Building the 4345/4344

[Ian Mackenzie]

Here is another graph,

Some explanation is in order.

Over the past few weeks I have been evaluating the 4344mk11 network to assess if its horn and slot passband filters would work for the 4345, saves the split chokes.

All the above graphs used the original 3145 mid passband filters, but the 4344mk11 horn and slot passband filter topologies.

There are some differences but its works well enough. (namely in the UHF passband.) So if you are stuck for the split chokes you can use the values shown in the 4344mk11 network for the horn and slot including the fixed resistor Pads.

However, tonight I returned to the original 3145 network (4345 original network) and experiemented with chokes of various Dcr. The design is reasonably tolerant of choke Dcr, but try and keep it as close to spec as possible, (JBL works to 5% tolerance).

The graph below represents what I consider the state of art crossover for this system (3145 with Giskard/GT alternative split choke values).

The response is on axis at 2 metres indoors and is unsmoothed, not even 1/3 octave smoothing. The divisions are 6 db, the scale is linear and not log so there is more detail at high frequencies and less at low. (The JBL graphs have a log scale).

In comparison to GT's test data, under the microscope the similarity is remarkable and the transitions are perfect.

Adjustment of the pads can fine tune the balance overall and that is up to the user.

Ian

[Ian Mackenzie]

This is the 2405 slot run at near field (30 cm), the divisions are 6 db linear scale as above.

Ian

[Ian Mackenzie]

The 2307 horn response with the 2425 diaphrapm (with 2308 lense ) as per above measurement conditons.

Ian

[Ian Mackenzie]

Here, the 2122H midrange near field response.

Ian

[Ian Mackenzie]

So there you have it, a complete set of graphs for the diy JBL 4345.

If you are planning to build either the 4345 or 4344 I am happy to assist.

Ian

[Ian Mackenzie]

Having a JBL day off (home with the flu) I have quietly developed some techniques for tweaking the response for ruler flatness.

Previous mid field response measurements drew to much interference even with tight time gating.

So I began carefully measuring and documenting the exact near field response levels for the mid, horn and slot against the zero marker on the Foil cal for the midrange driver (2122H).(referenced (-3) db from maximum.

I was able to then adjust the pads on the horn and slot for each to be level with the zero line on the response output.

As it turns out, adding a 20 ohm shunt resister across the horn cpmpressio driver (8 ohm driver) terminals shaved a db or two off its sensitivity and when its pad is at the zero position this is now correct.

Below is an overall full response taken near field mid way on axis between the horn and slot so as to provide the best overall mean response. The mid cones dispersion is sufficiently wide that its sensitivity is only slightly down.

The response is now very smooth and even overall. So its can be seen that with even modest test equipment good results can be obtained with the right approach.

The ultimate test is however listening, and I will do that later over a few ales. (after I have calibrated the other monitor)

Ian

[Ian Mackenzie]

The subjective performance mirrors the response measurements above.

After trying several different pad levels for the Mid, High and Uhf I settled for zero (0) for the UHF, zero (0) for the HF and (-1) for the midrange.

The latter is most likely the result of an anomally with my ealier measurements but non the less the response envelope did not lock in correctly without a slight reduction in the midband level.

The drivers now behave as one, and their individual outputs are indistinguishable at the listening position.

Setting the UHF at +1 and the HF at -1 while maintaining the above mid level is altenative alignment of the Pads . This give a sort of BBC (reserved) dip in the upper midrange with a nice crisp top end. But I prefer the former setting for the classic JBL presentation.

The Foil Cal is now calibrated from -3 to +3 for each driver Pad so adjustment can be made with some degree of accuracy based on the actual acoustic response of each driver.

If you are planning to build the 4344 monitor with the 2235 woofer using a full passive crossover network it should be noted that the above references for adjustment levels of the Foil Cal relate to the 2245 woofer sensitivity of 95 db 1 watt @ 1 metre.

So the zero level positions for midrange on the 4345 are (-3) db from maximum, and (-4) db for the HF and UHF.

For the 4344 the pads levels will need to be referenced to the sensitivity of the 2235 woofer which is 93 db 1 watt @ 1 metre.

Therefore, the zero level positions for midrange on the 4344 are (-5) db from maximum, and (-6) db for the HF and UHF.

(This assumes you plan to use low loss inductors as specified by JBL)

The point of providing the above detail on the acoustic alignment of the system is that without a reasonable degee of calibration it is nearly impossible to setup the system correctly. So to avoid dissapointment and frustration some care must be taken to calibrate the level pads.

Ian

[Ian Mackenzie]

I have just reviewed the thread and noted that we have not looked at the Dog Box dimensions or its position on the front baffle.

Some of you may wish to adapt these drawings to suit your own interpretation of the driver layout so they are for here for reference.

The Dog box internal measurements are 10 x 6 x 14 1/2 inches, the internal volume is 1/2 cubic ft3. The Mdf walls are 3/4 inches. Similar construction methods can be used from the main enclosure.

I have chosen to align the Dog Box with the edge of Foil Cal position for drawing purposes. Again you may wish to vary the dimensions somewhat or even flush mount one side to the main enclosure.

The Dog Box should be securely fastened to the front baffle with PVA glue and screws once you are happy with postion.

The thickness of the side wall bracing will also need to be consider or moved to allow clearance of the Dog Box.

Ian

[Alex Lancaster]

The bad news "Messenger" always got shot, and while We are at it, You Merciless pagans, throw a few prayers for Charlie Rummel, it works.

[Ian Mackenzie]

There's above 5000 views on this thread now although not many posts from interested members.

If there's sufficient interest I'll start posting the 4345 drawings during the next week or so.

Ian

[andresohc]

If there's sufficient interest I'll start posting the 4345 drawings during the next week or so


yeah, yeah, yeah, yeah, yeah!

[Figge]

Originally posted by Ian Mackenzie
If there's sufficient interest I'll start posting the 4345 drawings during the next week or so

[andresohc]

I will be building the 4345 system in the next three to four months (hopefully). I have collected all the parts (minus the crossover stuff yet), and have been waiting to see the cabinet blueprints/ info. I have bought the mdf, the jigs, router guides bits, glue, mahogany veneer. I have printed this thread and the others (as best I could in that the borders are too wide) and reread them several times. I am waiting a while to start the project, but am also anxiously anticipating the blue prints. Please dont mistake lack of response to threads as lack of interest. Basically I dont have much to contribute, but try to absorb as much as I can. When the chips start flying I am sure I will have some educated questions. I greatly appreciate all the documentation you have provided allready and thank you for the committment to get this stuff out. I can reverse engineer most anything if necessary, but I would rather follow at this point then take off into the jungle with a machete.

[andresohc]

"but I would rather follow at this point then take off into the jungle with a machete"

(To blaze my own path is what I meant in case anyone is scratching their heads and ducking),

[Ian Mackenzie]

Okay,

The 4345 is basically a larger version of the 4344, the box is 9 cuft3 with the 18 inch 2245 woofer, all other aspects are similar.

The internal dimensions are in inches 28 wide, 39 high , 16 deep.
The material is 1 ich mdf but would consider laminated MDF for birch ply for the front baffle.

Here is my earlier sketch of the front baffle.

The woofer in this model is centred in the baffle , theres no where else for it to go. I will post the other drawings soon enough which were redrawn for the 4344, so I will modify the dimensions to avoid a total re work.

The 4345 is more difficult to build because its bigger and heavier to handle, so enter at your own risk; hmm: The Waf factor ainý so good either and your neighbours might move home..LOL