NOS 044Ti Frequency Response

[Andyoz]

Guys,

I finally got around to measuring frequency response plots of the one NOS 044Ti and the other "old" 044Ti I still have installed in my 250Ti's.

Two graphs here, one is 1/6 Octave "smoothed" response, the other is "unsmoothed". Graphs are over the 5.2KHz to 20KHz range only. The Blue trace is the NOS unit.

Measurements were done using EASERA and Bruel & Kjaer mic so measurement chain is good. All measurements are done inside (would have preferred external "free-field") with mic on-axis 100mm from centre of 044Ti dome.

This sort of measurements isn't really my thing (more into the room acoustics side) so am open to suggestions from others more experienced on the measurements method.

[opimax]

I would guess (and i do mean guess ) that the dampening foaml is no longer dampening so the old diaphram is "ringing"...

I wait for more and better educated info but thanks for measuring...

Mark

[Andyoz]

Yes, although the difference in the 10kHz to 15kHz region is only about 2dB which is audible (not major though really). The traces in the 5.2kHz to 7kHz range are very close indeed which gives me more confidence in my measurement procedure...

To be honest, I had expected to find a more "peaky" trace for the "old" 044Ti trace (in the second "unsmoothed" graph I mean - sorry it is incorrectly marked on the graph header). Anyway, that's how they sounded to me although I could have sworn that their sound has changed since I posted my initial impressions. the NOS units seems to be more similar in level to the old ones now.

There's probably loads of reasons for the variance and I will wait for someone with more experience to comment.

Really, not as marked a difference as I would have thought though.

[Robh3606]

Your measurements look similar to mine using CLIO. I am guessing you are making an MLS measurement. Here are a couple of measurements on a tired 035Ti. The first is MLS red is raw, Green is 1/12 and Blue is 1/6 smoothing.

My scalling is different but the noise seems a bit worse, hard to tell. Yours look to be about 2dB peaks which is primarilly what I see in this one. I will rescale it to look more like yours for a better comparison.

The Sine measurements seem to have less hash/noise. The Red is raw and the Green is 1/12.

They are baffle mounted measurements??

Rob

[Andyoz]

Cool,

I am using a sine sweep excitation.

I have redone the graphs using a similar 10dB wide Y-axis to yours. The first one is the old 044Ti. Have given 1/12 and 1/48 smoothed traces. My "raw" data for the sine sweep sure doesn't look as smooth as your second graph. Notice that both graphs start at around the same level at 5.2kHz (86dB). I have repeated the measurements a few times and get the same traces to within +/- 0.2dB so am happy enough.

Anyway, expanding the Y-axis makes the Old 044Ti look a little more "peaky" but it's only a dB or two.







This last trace compares the NOS and "old" 044Ti's using the same scales and 1/12 smoothing. The two units are incredibly similar in the 5.2kHz to 7kHz range. I am running the x-overs with the attenuator links running "flat" to remove as much x-over variance between speakers as possible.

They also appear to come back into line at the very high frequencies, above 17kHz (I really can't hear that high). I would need to repeat this with a few units to see if the same pattern occurs (wish the bloody 044Ti's were easier to get in and out of the enclosures!!)

[Robh3606]

OK you using Sine. I have a gated MLS attached here. The Red is Gated Raw Green is 1/6 smoothing. It cleans things up quite a bit.

It's hard to say exactly what's going on between the two. They could be years apart as far as there manufacturing dates. They look close in the sense that they have about a 1-1.5 dB difference between them in the upper range above 9k. I don't know what a normal variation should be for them??

If your doing Sine can you compare the THD of the two drivers???

Rob

[Andyoz]

It's hard to say exactly what's going on between the two. They could be years apart as far as there manufacturing dates.

If your doing Sine can you compare the THD of the two drivers???

Rob

The "old" unit is from 1988 but has been exposed to the elements shall we say and there seems to be a lot of evidence that the foam packer behind the dome rots over time.

The NOS units are from 1986 but have been sealed up nice and cosy in their plastic wrapper and boxes in Japan. I'd love to know if the foam is ok, they definitely sound different to me.

I don't have the THD option on my version of EASERA...

The units are baffle mounted and are operating behind the 250Ti x-over, which I understand is at 5.2kHz and 6dB slope. Not ideal conditions for what I am trying to do I guess and could be one of the reasons why the traces are so close below 7kHz.

I really don't know enough about this, I only ever use EASERA to measure room acoustics parameters like RT60, EDT, C80, etc.

[Robh3606]

Just for fun what happens if you pad the louder one down 1dB using the network attenuator straps??

I really don't know enough about this, I only ever use EASERA to measure room acoustics parameters like RT60, EDT, C80, etc.

Well if you are getting repeatable measurements that make sense your doing just fine. You can verify that by taking a baseline measurement, leave the set-up exactly the way it is and change the attenuators. When you come back to 0 you should get a measurement very close to the original baseline measurement. It should almost retrace the original.


Rob

[Andyoz]

I may try that later. I want to do a couple of repeats with each tweeter and average the results so I am sure that the baseline is correct. Also, these F'ing speakers are hard to move around and get to those attenuator straps.

Would you agree with my method of positioning the mic about 100mm from the tweeter, on-axis? Each speaker is sitting about 500mm from the side wall but that shouldn't cause any issues, should it?

I have noticed that when I replace the mic into the approx same position as before and remeasure, the peaks and troughs move around a wee bit but the overall pattern stays the same. Maybe due to the small wavelengths I am dealing with here I guess.

[Andyoz]

The issue with the tweeter foam was played out here FYI, http://audioheritage.org/vbulletin/s...ighlight=044ti

[Robh3606]

I had issues doing sine measurements a couple of times. I got what looked like ringing from the driver that were actually reflections from a lamp that was too close. I moved the lamp and got a smooth curve. You might want to get the microphone a bit closer. Just see what gives you the most ripple free measurement. Take a couple of repeated baseline measurements like you plan on doing and don't physically change anything when you have decided you are good to go.

Rob

[Andyoz]

Yep, makes sense. Those ripples do seem to move around a bit with even the slightest variation in mic placement.

[Zilch]

Heh. A new Curve Junkie recruit!

[LOVE this stuff.... ]