Passive Radiator CSS SDX10 Design and Build

[EngineerNate]

Not sure what’s going on with that wiggle at 75hz on the one. Was going to remeasure before getting too worked up over it.

I’ve been doing some additional modeling and honestly 5 washers (235g) on each PR looks pretty great. A little peaky (2-3db) at resonance but that’s easier to eq out than a hole.

I have a few hours today without the older kiddos so I’m hoping to take some measurements.

 

[mwmkravchenko]

Not sure what’s going on with that wiggle at 75hz on the one. Was going to remeasure before getting too worked up over it.

I’ve been doing some additional modeling and honestly 5 washers (235g) on each PR looks pretty great. A little peaky (2-3db) at resonance but that’s easier to eq out than a hole.

I have a few hours today without the older kiddos so I’m hoping to take some measurements.

75 hertz is a resonance. It's out of phase with the dominant resonance.

Top graph. I'm pretty sure you can read a graph. On a dB scale it is a little bit different to read. Top graph is measurement of the signal sent to the driver via an amplifier and picked up with a microphone. A SPL based frequency response. Red and blue is where this driver is singing along with the signal. The driver is adding in different parts. A second harmonic is one octave above and the third harmonic is 2 octaves above the fundamental frequencies. A difference between the measured signal black line and any other line 40dB lower is expressed as 1% Harmonic Distortion.

THD to dB - convert percent % to decibels dB percentage voltage % vs per cent converter THD+N total harmonic distortions calculation signal distortion factor attenuation in dB to distortion factor k in percent decibel damping - sengpielaudio Sengpiel

Calculate THD and distortions decibels dB to percentage % per cent percent voltage % vs converter and dB signal distortion THD+N total harmonic distortions factor attenuation damping - Eberhard Sengpiel sengpielaudio

sengpielaudio.com

If you really want to do some sleuthing you want electrical phase, SPL and Impedance on the same graph. They can tell you a fair bit about what is going on.

Now that you have your leaks plugged you can do some better measurements.

Until you actually have your drivers measured our simulations are best guesses. But they do point you in the right direction.

If you had your drivers measured, the simulations could be very accurate.

Should the build your own loudspeaker become a hobby you should always start with a driver that has been exercised for about an hour at a few watts of input power via noise signal. And then take some measurements for the basic driver parameters. Let your driver cool for a few hours and then measure again. That is the best way to measure power versus small signal. The idea that high power Thiele Small calculations can be made means that you need alternate mathematics to do the large signal calculations. Taking small signal (millivolt level as they should be) on a warmed up driver is the most accurate way to get the different functional and cold difference. There will be differences between a warmed up driver and a cold driver. As a mechanical system your woofer is less than 0.25% efficient. That is right. 99.75% of the power going into your woofer is being turned into heat. Thankfully the power input is low, and the duty cycle is fairly low.

Mark

 

[EngineerNate]

75 hertz is a resonance. It's out of phase with the dominant resonance.

Top graph. I'm pretty sure you can read a graph. On a dB scale it is a little bit different to read. Top graph is measurement of the signal sent to the driver via an amplifier and picked up with a microphone. A SPL based frequency response. Red and blue is where this driver is singing along with the signal. The driver is adding in different parts. A second harmonic is one octave above and the third harmonic is 2 octaves above the fundamental frequencies. A difference between the measured signal black line and any other line 40dB lower is expressed as 1% Harmonic Distortion.

THD to dB - convert percent % to decibels dB percentage voltage % vs per cent converter THD+N total harmonic distortions calculation signal distortion factor attenuation in dB to distortion factor k in percent decibel damping - sengpielaudio Sengpiel

Calculate THD and distortions decibels dB to percentage % per cent percent voltage % vs converter and dB signal distortion THD+N total harmonic distortions factor attenuation damping - Eberhard Sengpiel sengpielaudio

sengpielaudio.com

View attachment 526966



View attachment 526972

If you really want to do some sleuthing you want electrical phase, SPL and Impedance on the same graph. They can tell you a fair bit about what is going on.

Now that you have your leaks plugged you can do some better measurements.

Until you actually have your drivers measured our simulations are best guesses. But they do point you in the right direction.

If you had your drivers measured, the simulations could be very accurate.

Should the build your own loudspeaker become a hobby you should always start with a driver that has been exercised for about an hour at a few watts of input power via noise signal. And then take some measurements for the basic driver parameters. Let your driver cool for a few hours and then measure again. That is the best way to measure power versus small signal. The idea that high power Thiele Small calculations can be made means that you need alternate mathematics to do the large signal calculations. Taking small signal (millivolt level as they should be) on a warmed up driver is the most accurate way to get the different functional and cold difference. There will be differences between a warmed up driver and a cold driver. As a mechanical system your woofer is less than 0.25% efficient. That is right. 99.75% of the power going into your woofer is being turned into heat. Thankfully the power input is low, and the duty cycle is fairly low.

Mark

Does warm up make the impedance measurements better? I did them again on one of the units this AM and the wiggle was back, either the driver being warm from me chasing leaks matters or something came unsealed overnight which would be... Strange? Unless my gasketing material squished more and I need to tighten the bolts up again until that stops happening or use a different material.

The gasket is the grey non-hardening rope caulk right now.

 

[EngineerNate]

Also yes I see the wiggle in the distortion plot.

 

[EngineerNate]

Well, turns out some of the wiggles were my 1/4" to RCA adapter failing catastrophically. I setup with my RME interface instead of the audient now that I am confident I'm not going to ruin anything (electrically...) with my measurement jig. The adapter promptly broke off inside the jack while switching speakers.

But I got my cleanest sweep yet, so the wobbly measurement this AM was something with my test setup (probably the jack) and not the speaker.

 

[mwmkravchenko]

Does warm up make the impedance measurements better? I did them again on one of the units this AM and the wiggle was back, either the driver being warm from me chasing leaks matters or something came unsealed overnight which would be... Strange? Unless my gasketing material squished more and I need to tighten the bolts up again until that stops happening or use a different material.

The gasket is the grey non-hardening rope caulk right now.

They are not better, warm is a way to make a parameter measurement that reflect what your woofer does when it is warm.

When you read about how the measurements are described in the original papers by Nevile Thiel and the extension paper by Richard Small you learn that you want very little coil movement. Large scale coil movement makes the mathematics inapplicable. You have basically two physical things you are measuring. Compliance and impedance. And from those things you are getting your parameters. The compliance and the impedance are physical measurements. I use small ferrite magnets that I measure in a thick padded box to not influence my scale. I place them on and inside the cone and outside the cone against each other in opposite polarity. They hold themselves in place. And place in a symmetrical pattern to have a mass that does not vibrate, and doe not unduly influence the balance of the cone.

The key to a reasonable seal is that you have firstly a compliant sealant to seal the frame to your enclosure, and secondly a reasonably even amount of torque on the fasteners. I have found that rubber wrapped frames are almost impossible to seal. And I remove the rubber after sufficiently cursing it. #*&(^$*&%(@#%(*@ so there!


Personally I used a closed cell neoprene foam tape used for weathers stripping or gasket applications. I have found the rope caulk to be little more than an exercise in my keeping my swears at a minimum. It is very prone to making leaks if you squeeze it all out while tightening the fasteners. You can use the rope caulk, it will work. You just need a to get a feel for it.

Mark

 

[mwmkravchenko]

Well, turns out some of the wiggles were my 1/4" to RCA adapter failing catastrophically. I setup with my RME interface instead of the audient now that I am confident I'm not going to ruin anything (electrically...) with my measurement jig. The adapter promptly broke off inside the jack while switching speakers.

But I got my cleanest sweep yet, so the wobbly measurement this AM was something with my test setup (probably the jack) and not the speaker.

View attachment 527001

This is indeed a clean sweep.

At this point you have drivers in a cabinet. We don't really know the drivers parameters. So, add and remove mass and see what you get! The good old cut and paste method.

 

[EngineerNate]

Took several attempts and swear words plus sacrificing one of my other adapters but I got it out and I think the jack is okay.

 

[EngineerNate]

This is indeed a clean sweep.

At this point you have drivers in a cabinet. We don't really know the drivers parameters. So, add and remove mass and see what you get! The good old cut and paste method.

I need to do this free air or in the cab?

 

[mwmkravchenko]

View attachment 527008

Took several attempts and swear words plus sacrificing one of my other adapters but I got it out and I think the jack is okay.

Ouch.

Gotta love stuff ordered to the fraction of a penny. I can tell you stories of working in China at very high quality levels and also corners cut to meet the lowest price possible. It's always a get what you pay for if you are dealing with reputable manufacturers.

If they have a flashy website, they are a distributor. Run away. Alibaba only, probably real manufacturer. They vet their vendors.

Mark

 

[mwmkravchenko]

I need to do this free air or in the cab?

Simulations at this point are not really useful. If you have everything sealed up, play with the weights and measure the SPL. Taking it all apart again to measure your drivers and simulate, and add weights and measure...... You get the point? Simulating now is worthless. You have the real McCoy to measure and manipulate.

Mark

 

[EngineerNate]

Playing with alignments. 3 and 4 washers here.

 

[EngineerNate]

5 washers feels like the rolloff is getting to be too much.

 

[EngineerNate]

A couple of graphs that tell a story.

 

[EngineerNate]

One last modification. Replacing the wingnut and lock washer with a nordlock and a grade 8 nylock nut.

 

[LSPhil]

Kilka wykresów opowiadających historię.
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View attachment 530317


View attachment 530318

 

[LSPhil]

"I don’t think the second version was released without a reason. I have the second one installed in a closed IKEA Kallax enclosure. A Wavecor driver is almost identical, but you can’t really compare them directly.

The SCC10 has a diaphragm that is about 50% heavier, which makes it around 2.5 dB less efficient. It would be interesting to hear what acoustic differences you can share with us.

In my case, when I turn it up to around 200W, it reaches a pleasantly loud level—but my neighbors don’t like my music at all. Tastes really do differ a lot. Of course, traditional German folk music doesn’t stand much of a chance against Make Us Stronger by Ghost Rider.

 

[EngineerNate]

Yes for clarification these were the updated SDX10. They sounded great, but I am a bit of a measurement nerd.

 

[EngineerNate]

Speaking of. Brand new driver vs the one I bought "broken in/second hand" on eBay.

I'd peg the tuning at 22hz.

 

[mwmkravchenko]

Have you ever run across something that Seigfried Linkwitz shared called a wedge micrometer?

https://www.linkwitzlab.com/images/graphics/wedge-micro.gif

My guess being that there is a marked difference in distortion is that your PR is moving differently with the different weights.
A wee bit of drafting and some tape and you will be able to see what you excursion is to a realistic degree.

Your test frequency needs to be below 60 hertz for you to be able to see excursion. The triangle is a 2 times width to height ratio, so you can make it 50 to 25 mm if you choose. You can actually directly rad your excursion via this method within a mm.

It's not an answer, just an indicator as to why the difference may be showing up.

View attachment 530458

One last modification. Replacing the wingnut and lock washer with a nordlock and a grade 8 nylock nut.

You are hoping that it will not come loose! I think that you will win this one

Mark