Sealed driver in ported box

[presscot]

Hi everyone,

I have a pair of 5.25" mid-woofer drivers. Their parameters are as follows:

fs = 68 Hz
Vas = 0.23 cu.ft.
Qts = 0.45
Xmax = 6 mm.
Imp. = 4 Ohms
Power = 65 W

According to Loudspeaker Cookbooks, a rule of thumb suggests that drivers with Qts of greater than 0.4 and high voice coil overhang (Xmax) be used with closed box. Nevertheless, I wonder if I use these drivers with vented box, what will be the results?

Actually, I'm going to use them in passive radiator system. But, AFAIK, the PR system gives the same result as vented system, doesn't it?

 

[Lojzek]

You have started 3 threads for one and the same project.

 

[presscot]

Don’t think that way, please, because this thread is about theory and different problem.

 

[markbakk]

The result will be OK. Ported systems reduce cone displacement above fc (given a desired SPL).

 

[mattstat]

Qts = 0.45 . . . . rule of thumb suggests that drivers with Qts of greater than 0.4 . . . be used with closed box

You're only ~10% away from the rule of thumb's boundary - most people would say "close enough" since it sounds like you're making do with drivers you already have.

AFAIK, the PR system gives the same result as vented system, doesn't it?

In theory, basically yes. In practice, not always. The passive radiator has its own set of parameters that affect response when combined with those of the enclosure and woofer, so there can be minor or significant differences from a proper ported design depending on the exact units used.

 

[GM]

Nevertheless, I wonder if I use these drivers with vented box, what will be the results?

Greets!

Vented net volume (Vb) (L) = 20*Vas*Qts'^3.3 (Ft^3 = (Vb)*~28.31685)

Vented box tuning (Fb) (Hz) = 0.42*Fs*Qts'^-0.96

F3 (Hz) = Fs*0.28*Qts^-1.4

When Qts' is:

~0.403, Vb = Vas, Fb = Fs

< ~0.403, Vb = < Vas, Fb = > Fs

~0.403, Vb = > Vas, Fb = < Fs

Qts' = Qts + any added series resistance [Rs]: http://www.mh-audio.nl/Calculators/newqts.html

 

[GM]

AFAIK, the PR system gives the same result as vented system, doesn't it?

Not IME, but I DIYed since it was my only option way back when AFAIK. Regardless, PRs when tuned to the same as a vent tended to 'ring' due to peaking at Fb, an audible problem since it was typically tuned around/at driver Fs in the mid 20s - low 30s where room modes wreaked havoc on speaker response, so always tuned a bit lower based on the desired in room performance.

Note too that I was comparing them to 'critically damped' vents and tuned each cab individually, so YMMV, etc..