2470 Franken drivers

[GoldcountryJim]

I've been all over the forum looking for information on what to do with 2470 drivers without diaphragms. The general answer seems to be the original phenolic ones are discontinued, install 2425h diaphragms. This has me wondering:

1) How will the different BL affect the sound? The 2470 motor is 19,000 Gauss and the 2425 is around 17,000.

2) What are phase plug differences and how might that affect the frequency response? 2425 is 800 hz to 20,000.

I understand there are limited options with drivers like these. The drivers were free and in pretty bad shape when I got them, dirty, missing screws and terminals. I cleaned them up and put them aside for years. They've been handy at filling empty shelf space. Its time to do something with them, but it just raises a lot of questions about what the result will be.

Any input would be helpful. Maybe someone who has installed the 2425 diaphragms could chime in.

[grumpy]

For $80/ea, a pair of radian dias will make those cores usable again. A bit more for titanium from JBL.
Regardless, the phenolic drivers didn't warrant a impedance control ring on the pole piece to extend the
frequency response, so I wouldn't expect them to turn into 2420 or 2425 equivalent drivers, but maybe
close enough, depending on your application (i.e., might need a tweeter).

[GoldcountryJim]

Thanks for the reply grumpy.

This helps with my expectations. It'll be short on the high end.

I'm planning to use these, for a while, in a man cave setup. I scored some 2226's in very good condition for mid-bass, am hunting for 2241's or something for subs, mids and possibly a tweeter. I've got a driverack px, but will upgrade to the driverack PA and run 3 way from crown x1000/xls 1002's. Something that could cover mids and highs would be good.

So, I was looking at the 2470's and thinking mids and highs. I know I will want to upgrade at a later date. I would have to push the xover to 800 or above, which doesn't fit perfectly with the 2226's. It would be an ongoing project. I'm still relatively young! LOL

I actually have some Radians in my 2410's and could upgrade those to free up the Radians. I had been thinking of that anyway.

Thanks again. This should get me going.

Jim

[speakerdave]

According to the data sheets the 2420 and the 2470 both have the silver ring.

[GoldcountryJim]

SpeakerDave,

You're right! Its right there on page one of the literature, just waiting for me to read it. Actually, I did read the sheet, but the part about the silver ring didn't really register. I'll be doing some more reading.

I'll probably have to run a sine wave sweep and see what it can actually produce in the higher range. I'm curious to see how the stronger motor will affect the lower range as well. Its about 4000 Gauss bigger than my 2410's and it will be interesting to see how the Radian diaphragms behave. Testing will be a bit crude. I'm planning to run pink noise and record with RTA into Pro Tools 12, then run frequency/spectrum analyzer. The preamps tend to color the signal, but it should be good "ballpark" data. If I get anything useful, I will post it. I'll have to get new diaphragms for the 2410's first. I can try both diaphragms, just to get a reference.

Now I'm excited to see what I get! It will take a few weeks for the new diaphragms.

Thanks,

Jim

[grumpy]

Always happy to be corrected
May have had 2460 on the brain (shrug). Seems odd they’d bother trying to extend response with a phenolic diaphragm, but looking forward to your result.
Maybe someone can confirm or debunk same motor/plug was in common to both 2420 and 2470? both being 19000 Gauss.

[GoldcountryJim]

Ian,

What you are pointing out makes sense. With the correct EQ, the hi frequency range may be extended out, possibly and hopefully, to the frequency range I'm aiming for. This is for the driver output. The horn selection is the second part that determines what I'm actually going to hear and the sound field. In reading the articles, the 2344 may provide a single compression driver solution, as it was designed as a two-way component. The 2307/2308 has a higher directivity and will roll off so that I need a UHF driver. I also noticed that the vertical alignment of the woofer and 2344 driver are closer, which may help with phase alignment. The 2344 was designed as a studio monitor, if I'm reading this right, and that means near field. This is not good or bad for me, just part of the trade offs. Much to think about.

I also read JBL Technical Notes Vol.1, No.8 focusing in on the differences of the 2" diaphragms vs 4" diaphragms (2445/2446's). This was pretty enlightening on the second and third harmonic distortion differences between the two sizes. I've worked with the 2445's on 2380 horns and compared them, subjectively to my 2" diaphragm drivers. The 2445's do have a "clarity", but I always attributed it, incorrectly, to the 2380's rapid expansion/lower distortion. I'm left wondering if it will be inevitable that I upgrade to 2445/2446's on this project in the future.

I have to assume the rapid roll off on the plots is the mass break-point frequency and -6 db/octave drop above that point. This is really interesting to me, as I am targeting a flat response. What constitutes a "studio" monitor "flat" versus listening "flat" may be subjectively different. The Driverack could store both as presets, which would be pretty cool. I'm going to have to look at what the cut/boost limits are in the Driverack. I do a little home recording with Pro Tools and I could see a use for this.

The Driverack PX has one crossover built in, though its really supposed to be used for the sub/main feed. I could use this if I go with the 2344's and have something (two way) that I can implemented quickly and then build on later. Its actually a pretty robust xover, but I don't think it has the ability to set a delay/phase correction. I'll have to explore it.

I'm also still reading up on why 1" throat drivers are not as good on Smith horns. Enquiring minds want to know.

I've got to thank everyone for the input. My brain is full and I'm going to bed!

[Ian Mackenzie]

One question

What are you planning on using your system for?

Home theatre?

If you plan to start off and use the 2470 cores then 2344 is a good entry point and can operate down to 800 hz.

What you learn from that can be applied to something more ambitious

Another option is this horn for a 1 inch driver

Elsewhere on the forums this thr as investigates some horn
Horns including a 1 inch horn here

http://www.audioheritage.org/vbullet...50-vs-PT-F95HF

[Ian Mackenzie]

I've been all over the forum looking for information on what to do with 2470 drivers without diaphragms. The general answer seems to be the original phenolic ones are discontinued, install 2425h diaphragms. This has me wondering:

1) How will the different BL affect the sound? The 2470 motor is 19,000 Gauss and the 2425 is around 17,000.

2) What are phase plug differences and how might that affect the frequency response? 2425 is 800 hz to 20,000.

I understand there are limited options with drivers like these. The drivers were free and in pretty bad shape when I got them, dirty, missing screws and terminals. I cleaned them up and put them aside for years. They've been handy at filling empty shelf space. Its time to do something with them, but it just raises a lot of questions about what the result will be.

Any input would be helpful. Maybe someone who has installed the 2425 diaphragms could chime in.

I am using 2470 cores with 2425 diaphragm

They are fine.

If you look closely the difference in spec is 117 dB versus 118 dB plane wave tube

Depending on prior use the age of the driver being alnico is possibly going to impact on the bl

Clean them up that’s s what l did and see how you go

Get all the dust and dirt out of the gaps.

For religious reasons l prefer alnico over ferrite compression drivers

I can post a FR response if you want on a 2307/2308

[grumpy]

Thanks Ian. I’d be interested in your 2307/8 plots when you have time.

[Ian Mackenzie]

On the weekend.


Of course a new diaphragm always sounds better than an old fatigued diaphragm...Lol.

I had to really clean them out to get them working but they are good now.

Maybe we should find Ken’s cleaning post?

I think it was double sided tap, a solvent clean and compressed air?

Then the diaphragm alignment. That’s the tricky bit as sometimes the holes needs a slight ream out to centre in the gap.

Then check the pad on the back plate.

That stuff matters

[GoldcountryJim]

Ian,

The PT's are an option. They certainly are easy on the pocketbook! I think the stx825 horn (JBL part #5006815) at Reconing Speakers is the 1" horn.

I checked out Jammin Jersey and he has some 2344's. It was difficult to know the condition.

Its a little harder to find 2307's.

I came across JBL/Selenium, which has some horns. Some are plastic, some aluminum. There's some discussion on the forum of the HL 14-50 as being similar to the 2311. The JBL/Selenium HL 14-25 is a 1" conical horn that may be based on the 2307. However, its ABS plastic or similar material. I didn't find much information on them other than you can get them for about $6. LOL

[ivica]

Ian,

The PT's are an option. They certainly are easy on the pocketbook! I think the stx825 horn (JBL part #5006815) at Reconing Speakers is the 1" horn.

I checked out Jammin Jersey and he has some 2344's. It was difficult to know the condition.

Its a little harder to find 2307's.

I came across JBL/Selenium, which has some horns. Some are plastic, some aluminum. There's some discussion on the forum of the HL 14-50 as being similar to the 2311. The JBL/Selenium HL 14-25 is a 1" conical horn that may be based on the 2307. However, its ABS plastic or similar material. I didn't find much information on them other than you can get them for about $6. LOL

HI JIm,

I think that for 1" driver you have to use
http://reconingspeakers.com/product/...ns-338800-001/

horn, as STX825 / 815 horns are 1.5" horn throat.

Mentioned HL-14-50 is 2" throat horn, but a kind of 2308 like lenses have to be applied to prevent beaming. The same would be for HL 14-25 as i it is 1" throat horn.....

regards
ivica

[GoldcountryJim]

Music listening and home theater will be the primary use. Mixing and reviewing recording tracks would be a pretty small part of it. My experience has been that studio monitors reveal more about the recording process and content, while listening systems tend to be more "musical". I suppose its about psycho acoustics and whether you perceive a true flat response as "natural".

With regard to the difference I'm hearing between 2" and 4" drivers, I should be cautious of ascribing sound differences to particular causes. There's a lot of factors that could be involved. I do hear a difference, but it could even be the different rooms that I'm hearing. I am trying to be more methodical in analyzing these things.

I'll read the linked material tonight. I remember seeing something about those horns in my readings.

Thanks!

[GoldcountryJim]

Earl,

That's really good information! I had a moment of enlightenment about the "potato masher" horns in there. It starts to make sense, but also spawns so many questions like: Can you shape the waves differently to improve the stereo image? Why did JBL choose a V notch rather than a curve on the 2308? Could I filter particular frequencies by changing the lense plate (2308 style) density?

This is going to be more interesting than I expected. I was thinking of the 2308 as more of a directional device.

I think my question of plate spacing remains. I'll keep digging.