Ae IB15 Dipole x

[Beau]

Hi all,

Anyone have an idea of how high these drivers can be crossed before they run into problems? I know the old ones (Lambda) were capable of going pretty high but these versions no longer have the phase plug.
Beau

[ThomasW]

Probably the best thing is to contact John J and ask him your question

[AJINFLA]

Hi Beau,

I doubt very much a phase plug will have any effect on a 15" subwoofer's FR. It's going to get directional at frequencies (500hz-ish) way below where it would have any effect and is largely cosmetic IMHO. Does look pretty cool though :T . The on axis may extend (straight) up a bit, but you probably don't want to actually use it up too high, unless you want your off axis to look like a mountain range .


Cheers,

AJ

[JohnL]

I would think it would get directional around 500 as well, but they don't. I think he used some black magic in these. I have TD12s and they don't seem to beam until a lot higher as well. Maybe one day I'll actually measure them off axis...

Lambda 15 Off Axis

[ThomasW]

One recent buyer measured significantly different T/S parameters compared to those posted on the website.

The Le of the 4 drivers he received was 2.906, not the published 1.25. That difference is going to have an impact on the high frequency extension.

This is the reason I suggested contacting John..

[Paul H]

Your mileage may vary ...

For what it's worth, here's a measured on-axis frequency response made using JustMLS, with two drivers mounted in a large dipole baffle as shown in this thread:

Dipoles sorta like bob/arvo




There is no crossover or equalization applied to these; smoothing is applied at 1/6th octave.

I would expect greater extension on the low end in any sort of box rather than the dipole setup these are in.

This frequency response doesn't tell you anything of course about beaming, distortion at higher frequencies, etc.

Paul

[AJINFLA]

It certainly has good extension/off axis for a 15" driver, but again

know the old ones (Lambda) were capable of going pretty high but these versions no longer have the phase plug.

I don't believe having or not having the phase plug will be an issue anywhere near where you would cross the driver (I would say 1k - max ). It looks cool and could also serve as a heat sink, but that should be the least of Beau's concerns. Unless of course the rear vent is too small and creates aerodynamic noise (dipole use), but that's also curable.

Cheers,

AJ

[ThomasW]

The drivers that are currently shipping may not be close to what Paul has.

Here are the measured T/S parameters from one of the most recent shipments. 4 drivers measured this way. The numbers in ( ) are the published specs. We're awaiting comment from John about this.....


fs 32.24 (16)
Qms 4.43 (4.9 )
Qes 1.2773 (.48 )
Qts 1.0201 (.44)
VAS 190.57 (467)
Re 5.50 (5.6)
Le 2.906 (1.25)
Mms 132.63 (218 )
BL 10.743 (16)

[Scott Simonian]

Woah! Those are way off! These were always cool low-cost drivers. It's almost like these are new drivers made for some other application. Now I think I changed my mind on these.

I sure hope all these other companies aren't doing the same thing.

[ThomasW]

I don't want to start a panic.

John J is handmaking drivers to order, so it's not a running change in someone's production cycle.

These results are from one of the "Cult" members who ordered 8 IB15"s, he tested 4 drivers several times.

He used the sometimes suspect PE Woofer Tester I for these measurements. He states he's measured a hundred or so drivers and not seen variations like this.

He's trying to contact John J. (not all that easy these days) for comment. It's possible there was some screw up with his particular drivers, and that won't impact other purchases, but we just don't know.....

[Paul H]

Thomas is right about the AE IB15's I have - the newer ones may be different.

I received mine this spring, and they are some of the very last ones John was making with phase plugs.

Paul

[ThomasW]

John J posted this reply to the "Cult" thread where the oddball T/S parameter info was first posted.

Re: IB15 measurements?
« Reply #8 on Today at 9:27am »

--------------------------------------------------------------------------------
I see a few things that cannot be right. First off, Mms cannot be measured correctly. The physical mass of the cone should be about 100grams, plus the coil around 65, plus half surround, spider, glue, dustcap, plus the loading. Mmd should be a little less than Mms because it is the physical weight only.

Also, Vas is much stiffer than it should be. The spiders do have a very stiff ring of resin on them towards the middle, but that shouldn't affect things that much. My initial guess is that the method(delta mass) to measure Vas and Cms was a mass added method. This is often not very reliable. If mass moves at all it will greatly throw off the measurements. Both with the woofer tester and with praxis I used to get erratic results. A much more reliable method is the delta volume where you take measurements in different known volumes.

Although everything looks off by a lot, putting the Mms in the approximate range it should be in shifts parameters back to where it should be. Cms being about .44 instead of the .19 that it measured at shifts everything else dead on. Both of those parameters would be wrong together as I said if the mass added method wasn't right. The mass as measured cannot be correct because the parts alone weigh much more than that.

In regards to the Le measurement, this is about the most difficult thing to measure. Le is different at all frequencies. It depends where you take the measurements. Madisound specs Le at 1Khz and 10Khz. Neither of them is at all useful for a subwoofer really. If you take a meter and actually measure Le across the terminals you should measure pretty close to 1.25mH.

John

[Paul H]

If you take a meter and actually measure Le across the terminals

Don't most meters measure impedance somewhere around 1000 Hz?

Paul

[Beau]

So after all, I think my question has been answered. I was planning on crossing at around 250-300HZ, so I should be fine. Would these drivers have any major dis/advantage over TC12'S?
(other then outright displacement)
Beau