Passive Radiator tuning calculation

[SpeakerBoy 64]

I'm having trouble getting the right mass to tune a PR enclosure

 I got ~1200 grams when I used a calculator online but 158 grams when I used the mass of the air in the port as my starting point. I feel like i'm missing something.

i'm aiming for 8cu @ 26hz with a single 18" and two 18" PR's

What do I need to do to get the correct calculation? The reading seems straightforward but I keep getting these two opposing answers. 

 

Thanks, 

          -Chris

 

[///M5 2,833]

Perhaps you should share what you are using.  Obviously something is drastically wrong...

[SpeakerBoy 64]

(2) PSI 18" PR's and my BTL18. As soon as I figure out how to calculate the tuning I'm ordering the PR's. I figure I can just add mass til it sounds right but I kinda wanna know what's going on.

 

WinISD says 650g (not sure if that's each or total) and has a curve I think fits what I'm looking for, don't know how to factor in cabin gain in relation to the graph but it slopes down til about 35 then rises back up til 26hz where it begins to drop off. Mid 20's is what I want to emphasize with less pronounced upper 30's-40's. I just want some trunk back, not to mention it looks sexy.

I can upload the winisd plot if it means anything.

 

I've heard rumors Fi makes PR's? Only going with the PSI's because they were easy to find, not too expensive, and I can get blank dustcaps. They seem beefy enough for this build.

Edited December 14, 2016 by SpeakerBoy

[///M5 2,833]

Don't you have vance dickasons book?  I remember you buying it I thought.  Always best in a first design to calculate by hand.  

[SpeakerBoy 64]

No, that's definitely still on the list of things to buy.

[altoncustomtech 773]

Fi built the passive radiators I'm using in my Jimmy to match my XCON after getting Aaron and Marks blessing. I'm certain they could build some for you but it will definitely take a lot more time and probably cost more as well. If you can get the PSI's faster and for a reasonable price I would. 

I beat myself up trying to figure the weight needed to get the tuning I wanted as well. The problem was that I didn't have any known T/S or any data at all for the PR's to do any useful calculations. I ended up mounting them backwards and tuning them. The subwoofer cone movement works the same with PR's as it does with a standard ported enclosure. The sub moves the least amount at the tuning frequency. I added weight and adjusted until it was tuned ever so slightly lower than my target frequency. Then I used a little bit of silicone to help ensure the bolt wouldn't back out then mounted them correctly. 

They're still running great about 3 years later and the tuning frequency is still right where I had adjusted it to (30hz). I wish you were closer so I could demo it for you. I absolutely LOVE the way it sounds as does everyone I have given a demo to. 

I'm not certain that how I did it is perfectly correct but it worked fine for me. 

[Ernestgary 0]

How much weight did you end up using on each of your pr's

[altoncustomtech 773]

On 3/8/2017 at 7:55 PM, Ernestgary said:

How much weight did you end up using on each of your pr's

Sorry, missed this in the recents list. 

I honestly don't know for sure, I never measured it. It ended up using a two or two and a half inch long 3/8" bolt and about eight or ten 3/8" washers. 

It doesn't really matter because I just added weight until I achieved the desired tuning. 

[///M5 2,833]

5 hours ago, altoncustomtech said:

It doesn't really matter because I just added weight until I achieved the desired tuning. 

...which is your end goal

[Ernestgary 0]

No prob bob was just wondering