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Speaker magnet size


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reading the 'describe your 1st PA' thread, I was recalling the speakers we used back then. In my case, EV SRO 12s in my Sunn Solaris guitar amp and SRO15's in the PA and bass cabs. Both had huge, heavy magnet structures, 15 lbs and 18 lbs respectively if memory serves. My bandmates guitar amp had a JBL 15 with a similarly large magnet. Seems like just about any upgrade speaker back then had much larger magnets than the stock speakers (Jensens in my case).

 

Today's speakers don't seem to have anywhere near as large/heavy magnets. I'm curious as to the difference in engineering of today's speakers vs. those from that time period.

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Older alnico magnets were smaller compared to ceramic and now neo dwarfs them all in size/weight. But if the magnetic flux density were all the same, the speakers would all be the same, save maybe some minor differences caused by heat wicking.

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reading the 'describe your 1st PA' thread, I was recalling the speakers we used back then. In my case, EV SRO 12s in my Sunn Solaris guitar amp and SRO15's in the PA and bass cabs. Both had huge, heavy magnet structures, 15 lbs and 18 lbs respectively if memory serves. My bandmates guitar amp had a JBL 15 with a similarly large magnet. Seems like just about any upgrade speaker back then had much larger magnets than the stock speakers (Jensens in my case).


Today's speakers don't seem to have anywhere near as large/heavy magnets. I'm curious as to the difference in engineering of today's speakers vs. those from that time period.

Pretty sure Standard EV have about the same size mags today as they had 30 years ago. Same with most of the similar models. There's still a huge difference between a stamped frame guitar speaker and a high-end cast frame model.

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How important is the magnet size? how does it affect the sound quality?

 

 

Magnet size means nothing.

 

Magnet strength and how the magnetic field is focused into the gap is what matters. High magnetic field strength and number of turns of wire in the gap defines the available force and is one parameter that is used to develop a speaker's properties. Means different things dependingon the speaker's bandwidth.

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agedhorse...how then does a magnet 'strength' affect the speaker's frequency response? The stronger the magnet 'force'...the more 'pwoerful' it is? Sorry for the silly question.

 

 

and maybe a followup question; what parameters determine a speakers 'efficiency'? Going back to my original post, the difference in sound output from the stock Jensens in my Sunn Solaris vs. the EV SRO12s was substantial. Being young and uninformed at the time (now I'm older and still uninformed), I assumed the magnet size was involved, and maybe the 'edge wound voicecoil' advertised with the SRO's. I'm sure it's not that simple.

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This is a much more complicated question than I think you realize.

 

Magnet strength is one parameter that geverns the available force to move the cone. There are other parameters (such as weight, wire turns in the gap, spring constants, piston area, damping, winding height and inductance that affect the frequency response and efficiency/sensitivity. All of these tradeoffs interact with each other.

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agedhorse...how then does a magnet 'strength' affect the speaker's frequency response? The stronger the magnet 'force'...the more 'pwoerful' it is? Sorry for the silly question.

 

 

Generally the magnet strength itself bears little to frequency response. There are mechanical issues, suspension, cone weight and material that greatly affect things.

 

So here's one you wouldn't think of ... too strong a magnet will limit low frequency response ( at least with current technologies). More than about 14k gauss.

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this is not as easy to grasp as I thought...but I appreciate the effort you gusy took to reply.

 

 

Rarely can quality or performance be judged by just one parameter... otherwise, if bigger magnets = better, choices would be simple.

 

FWIW: The tomatoes from my garden were red when they were ripe, but not nearly as strikingly red as the tomatoes in the grocery store... but the tomatoes from my garden generally tasted considerably better.

 

There was a great quote in the movie Jerrasic Park, when the kid was playing with the binoculars. An adult (possibly Dad) said: "Quit playing with those." The kid said: "Why?" Dad said: "Cause they're expensive" Kid said: "How do you know?" Dad said: "Are they heavy?" Kid said: "Yea!" Dad said: "Then they're expensive.".

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There was a great quote in the movie Jerrasic Park, when the kid was playing with the binoculars. An adult (possibly Dad) said: "Quit playing with those." The kid said: "Why?" Dad said: "Cause they're expensive" Kid said: "How do you know?" Dad said: "Are they heavy?" Kid said: "Yea!" Dad said: "Then they're expensive.".

 

 

Not that it really matter, but I'm pretty sure that it was actually a lawyer who said that in the movie. In some ways, I think that makes the analogy even better.

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i have an old sunn cabinet with a 15" jensen driver. the magnet on that speaker is not visible on the outside, and the area the magnet resides inside is no bigger than the tip of my thumb. i have been feeding that thing 100 to 200 watts for 15 years, and that speaker is louder than any other speaker i own or use (for the power given to it).

 

it also weighs nothing. the entire cab is like 30 pounds and can be lifted with one finger.

 

i wont begin to pretend i understand how that works at all but it does, and i like the speaker a lot. its older than dirt.

 

my point is that sometimes teeny tiny magnet = huge sound, possible at the expense of accuracy.

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I'd be hard pressed to move my old Sunn; it was the Solaris combo, not the head with speaker cab. so I had to heft the whole big awkward thing. Having 30 lbs. of magnets on the speakers didn't help. My 65' Fender Super Reverb has the original Jensens with smaller lighter magnets and they ain't going anywhere. Older than dirt, rusty and covered with dust.

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i have an old sunn cabinet with a 15" jensen driver. the magnet on that speaker is not visible on the outside, and the area the magnet resides inside is no bigger than the tip of my thumb. i have been feeding that thing 100 to 200 watts for 15 years, and that speaker is louder than any other speaker i own or use (for the power given to it).


it also weighs nothing. the entire cab is like 30 pounds and can be lifted with one finger.


i wont begin to pretend i understand how that works at all but it does, and i like the speaker a lot. its older than dirt.


my point is that sometimes teeny tiny magnet = huge sound, possible at the expense of accuracy.

 

 

That speaker uses an ALNICO slug magnet as the pole piece with the return circuit around and over the back.

 

One thing that is different is that the driver has a very small Xmax, lightweight cone, small VC, low power handling and low frequency response is very poor by today's standards. Those variable tradeoffs are what also make it more efficient, probably by >3dB and especially from about 100Hz up. And correct, not very flay or accurate and THD is likely going to be pretty high too.

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