big speaker, tiny magnet,..

Archived from groups: rec.audio.tech (More info?)

From an old Magnavox tube stereo. It used two cabinets, each with 3
speakers. The largest is 15" but it only has a 1 inch or so magnet.
This is to save money or is there another reason? The other two
speakers had similar sized magnets on 6" and 2" speakers. It looks
like they had a capacitor across each speaker to divide the signal
into bass, mid, treble sections.
I salvaged the speakers to make a bass amp but they look kind of
anemic now that they're out of the cabs. What say all of you?

Archived from groups: rec.audio.tech (More info?)

On Mon, 20 Jun 2005 06:37:41 GMT, spudrick <oblahdee@blahdah.com>
wrote:

>From an old Magnavox tube stereo. It used two cabinets, each with 3
>speakers. The largest is 15" but it only has a 1 inch or so magnet.
>This is to save money or is there another reason? The other two
>speakers had similar sized magnets on 6" and 2" speakers. It looks
>like they had a capacitor across each speaker to divide the signal
>into bass, mid, treble sections.
>I salvaged the speakers to make a bass amp but they look kind of
>anemic now that they're out of the cabs. What say all of you?
Some tube sets had 12-15" speakers with electro magnets (extra leads
to a coil near the typical magnet position) wired in series with the
B+ supply. IIRC these speakers also had a 3.2 ohm VC

, _
, | \ MKA: Steve Urbach
, | )erek No JUNK in my email please
, ____|_/ragonsclaw dragonsclawJUNK@JUNKmindspring.com
, / / / Running United Devices "Cure For Cancer" Project 24/7 Have you helped? http://www.grid.org

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"spudrick" <oblahdee@blahdah.com> wrote in message
news:ilocb1ls9sg5q3fs3f2mj4kl6ve06bcur8@4ax.com...
> From an old Magnavox tube stereo. It used two cabinets, each with 3
> speakers. The largest is 15" but it only has a 1 inch or so magnet.
> This is to save money or is there another reason? The other two
> speakers had similar sized magnets on 6" and 2" speakers. It looks
> like they had a capacitor across each speaker to divide the signal
> into bass, mid, treble sections.
> I salvaged the speakers to make a bass amp but they look kind of
> anemic now that they're out of the cabs. What say all of you?

These speakers were designed to play loudly with only a few watts input. You
might notice that the cones are made of a thin taut paper not unlike a
guitar amp speaker. They probably can't handle any more than 10 or 20 watts.
For a bass amp, you might look at true woofer drivers.
John

Archived from groups: rec.audio.tech (More info?)

dpierce@cartchunk.org wrote:

> There's more functionality and acousticalt performance in a $400
> boom box today than there was in a 1960's Magnavox stereo console.
> Hell, there's even more magnet on them.
>

So I take it, then, that you don't like Magnavox, circa 1960s. LOL

CD

Archived from groups: rec.audio.tech (More info?)

dizzy wrote:
> On 21 Jun 2005 04:13:10 -0700, dpierce@cartchunk.org wrote:
>
> >dizzy wrote:
> >> As to Thiele and Small, AFAIK that's for bass-reflex designs,
> >
> >Wrong. Consider the series of articles written by Small in the JAES:
> >
> > Direct Radiator Loudspeaker System Analysis (1972 June)
> > Closed-Box Loudspeaker Systems, (1972 Dec, 1973 Jan-Feb)
> > Vented-Box Loudspeaker Systems. (1973 Jun, July/Aug, Sep, Oct)
> > Passive-Radiator Loudspeaker System Design, (1974 Oct, Nov)
>
> I stand corrected, but this doesn't change the overall point I was
> making.

Which was what?

> >> which that old stuff was generally not.
> >
> >Also not correct. Most of the stuff made by Magnavox and the like
> >were nowhere near sealed box.
>
> Suffering from reading comprehension problems? "Not bass-reflex" does
> not equal "sealed box".

Then what, in your estimation, were they?

(In fact, their operation is just as well covered by the Thiele
Small model).

> >> I have no doubt that (at least the more thoughtful) designers back
> >> then made reasonable attempts to design systems with decent
> >> performance,
> >
> >Yes, and NONE of them have worked represented by the likes of
> >Magnovox.
>
> Wrong.

Well I guess that settles it, then.

You want to provide at least SOME substance to your assertion?

> >> Large magnets as what are common today simply
> >> were not appropriate back then.
> >
> >Not "appropriate?" Do you mean to say that physics has changed,
> >and what is "appropriate" now wasn't then?
>
> Idiot. Technology has changed.

Utter nonsense. Ferrite magnet technology has been available
since the early 1950's. Manufacturers had substantially larger
magnet assemblies, specifically, larger Bl products since
the early 50's. The technology WAS there. You just don't know it.

> >> Most stuff sold back then was not nearly as "junk" as most stuff sold
> >> today...
> >
> >There's more functionality and acousticalt performance in a $400
> >boom box today than there was in a 1960's Magnavox stereo console.
> >Hell, there's even more magnet on them.
>
> So what? That doesn't make the old stuff "junk".

Try reading. There's more functionality and acoustical performance
in a $400 boom box of today than there was in a similarily or higher
priced Magnavox system of 40 years ago. You claimed the stuff back then
is less "junk" than the stuff sold now, and other than your personal
opinion and insistance, you have no data to back that up.

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Codifus wrote:
> dpierce@cartchunk.org wrote:
>
>> There's more functionality and acousticalt performance in
a $400
>> boom box today than there was in a 1960's Magnavox stereo
console.
>> Hell, there's even more magnet on them.
>>
>
> So I take it, then, that you don't like Magnavox, circa
1960s. LOL

Indeed. Maybe you had to be there...

I was.

The brown-box goods of the 60s were pretty horriffic.

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dizzy wrote:

> >Try reading. There's more functionality and acoustical performance
> >in a $400 boom box of today than there was in a similarily or higher
> >priced Magnavox system of 40 years ago.

> So what? That doesn't make the old stuff "junk".

Go check what JBL and Altec was building back then. The technology and
the understanding was there.

> >and other than your personal
> >opinion and insistance, you have no data to back that up.

> Bullshit. The hardware still exists as evidence.

Yes, but it is Dick's point that is made by it, not yours. Go see
http://www.audioheritage.org ....


Kind regards

Peter Larsen



--
*******************************************
* My site is at: http://www.muyiovatki.dk *
* The Vienna Copyright convention applies *
*******************************************

Archived from groups: rec.audio.tech (More info?)

dizzy wrote:

[lots of arguing about not very much]

> On 21 Jun 2005 04:13:10 -0700, dpierce@cartchunk.org wrote:
> >There's more functionality and acousticalt performance in a $400
> >boom box today than there was in a 1960's Magnavox stereo console.
> >Hell, there's even more magnet on them.

> So what? That doesn't make the old stuff "junk".

Budget was what determined the size of the magnet then, and it is today.
One difference that has not been discussed is that the magnet probably
is alnico, even if small, and thus stronger pr. cubic inch of magnet
that the magnet in a boom box.

Just as today the component cost allowable was derived by the retail
price range specified for the product. The design process for such a box
was not based on theory, it was a "practitioners throw together" within
the frame defined by price and by outer design. A lot of old radios and
stuff actually do have a "good sound", they were often good
practitioners,
but theory - nah, not a part of the design and perhaps not really all
that well understood. My brothers father in law was a jukebox repairman
from that period in the audio industry and I know some of the people
from the quality part of danish audio manufacturing (Movic), I don't
think I am unfair to the state of the art of the general "audio
furniture" industry back then.

There are manufacturers still building the same general kind of
loudspeakers that the old Magnavox thing in question had. Efficiency pr.
currency unit of manufacturing costs is good, and they can have a decent
lower midrange, but they are not bass loudspeakers. If you want to use
them for something, they are perhaps best deployed on what they are
designed for: an open, or semi-open, baffle, powered by no more than 5
watts. It is possibly possible to get the innards of that old Magnavox
to do good "wall to wall music" in a living room by proper deployment
within their limits and design genre - it could even be fun - but they
are not for HiFi, and was not so then.

What you need to understand that the target frequency range for such a
product back then was from something 100 Hz to something 5000 Hz, the
main use for the Magnavox was assumed to be AM reception or similar
quality broadcasts. The state of the art of the Audio industry back then
was considerably more advanced, products like the Magnavox are mostly
from the furniture industry.


Kind regards

Peter Larsen

--
*******************************************
* My site is at: http://www.muyiovatki.dk *
* The Vienna Copyright convention applies *
*******************************************

Archived from groups: rec.audio.tech (More info?)

Tim Martin wrote:
> "spudrick" <oblahdee@blahdah.com> wrote in message
> news:ilocb1ls9sg5q3fs3f2mj4kl6ve06bcur8@4ax.com...
> > The largest is 15" but it only has a 1 inch or so magnet.
> > This is to save money or is there another reason?
>
> I imagine it's because the speaker was designed to handle only a few watts,
> not the hundreds of watts of today's designs. It may have an alnico magnet,
> too, which is I believe a more powerful magnetic material than modern
> ceramic magnets.

This has been mentioned elsewhere in this thread, but there's a
misconception that needs to be cleared up.

The "strength" of the magnet, in term that are important to the
operation of the speaker, is directly related to the flux density
in which the wire of the voice coil is immersed. The relevant
parameter is referred to as the "Bl product" (that's "bee-ell" ).
It is the product of the flux density, B, measured in Tesla and
the length of the wire, in meters, that's immersed in that field.
The Bl product is measured in units of Tesla-meters, and is
equivalent to the amount of force per amount of current (actually
1 Tesla meter is equal to 1 Newton of force per ampere of current).

Speaker magnets using Alnico have traditionally been claimed as
being "more powerful" than magnets using ferrite ceramics, but
this is simply not the case.

WHat IS true of Alnico is that it is capable of storing more
total energy per unit volume than ceramics can. But the SIZE
of the hard magnet material is NOT what determines the important
factor here, and that is the flux density in the voice coil cap.
That's something the magnet material used cannot determine.

In BOTH the cases of Alnico- and ferrite ceramic-based magnet
structures, the material used to actually focus and concentrate
the magnetic field in the gap is almost always common, soft,
low-carbon steels, for several reasons:

1. They're inexpensive

2. They're ductile and malleable and thus can be shaped using
common metalworking methods (stamping, forging, diecutting)
into the desired shapes and configuration,

3. They are capable of supporting substantially flux densities
than most hard magnetic materials such as alnico or the
ceramic ferrites.

The first two speak to the manufacturability of the assembly,
especially since both of these material are VERY hard to machine.
Try to machine Alnico, and you'll wear you tools out much faster
than the alnico, and if you try to force the issue, it will shatter
like glass. And ceramics are like trying to machine brittle rocks.

But the last point, the issue of flux density, is VERY important
in the design of the magnet.

The problem is that while both Alnico and ceramic hard magnet
materials are capable of storing large amounts of magnet
energy permanently, they have a limit: the flux density the
can store is limited. HOwever, the flux can be concetrated and
directed by using the auxiliary soft-iron structure.

Fo, for example, the typical flux density at the surface of a
ceramic magnet might be on the order of only 0.2 Tesla. But if
we could concentrate that same total flux in a smaller area, the
flux density would, obviously, be greater. Look at the relative
cross-sectionaly areas of the magnet vs the surrounding magnet
structure, and you can see how the relatively low fux density
of the magnet is conctrated to a higher flux desnity at the gap.

However, there is a limit, and that is that the amount of flux
you can direct through these auxiliary structures is limited.
At best, soft, low-carbon steels "saturate" at flux densities
of about 1.2 Tesla. Any attempt to put any more flux into them
will not result in any increase in flux desnity, the extra
flux will simple "spill out" of the structure into the air.

Because, then, BOTH Alnico-based and ceramic-based magnets rely
the same low-carbon steels to concentrate and direct the magnetic
flux, these materials impose their own limits on the maximum
flux density in the gap. The result is that, all other things
being equal (same gap depth, same diameter, same voice coil),
a speaker magnet using Alnico will not be any more "powerful"
than one using ceramic.

In essence, the "strength" of the magnet field where it counts,
that is in the voice coil gap, is limited NOT by the magnet
material, alnico or otherwise, but by the soft iron.

So what's the advantage to Alnico? In this day and age, not a lot.
For any given Bl product, an Alnico-based magnet can be physical
smaller and lighter. But it will also be more expensive, because
of the ioncreased cost of the material and the difficulty in
handling it.

So, just because a speaker has an Alnico magnet, don't assume
that it's "more powerful." In all likelihood, it's not.

Archived from groups: rec.audio.tech (More info?)

"Peter" <reply to newsgroup only> wrote in message
news:1N2dnWvv6vfsvCDfRVn-2w@comcast.com...
> I thought that the magnetic force in all magnets eventually diminishes,
> although probably so little that the performance of a loudspeaker would
not
> be affected during a listener's lifetime.


I think Dick already covered in previous posts how some magnetic materials
are more affected by heat etc. than others. Noticeable loss of magnetism can
occur with high voice coil temperatures or high shock loading in some
instances. Time duration alone will be much less significant I believe.

MrT.

Archived from groups: rec.audio.tech (More info?)

We had a Magnavox in my family that my dad purchased from a neighbor in
about 1960. While I was growing up, we always called it the "hi fi" (our
neighbor replaced it with a real hi fi). This thing had:

o A lousy FM tuner that drifted like crazy. You had to keep tuning it. AM
was stable and sensitive, but very narrowband.
o A rumbly record changer with a very low compliance crystal (not ceramic)
phono pickup. Tracked around 6 grams, maybe more. It sounded horrible.
o Maybe a 5 or 10 watt power amp. It might have been push-pull. I don't
remember the tube complement, but it had a 5Y3 rectifier which gives us some
idea of the amount of energy going *into* the circuit...
o The most horrible speaker system I ever saw. It had a very low compliance
12 inch "woofer" (with a very small magnet structure - the same open frame
rectangular assembly you would see on most cheap speakers built in the late
'50s), It can't have had any useful output below about 150Hz. I have no idea
why they needed a 12 inch speaker for a design like that, especially since
the cabinet was not tuned, sealed, or bass reflex. It was just open. The
sound from the back of the speaker simply radiated out of the back & bottom
of the cabinet (it stood on legs) and canceled out any wavelengths longer
than the distance from the speaker to the bottom of the front panel (about 8
inches).
o For the punch-line, it was a "two-way" speaker system. They coaxially
mounted a "tweeter" in front of the "woofer". The "tweeter" was another
conventional speaker about 4" in diameter. A non-polarized capacitor
provided the "crossover" -- or at least prevented whatever bass happened to
escape from the lousy electronics from frightening the "tweeter". The funny
thing is, they probably could have saved a lot of money, and achieved the
same mediocre result by using a single, slightly higher quality 6" speaker
with a whizzer cone.

Hi fi was certainly possible in those days, but most consumer products were
far from it. In the '60s, we called those big expensive stereo consoles
"coffins" because everything inside was dead. They were just musical
furniture, not audio equipment.

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"Arny Krueger" <arnyk@hotpop.com> wrote in message
news:i4adnRm7EsrQUCDfRVn-tA@comcast.com...
> Karl Uppiano wrote:
>> "Arny Krueger" <arnyk@hotpop.com> wrote in message
>> news:Y8GdnT2eDatjhCTfRVn-gg@comcast.com...
>>> Codifus wrote:
>>>> dpierce@cartchunk.org wrote:
>>>>
>>>>> There's more functionality and acousticalt performance
> in
>>> a $400
>>>>> boom box today than there was in a 1960's Magnavox
> stereo
>>> console.
>>>>> Hell, there's even more magnet on them.
>>>>>
>>>>
>>>> So I take it, then, that you don't like Magnavox, circa
>>> 1960s. LOL
>>>
>>> Indeed. Maybe you had to be there...
>>>
>>> I was.
>>>
>>> The brown-box goods of the 60s were pretty horriffic.
>
>> For the most part. I do remember a friend of the family
> bought a
>> Fisher stereo console in 1969 that was pretty impressive,
> relatively
>> speaking. It had a Dual turntable with a magnetic pickup,
> a
>> respectable AM/FM tuner, built-in pair of air suspension
> speakers
>> (might have been AR?), maybe 20 watts/channel. It actually
> sounded
>> pretty good compared to the run-of-the mill stuff back
> then. Of
>> course, I doubt in the intervening 15 years, that they
> ever replaced
>> the "needle" in that Dual...
>
> That is all fine and good, but this is hardly your typical
> brown-box goods of the 60s. It might not have even been a
> Fisher product per se, but rather a bunch of
> really-pretty-good audio components of the era assembled
> into a piece of furniture by a local reseller. The tip-off
> would be the AR speakers - Fisher had their own line of
> speakers and they would have been used in a 100% Fisher
> system.

This was all basically a Fisher product. Perhaps the speakers were Fisher.

I wasn't arguing with you. This was a better than average system.

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"Karl Uppiano" <karl.uppiano@verizon.net> wrote in message
news:lIBve.2869$J12.934@trnddc05...
> A lot of money is a relative term with mass-produced items. Even if the
> parts are cheap, if they save a few pennies on the part, multiplied by the
> number of units produced, especially when it had to be assembled by hand,
it
> adds up.

Agreed, and in this case the point I was making is that it adds up to very
little.

MrT.