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HD15 Measurements

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JulianDA View Drop Down
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    Posted: 24 July 2020 at 1:27am
Greetings!

Since I could'nt find any measurements of HD15 when my friend and I thought about building our first ones and since there are people asking for those over and over again, I decided to take some measurements before we sell our HD15 and post them on here.

We did measurements of 1, 2 and 4 HD15 loaded with Oberton 15B450 drivers in a parallel configuration. They were done in a field with just some bushes to the side (2 Pi) on the ground with approx. 3,5m distance from the stack. The Mic was the Beyerdynamic MM1 which is not calibrated for actual soundpressure, so just ignore the absolute dB-levels.

This is the result and some pics of the setup/measurement-conditions:











I hope these measurements can help some people to decide wether or not to build their own HD15 :)
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bob4 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bob4 Quote  Post ReplyReply Direct Link To This Post Posted: 24 July 2020 at 5:30am
Hi Julian, great post! Thank you for sharing this. This is highly useful! It is lacking a bit of circumstantial information though, which would add greatly to its value. Amping, power levels......

 Could you also please add information about the processing? I assume you have had a high pass filter in place? If so, please add cutoff frequency and filter order to your previous post. This is crucial. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JulianDA Quote  Post ReplyReply Direct Link To This Post Posted: 24 July 2020 at 1:30pm
Originally posted by bob4 bob4 wrote:

Hi Julian, great post! Thank you for sharing this. This is highly useful! It is lacking a bit of circumstantial information though, which would add greatly to its value. Amping, power levels......

 Could you also please add information about the processing? I assume you have had a high pass filter in place? If so, please add cutoff frequency and filter order to your previous post. This is crucial. 


Hey Bob,
since I wanted to provide accurate frequency response plots, there is no processing involved. No EQ, no HPF or LPF, just the fullrange signal to one ampchannel of a T.Amp TSA 4-1300. I did not alter the gainstructure when connecting more Speakers in a parallel configuration (so its a load of 8, 4 and 2 Ohms)
I would assume the cabs got something in the range of 10W but i just made sure its loud enough for a good measurement. Like i said, the mic is not calibrated for absolute levels, so the 130dB have no meaning. I can just provide the relative difference in soundpressure when using 1, 2 and 4 cabs and the change in the frequency response :)

But if it helps: We used the Yamaha Steinberg UR12 audio interface connected to a DCX2496 (without any processing enabled) which itself was connected to the TSA 4-1300 with just one channel used. There where no changes made when connecting more cabs :)

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odc04r View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 24 July 2020 at 3:38pm
Interesting stuff, thanks for posting the data. I don't suppose you measured THD % at the same time? You can certainly see the useful bandwidth broadening as the mouth area comes up. Rapid fall off at 80Hz due to horn length as any fule kno, hence great partner to X1 etc when aligned well.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote VECTORDJ Quote  Post ReplyReply Direct Link To This Post Posted: 25 July 2020 at 12:55am
A+

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JulianDA View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote JulianDA Quote  Post ReplyReply Direct Link To This Post Posted: 30 July 2020 at 2:10pm
Originally posted by odc04r odc04r wrote:

Interesting stuff, thanks for posting the data. I don't suppose you measured THD % at the same time? You can certainly see the useful bandwidth broadening as the mouth area comes up. Rapid fall off at 80Hz due to horn length as any fule kno, hence great partner to X1 etc when aligned well.


Thanks :) 
You are right, we did not measure the THD... but I would like to do that if someone can tell me how to accomplish this with ARTA as the measurement software. 
But I will just measure it for 2 HD15, since we already use two of the drivers in our new horns and its such a PITA to put the drivers back into the HD15. 
If you can tell me how to measure the THD, I can compare the HD15 to our new horn if this is interesting to you :)

Regarding the bandwidth broadening of the HD15, I would say that the effect of the bigger mouth area is probably located higher up frequency. In my opinion this effects reduces the ripples in the range of 150 to 500Hz. The "bassextension" down to 80-90Hz is achived by the bandpass effect of the frontchamber and shows just a little improvement with the bigger mouth.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote odc04r Quote  Post ReplyReply Direct Link To This Post Posted: 30 July 2020 at 4:34pm
Ah yes, not so sure about ARTA. Tend to use REW for this type of thing. Quick check of ARTA's manual online says it will do THD, doesn't seem too complicated. Investigating THD as a function of power would be interesting, maybe gives a clue as to why people think HDs can honk high up.

Yes fair point re. that resonance that is suppressed with increasing mouth area. It is an interesting one albeit a bit of a moot point as no-one would ever play the cabs that high. It could be related to the L/A relationship of the bandpass port. I wonder also if the presence of that resonance is another reason that people find HDs honky up in that region near 200Hz.
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