Box design for JBL 2205A

[speakerdave]

Hi Ruedider,

Thank You for your reply, your reply is quite technical for me to understand, can you help me to change the design to fit the requirement? I am looking at a general purpose bass box of about 30 to 40 Hz. Look forward to your reply. Thank You

Are you able to respond to this?

[Ruediger]

Hi Ruedider,

Thank You for your reply, your reply is quite technical for me to understand, can you help me to change the design to fit the requirement? I am looking at a general purpose bass box of about 30 to 40 Hz. Look forward to your reply. Thank You

Your speaker simply is no good for the box which You want. No 30 Hz, no 40 Hz.

As I wrote before: You cannot pick any box and any tunnel and combine them with any speaker.

Your large box is not a design but a wish. It does not work.

The box #6 from the table which speakerdave posted seems to be the best compromise for Your wishes:

It will have a -3dB frequency of 48.6 Hz, and a ripple of -0.47 dB.

If that is too large, then the second of the boxes which I calculated is right for You:

A vented box, ca. 70 to 75 liters net volume. This will have a -3dB frequency of ca. 53 Hz and no ripple.

If You want that box let me know. Then I'll calculate the missing data such as port size and length.

The 1st box gives a bit more bass, but it is larger.

For both cases I calculated with a Q-value of 0.26. I will tell You how to achieve that.

Ruediger

[speakerdave]

Thank you. I was not able to give any more-specific help.

[acmv]

Hi Ruediger,

Thank You for your reply, would appreciate very much if you could help to provide the rest of the data for your suggested box design. Thank You for the time and effort spend on my thread.

Hi speakerdave, your contribution towards my thread is most appreciated, Thank You.

Regards
acmv

[speakerdave]

. . . . Hi speakerdave, your contribution towards my thread is most appreciated, Thank You. . . .

Well, I tried to get my oar in. Hope it works out for you.

[acmv]

Definitely! Thanks a lot. Cheers!

Well, I tried to get my oar in. Hope it works out for you.

[Ruediger]

Box material: 19mm resp. 0.75”

Box inner height: 52.6 cm
Box inner width: 43 cm
Box inner depth: 33.9 cm

Box outer height: 56.4 cm
Box outer width: 46.8 cm
Box outer depth: 37.7 cm

Build a shelf into the bottom of the box. Make the shelf 29.2 cm long. Mount the shelf with a spacing of 4.7 cm from the bottom. The spacing from the rear must also be 4.7 cm.

The shelf forms a tunnel with a length of ca. 33.9 cm + 1.9 cm (front panel). The area of the tunnel (vent area) is 4.7 cm (the spacing) x 43 cm (inner width) = 202 cm**2. A circular tube with the same area has a radius of 8 cm. The “equivalent radius” is 8 cm. Both ends of the tunnel are flanged. The end correction is 2 * 0.85 * 8 cm = 13.6 cm. The total length of the tunnel incl. end correction is 33.9 cm + 1.9 cm + 13.6 cm = 49.4 cm.

Box net inner height without space occupied by tunnel is 52.6 cm - 4.7 cm – 1.9 cm = 46 cm. Box net volume without space occupied by tunnel is 46 cm x 43 cm x 33.9 cm = 67 liter. The volume occupied by the inner end correction is neglected.

Box resonant frequency is 42.6 Hz.

The volume occupied by the driver and the volume occupied by the bracing is not compensated for. From the JBL enclosure guide:

Use fiberglass to line 5 or 6 sides of the box interior. Any fiberglass will do, but if you use R-19 or R-25 insulation type fiberglass, you can ignore the volume of the bracing in the box because thick fiberglass adds virtual volume.

Qt value:

If the speaker (2205A) were directly connected to a very good amplifier it would see a generator impedance of almost 0 Ohms. The resulting Qt would be 0.21.

We need a Qt value of 0.26. We can achieve that by presenting a generator impedance of 1.36 Ohms to the speaker.

An amplifier with a damping factor of 200 at 8 Ohms does have an output impedance of 8/200 Ohms = 0.04 Ohms.

10 meter loudspeaker cable with 2.5 mm cross section will have a resistance of 0.14 Ohms.

The sum is 0.04 Ohms + 0.14 Ohms = 0.18 Ohms. For a total of 1.36 Ohms we need 1.18 Ohms more.

An affordable series inductor for an xover will have such a DC resistance.

Ruediger

[acmv]

Hi Ruediger,

Thank You for the enclosure plan, will try it out and let you know, you are of great help! Thank You.

[acmv]

Hi Ruediger and All,

I have completed the the box as per discussed in the following thread, the result is astonding. It is very good, please do not ask me about what frequency I cut and how is the frequency response, as I do not have the equipment to test it out.

I have used 3mh inductor to do a simple crossover that I get best results after trying a few values.

Ruediger, will you be able to advice me on a box for the for the JBL 2225j, I want to try this ouy as my next project. Will be very grate if you could help, Thank You.


Sorry, forget to add, looking to cut at about 30 to 40hz as a bass unit.


Regards

Hi Ruediger,

Thank You for the enclosure plan, will try it out and let you know, you are of great help! Thank You.