post
You mean, another 46 years more?

Bass cabinet design was primitive voodoo witch doctor guesswork in those days. Most likely, they just don't have good bass.

Leave the bass up all the way and the heck with it, or get some other speakers.

Your characterization of loudspeaker design circa 1960s reflects naivety regarding its history.
The works of Leo Beranek [1], Harry Olson [2], and others as well, published before 1960, contain the tools necessary to design loudspeakers of excellent performance. The practice of “Voodoo Guesswork” design during this period as well as today, remains alive and well, as its demise was not brought about by the improvements in methodology introduced by Thiele, Small, and their contemporaries later on.

Regards,
WHG

[1] Acoustics: Welcome to Leo Beranek.com
[2] Acoustical Engineering: BKPA1 - Acoustical Engineering
Biography: http://www.nap.edu/html/biomems/holson.pdf
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Old 23rd December 2010, 11:32 PM   #7
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Quote:
Originally Posted by whgeiger View Post
Your characterization of loudspeaker design circa 1960s reflects naivety regarding its history.
The works of Leo Beranek [1], Harry Olson [2], and others as well, published before 1960, contain the tools necessary to design loudspeakers of excellent performance. The practice of “Voodoo Guesswork” design during this period as well as today, remains alive and well, as its demise was not brought about by the improvements in methodology introduced by Thiele, Small, and their contemporaries later on...
I actually know a fair amount about the history of speakers, and even worked for Jim Novak (a super nice guy). So I stand corrected that it was not completely like a Middle Ages full of ignorance and superstition...and hey, the Klipschorn was introduced way back in 1946. But for the vast majority of designers, I would still stand by my statement. Even in the 1980s I had professional coworkers who didn't really have a great understanding of how to use parameters to design a woofer/box combo, even given the relatively easy-fied methods refined by Benson, Thiele, and Small.

Maybe I should more correctly have said
"Back in the days that speaker was designed, there were very few tools for designers to use, none of them easy, and very very few designers who knew how to use them. Design and production technology were much more primitive than today. Therefore it is quite possible your speakers just never had good bass, due to design limitations (or bad tuning from bad ears or marketing dictums)."

As for
Quote:
Originally Posted by whgeiger View Post
...The practice of “Voodoo Guesswork” design during this period as well as today, remains alive and well, as its demise was not brought about by the improvements in methodology introduced by Thiele, Small, and their contemporaries later on...
...well, I still can't stop laughing when I re-read it.

Last edited by head_unit; 23rd December 2010 at 11:36 PM.
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Old 24th December 2010, 05:04 AM   #8
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Default Sorry!

Quote:
Originally Posted by head_unit View Post
I actually know a fair amount about the history of speakers, and even worked for Jim Novak (a super nice guy). So I stand corrected that it was not completely like a Middle Ages full of ignorance and superstition...and hey, the Klipschorn was introduced way back in 1946. But for the vast majority of designers, I would still stand by my statement. Even in the 1980s I had professional coworkers who didn't really have a great understanding of how to use parameters to design a woofer/box combo, even given the relatively easy-fied methods refined by Benson, Thiele, and Small.

Maybe I should more correctly have said
"Back in the days that speaker was designed, there were very few tools for designers to use, none of them easy, and very very few designers who knew how to use them. Design and production technology were much more primitive than today. Therefore it is quite possible your speakers just never had good bass, due to design limitations (or bad tuning from bad ears or marketing dictums)."

As for

...well, I still can't stop laughing when I re-read it.
I am aware of Benson's work and that early work of Klipsch as well. My first introduction to "Hi Fi" was in the early 1950s. At that time, I was privileged to audit a Klipsch corner horn pumping out some pretty amazing stuff. My first speaker designs were based on what I studied in the referenced books of Olson and Beranek. Back then, only a big mechanical Monroe calculator was at my disposal to iterate through the formula. Later on, an IBM 1130 became available. Today these basics are now a comparative 'cake walk'. We are all pigmies standing on the shoulders of giants. Glad you found the closing remark humorous.

Regards,
WHG
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Old 24th December 2010, 06:44 AM   #9
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Too many 'facts' not in evidence. Have you measured the amplifier so you _know_ it's putting out bass? Never overlook the obvious.

Before you destroy the speakers you might want to measure the system resonance and the free-air resonance.

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