BK XLS-300/pr

HiFiRuss71

Distinguished Member
Big subs are great. They go louder, they go deeper and generally speaking, they do it all with less distortion than a smaller sub for similar money. That's all very well if you've got the room for one. Back in the real world where not everybody has the room, a detached house, or sufficiently detached wife, the reality is they're too big, the neighbours are too close and the wife, or significant other, ain't gonna let it happen.

So, what to do? Up to now the choice has been broadly limited to simply buying a smaller sealed sub and doing what you can with boundary reinforcement to prop up the lower frequencies. The single driver in a small cube, with as much power as the budget will allow, has been the staple sub of virtually every manufacturers range for going on decades and that probably isn't going to change anytime soon, but small sealed subs bring their own set of compromises to the table.

They're inefficient. Power that is needed to power the driver, is soaked up simply squeezing the air in the box. 1000w RMS is not uncommon in more expensive examples, but even that is insufficient to allow the low frequencies and high SPLs that a big ported box will do with 300w.

This efficiency advantage of the big sub is down to having a larger internal volume of air that resonates lower and requires less squeezing. The eagle eyed will have noticed that most of these big subs also have a port and that's crucial. A port is free output. It makes use of the output from the back of the driver (which you never actually hear, so it's wasted) to resonate a column of air contained within the port. By adjusting the length and width of the port, you tune the resonant frequency to somewhere below the natural resonance of the box/driver combination so that as they roll off, the port starts to fill in. Win, win. Lower frequencies delivered for free and without massive power requiring massive driver travel and if it's done well, with much less distortion as a result. It's a cheap solution too, as the port is a tube with no moving parts. It's not a free lunch, but as solutions go it's elegant and damned effective for the price.

The problem for the small box, is that it's too small to fit a sufficiently large port in. You could fit a 20Hz tuned port in, but it would be so narrow that the air traveling in it will move too fast and it's motion will start to become audible as chuffing or even whistling in extreme cases. This is quite possible, even in larger boxes, which is why you see multiple ports in designs like the big SVS subs. So what can the small box do to compensate?

One option, is to use enough power and equalize the amplifiers output to increase as frequency descends. That has it limits too, namely, the amount of power required to do it, the increase in distortion caused by extreme driver excursions, as the drivers travel becomes less linear, the fact that the natural response will roll off even quicker after the artificially forced tuning point is passed and that to make this physically possible, you'll need a damn good (read expensive) driver.

The other solution is to use a passive radiator (PR) which is basically another driver without the motor assembly. It basically does a similar job to the port which is to use the free output from the back of the real driver to cause it to resonate. By adding weight to the diaphragm, it's resonance can be lowered and thus tuning the enclosure to a lower frequency than the box and driver can manage alone.

So what's the problem? Well there isn't a problem as such, but there is a set of compromises as with any other solution.

The obvious one is that adding another 'driver' isn't cheap, certainly not as cheap as a port. It's not as much as another complete driver, but it's not far off. The next is that a diaphragm that is the same size as the main driver, is being asked to do lower frequencies than the main driver. These frequencies require more air to be shifted, which requires greater travel and the lower you tune it, well you see where this is going.... The next is that whilst a port may start to chuff and will just chuff more with increasing volume as it limits are reached, a PR will simply run out of travel. This can be cured by using more than one PR just as it can with extra ports, but PRs are expensive and so, predictably, are the subs that use this multiple PR method. In so far as I am aware, the only commercially available subs that do use multiple PRs are Genelecs and in the case of the HT3B (which incidentally uses the same drivers as the subject of this review) cost's circa £1500. Gulp! Finally and perhaps least of all, a sealed sub naturally rolls of at 12dB/octave. A ported sub rolls of at 24dB/octave. A PR sub rolls off at 30dB/octave. In other words it goes as deep as it's designed to and that, really is that. If it's a no-no to try and boost a ported sub below it tuning point, it's a really big no-no with a PR.

So why bother? Well, if you take it's limitations into account, it works rather well. I've spent this long preambling (if that's a real word?) because to understand what this sub is capable of, is to understand it's well engineered set of compromises and choose it if it suits your circumstances. Namely, you want something that will go deeper than the usual fayre, but you're space/neighbour/wife constrained so you don't need and can't use an SPL monster big box. Putting it another way, no, this thing isn't a Monolith quart in an XLS-200 sized pint pot.

Let's get to the sub itself.


grillonoffgu1.jpg


First Impressions.


To many of us, the XLS-300/PR will look remarkably familiar. It looks like a slightly larger XLS-200 that's nicked the grill off a Monitor Audio RSW-12. At this point, I'll get the one thing I don't like off my chest. Inspite of it's exactly equal 350mm dimension on all sides, the grill pins are not spaced symmetrically - they're spaced closer on the bottom than on the top. This means that if you like your driver on display, you have to pay attention to which way up the grill goes when replacing it and if you prefer the look of the grill curves sideways, rather than up/down, you can't change it. It's a minor niggle and one with no performance implications what-so-ever and I do realise that in it's intended orientation, the grill keys in with the look of the HC-1 speaker package that BK make. The choice would be nice, that's all. That one grumble out of the way, there are some really nice visual touches to this sub. As with all BK subs the drivers (and obviously the plate amps) are rebated flush into the cabinet and the fit is as tight as the proverbial gnats chuff. This is nice finish. My old MJ Ref 200 (and there's an obvious parallel to be drawn there) didn't bother with such tidy detail and that retails for £750. However, they've gone one step further with the main (visible) driver and recessed it a little further and then radiused the edges of the rebate. There's no acoustic justification for this, but as a 'grill off' kind of bloke, it looks damn sweet. The feet depart from the norm also, being a rounded cone rather than cylindrical, which again has no obvious benefit beyond just looking nice and that's not a bad thing. Finishes are the usual selection of very tidy veneers and dare I say it, they'll do a few others too if the Monolith thread is anything to go by. You have nothing to loose by asking them.

plateampgx5.jpg


Round the back is a new plate amp sporting 300w continuous and 600w peak, plus dual high/low level inputs that can be run simultaneously should that be your bag. Rather than duplicate all controls, there is only one crossover (40-120Hz), but there is a switch to defeat the low level input to 'LFE' thus allowing your AV amp to handle the crossover, whilst leaving the subs crossover to affect the high level input only. There are separate gain controls but only one phase control because that's precisely as many as you need. Under duress of a stern testing with my favourite film clips, the amp got mildly warm, but no more. Incidentally, the XLS-300 comes with all the cables necessary to hook up all of the inputs at once. The Neutrick Speakon lead for the high level input, is partnered with a shielded stereo 5m RCA phono to phono cable for low level duties. I have been using this cable (or at least the one that came with my Monolith) since the dual subs thread and have never once suffered an untoward hum or buzz. A three pin IEC power chord of longer than average length is present also. I'd tell you about the instruction manual, but I'm a bloke and have thus far resisted refering to it.

How?

The sub was fed via my Velodyne SMS-1 and equalised to flat. Given my significant room booms below 35Hz this results in a lot of cut being applied, although the amount was considerably reduced, compared to my Monolith, as 20Hz was approached, indicating it doesn't have the same level of extension. In comparison, in my room I would say it rolls off about 3-5Hz earlier with 20Hz being about it's -3dB point. Below this point, output dropped like a stone. It's smaller size was an advantage, giving a lot more latitude in positioning and finally allowed me to try a position in between my front three speakers......where I found I had a mahoosive null at about 60Hz which I couldn't dial out. Somewhere along the front is always a good place to start, but it isn't always the answer.;)

I tested with my usual set of demo pieces with the kit listed in my signature*. Music is replayed at approximately 12dB below Dolby/THX reference because this is where music still sounds sweet through all the other speakers. Movies, in deference to the fact that this is smaller than my usual box were tested at 6dB below the same reference. I did not get the time to try it in a dedicated stereo system via the high level input.

So, what does it sound like?


Paul Simon's 'Graceland 20th Anniversary CD was most impressive. The intricate plucked, struck and strummed notes and chords had real attack and pace, stopping and starting where they should. The individual character of each technique, nicely preserved and note pitch maintained it's individuality. It played the tunes in short and was comfortable doing so when the volume was upped. Madonna's 'Ray Of Light was similarly despatched with the deeper synth notes maintaining their power and presence and the beat pulsed along with authority. I didn't try anything more club/dance orientated, because it's arse. Dusting off trusty old favourite, Metallica's 'Black Album', provided no surprsies with the crunching riffs underpinned and thrust out of the system like metal still rules the world. In my heart, I'm sure it still does. What can I say, I'm a child of my times. Anyhoo, being a predominant listener of real instuments I was well served and was very happy with this sub in music mode up to and beyond, the comfortable limits of my system.

From there to a couple of less mainstream sub breakers. First up, the Telarc SACD of the 1812 (the one with the real cannons!). Ok, you can scare newbies with this one and a fart box, but real cannons have a real instantaneous crack that leads a pressure wave of explosively compressed air that is more about feeling than hearing. The audible reverberations that follow, are a result of the venue/scenery reflecting this pressure wave.The XLS-300 delivered a convincing initial hit, but unsurprisingly given it's size, moved to delivering the reverberations well, without pressurising the room in between as the concussion hits. The temptation to turn a sub up to try to deliver this effect should be avoided. If you want it, buy a bigger sub - it's all about shifting air. I wasn't expecting it to do this well, but I was impressed by the scale the reverberations portrayed. Still not big box convincing, but it pencilled in a convincing impression. On to, Blue Man Group's 'The Complex' (CD) and it was a similar story. Deep notes (?) were all present, with only the deepest fading from view slightly. I say notes, but that's because I'm not sure the word has been invented for a blue dude hitting a 16ft PVC pipe with a stick. Again the big hits (and they are BIG) of 'Piano Smasher' lacked that crushing pressurisation and effortlessness of a big sub. The Dynamic edge was there, but the real meat to the bones that shakes the room wasn't.

I need to put this in perspective and this holds true for the film clips also. Turning the sub off (in the receiver) and running the (bi-amped) PMC GB1s full range, resulted in renditions that were embarrassingly anaemic by comparison. They're not big, but the transmission line design delivers extraordinary depth from a given enclosure size. Even when reducing the volume to give their 125mm cones a fighting linear chance, there wasn't even the slightest hint of the depth, power and scale that the XLS provided. Cannons simply cracked, more like a breaking branch, with no follow through and smashed pianos with their sustained peaks just drove the little PMCs hysterical by comparrison. Even with truly testing material, the XLS obviously had a lot of extra quality to add to the rendition.

Bring on the Movies. I was actually rather surprised how well it delivered some of the big bangs in 'Children of Men'. The terrorist bomb about two minutes in wasn't quite as concussive as it can be, but it was near as dammit as shocking as normal, as it was delivered as sudden as it should be. Movie sounds can sometimes be complex beasts and convincing can be about doing enough of it right to paper over the cracks. I'm sure that as an SPL peak, it may have been down on power, but it got to where it was going damned quick, if you see what I mean. The tanks later on, rumbled nicely, perhaps lacking a little texture, but the scale was well preserved and the shell shocks again impressed. I wasn't expecting great guns (ha-ha!) in the light of the 1812 experience, but it's about context and the rumblings of distant battle gave an expansive backdrop, lending the soundtrack real depth and involvement.

Likewise, the 'drum game' in House Of Flying Daggers provided kick after kick, indicating real strength above 30Hz with only the crescendo starting to push the limits and compress a bit. Flight of the Phoenix was suitably impressive, with the big barrel roll basso drop tailing off without drama if a touch earlier than normal, whilst all of the buffeting wind noises had suitable violence. The eyeball flattening WHUMPH! of the engine letting go was missed, but then only an SVS Ultra has delivered that particular fix, so there was nothing to be embarrassed about there.

So what's the conclusion?


Most people don't play music and movies at the level I do. Whilst the levels I used were slightly reduced, they're still comfortably ASBO loud if you are attached to your neighbours. All of the above has to viewed in this light.

I've had the XLS-300 in my system for about three weeks and that in itself is a big comment. 95% of the time, I use my system for day to day viewing with a mixture of HD DVD, DVD, Sky HD and vanilla SD off air viewing. This is done at more sensible volumes that will allow me to remain married, although our friends still think we're nutters when visiting. In this mode, the thing that quickly became apparent was that I seldom missed the big box presence whilst something suitably gripping was on the screen and even less if I was playing my sort of music. I can't believe I've just said that, but upon reflection, it's true. At lower volumes where stupid levels of EQ would be required to make the deepest notes actually audible, it makes surprisingly little difference having the smaller sub. Take EQ out of the equation and it's slightly lighter bottom end may actually be an advantage in average room integration, although I think that may hold truer for movies where the extra bottom end weight is more about fun and a bit of 'boost' doesn't go amiss.

So, is the XLS-300 a Monolith Lite? No, it's not. Whilst it delivers remarkable depth for it's size it can't plumb that extra few Hertz at any volume. If you've had those extra Hertz, you'll know they're not there and when the opportunity arrives to turn the wick up, you'll feel it, all the more so. There is still no substitute for cubes and only having a single PR puts a limit on what can be expected as you increase volume.

So forget it being a big box alternative. Compare it instead to the raft of mass market sealed compact subs that generally inhabit a volume only an inch or two less and are remotely comparable in price.

Here's where it really scores and all of the above is turned on it's head. It's really is as musical as anything I've had through my front room, but adds an extra dollop of depth not available from a single driver sub. In this respect it may take an extra bit of care with regards to positioning, but no more than any sub that actually delivers flat into the mid to low 20Hz range. None the less, the portrayal of acoustic ambience is greatly enhanced and compared to even half decent floor standing speakers (and I include my GB1s as an example), the XLS-300 offers an authority that moderate floor standers only really pretend to deliver on paper. For movies, it makes a really good fist of impact at frequencies that used to have the afore mentioned MJ Ref 200 rattling like a 'goodun' as a yard stick. Lest we forget, that was a multi award winning sub, y'know.;)

Again, by the measure of it's more size equivalent competition, it delivers impact in a very impressive manner that the sealed competion struggles to match. The nature of a sealed sub may result in a slightly more progressive compression as the limit is reached, however their limits will come earlier as the PR delivers greater efficiency of the Watts on offer and definitely extension that you wouldn't otherwise experience.

If you haven't got the room for, or can't use a big box, relax. There are now some seriously competent alternatives worth spending your hard earned on of which, this one seems to be a fine example.

Russell

* Edit 15/12/08: Of course my kit has moved on since the review, so my signature no longer reflects the system as tested. Speakers were PMC GB1 & TB2+, amps were a Denon 3806 plus Rotel RB-985 and sources were a Toshiba HD-EP35, Denon DVD-3910 and a Marantz CD52 MkII acting as a CD transport.
 
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HiFiRuss71

Distinguished Member
Excellent review thanks Russell. I'd love to get my hands on this and do some measurements! :smashin:

I'm not sure about the feet but the fully recessed driver looks ace. :)
No need. Ilkka has just published his long awaited results here.

I'm still drinking them in, but they're dead interesting. I could tell that there were limits to be hit as the PR maxed out, but I didn't suspect they'd look that vicious in graphical terms.

It certainly doesn't sound that immediate, but by the time room gain is taken into account the effect may be softened, especially as I use EQ which prevents the sub from reaching it's low frequency limits as early as it does in the field.

I was happy to see the remarkably low group delay results. Lower even than the REL T1 at which the XLS-300/PR is squarely aimed. With respect to, so called, musical subs, this measurement seems crucial.

It was certainly a really good sub for music and I'll stand by that.

Russell
 

Repton

Active Member
Great review again, now it got me thinking whether to purchase this or the SVS PB12 plus for an upgrade over the XLS200DF that I have. Will there be noticable improvements?
 

HiFiRuss71

Distinguished Member
As I say, if you can accommodate a big box (you did mean PB and not SB 12?) then do so.

Russell
 

Repton

Active Member

danmc_82

Distinguished Member
Think im going to go for the xls300. Not sure if its worth £100 more over the xls200 but hey, its only money :D
 

micb3rd

Active Member
Excelent write up Russel. I have been waiting for this and I enjoyed reading that!

I think the PR tuning point is 25hz, this could be tested buy running a few sweeps and watching for the minimum cone excurion but maximum PR excursion. This will be partly the reason for the 20-25hz region not being as strong as the monolith of couse smaller box size and less total swept vd (air placement) from the XLS10 driver being part of the combination.

If high silly SPL is not required and small box is needed this clearly steps ahead of the normal *sealed box* compertition it is up against.
 

Repton

Active Member
Think im going to go for the xls300. Not sure if its worth £100 more over the xls200 but hey, its only money :D

If you do, let me know what improvements you would hear!:)
 

AngelEyes

Distinguished Member
Great revue Russ, thanks for keeping it shorter than your average posts ;)

It certainly seems typical excellent BK fair :smashin:

I have to admit, aesthetically I am not that keen on the grill or the feet but then I would most likely have the grill off anyway and unless you spend far too much time on your hands and knees thge feet would mostly be out of sight :)

Adam

PS. :offtopic: Can you give me some dates in early January, as things look to be going ahead.
 

Sniper

Active Member
Super - nice review! Was waiting for this.

I'm actually very happy with my XLS300/PR. Mine's is in gloss black and i got them to install Monolith "feet" as I didn't like the look of the standard ones.

First album i tried was the "black" album - russ.will metal does rule!
 

Spangle2k5

Active Member
Placed an order for one of these yesterday. This is my first sub and to be honest I am happy to pay a lot more, but I am impressed by what I have heard about BK and their previous offerings.

I am looking forward to being impressed!

Been quoted 7-10 days, this seems pretty reasonable if it turns out to be accurate.
 

chrisgeary

Well-known Member
Nice one Russ (only just seen this)! Your findings are very reminicent of mine with the PB12+ and SB12+

I'd love to know what your thoughts are comparing the XLS300/PR and the SB12+
 

HiFiRuss71

Distinguished Member
Nice one Russ (only just seen this)! Your findings are very reminicent of mine with the PB12+ and SB12+
Thanks Chris. The comparison between the two product lines is inevitable, especially round these parts. The PB-12 stretches the bid v small difference somewhat further, but neither of the small subs presses its larger sibling that hard.

I'd love to know what your thoughts are comparing the XLS300/PR and the SB12+
Although I've played with both, I've never had them to compare back to back. Based on experience and a little bit of educated guesswork, I'd expect very little difference in raw performance. The XLS-300 does go lower, cleaner, but in practice I reckon you'd be really hard pressed to hear the difference.

To my mind, you may aswell base your decision on the feature set and looks. One is personal opinion, whilst the extra cost of the SVS could be viewed as being tied up in the room integration controls, which for some will be enough. It should be noted that a BFD can be had for less than the price difference between the two and the BK does support true simultaneous connections to suit the hi-fi crowd.

Russell
 

Nakano

Standard Member
Hi Russ.will, I'm interested in the BK subs, but not sure which one is best for me. Leaning towards the Monolith, but thinking it might be a bit overkill and if I can get away with a XLS200 I'll save a bit of money too!

My room is L shaped about 19feet by 20feet (12feet living room) and I just bought a Onkyo 605 with a pair of MA radius270 and a 225 centre, but no surrounds. I'll be using this pretty much for watching movies only, what do you think and thanks in advance! :)

Also I don't turn the volumes right up if that makes a difference.....
 

Flash3d

Active Member
Russ,

Very well written review. Ordered my 300xls after reading.
Had a demo unit at home by rasubs from Holland. Was a terrible experience when he had to take the bk home again ;)

Have to wait a week more till its in, replaced several components from my home setup already based on AVforums member experiences.

I'm gonna pair it with my new onkyo 705 and my old missions (missions have a total new value with the new 705 :D)

Thx again!
 

RHK98

Standard Member
Hi All
I am looking to assemble my first ever home cinema system. It will be used about 50/50 between movies & music.
I have decided on the ONKYO SR605 as the receiver.

For the speakers, I am veering towards the following:
Tannoy F1 customs as front/rear speakers.
Tannoy F1 Centre

Subwoofer: Either the XLS200 or the XLS300. This is where I would like some advice from the experts on this thread. My room size is small (approx. 16feet by 10 feet). Will I experience the extra benefit the 300 would bring over the 200 or would I just be wasting my money by shelling out on the 300.
Any advice would be greatly appreciated!!
 

HiFiRuss71

Distinguished Member
There are people running much larger subs than either of those in smaller rooms and feeling the benefit probably describes the experience that gives. My own room is only 18x12 and I've just had one of the largest subs in christendom working very nicely indeed, so don't worry in this respect.

There is unlikely to be any problems running a 300 in a space that can accommodate a 200 (and yours can) and you'll definitely benefit from the added punch low down. The extra power (and efficiency of the PR design) will deliver lower distortion, cleaner bass at any volume which always a positive benefit and this advantage will become more apparent with increasing volume.

One thing worth considering though are your rooms dimensions and the flexibility of positioning available. I say this because with a 16ft dimension, you have a repeat factor of the likely 8ft floor to ceiling dimension which could signal a fairly strong room mode. I say could, because nothing is definite and the postition of both you and the sub can have a strong effect on the outcome.

Either way, Id knock the XLS-200 off the list and unless it's too much of a stretch, also have a look at the SVS SB-12/Plus in the forum power buy here. The raw performance of the BK is slightly better especially low down at higher volumes, but the SVS has a single band of EQ that could dial out a particularly annoying room boom and that can really transform the sound.

Russell
 

RHK98

Standard Member
Thanks Russ for the prompt response.
I am tempted by your SB-12/Plus suggestion.
One thing I forgot to mention is that my room has laminate flooring. It is also a bit light on absorbent materials. Only a couch at one end of the room. No Curtains. Just a blind. Plasterboard walls though. Do you think with characteristics like these, the extra electronics of the SB-12/Plus would be a definite advantage.
Once again your help is much appreciated.
 

HiFiRuss71

Distinguished Member
The long wavelengths of bass mean sofas, carpets (or lack of), curtains will make very little difference. Some would say no difference, which is wrong, but certainly very little.

The construction of the room can certainly make a difference, with flexible stud walling being quite capable of absorbing bass. The effects of everything, combined, plus the positional variations possible, mean the likely outcome is entirely unpredictable though.

As such the PEQ and Room Compensation Control of the SVS, just provide extra possibilities to cope with what might crop up, but there are no guarantees.

One thing is almost certain though. The harsh reflective environment of the room means the main speakers will quite likely end up sounding just like that - harsh.

In the Speakers Forum, there are quite a few threads on speakers being declared harsh, when it is in fact the rooms contribution that is to blame. Search them out, they're worth a read.

Russell

PS. Welcome to the forum by the way.:thumbsup:
 

stuart2

Active Member
Very helpfull review Russell, thanks a lot.

I notice BK give a choice of a mono or stereo RCA lead. Excuse my ignorance but what would be the advantage of a stereo lead for what is a a mono speaker?
 

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