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Welcome to my build of a Focal Utopia speaker clone with active crossover. The Idea My interest for a new project started at the 2017 Scalford show where I was impressed by the 4 way open baffle speakers with active crossover built by rv295 and the Linn linear active crossover demo which got me thinking that a self-build speaker would be a lot less hassle and more fun without the passive crossover which I always found frustrating as the design is fixed, difficult to alter and has so much bearing on the sound. I have done one DIY speaker before, a ProAc 2.5 Response clone with components and crossover supplied by Wilmslow, it did the job but I thought it could have been better if I could tweak the crossover. I had been thinking of doing another DIY speaker for a workshop/studio I am building in my garage and have always been a fan of the radical design of the Focal Utopia range. Then I came across an advert for a 3 way set of Focal AudioM drive units (15" WX woofer, 6.5" WM mid, TD5 tweeter) and struck upon the idea of building a Utopia clone with these drivers giving some lineage to the original, although not the same units used in the current Utopia range by any means, they do have some similarities and probably very similar to the 1st generation Utopia from 1999. I did considered doing my own design but there is something rewarding about building a clone speaker as it fulfills a desire for a recognised high end product at a fraction of the cost and most of the design work is already done for you if you follow the same dimensions, baffle, port etc. So I decided to take a gamble on the 12 year old drive units, the seller did demo them individually (thanks Mani!), but its pretty difficult to know what your getting into by listening to each unit on its own. The Prototype As this a pretty complex cabinet build and Im not sure of the integrity of the second hand drive units I decided to build a prototype to help me understand the angles and taper of the cabinets while testing the drive units do actually sound decent before launching into a full scale build. This also gave me the opportunity to get to grips with the woodworking as it has been a while since I used a router. As I only have 3 way drive units I am aiming for something that looks like the Utopia Scala but with the size of the Stella to accommodate the 15" woofer. I'm keeping a 4 way design in mind for the future to achieve the full Grand Utopia III with additional drive units, if the project is a success and I can source the drivers on the cheap (I have since purchased another set of 6.5 mids almost identical which were previously used in car audio where there is a healthy 2nd hand market for Focal components, and now intend to aim for something more like the Stella, probably a 3 1/2 way design). I have been using the original Utopia speaker dimensions and photos as a guide to the design with a lot of guess work. The rear taper and angles on the baffle are proving a challenge and I can't find this info anywhere on the web. For the first prototype I built a simple frame to support the baffles and give me an idea of the various angles to achieve the 'Focus Time' idea of all drive units directed to the listeners ear, I used the laser on my skill saw to line up the angles against a point on the wall at ear height ;). For the second speaker I decided to build enclosed cabinets for the woofer and mid to give me an idea of how the volumes and porting affect the sound. This was more work but helped me to understand the angles required for the tapered rear of the cabinet. I used the volume provided on the drive unit spec sheet as a guide. I already like the look of the speaker very much, like an alien creature. My wife calls them 'The Dominators' and at 1600 H x 600 W x 800 D they definitely have some presence. Such is the luxury of having a dedicated listening space (i.e. a garage) you can go wild on size and looks and still get it past the missus. If the prototype is a success I will add another 25mm baffle to the 18mm prototype to get the curved baffle and flared opening. I have not used any glue on the prototypes so I can change the design easily. When Im happy with the design I will add internal bracing and glue together using compression straps to get proper sealed units. Initial Testing With the prototypes roughly screwed together and resting on the 2 x 25mm MDF for the plinths I setup all the components and connected speaker cable to each drive unit using crocodile clips. For the electronics, the drive units came with a Furman TX-24 Tuneable Active Crossover unit which I can use for testing before deciding on a digital active crossover (likely to be MiniDSP as the Linn offering will be too expensive for me), I need 3 amps and didn’t want to invest too much so went for fanless pro audio amps (Behringer A500) which I got on eBay for £80 each. I brought a bunch of XLR leads and reused some existing speaker cable. This will give me a cheap way to get started and will upgrade each component as the system proves itself. Although I found a manual for the Furman Crossover online I really don’t know what Im doing and it took me a long time to get any kind of coherent sound. By slowly adjusting the crossover point and outputs to each component and the volumes on each amp, I managed to get a full bandwidth sound and proved that the drive units are all in good working order. The crossover frequencies I Ianded on with the Furman are: Low-mid 60 khz, Mid-hi 1500 khz. Although I ran into problems with vibration from the bass units at volume due to the roughly built prototypes, I ended up with a controlled large scale sound with excellent projection into the room and my impression is that the drive units are high quality and I should be able to achieve a very good end result once its all put together and coupled to decent electronics. This was a welcome result at the right time as even building the prototypes has been a lot of heavy dusty work and I was starting to question what I was doing. I now feel motivated to continue the build and purchase the other components needed to complete. I will replace the 18mm side walls on the bass units with 25mm as there is a lot of vibration from the 15" woofer and I don’t think cross bracing will fix this. The next challenge will be the curved baffle where I will sandwich 25mm MDF onto the 18mm prototype and curved side walls. My experience with the cheap pro audio amps was not very positive, I ended up returning 2 of them due to defects, and found the sound quality pretty poor with very high SPL and a coarse, grainy sound not suited to home listening. Cabinet Build Before I started on the build proper I visited a well-known London hifi store to see the Stella in person. This was very helpful to get a feel for the overall size and the various curves of the cabinet. They are very impressive in scale and design. To understand the volume and port size of the woofer cabinet I played around with Unibox but this just confirmed the dimensions I already had in mind from dissecting the actual Utopia speaker dimensions. I bought a belt sander which is very good for shaping wood quickly and found this to be the best way to make the curved baffles and flared opening for drivers which was easier than expected. For the curved sidewall I used 6mm MDF bent around a baton and glued and screwed into place as I dont trust glue alone to hold the pressure on the curved panel over time. For most of the construction I have used glue and screw method into batons to join panels together. I looked at jointing methods but the angled side walls makes it tricky to get a flush finish to both sides of the join. I then used flexible wood filler to complete any gaps in the cabinet to avoid leakage. The build process on the first speaker was slow with a lot of thought required how to achieve the curves on the baffles and how to join the boxes together. Each box took around 12 hours or more work to complete over about 4 months of late evenings. I made all the baffles for both speakers in one go, doing all the cut outs while the router was setup for that cut and machined from a single piece of wood where possible so that the curved sides were consistent and then cut to length. This sped up the construction of the second speaker massively which was done in about 2 weeks. Building such large elaborate boxes for the tweeters did seem over the top but once the whole speaker is put together it makes sense and the long hours are forgiven. The joining blocks between each box were tricky to construct as it need to be angled on both sides like a V somewhere near 20 degrees and solid all the way around. When shaving down these blocks I ended up with a LOT of waste material but it was the only way to get solid angled blocks. The angle of the boxes to the listener, or the focus time , will be fixed but can be adjusted using spacers if needed. The bolts and wingnuts give a way to break down the cabinets without too much trouble if needed for transport but took some thinking through as the cabinets will be closed before painting so had to put all the bolts in place first and hold in place with nuts. The photo below shows the waste material from the slim angled panels before being cut and joined together to form a V shape for the joining blocks. A real mess! Finally I had the cabinets completed and sanded ready for painting. There was a lot of work to get a consistent shape and depth to the overlapped edges between the top panels and side panels. The front baffles cover the front edge of the top and bottom panels on most boxes to avoid a join on the baffle face. I did some simple testing with the woofer in place to ensure bass response was effective with no vibration from the cabinet. I did consider putting all the drive units, cabling and electronics together in the unpainted state to test the sound and make adjustments but the design is already complete and I don’t fancy changing it so going straight to painting. Painting While I like the look of the black baffle and coloured side panels and the definition of the black edging around the boxes that the actual Utopias use, it would require a lot of masking to get the same finish because of the way I have fixed the side panels in place. So I opted for one colour all over on the boxes and a matt black finish to the plinths and tweeter units for contrast like the Utopia Evo series. I used a 2K auto paint, primer, base coat and clear coat finish, all applied using a HVLP spray system I had used previously for my house. The 2K paint is nasty stuff and although I used proper breathing apparatus it was still a very toxic job and Im lucky my garage is far away from other houses. Next time I would use a water based primer and base coat and a 2K clear coat but I took what the local paint shop gave me. I had a few runs in the clear coat but managed to sand these out with fine grit paper and very pleased with the end result. I could have spent more time perfecting the finish by wet sanding and respraying the clear coat to get a mirror finish but I just cant justify the time. I had considered taking to a local paint shop but Im pleased I could do the whole thing myself and avoided having to transport the heavy units. This photo shows the tweeter units with the bolts fixed in place for connecting the units together. Putting it all together After joining all the boxes together and running internal speaker cable through holes from top to bottom I used crimped terminal connectors to connect the drivers which I found much easier than soldering. I then crimped the internal speaker cable directly onto the external cable so the cable is fixed to the speaker but easy enough to change as the rear panel of the bass unit is removable. The external speaker cable is 8 core Van Damme 2.5mm. I figured 2.5mm would be fine for each drive unit and the heavy duty 8 core touring cable is a neat solution. I used hex bolts on all the drive units which gives a great finish. The large hex bolts on the baffle of the tweeter unit are for looks only to mimic the original. I added some absorption foam inside the units on the sides and rear to soak up reflections and some internal bracing to support the woofer from underneath as they are very heavy units. First Listening For the crossover I ordered a miniDSP OpenDRC DA-8 so I can try the FIR filters for linear phase but for the initial setup I just used the same crossover frequencies that I used on the Furman and with no PEQ, levelling or timing adjustment the sound was better than expected in all areas which is very reassuring and it appears the cabinets are not negatively affecting the sound, at least to my ear. In fact the sound was good enough for an impromptu Friday night disco as word got around the neighbourhood. The sound output is pretty massive and easily fills my 9M x 5M garage with bass levels to rival a night club. The speakers start to reveal themselves at high volumes and are better suited to bass driven electronic music but it is still possible to speak easily over the sound so I would say the sound is pretty clean. There is no real sweet spot as the presentation is very wide which encourages you to get up and walk around while listening or dance. The bass extension is pretty phenomenal and will easily rattle the windows and vibrate the ceiling but is easy to tame with the volume control on the amps. This is a speaker that is suited to a large dedicated listening space and would be pretty antisocial in your average terraced house. I have since played around with measurements in REW and PEQ filters but didn’t find much improvement so may not be doing it correctly. I am now moving onto rePhase and FIR filters but struggling with importing the measurement into rePhase. The learning curve is pretty step and the miniDSP application notes while useful leave out a lot of important details. I'm running the two sets of mid-range drivers on the same XO frequency on different output channels so they are insync and this works well. I have experimented with overlapping one of the mid-range channels further across the spectrum with different filter types which also sounds good but not consistently. Having two sets of mid-range drivers really adds to the overall sound presentation and Im happy I purchased the second set and went to the effort of building the additional boxes. For the amps I bought a NAD CI 9060 6 channel amp and kept one of the A500s for the bass to get 8 channels total. The NAD has enough omph to bring things to life but will need more re-enforcement in the bass and will look at Hypex when funds allow. Conclusion Im proud of what I managed to build and very pleased with the end result. Visitors are quite literally blown away by the scale and sound of the speakers which is fun in itself and its been a very enjoyable project. I still have a way to go with tuning the XO and will hopefully achieve linear phase at some point. The finish on the cabinets is nothing like that of the actual Utopias and puts into perspective the workmanship and man hours that goes into a speaker like that. But still, it gives me a little taste of the Focal Utopia experience, a poor man's Utopia. Now onto building the studio to house the speakers.
Does anyone have experience with building DIY conical horn speakers using compression drivers? I am looking into building something like the OMA Imperia for my next project and have started researching compression drivers but don't know enough about it to make an informed decision. I can find plenty of pro compression driver units on eBay from brands such as JBL, Beyma, B&C but suspect these drivers are built for reliability and not hi-fidelity. If I look at RCA and Cogent style high end compression drivers these are phenomenally expensive like £2,500 a pair. My question is are there any alternatives with decent hifi performance at a reasonable price point and where to source them. Second would be any advice or software to understand the throat dimensions and conical horn dimensions to arrive at a coherent sound output. Has anyone achieved a good quality sound with conical horn speakers and could they recommend a DIY build thread to follow. Thanks