Martin Poulin
June 2018
Received a pair of Radian 950PB’s from Portugal.
​
I let a friend borrow the JMLC horn, and therefore am only able to provide free air measurements for the time being. I’ll follow-up with horn mounted measurements with rear cover removed, at a later date.
​
The green trace is unit #1, and red/blue unit # 2.
They both measure very close and FS is ~487 Hz. With the rear cover removed, I expect it to drop to ~450 Hz. This bodes very well for a ~510 Hz crossover point in the new setup :)
Hopefully, the reflection at 1800 Hz will be eliminated with a horn mounted on the CD, as was the case with the 760PB.
Update: October 2018
​
No big surprise here. I tested the 950PB mounted on the 340 Hz JMLC horn.
​
With rear cover in place, on the stock item, the resonance dropped to 340 Hz from 487 Hz in free air.
​
With the back cover removed, this is my subjective favorite option. The resonance frequency dropped to 296 Hz., which is low enough to safely load the driver to ~450 Hz with a 4th order steep crossover.
​
The 340 Hz cut-off of the JMLC horn (500 Hz crossover point recommended) accounts for the shadow crossover slope (12 Db). If you use a more aggressive curve, 400 Hz is feasible.
​
A subjective result suggests that 470 Hz is the current sweet spot. Below 450 Hz, the 3rd harmonic rises quickly, which I don’t like. The 15" woofer does better there.
January 2020
​
Purchased a brand new Radian 950PB and a Tractrix 350 Hz horn from AutoTech.
​
Unlike my previous 950PB’s, the new one shows a higher impedance FS than the other two. This may be the result of reflection on the back cover, as the stock Radian has no damping material there, whilst I installed felt onto mine.
After 60 hours of burn-in, there was no change whatsoever.
​
I then emailed Radian about the issue. Perhaps the suspension had undergone a revision and now doesn’t behave like the older ones.
​
See right below image. The data that came with the driver clearly shows the 1050 Hz resonance.
Additionally, the horn used for FR measurement was not specified.
DATS measurement mounted on Tractrix 350 Hz horn
​
The 350 Hz horn does nothing to tame the big impedance peak at 1062 Hz.
​
This is very weird, as my other 950PB’s don’t act the same.
DATS measurement mounted on Tractrix 350 Hz horn
​
With 60 hours of music burn-in @ approximately 1.5 Watts at 150 Hz -20 kHz. This was very loud...
​
There was nothing to tame the big impedance peak at 1062 Hz. It appears I’ll have to install a Zobel.
But first however, I’ll wait for Radian customer service to reply.
February 2020 - Response from Radian
...
Our production line QC system tests the driver on a horn that is directed into a box. The resonance above 1000 hz is due to the horn used.
The test sweep begins at 500 hz (min XO). As such, the test does not capture resonance right at 500 hz. The resonant frequency of the diaphragm is therefore not captured. The main purpose of this production line test is to check that the diaphragm has the correct nominal impedance.
There have been no changes in the suspension or any other part of the diaphragm.
More detailed testing confirms that the performance of drivers assembled today closely matches golden samples that are several years old
...
​
​
I’ll have to remove rear cover and do my own test, at a later date.
The impedance does show a ripple at 400 Hz which tends to correlate with the resonant frequency of my older 950pb.
​
In the meantime, this driver will remain in storage, as my plans for this 3rd 950PB are for summer of 2020, or perhaps winter of 2020.
I’ll do a full 5.1 or 7.1 system with this being the center channel.
​
Stay tuned.
​