EEVblog Electronics Community Forum
EEVblog => EEVblog Specific => Topic started by: EEVblog on December 22, 2018, 01:13:15 am
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Review and teardown of Little British Monitors, a small compact bluetooth monitor available as a kit on Kickstarter:
https://www.kickstarter.com/projects/1439311797/little-british-monitor-mkii-reference-micro-speake (https://www.kickstarter.com/projects/1439311797/little-british-monitor-mkii-reference-micro-speake)
https://www.youtube.com/watch?v=IcKlyIEfoPI (https://www.youtube.com/watch?v=IcKlyIEfoPI)
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Get out your spectrum analyzer and do a comparison against some $50 stereo speakers.
I would have liked to see an option for wired digital input (S/PDIF and/or USB) in order to eliminate the need for a decent DAC. The piece of wire attached to the Bluetooth module looks like a tack on with no RF knowledge so it would be interesting to see if removing it actually improves RF performance - yet another use for the spectrum analyzer. As for the heatsink being positioned with the fins horizontal, that's a design fail - it would perform much better with the fins vertical. (I'm in the process of evaluating a Silverstone passive cooled PSU with the same design mistake...)
I also note that you didn't comment on the PCB designed with an unlicensed copy of DaveCAD, and there doesn't seem to be an AvE reference I saw in other videos about that speaker.
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When they don't have XLR I feel like they should be called minitors. Or monitettes.
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To bad that the amplifier board didn't have discrete transistor driver and output power stages for each channel , instead of one of those Class A/B modules which have a lot more T.H.D. when driven hard
T.H.D.= Total Harmonic Distortion 8)
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been a while :)
The vid prompted me to check my memory of this little speakers spiritual great grandmother the ls3/5a, currently selling 2nd hand for >£1000 !!
On the way I found the following thread discussing why the BBC went in search of thin walled cases and why they apparently work so well.
https://www.harbeth.co.uk/usergroup/forum/the-science-of-audio/speaker-design/215-bbc-style-thin-wall-cabinets-why-so-special (https://www.harbeth.co.uk/usergroup/forum/the-science-of-audio/speaker-design/215-bbc-style-thin-wall-cabinets-why-so-special)
enjoy.
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Around 22m there is a 'bug' in the video and some remarks about the Weller no fuse problems are audible. Look like some editing go wrong.
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Yeah, that's really not a transmission line....
The 4x50watt power claim is interesting as well...
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The low frequency response of those woofers doesn't look like anything to write home about - falls off abruptly below ~100Hz. Do recording studios really rely on such as these? Or do they add a big woofer third channel?
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The low frequency response of those woofers doesn't look like anything to write home about - falls off abruptly below ~100Hz.
Looks more like 65Hz to me.
Still not ideal, but for most "pop" music, people aren't really going to care.
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I saw the title and expected to see small CRTs from Sir Clive.
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Yeah, that's really not a transmission line....
The 4x50watt power claim is interesting as well...
It is not, I just modeled and simulated the speakers and for this little volume you just need a pretty long bas-reflex port.
Which "magically" is exactly the length of the port in the design.
These little Dayton woofers are actually pretty nice.
300 pounds for these things is a big scam though.
The PCB is dirt cheap, no DSP is being used, only simple opamps with some of these Class-AB audio chips.
The woofer is a Dayton Audio ND91-4 which can be ordered very cheap in higher number (100-500 pcs), the tweeter isn't acutally a tweeter but a full range driver from Tymphany, looks like either a PMT20 or PMT30. Those little buggers were optimized for budget fullrange solutions for TV sets (or those cheap computer speakers).
Go for around 3-5 bucks a piece (you can find them on digikey)
Put some costs for some simple plywood and stuff in there and you're done.
Anyone who is only slightly involved in acoustics and audio knows this ain't the right price at all (and can probably guess the used materials, parts, speaker units, since they are VERY common)
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To bad that the amplifier board didn't have discrete transistor driver and output power stages for each channel , instead of one of those Class A/B modules which have a lot more T.H.D. when driven hard
T.H.D.= Total Harmonic Distortion 8)
Well, that really depends how good (or bad) your discrete design is.
But technically you could make a composite (or nested) amplifier to get a VERY low THD (if that is what you're looking for)
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OK Im old, but what I see is one volume control for both speakers. So how would
one adjust the "balance" for proper separation which is dependent on listener location and room response?
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OK Im old, but what I see is one volume control for both speakers. So how would
one adjust the "balance" for proper separation which is dependent on listener location and room response?
I would think adjusting balance is a job for the preamp that is feeding the speakers. Are you aware of powered speakers that have a balance control? I've never seen any with that feature.
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Around 22m there is a 'bug' in the video and some remarks about the Weller no fuse problems are audible. Look like some editing go wrong.
:-DD
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Here's a video of a girl building a pair:
https://www.youtube.com/watch?v=-f513rpfs88 (https://www.youtube.com/watch?v=-f513rpfs88)
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Here's a video of a girl building a pair:
https://www.youtube.com/watch?v=-f513rpfs88 (https://www.youtube.com/watch?v=-f513rpfs88)
A pair of rubber tires :o 8), jeez
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Here's a video of a girl building a pair:
Definitely a male attraction dress she wears, but if see does everything by herself she is fairly good at building stuff.
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I can't see why they would not be classified as transmission-line speakers?
TL speakers are a rarity, which is probably why Dave seems to wonder if it is even "a thing", and it is certainly both unusual and probably hard to get right in such a small enclosure.
Their rarity is due to not many woofers having what it takes (see below) and because there is (still!) no way to create a good TL design, except trial and error.
The best-selling TL speaker design ever was probably Bo Hanssons "Rauna Njord", which were made from concrete and therefore weigh 35kg each. (https://vintagehifiproducts.wordpress.com/2014/06/19/rauna-of-sweden-the-story-continues/)
TL designs often have high cross-over frequency. The physical requirements of a bass unit to drive a transmission line are almost the same as for full-tone units in horn-enclosures, and if you have a full-tone unit as bass anyway, you can get the cross-over out of the midrange by pushing it up, instead of down. The Rauna Njord's cross-over is 3.5 kHz and the tweeter is mounted coaxially on the lower of the two bass units.
TL designs and some horns can be used with current-drive, where the amplifier delivers a current rather than a voltage proportional to the signal. At least in theory this is better, because the magnetic field in the speakers coil depends on the current, not the voltage. In practice it takes a lot of experimentation. See also Nelson Pass' F1 and his writings about it.
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Here's a video of a girl building a pair:
Definitely a male attraction dress see wears, but if see does everything by herself see is fairly good at building stuff.
Her FAQ is a refreshing read: https://pastebin.com/V3474kYs
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I can't see why they would not be classified as transmission-line speakers?
A 20cm long port, does not a transmission line make...
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I can't see why they would not be classified as transmission-line speakers?
A 20cm long port, does not a transmission line make...
That's correct.
Although there is a grey area, but in general a transmission line for around 65Hz would be a lot longer.
Also the placement of the woofer and the "entrance" of the line would be different, as well as that most transmission lines are tapered.
(technically you can also get a straight transmission line)
Like I already said before, I simulated this speaker as a ported design and basically came to the same port length.
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OK Im old, but what I see is one volume control for both speakers. So how would
one adjust the "balance" for proper separation which is dependent on listener location and room response?
I would think adjusting balance is a job for the preamp that is feeding the speakers. Are you aware of powered speakers that have a balance control? I've never seen any with that feature.
I am old school and prefer passive speakers and separate electronics.
I have seen powered speakers where each speaker has it's own volume control, making balancing possible.
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It certainly does, the question is only question is at what frequency and how that sounds.
First of all, I judge the actual transmission line to be approx 12+15+5 = 32cm long. It goes along the bottom, up behind the partition and down in front of the partition to the woofer.
The line is also very heavily damped, so the speed of sound is severely reduced, probably as much as 40%, and that brings us to a plausible TL frequency of (40% 340m/s / 32cm ~= 425Hz)
I'm pretty sure the high aspect ration of the TL, something like 1:7, will also increase the wavelength, but no idea by how much. (Ask any microwave plumber: There is a reason wave-guides have low aspect ratio)
The TL port only needs to be N+½ wavelengths, where N is allowed to be zero, which improves the impulse response, but there are trade-offs.
The bottom octave of a TL design is delivered by the port, and from around 60Hz these speakers drop dead in precisely the way TL designs do at their bottom.
If the port kicks in around 120-180Hz and a half wavelength of the port below 210Hz is well within the uncertainty here.
All that said: A speaker which goes silent below 65Hz, can be wonderful for speech, lieder and chamber music, but a bass-reflex design of the same outher dimensions, would at least pretend that the double- and electric bass were invented.
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Hey, if you wanna call it a transmission line, go for it! :-//
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At the end of the discussion, I don't really care if it is a pure a transmission line or bass reflex or a mix between the two.
That is just nitpicking about the details. You can make wonderful design with either of both approaches, or completely fail as well.
It doesn't make a speaker a million times better and it certainly doesn't make the speaker worth around 350 bucks for a self made kit with jellybean parts and a bad PCB design.
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It doesn't make a speaker a million times better and it certainly doesn't make the speaker worth around 350 bucks for a self made kit with jellybean parts and a bad PCB design.
For something as "entry level" and consumer grade as these, I would have used an off the shelf class D amplifier, with Bluetooth module built in, and simply run a single full range driver, without the added complexity of active crossovers and bi-amping... especially seeing its using a pretty low end automotive amplifier chip...
Perhaps I should launch a Kickstarter campaign...
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It is not just a matter of nomenclature or preference, there is a big difference in how it works and what follows.
For instance BR has high efficiency whereas TL are inefficient, basically: does the port help or hinder the woofer.
(That is another datapoint here: 4x50W amplifier for 2x1800cm³ internal volume is horribly inefficient.)
In the end the best way to teil is to listen: TL has a tight and controlled bass whereas BR is loose and resonant.
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It doesn't make a speaker a million times better and it certainly doesn't make the speaker worth around 350 bucks for a self made kit with jellybean parts and a bad PCB design.
For something as "entry level" and consumer grade as these, I would have used an off the shelf class D amplifier, with Bluetooth module built in, and simply run a single full range driver, without the added complexity of active crossovers and bi-amping... especially seeing its using a pretty low end automotive amplifier chip...
Perhaps I should launch a Kickstarter campaign...
And ask $250 for it 8)
I would have done many things different.
Don't get me wrong, I admire this kid for being all excited about his fancy ideas (I give him the benefit of the doubt).
But the whole design looks, feels and smell just like an hobby project.
Absolutely nothing wrong at all with hobby projects, but selling that for 350 bucks feels VERY wrong to me.
I have seen kids his age doing much much better.
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(That is another datapoint here: 4x50W amplifier for 2x1800cm³ internal volume is horribly inefficient.)
The 4x50 is an optimistic, unrealistic figure.
The part mentioned somewhere (I can't find it now) suggested 4x35watts at 1% THD, if run off 18volts. I don't know what supply voltage he's using...
I would have done many things different.
Don't get me wrong, I admire this kid for being all excited about his fancy ideas (I give him the benefit of the doubt).
But the whole design looks, feels and smell just like an hobby project.
Absolutely nothing wrong at all with hobby projects, but selling that for 350 bucks feels VERY wrong to me.
I have seen kids his age doing much much better.
It's a fantastic project!
I good step into both reading, understanding, and implementing datasheets, along with PCB design and layout, as well as speaker enclosure design and construction.
It's the exact type of project I'd suggest to people who wanted something to design and build (although using electronics kit(s) while I was working in an electronics component/kit retail store...
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At the end of the discussion, I don't really care if it is a pure a transmission line or bass reflex or a mix between the two.
That is just nitpicking about the details. You can make wonderful design with either of both approaches, or completely fail as well.
It doesn't make a speaker a million times better and it certainly doesn't make the speaker worth around 350 bucks for a self made kit with jellybean parts and a bad PCB design.
100% agreement there.
While I do admire squeezing a TL design into that tiny size, and would love to listen to them, to see how well he did it, I'm not paying 400 quid for the privilege.
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In the end the best way to teil is to listen: TL has a tight and controlled bass whereas BR is loose and resonant.
I was already afraid of this comment.
Basically it comes down that you never designed a proper BR design.
They all have their pros and cons, even closed designs, dipole and cardioid.
When designed properly and more importantly USED properly, they can all sound much better than anything else.
When there is a mismatched, the result is getting tons of myths on the internet about nude elves, snake oil and such.
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(That is another datapoint here: 4x50W amplifier for 2x1800cm³ internal volume is horribly inefficient.)
The 4x50 is an optimistic, unrealistic figure.
The part mentioned somewhere (I can't find it now) suggested 4x35watts at 1% THD, if run off 18volts. I don't know what supply voltage he's using...
From Marco Reps video I understand that he is using a TDA7850 amplifier chip.
That thing is ancient, and definitely not something to be proud off in an "high-end" design.
For the tweeters you don't need that much power anyway.
But since he is using some kind of awkward fullrange driver that is only capable of a few watts, that number is already a lot less lower.
The Dayton ND91-4 can only do 30W in RMS and (although not stated in the datasheet) 60W in peak (crest factor 8 or 12 normally)
The whole point is, nowadays Class-D amplifiers perform better in noise and THD plus you don't need such a big and ugly (wrongly mounted) heatsink.
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Basically it comes down that you never designed a proper BR design.
They all have their pros and cons, even closed designs, dipole and cardioid.
Again: 100% agreement (And for the record: I coined the concept "Audio-homeopathy" :-)
But there is a physical difference between BR and TL, and it largely amounts to TL using/wasting electrical power to improve the pulse-response in the bass domain.
And given that TL is hard to design, demands a lot from the woofer, have low efficiency, they are justifiably rare.
But good TL's, like the Rauna Njord, make it all worth while.
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Basically it comes down that you never designed a proper BR design.
They all have their pros and cons, even closed designs, dipole and cardioid.
Again: 100% agreement (And for the record: I coined the concept "Audio-homeopathy" :-)
But there is a physical difference between BR and TL, and it largely amounts to TL using/wasting electrical power to improve the pulse-response in the bass domain.
And given that TL is hard to design, demands a lot from the woofer, have low efficiency, they are justifiably rare.
But good TL's, like the Rauna Njord, make it all worth while.
I guess yeah.
Although, if you're looking for efficiency I would rather suggest a horn.
The thing is though, nowadays (sub)woofers are made so much better than 40 years back.
But even more is amplifier power that is dirt cheap and small.
So generally I just advice a multi-subwoofer closed system for the lower-end because that also tackles all the standing waves in your room
(Floyd Toole: Sound Reproduction if you want to read more on that)
Even for the high SPL professional audio speakers it is mostly just BR for convenience.
I have designed and made some nice TL speakers in the past, but to be very honest; it's to much work, effort en problems in the end compared to a WELL designed BR speaker.
One thing that is absolutely noticeable are the standing waves and other crap in a TL design.
Like I said, nothing comes for free.
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I have seen powered speakers where each speaker has it's own volume control, making balancing possible.
That makes it a bit cumbersome to adjust the volume in that the balance would also have to be readjusted.
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I have seen powered speakers where each speaker has it's own volume control, making balancing possible.
That makes it a bit cumbersome to adjust the volume in that the balance would also have to be readjusted.
Most monitor speakers are designed to use with a computer, so that is just simply adjusting a setting in your audio settings.
For the 1% that uses these things for their home-audio (and even thinks about adjusting it), meh, can't be bothered.
A lef-right control with just one (passive) potentiometer adds some margin of error anyway in neutral mode.
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The thing is though, nowadays (sub)woofers are made so much better than 40 years back.
But even more is amplifier power that is dirt cheap and small.
[...]
I have designed and made some nice TL speakers in the past, but to be very honest; it's to much work, effort en problems in the end compared to a WELL designed BR speaker.
One thing that is absolutely noticeable are the standing waves and other crap in a TL design.
Like I said, nothing comes for free.
Again, 100% agreement.
My only complaint were the people who dismissed this as not being a TL design or who as Dave not even knew that at a TL design "is a thing".
I think the right way to think about this speaker is a working 1:2 scale model of an Austin Mini: Possibly an impressive feat, not very useful or relevant for transportation :-)
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My only complaint were the people who dismissed this as not being a TL design or who as Dave not even knew that at a TL design "is a thing".
Well, my complained to Dave in general is that if it's not something like scopes or something, it's just a quick peak and nothing more else.
He didn't even give any information about which IC's were being used.
For the record, TL074, or in other words; the cheapest of the cheapest.
I never use these things in any modern and new design anymore unless it needs to be cheap as chips.
They are even being sold as (quote) general purpose opamps.
All together it says a lot about the design.
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This is a great project and we need more people like him to resurrect kitting to help kids and others to learn electronics. This one is particularly good because it is not a throwaway kit, you get a working useable device in the end. And there is a Lot of efforts required to make kits, the smartasses here in this thread just have no clue what it takes.
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This is a great project and we need more people like him to resurrect kitting to help kids and others to learn electronics. This one is particularly good because it is not a throwaway kit, you get a working useable device in the end. And there is a Lot of efforts required to make kits, the smartasses here in this thread just have no clue what it takes.
What the industry needs to get more interest from kids (and adults) in hobby and DIY electronics, and assembly, is affordable kits.
This is not the project for that...
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a bass-reflex design of the same outher dimensions, would at least pretend that the double- and electric bass were invented.
Even if it pretends they're single-stringed instruments that can only play one note.
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Who else is offering a kit similar to this? It looks like a fun project and a bit high in price for my tastes especially crossing over the Atlantic. Perhaps the loudspeakers and electronics could be split out as two kits.
Of course you can improve the design to absolute perfection.
I've had poor results with shelf-type vents (air) doing two 90 degree bends. Also with the vent's foam filling, it might act like a Variovent. I don't know if it has active EQ seeing the steep 50Hz rolloff.
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Who else is offering a kit similar to this? It looks like a fun project and a bit high in price for my tastes especially crossing over the Atlantic. Perhaps the loudspeakers and electronics could be split out as two kits.
Of course you can improve the design to absolute perfection.
I've had poor results with shelf-type vents (air) doing two 90 degree bends. Also with the vent's foam filling, it might act like a Variovent. I don't know if it has active EQ seeing the steep 50Hz rolloff.
I used to make kits and plans all the time on forums, but eventually it's just always a lot of work.
Nowadays it's easier just to come up with something yourself
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I can't see why they would not be classified as transmission-line speakers?
TL speakers are a rarity, which is probably why Dave seems to wonder if it is even "a thing", and it is certainly both unusual and probably hard to get right in such a small enclosure.
Their rarity is due to not many woofers having what it takes (see below) and because there is (still!) no way to create a good TL design, except trial and error.
The best-selling TL speaker design ever was probably Bo Hanssons "Rauna Njord", which were made from concrete and therefore weigh 35kg each. (https://vintagehifiproducts.wordpress.com/2014/06/19/rauna-of-sweden-the-story-continues/)
TL designs often have high cross-over frequency. The physical requirements of a bass unit to drive a transmission line are almost the same as for full-tone units in horn-enclosures, and if you have a full-tone unit as bass anyway, you can get the cross-over out of the midrange by pushing it up, instead of down. The Rauna Njord's cross-over is 3.5 kHz and the tweeter is mounted coaxially on the lower of the two bass units.
TL designs and some horns can be used with current-drive, where the amplifier delivers a current rather than a voltage proportional to the signal. At least in theory this is better, because the magnetic field in the speakers coil depends on the current, not the voltage. In practice it takes a lot of experimentation. See also Nelson Pass' F1 and his writings about it.
Yes, TL speakers are more difficult to model and design. That is why most end up avoiding this route, and go directly to bass-reflex or sealed designs.
Folded horn, and tapped horn are some other uncommonly used bass enclosure designs.
I had no idea Bo Hansson had his name put on speaker designs. I do enjoy his albums, El-Ahrariah is one of my favorites.
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Great video! I have always been interested in various speakers. The second last ones I found curb-side were Kenwoods and it was only after several years that I realized one had a blown tweeter. Of course, I couldn't tell because both main speakers were ok and the one tweeter that did work seemed to cover for both.
Then I lucked out and found a pair of JM Labs Chorus 715 which apparently are now Focal. The pair of towers also came with a center unit called the Chorus CC 700. In the image below, it is what you see on the left side of the picture (not the speakers on the right side of the photo stacked on each other, which appears to be a large woofer SW700 and surround SR700):
(http://www.soundstagexperience.com/equipment/pics/jmlab_chorustheater.jpg)
I always wondered how these fare in the speaker world, and how Focal is compared to JM Lab as far as quality, materials go. These things are supposed to be made in France. Perhaps Focal switched over manufacturing to China? I also still can't figure out why someone dumped these on the curb (no obvious performance issues, although the color is awful in that orange-wood).
I see a pair of 715's advertised here for $300:
https://marche.quebecaudio.com/occasions/index.php/annonces/jmlab-chorus-715/ (https://marche.quebecaudio.com/occasions/index.php/annonces/jmlab-chorus-715/)
And the center speaker was sold for not much either:
http://kahlaudio.com/products/focal-jmlab-chorus-cc700-center-speaker-current-model-lots-of-positive-reviews-650-msrp/ (http://kahlaudio.com/products/focal-jmlab-chorus-cc700-center-speaker-current-model-lots-of-positive-reviews-650-msrp/)
Probably lower-end in terms of "audiophile" quality, but better speakers than I have ever actually owned? Maybe the previous owner chucked them because these are considered not good enough for their audiophile system? I don't even know what you would consider a "good" pair of speakers cost range to be. Sadly I am plugging only the pair of 715's in to my garbage tuner which only has 2-channel left/right stereo out, there is no surround output and therefore I can't even use the CC 700! Perhaps someone will curb-dump a 5.1 channel surround tuner amp. ;)
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For that price you can buy commercial "PC monitors" that are quite good, surprisingly so.
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I can't believe how expensive these are. I got a very good pair of KEF 104/2s for about £350 recently!
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..so... its not a transmission line...
makes the whole thing a bit more questionable...
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I can't believe how expensive these are. I got a very good pair of KEF 104/2s for about £350 recently!
Were your KEFs also made in a garage/home by a single person?
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I can't believe how expensive these are. I got a very good pair of KEF 104/2s for about £350 recently!
Were your KEFs also made in a garage/home by a single person?
This is good why?
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I can't believe how expensive these are. I got a very good pair of KEF 104/2s for about £350 recently!
Were your KEFs also made in a garage/home by a single person?
This is good why?
I wasn't sure if he was claiming this to be a good thing or a bad thing... I'd want to assume bad...
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I don't wan't to write a long post about it, but in the discussion bass-reflex vs transmission line, those little boxes are bass-reflex.
Someone mentioned kef 104/2, those are band-pass (low-end).
All of the above are poor choices for faith full sound reproduction as they add smearing in the time domain.
Any serious studio monitor is sealed.
https://zstereo.co.uk/2015/06/24/bbc-ls35a/ (https://zstereo.co.uk/2015/06/24/bbc-ls35a/) (warning: 40% wank)
https://www.soundonsound.com/reviews/yamaha-ns10-story (https://www.soundonsound.com/reviews/yamaha-ns10-story) (actually mentions time domain :-+)
Tannoy and Genelec also had some (certainly not all :palm:) good boxes.
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In the end the best way to teil is to listen: TL has a tight and controlled bass whereas BR is loose and resonant.
Many bass-reflex designs are not tuned very well leading to poor impulse response and poor intermodulation distortion at low frequencies. In production this is a problem because driver characteristics vary from unit to unit and nobody wants to individual tune enclosures.
And given that TL is hard to design, demands a lot from the woofer, have low efficiency, they are justifiably rare.
At least with low efficiency, the high noise from the power amplifier will not be noticed. Is that a marketable feature?
He didn't even give any information about which IC's were being used.
For the record, TL074, or in other words; the cheapest of the cheapest.
I never use these things in any modern and new design anymore unless it needs to be cheap as chips.
They are even being sold as (quote) general purpose opamps.
Aww, TL074s are not all bad. They have the increased bandwidth and slew rate needed for audio and their low input bias currents make design easier. The circuit topology like avoiding common mode distortion by using inverting stages is more important and would ruin the performance of a better operational amplifier anyway.
Must ... look ... away ... from ... her ... speakers. She needs to learn to solder properly; wipe the tip before soldering and not after to protect the surface from oxidation.
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Someone mentioned kef 104/2, those are band-pass (low-end).
All of the above are poor choices for faith full sound reproduction as they add smearing in the time domain.
I seem to remember Kef 104s were quite good. Back in the 1980s. They're ported but it's a big, front-facing port. Not as much of a band-aid as a typical 50Hz port on a tiny speaker.
Any serious studio monitor is sealed.
Yep. Or at least small, front-facing ports. Anything that blows air backwards at the walls is asking for trouble.
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I can't believe how expensive these are. I got a very good pair of KEF 104/2s for about £350 recently!
Were your KEFs also made in a garage/home by a single person?
No, but they came fully assembled for that price!
OK, the KEFs weigh about 35 kg each and are huge floorstanding speakers, but for my money I'd rather have the best thing I can get for that amount of money than something brand new part built in someones shed somewhere in England. The whole "built in England" thing is a load of wank anyway - most of the stuff will have come from China.
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OK Im old, but what I see is one volume control for both speakers. So how would
one adjust the "balance" for proper separation which is dependent on listener location and room response?
I would think adjusting balance is a job for the preamp that is feeding the speakers. Are you aware of powered speakers that have a balance control? I've never seen any with that feature.
My Genelec and KRK monitors have a volume control on each cabinet, so you could do balance there. The key to any successful monitoring room, of course, is to calibrate the whole system.
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The low frequency response of those woofers doesn't look like anything to write home about - falls off abruptly below ~100Hz. Do recording studios really rely on such as these? Or do they add a big woofer third channel?
Recording and mastering studios have several sets of monitor speakers, ranging from soffit-mounted three-way boxes with large (15") woofers and two or three pairs of console-top mounted nearfield monitors, and a pair or two of some small "TV speaker" monitor. The nearfields are something like the Genelec 1031A with an 8" woofer and the Yamaha NS-10, and I see a lot of the ADAM monitors (very nice) too. Those "tv speaker" monitors are usually something like an Auratone cube, with a single driver, meant to sound like what one might hear in the car or through a television's built-in speaker.
Which speakers are being used depends on what the engineer wants to hear.
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To bad that the amplifier board didn't have discrete transistor driver and output power stages for each channel , instead of one of those Class A/B modules which have a lot more T.H.D. when driven hard
Agree. Chip power amps have two problems; crossover distortion at low levels because they have no standing current adjustment, and running out of power transistor drive at high levels because they typically use multi-NPN darlington arrangements with high burden volts.
Class D ICs using FET output stages tend to give better sound quality, only IME they are very blow-up prone. Even driving into distortion can cause some of them to pop.
For any critical application I'd go for a discrete complementary arrangement though.
Other point, that heatsink is the wrong way round and won't dissipate much. Plus, stainless may look nice but it's not a very good conductor of heat. (Ever watched a blacksmith hammering the red-hot end of a piece of steel whilst holding the other cold end in his hand? Try that with ally or copper and it will be ouch time.)