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Passive Radiator CSS SDX10 Design and Build

OK, Lets set up your enclosure your driver and your PR in a simulation so that you can get a handle on what it should look like.

1776541643499.png

Unless you have a ripple in the Impedance and phase here to, then it's a suspension non-linearity. I just looked at the graph with the phase included. It's suspension.

OK. I'll dig up my SDX10 file and do a simulation for you.

Mark
 
mwmkravchenko said:
OK, Lets set up your enclosure your driver and your PR in a simulation so that you can get a handle on what it should look like.

View attachment 525996
Unless you have a ripple in the Impedance and phase here to, then it's a suspension non-linearity. I just looked at the graph with the phase included. It's suspension.

OK. I'll dig up my SDX10 file and do a simulation for you.

Mark
Click to expand...

I do still need to do a frequency sweep and go around listening for audible leaks or other issues, make sure the testing didn’t shake the lock nuts loose on the passive radiator weight stacks, etc.

Overall it seems like the box tuning turned out correct but I do want to investigate that ripple.

I’m currently at the hospital with a newborn on my chest though.:)
 
For the record:

Target enclosure size is 2.5cuft and 9 washers/427g of additional weight added to both PRs for 18hz tuning.
 
one thing, the passive radiators weight stacks are locked with a wing nut and lock washer. From professional experience, lock washers are basically useless in high vibration applications. Once I finalize the tuning I want to run a real locknut on.
 
Welcome to the new member (in this world), and all the best to mother and father.
 
A stimulating I go.

So In Hornresp all the drivers and PR's are modeled as a lump. One lump for the active side, one lump for the Passive Radiator. I doubled the Sd and the Mass on the PR to make it legitimate. I also remembered to include the base PR mass.

System Schematic:
1776565327170.png


System Model:
1776565408786.png


Driver parameters:

1776565444167.png


Hornresp models via the Benson model. It's perfectly accurate and predates the work of Neville Thiele. Also give you an idea of how long Hornresp has been used!

Passive Radiator Parameters:

1776565536275.png


Simulated frequency response:

1776565583676.png



Impedance:

1776565687723.png

Note that Hornresp does not model any losses. So your Impedance peak is in the right place. It will be lower than the simulation.


Unwrapped phase:

1776565850599.png

When you see the spikes, those are internal box resonances. Same goes for the Frequency response. The spikes are internal resonances.

So you have a really dropped shelf.

What can this box do?

1776566007536.png


This is modeled as 500 watts input for the 2 drivers as a set. The red line is 19mm X-max. That's pretty much maxing out what you can get out of this enclosure. EQ or not.

Now a little different mass loading.

1776566323021.png


Black is the PR mass only. Grey is your current PR loading.

1776566410942.png


This is a simulation of No mass added to your PR's and you have this tuning. Will your mass added the System tuning is below 10 hertz. Not exactly useful.

If you have the capability to EQ:

1776566703669.png


Looks good eh? Red is the EQ'd response. Grey the natural response.

Driver displacement required for this lovely graph:
1776566774816.png


Grey is no EQ, Red is with the EQ shown.

So your maximum output cannot change. That is a physical limit. But with a a little judicious EQ you have a rather flat system that in a basement as an example will be flat to 20 hertz. Sadly our Stick lumber framing in North America is basically see through at frequencies below 30 hertz.

1776567094540.png




1776567136781.png


1776567280426.png


So checking into my treasure trove of CSS Designs, (I consulted for CSS between 2012 and 2014) I can tell you that the SDX10 rapidly runs out of Motor force at about 22mm one way.

1776567673787.png


1776567717237.png

Which is pretty close to what Vance Dickason measured in Voicecoil Magazine. They ran out of power in this test. And the distortion maximums were hit. This driver has rather high distortion in it's current build incarnation.

Mark
 

Attachments

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Hmm, 10 hz for the box tuning is much lower than I was predicting, and seems lower than my impedance measurement suffer suggests. Where is the disconnect? Should be closer to 18hz, with the added mass.

Predicted:
1776580412245.png


Measured, arrow where I think the resonance is, visually smoothing the ripple:
IMG_4631.jpeg


Some of the driver parameters also seem quite different. MMS and Le jumped out at me. I checked these numbers vs Dickason’s on audioxpress and didn’t see any big discrepancies.

IMG_4628.jpeg
 
Last edited:
I used the small signal specs from css to check the impedance curves and the large signal to predict in-use response.

I’m out of practice and have only designed one other speaker myself so I wouldn’t be surprised if I goofed somewhere in the sim, but the numbers lined up with what Dan at CSS said they should be (18hz resonant frequency) so I didn’t interrogate things too intensely.
 
How does hornresp calculate the Fs and Qms here? The Fs seems about as high as the css specs predict for the maximum washer spec on the apr10 and I’m only using about half.

IMG_4633.jpeg



When doing the lump model for the dual PRs how is the doubled suspension stiffness accounted for?

I can send you my VitiuxCAD enclosure models as well if that helps.
 
Last edited:
EngineerNate said:
How does hornresp calculate the Fs and Qms here? The Fs seems about as high as the css specs predict for the maximum washer spec on the apr10 and I’m only using about half.
Click to expand...
Those are entered values for Sd ( Cone area ) and Cms ( Compliance of the spider ). The Fs is computed via the mass added against the spiders spring compliance. And as the PR's are lumped together, the mass is two times that of one PR.

EngineerNate said:
When doing the lump model for the dual PRs how is the doubled suspension stiffness accounted for?
Click to expand...
The stiffness does not double. It's a balance between the mass and the suspension stiffness. The doubling is in Sd. Stiffness or Cms is a relative constant.

EngineerNate said:
I can send you my VitiuxCAD enclosure models as well if that helps.
Click to expand...
Well since you are using the same driver parameters I am, and I have the PR parameters I can do this is Vituix rather quickly myself.

You net cabinet is about 58 litres? It really changes very little. Your stuffing makes up for it.

Mark
 
Regarding suspension, one cone with 900g added mass and two with the same will have different resonant frequencies right? You're working twice the suspension in one vs the other.

I've been assuming my cutouts and thick baffles mostly offset the volume taken up by the magnet and frames and left my sim at 70L

When I calculated the box volume during the design phase I did not count the cylinder that sticks out from the back of the baffles to the front for each cutout.
 
This shows what I'm wondering about for the suspension compliance. If you lump sum the PRs there should be some summation of their individual "spring constants."
IMG_4640.png
 
EngineerNate said:
Regarding suspension, one cone with 900g added mass and two with the same will have different resonant frequencies right? You're working twice the suspension in one vs the other.

I've been assuming my cutouts and thick baffles mostly offset the volume taken up by the magnet and frames and left my sim at 70L

When I calculated the box volume during the design phase I did not count the cylinder that sticks out from the back of the baffles to the front for each cutout.
Click to expand...
OK, maybe I am not explaining this properly. For purposes of modelling multiple drivers in Hornresp they get lumped into one driver that equals the SD of the full complement. So 4 driver 4 times the SD. The mass is also increased by a factor of 4 to keep the model accurate. Spring properties and electrical properties remain the same.

Edit:
What I have not found a clear answer to is exactly how the PR are summed. What I do know is that Hornresp is very thoroughly tested by hundreds of people on diyaudio, and thousands across the world. We regularly post almost overlay sims versus measurements. Sorry that I don't have a concise answer for you!

Mark
 
Last edited:

I need help with Hornresp passive radiator simulation

Post says it all: I need some help simulating a passive radiator in Hornresp I have a few questions: I am not seeing anywhere that I can enter the data for the passive radiator itself. Can someone show me where this is? I am trying to simulate two radiators and two drivers like such. Is...
www.diyaudio.com www.diyaudio.com
 
1776613475711.png


This is what I have set up. I corrected the Parameters in Vituix for your driver. Now I have closer to what I have simulated in Hornresp.

I keep checking to see if I have made an error in either Hornresp or Vituix. Although I do this professionally I am perfectly capable of messing it up too! I don't simulate PR enclosures very often.

Mark
 
Vap of the passive looks much too high as well, I was using 68 and QMS is also different.

IMG_4629.jpeg
 
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