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Ittaku

Amateur OB speaker builder and his ARC based digital system

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Posted (edited)

I've been making my own custom speakers on and off for over 20 years and recently got inspired to start all over again with an open baffle design and all the latest scanspeak drivers, and upgrade pretty much all of my components. Apart from the baffle itself being only temporary still, I'm extremely happy with the final result. I set out to create something that should be very natural sounding and be scalable to recreate large scale symphonic works and organs. Here is the executive summary of how it looks, before I introduce the family members:

 

7nNZjLE.jpg

 

As you can see, Dspeaker DAC feeding into a Supratek Preamp, then into Audio Research Power amps and an SVS subwoofer. The power amps feed via XLO cables into my custom open baffle speakers. Everything is sitting (standing?) on solidsteel racks. Things aren't spaced evenly to make up for inadequate interconnect lengths :P Before you ask, the round thing at the back left is a fan... it gets awfully hot in here in summer with all those valves even with the ducted aircon running so I need extra airflow. That particular Dyson fan has a very low speed setting which isn't too noisy which is why I chose it.

 

Music feeds predominantly from my Linux PC (not pictured) at the rear end of the same room, a good 5 metres away. Music is played via a personally hacked version of the Clementine media player (I'm a software engineer) that guarantees it plays native resolution without resampling. Then it plays via pulseaudio upscaling to either 178.6k or 192k 24 bit with the sox very high quality filter before playing on USB out.

 

USB is fed to a USB over ethernet device and an ordinary cat7 cable to the remote ethernet to USB receiver:

aCKJgN4.jpg

which is powered by a linear power supply:

 

2iRcKEn.jpg

 

This acts as a USB decrapifier, extender, and way to dissociate the PC's USB noise from the DAC.

 

The DAC is the new reference Dspeaker X4 DAC (the same company that made the antimode dual core):

N1RC8AB.jpg

 

The X4 does reclocking, dejitter, room correction and the crossover to the subwoofer, with 2 sets of outputs after the room correction, DSP and crossover. This is a sweet sounding new device from them with still some software quirks that need addressing but is getting new firmware every couple of months. Internally it uses 3x TI PCM1792 DACs and some pretty good ADCs too but I don't use the analog in at all. Here are its internals:
IJfKYCz.jpg

 

This DAC then feeds into a very unique Dual Cabernet preamplifier made by Mick at Supratek for my custom use which is basically a 4 channel preamp with separate inputs and outputs for mains and subwoofer. It has an amazing ability to simply flesh everything out and give the dynamics far more realistic contrast. Additionally with the DSP room correction I needed more gain. The reason this is a custom version is the default preamp is a 2 stage preamp which is normally considered advantageous but it added too much noise to my quite high gain amps so he redesigned it with bigger transformers and to be single stage only. I have it positioned here because the old one used to easily pick up noise from almost anything that was too close:

IMG_20180716_144440.jpg

 

The subwoofer channels are using some NOS Czech WWII military 6SN7s while the main channel has PS Vane Treasure Globe SE 6SN7s on both the driver and output stage. Those are herb's audio dampers on the valves.

The preamp has a completely separate power unit:

Q4rL5Sx.jpg

 

The subwoofer is an SVS SB16 ultra, it only handles below 30Hz with a 4th order crossover, but measurements show room response down to 10Hz:

unpftwq.jpg

 

An old beloved Esoteric P700 transport is still around but basically gets no use any more since ripped music from the PC via USB sounds better in my setup and most of my music these days is highres digital. It's there for convenience on the rare occasion I want to listen to a CD I haven't ripped or someone has brought CDs. I've been meaning to put it up for sale but it's not hurting anyone there so I haven't bothered:

q4USQny.jpg

 

Power amplification is via my beloved Audio Research Reference 250SE monoblocks:

Hr2Z4Mo.jpg

They are no doubt the heart of this system and responsible for the most musical, scalable and controlled sound I've ever heard. I took the covers off even though they have fans in them since they're relatively protected in those stands and a bit more cooling won't hurt. I recently upgraded from a Reference 150SE which I already loved more than enough but snatched the opportunity for these babies because I've always wanted monoblocks just because. They have way too much power for my system which is reasonably efficient already. I have the Ref 150SE up for sale now.

 

My speakers are a combination of drivers from Scanspeak: a 32cm cone woofer, 2 x 12cm cone midranges and 1 beryllium dome tweeter:

DpgpqJV.jpg

The baffle was meant to be temporary only and no doubt is holding them back from their full potential, but I haven't found quite the right manufacturer to mill me something out of aluminium or explore other options. The design also needs to change as I feel they're a bit short. The spacing was carefully chosen but the tweeters are a little low so the whole baffle needs to be taller. The temporary baffle was simply to see if it works before making a final design, but it sounds so good now I haven't progressed any further. The reason for 2 midranges was they were (8 ohm) less efficient than the other (4 ohm) drivers and did not handle as much power and I really want all the drivers operating only ever in their linear range. I had experimented with multilevel crossovers for each midrange but felt both doing exactly the same range was better. DSP is essential for these designs given their open baffle design and my small room, and the Dspeaker and this make for a wonderful match.

 

Speaking of crossovers, they're 12dB Linkwitz-Riley made from film and foil multicaps where possible, otherwise metallised poly films for the larger values but still bypassed. The smaller values are polystyrene caps. I found these caps sound better than the very popular mundorfs myself and I put it down to their internally self-bypassing designs which actually measure better than those exotic alternatives. When caps were not in the signal path, I used solen caps. The inductors are 10 gauge solen inductors, solid core for the lower frequencies and litz for the higher frequency applications when the skin effect resistance was significant below their crossover point. Resistors (only go to midranges) are Mills non inductive. Wiring is cardas crosslink. Terminals are cardas copper tellurium - I originally used the silver rhodium connectors but I wanted to solder directly to the terminals and this material is not suitable for such use. Soldering is with wonder solder. The soldering is dodgy as but it works. My lack of final production skills is the reason I never got into professional speaker building. Maybe if I can employ someone to do the building after I design them it might work...

i1eSMkA.jpg

 

Power is cleaned by a thoroughbred sequenced power interface:

JUWeEcJ.jpg

 

Power cables as you can see are shielded thick cables, but not big name brands. I can't hear any differences between power cables so I don't bother. USB cables are cheap generics with power disconnected; again I can't hear differences between different USB cables, nor network cables.

 

Interconnects are WyWires silver balanced from DAC to pre and pre to power for the main channels, and WyWires blue and XLO to subwoofer. Speaker cables are XLO reference 3 gunshot:

gXWxeB8.jpg

The observant amongst you will have noticed the left power amp is on the right and vice versa. These speaker cables are so thick and unwieldy it was the only way I could make it work.

 

I think @andyr is the only person from these forums to have heard this system, but at a slightly earlier stage of its evolution. Music is predominantly classical; some Bach, a lot of romantic era and plenty of early 20th century music. Most is sourced from prestoclassical. I do listen to other types of music, especially some ambient electronic music, but as the system has improved I've found myself listening to more and more classical. My rock collection hasn't been played in many years.

Edited by Ittaku
Updated pics

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Yes, indeed, Con - I enjoyed listening to it a couple of months ago, very much.  👍

 

I'm sure the dual AR monoblocs have pushed it up a notch or two!

 

Andy

 

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2 hours ago, andyr said:

Yes, indeed, Con - I enjoyed listening to it a couple of months ago, very much.  👍

 

I'm sure the dual AR monoblocs have pushed it up a notch or two!

Thanks Andy. I much enjoyed listening to your system as well which had a completely different approach entirely to getting great sound.

 

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Posted (edited)

Interestingly I think Mick hinted at my particular preamp variant in this blog post which he says will now be the default design:

http://supratekaudio.blogspot.com/2018/03/were-back.html

Here's hoping the noise issue in my system has helped make his preamps even better for everyone :)

Edited by Ittaku

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Apologies to those interested in the P700 transport; during a recent computer upgrade the CD transport came in handy again so I've decided not to put it up for sale.

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Here's the USB cable I'm using which keeps the power away from the DAC. It allows me to power USB separately but the DAC doesn't need power from USB so I simply don't attach it to anything:

IMG_20180607_092843.thumb.jpg.f3dc0700ee450a083e1e3c08038ecff0.jpg

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Upgraded the valves in the primary channel output stage on the preamp with the PSVane treasure globes. This was a complete gamble but paid off. They've given substantially more leading edge to the sound with bite to rosin on steel in violins, faster attack to all percussive sounds and more detail across the board. Initially they were cold sounding but after a couple of hours of burn in that went away. The instruments now are substantially larger vertically, have more air around them and more recessed in the stage. All in all a great improvement. Photos linked from my other thread:

IMG_20180621_120412.jpg

IMG_20180621_120840.jpg

 

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Posted (edited)

Next experiment: I've replaced the NOS tubes the preamp standalone power supply came with newer tubes, nothing special except that they're all significantly higher rated output (but still compatible) than the ones included, on the basis that the power supply is everything. The rectifier is a standard Sovtek 5AR4 which is rated at higher current output than the 5U4M it came with, and the power output tubes are matched Tungsol 7581As which are a drop in replacement for 6L6GC which the preamp was designed for but again produce significantly more power than the NOS 6N3C it came with. So far so good. The rectifier runs 25 degrees cooler (115) than the old one which is reassuring, while the power output tubes are at the same temperature (115). What difference do I hear? I don't hear any timbral or tonal balance changes, no changes to air, detail or stage... but the dynamics feel more solid, linear, and effortless going from the ultra quiet passages to explosions. I do believe the channel balance is slightly different too, possibly because these are matched tubes where the previous ones weren't but it could be my imagination. The only thing that's annoying is "thetubestore.com perfect pair" sticker they put on the base - it doesn't easily peel off without leaving residue so I had to leave them there which I'm not fond of 😕 . At least these guys delivered much faster than psvane.com even though both sent from Canada. Go figure. The tube dampers are a generic token gesture - I can't hear any difference with them on or off but they cost almost nothing so I leave them there :P

 

IMG_20180622_130008.thumb.jpg.3772531f8ff1ac10409a90e985866ad5.jpg

Edited by Ittaku

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Hi Con,

That's some journey you've been on. I totally admire your single minded devotion to the cause. 👍

 

Just one thing - the sub and its proximity to sensitive thermionic signal processing. Personally I would have it at far away from tubes as practicable.

cheers

Paul

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2 hours ago, mach1 said:

Hi Con,

That's some journey you've been on. I totally admire your single minded devotion to the cause. 👍

 

Just one thing - the sub and its proximity to sensitive thermionic signal processing. Personally I would have it at far away from tubes as practicable.

Thanks Paul, while I did find it made a difference with the earlier preamp I didn't notice a difference once the preamp was changed to a low gain version, and it didn't seem to have any effect on the power amps.

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Hi Con,

 

Seems open baffle design is becoming quite popular, I had the opportunity to check out a friends system recently, same amp and phono stage pre as me, OAD UltraAudio,  the focus and reason for my visit being his newly tuned Linkwitz LX 521 OB's, I've got a great system, one that I have finally been close to content with for some time that was until I got to hear the LX 521's, this system is on another planet compared to some of the best systems I've heard anywhere in every conceivable way, atmospherics and sound stage is a quantum leap ahead of my really very good box speakers, the bass is something one has to experience, magnificent, unbelievable shocking so now I'm saving again for my pair of open baffle design for my room. 

 

My compliments on your patience setting these things up, I know it can be a hit and miss nightmare till you nail it. Keep us interested people up to speed on your project.

 

Just wondering do you think the shelf above the woofer would be interfering at all also I agree with your plan to extend the baffle length,  I did think the driver array in your speakers needed some space, the tweeter is a bit crowded and close to the top mid driver, I noticed your using  beryllium dome tweeters, are you happy with the top end, Seas has some very nice soft dome's available if you find the top a bit bright and could maybe negate the need for the foam.

 

Regards

 

Phill.

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4 minutes ago, Phill said:

LX 521

The key to this speaker is it's constant coverage pattern (helped by the funny shaped baffle).

 

4 minutes ago, Phill said:

Just wondering do you think the shelf above the woofer

I have a similar shelf (just below) the lower-mid woofer in my OB .... and I spent a lot of time worrying about it, but it didn't seem to have much negative effect ... and the shelf was kinda unavoidable for me.

 

4 minutes ago, Phill said:

I did think the driver array in your speakers needed some space, the tweeter is a bit crowded and close to the top mid driver

The tweeter really needs be to be close to the mid driver.    If anything, I'd say it's not close enough.

 

4 minutes ago, Phill said:

negate the need for the foam

One way to do this, would be like in the 521, to get rid of the baffle around the tweeter ...... but the baffle shape needs to be part of the 'whole design', so it would mean kinda revisiting the entire speaker.

 

14 minutes ago, Phill said:

saving again for my pair of open baffle design for my room

 

The 521, or any of JohnK's designs, are really really good  (as mentioned, the funny shaped baffles are a big part of it).

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Posted (edited)

Thanks for your comments. Phil, you're absolutely right about the open baffle. I've been tinkering with speakers for 25 years and this is my first OB design - the woofer was the reason I finally felt it was possible to do as this particular woofer handles 300W of power and is flat to 30Hz in free air. There are some unique challenges in making OB work at loud levels and be controllable at the same time. I'm actually considering changing from the one 4ohm 13" woofer to two 8ohm 13" woofers when I "finalise" the design in the future just to handle even more power - an unloaded woofer can't really handle the same sorts of power levels as it can in a box. Additionally it's impossible to get a flat frequency response in a real world room but modern DSP has made it far more manageable (I'd say it's essential if you're aiming for full range from OB woofers). However when you get it right, the incredibly tightly damped bass is second to none; the speed and lack of smearing and the group delay is unbelievable. Listening to a speaker with a box - any speaker - even up to hundreds of thousands of dollars, is disappointing now. The box is always audible. That said the current baffle I have is terrible with its own vibrations since the woofers do so much excursion. I don't think timber of any thickness will ever suffice which is why I'm having a friend help me with some finite element modelling on an aluminium billet baffle instead. The challenges are much bigger than I originally thought... The parcel above the woofer is there to hold the crossover components for the mids/tweeter, but also to give it some physical structure and rigidity to stand up. The sloped front baffle would flex like a tuning fork otherwise lol.

 

As for the tweeter - it's supposed to be as close as possible to the midrange to minimise lobing. The crossover being 2500Hz means it's impossible to avoid lobing entirely. It's physically impossible to get this much closer than it currently is @davewantsmoore You can't see it but the foam is over some of the physical surround of the tweeter. As for the foam - it is not there at all because these are bright in any way shape or form - it's there to minimise the diffraction from the extra wide baffle. The baffle design was always meant to be temporary and in its final form would be sloping away from the tweeter and much narrower either side of the tweeter. There is no soft dome tweeter I've ever heard that sounds anything close to this beryllium tweeter - any preconceived ideas you may have about what a tweeter will sound like just because it's made of metal will be smashed if you hear what these sound like. The tweeter is the most transparent part of the whole design as it's virtually impossible to attribute any particular sonic signature to them. They just have an unlimited extension to the sound and just completely disappear, replaced only by music. Nothing tizzy or bright or sharp or fatiguing, purely liquid sounding natural tones without any artificial warmth the way ribbons do, either.

 

Where's all this going? Well I've been considering starting an actual speaker business and as awful as this temporary design looks, I do have potentially grander plans, getting a few friends involved with expertise to get me over some of the other hurdles. However the parts alone cost many thousands so a production version of these sorts of speakers would be in the tens of thousands, but I also have a more minimalist smaller design in mind; it'd still be very expensive. I'd only be making very small numbers for very particular customers, and I would only be doing it for love, not money. Watch this space (but very very patiently)... or not. It may never eventuate.

 

Actually I'd be happy to have people come around and have a listen even it this form, though one at a time because my listening space is currently confined.

Edited by Ittaku

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50 minutes ago, Ittaku said:

. .. The parcel above the woofer is there to hold the crossover components for the mids/tweeter, but also to give it some physical structure and rigidity to stand up. The sloped front baffle would flex like a tuning fork otherwise lol.

 

i1eSMkA.jpg&key=b1e98efd7f3d5ed3aaee79bd

 

Well this is an opportunity if you want to experiment. Just add side walls under the shelf and leave the back open you will very quickly make a U-baffle to experiment with. Your low bass will get appreciable gain to fill in to your sub at 30Hz.

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Just now, Nada said:

Well this is an opportunity if you want to experiment. Just add side walls under the shelf and leave the back open you will very quickly make a U-baffle to experiment with. Your low bass will get appreciable gain to fill in to your sub at 30Hz.

Thanks that was actually considered in my original design as well, however I wanted to avoid parallel walls of any sort so they would have been flared out. Again this was a temporary design and I may consider it to minimise the wrap around loss, but it wont have any effect at 30Hz - that waveform is just too darn long to be stopped by that. Nonetheless you are right and something I may do next iteration.

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Wouldn't it be better to try the U-baffle now in the temporary frame? It is a "test bench" and happens to be just crying for a quick U-baffle mod.

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1 minute ago, Nada said:

Wouldn't it be better to try the U-baffle now in the temporary frame? It is a "test bench" and happens to be just crying for a quick U-baffle mod.

Absolutely :thumb:

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31 minutes ago, Ittaku said:

Absolutely :thumb:

 

Oh great. Im way too lazy to build a U-baffle so hope you try it and let us know how it sounds.

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22 minutes ago, Nada said:

 

Oh great. Im way too lazy to build a U-baffle so hope you try it and let us know how it sounds.

I think that there is a problem with a U baffle with parallel sides.

Easily done though, four square pieces of MDF and stand them in place.

 

As quoted from  @Ittaku 's post above "The box is always audible." a U baffle is nearly a box and as such I think you will hear it.

 

I suggest that any if extra sides be used, as  @Ittaku says, they should be flared, even then you may well hear a negative change in sound quality.

 

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There is one thing I have on my side though with the woofers - they cross over at 230Hz and the side walls will be too close for that frequency or below to form standing waveforms. However it is also giving it more material that can resonate.

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Posted (edited)

A really interesting system.

Are those Scanspeak Illuminator 12MU midranges as used in some of the most expensive speakers in the word?

Nice to see the speckled /black spot jarrah cabinets on the Suprateks.That is pretty rare timber.

Edited by THOMO

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Posted (edited)
6 minutes ago, THOMO said:

A really interesting system.

Are those Scanspeak Illuminator 12MU midranges as used in some of the most expensive speakers in the word?

Nice to see the speckled /black spot jarrah cabinets on the Suprateks.That is pretty rare timber.

Yes those very midranges; the same as in the Wilson WAMMs. I can't tell for certain but it appears to be the same woofer too (but my tweeters are better the WAMMs' ;) )

Edited by Ittaku

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4 hours ago, Ittaku said:

Thanks that was actually considered in my original design as well, however I wanted to avoid parallel walls of any sort so they

would have been flared out.

 

As long as you operate it below the cavity resonance you will be fine.... although I suspect you are operating the driver at a higher frequency because of the small midrange, and 12dB filter.

 

I did a fair bit of measuring of a smaller cavity  ~20cm x 50cm cavity with a "Z" frame in it ..... and it was fine with a 24dB octave slope low pass filter at ([email protected]) 120Hz.

 

4 hours ago, Ittaku said:

Again this was a temporary design and I may consider it to minimise the wrap around loss, but it wont have any effect at 30Hz 

It will give you more gain at 30Hz (than what you have now) .... but not enough unless you apply more EQ somehow.

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Posted (edited)
7 minutes ago, davewantsmoore said:

 

As long as you operate it below the cavity resonance you will be fine.... although I suspect you are operating the driver at a higher frequency because of the small midrange, and 12dB filter.

 

I did a fair bit of measuring of a smaller cavity  ~20cm x 50cm cavity with a "Z" frame in it ..... and it was fine with a 24dB octave slope low pass filter at ([email protected]) 120Hz.

 

It will give you more gain at 30Hz (than what you have now) .... but not enough unless you apply more EQ somehow.

Roger on that, it's a 12dB LW design without L-pads or zobels (they only make the sound worse in my experience). I drive the woofer up to just before cone cry at 230Hz and cross over to the two midranges there. It allows me to still use an air core inductor (for extreme power capability with no saturation) with 10 gauge wire thus keeping the resistance of the inductor lower than if I had to cross it over lower - thus minimising any loss of damping, and is high enough above the natural roll off of the midranges (which is 150Hz) to not destroy them from too much excursion, but since they don't handle as much power with linear response, that's why I have two of them. Alas that means I had to put a resistor to the midrange components even though they're less efficient due to the crossover exciting the band pass component. I like to have as few components in the signal path as possible but the resistor was essential for balance.

Edited by Ittaku

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What do you do about EQ needed for each driver, eg. the 6dB extra slope, or the 'dipole peak' EQ?

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