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Joespride
02-25-2011, 08:10 AM
I want to build a midbass enclosure that will go down to about 40 hz using the jbl 2215h drivers (only because I already have them and they have been recently refoamed) anyone know the L X H X W of the internal volume this driver would require. Also reccomended port size any help much appreciated. Joe

Ruediger
02-25-2011, 09:08 AM
You should 1st design the crossover network, and decide which series coil You can afford. The DC-resistance of that coil will determine the resulting Qt of the driver. According to the TS-params table the driver alone has a Qt of 0.21, with a series coil it will get larger.

The formula for Qt is:

1/Qt = 1/Qa + (1/Qe) [Re/(Rg + Re)]

Re is the DC-resistance of the speaker's voice coil.
Rg is the "generator" resistance: Output impedance of amplifier (8 Ohm / 200 or better), cable resistance and series resistances in the crossver.

TS-params for the 2215 from the table:
fs = 20 Hz, Qt = 0.21, Vas = 736 ltr,
Qm = 5.5, Qe = 0.22, Re = 5.7 Ohms

In the Technical References Thread (General Audio Discussion) there is the Thiele paper. In table I there are the alignments.

Say Your drivers Qt would become 0.259 (3rd entry in table), then
f3 = fs * 1,77,
f3 / fb = 1.25,
Vab = Vas / 4.46

f3 would be 35.4 Hz, Vab would be 165 ltrs

Other alignments with a not ideally flat response curve are possible, but the 1st thing You need to do is to estimate the effect of the crossovers DC-resistance (see the table in the papers and experiment a bit), and then let somebody with a PC-program do the calculation for You.

Let him do the calculations with the corrected Qt!

Ruediger

Joespride
02-25-2011, 01:13 PM
You should 1st design the crossover network, and decide which series coil You can afford. The DC-resistance of that coil will determine the resulting Qt of the driver. According to the TS-params table the driver alone has a Qt of 0.21, with a series coil it will get larger.

The formula for Qt is:

1/Qt = 1/Qa + (1/Qe) [Re/(Rg + Re)]

Re is the DC-resistance of the speaker's voice coil.
Rg is the "generator" resistance: Output impedance of amplifier (8 Ohm / 200 or better), cable resistance and series resistances in the crossver.

TS-params for the 2215 from the table:
fs = 20 Hz, Qt = 0.21, Vas = 736 ltr,
Qm = 5.5, Qe = 0.22, Re = 5.7 Ohms

In the Technical References Thread (General Audio Discussion) there is the Thiele paper. In table I there are the alignments.

Say Your drivers Qt would become 0.259 (3rd entry in table), then
f3 = fs * 1,77,
f3 / fb = 1.25,
Vab = Vas / 4.46

f3 would be 35.4 Hz, Vab would be 165 ltrs

Other alignments with a not ideally flat response curve are possible, but the 1st thing You need to do is to estimate the effect of the crossovers DC-resistance (see the table in the papers and experiment a bit), and then let somebody with a PC-program do the calculation for You.

Let him do the calculations with the corrected Qt!

Ruediger


I plan to use my marshand active to cut off high side at around 350 or 400 hz. This is going to be a midbass cabinet for an oris orphean horn and may or may not stay depends on integration I'm not set on the amp either at this point although I'm thinking muse 160 I have on hand. Guess I'm more looking for a generic size enclosure that I can tweak by ear. Joe

Ruediger
02-25-2011, 11:16 PM
Okay, alignment no. 2 from table:

Qt = 0.209,
f3 / fs = 2.28,
f3 / fb = 1.32,
Vas / Vab = 7.48

=> f3 = 45.6 Hz, fb = 34.5 Hz, Vab = 98.4 ltr

You should calculate a proper port, not tune by ear.

Ruediger