the 2360, Getting it Flat

[1audiohack]

Hi All;

I have long thought about making a thread string called 'Getting it Flat' and posting measurements with the corresponding EQ corrections for some of the common horns and drivers that I have worked with. I just never have much spare time.

I have a pile of big stuff on the patio that I plan to stack and play and finally got some of it together over the weekend but is was cold and windy so I tried something different and ran the cable form the DBX 260 in an amp rack by the speakers into the house and measured and tweaked remotely in the comfort and silence (except the music) of my living room. It was kind of like having an anechoic chamber.

Side note, the DBX 260 and 4800 (and likely the PA, 4820 and others) use only two of the conductors and the shield/ground in the RS232 cable which makes it a snap to cut the cable and install a pair of XLR connectors to it and use an extra channel in a snake or a long mic cable to run remote on a laptop.

Here is a measurement of a 2360 driven with a 2450J properly loaded with a D16R2450 at about 10 feet / 3M on axis with a 24dB Butterworth hi pass at 500Hz. The PEQ filters (four of them) are just above the graph panel. It is tough to really read and dig in without cursers but if you look at the scale carefully this horn is flat from 600Hz to past 4kHz within 1dB with a total variation of less than 6dB from 500 to about 17kHz and about 4.7dB of the slope on the top is intentional. There is in the notation a mistake where it says distance is 2M, it is 3M

I am kind of curious to know if anyone finds this kind of information useful so this is a test. Questions and comments welcome.

All the best,
Barry.

[ivica]

Hi All;

I have long thought about making a thread string called 'Getting it Flat' and posting measurements with the corresponding EQ corrections for some of the common horns and drivers that I have worked with. I just never have much spare time.

I have a pile of big stuff on the patio that I plan to stack and play and finally got some of it together over the weekend but is was cold and windy so I tried something different and ran the cable form the DBX 260 in an amp rack by the speakers into the house and measured and tweaked remotely in the comfort and silence (except the music) of my living room. It was kind of like having an anechoic chamber.

Side note, the DBX 260 and 4800 (and likely the PA, 4820 and others) use only two of the conductors and the shield/ground in the RS232 cable which makes it a snap to cut the cable and install a pair of XLR connectors to it and use an extra channel in a snake or a long mic cable to run remote on a laptop.

Here is a measurement of a 2360 driven with a 2450J properly loaded with a D16R2450 at about 10 feet / 3M on axis with a 24dB Butterworth hi pass at 500Hz. The PEQ filters (four of them) are just above the graph panel. It is tough to really read and dig in without cursers but if you look at the scale carefully this horn is flat from 600Hz to past 4kHz within 1dB with a total variation of less than 6dB from 500 to about 17kHz and about 4.7dB of the slope on the top is intentional. There is in the notation a mistake where it says distance is 2M, it is 3M

I am kind of curious to know if anyone finds this kind of information useful so this is a test. Questions and comments welcome.

All the best,
Barry.

Hi Barry,

Interesting how smooth the response is, my experience with 2450J drivers always have shown huge ringing over 12~13kHz, id ribbed diaphragms were used.
Can you give us the PEQ parameters used.

regards
ivica

[grumpy]

You have to squint a little (3rd line of text from the top, above the plot itself).
Seems like there are three filters listed, and that perhaps with an initial 2360 EQ
from the dbx device itself? (guessing)

[1audiohack]

Hi;

I didn't realize there was a limit to the notes that would show up on the TEF graph page so I edited it down to show the fourth PEQ filter and corrected the distance to 3M.

The horn driver measurement previously attached has no HF limit. I might after some listening drop a low pass filter on top to tame that peak about 17kHz, if it glares at me.


Below is the transfer function of the four PEQ filters through the DBX260 Besides the 500Hz 24dB Butterworth HP no other shaping or passive devices are in the chain.
The upper line is magnitude and the lower is phase. I didn't change the dB SPL scale on the left to dB V, sorry.




Below is the Plane Wave Tube measurement of the 2450 used in this setup.
The line that drops like a rock at about 12kHz is phase trace. This is where the diaphragm breaks up and the signal becomes uncorrelated in time form the output. This shows up clearly in the measurement of the horn first posted as well.

Even though I consider the output of these drivers virtually noise at this point, the 2360 sounds better to me with this driver and diaphragm than any other largely due to the fact that you have to push the HF of all other diaphragms even harder via EQ to get them to sound reasonably bright and they sound strained.

The above sentence is of course just my opinion.




Hi Ivica;

There is a fair amount of smoothing on these measurements that takes out the HF hash that would be shown in a raw data measurement. Since we don't seem to hear these very narrow notches (I think this does contribute to listener fatigue) and it is above the fundamental tone of any natural instrument, coupled with the fact that one certainly cannot EQ for such, I smooth it out in the display if there is absolutely nothing I can do to eliminate it at the source.


All the best,
Barry.

[grumpy]

So presumably, with a non-PEQ corrected 2450/2360 plot, you were able to see and then compensate for
the constant directivity correction, as well as a few driver/horn interactions (not shown on
the PWT test plot), and achieving a "house" curve... using relatively few filters to good effect.
A bit of an art form.

If anyone else needs to convert from Q to octave/width for the PEQ units available
for a particular instrument or software package/system, this is an interesting read (and calculator):

http://www.sengpielaudio.com/calculator-bandwidth.htm

[ivica]

Hi;

I didn't realize there was a limit to the notes that would show up on the TEF graph page so I edited it down to show the fourth PEQ filter and corrected the distance to 3M.

The horn driver measurement previously attached has no HF limit. I might after some listening drop a low pass filter on top to tame that peak about 17kHz, if it glares at me.


Below is the transfer function of the four PEQ filters through the DBX260 Besides the 500Hz 24dB Butterworth HP no other shaping or passive devices are in the chain.
The upper line is magnitude and the lower is phase. I didn't change the dB SPL scale on the left to dB V, sorry.




Below is the Plane Wave Tube measurement of the 2450 used in this setup.
The line that drops like a rock at about 12kHz is phase trace. This is where the diaphragm breaks up and the signal becomes uncorrelated in time form the output. This shows up clearly in the measurement of the horn first posted as well.

Even though I consider the output of these drivers virtually noise at this point, the 2360 sounds better to me with this driver and diaphragm than any other largely due to the fact that you have to push the HF of all other diaphragms even harder via EQ to get them to sound reasonably bright and they sound strained.

The above sentence is of course just my opinion.




Hi Ivica;

There is a fair amount of smoothing on these measurements that takes out the HF hash that would be shown in a raw data measurement. Since we don't seem to hear these very narrow notches (I think this does contribute to listener fatigue) and it is above the fundamental tone of any natural instrument, coupled with the fact that one certainly cannot EQ for such, I smooth it out in the display if there is absolutely nothing I can do to eliminate it at the source.


All the best,
Barry.

Hi Barry,

Many thanks for the data You have presented here.
As over 12~13kHz, the ribbed diaphragm can produce 'problematic results' may be LP filter at such frequency can give more pleasant sound (I can only imagine).
Interesting from my experience non-ribbed diaphragm has 'more smoother' response over 10kHz then ribbed one, but need several dB more EQ.
Have You tried 2360 horn with 'non ribbed' diaphragm?

Interesting is a kind of 'notch' over 1kHz, may be a kind of the horn-reflection.

regards
Ivica

[1audiohack]

Hi ivica;

What is interesting about the notch at 1.12kHz is that it is not in the native driver response and yet it is a linear phenomena. The filter to correct the magnitude deviation at 1.12kHz is a +6dB push that also corrected the ripple in the phase response at 1.12kHz as seen in the first graph.


I really should read my notes before I write. The 2450 is a J with a new D8R2450 diaphragm. I built and tested it a couple of months ago and my memory is short.

I have used the D16R2445 and D16R2441 on the 2360 and didn't love them. It takes a pair of 2404 motors on 40 degree horns to add to the 2360 what you loose if you turn them off at 10kHz at fairly moderate levels and you can still eclipse those in sound pressure with the 2360 if you get loud with them.

In my opinion if you are going to play them loud, the D__R2450 is the diaphragm of choice.

Barry.

[ivica]

Hi ivica;

What is interesting about the notch at 1.12kHz is that it is not in the native driver response and yet it is a linear phenomena. The filter to correct the magnitude deviation at 1.12kHz is a +6dB push that also corrected the ripple in the phase response at 1.12kHz as seen in the first graph.


I really should read my notes before I write. The 2450 is a J with a new D8R2450 diaphragm. I built and tested it a couple of months ago and my memory is short.

I have used the D16R2445 and D16R2441 on the 2360 and didn't love them. It takes a pair of 2404 motors on 40 degree horns to add to the 2360 what you loose if you turn them off at 10kHz at fairly moderate levels and you can still eclipse those in sound pressure with the 2360 if you get loud with them.

In my opinion if you are going to play them loud, the D__R2450 is the diaphragm of choice.

Barry.

Hi Barry,

I have done some measurements with 2450J-2 drivers equipped with D16R2450 diaphragm (ribbed) and using my designed horn I have get quite " linear" behavior up to 12kHz then over that frequency 'enormous' FR bouncing have started...that is why I have thought that a king of LP filtering over 12kHz would be expectable, but as I have understood Your experience, such 'bouncing' would not influence listening music....

First is with ribbed , and the second is with non-ribbed diaphragm 2450-2 driver, with 16 Ohms impedance.

regrads
ivica