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Acoustics, or maximising your sound.

Discussion in 'Home Cinema Speakers' started by uncle eric, Dec 11, 2001.

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  1. uncle eric

    uncle eric
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    Ok, as I mentioned before in this forum, I dont plan on any hardware upgrades for a little while and instead wanted to look at acoustic treatments for my HT room and acoustics in general.
    Finances allowing, I hope to have started by the time Gordon comes over to buy me a drink ;) and finish it when he lends me a twenty quid.

    For those that downgrade the importance of good acoustical room treatments, I will say this. Many top Audiophiles regard these treatments as the single most important upgrade that can be made to a rooms sound quality.

    With correct implementation of these acoustical treatments the audible difference would be more than any hardware, speaker or cable upgrade.

    The fundamental aim of acoustic treatments is to counter what is in effect acoustic distortion. When a room such as those expensive dedicated rooms we have seen in the pages of HCC (an example of which I looked at 'Cab Ride To Happiness'), do not utilize correct treatments (or any in most examples, I do not regard curtains as correct acoustical treatments) many complex things occur that will invariably wreck any notion of optimum sound quality in that room.
    Some of the sound that leaves your speakers do indeed reach your ears first (direct sound), however, depending on your set up and room design, much of the soundtrack comes from early (and secondary) reflection from furniture, coffee tables, bookcases, equipement racks and most importantly untreated parellel or near parellel surfaces such as walls and floors.
    To make matters worse, because its very difficult to isolate direct sound alone, both the direct and indirect reflections interact (or crash into) each other to produce an incredibly wide range of effects leading to even poorer sound quality

    What this all adds up to is that the listener or the guy who paid a small fortune for this room, will be prevented from hearing much of the detailed information that his expensive equipement is capable of delivering.
    Another way of looking at it, they are getting Bose sound quality with M&K THX spec speakers.

    There are many culprits for acoustic distortion but the main causes are,
    1)Poor Diffusion, notes below
    2) Speaker Boundary Interference, the interaction and interferance between direct sound and early reflections from the rooms boundarys.
    3) Comb Filtering, when DIRECT sound is combined with reflected sound, notches and peaks are produced. The result being that these reflections enhance or cancell the DIRECT sound to varying degrees, dependent partly on path length and many other variables.

    On this occasion, I want to take a brief look at what is probably the most talked about aspect of acoustics and indeed room and speaker design, Diffusion!

    Many Home Cinema fans try to aspire to the very best mulitplex Cinemas by trying to create the diffuse, enveloping surround soundfields of these cinemas by using dipole speakers.
    I believe these speakers are actually the worst design that can be used in Home Cinema. More on this later.

    In order to understand why, lets take a look at how the Leicester Square Odeons of this world acheive their all involving, enveloping surround.
    Very simply, they use what is in effect multiple arrays of monopole speakers and in best examples correct diffusion treatment. Thats it.
    Well, not quite, in the top cinemas there is a great degree of equalization that takes place which involves the use of very sophisticated and specialized equipement. Why the 'backwards' correction, why not design a cinema that is acousticly optimum in size and shape in the first place so they dont have to re-correct.

    Firstly, we must remember that in the days when some cinemas were built, sound was still in its infancy. In fact many of the very first cinemas were theaters or concert/music halls that had been converted. In later years when the Muliplex idea was born from the USA (where else) apart from building new complex's, these 'old' cinemas were once again redesigned and need I say wrecked, internally and acousticly.
    Usually, and as is the case of the Barnet Odeon which I visited for the first time last month, the circle upstairs would be 'cut off' and used as the biggest screen 1. This would invariably leave the lower and larger stall areas which were split into a further two or even three smaller screens. If the Barnet Odeon cinema experience is anything to go by, I would rather be poked in the ears with a sharp stick!

    These old concert halls that were not tampered with, were believe it or not, acousticly the best sounding. Why. They already had acoustic treatments in place many decades before treatments were taken seriously at all.
    Many of these concert halls had design orientated space rather than the squeeze every bum onto as many seats as possible concept that is todays money driven world.

    These spaces were like mini areana's that were made up of fancy semi circular spaces, multi-tier shapes and even viewing box's at the sides for the upper classes. The result being the reduction of unwanted parellel surfaces to a minimum which basicly killed of any boundary interference.
    More importantly, the elaborate, ornate mouldings and other surface relief that was on virtually every wall and corner of the halls acted as superb 'natural' diffusers. Fantastic. Just imagine, perfect diffusion 100 years ago.

    A note here* By perfect diffusion I dont mean that each listener in the hall hears the same total loudness. Direct sound decreases as the distance between the sound source increases. BUT, by acheiving EVEN reflected energy around the hall or room, the problems caused by too little or to much reflected sound is to a great degree avoided.
    Anyone who has visited the Royal Albert Hall for example will no doubt testify to the incredible acoustical properties of this great place which are mainly due to the reasons I have outlined above.
    You can sit ANYWHERE in this areana of sound and still be rewarded with amazing sonics. Yes, there was surround sound before Luca$........

    Getting back to our home cinemas, I regard the use of di-pole speakers a backward step in any situation you care to mention.
    The fact that these speakers are designed to actually produce a diffuse sound is suspect enough.
    Dipoles in effect try to achieve the diffused sound that results from proper reflective surface dispertion by trying to replicate these diffusive qualitys.
    Indeed you can say that they try to pre-empt these effects with their own diffusion. This diffusive sound that is produced is very far from ideal and by the time these 'diffused' soundwaves bounce around the room and into each other, you basicly have a mushy, incoherent mess, with or without treatments!
    Di-poles were a little more acceptable in the days when Pro-Logic and the limited mono rear channel with its even more limited frequency limits ruled. However, there is no room (in my book anyway) for the continued use of this 'compromise' design.
    Diffusion should be achieved AFTER it has left the sound source be it singer, band, or home cinema system, not during.

    As I've said, I plan to do much research and completely re-think my HT room in terms of acoustics. When these (costly) treatments are complete I plan to post pictures for anyone who is interested.
    Hopefully it will transform the sound in my room which is already not terrible.

    Thanks for taking the time to read.

    Eric
     
  2. Jase

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    Interesting stuff.

    I´m looking forward to seeing the results of your investigations!!
    even if you dont like Dipole speakers like i´ve got!;)

    cheers
     
  3. zcaps57

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    Very, very good point.

    Myself, as a physicist, agree with my whole heart that room acoustics have the most fundamental effects on sound quality.
     
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    before i get into room acoustics i must completely disagree with the statment that Di-pole effect spkrs are wrong!,well their not ! they have been designed to do 1 thing and 1 thing only, and that is to create the same effect as a large array of spkrs running down the side of a full size theatre.
    that doesnt mean that if u put lots of small spkrs in a small room it will do the same job cos it won't

    And as with room acoustics PAY SOMEONE who has the knowledge and experience to set your room correctly,its very nice to see someone understaning that the room is just about the most important component in your system(if you have the luxury of a room dedicated thats even better).
    I have been in the industry for over 10yrs and i am still learning but when i design a Theatre it can take Hrs even up to 60-70 Hrs for calculations,designs,computer modeling,modal analysis and so on.
    Take it from me is easy and cheaper if u pay someone to do all this for you ,cos if u get it wrong its gonna cost YA BIG TIME
     
  5. uncle eric

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    Diden't you say "Before you get into room acoustics"
    You never did. Oh well maybe you forgot.

    As you are a Pro with "10 years experience" that is still learning, please allow me to teach you a few things.
    (not in 60-70 hours)

    First off, it is a common misconception that Dipole speakers are used to emulate the "large array of speakers running down the side of a full size theater"
    Dipole speakers are actually designed to give you the 'effect' of the reflections that takes place in a large theater. That is to say, Dipoles mimic the way diffused sound waves travel.
    After sound has left the array of side speakers in a large theater, if the theater has been designed correctly, much needed diffusion takes place. This diffusion enhances the width, depth and height of the rear soundfield with the result of a more life like spatiality.

    Please read my post again if not understood.
    Diffusion should take place AFTER it has left the sound source be it Singer, Orchestra or Speaker, not emulated at source.

    Bipole speakers are actually better at mimicking this effect. Tri-pole speakers such as the M&K models are better still. As you might know, many authoring houses and studios use M&K speakers. Of note, George Luca$ uses M&K in his Skywalker Ranch (home, training facility and studios.

    Notice that M&K who was there from the beginning of Surround sound have never actually produced a Dipoler speaker.
    I wonder why?

    Eric
     
  6. Stuart Wright

    Stuart Wright
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    I think I spot a charles
     
  7. Phil Hinton

    Phil Hinton
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    Hey Charles not seen you for a while matey, nice to see you still try to join us with your inane banter.

    Eric,
    Love your post, and cant wait to see your findings as this is a problem i have with thick stone walls, lots of reflection that is not wanted.

    Cheers
     
  8. Stewart C

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    I have M&K SS-150THX Tripole/Dipole speakers.


    I have them switched to tripole at all times. I like the diffusion I must admit, but I also like directionality using the tripole effect. This gives me the best of both worlds.

    Unfortunately, I can't afford to buy expensive acoustic materials and would not be able to integrate this with my living area. The Dipole processing therefore helps my situation.

    My accoustics are fine for my needs. The carpet and Sofa works well at defeating standing waves and nodal effects and my hardish lined walls ensures that the sound is not too dead but in fact allows for some movement without distorsion.

    I bought a really good book called "How to build a Studio on a Budget".

    Regards
     
  9. uncle eric

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    Phil,
    I particularly like Charles/Marks unsubtle little insult that was his signiture with this latest incarnation.

    "A little knowledge can be dangerous", carefull you dont hurt yourself Charles.

    Eric
     
  10. dUnKle

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    Whos Charles ?
     
  11. uncle eric

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    Duncan,
    Charles was a member here a while back. Because he has been baned from this and several other forums he occasionally tries to re-incarnate himself in an attempt to re-join this and other forums.
    On his last attempt to join as a new member here, he came back as a female assistant bank manager. I nearly asked for a loan :rolleyes: . Its actually not that difficult to spot him when he is re-born.
    This guy usually likes to try and discredit me (I take this as a compliment, he must think very highly of me to mostly pick me as his prime target) , so his first posts mostly end up in one of my threads.
    Also, his inability to articulate with any coherent writing is always plain to see. His general style is also fairly unique with lots of SHOUTING.
    Scary guy. I'm sure we haven't seen the last of this lunatic. Mark the hometheater designer in this life. Lets see what he comes back as next time.

    Eric
     
  12. uncle eric

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    Hi Stewart,
    It seems that very nearly all SS150 owners, myself included, operate these fine speakers in the more directional tri-pole mode.
    M&K mostly added the speakers ability to go di-pole (if wanted) to meet the THX requirements. Without this ability they would not have been able to achieve THX certification.

    As you might know there are several items in the THX spec I dont agree with, (maybe another thread on this when I find the time), one of these being the use of dipole speakers.
    The THX reasoning for their prefered use of dipoler speakers is as follows. In correctly designed Cinemas the goal of the resulting diffusion that was due mainly from good acoustic design in the theaters, from these multiple arrays of monopoles results in a uniform 'illumination' of the surround information for most seating positions.
    For a clearer understanding, think in terms of light. Its like using fluorescent lights instead of spotlights.
    THX correctly assumed that as most home theaters would end up in peoples living rooms, the use of large unsightly diffusion treatments in living rooms would be rather limited. Because of this assumtion they tried to mimic the use of this 'fluorescent' envoloping effect with the inclusion of di-poles into their spec.

    As with many things in life and home theater, this is of course a compromise. For people lucky enough to have a dedicated room however, there is no excuse. Personally I dont find these crazy looking treatments any more unattractive than the car like CRT I have stuck to my cieling.

    During the course of my look at these acoustic treatments I will also try and find treatments that can be used in living room environments such as yours. While in Hong Kong last year I visited TK Chan a friend and very knowledgable fellow AVS forum member who had his (very elaborate) theater in his living room. TK managed to find a special acoustic wallpaper from Germany which looked great but actually held great benifits and improved his sound in the room by a very wide margin.

    Best Wishes
    Eric
     
  13. pegFACE

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    Just a point - diapoles or tripoles or bipoles will not be able to produce the realistic bass of a full size speaker,

    if you have space behind you, get full sized speakers - big difference mateys...

    this charles fellow probally has a vested interest in what he says and that is he wants to sell you his consultancy.... pretty unethical and unproffesional, much similar to my old mans local hifi dealer robert richie, he knows his stuff, just empahsises things that wont make a difference, and says they will... (eg NAIM frame) which costs £1000 or so, and makes a massive difference, MASSIVE i tell you :rolleyes:
     
  14. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    Pegface,

    There's no reason why multi-polar speakers won't reproduce bass frequencies. Apogee, Martin Login....these large panel speakers are multi-polar. I won't comment on whether they'll sound good;)

    I also think that Bob Ritchie isn't unethical. He trully believes in what he does, and is because of this belief, very good at getting the best out of what he sells. If you don't agree with what he does that doesn't mean he is wrong or unethical....

    Gordon
     
  15. Confucius

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    Def Tech BP3000s are a BiPolar design that go down to below 20Hz (+/-3dB). OK, it's got a built in sub, but their passive BP30bs reach below 25Hz (+/-3dB).

    Low enough for ya? It's (30b) Better than many active subs...
     
  16. pegFACE

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    Gordon > They will reproduce bass freq's, but they wont go to ground properly

    oh, and with regards to robert richie - in his home he uses BnW 801s with a CD12 and chord amps, of which both the CD12 and chord amps are stored in a cuboard with MDF shelves...

    IMO its unethical to allow sales to overtake whats accurate in hifi and sell something that wont make any real difference... ie a NAIM frame or someother thing....

    I belive that what a dealer has at home will be genuinely good
     
  17. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    Peg:

    What you put equipment on does make a difference, even to amplifiers. Electronics are micro-phonic....Next time you're through in Glasgow let me do you a dem....

    Gordon

    My equipement sits on the floor just now but I still believe it'd sound better if I put it on a decent stand.....just I have other priorities for my money.
     
  18. pc

    pc
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    steady on fellas!! this is supposed to be a friendly forum to exchange ideas, not just try to discredit and insult people. I think uncle eric and mark could either step outside and settle this, or maybe accept a degree of misunderstanding. I know Mark. I've been in this industry for over 7 years and know that Mark knows his stuff and does and good and proffesional job. He also reccommends and sells M&K SS150's and installs them in tripole mode because he actually agrees with the majority if what eric said. Maybe the tone of some of these postings has got people responding agressively when actually we all tend to agree with the content.
     
  19. pegFACE

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    Just to straighten one thing up, i consider myself to be a mini mate of gordon's, even tho i dont know him too well, and when i type these words i'm not typing in vain...

    With regards to the dem, sure - i'll send you a mail next time i mosey through glasg0w

    regards

    peg0r
     
  20. uncle eric

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    PEG,
    I think youv'e lost the plot here a little. Charles aka Mark, is NOT a HT or any other consultant. If you read my post I did say that this guy came back as a girl in his last attempt to join here. He/She claimed to have a job as an assistant bank manager.
    This is Norman Bates stuff we are talking about here.

    Eric
     
  21. pegFACE

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    I just looked at his profile and it said HT consultant...

    ooopsie

    Female bank manager, cor, i could do with a loan (HT=expencive habbit)
     
  22. uncle eric

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    Gordon,
    Ever thought about going into politics ;)

    Best Wishes
    Eric
     
  23. Stuart Wright

    Stuart Wright
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    mmm if you look up the domain thx-ultra.com, it checks out as being registered to Mark Cheffins in Kent. So I think he's not Charles. I don't think PC is, either since he's posted 20 times and they look reasonable.
     
  24. uncle eric

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    PEG,
    I think Gordon gave you the answer for your first point. They indeed can.

    Having concentrated all day on food and drink, I now have a chance to answer your second point.

    Presumably by full sized speakers you really mean full range. Before anyone shouts out Monitor audio silver series, B&W S2 series or indeed most other popular full range of HT speakers, let me point out that these are not full range at all. I dont care much for most published spec's out there. One of the Plasma manufacturers is quoting 1100-1 contrast ratio. Yep, and I'm Elvis.

    I consider TRUE full range speakers to acheive a frequency response of 20HZ to 20kHz.

    Speakers that can perform to these spec's are pretty thin on the ground. They are also usually costly, large and of course floor standers.
    Lets now look at the application of these full range surround speakers used as surrounds in a Home Cinema set up (dedicated or not).

    First, the most obvious problem, placement. Where would you place them. You mentioned "If there is space behind".
    As you know, the side surrounds should be to the left and right of the main seating area. The precise or exact location of these speakers pretty much depends on the room dimensions and seating arrangements par se.

    Now, as I've mentioned in many of my posts (including the thread 'More Install Opinions'), I believe that corners are quite possibly the worst position for a Subwoofer. While more bass is indeed generated by the close proximity of boundary walls and corners, the cleanest, fastest and smoothest bass is obtained well away from any of these boundarys. If you have a sub or subs try placing them at least 4 feet away from any boundary walls. Space permiting, this may indeed be acceptable as most subs are nearer the screen area of a Home Cinema where there is no seating hence will not pose to much of a problem, particularly in a dedicated room.

    Going back to the idea of full range surround speakers, where would you place them? Would you or could you wall mount full size speakers. No twice. Firstly for reasons above and secondly the logistics would be difficult.
    Ok say you can place them away from the side walls to avoid the boom (amongst other things) that would otherwise be generated what would happen? Would they not be TOO close to the relative side located listeners?
    The answer in most cases would be yes. With this kind of proximity, no matter what delay times you care to set up in your proccessing, ANY kind of speaker design immeadiately near the side seating positions would be localized by these listening positions. Also, remember the importance of diffusion and how important it is to produce an enveloping and uniform soundfield to 'surround' the audience. Something else, as these floor standers would be comparitively lower than the wall mounted speakers they would replace, diffusion would struggle to occur as less reflections would invariably take place leaving an even more localized sound.

    Dont underestimate how important correct diffusion is in a Full size or Home Theater environment. The object would be to transform information from the surround channels to give you a diffusive pattern of sound with a uniform linear decay.
    This would not be possible in most case's with full size speakers in everyday surround L/R and Rear positions and everyday Home Cinema environments.

    I say everyday positions because Gary Reber's 'Widescreen Review' Holosonic lab does indeed use full size full range speakers for every channel. However, this is far from an everyday set up. It even makes the 50-100 grand setups seen in UK or USA magazines look like a childs play things.
    Gary uses Dunlavy SC5-5 speakers for all channels plus a pair of Dunlavy TSW-5 Subwoofers. To power the Dunlavys, they used custom made CAL (California Audio Labs) amps with two channel amplification on each amp. Rated power? 1000 watts per channel into 8 ohms. Five of these are used for their set up.

    Reber has created what he calls a circle of sound. In effect, he has a carpeted 20 ft cirlcular area in the middle of which sits his chair which is the main listening position. Each and every speaker is not less than 4 feet from any boundary wall, while the main listening position is exactly central to all sound sources. Above this 'circle of sound' is an acoustic cloud so elaborate not to mention expensive its mind blowing.
    The Acoustic treatments and design of this incredibile room was designed by one of the leading acoustic experts on the planet. With a reputed cost of well over a million dollars, what can I say.

    In the meantime lets stick to whats possible for us. Lets also allow a few other seats for other members of the family to join us. At the end of the day, if I can produce comparable sound to the very best Professionall THX Specified Cinemas around, then I'm happy.

    On the other hand, If I win the lottery one day, Gary Reber, get your WR Holosonic Theaters plans out and switch on the photo copy machine.

    Eric
     
  25. Jase

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  26. uncle eric

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    Thanks Jase, there are so many tweek theorys on as many web sites its unreal. Just a case of sorting out the 'Snake Oil' from the valid points really.

    Eric
     
  27. pegFACE

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    When you say full ranged speakers, i mean full sized speakers, although 20khz - 30hz would be enough in my opinion...
     
  28. uncle eric

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    Hi Peg,
    To be honest I think 30hz is still not really low enough. There are cheapo subs on the market that only go down this far, but I really dont think of them as subs. More like bass extenders.
    The Benchmark level is 20hz. This is acheived by quite a few subs on the market, but of course there are many more variables in a sub to consider other than how low it goes.
    Of note the high end subs such as the M&K 5000 go down as low as 18hz.
    The state of the art, no compromise Dunlavy design (Model No TSW-5) goes down to an ultra clean 16hz. Gary Reber mentioned once that he could feel his shirt fluttering while viewing 'The Phantom Menace', scary.

    On another note, while reading SGHT mag today, I had a glimse of the new THX Ultra 2 requirements for certification and came accross this.
    Quote " Ultra 2 proccessing will also feature switchable Boundary Gain Compensation (BGC) to alleviate the boomy bass performance that can occur with near-wall listening positions".

    Seems like 'The Audience is Listening'...to the accoustic experts at last.

    Also, " Ultra 2 certified subwoofers must have bass that extends to at least 20hz".

    Lucasfilm still require Di-poles for the side surrounds (which as you know I dont agree with along with other THX criteria that I will discuss in another thread shorly), however, they NOW recommend monopoles for the back surrounds.
    (At least I'm not too far away, SS150 tri-pole sides and almost identicaly sized S85 monopole rears)

    Best Wishes
    Eric
     
  29. pegFACE

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    no no eric...

    I mean speakers!

    Speakers should have a range of 20khz + to 30hz....

    with regards for subs 30hz to 12hz is probally good enough.. (read sono sub)

    IMO THX is just another way of lucas to get cash into his pocket from royaltys...
     
  30. Nic Rhodes

    Nic Rhodes
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    And people wonder why high-end subs are described as giving something different. My Servo 15s go to 14Hz at 115dB by reputation (low distortion), certainly I can vouch for 15hz signals at high levels on their own, with two….:D

    It brings a whole new dimension to the sound and the reason why I am critical of subs now I have experienced it. (Substitute top M & K / Velodyne 18 as appropriate). I honestly believe that people don’t know about low bass, being happy with something like the excellent small REL’s. It is good at what it does but it doesn’t do everything (it doesn’t claim to either).
     
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