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Multi-Way Conventional loudspeakers with crossovers

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Old 17th December 2012, 08:17 PM   #11
tooppy is offline tooppy  France
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Mark,

Sound like a good option, but you are saying the rod is screwed to the back of the driver ? Can it be unscrewed or there is another nut inside the bass driver ? If there is no bolt behind then I will dare to force unscrewing it and replace it with a metric threaded rod. Start from there I can get all the nuts I want.

Your option is far more simple, if the idea is to have just a slight compression, then I cut the rod which might vibrate into the wooden block and apply your solution, filling the back hole being no problem. But I thought that rod had a more complexe role without knowing exactly what it could be.
Can you confirm your thought on the purpose of that rod ?

Something else, have you ever change the crossover completely with new components when the caps died ?
Actually I just recover these baffles, they haven't run for at least 15 years.
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Old 17th December 2012, 11:09 PM   #12
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Quote:
Originally Posted by tooppy View Post
Mark,

Sound like a good option, but you are saying the rod is screwed to the back of the driver ? Can it be unscrewed or there is another nut inside the bass driver ? If there is no bolt behind then I will dare to force unscrewing it and replace it with a metric threaded rod. Start from there I can get all the nuts I want.

Your option is far more simple, if the idea is to have just a slight compression, then I cut the rod which might vibrate into the wooden block and apply your solution, filling the back hole being no problem. But I thought that rod had a more complexe role without knowing exactly what it could be.
Can you confirm your thought on the purpose of that rod ?

Something else, have you ever change the crossover completely with new components when the caps died ?
Actually I just recover these baffles, they haven't run for at least 15 years.
Hi again, the rod is tapped directly into the back plate of the driver with no nut used, and if I remember correctly is made of brass. You will have to be careful if you do decide to unscrew the rod from the back plate, I broke one once attempting to do this, the brass rod had corroded owing to electrolytic corrosion with the back plate. If you do manage to unscrew it, you will have to drill and re-tap the backplate to take a steel metric rod, and be careful of any metal swarf will can contaminate the voice coil gap. The rod tensions the frame of the driver, which is bolted to the front panel, to the back panel, and together with the wooden block act as a brace. This has the effect of drastically stiffening both the front and back panels, which would vibrate without this feature, as they are made of thin wall plywood around 12mm thick, with extensive bitumin damping panels fitted. The rod, which is a crucial part of the design, runs through a softwood block which the crossover is mounted on. The capacitors are electrolytic and are probably old and dried out, and are worth replacing with some non electrolytic ones, especially the ones in the tweeter circuit. I would only spend a few dollars on these but changing them should be a worthwhile improvement. The inductors will not need replacing, but resoldering all crossover connections would be a good idea as the speakers must be around 40 years old. Mark.
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Old 18th December 2012, 05:57 AM   #13
Bon is offline Bon  Australia
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A word of caution. If your Leak 600 is a later version, then it will not have the threaded rod connecting the woofer to the rear baffle, since Leak abandoned this later. Check through the grille cloth if the tweeter and mid-range are side-by-side on a small plywood block that is attached to the main baffle. If this is the case then there is no tensioning rod to deal with. Instead, when you eventually get inside the enclosure you will find 2"x2" hardwood brace between the front and rear baffles. If you you do have a later Australian made cabinet, then the grilles are just a very tight fit to the metal frame. I suggest a small screwdriver to prise out the grille, starting from the bottom where marks are less noticeable. Toss this grille and make up something you can attach with stick-on Velcro tabs.
If you are in Sydney, Speakerworks in Concord do excellent work and have been around for ages
SPEAKERWORKS (CONCORD NSW), SYDNEY, 137 CONCORD ROAD, +61(2) 9746 5...
They replaced the surrounds for my Leak 600 woofers but they are not cheap. Here is a thread on a refurbish project
Leak Sandwich 600 project
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Last edited by Bon; 18th December 2012 at 05:58 AM. Reason: typo
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Old 18th December 2012, 09:26 PM   #14
tooppy is offline tooppy  France
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Mine are two ways, 8 ohms, with the rod and this is the reason I wrote here, I am missing the nut at the back.
But I wonder if this "tensioning rod" has other purposes than just brace the woofer in its axe to the back panel to the aim of limiting vibrations ; and I am not convinced this is effective, for one you bring to the woofer thru the rod the back panel vibrations and second the rod rub inside the piece of wood which makes the system to rattle.
That's the way it has been engineered, I guess they made a lot of trials, but they ended cancelling this system with the following versions, so was it that good in the first place?
So if this threaded rod has no other purpose than limiting vibrations, I can just go without it using Mark's suggestion.
The thread isn't metric so I have a hard time to find it, I have a bolt wich is fitting but the thread is of course sligthly different, it works over one turn and half roughly. So I could force it gently back and forth until it screws nicely, far from ideal and mechanical rules, I don't like that.
The real solution is to get the nut
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Old 18th December 2012, 10:07 PM   #15
Bon is offline Bon  Australia
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Quote:
Originally Posted by tooppy View Post
But I wonder if this "tensioning rod" has other purposes than just brace the woofer in its axe to the back panel to the aim of limiting vibrations ; and I am not convinced this is effective, for one you bring to the woofer thru the rod the back panel vibrations and second the rod rub inside the piece of wood which makes the system to rattle.
That's the way it has been engineered, I guess they made a lot of trials, but they ended cancelling this system with the following versions, so was it that good in the first place?
It seems like you have the original 2-way version with the tweeter fixed to the front grille. I agree with you that the tensioning rod on it's own does not seem an effective solution to baffle vibration. In effect, both front and rear baffles will just move together. A full shelf brace is much more effective since it couples the baffles to the side walls which are much stiffer in the front-to-back direction. The Leak enclosure is a typical example of the bitumen pad damped plywood construction popular at the time in the UK.
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Old 18th December 2012, 10:55 PM   #16
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Quote:
Originally Posted by Bon View Post
It seems like you have the original 2-way version with the tweeter fixed to the front grille. I agree with you that the tensioning rod on it's own does not seem an effective solution to baffle vibration. In effect, both front and rear baffles will just move together. A full shelf brace is much more effective since it couples the baffles to the side walls which are much stiffer in the front-to-back direction. The Leak enclosure is a typical example of the bitumen pad damped plywood construction popular at the time in the UK.
This thin walled, highly damped style of construction used in the Leak's favours the damping of midrange resonance, the cabinet walls are designed to move somewhat whilst frictional losses from the bitumen panels reduce cabinet talk in both amplitude and duration. This flexible type of construction tends to soften bass transients. I was never happy with the Leaks I owned for this reason, I like my cabinets to pass the "knuckle test" Shelf braces if fitted to the rear panel would improve bass response as the back panel would move less, but might increase amplitude of midrange resonance as the resonant frequency of the panel would increase, the damping effect of bitumen panels becoming less effective in damping the stiffer panel. I would suggest using shelf braces set at uneven interval on all panels, which are then all connected by cross braces, birch or hardwood ply being my first choice. I would also use a cross brace virtually touching the backplate of the Leak bass driver with a piece of foam between to tension them together. It depends on how far you want to go! Mark.
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Old 19th December 2012, 11:22 AM   #17
tooppy is offline tooppy  France
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Thanks for these answers, it helps to understand the ideas of the builders behind this setup.
To know if I want to go further in this project, I want to put them to work and listen to get an idea of they are capable of.

Following your explanations, it seems this rod has no other prupose than tightening in some ways to eliminate vibrations. If that to be the case, I don't have to worry about the back nut.
That was the first point to be clarified before doing any big mistake.
The second point is to try them the way they are before deciding to change few components of the crossovers.

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Old 19th December 2012, 09:31 PM   #18
tooppy is offline tooppy  France
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Today I solder the cable to connect them to my Nait2 and finally plaid them. One tweeter was out. These weren't genuine, so I replaced them with some 3" / 8ohms full range I have.
I didn't fix them to the grille but instead filled the inner shell with dacron, placed them in and tape them to the board. This way they are completely disconnected from the vibrations of the woofer.
I was surprised it works, but it should be a good idea to change components from the crossovers.
I could listen just a few minutes as they are now, it is pleasant, the bass seems clean, nothing spectacular which is a good thing.

I will get back to you for the crosssover.
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Old 19th December 2012, 10:21 PM   #19
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The thread will almost certainly be BSW (British Standard Whitworth), which was pretty much universal in British engineered products at the time these were made. It should be easy to obtain a nut of the correct thread from eBay or Namrick - The Nut & Bolt Store
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Old 20th December 2012, 10:25 PM   #20
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Quote:
Originally Posted by tooppy View Post
I wake up this thread because I have a pair of Sandwich and I am missing one of the nut on the back panel.
If someone know where I could get it it would be of great help.
It is true that the front grill is very tight and difficult to pull out, to access the crossover you need to open it up, then unscrew the woofer four screws in the front and at the back of the speaker the nut I am missing.
Without this nut, the speaker would rattle a lot, so I am in big trouble if I cannot find one somewhere.

Thank for your help
The nut should not be difficult to find, Toopy. I know nothing at all about the speakers in question, but it's likely the bolt in question is non-Metric. This can be a problem, as UK and US have differing threads, its not just a matter of knowing the shaft size like Metric nuts & bolts. A replacement nut WILL be available, it's a matter of finding the shaft size out (measure with micrometer) and then heading off to a hardware store which carries Imperial/US nuts, the nut could be BSF, BSP, UNF, UNC , Whitworth SAE or something else. Most likely one of the "Fine" threads though. C- Coarse, is used on big nuts. A motorcycle shop which specialises in old British bikes would be very useful as older bikes have a plethora of varying threads. Don't try to force the wrong pitched threaded nut on- you may find one in right size but wrong thread or wrong thread pitch. Bear in mind too that Imperial shaft sizes come in fractions of an inch (eg 9/16") so if you measure the shaft in mm, or even thousandths of an inch like my micrometer will do, you would need to find the correct fractional equivalent (my 9/16 example above would be 563 thou., 625 thou. would be 5/8").

If you can remove the bolt/shaft it would be very much easier, take it to the bike shop. Many mechanics can recognise the correct thread after years of experience (if they are still alive and sane after years of working on British or American bikes/cars etc)

One of the reasons I went European in my motorcycling days was that British bikes were forever losing nuts and bolts and even 20-30 years ago finding the right non-Metric nut was a hassle. With Metric it's easy- if it's a 6mm shaft a 10mm (across flats) nut will fit.

I have many non-Metric nuts & bolts but without a thread/pitch gauge it's a matter of trial and error to fit, but then I rarely come across non-Metric bolts any more, thankfully.

Last edited by MikeCobar; 20th December 2012 at 10:33 PM.
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