Null and Void at 630 and it Hertz!

[Robh3606]

Hello Toddalin

Are you sure they used JBL cone kits when they re-did these?? The reason I am asking is the free air peak that Ian is asking about, but it could be the way they were held when you ran the sweeps. I can run one of my 2235's in the 4344 cab just to see if I get any peaks in the same range when I get home from work.

Rob

[Ian Mackenzie]

Hello Toddalin

Are you sure they used JBL cone kits when they re-did these?? The reason I am asking is the free air peak that Ian is asking about, but it could be the way they were held when you ran the sweeps. I can run one of my 2235's in the 4344 cab just to see if I get any peaks in the same range when I get home from work.

Rob

Hi Rob,

That could be but the data had aclassic bass reflex impediance peaks and the tuning was right on 29 hz.

If another oppoortunity arises the impediance run should be with the woofer mounted in the box without the crossover connected.

Ian

Ian

[toddalin]

Hello Toddalin

Are you sure they used JBL cone kits when they re-did these?? The reason I am asking is the free air peak that Ian is asking about, but it could be the way they were held when you ran the sweeps. I can run one of my 2235's in the 4344 cab just to see if I get any peaks in the same range when I get home from work.

Rob

Yes, OCS used real JBL cone kits.

[Ian Mackenzie]

Hi Todd,

I need to know where the compression driver top place is ie the diaphragm relative to the front panel.

[toddalin]

Hi Rob,

That could be but the data had aclassic bass reflex impediance peaks and the tuning was right on 29 hz.

If another oppoortunity arises the impediance run should be with the woofer mounted in the box without the crossover connected.

Ian

Ian

Been there done that before the recent recharge. Will send you the tests. They also show the impediance hump in the same range.

As an aside, at one time I noted that putting a resistor on the woofer took care of the problem. (Of course most people on this site poo-pooed the idea of using a resistor on the woofer.) I think this helped because the impedience hump became smaller relative to the overall impedience curve.

[Ian Mackenzie]

Todd,

I looked up the horn length and driver details in the Library.

Here is the modified simulation with the woofer and horn out of phase (tweeter also out of phase relative to the woofer).

The first curve is with the mic mid way between the woofer and horn centres.

You can see a much improved crossover function than earlier.

The second curve is with the mic on axis with the horn.

The third curve is the mic on axis with the woofer.

The fouth curve is the voltage drivers with the network loaed by the drivers. As mentioned above I have used purely resistive loads for the horn. The 2235 is from your WT T/L data.

All simulations are with the mic at 2 metres (what would be the minimum listening distance)

This effectively proves that the crossover modelled and the drivers located as are reasonable well optimised.

Unfortunately Todd the issue of the woofer response hole lay else where.

I would suggest its the location of the woofer relative to the side walls or in internal standing wave problem. The action of the dust cap could also be an issue.


Ian

[toddalin]

Hi Todd,

I need to know where the compression driver top place is ie the diaphragm relatice to the front panel.

HL-91 is 7-3/4" behind the baffle panel and driver is 3-7/8" deep. Assuming that the diaphram sits 2/3 of the way in and baffle board is 3/4", front of baffle to diaphram is probably ~11".

[Ian Mackenzie]

Todd,

I used this data:

http://www.lansingheritage.org/image...omp/page10.jpg

If your horn is the longer 800 hz horn the extension behind the baffle is 10.75 inches, add the depth of the compression driver and estimate of the top plate my guess is 13.9 inches to the diaphragm.

As discussed above I think this is reasonably accurate as the sims show.

Ian

[toddalin]

Todd,

I used this data:

http://www.lansingheritage.org/image...omp/page10.jpg

If your horn is the longer 800 hz horn the extension behind the baffle is 10.75 inches, add the depth of the compression driver and estimate of the top plate my guess is 13.9 inches to the diaphragm.

As discussed above I think this is reasonably accurate as the sims show.

Ian

You are looking at the HL-92 (used in the L300 and 4333). HL-91 is 3" shorter, or about 11" to the diaphram as I noted.

[4313B]

As an aside, at one time I noted that putting a resistor on the woofer took care of the problem. (Of course most people on this site poo-pooed the idea of using a resistor on the woofer.) I think this helped because the impedience hump became smaller relative to the overall impedience curve.

That's right, one doesn't usually put a resistor in series with a woofer, oftentimes one does put one in parallel if it helps the overall situation.

In another thread I suggested removing the conjugate. You can then place a 50 to 100 ohm resistor in parallel with the 2235H. Run both if you have to.

I would suggest its the location of the woofer relative to the side walls or in internal standing wave problem.

All one has to do is set their oscillator at the frequency where the impedance blip occurs and listen for any anomalies. Standing waves will sound quite nasty.

[edgewound]

HL-91 is 7-3/4" behind the baffle panel and driver is 3-7/8" deep. Assuming that the diaphram sits 2/3 of the way in and baffle board is 3/4", front of baffle to diaphram is probably ~11".

The distance between the top plates of the H-91/LE175 and 2205 is 8 inches when mounted to a 3/4" baffle...2205 mounted from the front.

[Ian Mackenzie]

So your definately using the shorter horn?

Why on earth use the shorter horn?

Here is the updated simulation with 8 inch placement of the path lengths on axis with the mic horn on axis in the first curve and mid way between the woofer and horn centres for both in and out of phase.

Its not pretty.

Ian

[toddalin]

So your definately using the shorter horn?

Why on earth use the shorter horn?

Ian

Longer horn does not fit in L200 cabinets. The driver would stick out the back ~2".

[edgewound]

So your definately using the shorter horn?

Why on earth use the shorter horn?

Ian

Because it's an L200 cabinet that came with the H-91. The H-92 is too long for the box. It's shallower than the L300.

The L200B components were 136A and LE85-16 ohm on H-91 horn.

[4313B]

Why on earth use the shorter horn?

JBL didn't know everything back then, they did the best they could with what they had. Some of the guys thought they could get away with using any horn with any woofer. It was the later crowd that brought in or designed the gear required to design more advanced systems.