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JBL 4345 clone, new build


Andrew Tilsley
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Just finished this JBL 4345, which I used American Walnut veneer over euro birch ply.

 

RAL 5007 blue for the baffle, in two pack poly.

 

Drivers to be fitted, feature standard JBL fare, 18 inch bass, 10 inch mid, two inch horn and bullet tweeter.

 

Uber bracing to compensate for large panel sizes. Rear top 1/3 panel removable for driver fitment.

 

Solid walnut trim, chamfered/mitred (that was tricky).

 

For fun, check the size against the Otto bin and car.

 

These large monitors put out an amazing sound....I particularly like the bass depth.

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inside.jpg

jbl1 (2).jpg

drivers.jpg

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with car.jpg

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Very impressive and well done. Nothing like making something. Gives a little more enjoyment each time you use it. I am interested in having a go at doing something like this but don't really have a point to start from. Is there somewhere that supplies plans for stuff like this and the speakers. What are the costs involved. I guess google will know.  Would like to see some photos of the finished item if possible.

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Hi. 

 

Drivers can be sourced from from the net

 

public drawings are available. 

 

I have converted the baffle into cad Cnc for easier building. 

 

Here’s an earlier project in Oak veneer and tassie oak hardwood trim. 

 

Happy to help. 

 

Andrew. 

6E9EF6AA-4719-4604-9786-B51A5C126BA8.jpeg

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2 minutes ago, JD1 said:

Thanks Andrew

 

Nice finish. Will have a look around do some research. How big is the room you have them in. My room is 4 X 5 so may be a bit small for them.

The horn is jbl 2307. The pics do not show the horn lens, fitted later. 

 

For your room, consider jbl 4343, uses 15 inch bass, smaller cab. 

1606D119-2049-4A56-A8E7-289902012A16.jpeg

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  • 9 months later...

Guest jakeyb77
On 23/05/2020 at 7:40 PM, Gigsinkal@hotmail.com said:

Hi, great job, for sale?

The guy runs a business in Sydney called creation audio. Seems he sells flat packs of the speakers above 

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2 hours ago, Andrew Tilsley said:

Charge-coupled custom xover with x3 adjustable attenuation. The 4th channel was active, hence xover was passive for the mid, horn and tweeter.

 

 

What an amazing looking crossover! :thumb:

 

Please tell us more about what it does over a standard passive crossover circuit?

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5 minutes ago, Steve M said:

 

What an amazing looking crossover! :thumb:

 

Please tell us more about what it does over a standard passive crossover circuit?

It is technically still the same crossover circuit. The lead engineer started charge coupling/biasing the crossover in TOTL JBL's models in and around the early 90's. Vandersteen also jumped on to this as well as other manufacturers. Below is a quote from Greg Timbers, the JBL Engineer, on charge coupling

 

The capacitor biasing is something that has existed for many years. Tube equipment does it automatically since there is usually a large DC offset between stages. Some early transistor amps/preamps had two polarized caps in series with the center point going to ground through a large resistor.

I personally became aware of this technique for speaker systems through communications with Ed Meitner, currently of EMM Labs. He is a wealth of information regarding these "tricks" to help linearize or improve the sound of passive components.

It turns out that the bias trick actually increases measured IM distortion and the higher the bias voltage, the greater the increase. It is not by a great amount, but it is measureable. The sound imporvement (or change) is very rarely perceived as worse and is never linked with a increase in IM distortion. The sonic effect is one of smoothness, increased spaciallity, detail and stuff like that. IM has a muddling or confusing effect so I doubt that this particular steady state measurement is explaining the sound difference either way.

Simply put, we are striving to create a class A situation but as was just pointed out, depending on the bias voltage with respect to the voltage across the capacitor, we may only have an "A" condition up to a particular drive level. So if it makes you happier, consider the change to be class AB, but heavily biased to A. You must also keep in mind that the voltage across the input terminals of the crossover network does not tell you what voltage or current is applied to any individual component. Some parts block signal and others shunt signal so the loading on a particular part is not obvious. For the most part, the caps are well taken care of with 9 volts, even at healthy drive levels. The obvious choice for 9 volts is the small cheap battery and holders that are available. No current is involved so a smoke detector battery and holder is a natural choice.

We did do one system with 18 v (M9500). Certain of the Japanese reviewers thought it was an improvement. I can't personally tell any difference. I am also told on a regualr basis (again by our Asian customers) that the battery must be changed at least every 90 days and that the sound degrades after that. Once again, I have not been able to "hear" any difference after 90 days and the battery is certainly still good for many years from a voltage standpoint.

What playing around I have done with initial application of a battery to a biased circuit (that has not been previously powered up) is that it takes about 3-5 seconds for the soundstage to change. I have tried to measure the voltage level in that time period and it seems that several volts is all that is necessary to accomplish 90% or more of the improvement. Once a circuit has been energized, it is nearly impossible to return it to zero. You have to individually short out each cap and leave them shorted for a while or else they will creep back up somewhat. If you replace the battery with a short and play the system for a while, the caps will start to bias themselves, although not to anywhere near the same degree.

You can take this opinion for what it has cost you. I have been very pleased with biasing for many years. I use it in all applications that involve a capacitor and I have rarely been disappointed. Results may vary so if it doesn't do it for you that is okay too. It cost a bloody fortune to implement as it requires 4 times the capacitance and double the capacitor parts count. The network size gets huge as well. Inspite of this, I have never heard a capacitor type that didn't improve (or change) including the nearly perfect teflon variety.

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