neodymium vs ferrite magnets in loudspeakers

[Folderol]

My guess is that with lower mass and therefore lower inertia, the magnet assembly is more inclined to move in the opposite direction to the cone at low frequencies. Don't forget that it's not just the cone that it's working against, it's also the mass of air it's trying to move.

[AdiT]

In a sealed system air pressure has an influence, but is not significant in a bass reflex system.

[ef37a]

In a sealed system air pressure has an influence, but is not significant in a bass reflex system.

Surely "air pressure" is the same on both systems because IBs must not be completely airtight?

Then, someone smarter than I can probably confirm this from Small's work but I am willing to bet the air load on the cone is the same in both cases except it probably gets weird around the two reflex Z peaks and of course reflex cones are unloaded at VLF.

Dave.

[AdiT]

In a sealed system air pressure has an influence, but is not significant in a bass reflex system.

Surely "air pressure" is the same on both systems because IBs must not be completely airtight?

Then, someone smarter than I can probably confirm this from Small's work but I am willing to bet the air load on the cone is the same in both cases except it probably gets weird around the two reflex Z peaks and of course reflex cones are unloaded at VLF.

Dave.

On a Dynaudio BM9S II and a Genelec 7060 the driver has same dimension, 10 inch, the cone has to do with the same compression ?

This can be clarified with a simple test, take a small bike air pump, once try to move the handle with the hole close and once open.
This is why a sealed system will always have a better return time in position 0, than any bass reflex system.

[ef37a]

In a sealed system air pressure has an influence, but is not significant in a bass reflex system.

Surely "air pressure" is the same on both systems because IBs must not be completely airtight?

Then, someone smarter than I can probably confirm this from Small's work but I am willing to bet the air load on the cone is the same in both cases except it probably gets weird around the two reflex Z peaks and of course reflex cones are unloaded at VLF.

Dave.

On a Dynaudio BM9S II and a Genelec 7060 the driver has same dimension, 10 inch, the cone has to do with the same compression ?

This can be clarified with a simple test, take a small bike air pump, once try to move the handle with the hole close and once open.
This is why a sealed system will always have a better return time in position 0, than any bass reflex system.

Sorry, simplistic tosh. Bike pumps are "DC" speaker systems don't like that. Then again, never saw a furking great magnet on a bike pump?

The poor transient performance of many reflex systems is due to poor design. The really good expensive ones are fine as Hugh has attested in reviews.

Dave.

[Logarhythm]

Surely "air pressure" is the same on both systems because IBs must not be completely airtight?

I'd have thought this is the case in stationary state - otherwise changes in weather, altitude etc would do some very strange things to system behaviour. Not so sure in a dynamic scenario though - under these conditions, is it not the case that the sealed cab is supposed to have a ΔP w.r.t. to the outside, i.e. the rate of "leaking" is very slow compared to δp/δt in in actual use?
Otherwise it would effectively be a sh!tty sort of comprise, with far less of the damping inherent to IB, and none of the "extra" bass of a true reflex design.

With the cone in an IB cab on an inward stroke, my understanding is that the momentary increase in pressure within the cab happens faster than the cabinet would "leak" air and stabilise with respect to external pressure, and similar on the outward stroke where there is a negative pressure differential with respect to the outside. Is it not in part due to this force that IB can potentially provide such good time-domain accuracy?

There is a great temptation to get experimental and pour flour all over the outside of my monitors and crank up some "phat beatz" to see how much the cabs do/don't leak! (Although as they're probably ~25 years old it may not be that conclusive anyway...).
Can someone more learned in the art of speaker design offer any input please, before I cover my lounge in baking ingredients?

[AdiT]

In a sealed system air pressure has an influence, but is not significant in a bass reflex system.

Surely "air pressure" is the same on both systems because IBs must not be completely airtight?

Then, someone smarter than I can probably confirm this from Small's work but I am willing to bet the air load on the cone is the same in both cases except it probably gets weird around the two reflex Z peaks and of course reflex cones are unloaded at VLF.

Dave.

On a Dynaudio BM9S II and a Genelec 7060 the driver has same dimension, 10 inch, the cone has to do with the same compression ?

This can be clarified with a simple test, take a small bike air pump, once try to move the handle with the hole close and once open.
This is why a sealed system will always have a better return time in position 0, than any bass reflex system.

Sorry, simplistic tosh. Bike pumps are "DC" speaker systems don't like that. Then again, never saw a furking great magnet on a bike pump?

The poor transient performance of many reflex systems is due to poor design. The really good expensive ones are fine as Hugh has attested in reviews.

Dave.

The discussion has deflected from the title.
Anyway, read especially the page 3 from the Genelec document "An Insight into Subwoofers" that you'll find on the end of the page from the link http://www.genelec.com/learning-center/key-technologies/lse/

All the best

[Wonks]

This is why a sealed system will always have a better return time in position 0, than any bass reflex system.

What is 'better'? Faster? Faster does not always mean better. The speaker is supposed to be duplicating the electrical signal provided to its voice coil.

As I see it, there are 4 steps in loudspeaker movement. For a sealed enclosure and starting from the neutral position 0 we have

1. Speaker moves forwards from 0. The air in the enclosure becomes slightly negatively pressurised (and its temperature drops slightly). The further forwards it moves, the greater the negative pressure and hence greater resistance to it moving forwards, slowing the cone's excursion slightly.

2. Speaker returns back to 0. The negative pressurisation of the cabinet in this phase means that the speaker cone is moving slightly faster than under magnetic power alone.

3. Speaker moves backwards from 0. The air in the enclosure becomes slightly positively pressurised (and its temperature rises slightly). The further backwards it moves, the greater the positive pressure and hence greater resistance to it moving backwards, slowing the cone's excursion slightly.

4. Speaker returns back to 0. The positive pressurisation of the cabinet during this phase means that the speaker cone is moving slightly faster than under magnetic power alone.

So there is a slight 'slewing' effect on the sound wave produced compared to the input wave, a bit like capacitance does in signal cables.

A similar sized ported enclosure speaker still has to try and move the same volume of air as the sealed enclosure speaker, but without such large positive and negative pressure factors.

I have absolutely no idea of the magnitude of this effect and whether it is at all measurable in real-world conditions. But please don't confuse 'faster' with 'better' without taking all other factors into consideration. Sometimes it is, and sometimes it isn't.

All speaker designs are compromises. The art and the science of speaker design is to make the best compromises you can to get the best sounding speaker (for the application) at a given price-point.

[AdiT]

Thanks for the idea with the BBC paper, I haven't find yet the doc Ls2,
but I found and read others from BBC paper, from here http://www.bbc.co.uk/rd/people/h-d-harwood

[Hugh Robjohns]

Never mind all this poncy and expensive rare-earth magnet stuff...

Given that most studio and stage speakers are now powered, why not revert to using 'field-coil' speakers like they did in the 1930s? (using a mains-powered energising solonoid coil to generate the required magnetic field). You could then have as much flux as you wanted, and with a negligible weight penalty! Yes, it would take a bit more power, but only when it was running...



H

[IvanSC]

So anyway.

Objectively AND subjectively there may well be slightly less perceived bass from the neos.
My 2x10 cabinet previously had Ashdowne bluecone speakers in it and they were wimpy and flabby but DID have a fair bit of bass.
Along with poor power handling and an assortment of other nastiness.

The neos, besides being light, can put out way higher clean spl, so in order to even out bass response, I use this ground-breaking method I just discovered.
Turn up the bass EQ on my amp.

I know this is a simplistic approach and that I could actually get far better results from a better quality purpose-built cabinet for the neos, but realistically I am up and running for £140 the pair & can now compete with the piano and guitar that are run through the PA.
I am not.

AND it doesn't break my back carrying the thing.

We will now return you to our normal programming, "Wot I lerned in fizzicks clarse"

[AdiT]

This is why a sealed system will always have a better return time in position 0, than any bass reflex system.

What is 'better'? Faster? Faster does not always mean better. The speaker is supposed to be duplicating the electrical signal provided to its voice coil.

As I see it, there are 4 steps in loudspeaker movement. For a sealed enclosure and starting from the neutral position 0 we have

1. Speaker moves forwards from 0. The air in the enclosure becomes slightly negatively pressurised (and its temperature drops slightly). The further forwards it moves, the greater the negative pressure and hence greater resistance to it moving forwards, slowing the cone's excursion slightly.

2. Speaker returns back to 0. The negative pressurisation of the cabinet in this phase means that the speaker cone is moving slightly faster than under magnetic power alone.

3. Speaker moves backwards from 0. The air in the enclosure becomes slightly positively pressurised (and its temperature rises slightly). The further backwards it moves, the greater the positive pressure and hence greater resistance to it moving backwards, slowing the cone's excursion slightly.

4. Speaker returns back to 0. The positive pressurisation of the cabinet during this phase means that the speaker cone is moving slightly faster than under magnetic power alone.

So there is a slight 'slewing' effect on the sound wave produced compared to the input wave, a bit like capacitance does in signal cables.

A similar sized ported enclosure speaker still has to try and move the same volume of air as the sealed enclosure speaker, but without such large positive and negative pressure factors.

I have absolutely no idea of the magnitude of this effect and whether it is at all measurable in real-world conditions. But please don't confuse 'faster' with 'better' without taking all other factors into consideration. Sometimes it is, and sometimes it isn't.

All speaker designs are compromises. The art and the science of speaker design is to make the best compromises you can to get the best sounding speaker (for the application) at a given price-point.

if we have a drummer that strikes the drum once, we have 4 stroke? the drum creates pressure on the microphone only when it hit

if coil loudspeaker makes a shift from 0 - 10 and takes place next shot when the coil is on 3, counts the speed of return?

Tony Royster Jr. is my favorite drummer

[AdiT]

A large part of today manufacturers focuses too much on marketing, the professionals do not need too much advertising, because if you want quality you can buy only from them.

[ef37a]

Never mind all this poncy and expensive rare-earth magnet stuff...

Given that most studio and stage speakers are now powered, why not revert to using 'field-coil' speakers like they did in the 1930s? (using a mains-powered energising solonoid coil to generate the required magnetic field). You could then have as much flux as you wanted, and with a negligible weight penalty! Yes, it would take a bit more power, but only when it was running...



H

I guess you ARE joking Hugh? Maybe you are not quite old enough to remember LS field coils? Big they were even for domestic speakers and heavy (copper is denser than steel and probably Alnico?)and you still needed the same iron magnetic circuit.
They consisted of 1000s of turns of very fine wire (around 32G IIRC)and got hot! They were also rather prone to o/c'ing!

But, back to cabs and transients: The work was done in the early 70s in a series of papers published in the AES journal by R.H.Small. I did not understand the math then and certainly won't now but I am sure the likes of Hugh, Dan and Seablade could grasp it but it would require a serious commitment over a day or more, time such people do not have I am sure.
Nonetheless, the conclusions that Small draws re bandwidth, cab V, flux D, sensitivity, power handling etc still hold today unless anyone here knows of a challenge?

One modern change? We can now take amplifier OPZ as buggerall compared to voice coil resistance.

(Oh!And bike pumps don't have voice coils and are not therefore part of the amplifier/speaker "system")

Dave.

[Logarhythm]

The work was done in the early 70s in a series of papers published in the AES journal by R.H.Small.

Anyone have a link to these, or a rough idea what original titles / publishing dates might have been so I can try to find please? Am now curious

[Wonks]

There's this: Thiele Small analysis

[ef37a]

The work was done in the early 70s in a series of papers published in the AES journal by R.H.Small.

Anyone have a link to these, or a rough idea what original titles / publishing dates might have been so I can try to find please? Am now curious

I have the original journals (I hope I can find them all). Would I get a visit from the AES heavies if I did a scan?

Or:http://www.aes.org/e-lib/online/search.cfm

It is the Small Signal Analysis you want.

Dave.

[Logarhythm]

Thanks Wonks, looks interesting.

Dave - That's a very kind offer, thank you. Doesn't look like it's necessary though, as various papers appear to be included in the references on the link from Wonks, and with the titles/dates from these the first few I've checked have been easy to locate via google.
Now just got to find time to read it all!

Edit: Dave, saw your edit after I'd posted, thank you. Found e.g. this online already.

[Hugh Robjohns]

I guess you ARE joking Hugh?

I used a handy visual aid which I think answers that...

H

[Logarhythm]

I used a handy visual aid which I think answers that...

Appreciate it's (still) miles off the original topic, but have to ask - do you think it's actually a flawed concept, or could you see merit to it if the materials/technology could support it?

Last time I was playing (erm, busy taking important measurements...) with superconducting solenoids I wondered whether I could rig them to drive some sort of rudimentary subwoofer.
There are obviously challenges relating to DC vs. an AC input signal, and it's hardly practical, or cheap, or energy efficient, and potentially quite dangerous, but aside from the many drawbacks it seemed like a great idea - mostly due to being able to pump out around 13 Tesla fairly comfortably

Being able to generate relatively high B field flux (or indeed the the exact strength required in any given situation, by varying input) would potentially have some merit, if it could be done using lightweight room-temp superconductors?
Suppose I may answer my own question once I've eventually read through all the bits that Wonks and Dave pointed me towards

We will now return you to our normal programming, "Wot I lerned in fizzicks clarse"

Erm, yes, oops. Sorry!

[Hugh Robjohns]

Appreciate it's (still) miles off the original topic, but have to ask - do you think it's actually a flawed concept, or could you see merit to it if the materials/technology could support it?

It's not a flawed concept at all, and it only became obsolete (in convemtional speakers) in the late 30s when better magnetic materials were developed during WWII. Funnily enough, Peter Thomas (PMC) mentioned the subject to me a couple of years ago as a technology he was interested in developing.... And I suspect there are applications where this kind of technology could become cost effective again.

H

[ef37a]

Blast yer eyes Logs! I was going to josh Hugh with superconductors (you REALLY get to work with them?G.R.E.E.N! And highly impressed!)

But I seem to recall reading that the pole tip are already close to saturation with the strongest PMs?

Dave.

[Folderol]

But I seem to remember reading somewhere that you can't saturate a superconducting magnet. It doesn't need a core.

[vinyl_junkie]

I remember few years back Tony Andrews of Funktion One said there was a bit of a shortage of Neodymium caused by the car industry (electric motors in hybrids and electric cars) which caused the price to sky rocket let alone having enough for the demand

[Logarhythm]

It's not a flawed concept at all...

Thanks Hugh, I did wonder if I was missing something. Should have pressed on and tried to build the superconducting sub while I had the chance!
Now just got to wait for someone to find a material that can maintain the Cooper Pair bonding at a sensible temperature

I was going to josh Hugh with superconductors (you REALLY get to work with them?G.R.E.E.N! And highly impressed!)

I used to, once upon a time. Meant I also got to play with superfluid helium, scanning electron microscopes, atomic force microscopes, e-beam lithography etc.
Now a food scientist - possibly a downgrade from physics research in many respects, but pays the bills a bit more effectively

But I seem to remember reading somewhere that you can't saturate a superconducting magnet. It doesn't need a core.

Yeah, they don't really behave like "normal" magnets (or conductors, for that matter) - generally find that there is a tiny layer of surface penetration, but external B fields are pretty much completely rejected by the bulk of the conductor. You can overcome the effect by applying a strong enough field, but then you generally destroy the superconducting state (the exact way this occurs depends on type of superconductor - can be pretty much an instantaneous threshold, or a transition to a critical point). There are similar limits on current, so you're fine up to a critical threshold (often reasonably large - I'd run at about 100A to generate a 12T field and still have a large safety margin). The danger is when you cross any of these critical limits - superconductors are often pretty poor "normal" conductors, so you suddenly have a massive current in a material with very high resistance, instantly generating huge amounts of heat. Make a great combination with systems that are cooled by e.g. liquid He, which tends to vaporise *extremely* quickly when you apply heat