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Thread: BBC Monitor (LS3/5a) Clone

  1. #1
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    Default BBC Monitor (LS3/5a) Clone

    Well, sort of a clone. Built in essence of it.

    A little history grabbed from Wiki: "The LS3/5A is a commercially produced loudspeaker driven by the need of the BBC to monitor and assess broadcast programme quality. It was derived from the LS3/5, which was conceived and developed by the BBC Engineering Department in the early 1970s, when it was under the stewardship of Dudley Harwood. Having found no commercially produced small loudspeaker that met the requirement for naturalness and sonic neutrality, the BBC specifically set out to design a speaker to achieve natural overall sound quality and good dynamic range for monitoring broadcasts in tightly confined spaces."

    Anyway, I heard a pair of the originals somewhere about the late 70's-early 80's and I was surprised such a small speaker could sound so nice. Everything else at the time at consumer level was rather large, comparatively. I don't have a huge interest in bookshelf/desktop sized speakers. I kept seeing this kit but never really paid it any mind until I happened upon the design goal and saw the BBC monitor mentioned.

    At any rate, this version, named "Continuum", designed by Jeff Bagby, sounds even better than what I recall of the original. I've been sitting here since I got home from work, having just put the final touches on the crossovers and other associated wiring just last evening, feeding them everything I could care to listen to and being repeatedly blown away by the sound of these little speakers that could.

    The crossovers are always the part that causes me procrastination. I need to have time which usually leaves me after work and I have to feel like it. This time I just went at it.

    Started with a component layout. Everything is wired point-to-point, which is good because I somehow keep forgetting to get a good pair of wire strippers, which plays hell on my thumbnail.


    Got them all fit and soldered up. I don't like soldering or starting on the cabinets until I hear life from the drivers once the boards are fit and the components just twisted together for a trial first. Everything worked. Speaker drivers sound really wimpy outside of their cabinets. If I didn't know this from past experience, I would think I made a bad choice.

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    Default Re: BBC Monitor (LS3/5a) Clone

    I had enough leftover MDF from prior projects. Still, in spite of these speakers reputation, I was not going to sink any money into anything spendy without hearing them first.



    I used rabbet joints cut on my router table. It makes for tidy and perfectly square boxes and easy assembly. I just tack them together with the brad nailer and wood glue.


    And then because epoxy rules, I thin it with alcohol and let the MDF soak it up, which helps me not to hate MDF so much anymore. Preserves the nice sharp corners this way and keeps from soaking up so much contact cement in the event I put veneer on them. Good primer for paint as well.

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    Default Re: BBC Monitor (LS3/5a) Clone

    This speaker gets the 5.25" Aurum Cantus woofer mounted in a recess on the back side of the front baffle. The front baffle and rear panel are removable and are screwed to battens fastened to the inside of the cabinet. You could not get the woofer out if these parts were permanently fastened. Here's the layout for the woofer, and while I was at it, I set the baffles on the layout and transferred the clearances on those as well.



    I used a circle jig for the first cut to the lines on the woofer recess, and just free-handed the irregularities. This is hidden anyway.


    The tweeter, Dayton RS28A-4, gets flush mounted on the outside of the baffle as is typical. There is something about a time phase between the woofer and tweeter in this arrangement as well, IIRC, and the crossover would have to be changed slightly if I were to flush mount the woofer on the face.


    Good fit.

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    Default Re: BBC Monitor (LS3/5a) Clone

    Here's a picture of the two drivers. I like the look of the woofer. The cone is IIRC, mica filled, polypropylene. Looks like graphite, with about a graphite color as well.



    The backs and fronts are attached with weatherstripping between them and the battens since these are sealed cabinets. I did put the wire binding posts on last night, after this photo was taken.


    Here's a shot of how the fronts are done. I like the look of the screws and the removable panels.


    Now that I have heard them, I will be giving them a nice finish. Thinking some kind of curly veneer finished natural. I'll fake the grain etc on the woofer recess. These things really do sound 'that' good!

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    Default Re: BBC Monitor (LS3/5a) Clone

    I am again impressed with the build... and wish I could hear the results.
    If I use the word "God," I sure don't mean an old man in the sky who just loves the occasional goat sacrifice. - Anne Lamott

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    Default Re: BBC Monitor (LS3/5a) Clone

    Quote Originally Posted by TomF View Post
    I am again impressed with the build... and wish I could hear the results.
    I'll take that a step further and offer to beta test them, while your build the "real" set.

    These look fantastic, yo!

    Peace,
    Robert

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    Default Re: BBC Monitor (LS3/5a) Clone

    Lew could probably run them over to you in his new Lotus - shouldn't take too long.
    If I use the word "God," I sure don't mean an old man in the sky who just loves the occasional goat sacrifice. - Anne Lamott

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    Default Re: BBC Monitor (LS3/5a) Clone

    After much listening, thinking of the scale of the size of these little boxes, I am going to cover them with this, Karelian Birch veneer.



    Probably either let in some solid birch wood around the opening for the woofer, or try my hand at some 'faux bois' in this area first. It's unbacked veneer so I should be able to pull it off somewhat seamlessly. I'll practice on the rear returns where the back cover fits into and the edges of the front/rear panels.

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    Default Re: BBC Monitor (LS3/5a) Clone

    Very nicely built... good job!

    One minor comment: I notice, in the crossover, that there's one power resistor with finned metal case. If that resistor REALLY needs to be of that power rating, then I'd be a bit concerned about using a plastic tie-wrap to hold it to the board. Similarly, with the long composition power resistors, if they actually dissipate that much power, I'd be concerned about charring the substrate they are mounted on.

    Granted, at average listening levels, it's unlikely to happen... so, perhaps the component ratings are just overkill?
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    Default Re: BBC Monitor (LS3/5a) Clone

    Quote Originally Posted by TomF View Post
    I am again impressed with the build... and wish I could hear the results.
    I used money what most ppl spend on fast food and other bs expenses. I started saving for these about 4 months ago. I figure it was around $3.00/day. Every time I avoided something impulsive, I stuck it in a jar and forgot about it. I am out of vices. Quit smoking 4-5 years ago, don't drink, no car payments etc. Had to have something I do that's not entirely practical instead of just work all the time and pay bills.

    As it turns out, these relatively humble goals turn out to be towards better health across the board. Just considering all of the bad news and politics I have managed to avoid in the process and the knowledge gained. Social media and the internet forums haven't missed my otherwise mundane, redundant contributions, and I have managed to fill my space instead, with beautiful music.

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    Default Re: BBC Monitor (LS3/5a) Clone

    Quote Originally Posted by Norman Bernstein View Post
    Very nicely built... good job!

    One minor comment: I notice, in the crossover, that there's one power resistor with finned metal case. If that resistor REALLY needs to be of that power rating, then I'd be a bit concerned about using a plastic tie-wrap to hold it to the board. Similarly, with the long composition power resistors, if they actually dissipate that much power, I'd be concerned about charring the substrate they are mounted on.

    Granted, at average listening levels, it's unlikely to happen... so, perhaps the component ratings are just overkill?
    I had the same concern. Half of why I tested the crossover before soldering anything. Only thing I can think of, is they have a bunch of these to get rid of with the right value, or it fits the wiring scheme better. I saw some older crossovers built of this speaker and it had a more traditional resistor. I also see now that where I got this kit from is "out of stock." So, perhaps they had to scrape the bottom of the barrel, so to speak.

    Typically if there is a concern, there would be warnings about putting insulation foam near the crossover etc. as well.

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    Default Re: BBC Monitor (LS3/5a) Clone

    Quote Originally Posted by pipefitter View Post
    I had the same concern. Half of why I tested the crossover before soldering anything. Only thing I can think of, is they have a bunch of these to get rid of with the right value, or it fits the wiring scheme better. I saw some older crossovers built of this speaker and it had a more traditional resistor. I also see now that where I got this kit from is "out of stock." So, perhaps they had to scrape the bottom of the barrel, so to speak.

    Typically if there is a concern, there would be warnings about putting insulation foam near the crossover etc. as well.
    Well, as I said, at reasonable listening levels, it probably isn't a problem.

    Actually, I'd be just as concerned with the heating of cored inductors; up until a year ago, I was involved in a project which dealt with the core loss of large inductors... and it's surprising, just how hot they can get. The air core inductors don't suffer as much... although resistive losses can make them hot, as well.
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    Default Re: BBC Monitor (LS3/5a) Clone

    Lovely speakers... Very interesting.

    Apart from cheapness, and perhaps uniform material to work with, why mdf? I had a guitar with an mdf body, and it was terrible, even a cheap solid wooden guitar was miles better. Would real wood add anything to the sound? Perhaps with monitors you want no added colour?

    i do a lot of amateur music production, home studio stuff. Hence interest.

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    Default Re: BBC Monitor (LS3/5a) Clone

    Quote Originally Posted by lupussonic View Post
    Lovely speakers... Very interesting.

    Apart from cheapness, and perhaps uniform material to work with, why mdf? I had a guitar with an mdf body, and it was terrible, even a cheap solid wooden guitar was miles better. Would real wood add anything to the sound? Perhaps with monitors you want no added colour?

    i do a lot of amateur music production, home studio stuff. Hence interest.
    Mostly because I had it already. Also, what poses as quality plywood these days, ends up being it's size under, metric equivalent. So basically, if I want cabinet grade plywood, I have to go to a specialty outfit because all the home centers offer is "Baltic Birch," which is supposed to be something special. It's lightweight and cheap feeling to me, which also manages to go with why the 'big deal' home centers would carry it.

    Honestly, I am not a fan of MDF, but acoustically, it is superior to plywood for this use. It's high humidity here also so long term stability is a concern. These are small enough to where I could build another set of cabinets for them without much sweat, but I really wanted to hear them first before investing anymore in them. As they play now, these cabinets are pretty much inert. Can hardly feel any resonances or vibes from them at all. They have some heft to them for their size. For all I know, this could be contributing to their great sound. I'm almost afraid to change it.

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    Default Re: BBC Monitor (LS3/5a) Clone

    From memory (and we used to have a part number for these) - the original cabinets were birch ply.

    Really good near field monitors and surprisingly cost effective.
    Someday, I'm going to settle down and be a grumpy old man.

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    Default Re: BBC Monitor (LS3/5a) Clone

    Quote Originally Posted by Norman Bernstein View Post
    Well, as I said, at reasonable listening levels, it probably isn't a problem.

    Actually, I'd be just as concerned with the heating of cored inductors; up until a year ago, I was involved in a project which dealt with the core loss of large inductors... and it's surprising, just how hot they can get. The air core inductors don't suffer as much... although resistive losses can make them hot, as well.
    Good points. Which is also why I post these things here. At least the covers are removable so I can check them tonight after they've been playing all day. These speakers are rated at 85 watts RMS. I am probably using 15w at the levels I listen at. I am curios though. So far, the cabinet surfaces don't feel the slightest bit warm and they've been going about 4 hrs now.

    Here's where I have the crossovers mounted up top behind the tweeter. Figured the least amount of interference from the driver magnets, and it still allows me to get the acoustic foam behind the crossovers without covering them with anything.

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    Default Re: BBC Monitor (LS3/5a) Clone

    Quote Originally Posted by P.I. Stazzer-Newt View Post
    From memory (and we used to have a part number for these) - the original cabinets were birch ply.

    Really good near field monitors and surprisingly cost effective.
    There was a supposed "dip" ("BBC dip") in the mid frequency range somewhere that gave these monitors a pleasing sound, although, some say that is a myth. Still, it would not be surprising considering the lack of computer modeling software in those days, where much of this sort of thing was reasoned by ear. Just considering how to figure out things like Baffle Step Compensation (BSC) if they even really knew about the need for such things back then would be a feat, I would think.

    I had a foreman who was from England who had them, is where, and the only time I ever saw/heard them. He had carried them allover the world by that point and I bet he still does.

    They would be incredible in a small room or at a desk. I am surprised how good they manage to sound in my somewhat small living room.

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    Default Re: BBC Monitor (LS3/5a) Clone

    Quote Originally Posted by Norman Bernstein View Post
    Well, as I said, at reasonable listening levels, it probably isn't a problem.

    Actually, I'd be just as concerned with the heating of cored inductors; up until a year ago, I was involved in a project which dealt with the core loss of large inductors... and it's surprising, just how hot they can get. The air core inductors don't suffer as much... although resistive losses can make them hot, as well.
    I should also note that I have these crossed over at 80hz to my subwoofer, which is suggested how they be used by the designer. So I imagine that takes a bit of load off them as well. They sound fine without the sub, and have a surprising amount of bass on their own but really shine not having to share the lower freq.

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    Default Re: BBC Monitor (LS3/5a) Clone

    I'm keen to build a pair. I've been looking at studio monitors for a few months. Seems you get decent neutral reference at about 1000 (1500$). Bet these cost you couple hundred and a few days, right? I'm not in front of a computer right now, otherwise I'd google it , but is a parts list available?

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    Default Re: BBC Monitor (LS3/5a) Clone

    Someday, I'm going to settle down and be a grumpy old man.

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    Default Re: BBC Monitor (LS3/5a) Clone

    Quote Originally Posted by lupussonic View Post
    I'm keen to build a pair. I've been looking at studio monitors for a few months. Seems you get decent neutral reference at about 1000 (1500$). Bet these cost you couple hundred and a few days, right? I'm not in front of a computer right now, otherwise I'd google it , but is a parts list available?
    Even pricing the components separately from other sites is not much of a savings and without the crossover circuit as well, so the kit is actually the deal.

    It's called: "Continuum" for when you do get next to a computer.
    https://meniscusaudio.com/product-ca.../speaker-kits/

    Also, there is a post from the designer posted down the page under user Jeff B. that explains how he came about this design.

    I've built one other of his designs. Equally impressed with that one.

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    Default Re: BBC Monitor (LS3/5a) Clone

    Quote Originally Posted by P.I. Stazzer-Newt View Post
    I've actually been to that site when I first came across this speaker. They have a lot of information on the originals.

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    Default Re: BBC Monitor (LS3/5a) Clone

    Quote Originally Posted by lupussonic View Post
    I'm keen to build a pair. I've been looking at studio monitors for a few months. Seems you get decent neutral reference at about 1000 (1500$). Bet these cost you couple hundred and a few days, right? I'm not in front of a computer right now, otherwise I'd google it , but is a parts list available?
    More specifically, here's what comes with the kit.

    2 x Dayton, RS28A-4, Metal dome tweeter
    2 x Aurum Cantus, AC130F1, 5.25″ Poly Cone mid woofer
    2 x Crossover parts, featuring Audyn Q4 caps and Specified inductors
    Wiring scematic
    “Big Post”, gold binding posts
    Mounting hardware
    Gasket tape
    Hook-up wire
    Acoustic foam Internal damping (not pictured)
    Build plans for the cabinets

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    Default Re: BBC Monitor (LS3/5a) Clone

    Beautiful work, as always.

    I am happy to learn these live up to their reputation!

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    Default Re: BBC Monitor (LS3/5a) Clone

    Next up is old school sound with Full Range drivers and no crossovers. This type of speaker driver is done with different cabinet configurations with what is known as transmission lines and different types of horns and even some that sit on an open baffle with no cabinet behind them at all. I have a pair of these drivers just to see what I can learn about what all the fuss is about.



    Apparently, what these types of drivers do is, a really good midrange presence, which is what human hearing does the best with. These horns and transmission line enclosures use the cabinet to boost the lower frequencies, which these drivers don't do all that well. This is where the tradeoffs occur most logically. In other words, if you have a full range driver that has a decent low end and midrange, the high frequencies will be lacking, and vice versa.

    Here's a fellow that takes it to a whole other level, with building his own amps and paper mache horns which, are actually quite stunning.
    http://www.inlowsound.com/

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    Default Re: BBC Monitor (LS3/5a) Clone

    This way madness lies - trust me.


    Tannoy GRF. - corner folded horn cabinet for the Monitor Gold series drivers
    Someday, I'm going to settle down and be a grumpy old man.

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    Default Re: BBC Monitor (LS3/5a) Clone

    Quote Originally Posted by P.I. Stazzer-Newt View Post
    This way madness lies - trust me.
    I am curious as to why you say that. Although, after reading a lot about what is going on with these types of drivers, and what people are willing to go through to make it work, I may have an idea.

    Is this something you have done before? Did you give up?

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    Default Re: BBC Monitor (LS3/5a) Clone

    Not folded horns - though I knew a man who specialised in high efficiency folded horns - have built transmission lines and memorably a pair of Bass Bins modelled on an old Altec design - about four foot six tall, three wide and a royal pita to lug up stairs for pub gigs.
    Someday, I'm going to settle down and be a grumpy old man.

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    Default Re: BBC Monitor (LS3/5a) Clone

    Quote Originally Posted by P.I. Stazzer-Newt View Post
    Not folded horns - though I knew a man who specialised in high efficiency folded horns - have built transmission lines and memorably a pair of Bass Bins modelled on an old Altec design - about four foot six tall, three wide and a royal pita to lug up stairs for pub gigs.
    Transmission lines are intriguing. A lot of tower speakers are built on this concept these days. IIRC, Irving "Bud" Fried was one of the early proponents of the transmission line in the golden age of audio.

    In my case, it's not totally necessary. I don't feel I possess that purist, audiophile ear. I am certainly covered with good sound with the limits of my hearing capabilities using what's considered typical or what I already own. Still it's interesting to see how these systems work, and the lengths some people will go to in which to achieve it.

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    Default Re: BBC Monitor (LS3/5a) Clone

    15 ohms requires a dedicated amp no? What are you using for that Pipefitter?

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    Default Re: BBC Monitor (LS3/5a) Clone

    Quote Originally Posted by lupussonic View Post
    15 ohms requires a dedicated amp no? What are you using for that Pipefitter?
    What is 15 ohms? The full range drivers I have are Markaudio Alpair-10's. I think those are right around 8 ohm. The Continuums I just built are 8 ohm.

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    Default Re: BBC Monitor (LS3/5a) Clone

    Sorry, possibly confused..this from Stazzers link.

    "The 15 ohm version crossover boards were made by the manufacturers themselves or by a sub contactor and so differ slightly in appearance. In the case of Rogers' LS3/5As the board material changed during the long production run of the speaker. "



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    Default Re: BBC Monitor (LS3/5a) Clone

    Quote Originally Posted by lupussonic View Post
    Sorry, possibly confused..this from Stazzers link.

    "The 15 ohm version crossover boards were made by the manufacturers themselves or by a sub contactor and so differ slightly in appearance. In the case of Rogers' LS3/5As the board material changed during the long production run of the speaker. "


    I don't recall exactly what amp our foreman used but I want to say a Luxman, but it's been almost 40 years since I heard them and I am not sure which version of the speaker he had.

    The Continuum, OTOH, knowing the designer, he would have considered most people these days powering them with more available equipment and AV receivers.

    It seems as if I got one of, if not the last available kit for these speakers, as the specific tweeter used is NLA. Whether this is temporary or not, I don't know, but Parts Express, which is the distributor for Dayton products, no longer has the tweeter listed on their site. Usually it would just say out of stock with an expected availability date, otherwise.

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    Default Re: BBC Monitor (LS3/5a) Clone

    Quote Originally Posted by lupussonic View Post
    15 ohms requires a dedicated amp no?
    No, not if you're using a solid state amp, most of which are just as happy looking at 15ohms as they are looking at 8 or 4.

    P.S. Most speaker impedance figures are somewhat nominal.
    Someday, I'm going to settle down and be a grumpy old man.

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    Default Re: BBC Monitor (LS3/5a) Clone

    Quote Originally Posted by P.I. Stazzer-Newt View Post
    P.S. Most speaker impedance figures are somewhat nominal.
    It's even worse.... the impedance rating is barely grossly correct.... it varies all over the map, as a function of frequency... and even drive power.

    Transistor amps don't really care, for the most part, as long as, at any particular frequency or drive level, there's enough 'ooomph' in the output transistors to supply the current taken by the load. Tube amps are a different story, since they depend on an output transformer to match the load; this is not to say that any given tap on the output transformer is necessarily correct; just that the 'correct' tap will keep the tubes out of trouble. If you connect the wrong tap, you might hit a current or voltage limit.
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