Unfortunately, not only are the Metric and USA R-values not equivalent, they don't seem to relate well to fill weight.
And fill weight does not equal the same acoustical absorption coefficients from different material.
The diameter of the fill material fiber and matrix all can result in quite different absorption at different frequencies.
https://www.bobgolds.com/AbsorptionCoefficients.htm
Joe measured the 180mm Bradford Polymax he's using at around 14-15g per Litre density, while the Bradford Gold 185mm fiberglass is only 7g per litre:
The USA "R-19" fiberglass batts at around 6.25-6.5" are ~27-31g per liter (.44 pound per cubic foot).
At any rate, I didn't even know Joe's speakers were ported before yesterday, if you fill them with 50 liters of fiberglass, the port might as well be sealed
http://sound-au.com/articles/boxstuff.htm
With a rear mounted port, the upper pipe resonance peak in the combined response seen in Rod Elliott's test above is usually not much of a problem, don't go overboard with damping material...
Art
Yes. sorry about the delay. It has come down to the battle of the tweeters. Steve originally was the reason I went down the NBAC route and use the ceramic coated tweeter. But I have lately been working on a 2-Way loudspeaker (not DIY) and using the silk dome tweeter and the results I got were so pleasing. So I made a decision to try that with the NBAC drivers. There was a subtlety I was getting that I liked very much. The good news is that I am well along doing that, the Crossovers have been built and I now need to change the tweeters and waveguides and then make it work. I do not think that will be hard or take too much time. I have also been dealing with a few health issues, but that situ is much better now.
So not too far away now...
Finally getting everything in hand to start on a ULD Elsinore build after a couple of months waiting on drivers. I have two packages from PURIFI coming tomorrow (finally!) with the 8 drivers, the crossovers are already built, and have wood in hand. BTW, I am using 1” thick bamboo plywood countertop for the top, back and sides with some 3/4” bamboo plywood for the baffle and plywood or plywood/MDF laminate for the bracing. All in all, not that much more expensive than BB plywood. I still have a couple pairs of 211 SET amplifiers to finish for friends/clients, but after those are finished, I can begin on the Elsinores. Progress reports in a couple of months (hopefully).
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Well, I do have a pic of the crossover boards. I decided to separate the crossover into two boards, one for the tweeter and upper mid-bass drivers that will be mounted between the braces on the back panel, and the one for the lower two mid-bass drivers to be mounted at the cabinet bottom.
The 211 amps that are keeping me from starting on the ULD Elsinores is shown in this gratuitous photo, next to my first Elsinore build. It is a Class A2 25W 211 SET of my own design with Tamura output transformers, D3A CCS loaded input, direct coupled EL34 pentode follower driving the 211 grid. I built one pair as a one-off, but people who hear them keep asking me to build a pair for them, so on pairs 4 and 5 right now (I did sneak a pair in for myself). I really need to put together a construction article on the design and build. But not in this thread or forum.
The 211 amps that are keeping me from starting on the ULD Elsinores is shown in this gratuitous photo, next to my first Elsinore build. It is a Class A2 25W 211 SET of my own design with Tamura output transformers, D3A CCS loaded input, direct coupled EL34 pentode follower driving the 211 grid. I built one pair as a one-off, but people who hear them keep asking me to build a pair for them, so on pairs 4 and 5 right now (I did sneak a pair in for myself). I really need to put together a construction article on the design and build. But not in this thread or forum.
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Elsinores, of course. It seems these amps and these speakers are an incredible sounding combination, they really completely disappear so that music is just present in the room and one is emotionally drawn into it. The Elsinores are really easy to drive (flat impedance curve) and work great with a 20W amp.
Hi Joe, hope you've been well. Is there any update on the NBAC version?
Yes, worked on it yesterday and will be doing some more adjustments in the next few days. I have somebody coming on Friday to listen to it and I want it completely finalised by then. The area that I am working on is exploring the 'BBC dip' and getting the final level of the tweeter right. This is about getting the final tonal balance right and I am a stickler for that. Elsinores have always been about getting that right and it is why I find many commercially speakers woeful in this area.
Re NBAC bass alignment: As discussed before, the variations of the Elsinores drivers, that with the exception of varying the vent length, the volume stays the same and I only choose and use drivers that will work in that box. This is obviously a very different approach to that usually employed, where you pick the driver and then design the box to suit.
Here we have a box design and I look for drivers that will work.
The reason I point this out is because the alignment we get with the NBAC is definitely a bit different, but I am happy to say that it works. But finding the right word is difficult, but I believe I have described the NBAC as being on the "fruity" side, but it works musically very well and the rest of the system balance takes that into account. This takes time.
So I have them running in my system right now and Friday is the day.
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Yes I am. In the end it worked for me better than the ceramic/aluminium tweeter. I did that design for Steve in Melbourne and passed the design on to him. This is one of the reason it has taken so long.
We have spent a number of days to the NBAC Elsinores and have had some friends over. I am now ready to publish the all important final crossover design and working on that right now. The box is exactly the same as the MFC polycone version, indeed it is possible to change an MFC into NBAC by replacing the eight main drivers and the crossover. Whether anybody would want to do that, I do not know, but it would be interesting if somebody did and then reported back here on the thread.
The next post will be the NBAC Crossover schematic & details.
The next post will be the NBAC Crossover schematic & details.
Although below is beta, don't worry too much about that. All it means is that a more full (as with the other versions) tabulated version of the schematic is coming and it will add detail but not change values. The information will be similar as before, so look at the MFC as a guide. Trust me, gone over it, and over it, as you must do, to get it to this point. The crossover is still external and no more changes to be made. Perhaps one point need to be made about crossover components and the quality of parts, they should be of course very good, but take especially care with the 1.8uF capacitor on the tweeter. I favour real copper caps and one you could consider is the Miflex KPCU03F518J - not cheap I know, but not Duelund price either.
https://www.hificollective.co.uk/catalog/miflex-kpcu03-1-8uf-250v-kpcu-copper-foil-capacitor.html
Re 20W resistors, stack 10W wire-wound resistors that are available everywhere. By stacking values you can get close to the target value and maybe even add a third, these resistors are cheap. Again, the DC resistance that the 18mH coil will have needs to be taken into account when adding series resistance to get as close as possible to the 6R6 target. My inductor had 3R2 and I used two 6R8 10W in parallel to get to 3R4 and then the 3R2 of the inductor was added and that gave me 6R6. So use common sense and if you need any help, everybody here will only gladly help. We all can get confused sometimes.
BTW, if any of you are in the neighbourhood, please feel free to drop in for a listen and then maybe report here you impressions, but even if not, come around anyway.
https://www.hificollective.co.uk/catalog/miflex-kpcu03-1-8uf-250v-kpcu-copper-foil-capacitor.html
Re 20W resistors, stack 10W wire-wound resistors that are available everywhere. By stacking values you can get close to the target value and maybe even add a third, these resistors are cheap. Again, the DC resistance that the 18mH coil will have needs to be taken into account when adding series resistance to get as close as possible to the 6R6 target. My inductor had 3R2 and I used two 6R8 10W in parallel to get to 3R4 and then the 3R2 of the inductor was added and that gave me 6R6. So use common sense and if you need any help, everybody here will only gladly help. We all can get confused sometimes.
BTW, if any of you are in the neighbourhood, please feel free to drop in for a listen and then maybe report here you impressions, but even if not, come around anyway.
Hi Joe,
Thank you for publishing the crossover. I have one question. As far as I can see, there is no RLC trap on the schematic for the break-up of the aluminum diaphragm of the Sba 17 NBAC loudspeakers. Is this solution a certain compromise of the crossover, or is it simply your opinion that this break-up is not audible?
Thank you for publishing the crossover. I have one question. As far as I can see, there is no RLC trap on the schematic for the break-up of the aluminum diaphragm of the Sba 17 NBAC loudspeakers. Is this solution a certain compromise of the crossover, or is it simply your opinion that this break-up is not audible?
I have another question concerning the new crossover since I am still waiting to start on my ULD Elsinore build. Your recommendation on the tweeter crossover cap on the NBAC version is the Miflex whereas the ULD version uses the Ansar True Copper Max. I know the Miflex caps are excellent, I use the KPCU-01 600V in several of my tube amplifier builds due to their high performance/cost ratio. In fact, bypass them with a Duelund 0.01 uF Silver Foil PIO and they are close to the Duelund in overall performance. Anyway, I am curious if you found a sonic benefit to the Miflex caps over the Ansar, or is it too early to tell?
Thanks.
David
Thanks.
David
