Did L300 have damping material inside?

[mfaughn]

I'm in the process of restoring a set of L300. I started a while ago and don't remember removing any damping material from them but I noticed a small bit (size of an almond) of that sort of material in the bottom of one cabinet. It doesn't look like any of the damping material that I've pulled from any cabinets recently either (though I will doublecheck). So, is there supposed to be damping material in the L300? If so, how much of what kind of material to use?TIA!

[Odd]

There is glass wool on all sides except the baffle.

About 1 inch thick.

[DerekTheGreat]

That is a cool photo, Odd! I love cutaways.

[mfaughn]

Cool! Thanks for that. I wasn't looking too hard. It was only the damping in the bottom of the cabinet that was gone. Luckily the rest of it hadn't been yanked out. I put some fresh fiberglass in there and buttoned them up. Looking forward to getting them out of the garage and into the living room for a test drive. Anyway want to help me move them...please? FWIW, when I got them, the woofers had had rubber surrounds installed that were super stiff, like what you'd find on a subwoofer. They had already been reconed with 2235 cones. I removed those surrounds with less damage than I imagined (though the cones certainly aren't pretty) and installed proper surrounds. Contemplating rebuilding the XOs with external units so I can futz about with them and try some of the various configurations floating around here on the interweb.

[Ian Mackenzie]

Cool! Thanks for that. I wasn't looking too hard. It was only the damping in the bottom of the cabinet that was gone. Luckily the rest of it hadn't been yanked out. I put some fresh fiberglass in there and buttoned them up. Looking forward to getting them out of the garage and into the living room for a test drive. Anyway want to help me move them...please? FWIW, when I got them, the woofers had had rubber surrounds installed that were super stiff, like what you'd find on a subwoofer. They had already been reconed with 2235 cones. I removed those surrounds with less damage than I imagined (though the cones certainly aren't pretty) and installed proper surrounds. Contemplating rebuilding the XOs with external units so I can futz about with them and try some of the various configurations floating around here on the interweb.

It would appear someone has done something with them at some point.

In their stock form they are a popular music system of the 70’s and not entirely suitable for classical music. The original crossover was crude and nothing like the networks designed for the current JBL systems.

Your best bet is to audition them on milk crates. They can sound descent with a 4th order time aligned active crossover.

[mfaughn]

It would appear someone has done something with them at some point.In their stock form they are a popular music system of the 70’s and not entirely suitable for classical music. The original crossover was crude and nothing like the networks designed for the current JBL systems. Your best bet is to audition them on milk crates. They can sound descent with a 4th order time aligned active crossover.I think they were just reconed by a dingus -- very wrong surround and didn't replace the batting. At least the mass rings were still there.I have a miniDSP flex w/ DIRAC. That sorts a lot of XO issues but I may still try the Nelson Pass XO, e.g..

[johnlcnm]

Go with The Zonker92 charge coupled crossover board. He sells them on the e-pay. I have used them in the commercial version of the L300 with good results. I am not a fan of the Linkwitz Riley fourth order crossovers. Go with the stock second order xover and mid horn out of phase in relation to the woofer. The sound does a good job of escaping the boxes and the out of phase kills the intermods between the two drivers that reproduce the midrange. Regards, John

[Ian Mackenzie]

It depends on the implementation.


This thread is an enquiry on a specific question.

But since the choice if the crossover has reared its head on l provide below a perspective on where network options fit in the realm of diy loudspeakers:

Not everyone is interested in this because what happens in diy is entirely up to the individual. There is no way of controlling what the individual ends up doing so the results of a diy loudspeaker project can vary. Where a project ends up is the fun factor.

My philosophy in the diy audio space is to understand from professional practitioners the technical aspects of a loudspeaker design and then apply this knowledge as a learning through building and testing of diy projects. Sharing this knowledge helps others in the hobby achieve successful outcomes.

If a diy loudspeaker builder follows a properly engineered design loudspeaker design they don’t need to be too concerned about the technical stuff provided they follow the design closely. This refers to cloning of a JBL system. To appreciate this a JBL system goes through a rigorous prototype development including auditions by a panel of experts with trained listening skills over many years. To grasp this the diy builder is a mere mortal while the expert listening panel are Gods. The way around this is to use a commercial JBL system as a reference and compare it closely to your project. This will give you an idea of where your project is at by simply listening. Always judge with your ears before drawing any conclusions from measurements alone. The topic of psycho acoustic is worth exploring if you wish to know more about how we listen.

[Ian Mackenzie]

Looking at LR4 networks specifically most diy loudspeaker builders believe the 4th order refers to be the electrical voltage drive from the passive or active crossover. This is incorrect. It’s the final acoustic response of the drivers after the electrical voltage drive is optimised. Obtaining this is beyond the means of most diy loudspeaker builders unfortunately. Manual optimisation is a tedious and time consuming task. Commercial loudspeakers manufacturers use a CAD crossover optimisation engine which can model and accurately predict a final network optimisation.

Peter Larson who worked closely with JBL in the 1990’s to develop CAD design software now owns Loudsoft CAD systems used by loudspeaker manufacturers worldwide. These system start at US$10,000. It is far superior to the LEAP system used previously.

https://loudsoft.com/about-loudsoft/

[Ian Mackenzie]

Another key point is that for the LR4 topology to work correctly the phase relationship between the low and high frequency drivers in the crossover crossover region with the proposed network needs to be evaluated. This involves determining the physical alignment of the voice coils / acoustic centre needs and the group delay introduced by the electrical network.

This requires detailed measurement techniques and an in depth understanding of loudspeaker crossover network design. This can be implemented with a passive or active analogue network or with dsp FIR filters.

You can study the analogue approach on the Linkwitz website using direct radiators. Ideally in any crossover design the drivers should have a flat response at least one octave either side of the crossover point. This is often difficult to achieve where the user wants to push the horn down to the edge of its pass band. But they do it anyway often using too small a horn or wave guide.

The results are typically not optimal. The same applies to ribbon and Heil drivers. Adam monitors from Germany recognised this and they use a cone midrange driver in their top line systems to place the crossover point well above the edge of the passband

[Ian Mackenzie]

JBL generally scale their image control wave guides to suit a particular system design. Unfortunately the diy loudspeaker builder does have access to these optimal wave guides.

The implementation therefore can end up sub optimal. But as l mentioned above in the diy space it’s entirely up to the individual what they end up doing. My recommendation to to try a few options before settling on the final implement. You might be very surprised when evaluating an alternative. This particularly apply to attempting a two way system which is relatively difficult when the low and high frequency driver and horn/ wave guide are stretched in the crossover region.

[Ian Mackenzie]

Using a crossover switch box with a basic network simple try some different crossover frequencies and listen. I plan to post a switch box schematic in the next few weeks

One alternative will ultimately be preferred over the other. This is how Greg Timbers starts out early in the design of new systems. Don’t get too deep in settling on the crossover in the early stages of your project. Personal preferences cone in to most as well. It’s about what works best for you in your situation. Above all listen and keep listening using a reference loudspeaker if you can. The LSR 306 or 308 is a good inexpensive reference.

https://jblpro.com/en/products/308p-mkii

[Ian Mackenzie]

So unfortunately none of this is a plug and play exercise. Work best route his to keep an open mind with a cookbook diy system of your own.

To wrap up the question over LR4 networks l witnessed the correct implementation and it works very well. This is why numerous manufacturers including JBL use it in their top line systems such as the DD67000.

I will leave you with this. Imagine for a moment having access to a selection of crossover network options that have been optimised and pre determined for use by the diy loudspeaker builder for particular woofer drivers, compression drivers, horns and wave guides. Something that’s been tested, auditioned and it really works. Passive or active networks with schematics, parts lists and pcbs. Or a diy active options that can be easily implemented. A bit like the vintage JBL networks that were available in the 1970’s.

That’s the focus of my current work. I hope to provide more information about these innovative concepts early in 2024.

The image below is of a dinosaur stampede found in central Queensland Australia.

The little dinosaurs were being chased by a big dinosaur. Some of the smaller dinosaurs were apparently the size of a chook. The small foot prints can be seen.

Here is a joke. What did one little dinosaur say to the other little dinosaur when they were running away from the big dinosaur? Do-you-think-he-saw-us? Lol

[Robh3606]

Using a crossover switch box with a basic network simple try some different crossover frequencies and listen. I plan to post a switch box schematic in the next few weeks

One alternative will ultimately be preferred over the other. This is how Greg Timbers starts out early in the design of new systems. Don’t get too deep in settling on the crossover in the early stages of your project. Personal preferences cone in to most as well. It’s about what works best for you in your situation. Above all listen and keep listening using a reference loudspeaker if you can. The LSR 306 or 308 is a good inexpensive reference.

https://jblpro.com/en/products/308p-mkii

Hello Ian

I agree they are good speakers but they are limited as a reference. They need a sub and dynamically they are challenged unless they are used as intended, Near Field. They fall apart when asked to fill a room as far as SPL. The amps used just don't have the power needed.

I would move up in the JBL powered monitors.

[Ian Mackenzie]

That maybe so but I think moving up would be un affordable and if you did why build a diy loudspeaker.

The KRS708 is AUD$7000 over here.

More broadly the reference could be any other loudspeaker you own that you like.,

[Robh3606]

Hello Ian

Didn't realize the price jump!

Rob :

[Ian Mackenzie]

Yes unfortunately a post Covid thing.

Anyway I think most will get the reference idea. Just so you can track any changes and use as a baseline. It’s easy get lost otherwise.

Ha if the a project loudspeaker sounds better to your ears than your reference your on the right track.