Max / Recommended added weight for a passive radiator?

[Thump]

According to direct correspondence with PE staff on the topic I had in the past with them, what I have in my sig is direct recommendation unless specified otherwise by a manufacturer for a PR

Namely: A PR max weight is said to be its Mmsx3

[tomzarbo]

So sounds like Don and Thump have heard basically the same thing from PE staff...

Speaker Commandment #11 - thou shalt add no more than 150% of a passive radiator's existing Mms.

If there is an exception to this rule for a particular PR, we can post it here along with a pic of the shredded PR and call it good.

Thanks Don and everyone for helping to clear this up once and for all, it's really good information to have nailed down and searchable.

TomZ

[Chris Roemer]

Hmmm...

I interpret thump's sig to be okay w/adding 200% (to get to 3x)? No. ?

[tomzarbo]

Chris, you're right, they're not saying the same thing... my math sucks.

For "Moving mass x3" …..

if moving mass is 10 grams then 10 + 10 + 10 equals 30 grams.

if max added weight is 150% of moving mass with 10 grams Mms, then 10 grams times 150% equals 25 grams... not the same.

TomZ

[donradick]

Chris, you're right, they're not saying the same thing... my math sucks.

For "Moving mass x3" …..

if moving mass is 10 grams then 10 + 10 + 10 equals 30 grams.

if max added weight is 150% of moving mass with 10 grams Mms, then 10 grams times 150% equals 25 grams... not the same.

TomZ

Your first math statement I think is correct.

A PR has MMG (MMP) of 100g - you can add 200g more, for a total of 300g max.

The guy I talked to at PE really didn't have a clue, and he was struggling to answer the question, so I will accept Thumps answer as definitive.

[Thump]

donradick - exactly. 200g more = Mms x 3 given variable Mms in your example.

My goal was locating the simplest reliable repeatable calculation. It appeared almost no PR (that I came across) ever specified what the max safe weight really was. That set me hunting starting at the source.

I wound up chasing this a while back as Chris Roemer, myself and others were trying to help someone else. But I too needed to know this since tuning sets of parallel PR in my LCR was on the horizon. That got delayed again for other reasons as usual, but once unblocked I'll be tuning PR with it.


My emails covered several things, and they passed several sets of eyes. Ultimately it was Greg from PE Technical Support Staff stating with authority we can rely on Mms x 3 for our general rule unless noted otherwise.


I recommended they add this as a technical note / tip to their PR to cut confusion for customers, just like they have for some other stuff like displacement. No idea if they've done that or ever will.

[rpb]

I've never used a PR, and have a few questions. I would assume that a metal coned PR would have breakup. Is that an issue?

I have a 5.25" driver that has really nice mid-range, but needs a well damped box. Currently, the box is sealed, and could use a little boost at the lowest frequencies. Does a PR affect mid-range quality at all?

I have simmed a few PR, but I don't know what to look for in a PR. My goal is to get more spl at 25 hz, and reduce cone excursion in the 40hz range a little. This is what I think will work in my room. My room has a big gain at 45hz. I'd like more output at 25hz compared to sealed, but I don't need more than a couple dB more at 45hz.

If a PR has a fs of 18hz, why would you need to add mass? What about Vas? Wouldn't a larger Vas be an advantage?

I'm thinking of using an 8" PR, but a 10", or 12" may have specs closer to what I need. Mostly looking at the Dayton offerings.

[Chris Roemer]

Don't know what software you're modeling PRs in, but while WinISD (Pro) DOES do PRs, what it won't do is give you a suggested starting point.
PRs are so similar to vented boxes, that I'll 1st sim my driver in a vented box that I like, then run the PR sim shooting for the same box size and tuning.
PRs probably do have breakups, but even most driven cones are up at or above 1000 Hz, and that's way above a PR's pass band.
If you've got a sealed box, odds are you'll have to (roughly) double its size to get appreciable extension (just as you would a vented box).
What's your driver and (closed) box size now?

[rpb]

Peerless HDS.

https://www.parts-express.com/pedocs...ions-46553.pdf

I'd make new boxes. My preference would be under .6 cu-ft, but I can go larger, and possibly a tower design.

My concern on the breakup is that sound off the back of the driver, inside the box might excite it.

[donradick]

Peerless HDS.

https://www.parts-express.com/pedocs...ions-46553.pdf

I'd make new boxes. My preference would be under .6 cu-ft, but I can go larger, and possibly a tower design.

My concern on the breakup is that sound off the back of the driver, inside the box might excite it.

Ran a quick sim in Unibox (my favorite) -
.6 ft^3 = 17 liters
You might be able to use an 8 inch PR.
Using a PE DSA270 with 160 grams added weight, at 20 watts (about 100 dB passband) you can get a EBP alignment that exceeds xmax at 35 Hz, with 6-7 dB more output at 40Hz versus a sealed box.
Increasing the size of the box just causes a higher xmax exceeded Freq.

Hope this helps.

[Wolf]

In the case of an aluminum PR, the material resonance would likely be a non-issue because the woofer driving the PR would likely not be playing the frequency of concern due to the low-pass.

This is just one case. I have had another case with a flat HDF cone on an Eminence PR, and due to being flat, has an energy storage at a midbass frequency related to it's diameter. This had to xover really low to be avoided.

Later,
Wolf

[rpb]

Ran a quick sim in Unibox (my favorite) -
.6 ft^3 = 17 liters
You might be able to use an 8 inch PR.
Using a PE DSA270 with 160 grams added weight, at 20 watts (about 100 dB passband) you can get a EBP alignment that exceeds xmax at 35 Hz, with 6-7 dB more output at 40Hz versus a sealed box.
Increasing the size of the box just causes a higher xmax exceeded Freq.

Hope this helps.

I think I did a sim with that one possibly, but can't recall for sure. I tried a couple that were already loaded in the software too. Seems like I was able to get 6 or more dB at 30hz, and a couple dB at 40hz. I was tuning very low for a 5.25" 2-way. A 10" would look good in a tower design. I'm just not sure if it's worth building towers, considering the spl limitations. My preference is for a stand mount design that can be swapped in, and out of my system more easily. I think that limits me to an 8" PR that is mounted on the back of the box. I don't think the 8" can be tuned low enough to do what I want.

[donradick]

I think I did a sim with that one possibly, but can't recall for sure. I tried a couple that were already loaded in the software too. Seems like I was able to get 6 or more dB at 30hz, and a couple dB at 40hz. I was tuning very low for a 5.25" 2-way. A 10" would look good in a tower design. I'm just not sure if it's worth building towers, considering the spl limitations. My preference is for a stand mount design that can be swapped in, and out of my system more easily. I think that limits me to an 8" PR that is mounted on the back of the box. I don't think the 8" can be tuned low enough to do what I want.

Ah, my friend, the limitation on PRs is xmax and max mmpr. the Fpr is of less importance.

Generally, I can tune PRs xmax exceeded a bit lower than the DUT xmax exceeded.
At that point, I play with box size for the lowest woofer xmax exceeded, and usually play
with power and max spl. This is a sim, in the end. Often, max spl concerns yeald to "usual volume",
and I'll tune for lower SPL and lower bass. Say: 90-95 dB max.