Box design for JBL 2205A

[acmv]

Hi,

Recently, just aquired a pair of JBL 2205A. Now, I want to build the enclosure for the drivers. Can some kind soul recommend to me some box designs? Thank You.

Looking at horn bass design, but I am open to suggestions. Thanks for the feedback.

[LE15-Thumper]

Hi,

Recently, just aquired a pair of JBL 2205A. Now, I want to build the enclosure for the drivers. Can some kind soul recommend to me some box designs? Thank You.

Looking at horn bass design, but I am open to suggestions. Thanks for the feedback.

Search the old library, you'll find plenty of options there.

[speakerdave]

Hi,

Recently, just aquired a pair of JBL 2205A. Now, I want to build the enclosure for the drivers. Can some kind soul recommend to me some box designs? Thank You.

Looking at horn bass design, but I am open to suggestions. Thanks for the feedback.

As I recall the 2205 was first an Alnico design (2205A/B) which, after the switchover to ferrite (2205H/J) because of external reasons, soon morphed into the 2225H/J with what changes I do not know. You might be able to deduce some of them by studying the T/S parameters. For rear-loaded horn the C34/4530 style enclosure would be OK for that driver.

Also, for bass reflex for hi fi use decide what kind of alignment you want and use one of the enclosure design software programs to get dimensions and porting details.

For SR use the JBL Pro Enclosure Guide will provide data. (GI)

[Ruediger]

The relevant Thiele Small parameters for the 2205A are:

fs = 30 Hz
Qt = 0.21
Vas = 297.3 liter

Qt will become a bit larger when a passive crossover is used. The combined resistance of amplifier, cables and the crossover’s series inductors determines Qt. See below for details.

Of the alignments in Thiele's tables only two are feasible with this driver.

No. 2, QB3, f3/fs = 2.28, f3/fb = 1.32, Cas/Cab = 7.48, Qt = 0.209
No. 3, QB3, f3/fs = 1.77, f3/fb = 1.25, Cas/Cab = 4.46, Qt = 0.259

There result the following boxes.

No. 2, f3 = 68.4 Hz, Vab = 39.7 liter
No. 3, f3 = 53.1 Hz, Vab = 66.7 liter

Any Qt with 0.209 <= Qt <= 0.259 is feasible, You need to do a non-linear interpolation between Alignments No. 2 and No. 3. For that You need Thiele’s tables. Somebody with a good design program could do that for You.

Alignment No. 3 will supply good midbass with punch :) Depending on Your taste You may need a sub then.

This post contains the "formula" how to calculate the resulting Qt.

http://audioheritage.org/vbulletin/showpost.php?p=273909&postcount=105

The data for the 2205A is:

Qa = 5
Qe = 0.22
Re = 5.5 Ohms

Ruediger

[acmv]

Thank You for the replies. But being an amature in speaker building, I am unable to understand the phrases used here. Things like Q values, alignment, etc. :banghead::banghead::banghead:

So please pardon me. Is there any thing that I can read up, or maybe a few suggested designs that I can follow? Your effort will be most appreciated. Thank You.:D:D:D

[Ruediger]

Thank You for the replies. But being an amature in speaker building, I am unable to understand the phrases used here. Things like Q values, alignment, etc. :banghead::banghead::banghead:

So please pardon me. Is there any thing that I can read up, or maybe a few suggested designs that I can follow? Your effort will be most appreciated. Thank You.:D:D:D

You can either build:

a rearloaded horn which will be 60 cm x 60 cm x 110 cm. Plans are readily available, for example JBL 4530. This will not supply really deep bass.

or:

a vented box, ca. 70 to 75 liters net volume. This will have a -3dB frequency of ca. 53 Hz. That is plenty of bass from a very small cabinet. For really deep bass You will need a subwoofer.

Make up Your mind, then we can proceed.

Ruediger

[speakerdave]

Use this enclosure guide: here's the link: http://www.jblpro.com/pub/manuals/enclgde.pdf

Here's the first page: Build #6.

[acmv]

Thank You everybody for the reply. After reading thru the information, I have come out with my prefered dimension on the interior of the box. I am looking at 25" High by 20.5 Wide and 18" deep. Having a port of 1.4" high by 20.5" wide and length of 11" at the bottom. Is these dimensions workable? Please give your advice, your feedback will be most appreciated. Thank You.

[Ruediger]

The box is too large. You cannot pick any box and any tunnel and combine them with any speaker.

I calculated box net volume and box resonant frequency from Your data.

Box net volume: 25 x 20.5 x 18 in**3 = 9225 in**3 = 151 liter
Effective radius of vent: R = sqrt( 1.4 x 20.5 / pi) = 3.02 in
End correction for tunnel, both ends flanged: L” = 1.70 R = 5.13 in
Effective length of tunnel: 11 + 5.13 + 0.75 in = 16.9 in
Volume occupied by tunnel: (11 + 2.57) x (1.4 + 0.75) x 20.5 = 598 in**3 = 9.8 liter
Box net volume corrected: 9225 in**3 – 598 in**3 = 8627 in**3 = 141 liter
Box resonant frequency wb: wb = 2 pi fb
Lv / Sv = 1.84 x 10**8 / wb**2 Vb
fb = sqrt( 1.84 x 10**8 Sv / (Vb Lv) ) / (2 pi)
= sqrt( 1.84 x 10**8 x 28.7 / (8627 x 16.9) ) / (2 pi)
= 30.3 Hz

If I made a mistake let me know.

This gives a response which is down -1 db at 250 Hz and -7 dB at 35 Hz.

Ruediger

[acmv]

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

[speakerdave]

The box is too large. . . . This gives a response which is down -1 db at 250 Hz and -7 dB at 35 Hz . . . .

Maybe just right for his room.

[Ruediger]

Maybe just right for his room.

No, that is a sick response curve.

[speakerdave]

No, that is a sick response curve.

I am unable to semanticize "sick" in this context into technical or any other relevant terms. Do you mean one with a bump in the bass followed by a steep fall?

The picture I have of the curve is that it might be a smooth "banana" roll off, which JBL has used for a good number of years for speaker systems that will be used in relatively small rooms. In a typical domestic setting the room is part of the LF system from the lower hundreds downward. Some of the effect is a more or less gradual room rise, which a banana roll off may mate with well, and some is unfortunately peaky resonance modes which must be dealt with separately. In small rooms the classic extended shelf bass alignment results in a nice fat hump somewhere, not a desirable feature. The gradual roll off gives more extended VLF, though at a reduced SPL,as I understand it, which the room may support.

[Ruediger]

I am unable to semanticize "sick" in this context into technical or any other relevant terms.

ill-designed, not properly designed, mal-functioning, heavily overdamped.

Plot the frequency response in something like WinISD and You will see.

First I intended to write "pathological response" but then I thought it sounded too academically, so I wrote "sick".

Do a Google search for "pathological equation". See?

[speakerdave]

This is not at all helpful.


ill-designed, not properly designed, mal-functioning, heavily overdamped.

Plot the frequency response in something like WinISD and You will see.

First I intended to write "pathological response" but then I thought it sounded too academically, so I wrote "sick".

Do a Google search for "pathological equation". See?

[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!:applaud::applaud::applaud: Thank You.:D

[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!:applaud::applaud::applaud: Thank You.:D