How much does magnet size affect tone?

[catnine]

 I don't know if this is the proper way to put it .

 I have a Jensen C10R 10 oz magnet and  weber ceramic sig 10S witha 20 oz magnet. Both have the same frame and cones that look the same and a 1 inch voice coil.

 When I first build my AA764 champ I used the C10R and it sounded fine . I got the weber and put that in but right off I noticed the bottom was not as good as the c10R . The weber is broken in now but the bottom is really not round .

 I have had alnico weber 10's and they have a 7 oz mag same coil and cone and sounded much better .

 Is it just the type of magnet of does the size matter. It seems like it would take more power to move a cone with a larger magnet .

[PRR]

> It seems like it would take more power to move a cone with a larger magnet.

Hmmmmm....

The magnet does not move. It is the foundation for the "leverage" between the amplifier and the cone. 

A stronger magnet makes a better motor. A Highly Efficient speaker needs a strong magnet.

But efficiency is more limited by Cone Size. A too-strong magnet may help the midrange but can't help the bass.

There are more factors. Cone mass. Coil mass. Overhang. Bass damping. Wizzing damping.

Unless you are a well-financed engineer, looking for pure efficiency, I don't think magnet size has any strong correlation with speaker sound. I look at the magnet, but I am more interested in tap-tones.


> weber ceramic sig 10S witha 20 oz magnet
> alnico weber 10's and they have a 7 oz mag

Alnico is stronger for the same weight. I'm sure it takes 3 times as much low-price ceramic to "equal" Alnico, maybe more. OTOH, there are some new exotic ceramics. OTOOH, speaker designers seem to cling to the old heavy ceramic or go all the way to niobium-stuff.

[Frankenamp]

Hooo Boy! that is a deceptively complex question...

Let me start the cussions and discussions with some generalizations about the magnet its self. First and foremost is strength in Gauss, more lines of Gauss- the stronger the magnet. It dosent matter what the magnet is made of what matters is how strong it is. Until neodymium, the best stuff was a alloy of Aluminum. Nickel, and Cobalt. In the late '60's alnico became scarce and expensive, so the ceramic magnets were developed. Ceramic magnets are not as strong as alnico magnets, so a larger magnet is required to get the same gauss as a comparable alnico or neodymium (compare the Eminince ceramic and neo drivers-  it takes a seven ounce neo magnet to equal a five pound ceramic magnet).  A friend in the business of manufacturing speakers once told me a tip he got from the Focal people for getting big bass- use a weaker magnet. This brings us to point two, big bass needs a big magnet- up to a point. and the point is when back emf (Qes) starts driving the total Q (Qts) below about .3. Below .3, the back emf severly damps cone movement and bass falls off fast, but the speaker is efficient as hell! (great horn driver) Most musical instrument drivers walk a fine line between efficiency and bass response. Most old alnico drivers have a combination of light cone, stiff suspension, and a fairly (relatively) strong magnet. This is the cheap recipe for a loud (90+ dB) speaker. That recipe demanded a 12 or 15 inch driver for any kind of bass below 100 Hz at all. Which is why that 12 or 15 has a better bottom end than an 8 or 10, they move more air.  (a modern 6 or 8 inch woofer will kill a vintage 12 or 15 speaker in terms of bass output, but the vintage speaker will eat the modern woofer alive in terms of efficiency. A good modern woofer is lucky to be 85-89 dB efficient and can handle 100 watts while a vintage speaker is 93-95 dB efficient and 30 watts will send the cone flying off to never-never land )

VC size does matter (length and diameter)...
The reason there are so many speakers with 1" voice coils is that the average tube amp put out 10-20 watts, and 10 - 20 watts is about all a 1" paper voice coil can take using '40's technology- and that's being generous. A 1" VC let the manufacturer use a smaller magnet 1.25 - 2" VC's were luxury items, because the magnet needed to be a lot bigger to make the same Gauss in the VC gap. That gap was pretty sloppy in consumer and MI speakers. Making speakers was a cottage industry after WWII and Jim Lansing made the same crappy speakers everyone else did in their garages and workshops. He learned most of his speaker design skills working on a theater speaker project for Western Electric. The 4" VC he designed in the D130 was wretched excess in a world that had only recently discovered Williamson amplifier circuits. Even the D130 had an excursion design of about .125"  (1/8")  as did every other speaker of the time. Long voice coils were unheard of. (well practically speaking- conventional '40's design mantra was that it was better to make bass with a larger diameter than a longer stroke, because the longer stroke produced more distortion with the available materials.) The crimped cloth spider was a new-fangled invention at the time, the spider was originally an artfully curlicued piece of flat phenolic impregnated cloth or cardboard which was still sometimes mounted to a screw in the center of the pole piece, and glued to the inside-top of the VC. (think of a 45 rpm record adapter). Remember the 30" woofers?

Additonal note about excursion- a 6V6 PP amp makes 10 clean watts and you won't get much excursion with that, even monster theater or PA amps of 100+ watts spread that power around so that no single speaker got more than about 10 watts anyways. They didn't need or want Xmax in those days. (well truth be told they were limited by the materials at hand, paper can only bend so much...)

[catnine]

 I just have teo 10's . one is a weber ceramic sig 10s and the other a jensen C10R . The weber is fairly new , the jensen I got off ebay and it was used , how much I don't know.

 The only visable difference is the size of the magnet . the weber is 20 oz and the jensen 10 oz if i recall.

 Whne i build this amp all I had was the jesen and when I got the weber and installed it the weber did not seem to have a round and present bottom end but that may be due to the fact the weber was new and stiff.

 Weber only gives info on VC size and mag size and their description of the sound so I have no way to compare them other then to remove and install and play . I left the weber in because it is possible it is better made but that's just my own opinion , many new amps have jensen RI's in them .

 Some brands and models of mainly 12's people rave about that at the time I could afford to get and try sucked in my amp . I found of all the eminence 12's at that time the tonker was great as was the stonehenge they no longer make , the only diff was the tonker was a bit darker sounding . I had the texas heat and a canabas rex thought they were lame speakers and a 10 ram rod which did nothing over the stock pro jr 10 and even sucked in my pignose GV40. Yet the jensen mod 12/50 was real close to the eminence stone henge.

 A lot depends on the amp , in this case it is an AA764 champ build . I may have been better off routing out the speaker hole and installing a 12 which I could have done there is room .

 For me now to spend $60 to $100 for a speaker is out of the question .

 I have found weber sig 12's sound as good as most 12's of the same size VC and magnet or close enough.

 Perhaps with a 6 watt champ the weber needs more than 30 hours to break in since it is pretty stiff . I don't push on the cone to test . I really could not see a visual diff in the cone of the weber or Jensen they looked the same down to the dust cap and rib spacing and VC .