EEVblog #1162 - Little British Monitors

Review and teardown of Little British Monitors, a small compact bluetooth monitor available as a kit on Kickstarter:

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[Audio_Simon]

Thanks so much for the video Dave! I'd love to answer a few of your questions:

The tweeter is made by Tymphany.
I assembled the PCB by hand and the bodge wire was to adjust grounding. The final version will not have any bodges.
Op-amp choice. The NE5534 has low voltage noise and is great used with low impedances, but the TL074 has low current noise so is good used with high impedance like these filters.
Transmission line vs port. I would say TLs are longer than 'ports' with a proportionally larger section area, are folded and use damping material inside to reduce harmonics of the main resonance.

I'm already making improvements to the design for the final version in a number of areas.

[Berre]

No tweeter on the face of this planet is able to reproduce the frequencies of Dave's voice.

[Hiddensoul]

Love the main Cap labelled as Flux Capacitor

[DrakkarCalethiel]

Produced in DaveCAD - Unlicensed Version. :D

[Reefgc]

The venting on the back of the driver is for venting the voice coil. A difference between ported and transmission line is that transmission line adds bass over a wider frequency range then ported would.

[scottlarson]

I am still using the speakers I built (and more or less designed) myself around 1981. I bought a book at Radio Shack that told you how to do it (there was even math involved) and I used my dad's tools to put them together. Around 2002 the old paper cones withered away so I replaced the drivers with nice modern ones and I replaced the crude crossovers I had built myself with modern boards. They've never sounded better.

[PyroRob]

"Produced in DaveCAD - Unlicensed Copy"

[RussCottier]

As an audio pro I can tell you your comparison setup with the mic was better than most pro audio comparison videos. Good call

[nickwallette]

As an audio DIYer, my thoughts:

Those midwoof drivers are A BEAR to work with. To get good low end you need a huge cabinet - at which point you can just use a larger driver with less nonlinear distortion. They also have nasty resonances in the upper midrange that you have to filter out with a more complex crossover to your tweeter. (Somewhat typical of aluminum cones, TBH, but it rains on the "small driver therefore high M/T xover point" parade.) IIRC, they also have a weird impedance curve that makes a passive XO difficult to design - not that it applies in this case. To top it off, the stamped frame is flimsy - I even had one arrive new, pre-bent. Once mounted, maybe that's not such a big deal, but I have a hard time believing it does not contribute to distortion when that cone gets moving - and its excursion (and small light neo magnet) is its point of existence.

They can be fun to play with, but there are so many much better drivers out there if you're building a serious speaker.

The tweeter, I've heard, is surprisingly good. I have a few to play with but haven't used them yet. They were used by a reputable name in the hobby speaker design circles in an omni-directional speaker design, and were found to be quite pleasant to listen to. In a nearfield or generic BT application, where the strengths of that driver don't apply, I would stick to a typical silk dome - it's better at being a normal tweeter. Dayton has some 1/2" to 1" domes that are a complete steal at their price.

So overall, I feel like this design is a checklist of engineering experiments, not necessarily a great design in and of itself. Most DIY speaker guys go through something like this because it's unusual and therefore interesting. But it's unusual because many of the tried and true designs are just better suited for general use. There's always a fascination with making the smallest cabinet possible as well - but physics wants a Cerwin Vega floorstander, and clever engineering can only get you so far. Second best, for "good enough" cases, is a stout small driver with tons of DSP. Everything else is a compromise.

[hidenrage]

these are NOT MLTL speakers and the drivers do not appear to be high quality. Notice how none of the driver specs are given here or on the kickstarter. Go to partsexpress.com and you can build your own bookshelf monitors with an active crossover and add a blutooth module for a fraction of the cost. The $100 mark is not far off depending on how good of a crossover you want to build. Also, anyone that knows about resonance understands that for the density to mass ratio and quality control of the product, MDF is a better choice for cabs than plywood unless he is using the finest grade cabinet ply (9 layers or more) and checked for inclusions in the cab. This is a set designed for the recreational person who likes to think they know about something because they screwed nut A into hole B. Just an FYI, I built 3-way MLTLs as my main fronts and the crossovers in them were $300 so please do not mistake a product produced for noobs for quality just because the uninformed think it is.

[FordForTheWin]

Got to say the beech plywood does work well for diy speakers. I build them like this all the time!

[foxpup]

I like the inverted dome tweeter. That way you don't have to reverse them after the kids push them in. :-)

[kentlarsen]

electrons flying off the corner, thats good stuff!!

[sysierius]

Hi dave, the grill is to cool the voice coil down.
When the subwoofer moves it blows air in and outside the little hole, cooling down the voice coil

[johnnodge]

I'm stunned at the amount negativity towards a product, which by comparison to far eastern standards is very high quality. The number of comments that say they could build them for $100 is shocking. This of course is a complete impossibility, especially if they are to sell them at a profit and stay in business.

Ok the design of the PCB could be better, with more care taken with the layout. But in low frequency applications, it really makes little difference to the way the circuit functions. These are also pre-production samples, so there's going to be some elements of the design that won't get into the finished production models.

So can we stop with this "I could build them for 100 bucks" bullshit, because you can't period. If you can, then do it and send them to Dave for evaluation.

[bryede]

Although the full-range driver can be used without a tweeter, it will become more directional as the frequency increases making essential that you be directly in front of them to hear the full range. By crossing over to a tweeter, you can avoid that beaming effect.

[StreuB]

Vishay caps are quite good actually. We use their tant's at my work for making all our RF boards and Vishay is prime spec with no allowable sub's b/c of the strict temp. profile the systems is designed and tuned to operate in.

[cspower]

They look like nice little speakers but the price is over the top. It would actually be cheaper to make your own.

[francisvaughan]

So, some thoughts on the review.
Quite right to be dismissive of the cabinet being a real transmission line. A few have already noted this. The original "transmission line" design went back to Bailey, and was a design with essentially no theoretical underpinning. The idea was that the stuffed tapered line would adsorb all the energy off the rear of the driver was a nice idea, but the reality was always going to be something else. There is now quite good understanding of what is really going on, and a few useful design tools available, Martin King's work probably being the definitive, although tools like Hornresp can also model the system and get much the same results. What the enclosure seen is is a tapped line. The port is coming off part way down the line, and you will get a reasonably complex system. There will be a resonant system in the box with the speaker, and other in the box with the electronics, they couple, and there is a lossy resonant port. Add to that a quarter wave resonant system end to end. However, what you can do is tune this mess to produce a range of responses, and with care eventually end up with a flat response. For a small enclosure you might be able to create a more satisfactory (for some definition of satisfactory) result than a simple sealed or ported alignment.
On the subject of full range drivers, an eternal problem with any full range driver is the polar response at high frequencies. As the driver becomes large relative to the wavelength the speaker becomes quite directional. Whilst it is possible to make a flat response on axis, the frequency of the energy in the diffuse field is heavily skewed. Metal cone drivers invariably have a few quite nasty resonances at high frequencies, and part of the art of crossover design is to avoid energising them. All full range drivers, no matter what the technology, have significant resonance issues.
One notes that the bass drivers are about 40 USD each, and the tweeters are probably in the vicinity of 10-20 USD. So the BOM for just the drivers is already 100 USD. Cutting out the enclosure on a home gamer CNC router is not going to be conducive to a cheap result, even if the kit probably goes together with the precision of a Swiss watch.
The driver selected seems pretty nice. It has such nice design features as a shorting ring around the voice coil, and has clearly been carefully optimised. It is great for a small 2 way. One notes there is a subwoofer output. Does using it place a high pass before the bass drivers? Using it with a subwoofer would help greatly with reducing the excursion the drivers need, and would probably drop distortion quite a bit.
With Dave's experience in building stuff for manufacture, some comments on the expenses, and the margins would have been illuminating. Despite the apparently high cost of these speakers, and the moaning, it is not clear how unreasonable the price is. Without serious economies of scale, getting prices down is hard, and in the end, it isn't the ingredients alone that matter. If the final result is good, that is what you pay for. The modern world doesn't seem to value the work in getting it to that point, and expects the IP for free.

[illustriouschin]

Red painted screws, what kind of arbitrary expectation is that?