From BR to PR: How to?

[rho]

I'm planning on rebuilding my current 2-way speakers. They are 15 liter cabinets ported with a 5cm BR, 14,5cm long.
They are stand mounts now, but I want to make them floorstanding, with the filter and some sand in the lower part of the cabinet.
The problem I dealing with is that I want to use a passive radiator in the new cabinet and i don't know how to calculate the mass I should add to the PR to get the tuning right.
I'm planning on using the Seas SP 17R .

Thanks for any help.

[rho]

I've tried with WinISD, but I need Qms for that. (won't work with out that parameter).

According to the datasheet for this PR i need to add about 5gr.


Is there a way to calculate the correct mass I should add?Datashee tSeas SP 17R

[Ron E]

Qms isn't extremely critical, you can just guess, enter several values between, say, 3-20 and see what happens.

Qms affects response shape because it is a measure of how lossy the PR suspension is. If you have a very lossy PR you might want to add a bit less mass because the response would otherwise be droopy.

One way of calculating PR mass is to calculate the length of a port that has the same diameter as the PR. Calculate the mass of air inside the port and subtract the mass of the PR from that. The remainer is the amount of mass you must add.

[rho]

I've done some simulations with WinISD. I used 15 as a value for Qms (right in the middle of what you advised).

I can get a very good match to the curve I get with the port with a SP 21R and 33g of extra mass.

I don't know how accurate these simulations are, but I get the impression that the phase-plot and group delay curves look much better with a BR then with a PR.

Maybe someone could help me with simulations using diffent software?

As a low-mid I use a Seas H648
T/S:

Nom. Imp: 8 Ohm
Powerhandling: 100/250W
Fs: 33 Hz
Re: 6.1 Ohm
Sens.: 88.5 dB
Forcefactor: 8.5 N/A
Lc: 0.6 mH
Sd: 120 cm²
Mms: 16 g
Vas: 27.5 l
Cms: 1.4 mm/N
Qes: 0.3
Qms: 1.76
Hg: 6 mm
Hc: 12mm
Dc: 39mm
Xmax: 3mm

[Ron E]

I modeled your combo with the SP17 in my spreadsheet - I used a 15L box and 32g mass to tune to 30Hz and got the graphs attached assuming Ql=15, Qb=30 and Qp=10. You want to use a PR with a lower resonant frequency to move the PR notch a bit lower in frequency. The excursion plot could use a bit of explanation - this is what the excursion would be at 100W (40V peak) input if everything were perfectly linear. The excursion at 20V would be half and the excursion at 10V would be 1/4 this value, so you get a feel for maximum input capability.

[rho]

Thanks for the files!
This looks very similar to what I get out of WinISD.

What do you think about using the bigger PR? (PS 21R)

It's not that I want more bass out of the speaker, it's that I want less influence of the port. (portnoise, proximity to walls,...)

...and a PR looks cool.

[Ron E]

I think you should get slightly better performance from the larger PR. Depending on the size of your port currently, you might even get a bit more output near tuning.

[Notax]

More added mass (for the same Fb) and enclosure is smaller. It is hard to make good and deep bass, with floorstanding cabinet in this combination.
If you use this passive radiator without added mass, I calculate 14 litar and Fb=47.3 Hz. (recomanded)

You can go with lower Fb and bigger enclosure, but probably it will be lower SPL at low frequencies, then average.
Vb=32.3 litar , Fb=33 Hz, added mass 5 gram + 21.5 = 26.5 gram for passive. Probably, it could be low bass, but tiny.
Without added mass (21,5 gr) and same Fb=33 Hz, Vb=51 litar.

[rho]

I don't think the Seas will perform any better in a bigger box. 15 liter is about the biggest that the Seas will perform well in.