I have managed to get outside to do some measurements and it's looking very different to inside. I realised after taking these measurements that one of the wires going to the CD had snapped so it wasn't connected to the amp, Not sure whether that could affect them this much. I'm gonna fix it and try again tomorrow, hopefully I get the same results.
This was measured at 2.51m and scaled back to 1w@1m. It was also reduced by 6db for a ground plane measurement.
I haven't windowed these at all.
Interestingly this drops off at the exact frequency that the surface area of the horn where the ports are would be. I need to move the ports slightly closer to the CD to get above 2khz.
Also, measurements at different power levels. The plastic was getting pretty resonant and the cone will definitely have been hitting the plastic. I need to sort out filling the prints to make them more solid.
Smoothed is a bit easier to see
And this is where they were measured:
This was measured at 2.51m and scaled back to 1w@1m. It was also reduced by 6db for a ground plane measurement.
I haven't windowed these at all.
Interestingly this drops off at the exact frequency that the surface area of the horn where the ports are would be. I need to move the ports slightly closer to the CD to get above 2khz.
Also, measurements at different power levels. The plastic was getting pretty resonant and the cone will definitely have been hitting the plastic. I need to sort out filling the prints to make them more solid.
Smoothed is a bit easier to see
And this is where they were measured:
What was the diaphragm to plug depth for the outdoor measurements?
The deep notch ~2kHz seems to only be evident in the "more power" tests, was the wire snapped after the 1watt test?
The "100 watt" level is only around +10dB over the "one watt", should be around +20dB, am I missing something?
Interesting to see these comparative tests!
Art
As a guess maybe background noise not allowing for enough quiet to capture the low level test? I say that simply because the general shape and trend is identical between all tests, just the dip is less severe...
I'm assuming sweeps were used?
I'm assuming sweeps were used?
Sorry, I should have done them as seperate graphs. The 1W test is scaled for 1m but measured at 2.51m so actually 5.02v whereas the others are the exact voltage for that power.
the depth was 2.5mm for these measurements.
I am not sure when the wire snapped, I noticed it close to the end of doing it all unfortunately.
Yeah, I used REW sweeps, calibrated the microphone with a SPL calibrator and the voltage using a powersoft mezzo reading the voltage from Armonia.
@Gtimes I did try and wait for a quiet moment but it is next to a road so there is some background noise
I am really happy with that going up to nearly 1.8khz although I reckon I could push that a little further
I need to set it up and have a listen to some music at different crossover points and volumes, I will try and do that tomorrow.
the depth was 2.5mm for these measurements.
I am not sure when the wire snapped, I noticed it close to the end of doing it all unfortunately.
Yeah, I used REW sweeps, calibrated the microphone with a SPL calibrator and the voltage using a powersoft mezzo reading the voltage from Armonia.
@Gtimes I did try and wait for a quiet moment but it is next to a road so there is some background noise
I am really happy with that going up to nearly 1.8khz although I reckon I could push that a little further
I need to set it up and have a listen to some music at different crossover points and volumes, I will try and do that tomorrow.
Pointed at a microphone in the sky, the reflected waves from the front of the horn to the ground cause cancellation notches in the response not present in a ground plane measurement.
The depth of the cancellation notches could be reduced by suspending the DUT a great distance above the ground relative to the test distance.
Why don't you rent a crane for the OP 😉 ?
Well thats what I did, but I did it in the lawn. How does one calculate where the notch would be? I wonder if I have that notch in my measurements.
https://forums.audioholics.com/foru...rference-reflection-sibr-calculations.123492/
http://tripp.com.au/sbir.htm
Speaker Boundary Interference Reflections:
At 1/4 wavelength distance away from a boundary, the reflected wave reaches the output exit location at 1/2 wavelength (1/4 + 1/4 = 1/2), 180 degrees out-of-phase with the original output and causes an amplitude reduction at that frequency.
Grass attenuates HF reflections far more than LF, and the inverse distance reduction of 6dB per doubling of distance reduces the reflection level at the measurement mic.
The effect of boundary reflections are less in the near field, but horn measurements are more accurate in the far field.
http://tripp.com.au/sbir.htm
Speaker Boundary Interference Reflections:
At 1/4 wavelength distance away from a boundary, the reflected wave reaches the output exit location at 1/2 wavelength (1/4 + 1/4 = 1/2), 180 degrees out-of-phase with the original output and causes an amplitude reduction at that frequency.
Grass attenuates HF reflections far more than LF, and the inverse distance reduction of 6dB per doubling of distance reduces the reflection level at the measurement mic.
The effect of boundary reflections are less in the near field, but horn measurements are more accurate in the far field.
There is too many boundaries about, I need to find somewhere better to measure things.
I have tried moving the taps closer to the throat of the horn to get a little bit higher but I have only managed to make it worse so far haha
I'm just gonna keep iterating on it to try and get it to 2khz but not sure if it would be possible without reducing the front chamber size more.
I have tried moving the taps closer to the throat of the horn to get a little bit higher but I have only managed to make it worse so far haha
I'm just gonna keep iterating on it to try and get it to 2khz but not sure if it would be possible without reducing the front chamber size more.
Thank you for the answer, I thought it was 1/2wl but now I know and why. A horn pointed to the sky typically wouldn't have HF reflections from the ground due to directivity. I also never understood why a farther way measurement meant for accuracy. I listen at 1m.... but what I am hearing is more accurately measured at 6m?
I finally managed to get some proper outdoor measurements of this recently.
You can definitely hear the hf roll off with it.
These measurements were all calibrated for 1w/1m taken at 3 meters with no boundaries for 50m in any direction.
You can definitely hear the hf roll off with it.
These measurements were all calibrated for 1w/1m taken at 3 meters with no boundaries for 50m in any direction.
The HF was rolling off ~-6dB per octave from 4kHz to 8kHz in the tests with the mic at the horn mouth.
The 3 meter test is rolling off ~15dB per octave from 4kHz to 8kHz which seems too much of a change, like some filter has been applied or the mic was off axis.
The -14dB dip ~340 Hz is interesting.
Unless you used a 50m crane, the ground plane boundary was much nearer than that, and it's reflection could be responsible for the dip.
What was the horn center height off the ground, and the mic distance from the ground?
Art
It was a while ago I took the measurements now, I use a laser measure to get them on axis while tilting the top.
Sorry, yeah the measurements were taken on the ground. I had the microphone and speaker on the ground with the speaker tilted down to face the microphone.
The horn center Was about 19cm from the ground with the microphone placed dirctly on the ground
I will go out and get some more measurements when the weather gets a bit better to double check everything.
Sorry, yeah the measurements were taken on the ground. I had the microphone and speaker on the ground with the speaker tilted down to face the microphone.
The horn center Was about 19cm from the ground with the microphone placed dirctly on the ground
I will go out and get some more measurements when the weather gets a bit better to double check everything.
I am onto bigger and better projects so uploaded this to printables if anyone wants the files
https://www.printables.com/model/1210713-300hz-multi-entry-horn
Couldn't think of a better name other than 300hz multi entry horn haha
https://www.printables.com/model/1210713-300hz-multi-entry-horn
Couldn't think of a better name other than 300hz multi entry horn haha
That would be far too sensible haha, I am not. They are incredible drivers however it's hard to make a horn where the HF will keep up with them. I'm aiming to make something more balanced.
Thanks 🙂 I used PETG when printing