Hot Rod 093TI

[NewZenith]

[quote=Robh3606;146084]No that's a first as far as I know. Do you know what the flux density is in the 093 gap??

I have no idea, my guess would be very poor.
NZ.

"Well you don't really know that. Larger pot doesn't always mean higher flux density by itself. An example would be the LE-15 and k-145. Largest pots JBL made howerer lower flux density than say a K 130"

I realize that many things affect the flux density in the magnetic gap, i.e. top plate thickness, voice coil gap, voice coil diameter, magnet size, magnet material, the design of the pot and its efficiency. I realize 112A magnet pots may not have the same level of flux density as your typical compression driver, however I believe it is a safe guess that it is much stronger than the stock 093Ti. I do not believe that simply making the voice coil underhung was responsible for the sizable efficiency gain. If there is someone who can measure the flux density of a stock 093 magnet pot, I would gladly mail it to them with no need for it to be returned.
I imagine that some members here might even know what that particular specification is.
NZ.


"How do you know whats really happening??? You have any measurement capability??"

Well, it's not something I care to brag about. The only acoustical measurement capability I have is a RadioShack analog sound level meter, I use it for crude comparison on pink noise.

"That diaphram has limited excursion capability. I was designed to be used with a tuned and sealed pot structure. There are None avaliable from JBL. If you overdrive it and that fractures the surround your out of luck."

More limited than say a compression driver?
Anyhow I have six more diaphragms if somehow I need them.
If it's traveling beyond its design parameters I imagine it's going to be making higher sound pressure levels somewhere in its audio spectrum. I am not crossing this driver outside its designed range, I am also using 24 dB per octave slopes. If it is resonating so intensely that it is over excursioning then I believe it would sound appalling.
I am well aware that the pot structure is integral part of the driver design, however without proper testing I cannot know what is happening exactly in the resonance department. What I can say is that this driver seems to be behaving extremely well. Regardless I do want to be more scientific in my approach to this hobby. In any case there was no way for me, RTA or not, to know in advance what would happen by using the 112A magnet structure on the 093Ti diaphragm assembly.
NZ.

"You can do a lot more with a lot less money."

Then I will try.
NZ.

[NewZenith]

If you havn't tried it how do you know you dont like it ? Lets have a look please.

I'm going to clean up the cosmetics a little, for example I want to get the proper mounting screws installed and the 093Ti screens rather than the T030 jobs on there now.
Then I will post some pics.
NZ.

[NewZenith]

Here are some photos taken tonight. Hope to have impedance plots tomorrow; I will take a stock 093Ti and run it alongside the modified unit. Hopefully it will do well; I may have to remove the damper will see.

[Robh3606]

Hello New Zenith

Is that the final configuration??? You really need to do something to protect the insulation on the VC wires where it passes through the surrounds. If it chaffs through it will short to the diaphram. Can you get a piece of sleeving down the wire and into the pinholes to keep the wire isolated or pot it. You can't run the wire like the original 093???

Rob

[NewZenith]

Hello New Zenith

Is that the final configuration??? You really need to do something to protect the insulation on the VC wires where it passes through the surrounds. If it chaffs through it will short to the diaphram. Can you get a piece of sleeving down the wire and into the pinholes to keep the wire isolated or pot it. You can't run the wire like the original 093???

Rob

Rob, thanks for the input. I will seal the wires where they go through the diaphram in the near future.
It is not possible for me to route the wires on the underside of the diaphram assembly due to the excess size of a magnet, it would also necessitate irreversible negative modifications to the magnet structures which I am unwilling to sacrifice permanently, I like 112A’s too much to do that. Should cones turn up I will probably try and find some other magnets to use on the converted 093 diaphragms.
With a bit of luck this evening I will be running impedance plots on the composite driver and also on a stock 093Ti/112A /044Ti. I will experiment with the turning of the cavity behind the diaphragm and the homemade damper, which I did not put a photo of because of the five photo limit. I would be extremely interested in what you have to say in regard to the impedance curves and what that might mean in terms of driver performance and health.
Hopefully I can put the results up tonight.
Until then, thank you.
NZ.

[NewZenith]

Ok, well things not turn out as good as I'd hoped, but not as bad as they could have been.
I'm not an expert at interpreting the numbers but I would say it makes sense to me. The first plot is the 093Ti composite. and the second plot is the 093Ti stock with tuning can. Because I did not have enough time I was not able to attempt to tune the composite driver but I'm going to make a rudimentary impedance tester with a resistor volt meter and signal generator.
If I can tune out the resonance bump as did JBL I may consider this project a success.
Note the low resistance increase as the composite 093Ti extends into the higher frequencies, this may be because of the underhung voice coil but I am not sure. I will also test efficiency in the near future.
If anyone has suggestions on how to better tune this driver or how to better evaluate its performance I am all ears.
NZ PS, also note the phase scale for the composite driver is 0 to 50 degrees; it is 0 to 100 for the 093Ti in stock form.

[Robh3606]

What is that a WT2?? How many points on the impedance runs?? Did you do an X Q, FS run or an arbitrary sweep?? You may want to do more points to get a little better resolution. That resonance could be where the added response is coming from. Do you have the dampening ring installed under the diamond surround?? You obviously have a much smaller volume behind the diaphragm. What happens if you unstuff the pole piece vent??

[NewZenith]

What is that a WT2?? How many points on the impeadence runs?? You may want to do more to get a little better resolution. That resoance could be where the added response is coming from.

Yes, it is a WT2, is that bad? As far as the added response you could be right, but it's too soon to tell, I want to get the driver's response to flatten out before I make any more claims or judgments. As far as points on the impedance run is concerned, it is not my program so I have no idea how to use it. I want to get my own equipment so I can play and take as much time as I need to figure things out.
Yes I did do a X Q, FS run, I have those except I did not want to waste space or clutter things up, if it's helpful I will post them as well.
NZ.

[NewZenith]

Do you have the dampening ring installed under the diamond surround?? You obviously have a much smaller volume behind the diaphragm. What happens if you unstuff the pole piece vent??[/quote]

Well it's obvious you really know your $hitt,
first off you know I do not have a dampening ring installed around the diamond surround because these are old diaphragms and the dampening ring was liquefied beyond reuse.
I thought about making a new one but have not gotten that far yet. If you unstuff the pole piece vent the resonance peaks below 1000K go real ugly, with two distinct peaks, however if I recall correctly phase and output above 1000K look good. I have five plots with different configurations. I also tried adding extra dampening material to the dome but all that did was push up the Fs and put the ugly resonance closer to where I cross. What I want to do is basically what JBL did, put a chamber at the end of the vent, experiment with valium and dampening until it hopefully flattens out. If that works I will do extensive listing test, maybe I can even rent a good RTA until I can decide on one for myself.
By the way this driver measured best with the fiberglass packing in the vent hole, it had to be fairly dense to work. My next concern is want effect does the air valuem trapped between the diamond surround have on things, some energy must be lost as air rushes around the coil into the large magnet pot?
NZ.

[NewZenith]

Stock 093Ti

Q test completed: Wed Jan 31 20:12:15 2007
Q drive current 2389.34 uA
Shunts: No Shunts Used
;------------------------------------------------------------------
Revc 3.997 ohms
Fms 15.503 KHz
Zmax 8.062 ohms
Ro 5.383 ohms
F0 6.085 KHz
F1 16.278 KHz
Fmin 16.131 KHz
Qms 2.160E+00
Qes 2.124E+00
Qts 1.071E+00
Le 75.472 uH @1k
XLe 4.677 ohms @1k
PLe 5.819 Degrees @1kHz
;------------------------------------------------;
; Approximate Impedance Fitting Constants ;
; (Improved with Completion of Vas Test) ;
;------------------------------------------------;
Krm 0.000E+00 ohms Freq dependent resistance
Erm 0.000E+00 Rem=Krm*(2*pi*f)^Erm
Kxm 15.034E-06 Henries Freq dependent reactance
Exm 1.129E+00 Xem=Kxm*(2*pi*f)^Exm, Lem=Kxm*(2*pi*f)^(Exm-1)

[Robh3606]

Hello New Zenith

These are 2 runs I ran with an 093ti today. The first is the driver as is. The second is without the can with the back of the driver open. You can clearly see the resonance peaks without the can in place. It does not look anything like the measurements you did on your hybrid. There is obviously more going on than just loosing the back can dampening on the resonance peaks. I didn't know if the pad was there or not. In the driver I tested it's still there and if I remember right it's got a sticky back so it's glued in place to the frame. It's a white foam and was still quite flexible. No real signs of deterioration.

Rob

[NewZenith]

I tried the stock 093Ti with the can removed as well, but my foam pad was not glued in place.
Without the pad the driver behaved very closely to the composite. My guess is that this type of driver must stay acoustically loaded through its resonance, somehow the foam pad directly behind the magnet pot has a lot to with it.
I'm going to be making some measurements to find out exactly how I have affected the air volume behind the diaphragm; as you had gassed Rob the volume behind the composite 093's is less than with a stock 093. In one regard because I have not kept spacing from the magnet exactly the same, this I can correct with a gasket of the appropriate thickness.
Here is the impedance plot taken with a stock 093 diaphragm with its tuning can and padding removed, it looks nearly identical to the composite drivers behavior.

[WTPRO]

A hint on using the WT2 if you want to measure the TS of mids and tweets.

- Without Rem/Xem measurement and modeling, phase will never cross zero. (Got version 2.0 sw?)

- It looks like you are using the supplied test leads. Inductance will change quite a lot at this scale. You may want to make a set of test leads using ZIP cord to keep the wire spacing constant.

- The 1 pt Rem/Xem method should work well here

- If Rem/Xem is found properly, the sweep starting from the bottom will look for the first zero phase crossing (after subtracting Rem/Xem effects). If SweepLo is set too low, this could happen sooner than expected. Raise SweepLo.

- The double hump could also cause some fits, but from the plots I see it looks like the algorithm should find the first hump.

- The sweep step rate can leave a few of those jaggies. You can add more 'points of interest' using the left and right mouse button to set the test frequency and then add the data point. This does not affect the test results. It is just to beutify the plot.

Hope this helps,
WTPro

[NewZenith]

Thank you kindly for the input WTPRO.
NZ

[bldozier]

is your driver dead.