PCD Box Response for SB34NRXL75

[jimbones]

I ran a sim for a woofer I would like to use. Can someone take a look at it and let me know if it looks like I did it correctly? I see 2 boxes in red and not sure if that is right (Le coeff and Le expon)

[ernperkins]

That looks correct to me. You could also use Jeff's Woofer Box Model and Circuit Designer if you're interested in seeing excursion, vent velocity and other items of interest . The PCD version is a simpler version of the Woofer Box Model and Circuit Designer.

[DeZZar]

I get 'optimal' results in winISD with a 70L box tuned to 32hz.

-3db @ 34.55Hz, 113+ db capable @ 50hz (prior to any baffle step compensations), 200W max power handling - thermal limit in this case as 200 watts will only exceed xmax below 25hz (rather good result) and wont reach xmax above the tuning frequency at all.

I'd head somewhere around a 5 inch port to keep velocity down.

[andy19191]

Some discussion using it for a 3 way here.

[jimbones]

I get 'optimal' results in winISD with a 70L box tuned to 32hz.

-3db @ 34.55Hz, 113+ db capable @ 50hz (prior to any baffle step compensations), 200W max power handling - thermal limit in this case as 200 watts will only exceed xmax below 25hz (rather good result) and wont reach xmax above the tuning frequency at all.

I'd head somewhere around a 5 inch port to keep velocity down.

what diameter port are you using? also length? Thanks. I think I will use your recommended design as it is proven. Thanks

[DeZZar]

what diameter port are you using? also length? Thanks. I think I will use your recommended design as it is proven

Depends on what size tube you are able to get. So as an indication, keeping port velocity down, you could use:

2x 4 inch ports @ 24 inch long
1x 5 inch port @ 17 inch long
1x 6 inch port @ 25.5 inch long

HOWEVER....you would always check the tuning of your port once the cabinet is built, driver installed and any insulation/damping materials are in place. The standard figure coming out of any modelling software, in my experience, has never ended up being the final specific result. For me at least, its always ended up being shorter.

Whatever diameter tube you end up with, I would cut it just a little longer than spec, install, measure and then start tweaking the length to get to your final desired result.

[fpitas]

Whatever diameter tube you end up with, I would cut it just a little longer than spec, install, measure and then start tweaking the length to get to your final desired result.

+1 When I use Precision Ports, I don't glue them together until the port length has been experimentally determined. Although in my experience, WinISD comes very close in its predictions.

[jimbones]

Depends on what size tube you are able to get. So as an indication, keeping port velocity down, you could use:

2x 4 inch ports @ 24 inch long
1x 5 inch port @ 17 inch long
1x 6 inch port @ 25.5 inch long

HOWEVER....you would always check the tuning of your port once the cabinet is built, driver installed and any insulation/damping materials are in place. The standard figure coming out of any modelling software, in my experience, has never ended up being the final specific result. For me at least, its always ended up being shorter.

Whatever diameter tube you end up with, I would cut it just a little longer than spec, install, measure and then start tweaking the length to get to your final desired result.

I think I will go with 4 inch dia port tuned to low 30's.

[DeZZar]

Just note that that's TWO of them @ 4inch to keep the port velocities in check.

[jimbones]

I get 'optimal' results in winISD with a 70L box tuned to 32hz.

-3db @ 34.55Hz, 113+ db capable @ 50hz (prior to any baffle step compensations), 200W max power handling - thermal limit in this case as 200 watts will only exceed xmax below 25hz (rather good result) and wont reach xmax above the tuning frequency at all.

I'd head somewhere around a 5 inch port to keep velocity down.

BTW 70L seems small. not even 3 cu ft?? I'll run in win ISD as you suggest. Also I just noticed my home depot has 6 inch x 24 inch pvc pipe, hmmmm

[jimbones]

So I ran a sim in Win ISD please see attched and advise if I did this correctly. Also note that there is only one port. Is the velocity too high? How do I interpret the graph?

[a4eaudio]

Under Signal, what power level do you have? You can (1) enter the watts where driver reaches xmax in the "cone excursion" graph or (2) enter the watts at a somewhat loud level that you think you will actually listen at. My guess is that you currently have the starting point of 1w and thus very little output and therefore very little port velocity.

[Chris Roemer]

Port velocity is probably low because you're only feeding it 1 watt (signal tab)?
You've got a square port (click the "shape" icon to go back to round). (Looks like you've got the "default" 4.02" x 4.02" size - NOT 6" id.)
At the 32Hz Fb, your length is almost 14" (35cm).

If you go back to round, and change the dia. to 6", your "Cross area" will increase as well as your length.

THEN kick the signal up to 200w and you can see where your excursion and velocity end up (they'll be okay).

[jimbones]

Chris Roemer

attached are round port, excursion at 200w and port velocity at 100W (because it goes off grid at 200w

[jimbones]

here is 6 inch port, at 200w drops back onto grid. looks like I will need 2 4s or one 6 inch port.

[fpitas]

2 x 4 inch Precision Ports is what I've ended up with in a similar situation.

[a4eaudio]

You can click on the little wrench icon in WinISD and change the scale. I believe the rule of thumb is keep the port velocity below 14 or 17 ms. And then almost everyone breaks that rule of thumb because it's too demanding. Something in the mid to high 20s with a big roundover on the port is usually acceptable.