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Which Subwoofer ?

Discussion in 'Subwoofers' started by Gasman, Jul 18, 2002.

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  1. Gasman

    Gasman
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    Can anyone please help?
    I am a relative newcomer to the world of home cinema. My current amp/speaker combo is Sony strdb940 and Mission Cinema 7. I am looking to add a subwoofer to the set up, but have had lots of different advice.
    Speaking to my local Hifi dealer I was advised to look at a Yamaha YSTS SW 320, others have recommended the REL Q-150E.
    Looking on the forum, it seems this sub is not highly rated, although What Hi-Fi particularly rate it.
    I would be grateful for any further advise.
    Thankyou in advance
     
  2. sofaboy

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    I can recommend the Yamaha sub, I have a YST SW305 and it rocks.. it maybe lacks the performance of a REL but then its not as expensive as a REL

    The 305 has 2 8inch cones and I find it excellent. My mate has a REL and a good test for a sub is section 10 on the film THE HAUNTING, with the knocks.... my mates rel picks up the deeper bass a bit better, but my Yamaha doesnt come far behind..... His was £600 and mine was £250 (from Germany)

    :)
     
  3. Noman

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    The q-150 is excellent for music and powerful enough for good reproduction of movie LFE. Of course if size and money doesn´t matter there are better subs. I have only tried the yamaha yst-sw800 and I would not trade my q-150 for 2 sw800:s....
     
  4. Jase

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    Hi

    Have a look at the Power Buys Forum and the Velodyne CHT 10.

    Certainly worth considering and at a very good price as well.:)
     
  5. Brad_Porter

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    The REL Q150E is a super sub-woofer that is great if you have space limitations. It £500 and it sounds fantastic considerings the box is 12inch's square.

    Be under no illisions from reviews in the forum as bad room dynamics ans bad setup can make this sub sound a bit nasty. But nothing that cant be remedied with time and effort in the positioning and the set-up.
     
  6. Nic Rhodes

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    Brad

    I am not sure I entirely agree with your post. Correct set up is essential to get the best out of ANY sub. Where I, Eric and other have criticised the 150 (and to a lesser degree 200 / 201) is down to some fundamental problems with the sub design that can never be corrected for. These relate to the small driver size matched with low power of amp driving but in particular the high distortion levels. These can NOT be corrected for. The sub simply tries to do too much. If they had limited the low frequency extension, like the big Qs, then this subs distortion would be much reduced and the thing would work much better but REL have tried to get 18Hz out of this tiny box. If they had kept it to 25 hz, it might have been a different story. Quart in a pint pot comeS to mind….

    A REL owner.........
     
  7. Brad_Porter

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    Hi Nic - thanks for the reply.

    When you say 'hi distortion levels) exactly how much power are you pumping through the sub woofer at the time and what level settings do you have on the actual sub itself.

    I have not experience these distortions and really dont consider myself to be a listener that likes quite movies!!

    Im just trying to find out so I can test myself and try and see if this is true on my systems.

    Also, why are there some many good reviews out there and shops advertising it and recommending it?

    I now feel a bit deflated and worried I have purchase the worst sub in the world.
     
  8. Matt F

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    Please don't think that Brad. Nic and Uncle Eric are entitled to their educated opinions but bear-in-mind that Nic has two 15" 400watt servo subs and Eric's currently listening to a £2000 or so Velodyne so their standards are very high. For what it's worth, and although I respect both their opinions very much, I sometimes think their criticism of the Q150/200/201 is a little bit over the top. As for the distortion Nic talks about, I don't know for sure but I would suggest that this is more something you would measure rather than hear, unless you have a particularly trained ear.

    The bottom line is that REL don't make bad subwoofers - the Q150 is their cheapest model. Sure, there are better subs out there but there are also many that are worse. You're happy with it as are many others so don't be swayed into changing it because certain people don't rate it.

    I will admit that I haven't heard the Q150 but I own the Q200 and I was quite surprised to see it getting a fair bit of criticism on this site, albeit less than the Q150. To my ears, although it is by no means perfect, it's tight, fairly quick and goes pretty deep considering it's size and power.

    Matt.
     
  9. Brad_Porter

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    Thanks for the comments. Appreciated.

    Although I am sure that there will be some follow up remarks from some person who will remain nameless at the moment......... ;-)
     
  10. uncle eric

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    Brad,
    Ians busy digging up your other posts :rolleyes:

    I think Nic has mostly said it all.
    Attempts at making a decent subwoofer vary from manufacturer to manufacturer. At the end of the day, one thing does not vary. The laws of physics.
    When a company wants to make a decent sub, if they want it to be small in volume (size) one of the criteria to acheive decent levels of acurate bass is from a very hefty amp. If someone wants to use a small amp (eg REL Q50) the volume and piston (driver) must be large to produce decent performance at reasonable levels.

    However, there is nothing in the world like a huge driver in a big enclosure powered by a hefty amp.

    1250 Watts peaking at 3000 watts, an enclosure the size of Old Trafford and a monster 18" driver. Can't wait :devil:
    Nic, you know you can't live without a pair of these :devil: :D
     
  11. Nic Rhodes

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    Brad

    Please don’t get dis-heartened, it was not my intention. My intention was to correct some miss information from what appeared to be an expert opinion but as Ian J has already, mischievously pointed out, in the space of an hour you went from expert to novice! And dis-heartened 10 minutes later.

    It is not my job to knock pieces of equipment but I will state my opinion on technical issues to help peoples understanding. As Matt has correctly pointed out I do have very exactly standards. I make no apologies for this. I do this with everything I do. If I have £5 to spend on a bottle of wine, I want the BEST bottle possible for my £5 not a good one. If I do something I want to do the best there is, or I don’t try and leave it to others. [you won’t see me commenting on film reviews / games to often unless I have a comment or want info from others. AV hardware however I do know about]. My signature say it all. However please don’t confuse exactly standards with money. I have a track record here of championing high performance, good value kit, much of it has now become the norm in the forum, often changing the perceived wisdom of the time. We all need standards / aspirations / and we need to know what is possible with kit. For some this means dreaming of Tag / Lexicon (substitute your favourite), for others it actually means buying something like this. It is all relative. For subs most just don’t know what is possible, which is a shame, and sharlatan dealer don’t help. In fact many dealers are really poor here but like everything in life there are some stunning dealers as well. We also have as regulars here CRT Gordon, Power buy Eric, Plasma Joe, Richard A, good all round egg RetRo as well as many other serious trade people. All of whom I trust. To add to the list we have ‘gifted’ individuals like Jeff on HCPCs, Boris on Bass and many other who are keen to help and pass on their considerable experience.

    Take for example my KEF Ref 4-2 L and R speakers. I know these to be very decent performers but I also know there are much better out there for AV. B and W 800 series, new KEF Ref, Tag F1, Tannoy dimension are all AV speaker systems that will eat my Ref 4-2 for breakfast. I know the limitations of my Refs but also like their not inconsiderable strengths as well. It is a compromise. The compromise is right for me but would be wrong for others. I understand and know that. Subs are no different. The reference would be Velodyne HGSs or Paradigm Servo 15s (or any other servo subs). I know that not everyone can afford these (you missed the £499 Paradigm Servo 15s!) or the speakers are just the wrong size. This I accept but if a product falls below an acceptable standard then I am willing to stand up and say so. It gets me some flack often, but usually after some VERY long posts people see where I am coming from and often then agree with the arguments. I always put forward the truth and always pass comment from PERSONAL experience / demos (no chinese whispers). This is often missing from the forum where many people try and justify wrong decisions. If I don’t know, I say so, if I get something wrong I just admit it (Sony SACD!! Big boo bo). I just call it straight as I see it.

    It all done for the sake of education. It is a subject I am passionate about and go to great lengths to teach science and engineering. I am lucky that I have an excellent Tech background that I can call on, and also posses some excellent ‘analysis’ equipment both at home and work that I can call on. Final judgement are always mine but I feel confident balancing technical performance and what I hear / see. To give you some back ground, I currently have >12 PhDs doing work under my control around UK universities and even more post docs as well as my own ‘technical’ team. I have a similar background myself. I sit on national and international committee / panels / standards / working parties on technical issues. I also go into schools every week and teach engineering. This has become so popular that we have taken a small local west Cumbrian school to it current status as one of only four special engineering colleges in the country. We have >60 kids attending every week to ‘build robots’ etc. Last two weeks I have been busy down at Robot wars (we didn’t win) but I can honestly say our Tig welded aluminium framed, co2 flipper equipped robot was built by kids (13 – 15). It has also brought me awards, including Engineer of the Year in 2000. An honour I am very proud of.

    What I am trying to say I am here to help people understand technical issues. I am happy if people draw different conclusions once they know the facts but I just make them think a bit about what they do.

    In the end, I and many others here, are here to help. We spend much time and effort ‘helping’.

    I have no financial interest in AV and therefore I think have no bias. I make no money from my effort and even help train people in the industry if they want help. I receive nothing for this help I give (manufacturers and dealers), which actually puts me out of pocket. [Actually a merchant bought me a good crab curry the other night to say thanks but that is far as it goes]. One supplier this week is now quoting my review here. I answer up to 6 PM every day from forum members wanting help. I think I answer every one (working on the valve amp one honest!)

    Don’t take my criticism of the 150 to heart but understand you product better. Know it’s strengths and weaknesses. This way you will understand how to get the most out of it. For many here the tiny 12 inch cube is the over riding aspect, in which case the 150 is a dream come true. For other it is about performance. This is where I come in. Subs need to do three things. They need to produce low notes, at high levels with low distortion. Very few can actually do this and the balance is all about compromise. You need to be happy with your compromise.

    There are some excellent posts on this site on the 150 and good general stuff under the Paradigm Servo15 banner. We also have some excellent DIY sub woofer stuff. We are also lucky to have experts like Boris on bass issues (Ramius). There is a wide range of talent here for you to use, please call on it and don’t get to dis-heartened.

    Think of it like this.
    I have already posted good things about REL ST subs today. I own one (Stentor) and used to own a Storm. I also have experience of ALL the other models they ere really good subs, but not necessarily cheap (well they are in comparison with M and K!).They are no match for Eric’s HGSs however, even the top models, it is a matter of knowing their strengths and weaknesses. They have wonderful wood finishes and can look really stunning. My rosenut Stentor is a gem to look at but it just can’t compete with a servo sub on performance. I know it’s strengths and limitations. I just have to accept it but I still like my REL.


    Don't forget we are here to help:)
     
  12. Ian J

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    Who's on lead guitar and vocals :D
     
  13. Ian J

    Ian J
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    That reminds me Nic, When are you coming to service my boiler again.
     
  14. Nic Rhodes

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    That hurt. I'm sulking now:( ;)
     
  15. Steve.EX

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    I enjoyed that.

    Steve.
     
  16. MikeK

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    There are some laws of physics which can't be ignored when talking about subwoofers.

    One of the main bones of contention is driver size.
    It's fair to say that in terms of bass depth, it's hard to compete with the big 15" and 18" drivers.
    However, there's more to it than just simply how low you can go.

    The problem for large drivers is inertia. It's unavoidable.
    To maintain cone integrity, a larger cone has to be made stiffer than a smaller one if the cone shape isn't to distort when the cone is moved by the motor assembly. In terms of material choices for the cone, it's no different for 18" drivers than it is for 10" units. An 18"unit has a surface area roughly 3x that of a 10" unit, so assuming the same materials are used, even if the cone is the same thickness, then it's already 3x as heavy.
    However, the need to maintain stiffness to the same degree as the 10" driver dictates that the larger cone must be made thicker (it's a bit like a wooden lintel - a piece of 4x2 may be fine over a 3ft span, but it won't be stiff enough over say 6 or 8 ft - you must increase the thickness of the material to compensate - so a 6ft span would probably require 7x2 or 8x2). This increase in thickness also adds to the weight. The numbers depend on many things, but it's not unreasonable to assume that it may need to be twice as thick as a cone for a 10" driver.
    That means the cone is now around 6x as heavy.
    It will have a far greater inertia than the smaller cone. When the motor assembly moves the cone forwards, the heavier cone will not start at precisely the same instant as the smaller one - it's greater inertia sees to that - and when it's reached the end of the forward travel, it won't stop as quickly - again it's inertia will see to that. (it's called overhang). This means it's transient response is not as good as the smaller cone.
    There's little that can be done about it - it's simply a physical property of dynamic speakers.
    Servo control (in it's various forms) may be an attempt to work around these issues, but it doesn't mean the issues go away.

    What does this mean in the real world?
    Well, basically it means a large driver is not as agile as a smaller one, which can easily lead to plodding, monotone bass - quantity over quality perhaps.

    My advice to anyone who wants a subwoofer to reinforce the bass from the main speakers (especially if it's for music duties as well), in an average domestic environment, is to have a listen to the various types of subwoofer first, before attempting to select a specific model - and try not to be too impressed straight away with the sub's ability to simply go low. Many can do that, but not all can integrate seemlessly with other speakers.
    You can get to appreciate the differences the different types of designs offer.


    My opinion is that the best compromise all round is a well made sealed unit with a 10" or 12" good quality driver designed for such a unit, and a good quality 150-200W amp.
    Others will no doubt offer a different viewpoint - doesn't mean either is right or wrong.

    As with many things, selection of a subwoofer will depend on several things. Sure, if money isn't an object, then lucky you, but for the majority, it certainly will be, so that's certainly one main criteria.
    It's OK saying this or that 2grand sub is excellent - it bloody well should be for that sort of money - but relatively few people can actually afford such a unit (or want to afford one).
    Another statement I don't really agree with is that a sub has to produce high levels of clean bass - that's only if you want to listen at those sort of levels. Many people don't! It should be able to produce clean bass to a level, or just beyond, say twice, (so you stay in the performance envelope) the level, that the listener requires. Who cares if it'll shove out 130dB at 20Hz - if all you want is to shove out 100dB or so in your living room?
    Sure, in a cinema, it may be necessary, and that may require the use of very large drivers and very powerful amplifiers, but most people's front rooms don't require anything like that.


    Lastly, don't overlook making your own. It's not as hard as you may think (or as hard as some may tell you).
    Essentially, a subwoofer is a box, a driver and an amplifier - no great mystery (of course there's more to it, but essentially, when it boils down to it, that's all it is)
    The quality of components in the average comercially made £500+ sub, can easily be bettered for a fraction of the price, and constructing a square shaped box enclosure isn't that hard.
    Plus there's a kind of pleasure you get from listening to your own home-made subwoofer, that you simply can't get from just buying a commercial unit (no doubt in part at least that's due to the rather large savings you can make - essentially I think most of the commercial subwoofers available are a bit of a rip off really)


    Right then, flameproof suit on...........
     
  17. stranger

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    I derived enormous pleasure from obtaining a servo-15 (£450.00) r/sounds.
     
  18. Nic Rhodes

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    MikeK / other who may be interested

    Interesting stuff as ever. If I can add a few comments on my own to you excellent prose.

    Your comments re mass of bass drive units is quite correct. A larger one is heavier, need more power to get going and to stop. If it doesn’t stop in time you get overhang. This will happen in all conventional subs and is that nasty boomy bass you get in cheap speakers with large bass units. However servo units are different. We are not talking speed here but rate of change of speed, i.e acceleration. Modern servo subs have accelerometers and therefore overhang is just a non issue. These Paradigm / Velodyne servo units start and stop on a six pence. They are fast and agile. Look for Adzman post on this. I think when he demo’ed a Velodyne HGS 18, this was his biggest fear, which immediately evaporated, when he heard the sub. Modern servo subs have made overhang just a non issue. All the other servo manufacturers do the same.

    In ‘ordinary’ subs you are quite correct that large units are not as agile as small units.

     
  19. Ian J

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    Nic,

    You seem to have covered almost everything in your excellent post except one thing. What exactly is a Servo sub.

    When replying, could you bear in mind that I am an accountant not an engineer.

    Thanks
     
  20. JSW

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    http://www.hometheaterhifi.com/volume_6_3/velodyne-ct-150-subwoofer.html

    QUOTE

    The CT-150 has a 250 watt rms A/B amplifier with current sensing feedback from the driver voice coil (2 1/2"). Velodyne's top of the line subs use a solid state accelerometer mounted on the voice coil. Current sensing feedback is less accurate than servos, but it is also less expensive. Current sensing feedback works by knowing what the current is that is being fed to the voice coil by the amplifier, and sensing what the current is that is being generated by the actual voice coil movement within the gap of the magnet. The difference in the waveforms between the amplifier feed and the voice coil generated current (this difference represents distortion) is inverted and fed back into the amplifier. This cancels out much of the distortion produced by inaccurate movement of the driver cone. The CT-150 is the only member of the CT series that has current sensing feedback.

    UNQUOTE

    And some more from the same site:

    The servo-feedback type of mechanism employed by Velodyne consists of a 2.5 gram accelerometer which is attached to the voice coil of the speaker driver. When a signal is fed to the amplifier, which then is used to drive the speaker, the accelerometer senses the motion of the speaker cone, and this movement is converted to an electrical signal which is sent back to the built-in amplifier. The incoming signal from the main amplifier or preamplifier is then compared with the information supplied by the accelerometer. The difference, which consists mainly of harmonic distortion (even and odd order) produced by the speaker cone itself and effects on the cone by resonances inside the enclosure is electrically inverted and fed back to the speaker. Feedback occurs 3500 times per second, and the distorted movements of the cone are thus canceled out. This process works very well, and Velodyne has made a name for themselves, setting a standard in subwoofer design by which most others are compared.

    How do the Velodyne subwoofers sound? We have compared a number of subwoofer designs, including servo- feedback, push-pull, as well as passive radiators. The servo- feedback subwoofers, in our experience, produce the purest low frequency sounds of all the designs. All musical instruments generate natural harmonics, mostly even order (second, fourth, sixth, etc.). It is the harmonics that are added by speakers that can render the sound unnatural (called harmonic distortion). Usually, a speaker will produce a strong second harmonic (e.g., 10%) and a less intense third harmonic (e.g., 5%), particularly at low frequencies and at high intensity. Most amplifiers have less than 0.5% Total Harmonic Distortion (THD), which is not audible. Therefore, it seems appropriate to design speakers with this level of performance. The Velodyne servo-feedback mechanism appears to reduce the harmonic distortion to about 1% at the frequencies covered by their units (18 - 100 Hz).
     
  21. Nic Rhodes

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    You only ever want an engineer when you want you boiler servicing anyway;)
     
  22. dts_boy

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    Nic, seeing as you seem to know so much about subs, can you explain to me how an isobarik sub works? i have a monitor audio fb212 and this works on that principle. it has 2 12" drivers and a 360W amp driving them. the manual gives no attempt on how it works and the dealer i bought it from hasn't a clue and is honest enough to admit this. it does, however sound(feel) very good and i personally think its as good as a M&K mx350 which i was comparing it to. it hasn't ever been in any mag to my knowledge and was wondering if you/anyone else could give me more insight into this area?:confused:
     
  23. uncle eric

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    I had most of the day off today and just got in. What an interesting thread this is. Very good comments by Mike and Nic.

    One thing though, there is actually no such thing as slow or fast bass. In other words, smaller driver = fast bass, and large driver =slow bass is a complete myth. Its 2.46am and I'm off to bed.
    I'll leave the rest of this explanation till after breakfast.

    Eric
     
  24. Nic Rhodes

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    Agree totally.

    I think people are talking about distortion or more lilely overhang on this one and confusing stuff. With servo it just isn't an issue.

    DTS BOY. I am away for a few days but will knock something up for you if Boris or one of the others doesn't step intp the fold first.
     
  25. JSW

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    Isobaric - (Push Pull) is when 2 equally sized subwoofer drivers are installed face to face in a sealed box, one driver in the box the other outside of the box. This halves the VAS needed and enables the same output from a small enclosure as a single sub would give in an enclosure twice the size.

    Didn't think they would ever be used for Home theatre though, as they are generally only popular in car audio setups.

    You can go into this a lot lot deeper if it interests you, isobaric 4th order bandpass in a perspex enclosure done right looks and sounds amazing. (not as amazing as the 8 x 10" subs in the back of my nova gsi where all them years ago though lol )


    Do some searches for isobaric speaker in google and also search under car audio/soundoffs/spl competition etc etc.
     
  26. MikeK

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    This will happen in all conventional subs and is that nasty boomy bass you get in cheap speakers with large bass units.

    Just a quick(?) comment - there are several causes of what people refer to as boomy bass. The most common IMO is room or positional loading - the room itself will cause gain, and at certain frequencies, it's higher than at others. If you place a subwoofer in a corner (which is often the advice), then the room itself may well be cause of the boom effect. The effect can be more pronounced with rear ported designs, but it's certainly not limited to that design. However, if you are unlucky, you can get boom even if you place the sub right in the middle of the room - it's an acoustical effect which I won't drone on about here (standing waves, wavelengths, reflections, summation etc etc). Strangely, you MAY "accidentally" cure (or more accurately lessen the effect of) this simply by switching to a different subwoofer - this can lead to the possibly erroneous assumption that the original one was a bit crap, and the new one is much better. Usually though, the effect will be present to a greater or lesser degree with just about any subwoofer in the same position, and it's unlikely that simply switching one makers 12" ported sub for another of the same type (the points below notwithstanding) will make much difference.
    Another cause, is where a manufacturer attempts to overcome the natural low frequency roll off of the driver/enclosure by applying a boost (EQ) to the signal - ie if the sub starts to roll off at 40Hz for instance, you start to apply a steadily increasing amplification of the signal from 40Hz down - sounds fine in theory, but in practice, it's hard to get this approach to work properly - the best you can really hope for is to slow the rate of roll off, rather than artificially eliminate it.
    It's really because the manufacturer has not chosen a good design to start with (often by simply selecting a cheap big bass speaker which isn't really designed for sub-bass applications) - and this leads into what I think is the major cause of non room related boom.
    Subwoofers, especially at the lower end of the market (but not exclusively unfortunately) often sell on size and specification alone - people assume that if one sub has a -3dB point of 25Hz, it will automatically sound better than one which has a -3dB point of 35Hz. It may, but there's a lot more to it than that. What some manufacturers do, is to simply tune the enclosure (almost certainly a ported design, as it's cheap and easier to get a lower -3dB figure) for a lower frequency than is really feasible in an attempt to lower this magical -3dB point - and this approach inevitably leads to a boom effect (an artificial response peak at a certain frequency) - no amount of fiddling, tweaking and repositioning will ever get rid of this, as it's inherent in the design.

    I'm not sure that driver overhang itself will cause boomy bass (at least not as I understand the term) - muddy, monotone, fat, lethargic, bloated, slow, plodding (plus a few other terms) perhaps.



    However servo units are different. We are not talking speed here but rate of change of speed, i.e acceleration. Modern servo subs have accelerometers and therefore overhang is just a non issue. These Paradigm / Velodyne servo units start and stop on a six pence. They are fast and agile. Look for Adzman post on this. I think when he demo’ed a Velodyne HGS 18, this was his biggest fear, which immediately evaporated, when he heard the sub. Modern servo subs have made overhang just a non issue. All the other servo manufacturers do the same.

    In ‘ordinary’ subs you are quite correct that large units are not as agile as small units.


    In ALL subs, even servo types, a large unit will not be as "agile" as a smaller one.
    An accelerometer coupled with a servo feedback circuit, may well help (certainly if the motion overhang is excessive for a particular driver), but it can't overcome the fact.
    It can do nothing to prevent distortion due to cone flexure (while a cone may feel stiff when you push it in, that doesn't mean it won't flex when subjected to extreme acceleration, as it will be when used as a subwoofer), and may well make it worse (see later).
    I'm not arguing that servo control isn't useful (if done properly, which as you stated isn't easy), but it's not a panacea for all driver issues, and simply fitting a servo control system to a particular driver, won't suddenly turn a poor driver into a good one.
    What I would argue, is that it becomes more useful with a bigger driver, and can help to alleviate the problems traditionally associated with big drivers - but it can't overcome them completely.
    And just because a subwoofer doesn't have a servo control system on the main driver, doesn't in itself mean that it's in any way inferior - that would depend on many things. I would argue that as the main driver gets bigger, then the servo control system potentially becomes a bigger advantage over a similar driver without one.
    But consider that 2x 10" drivers can be equivalent to a single 15" unit.
     
  27. MikeK

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    Remember three things a sub needs to do for say ultimate performance. It needs to go low (40 hz just doesn’t cut it), it needs to go as loud as you want and it needs to do both of these at low distortion levels. Now the ear is much less susceptible to distortion at these low frequency but unfortunately distortion levels of 30% are not uncommon for ‘ordinary’ sub duties from typical subs. This is audible, VERY audible. It is also the norm.


    You'd need to qualify these distortion figures - servo controlled subs can also suffer very high distortion, although I wouldn't argue that typically a servo sub's distortion will be lower - but by how much? What I would argue with, is that if a subwoofer's distortion is at 30%, then simply fitting a servo control system won't lower that to levels of 1%. Velodyne themselves for instance only claim that their servo system offers half the distortion of conventional drivers.
    Other figures I've read suggest that reductions in distorion levels can range from 10% to 50%. But a 50% reduction would still leave the servo sub with distortion levels of 15% - although I suppose any reduction is welcome, if it was just 10% lower, then would you really hear much of a difference between a sub distorting at 30% and one distorting at 27%?
    I mentioned earlier about cone flexure - if you suddenly stop a large cone, then the centre of the cone may well be "clamped", but the outer's inertia will mean it continues to move forwards for an instant - ie the cone will flex - this will lead to distortion. The only way to stop that would be to make the cone thick enough so that it's natural stiffness would overcome this inertia. This makes the cone heavier - which in turn leads to more intertia.... and so on.
    There are limits to the size of the motor assembly which controls the cone and weight of the cone etc

    The distortion figures quoted need to be qualified - how was this measured? If it's a measure of cone motion tracked against input signal, then that ignores the audio distortion caused by cone flexure (the acclerometer is mounted on the voice coil) and the distortion of the cabinet itself (driver distortion is only one factor)

    The only real measure of distortion which counts, is the audible sound wave distortion which emenates from the cone and enclosure. ALL subwoofers will show this distortion - it's a culmination of many things - those we've talked about, plus cabinet coloration, rear standing waves dissipating through the cone/port, port noise etc etc.



    Now back to servo subs. They can go loud, low and have low distortion. The distortion levels are an order of magnitude lower than conventional subs. Velodyne don’t exceed 1% distortion. My Paradigm are higher but go louder in compensation. This is just a manufacturers choice. All the others are pretty much the same. The distortion is so low in comparison with ‘ordinary’ subs it is again a non issue. Remember we are less susceptible to distortion at the low frequencies and these levels are in the ‘of no matter what so ever category’.


    But Velodyne themselves claim

    The result is a driver than can generate less than half the distortion of conventional motor designs, and is capable of four times the heat dissipation.


    This simply doesn't correlate with claims of distortion levels of 1% vs 30% for "conventional" subs.


    There are of course other options that also add some benefits over our conventional boxes. Some of these are available to the DIYer and are becoming popular on this forum. One approach is as your sealed box naturally rolls off at a certain rate (12dB?), they boost the gain in the amp by the same amount to overcome the natural acoustic roll off. What you get is a sub that can go loud and low but still has distortion problems. However often these aren’t as bad as the sheer ‘over engineering’ needed for the drive to handle these massive loads means positive benefits on the distortion spectrum but not in servo league. These subs go really LOW and often leave even the mighty Velodyne HGS behind. Again like servo units they are flat (I mean all the frequencies are reproduced at the same level, which rarely occurs in ‘ordinary’ subs (only the really expensive ones)). They are actually capable of theoretical levels below what is on any of our sources (8hz).


    I wouldn't argue that if done properly, then this application of equalisation can be effective - but it's not as easy as it sounds.
    If not done properly, or applied to too high a level, it can easily lead to bloated boomy bass.


    DIY is a great route for someone wanting to save money, but if you want the ultimate performance, it just isn’t possible, or certainly not from my auditions of DIY subs. Some are really brilliant but they are not servo brilliant. Now if someone did a DIY servo kit there would be many friends here.

    Ultimately, if you are trying to comptete with £2000+ commercial designs, then you "may" have a problem. These tend to be specialist stuff (such as Velodyne HGS for instance) - but not always. The problem is access to materials. It's beyond the skills of all but the most advanced speaker DIYer to actually construct drivers, and even if someone could, getting access to baskets/cones/spiders etc etc in small quantities is next to impossible. Amps and enclosures pose no particular problem though - on one off designs, you can, for instance, make enclosures using difficult techniques which are impossible for a manuafcturer to use on volume production. Amplifiers - well you can design your own, but it's probably not really worth it, as there are good designs available at good prices ready built (remember, a subn manufacturer doesn't build the transistors or capacitors or transformers etc etc himself, he uses "off the shelf" items readily available to all of us (that's if he bothers with designing and manufacturing his own amp - often they sub-contract this out, or simply use a bought-in item (usually cunningly disguised).
    Which brings us back to drivers.
    Some are simply unavailable to the DIYer - but some are.
    The REL ST series of subwoofers for instance, uses Volt drivers - you can buy these yourself (not cheap as far as drivers go- probably £250-300 each, but quality often isn't :) )
    Perhaps the biggest disadvantage is access to test equipment and facilities (anechoic chambers etc etc), and the fact that building a series of prototypes isn't exactly cost effective for a production run of errrrrm.... one.
    However, you can turn even this into something of an advantage - you don't really need a chamber - you are designing a subwoofer for one specific room, your living room (or HC room if you are lucky enough to have one), and a series of prototypes may not be necessary - after all, a manufacturer has to design and build units which will sound good in a multitude of different environments.



    10 /12 inch units with 200w. A decent enough starting point but box size and type are also important. I would also consider this a ‘minimum’. It is interesting to note all the Rel models creeping up in power. I also prefer sealed units though I have both at home.


    Just as in hifi, there are those who go to the nth degree in pursuit of sonic excellence. They are relatively few though, and usually have deep pockets and/or a very understanding partner.
    I would suggest that for many, a well designed sealed unit of around 1.5-2cuft, with a good quality true 200W rms amp (with a high damping factor, and substantial PSU), and a high quality, purpose designed subwoofer driver (designed to be used in a sealed unit of that size) will provide all the performance and musicality they want, in a package which can be accomodated in most domestic situations.
    This can be achieved for less than £500 (as lowas £300 in some cases) - and will in most cases (if designed and built properly) give far more expensive commercial subs a "bit of a licking" :)


    One final point. £2k for a sub might sound like allot of money. In AV terms £2k for the TOP component around is small fry against the money needed for top amps, processors, DVD players and speakers. Hell some spend more than this on cables. £2k will buy you the best there is, and it is a buy and never need to change ever again type purchase. Hell, most people will just adore the baby HGS, the 10, let alone the 18 which gets all the press (they use the same amps!). For many this will be more than enough because it does things right. Now how many subs can honestly can say that?


    I think we'll just have to agree to disgree on whether £2000 is a lot of money.
    As I said before, there are a few people who can actually spend this amount (plus another £20k or £30k or more on the rest of their kit), but there aren't many.
    For most AV enthusiasts, several thousand has to do the lot, (TV, DVD, AV amp, speakers, sub, cabling ..... and whatever else I've forgotten off the top of my head). Some can't spend even that.
    For those lucky enough to be able to afford a HGS, then get one - I'm not saying that you'll be able to better it DIY for a lot less money.
    For others, I still suggest that there is AV life beyond that (or below that).
    While I think that DIY, you could easily better a REL Q150 for the money, that doesn't mean it won't still provide a level of performance which is more than adequate for many people.
    I entirely accept that DIY isn't for everyone.
    And lastly, from one perspective, it really doesn't matter in the end what you buy as long as you feel it has the right level of performance for the money - there's always something available either today or perhaps tomorrow, which, in absolute terms, is better, especially if you are prepared to pay for it.
    How much better is, and always will be, a matter of opinion and a subject for debate.
     
  28. MikeK

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    One final point I forgot to mention

    Distortion - now there's a word.
    What exactly does it mean and more importantly, what does it tell you.

    I'm not going into a long winded desciption - the info is probably available on the net if anyone's that interested.
    In it's simplest form, it means that any difference between the input and output is distortion.

    However, consider this.

    Most experts agree that the distortion of modern amplifiers is so low, that it's a non-issue - it's inaudible.

    So why will a range of amplifiers, which all have identical and negligible distortion (and signal to noise ratios - from the figures anyway), not all sound the same?
    I think most people realise they don't, even if they do have the same specification figures.
    It depends on what the figures are actually telling you, and let's just say that manufacturers are not beyond attempting to hoodwink the average punter with figures and specs and fancy technical names for everyday run of the mill, common technologies.

    Just an example :)
     
  29. uncle eric

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    Some folks prefer smaller subs (probably not for the reasons they think). I've lived with both and IMO there is nothing like a large, quality unit.
    As mentioned, I've been borrowing a Velodyne HGS-15 for nearly two weeks now. Just one example I will give you is the importance of "size" and our perception of it. No, I havn't gone mad. Bear with me for a moment.
    Apparent dimension(s) of reproduced sounds are largely ignored by all and sundry because it mainly applies to acoustical instruments. I think this is bad news. We all love music in one form or another. Most of us know how certain things sound. To this end, we also know that every acoustical instrument has size.
    A cello for example sounds bigger than a viola, a viola sounds bigger than a violin. The reason is of course that each is bigger in actuality. The larger the instrument, its larger wooden box resonates at a lower frequency. If a top end hefty sub can integrate brilliantly with their partnered mains, while at the same time meeting the distortion and good linear qualities I've outlined above, thats all you really need to think about. It will tell you of the exact dimensions of whatever you need unlike smaller weaker subs.
    Is this only important with music? Of course not. I've used up the best part of a 50 page notebook writing about what I've heard through the HGS during the last fortnight. Below 80Hz info does not solely exist in explosions, car crashes and spaceship engines.

    Dialogue (particularly mens voices have tons of <80Hz sound). I watched "The Majestic" just the other night and noticed a "floor" or substance to Jim Carreys voice that I've never heard before. At one point he walked down a set of wooden stairs to the basement in the old theater which in itself sounds boring but I swear you could hear and feel every ounce of that timber as his footsteps thuded down. Just eerie. In another movie, someone pulled up in a big Mercedes. When the car door shut, it felt and sounded like a quality heavy car door not a Citroen Saxo door. Tanks sound like tanks not Jeeps. Etc Etc.

    Eric
     
  30. GJC

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    This is a very good thread guys.

    You all sound very knowledgable.

    I am leaning towards wanting a Servo Sub. I have a budget of £1000ish.

    Any ideas pointers would be great.

    When is REL going to make a Servo Sub - that would sell well......

    I like the Velodynes but they are quite expensive.

    Previous Subs - Rel Storm and Rel Q400. Subless at the moment. Fronts are B&w 603s3.
     
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