Designing with the New Creative Sound Passive Radiators - Part 1

[Jeff B.]

Are you ready to design with a passive radiator? Let me show you how easy it is.

A short time back I was asked to design several subwoofers – all using passive radiators. Unfortunately, I did not really like the way most software functioned when it came to designing this type of a system. Most of them were not intuitive to me and did not perform some of the functions that I felt would have really speeded up the process. So, you know me, I pulled out my Benson book from the shelf, did my homework, and created a new version of my Woofer, Box, and Circuit Designer that worked with passive radiators in a more intuitive manner. The file is available here:

http://audio.claub.net/software/jbagby.html#WBC

So, first of all, why use a passive radiator? Many of our modern high quality woofers have much greater linear excursion than was available to us even a decade ago. The problem is that with this greater excursion comes the requirement for the port to have a greater cross-section as well in order to avoid high port air speed and noise, as well as avoiding too much compression due to port resistance. This is especially true if you need to tune a relatively small box to a fairly low frequency. In this case, it becomes nearly impossible to stuff a large enough port into our small box without excessive compromises. It is also true that with many woofers you can use them in a smaller than optimum enclosure with a passive radiator tuned to a very low frequency and increase output while decreasing the driver excursion at the same time, since many of our favorite plate amps have infrasonic filters built in anyway.

Recently, word of my new program reached Bob Reimer at Creative Sound Solutions (CSS). http://www.creativesound.ca/ CSS now has three new Adjustable Passive Radiators (APR). Bob wanted to know if his new passive radiators would work well with my program. It turns out they are a wonderful match, so I wanted to point those who may be interested in a passive radiator design, but who found it too intimidating (as I once did) toward the CSS passive’s and show how easy it is to design a subwoofer using them along with my program.

First a little more info regarding the CSS APR’s:

These passive radiators come in three sizes: 10”, 12” and 15”. They have a thick treated paper cone, very large foam surround, and a stamped basket with a spider assembly. Since there is no motor to support the stamped basket is more than adequate for supporting the linear excursion of the cone/mass assembly. The radiators have fairly decent Xsus as well of 26mm, 29mm, and 33mm respectively. And for those who have been around DIY subs for a while they were designed by Dan Wiggins of Adire fame.

Here are the three passive sizes



What makes these passive radiators unique is that each one has a plastic tube protruding from where you would normally find a dustcap. At the end of this tube is a screw on cap. Once the cap is removed you will find a thread bolt sticking up in the center of the tube. Each passive radiator comes with a small box of washers that fit very nicely in the ID of the tube and over the treaded rod. Each washer is 50 grams in weight, and you receive 20 of them along with a lock-washer and wingnut for securing them. Once the correct number of washers have been installed simply screw the plastic cap back on the tube and listen to your new sub.

I found these new passive radiators to be a very clever design. They allow you to fully install the woofer, plate amp, and passive radiator to the enclosure. Then you can do your tuning, and make any adjustments you may desire from the outside very easily and very fast.

Here are a few pics of the passive radiators:








Part 2 Follows......

[Jeff B.]

Here’s a little example……and how to use my program too.

Let’s take a look a subwoofer using some Parts Express items and one of the CSS passives. In this example we will use a Dayton RSS315-HO woofer, A Parts Express 2 cubic feet (17” cube) sub enclosure and a HPSA500 subwoofer amplifier. Also for our example we will use the CSS APR15 passive radiator. This passive come with the following specs:

Sd: 800 cm^2
Qms 7
Cms 0.48 mm/N
Rms 3 Kg/s
Vap: 463 liters
Mmp: 135 grams
Fp: 19 Hz
Xsus: 33mm one way
Maximum moving mass: 1200 grams
Minimum Fp: 6.4 Hz

Our subwoofer will look a little like the Sunfire subs with the woofer mounted on the front, the passive radiator mounted on the back, and the Dayton plate amp mounted on the side.

Now open up my Woofer, Box, and Circuit Designer 4.0 program and click the “Selected Box Mode” button until you see the green Passive Radiator appear. (If you are using the program straight from the download then the RSS315-HO is already loaded. Next enter the Vab for the project in the Box Parameters box of 56 liters, and I chose 23Hz for my “desired tuning frequency”. The program will calculate what it takes to achieve your desired tuning with the passive radiator parameters you enter, but the Fb that the program will use will only be the one that appears in the box labeled “Calculated Radiator Parameter”, unlike the vented the mode which uses the Fb you enter above.

Next, enter the parameters for the passive radiator. The program will then look like this (with amp set to only the built-in 18Hz infrasonic filter and an 80Hz lowpass crossover):



In the “Passive Radiator Parameters” box you will now see that the program is telling you that you need to add 714.91 grams to the passive radiator in order to tune it to your desired 23 Hz in this enclosure (it will be a different amount for different enclosure volumes). Since our CSS APR comes with weights that are in 50 gram increments we will enter 700 grams in the box below this. The program will automatically recalculate all of the passive radiator parameters with the additional mass included, and we see that the Fb is 23.2 Hz – which is close enough for our purposes. And below we will see this chart of the response:




A 21Hz F3 in 2 cuft box with no boost is pretty nice, don’t you think? And it would have been even a little lower if it hadn’t been for the infrasonic filter in the amp, but that’s OK, because this filter helps us control cone excursion below Fb, while the APR controls it very well at Fb and above.

Since this looks like a nice set-up we will now take 14 of the 50 gram washers – totaling to 700 grams, slide them into the tube over the threaded rod, install the lock washer, and tighten down the wingnut. Here’s what that will look like:




We may or may not be finished. If, after listening for a while, you decide you want to change the tuning to be a little overdamped you might want to add couple more washers. The program will model the change for you, and you can easily change the weights on the passive radiator simply by removing the wingnut. Once you decide you are finished all you need to do is screw the plastic cap onto the tube and enjoy the music – or the movie explosions



See how easy this is? You can apply what I have described here to any number of drivers and use any of Bob’s other radiators, or even multiple radiators, and you no longer have to be intimidated by a passive radiator design and what used to be a shot-in-the-dark or trial-and-error design method.

Oh, and this is important, knowing that CSS is in Canada, there is now a US source for the radiators too. Meniscus now carries them for CSS (that’s where mine came from).

If you decide to give them a try post a note and let me know how things work out.

Jeff B.

[nick29498141]

Great thread, Bagby!

[ctbowman]

what book is this? and where do I buy it?

[bobreimer]

Thanks alot Jeff. Dan and I are pleased with how these turned out. In about 2 months we will have a matching TRIO12 driver (same cone, basket, surround and spder) which was designed to work well with 2 of the APR12s.

Thanks also for developing software for the DIY community. It's a great service.

Bob
Creative Sound Solutions

[Mark65]

Great thread, Bagby!

+1.

I built a PR sub with shawn's design, but I've felt since before I built it that there was some voodoo involved, and have thus figured that designing a larger one was outside my (admittedly limited) abilities. Your new program and those PR's have me rethinking that position.

Thanks, Jeff!



Mark

[eyekode]

That does seem like a nice design for a passive radiator. The tunability sounds great. But how do you really take advantage of it?How do you measure system impedance when using a plate amp?

[dbe]

Are you ready to design with a passive radiator? Let me show you how easy it is.

How cool are those? Waaaaaayyyyyyyyyyyyyyyyyyyy cool.



Dave

[Jeff B.]

That does seem like a nice design for a passive radiator. The tunability sounds great. But how do you really take advantage of it?How do you measure system impedance when using a plate amp?

Wouldn't the same question apply for a vented design? There are ways to temporarily tap the woofer from outside to measure impedance. However, this really isn't necessary, resonance is easily measured externally at the cone if that's a question. The software is very accurate, at least as much as port tuning equations and probably a bit better.

[Jeff B.]

what book is this? and where do I buy it?

Book?

[philiparcario]

jeff I have a pair of rss390ho's sitting and waiting. i have two questions

1 ) I have only mac's will your software work?

2) if your software is pc only I want to use my 2 rss390's in a pair of 3 cu ft boxes with that radiator 15 inch. what weight should I use and what will the sub run down to an f3 of ? thanks phil

[dlneubec]

Very nice thread, Jeff and helpful for those (like me) who have not executed a PR design. Those PR's look very use friendly and cost effective as well. I may have to consider a PR design for my TC1000's.

You might consider doing one of these threads with a typical ported and/or sealed design with screenshots of your software setup, results, etc. That would be an excellent reference for newbies and new users of your software.

[Paul Carmody]

Very nice thread, Jeff and helpful for those (like me) who have not executed a PR design. Those PR's look very use friendly and cost effective as well.

Yes, what Dan said.

But nice job, Jeff! I've never done a PR design, however I have to design a sub for a friend soon, and space is a commodity, so this might be just the thing.

And so, Jeff Bagby continues his dominance of free speaker design software.

[brianbunge]

Jeff,

Very cool software! I've played with it once so far and like it a lot. I have one question though. You state above that the software comes preloaded with the Dayton RSS390HO. But when you look at the screen shots you posted you will see that it says the driver is the RSS315HO. When looking at the specs, they really don't match either of the HO drivers (unless they are actual measured specs) and the Sd would suggest that it's a 12" driver instead of a 15" driver.

So, needless to say, I'm confused as to exactly what parameters are loaded into the program and where they came from.

As always, thanks for all your work and for offering these great programs. I just can't figure out exactly what's going on here!

Brian

[Jeff B.]

Jeff,

Very cool software! I've played with it once so far and like it a lot. I have one question though. You state above that the software comes preloaded with the Dayton RSS390HO. But when you look at the screen shots you posted you will see that it says the driver is the RSS315HO. When looking at the specs, they really don't match either of the HO drivers (unless they are actual measured specs) and the Sd would suggest that it's a 12" driver instead of a 15" driver.

So, needless to say, I'm confused as to exactly what parameters are loaded into the program and where they came from.

As always, thanks for all your work and for offering these great programs. I just can't figure out exactly what's going on here!

Brian

Thanks for catching that. The driver in the example is the RSS315-HO. I have since corrected the text above. Sorry for the confusion.

[Fatcat]

This is great stuff Jeff. Thank you for sharing. I'm looking forward to messing around with it later.

Best.......Carlo.

[robertf]

This looks great. In fact I am working on a passive radiator design using the RSS315HO-4 in a two cubic foot box! I am going to look into the CSS radiators and I will report back.

[Jeff B.]

jeff I have a pair of rss390ho's sitting and waiting. i have two questions

1 ) I have only mac's will your software work?

2) if your software is pc only I want to use my 2 rss390's in a pair of 3 cu ft boxes with that radiator 15 inch. what weight should I use and what will the sub run down to an f3 of ? thanks phil

I do not believe my VBA routines run on a Mac. And, since I made the mistake of typing RSS390 in the text above, when I meant RSS315 - which is what the example really was (I have since changed that), I will give you results you requested.

If you use the RSS390-HO in a 3 cuft enclosure, with the 15" APR passive, then you would need to add 450 grams (9 of the weights). This would tune the enclosure to 23Hz and also yield an F3 of 23 Hz as well. Here is the graph for it. Since I didn't know what you might be using for an amp/crossover I turned those functions off for this simulation.



Jeff B.

[dwigle]

Jeff, great program! I understand that you need to use a PR with 1.5-2 times the Sd as your driver. If I plug in an undersized PR with a particular driver what will the program tell me? IE, what parameters will indicate I need more PRs or a larger PR? Will it tell me to add more weight than the PR can handle?Thanks,

[eyekode]

Wouldn't the same question apply for a vented design? There are ways to temporarily tap the woofer from outside to measure impedance. However, this really isn't necessary, resonance is easily measured externally at the cone if that's a question. The software is very accurate, at least as much as port tuning equations and probably a bit better.

For ported it is easy because you just feed the lead wires through the port. But with a ported system it is a done deal. There isn't much you can do after you constructed it. I thought with the external weights it would be neat to see the tuning change when you add weight. But in this case I don't see how I can measure impedance without making temporary holes in the cabinet...

You say resonance is easily measured externally at the cone: do you mean just sweeping slowly and seeing where the first "hump" in excursion is?