Digital Sources- Little Dot Dac1, Musical Fidelity E600 & Apple TV
Amplification-NVA P20 & A20 (both modded)
Speakers- Diy BBCubes; Ls6
Mini BMU to dc blocker
Maybe it is the best speaker for me (or will be) but i can't expect everybody to feel the same. I have spent many hours listening to every version with lots of different music so know them very well. Changes have not always been good especially in the early days. I am trying to be honest in what i say about them.
I have kept largely to the Doc's recipe . Doped drivers, no electrical xover, up firing bass and mids, isobaric, no ports or damping or stuffing. The aperiodic bass loading for the big bass cube is the only aspect that has strayed from Doc's recipe and i have only done that to get the box size down to a realistic volume. The top enclosure is still a sealed box (not infinite baffle ) I think my speakers are more omnidirectional than semi omni now as i have tweeters up firing (something doc never tried) and to both sides (the cubix did that). Up firing 12 inchers and up and down firing 5 inchers have never been tried all together that i know of
I don't think i am wrong saying i may have broken some new ground here. And the bonus is i haven't blown anything up in all my speaker, amplifier and cdp experiments
Another thing i notice is the bass gets slightly louder relative to the other frequencies when i stand up and stand real close to the speakers I never noticed that before with the old set up, the sound was the same wherever i was - seated, standing or sat on the floor. Must be something to do with the down firing 5" because essentially that is all that has changed. I will listen more extensively whilst walking and crawling around the room.
Not sure what to do to resolve that, it is very odd. Maybe it is not so bad as to make me abandon this design, time will tell. Bass is supposed to be omni directional Anyone got any ideas ?
Things to try
*remove down firing 5"
*try big bass cube front firing again
*remove down firing 5" and put it on the top baffle with the other
*build a one piece floor standing enclosure with up firing isobaric 12 inchers, side and front firing 5 inchers and side and front firing tweeters. 5 inchers would share the same enclosure as the 12 inchers.
*as above but with front firing 12", side, front and up firing 5", side, front and up firing tweeters
I am not going to be too hasty though because the sound is glorious in so many ways, just a couple of wrinkles to iron out. The detail, dynamics, smoothness, effortlessness, texture and musicality of this creation is just captivating.
Something else i tried. I turned off the bass amps and just used the top enclosure with 5 inchers and tweeters. It was very bass light but then i was expecting that. A 16 litre enclosure with two 5" drivers which have a VAS of 5 litres each and a Qts of around 4 was never going to be anything else. But married with the big bass cube it works so well. On it's own it doesn't - not a problem. I wanted it to be bass light in order to marry with the 12 inchers and less excursion at the bottom end equals less distortion further up, it works more like a true mid range rather than mid bass.
The issue (if it was an issue ??) with the bass being louder when i stand up has been resolved. Moving close to the speakers of course they are going to get louder, i am closer to them It was the shift in frequency response that bothered me in the end.
I have the bass cabs up firing of course and sat on a 2 ft sq. concrete slab. Initially i put some pieces of 3" x 3" fence post at each corner to leave a gap - because the back panel of the bass cabs is still off and stuffed wall to wall with 3" thick foam.
My thinking with the cause of higher bass volume when stood up was either (1) some reflection issues between the two panels where the magnets of the 12" and 5" meet or (2) something to do with the bass cab now being up firing and a 3" gap all the way around between the bottom edge of the cab and the concrete slab it is stood on.
I decided to mess around first with the easiest thing i could change. I removed the 3" fence post spacers i put in under the bass cabs and substituted them for 17 mm slats of wood running front to back at both sides.
This has made an amazing difference Reducing that gap from 75 mm to 17 mm has not only totally eradicated any shift in bass level between when being sat on the floor, seated or stood up but it has brought the lower bass up in volume. I was thinking it was a little too polite down there so that has come as a welcome change. The total height of the speaker has also been reduced by 58 mm and with it the height of every driver with respect to the floor and ceiling. Not sure what audible effect that has had if any.
So i can tune the bass response by altering the width of that gap I am going to try reducing it again and see what happens. Having so much fun listening to (and tweaking) these speakers. The clarity of the musician's playing is simply wonderful. I have never enjoyed the music so much. Big speakers can work in a small room if they are designed that way - tweaking the design in a small room as the process goes along helps a lot. Adding more 5 " drivers and tweeters has been a definite improvement each time. I could add more if the wallet allows Closed back tweeters are easy to add as you don't need any extra cabinet volume. 5 inchers are more tricky because the do but my top enclosure is deliberately over sized so i could get another two in there
You get a sneaky look at the equipment "rack" Notice the cap banks with the light blue 10,000 uf reservoir capacitors ? I have had these about three years but they are the exact same Vishay capacitors that NVA have decided to use in the latest version of their power amps. Good choice Paul and Tomasz
Going back to cardioid bass loading (i promised i wouldn't use that word again ) the bass volume is reduced behind the speaker (if front firing). If i have a crude version of a passive cardioid bass cab (the foam could be delaying and reducing the back wave just enough) then turning it so the stuffed end is facing the floor rather than the wall means that bass will get louder the further away your ears get from the floor.
Could be all of course but the theory ticks all the right boxes to me at this point in time.
Well now i have adjusted the bass response by reducing the gap around the bottom of my bass cabs, my thoughts turn back to this. By making a circular hole a bit bigger than the 130 mm hole i did before, making a rigid mesh for each face of the panel i can sandwich foam or other between them (like the scan speak variovent).
Of course the stuffing density can be played with to alter the effect. But you wouldn't want to do that between albums How about solid wood disks of the same thickness as the back panel which totally cover the vent on the outside. Make several with varying diameters of circular hole cut in the middle of them with the final one having no hole in it at all. It could be like a mechanical bass tone control going from bass on full with the vent totally closed to bass on low with the vent fully open and varying levels in between.
I need to patent this
The whole bottom half of the lower enclosure's back panel is the resistive hole. A wooden panel of same thickness and half as tall as the back panel can be slid up and down to alter the size of the resistive vent. It would need some way to lock it in place and stop it rattling. If i put all the binding posts right at the bottom then it wouldn't interfere with anything and when fully open the sliding panel would not stick up above the top of the lower enclosure.
The Doc (RIP) hated technical talk and i have been guilty of letting it creep in to my posts and it has certainly become more frequent since RD passed. Before i know it i will be talking complete technical talk that nobody can understand and i will get lost in my measuring and test equipment (and up my own arse if i'm not already there). Don't worry, it won't happen. I will just keep talking nonsense .Sorry Doc
Anyway back to this juggling. There are several balls - box volume, driver Qts, number of each driver size, orientation of drivers, aperiodic holes, different efficiencies of drivers, series or parallel, high pass filter caps , padding resistors, amounts of doping. That is a lot of balls to juggle. To some degree they affect the others, change one and it leads to a change in something else.
I am just about getting my head a round it all now. Thank god i don't have to design an electrical crossover It's not all about even frequency response . In fact for me it's very little to do with that although annoying humps that stick up like a sore thumb are not welcome. I will not sacrifice other more important things (to me) but i will chase it when i know i can safely without ballsing anything else up.
I want an exciting listen that does not fatigue or become annoying. There is a balancing act right there. Omni directional or semi omni definitely helped with that, it's not squirted in my face although the room is filled with lovely music. I want all the detail i can get. Having no filters on the bass and mid bass has helped there but the major thing with this has been adding more tweeters and mid bass drivers. Lower distortion lets the hidden detail out. Going isobaric with the 12 inchers very much helped with bass behaviour and detail.
I want the sound to be more or the less the same everywhere one could be in the room. Sat on the carpet playing with the kids, relaxing on the sofa in the traditional sweet spot if i am alone, sat next to my wife kids slightly off axis, sat on the other sofa which is in line with the left speaker. the semi omni thing definitely helped here. But adding tweeters and mid bass drivers has really opened up this aspect. Comb filtering - i can't say i have heard it. All the drivers of the same type are on different baffles which are at 90 degrees to the next.
I want bass you can feel as well as hear and i want it to be as tight as a duck's arse in water. This has been the biggest headache with these speakers. Having big bass drivers is the only place to start (yes, even in an average sized living room) Getting near the right box volume took a while - i had no T&S parameters to start with. I finally found some for the big 12 incher and could make a big box for it. The 5 inchers are much easier to deal with . The next thing was going isobaric with the 12 inchers. Wowsers. Making the big bass cube aperiodic has helped no end here as well.
I want a box that does not take up the whole room and can be up against a wall. Unfortunately big drivers need a big box or you get a huge bass hump that trust me sounds not too good. At first i looked to isobaric loading to help with this - it did by cutting the required box volume in half. Doc suggested that to do it properly i had to have an equal box volume behind each driver, which i did. But the box is still too big. What to do ? Do what Doc told me not to (sorry Doc) and go for a clamshell arrangement where the volume enclosed between the two driver cones is as small as possible. The only thing dividing the drivers is the 20mm of crappy chipboard. I suspect this could be reduced much further as at the drivers only have a maximum excurion (xmax) of 6mm and they never look like they are moving at the volumes i need. Apparently it is only the box volume behind the rear driver which counts, the volume between the two drivers does not count. So as little volume is used up as possible by the front driver. Aperiodic venting also drops required box volume so happy days
I am currently enjoying the best bass reproduction i have ever heard. Yes my big cube is no longer sealed enclosure and my isobaric configuration is how Doc told me not to do it. The box is no longer sealed (but it's not a tuned port either ) and the clamshell arrangement is against Doc's rues but neither of these brought about any reduction in bass quality that i can hear. In fact some things are improved.
I want a speaker that works at low volumes. People complain about ATC speakers not coming alive until you have them fairly loud. None of that problem here even though the drivers aren't particularly efficient. The lack of components between amp and drive unit has probably something to do with this and the parameters of the drivers themselves. No wadding in the enclosures has an effect on this too. Probably other things as well.
I want music to sound like music, a band to sound like a band not some photocopy of it or where the band are playing in different rooms. I want to know that they were enjoying the process of recording and loved the songs. A lot of this i believe comes down to phase and not going round in circles of phase change.
All in my opinion of course It would be interesting to hear what these speakers sound like with different sources (i can't bring myself to swap out the nva based amps). It is something i will have to do soon. Different cdp's and get the record player hooked up. I hope that even though i have been voicing these things mostly around my modified Naim CD3.5 that they will work with other stuff too.
That won't be ideal though as the big cab has a bigger foot print. Maybe better to mount the 5 inchers on the top of the big cube. Either both on top or one on top and one on the inner facing panel. Tweeters will have to go on little flat panels added to the top of the cube as the 12 incher takes up so much roomthere is'nt room for a tweeter on that baffle unless i use the visaton G20sc for that one. Only thing is i won't be able to flip between up firing 12" and front firing. Only separate cabs will allow that.
Ultimately i need to build a single enclosure with dimensions of the final build (no larger than 40 x 40 x 90 - slightly thinner if i can) for any final conclusions to be made. Flipping between front and top firing bass then becomes impossible without moving the drivers and isobaric makes it even harder. In an ideal world i would have all these different designs built and just swap between them but that would cost too much in drivers. So it will have to be done with multiple driver holes and blaking plates