I am posting this thread to assist anyone currently involved in a JBL repair, modification or building a diy system.
Why?
Currently the LHS Bulletin forums are down and no eta when it will be repaired.
I am offering this voluntarily as a gesture to any diy folks who have been caught out by the recent outage on the LHS site.
Over the past 25 years and 20 years prior to that l was involved in building complex four way JBL Pro monitors. I have also been involved in numerous modifications and built up several diy active crossovers.
At the moment l have several projects underway that may interest anyone looking into a system that can reproduce live sound
So what is live sound?
It’s the realistic translation of a recording at 2.5-5 m. Not just nearfield monitoring. For every doubling of distance from the source it requires 4x the power input.
This means a loudspeaker 3 m from the listener will require approximately 10db more power input than at 1 M. Generally speaking 85 Db is said to be a useful listening reference level. But you bee. To allow at least 20 db for dynamic peaks. If you are starting out with a 90 db sensitivity at one metre you are definitely behind the eight ball.
This poses many fundamental challenges for a typical hifi bookshelf or floor standing loudspeaker system.
The No 1 issue is efficiency and the rapid build up of heat in the voice coil. A voice coil can rapidly reach several hundred degrees. Typically a hifi driver is only 1% efficient.
I am not here to alienate anyone who is building a hifi loudspeaker system. However Mother Nature has a firm grip on the laws of physics.
Subjective a small loudspeaker sounds like a small loudspeaker no matter what you do. The compromises are more power, bandwidth and distortion. Only Purifi in recent times have tackled these challenges head on.
Included in my projects include a centre channel that is compatible with JBL M2 diy clones.
I am happy to field Q& A from anyone involved in the above space
Ian
Why?
Currently the LHS Bulletin forums are down and no eta when it will be repaired.
I am offering this voluntarily as a gesture to any diy folks who have been caught out by the recent outage on the LHS site.
Over the past 25 years and 20 years prior to that l was involved in building complex four way JBL Pro monitors. I have also been involved in numerous modifications and built up several diy active crossovers.
At the moment l have several projects underway that may interest anyone looking into a system that can reproduce live sound
So what is live sound?
It’s the realistic translation of a recording at 2.5-5 m. Not just nearfield monitoring. For every doubling of distance from the source it requires 4x the power input.
This means a loudspeaker 3 m from the listener will require approximately 10db more power input than at 1 M. Generally speaking 85 Db is said to be a useful listening reference level. But you bee. To allow at least 20 db for dynamic peaks. If you are starting out with a 90 db sensitivity at one metre you are definitely behind the eight ball.
This poses many fundamental challenges for a typical hifi bookshelf or floor standing loudspeaker system.
The No 1 issue is efficiency and the rapid build up of heat in the voice coil. A voice coil can rapidly reach several hundred degrees. Typically a hifi driver is only 1% efficient.
I am not here to alienate anyone who is building a hifi loudspeaker system. However Mother Nature has a firm grip on the laws of physics.
Subjective a small loudspeaker sounds like a small loudspeaker no matter what you do. The compromises are more power, bandwidth and distortion. Only Purifi in recent times have tackled these challenges head on.
Included in my projects include a centre channel that is compatible with JBL M2 diy clones.
I am happy to field Q& A from anyone involved in the above space
Ian
Thanks for the acknowledgment.
Yes l am actually talking about building a clone for a variation. In my journey l collaborated with Greg Timbers (ex chief engineer at JBL & Nelson Pass on a dedicated Jfet based crossover for the JBL project Everest DD67000.
A lot of the secret sauce in pulling such a complex project together can be applied to any passive to active loudspeaker conversion. Assume nothing and measure everything! Get out your REW and use the interface to measure the passive crossover voltage at the driver terminals. It’s a better approach than attempting a simulation.
The complex reactance of a passive network can generate passive voltage gain in the bottom end of a woofer pass band when looking at a woofers motional impedance.
House curves (Harman) can easily to created in an active system with shelf filter while also incorporating a Blaxandall style HF EQ to take into account room acoustics.
So if anyone is the the diy space and needs a tip on your Pass diy jfet active cross l have first and experience. This kit works like an absolute charm on JBL systems.
I maintain that these Jfet diy analogue active crossovers will subjectively outperform a Mini dsp based crossover. The proof in that is between Nelson Pass the late Dr Linkwitz who originally used a Minidsp based crossover for one of his designs.
Yes l am actually talking about building a clone for a variation. In my journey l collaborated with Greg Timbers (ex chief engineer at JBL & Nelson Pass on a dedicated Jfet based crossover for the JBL project Everest DD67000.
A lot of the secret sauce in pulling such a complex project together can be applied to any passive to active loudspeaker conversion. Assume nothing and measure everything! Get out your REW and use the interface to measure the passive crossover voltage at the driver terminals. It’s a better approach than attempting a simulation.
The complex reactance of a passive network can generate passive voltage gain in the bottom end of a woofer pass band when looking at a woofers motional impedance.
House curves (Harman) can easily to created in an active system with shelf filter while also incorporating a Blaxandall style HF EQ to take into account room acoustics.
So if anyone is the the diy space and needs a tip on your Pass diy jfet active cross l have first and experience. This kit works like an absolute charm on JBL systems.
I maintain that these Jfet diy analogue active crossovers will subjectively outperform a Mini dsp based crossover. The proof in that is between Nelson Pass the late Dr Linkwitz who originally used a Minidsp based crossover for one of his designs.
One of the projects l am working towards is a series of crossover pcbs that can be used individually or together to realise low pass, band pass and high pass passive filters.
This approach over a single pcb has a number of benefits:
1. The electro magnetic radiation from the low pass filter can be removed from the other filters eliminating cross talk.
2. The overall passive network can be customised to meet a particular need. The user can try different versions of a filter simply by swapping out the pcb with another.
3. The parts placement can be made more flexible
with additional parts for EQ sections for horns, attention and zobel networks.
Links will be provided to enable specific functions. For example attenuation of a horn for fully active system
4. The build can acquire the whole set or only what they need. This is more economical than a large complex pcb designed to be used with different systems. Such pcbs are in ebay for over US$300.00 a pair.
I don’t have an ETA on this yet.
This approach over a single pcb has a number of benefits:
1. The electro magnetic radiation from the low pass filter can be removed from the other filters eliminating cross talk.
2. The overall passive network can be customised to meet a particular need. The user can try different versions of a filter simply by swapping out the pcb with another.
3. The parts placement can be made more flexible
with additional parts for EQ sections for horns, attention and zobel networks.
Links will be provided to enable specific functions. For example attenuation of a horn for fully active system
4. The build can acquire the whole set or only what they need. This is more economical than a large complex pcb designed to be used with different systems. Such pcbs are in ebay for over US$300.00 a pair.
I don’t have an ETA on this yet.
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As l mentioned above the Pass diy Jfet crossover is an excellent kit for those keen to build their own. I recently heard it used in a system with the popular JBL pro 4345 monitor locally with Bryston and Krell power amps. The kit was assembled as a balanced version. The result was impressive.
Calculation of the parts values isn’t difficult. You can scale the values using known RC or use the equations. Alternatively the values can be obtained with a Spice simulation.
Calculation of the parts values isn’t difficult. You can scale the values using known RC or use the equations. Alternatively the values can be obtained with a Spice simulation.