Tannoy

[julius-6]

Przy okazji, czy wszystkie modele Tannoya z głośnikami współosiowymi - te z wyższej półki, a nie "słupkowe" hybrydy z dodanym głośnikiem niskotonowym - są na magnesach Alnico?

Nie.

[Moriarty]

Szukając informacji o tym, które modele kolumn mają/miały magnesy Alnico, trafiłem na ciekawą rozmowę miłośników Tannoyów. Jest tam poruszony wątek m.in. wojny domowej w Zairze, która najpierw ograniczyła dostępność kobaltu, a potem na stałe już wywindowała w kosmos ceny tego metalu, co wymusiło masowe odejścia od stosowania magnesów Alnico w branży audio począwszy od 1978 roku.

Są też ciekawe praktyczne informacje, na przykład jak łatwo przez przypadek rozmagnesować Alnico - wystarczy dosłownie sekunda. Poniżej wklejam najciekawsze wypowiedzi w tej debacie, a pod spodem wrzucam odnośnik do całości.



From 1947 to 1978 Tannoy Dual Concentric drivers used a metal magnet made from an alloy of nickel,
aluminium, cobalt and iron. Although of great strength this magnet material was not very efficient in
power to weight ratio and difficulty in the world supply of cobalt was generating a problem in
maintaining smooth production at the Tannoy factories in West Norwood, London and Coatbridge in
Scotland.

During the latter part of 1977 the decision was taken by Tannoy to design a new series of Dual
Concentric drive units using Anisotropic Barium Ferrite magnets. This material is more efficient in
power to weight ratio and had a much higher coercive force leading to fewer problems in
demagnetization under high power or low storage temperatures.

New magnet charging equipment was purchased to supply the much higher magnetizing force needed by the
new material. Magnets are supplied unmagnetized to Tannoy so that the magnet can be magnetized with
all its metal pole pieces in place for higher gap field strength. The process of magnetization is
called 'charging' the magnet and takes place inside a heavy coil that generates an exceptionally
strong magnetic field for a faction of a second to align the magnetic domains within the material.

The first unit to emerge with the Anisotropic Barium Ferrite magnet system was a very high power high
sensitivity midrange unit used in the Buckingham and Windsor cabinet models. This unit subsequently
went on to be used in the Buckingham Monitor and, with further modifications in high power music
concert rigs throughout Europe.

From 1978 the pace of research and development at Tannoy increased many times over. A strong
engineering team was assembled at the Scottish factory that was by 1980 the central focus of the
company. A long-term plan was developed that sought to improve every specification of the famous Dual
Concentric units while developing specialist units for varying applications. This was to remove the
inevitable compromise of using only 3 different units in a variety of applications.

(...)

In describing the events behind the switch to ferrite magnets from Alnico, I think we are down to discussing semantics. There is no question that availability is a function of cost. As with everything, you can purchase the "unavailable" if cost is no object.

However, for practical purposes, Alnico magnets were unavailable to loudspeaker manufacturers for a short period beginning in 1978. To my knowledge, all speaker manufacturers outsource thier magnet supply from third parties. In JBL's case, their supplier was Arnold Engineering. In 1978, Arnold informed JBL that they would not be able to supply Alnico magnets in production quantities for the reasons you cited. JBL had no choice but to begin a panic program of re-engineering their bass drivers to use ferrite magnets.

This change was not inconsequential. The first prototype ferrite conversions sounded significantly different from the Alnico drivers they were intended to replace. It took a fair amount of investigation to determine why. The main problem was due to higher flux modulation in the ferrite drivers.

For those who are not aware, flux modulation refers to dynamic changes in the strength of the permanent magnetic field. It is caused by the electromagnetic field generated from currents in the voice coil interacting with the permanent field generated by the fixed magnet. Even at low power levels, this modulation results in distortion. At high levels, it can permanently demagnetize an Alnico driver.

Alnico magnets are conductive and act as a shorted turn to stabilize the permanent field. Thus, this issue is largely mitigated in Alnico designs. Ferrite magnets are not conductive. Therefore, a copper shorting ring was added to the pole piece of ferrite designs to address this issue.

A second problem was the unsymetric fringe flux field generated by the external magnet topology of ferrite designs. The internal magnet Alnicos generally had magnets that were smaller than the pole piece so that they were inherently undercut. This meant that the fringe fields above and below the gap were symmetrical. The initial ferrite prototypes had the gap adjacent to the massive iron pole piece. The permeable pole piece generatied a much higher fringe field below the gap in comparison to above it and this resulted in a nonlinear response. JBL addressed this with an undercut pole piece in their SFG drivers.

JBL had an uphill battle to convince their customers that their final production ferrite drivers were as good, if not better, than the Alnicos they replaced. Part of this was due to their own advertizing. For years JBL had touted the advantages of their Alnico speakers over the "cheaper" ferrite designs of their competitors. The greatest skepticism of the change was in Japan where JBL had a cult-like following for their Alnico drivers.

One of JBL's engineers related to me an interesting anecdote about this issue. He was sent to Japan to introduce their 136H 15" bass driver that was a ferrite conversion of the Alnico 136A driver that was the primary LF transducer in all of JBL's studio monitors and large home systems. He replaced the 136A drivers in a Japanese reviewer's reference JBL speaker. Unexpectedly, the system sounded different.

The reason for the differnce goes back to the subject of this thread - Alnico demagnetization. The 136A's were found to be partially demagnetized. In a ported system, this resulted in around a 3db drop in output in the 200-500hz range. The ultimate low end was not affected since this is governed more by the enclosure tuning and not the direct output from the driver. By equalizing the ferrite driver to have the same response dip as the partially demagnetized Alnico, the overall sonic character of the system was restored.

What is interesting about this anecdote is what it has to say about the prevelance of Alnico demagnetization. You have to understand that speakers in Japan are seldom driven to high levels. The small rooms and lack of soundproof construction in a home environment prevent this. Nonetheless, the reviewer's reference system was definitely demagnetized. The reason was likely a momentary, unintentional power spike sent though the system.

In my twenty years as an audiophile, there have been more occasions than I care to admit where I have done something idiotic and found myself leaping for the volume control. Some of my more stellar moments include yanking out the headphone plug with the volume up, swapping cables with the amp turned on and dropping a tone arm onto a record with the volume set high. With an Alnico speaker, it only takes one idiot moment to partially demagnetize the motor without damaging the coil, cone or suspension. With a vintage speaker, you will never know unless you actually measure the gauss levels in the gap. The sonic difference can be subtle, and unless you have a reference to compare to, you likely won't realize that it has been affected.

I have to admit that with a Khorn, your chances of permanently demagnetizing and Alnico driver are less than with just about any other speaker. That is because its extrordinary efficieny means it is likely coupled to a lower powered amp. Nonetheless, it is not completely immune, and if I were having a driver repaired, I would have it checked for demagentization at the same time.

Tu całość:
https://pinkfishmedia.net/forum/threads/hey-tannoy-is-now-owned-by-behringer.172637/page-4

[Kangie]

Było na forum? Natknąłem się na ten materiał.

[Moriarty]

Rozpoznajesz może, jaki to model?

[Piterski]

Było.

[Kangie]

Rozpoznajesz może, jaki to model?

TANNOY SUPER RED MONITOR SRM-15X

[Lutek]

Tutaj rowniez jeszcze nie pisalem, ze planuje zbudowac nowe - ksztaltowo - inne i nieco wieksze obudowy do Tannoyi HPD 295. Wprawdzie pomalu sie to posuwa ale surowe ramki zostaly juz sklejone, okleinowane, pobarwione i polakierowane,      tak, ze juz sie cos wylonilo na ksztalt kolumienek. A w ogole, to jednoczesnie realizuje dwa projekciki, tzn. rowniez odgrody.
Na poczatku zaczelo sie od pomyslu, pozniej projekcik - rysuneczki - wyciecie ramek, z ktorych wyszlo cos takiego:

[masza19]

Fajne. Ile litrów?

[Lutek]

Ok. 35 albo 37 - nie odejmujac nic na glosnik i zwrotke
Musialbym jeszcze raz dokladnie policzyc, bo z pamiecia kiepsko. Producent (Tannoy) podaje, ze oryginalne Eatony (na tych glosnikach) maja 30 l, choc jak dokladnie zmierzylem skrzynki wewnatrz, to wyszlo mi 27 l.

[masza19]

Lutek, masz może gdzieś w czeluściach dysków twardych schemat zwrotnicy do SRM15x?

[goky]

sąsiad , a tu patrzyłeś
https://www.hilberink.nl/codehans/tannoy37.htm

Pozdrawiam
nowakAudio 8)

[Lutek]

https://www.diyaudio.com/forums/multi-way/234020-tannoy-crossovers.html

[masza19]

Dzięki!

[Lutek]

Moze przyda Ci sie tez schemat prosciutkiej zwrotki, ktora ja zastosowalem w swoich kolumnach z bardzo dobrym skutkiem, ktore przed wieloma laty zbudowalem na takich glosnikach jakie siedza w SRM-ach, lecz 12-to calowych - model 3149. Tyle, ze o ile pamietam,  w filtrze RLC  kondensator 6,8 uF zmienilem na 3 i cos uF - probuj.

[Lutek]

Mam jeszcze pytanie:
Jak u Was wyswietla sie moj nick, bo u mnie zamiast "Lutek", jest: "Lutka". Co ciekawe, tak dzieje sie na ostatniej - bierzacej stronie AM, natomiast na poprzednich, jak iw moim profilu jest ok? O co chodzi ...?

[miniabyr]

Ja widzę cię jako Lutek .

[Lutek]

No fajnie..., do tego jeszcze moj tekst napisany jako odpowiedz wkleja sie z inna trescia !!!
Modyfikuje w tej chwili i ponownie wklejam, choc widze, ze to zdanie wkleilo sie prawidlowo.

[miniabyr]

Cuda panie, cuda . :P

[Lutek]

I to jakie cuda...? Napisalem do moderacji z rzutem ekranu - zobaczymy czy uda im sie cos pomoc, bo jesli nawet nastepuja zmiany w tekscie przeze mnie napisanym po wklejeniu go, to watpie .

[Lutek]

O..., wkleilo sie 'what", zamiast " jakie "

[Melepeta]

U mnie też jest Lutka, ale to wina tego, że przeglądarka automatycznie przetłumaczyła stronę z angielskiego na polski  :o  :o  :o
Po wyłączeniu tłumacza już jesteś Lutek.

[frywolny trucht]

Jak włączyłem tłumacza, mam Lutek ( Lutek), mininiabyr i masza bez nawiasów przy nicku, ale u maszy jest sentencja "nie więcej spawów".
Wygląda, że to będzie  rzeczywiście kwestia tłumacza.

[vasa]

O..., wkleilo sie 'what", zamiast " jakie "

Używasz kompa czy telefonu?

[emoji486][emoji1660]

[Lutek]

Kompa... Wylaczylem tlumacza i jest ok.

[vasa]

Wylaczylem tlumacza i jest ok.

[emoji41]

[emoji486][emoji1660]