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Tiny Cube Speakers

Solar Paul

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Hi There

I posted a thread several weeks ago and got some good advice. My thinking has progressed and I have now developed a plan to build 5 tiny cube active speakers and a sub woofer to make up a 5.1 surround system with my Theta Casablanca III surround processor. I am looking for sound quality rather than volume but our AV space is fairly large and I’m a DIY newbie so I’m looking for advice. I can think of a few areas where informed experience could advise, but of course I don’t know what I don’t know so I am open to thoughts in other areas. Tiny speakers are a priority so I’m not really looking for advice on which 2 or 3 driver speakers in bigger boxes might give better quality or bigger sound. What I am interested in are:

  • Will the proposed speakers deliver adequate volume for the type of listening/watching we do (details of Intended Use below) in our fairly large space (details on Room below)? I calculate SPL at our listening positions as 92 dB at 100 W and 95 dB at 200 W (max). Current fronts are Vandersteen VLR Wood speakers (8 Ohms with an SPL of 86 dB (2.83V, 1 m). I calculate a max SPL of 96 dB at our listening position for the VLRs and I’ve never had them anywhere near full volume, probably no more than half as loud as they can go
  • Are there any problems with a cube design, for example with standing waves or other resonances, that I need to be concerned about?
  • I’m sure there are stability advantages to building enclosures out of MDF but I really want to use solid natural wood and I can design to allow for timber movement. Any other issues?
  • Are there any problems with my technical design? Am I walking into any obvious technical pitfalls?
The plan follows and then some background to explain. Any advice from those well on the road ahead of me would be very much appreciated.

The Plan
  • I want to stick with my Theta Casablanca III as the core of a new 5.1 system. I’m not planning on going the Dolby Atmos route at this stage. (If I was, I would lean toward swapping the Theta for a 2nd hand Anthem AVM60 or similarly musical surround processor and adding additional tiny cubes)
  • Add a new sub woofer:
    • My old Vandersteen 2WQ sounded great but it only had speaker level inputs and I had to choose between LFE and picking up the bottom end of my front speakers. And wiring was messy, so I ended up moving it on. But the sound just isn’t as full and complete without a sub, though, and I want to wire a new sub directly to the Theta surround processor for LFE and front channel signals below 80 Hz
    • I’m pretty set on a Rythmik kit from the US (F series 12 inch down firing) and building an enclosure for it. They aren’t cheap but they are very musical, and I think would be an excellent choice for us. Limiting it to 80 Hz means the sound won’t be localized and I have more freedom of placement (probably as an end table between our listening positions)
  • Build 5 Identical tiny speakers (for front L/C/R and rear surround L/R):
    • I am really interested in exploring a couple of things with these:
      • how small a speaker enclosure will provide a reasonable volume of audiophile quality sound down to 80Hz (With the sub dealing with frequencies below 80Hz)
      • How good active speakers really are? I propose to use active crossovers and separate amplification for each driver. (I keep hearing good things about active speakers and I really want to try them out)
    • I have had a devil of a time designing a tiny speaker (enclosure and driver) which reaches down to down to 80 Hz without chuffing or phasing issues. The best I’ve come up with so far is:
      • Seas Excel 5”Coaxial Driver (C16N001/F E0051-04/06) – quite pricey but I think very good quality
      • A closed box design with an internal volume of 8 litres and a Qtc of 0.7. I am drawn to a cube design of 200 mm (8 inches) externally rather than the traditional bookshelf speaker shape. We have some really wonderful timbers here in Australia and I am hoping to make something truly exquisite out of solid wood
      • This design results in SPL of 86 dB (2.83V, 1 m) but the Seas16N001 uses 4 Ohm drivers, so that is really 2.5 watts - 1 watt results in SPL of 82 dB (1.8V, 1m)
      • Our listening positing is 3.3 metres from the main speakers. I calculate a SPL at our listening positions as 92 dB at 100W and 95 dB at 200W (max)
    • Class D amplifiers, Linkwitz-Riley 2-Way Active Crossovers and DC power supplies for the tiny cubes as follows:
      • For the amplifiers I propose to use 2 channel amp boards from 3E-Audio (model TPA3255-2CH-260W) which will fit inside the boxes. They claim 0.01% THD+N @ 200W (1kHz, 4Ω) with the boards 90% efficient and not thermally challenged. These boards don’t include a power supply but they do include a suitable output to power the active crossovers
      • Linkwitz-Riley 2-Way Active Crossover from Xkitz can also fit inside the tiny cubes and can take their power supply from the amp boards. Based on the Seas Coax driver specs crossovers can be used between 2,000 Hz and 3,000 Hz and Xkitz crossover modules are available in this range
      • I like the idea of external power supplies so that I won’t be exposed to 240V shocks. I propose to use external computer DC power supplies of 150-180W (30 volts). The amp boards input range is 24-36V, but I think the boards might get too hot at 36V with low sensitivity 4 Ohm drivers
Intended Use

What we listen to has changed. It used to be 70% music and 30% home theatre. Now it is 95% home theatre, which for us is free to air TV (usually streamed via catch up) and Netflix (mainly series but a few movies). We’re into drama not action and we don’t need or want overly loud –bangs or crashes don’t need to eviscerate us our pulp our brains. What I am after is an immersive, enveloping sound.

The Room

Our living space is 8.4 metres (28 ft) by 6 metres (20 ft) with a vaulted ceiling 4 metres (13 ft) high. About a quarter of this space is used for AV with our system angled out slightly towards the centre. There is a rug on the floor between the front speakers and our listening position, with scattered rugs elsewhere.

Background

Back in the 90’s when we lived and worked in America, I walked into audio store in New Jersey planning to buy Bose surround system which I figured would be good for our nomadic existence. I was horrified to be plonked down in front of a set of massive tower speakers, exactly the opposite of what I wanted, and encouraged to listen for “just a couple of minutes”. I had never heard anything like it before and my ears and my heart overruled my head. 2 weeks later I took delivery of a pair of Vandersteen tower speakers and Quicksilver mono block valve amps. Later this was expanded to a full suite (5.1) of Vandersteens and after our return to Australia a Theta Casablanca III was added. I loved the sound quality for both music and home theatre, but it was always an effort to lug around and barely tolerated by my wife.

Fast forward 25 years and I’m retired and we’ve downsized. The big Vandersteens and the tubes are gone, and our house is now furnished as a home and not as a sound stage with personal belongings scattered around. My wife is much happier, and to be honest so am I, but I miss the beautiful rich clear sound we had in our lives. So, even though my hearing in my late 60’s probably isn’t as good as it used to be, I want to do something about it, and having trained as a cabinet maker and with and inquisitive mind and time on my hands, I am wanting to follow the DIY route.
 

Blumlein 88

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Are KEF LS50 actives too big? If not there is your answer for quality sound. I suspect they'll be larger than you want. 5 of those and add a woofer. They are also available wireless. Oh and what is your budget? You can get the non-active non wireless for much less.

These are actually two way coaxial designs. But let us know if this is too big. They are small, but not tiny.

1614493699618.png
 

Blumlein 88

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Other options if they aren't too ugly would be something like an active JBL LSR 305. They are also small, but not tiny. Very good sound, self powered and a huge bargain for the price. ($150 each). The small speakers in this picture are 305s. 5 inch woofers here too.

1614493915190.png
 
OP
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Solar Paul

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Hi Blumlein 88

Thanks for your replies and yes I am aware of the Kef LS50s. I nearly got them for my front channels but went with the Vandersteen VLR Woods on the basis that they might match better with my Vandersteen centre channel. I really like the way that they look too. But they are around 30% greater volume than my tiny cubes (which aren't really that tiny - it's just a relative thing). But I won't be going this route for a couple of reasons:
  • Budget (which you mentioned). LS50 Actives will cost around 270% of what I think I can make them for and that adds up to a difference of around AUD $10,000 (USD $7,000) and I really don't have that sort of money to throw at this
  • They are around 30% bigger than my (not so) tiny speakers
  • I really want to go the DIY route to extend myself
 

Blumlein 88

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My apologies I missed you preferred to do DIY.
 
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