RCA MI9584 mid/hf drivers

[Rajiv]

Hi,

A couple of months ago I lucked into a pair of RCA MI9584 drivers. I have been on the look out for these drivers for several years. Though I came across many, none had the original diaphragms.The RCA diaphragms are next to impossible to find and if available cost an arm and a leg.

Out of the blue one of my sources mentioned that a pair was available , and that the diaphragms were original. I took a chance and asked him to get them for me without seeing the actual drivers..

Apart from 50+ years of dust,screen paint overspray and grime they are in very good condition. the drivers are huge,luckily RCA provided handles to carry them around.

The RCA MI9584 and variants were the post war permanent magnet mid/hf drivers of RCA's cinema sound systems. The RCA drivers are arguably some of the best permanant magnet midrange drivers ever produced .They are designed to work from 300-8000hz. and use a phenolic diaphragm. For hifi use a tweeter is mandatory.

I plan to use these drivers to cover the range from 300-5000hz. Eliminating a crossover point in the midrange.

Lot of information about these rare drivers on the net.

rca mi 9584 - Google Search

Test driving the drivers with just a 16 mfd capacitor and without any horn.

MOV04682 - YouTube

MOV04683 - YouTube

Now to build/get the right horns for these drivers.

Regards
Rajiv

 

[quad]

WoWW! How on earth do you manage to get all these exotic stuff.

 

[anilva]

Shouldn't you test with some horn loading to avoid burning the drivers. I see bare drivers connected...

 

[Rajiv]

Hi,

Shouldn't you test with some horn loading to avoid burning the drivers. I see bare drivers connected...

Anil,I used a capacitor to block/roll off frequencies below 700hz,but you are right without a horn the chances of driver damage is very likely. I tried it for a little while at low volume to get a feel of the driver's sound.

I have to say they sound very good.

I have a 500hz conical around but have to drill new mounting holes as the existing ones are for the Altec 288.

Regards
Rajiv

 

[viren bakhshi]

Hi Rajiv,

Maybe a contradiction in terms, but this vintage stuff really is exotic!

Now, to find room for the big horns to do these drivers justice! No crossover in the entire midrange - that's quite the ideal. You have to do it.

Regards,
Viren

 

[Rajiv]

Hi,

Maybe a contradiction in terms, but this vintage stuff really is exotic!

Now, to find room for the big horns to do these drivers justice! No crossover in the entire midrange - that's quite the ideal. You have to do it.

Viren, how is the 400hz LeCleach progressing? Hoping to use them with the Altec and RCA's. With the rupee going south importing big horns is a very expensive proposition.

The old theater multicells can be had for little money but they are just too big and impractical at home.

Having no crossover in the entire midrange is something I have been wanting to do for a long time. These RCA drivers will allow me to do that.

Regards
Rajiv

 

[captrajesh]

Congrats on the acquisition. Evidently they have been taken out from an old movie theatre.

@Anilva & Rajiv
Since precautions are taken so that no LF content reaches the drivers and also since by limiting the volume it is ensured that they are not over-driven, how would the drivers get damaged without the horn? Pardon my ignorance.

 

[ranjeetrain]

Good stuff!

I have only seen (heard) these (similars) in old movie theaters. Wait for the build patiently.

 

[Rajiv]

Hi,

@Anilva & Rajiv
Since precautions are taken so that no LF content reaches the drivers and also since by limiting the volume it is ensured that they are not over-driven, how would the drivers get damaged without the horn? Pardon my ignorance.

Capt, the driver won't be damaged if you run it within its limits, but its limits have drastically changed. It is missing the acoustic loading it is designed for .Compression drivers are designed expecting the front air load to damp its excursion a bit, so the diaphgram excursion at the bottom of the band will increase a lot with no horn. Over excursion will cause the driver to eventually break the suspension,or voice coil leads.

I used a simple 6dB filter. There is still significant energy till around 200 hz, enough to cause driver damage due to over excursion if the volume is increased.


Regards
Rajiv

 

[captrajesh]

Compression drivers are designed expecting the front air load to damp its excursion a bit, so the diaphragm excursion at the bottom of the band will increase a lot with no horn. Over excursion will cause the driver to eventually break the suspension,or voice coil leads.

Thanks Rajiv, this is certainly an unknown piece of information for me. Learnt something new today.