Help me choose a speaker

[J M Fahey]

Raw images poste d on Imgur. Visible now?














Really donīt understand new Forum "upgrade" and not much free time to fight it.
Sorry.

[g1]

Yey, Juan returns! Hope you’re well and busy

Amen to that. Good to see you back here Juan.

[vintagekiki]

Welcome dear friend.
It's nice to see you after a long time.

https://www.google.com/search?tbm=isch&q=bugera+vintage+guitar+series+speakers

https://www.google.com/search?tbm=isch&q=jensen+special+design+speakers

1)
https://www.jensentone.com/

[J M Fahey]

Thanks to all

I see Jensen selected the unusual narrow slot frames for the lighter magnet speakers, both Alnico and smaller ceramics, for the heavier ones (C 12N, etc.) they used more conventional "6 spoke wheel" type frames, made out of heavier gauge steel and with more pronounced reinforcing ribs and edges.

This is the currently made (in Italy) Jensen MOD 1270



https://www.jensentone.com/mod-series/mod-12-70

Notice the huge treble loss in the 4 ohm response curve, compared to 8 and 16 ohm, caused by the too thick (and heavy) wire used there..

[Helmholtz]

Notice the huge treble loss in the 4 ohm response curve, compared to 8 and 16 ohm, caused by the too thick (and heavy) wire used there..

Very interesting, thanks.
Clearly shows that different impedance versions of the same speaker model not necessarily sound the same.
Kudos to Jensen for publishing such detailed data.

[Chuck H]

Very interesting, thanks.
Clearly shows that different impedance versions of the same speaker model not necessarily sound the same.
Kudos to Jensen for publishing such detailed data.

And kudos to Juan for being aware enough to bring it to light so we can all appreciate it

[J M Fahey]

Thanks.

Making and designing guitar speakers makes me VERY aware of all those details, usually not even mentioned in books.
A little detail here, another there, are carefully harvested and kept, everything matters.
No black magic by any means, Physics rules always, but lots of undocumented features out there.

Notice the "broken magnet" picture (somebodyīs cabinet fell on its back, HARD!) showing how it attaches to frame , in this case by 4 inadequate resistance soldering spots ... I typically use 8 to 12 !!!! , and details on voice coil hole punched on frame ... and mashed voice coil caused by user carelessly trying to fit magnet back.






Compare these 10 soldered spots, and on a wider circle, to:

[g1]

and mashed voice coil caused by user carelessly trying to fit magnet back.

Was there a way to salvage this speaker (at less cost than replacement) ?

[pdf64]

I think a beefy de / magnetiser and spot welder would be necessary, stuff only a speaker manufacturer may be likely to have handy.

[Helmholtz]

I think a beefy de / magnetiser..would be necessary

Why this? Ceramic magnets don't partly self-demagnetize like Alnico when removed from the magnetic circuit. Apart from that I think JMF would have the apparatus required as he builds his own speakers.
The main problem seems to be the mashed voice coil former.

[vintagekiki]

When mounting the speaker on the cab front panel, the same rule applies as when mounting the wheels on the car.
All screws must be equally tightened to the same kp. For this purpose it is best to use an adjustable torque wrench.
The same story applies when the neck of the guitar is attached to the body of the guitar.

[J M Fahey]

I think a beefy de / magnetiser and spot welder would be necessary, stuff only a speaker manufacturer may be likely to have handy.

Itīs a $70 "cheap speaker" so many wouldnīt even care but being a bad case of OCD *I* would recover it by :

* ungluing cone and spider from frame to remove intact moving parts.
Might straighten smashed VC former edge by running it around between thumbnail and index finger, and shims would straighten it during reassembly, reasonable chance of that.

* demagnetizing, dissassembling front plate to re-spot-welding to frame, reassembling everything and remagnetizing are technically possible, but more laborious than justified.

In a couple cases similar to this one I clamped frame to magnet plate , carefully covered magnet slot to avoid it catching all iron droplets flying around and briefly applied an arc welder rod tip to center of each hole for an instant.
The tiny molten iron puddle, 4 or 5 mm wide, joins both top plate and frame.

I would also drill 4 extra holes on frame and do the same, to spread load better, and safeguard from having a weak one which would eventually repeat the separation under vibration.

The few I saved that way, never returned.

But cardboard taped over gap gets full of tiny iron globules made by arc welding, they must be chased and removed, if they get inside the gap may stay there forever.

Ceramics do not demagnetize as much as Alnicos, still lose 10 to 20%, but the problem is that itīs a Herculean task to reassemble and specially recenter an already magnetized system.

[uneumann]

Always appreciate your insights, Juan. At the risk of going further off-thread, I wonder if you (or anyone else) could comment on speaker distortion.

How do you design a speaker to breakup, or not? I recall reading that ribs in the cone will facilitate breakup. Few of us have actually designed and built and measured speakers, so any comments or observations are welcome.

Can you look at a speaker and gauge it's likelihood to breakup early or late? Are there different ways and mechanisms (the physics) that cause distortion? I can imagine the cone vibrating at harmonics (like vibration modes of a string), but there are so many different speakers and tones they produce. It seems there must be more to it than that.

How about open vs closed cabs - do cabs impact distortion (as well as freq response)?

I imagine it's a big ask... so thanks in advance.

[pdf64]

I asked a Celestion guy about that many years ago, he advised that the ribbing etc helps to keep the cone under control and add harmonics. He gave an example of a Vintage 30 having about 5% harmonic distortion at 1 watt.
I guess that an unribbed cone may have less added harmonics at low power levels, but beyond a certain point it may flap and flub in an uncontrolled, unpredictable manner, distortion may not be harmonically related to the input?
Dunno how an EVM12L fits in with that model though, with its stiff, unribbed cone? As it was supposedly tweaked to give a typical guitar speaker type zingy edge to its response.

[Chuck H]

I asked a Celestion guy about that many years ago, he advised that the ribbing etc helps to keep the cone under control and add harmonics. He gave an example of a Vintage 30 having about 5% harmonic distortion at 1 watt.
I guess that an unribbed cone may have less added harmonics at low power levels, but beyond a certain point it may flap and flub in an uncontrolled, unpredictable manner, distortion may not be harmonically related to the input?
Dunno how an EVM12L fits in with that model though, with its stiff, unribbed cone? As it was supposedly tweaked to give a typical guitar speaker type zingy edge to its response.

Rated at 200W I think the idea is that the EVM12L has a guitar speaker tone and pointedly DOES NOT flap and flub in any case. So what you hear is what you get.?. I, personally, think they just sound ok. But in certain applications they've been popular. Making a 1x12 combo sound bigger is one (if not the primary) application they've been used for.