Choice of BD15 for our High-end Hifi project? (BD-Design)
by Jose Hidalgo 
, Sunday, April 15, 2007, 17:38 (6230 days ago)
edited by unknown, Sunday, April 15, 2007, 18:24
Hello everybody, greetings from France. 
Please allow me to introcuce myself.
I'm a part of a small team of friends working on a High-end, Home-Hifi, 3/4-way active, DIY speaker project (max SPL about 105dB, source a fine-tuned PC Audio with a Lynx TWO-B card, everything software-EQ'ed with IZotope Ozone, and some of the best lateral-MOSFET DIY amps you can dream of).
We are aiming to find some of the best modern drivers the technology has to offer today, regardless of their cost (well, *almost* regardless of course ! unfortunately we have a budget ). For example, for the mid we will probably work with the Thiel-Accuton C90-T6, which seems to be just one of the best modern mids out there. Now we are aiming to find a bass or mid-bass driver that will go up to 200-250 Hz and catch up very nicely with the Accuton.
We are very cartesian people, so we mainly believe in the technical specs (physics are physics, no miracles), in the optimization process (specs are nothing without a good measuring/optimization phase) and in the final results.
For this, our choices are as follows :
- 12" or 15" : not more than 15" because most 18" drivers will have trouble going up to 200-250 Hz. And not less because subjectively we do not want less than 12".
- Electromechanical specs close to Accuton's ones in order to facilitate a seamless active crossover (this includes a rigid membrane, a high BL but also a quite low Mms, a low Rms, a underhung motor, etc.).
We have searched... a lot. And when I say a lot, I mean... a LOT. We have looked at a bunch of driver manufacturers from all countries. Most of their drivers just don't fit our specifications (BL too low, Mms too high or not rigid enough, Fs too low, Vas too low...). And the very few of them that could eventually fit are either too expensive (Fertin 30EX...) or almost impossible to find (JBL 2220J, 2220B, 1500AL...).
And our search has leaded us... here, to the BD15. 
Now can the BD15 be THE driver we have long dreamed of ? Maybe... we hope so ! Its T/S parameters are very good indeed. But of course that's just the beginning.
So to begin with, we'd like to have your comments (positive I hope ) on the relevance of the BD15 choice for a High-end Hifi application up to 200-250 Hz, crossing over with an Accuton C90-T6.
After that, we'd like your advice on the best enclosure type for the BD15. For example, most peope today just go bass-reflex without even knowing why. Big sealed enclosures (Qtc = 0,50) have also their advantages (group delay / better impulse response). We do not have a preference here, so we really would like to hear your best BD15 enclosure advices for our application. BR or sealed ? Damped or not damped ? How ? Where ? When ? Etc.
Of course, although we're some very passionate (and crazy) guys, we're not professionals and we can make mistakes. But hey, that's just part of the fun of it don't you think ? :wink:
Thanks in advance and best regards,
Jose
P.S.1 : I have read that the early BD15's needed some coating with glue. I assume all the new BD15's are ready to use and don't need any additional work ?
P.S.2 : Is there a way to lower the BD15's impedance ? WinIsd says it's 20 Ohms, which is very high !! (of course we could put 2 BD15's in //, but that would also double the price ). Wouldn't it possible to have a version of the BD15 with a lower impedance ?
Choice of BD15 for our High-end Hifi project?
by Bert , Monday, April 16, 2007, 00:13 (6229 days ago) @ Jose Hidalgo
Hi Jose,
So to begin with, we'd like to have your comments (positive I hope
) on the relevance of the BD15 choice for a High-end Hifi application up
to 200-250 Hz, crossing over with an Accuton C90-T6.
The BD15 is fast and dynamic enough to follow the Accuton (reading its TS-parameters). Should work out more than okay...
After that, we'd like your advice on the best enclosure type for the BD15.
For example, most peope today just go bass-reflex without even knowing why.
Big sealed enclosures (Qtc = 0,50) have also their advantages (group delay
/ better impulse response). We do not have a preference here, so we really
would like to hear your best BD15 enclosure advices for our application. BR
or sealed ? Damped or not damped ? How ? Where ? When ? Etc.
This depends if you want to use a subwoofer below or not. Without subwoofer a dampened 165-225 liter reflex system with relative large ports would be the best choice for the BD15 (even better with a matrix inside).
P.S.1 : I have read that the early BD15's needed some coating with glue. I
assume all the new BD15's are ready to use and don't need any additional
work ?
They are ready to play.
P.S.2 : Is there a way to lower the BD15's impedance ? WinIsd says it's 20
Ohms, which is very high !! (of course we could put 2 BD15's in //, but
that would also double the price
version of the BD15 with a lower impedance ?
It is not possible to get a BD15 with a lower impedance. These are not 20 ohms either (15ohm flat with impedance correction) but still, you are making an active system, so what's the problem then? :wink:
Bert
Bert
--
BD-Design - Only the Best!
Choice of BD15 for our High-end Hifi project?
by Jose Hidalgo , Monday, April 16, 2007, 01:07 (6229 days ago) @ Bert
Hi Bert, thanks for that quick answer.
This depends if you want to use a subwoofer below or not. Without
subwoofer a dampened 165-225 liter reflex system with relative large ports
would be the best choice for the BD15 (even better with a matrix inside).
Well, there will eventually be a sub (a real one : JBL W15GTI, Adire Tumult, Beyma 18LX60...), but we'd prefer to use it only for HT applications. For Hifi, if the BD15's can go low enough, why would we want to turn on the sub ? I believe that in most music CDs there's almost no information below 30 Hz (provided you don't listen to big organ music of course). Take a look at these five graphs ( http://petoindominique.fr/php/caisson.php , scroll down the page). No problem if you don't understand french, the graphs are self-explanatory !
So we would have two separate Ozone configs : one Hifi config, without sub and with a low crossover for the DB15 (about 30 Hz), and one HT config, with a sub and with a slightly higher crossover for the DB15 (about 40-50 Hz).
It is not possible to get a BD15 with a lower impedance. These are not 20
ohms either (15ohm flat with impedance correction) but still, you are
making an active system, so what's the problem then?
All right, 15 Ohm is good. The only eventual problem was related to our DIY amplifiers' max power. I have contacted their creator, and he has just answered me at the moment. In fact they can deliver 160W/8Ohm and 80-90W/16Ohm. Theoretically (WinIsd), with a BD15 @ 80W in a 165L BR enclosure tuned @ 38,9Hz we can already get 105dB @ 30Hz, so that should be enough for a Home Hi-Fi application, even a High-end one. :wink:
Regarding the enclosures, your BR enclosures would suit us well. However, I have noticed (WinIsd) that a big BR enclosure (165L or more) will create a lot of group delay under 60 Hz, while allowing us to gain very few SPL (which we don't want since we're already over 105). Moreover, the Xmax (6mm, right ?) will be exceeded before 30 Hz. A smaller enclosure (120L ?) would allow us to have less group delay, at the price of a single dB @ 30 Hz (104 instead of 105 - big deal ), and with an Xmax exceeded under 30 Hz. Wouldn't that be better for us ? Or do you see other problems with a smaller enclosure ?
One last question : does someone have some measurement graphs for the DB15 ? We'd really like to have a look at the distorsion and impedance graphs for instance. I hope it's possible. Thanks in advance.
Choice of BD15 for our High-end Hifi project?
hi Jose Hidalgo
just wonderig ( it seems you took almost a decision and it's not subject of your threat ) but i would like anyway to ask:
For example, for the mid we will probably work with the Thiel-Accuton C90-T6, which seems to be just one of the best modern mids out there.
did you come to this conclusion by hearing it,( taste caNot be discussed ) ore just reading abought it, as it is used by many high-end manufactures out there ? i heard these accuton drivers at a view oportunities, and i must say: :wacko:
these sound to me horribly hard, like cristal breaking, no deepness and sounstage at all.... just my opinion.
rds Angelo
Choice of BD15 for our High-end Hifi project?
by Jose Hidalgo , Monday, April 16, 2007, 01:18 (6229 days ago) @ angeloitacare
edited by unknown, Monday, April 16, 2007, 01:21
Just a quick reply to Angelo :
did you come to this conclusion by hearing it,( taste caNot be discussed
) ore just reading abought it, as it is used by many high-end manufactures
out there ? i heard these accuton drivers at a view oportunities, and i
must say: :wacko:
these sound to me horribly hard, like cristal breaking, no deepness and
sounstage at all.... just my opinion.
The big problem with listening is that it is totally subjective. You didn't listen only to a pair of C90-T6 : you listened to the whole speaker cabinets, the amps, the source, and of course, the room. How do you know objectively that it was the fault of the mids ? You just can't. There are no ideal listening conditions. I caNot judge your listening conditions because I wasn't there. I could only objectively judge a pair of speakers if they were in my own living room.
This being said, and without opening up a debate because this is not the subject, please know that we are pursuing a "monitor" approach in our project. The "monitor" sound is quite different from the traditional "Hifi" sound. It's very straight and analytical. You do hear everything (the good and the bad - some bad recordings do even become difficult to hear !), and this really requires some hearing adaptation because it may seem too "hard" or "dry" at first hearing (like cristal breaking ? ). Have you listened to a Lynx TWO card in an audio PC ? You will probably get the same impression because your ears aren't used to it. I did... in the beginning. After that, it's just pure happiness. :wink:
Choice of BD15 for our High-end Hifi project?
Hi Jose Hidalgo
the most memorable listening experience i had last year in italy, at the manufacturer of extraordinary tube amp's, u propably don't know them, as they are not well known:
http://www.angstromresearch.com/pre_ita.html
i listened in a relatively small room,i don't remember the whole audio chain, but they where using their own amp's, ( pre and power cost 23th euros) and avalon medium sized speakers, ( i don't remember the model ) with these accuton drivers. The impression i had, certainly i will not forget that soon. But u are right, there are many factors to take in consideration, so it is all very subjective.
rds Angelo
Choice of BD15 for our High-end Hifi project?
by Jose Hidalgo , Monday, April 16, 2007, 01:41 (6229 days ago) @ angeloitacare
Hi Angelo,
I was once a tube amp enthusiast (I owned a Jadis Orchestra... heck, I still own it, it must be somewhere under the dust ). But I'm not a tube enthusiast anymore. Tubes sound good to the ears... and look bad when you measure them. This is well known. Lateral MOSfets can do it much better... if correctly used of course. But it really is another story. Regards. :wink:
Choice of BD15 for our High-end Hifi project?
hi José Hidalgo
i made my own experience recently , buying a 10th$ tube amp, and tried just for curiosity a Trends TA10.1 Class T amp , cost's a mere 100$ . The difference is so hudge, i guess, i'll never again buy a tube amp. 
rds Angelo
Choice of BD15 for our High-end Hifi project?
Hi Jose
You just go for that bass driver. It is until so far the best 15" there is among those I have used over the years. Period. 
Given the right cabinet etc. you can only expect the best from it. Trust me.
Good luck with your project.
GC
Choice of BD15 for our High-end Hifi project?
by madprofessor 
, 27777 Ganderkesee, Germany, Saturday, April 21, 2007, 20:30 (6224 days ago) @ Jose Hidalgo
Hallo Hidalgo!
I´m working myself at a speaker-project, containing the Thiel Accuton C78/6 and C 12/6, both with sperical horns.
For myself I consider the BD 15 as a very goodchoice. I will keep You informed about my results!
Best regards
Stephan
[img]images/uploaded/image271.jpg[/img]
Choice of BD15 for our High-end Hifi project?
by Jose Hidalgo , Monday, April 30, 2007, 20:26 (6215 days ago) @ madprofessor
Hi everybody, I'm still here. :wink:
I was just wondering how the BD15 can achieve such remarkable results (low distorsion, no breakup problems) with such a light membrane (Mms only 66g !). This means the membrane must have an exceptional stiffness / a very high Young module.
However, the diaphragm material seems to be a well known-one : paper.
So I was wondering, since paper alone probably can't achieve such good results (physics remain physics), is there some kind of secret recipe that Bert is using to increase the BD15 diaphragm stiffness ?
For instance, other manufacturers use different kinds of carbone fibers, with pretty good results (e.g. Davis 40RCA15). The BD15 doesn't. So in your opinion, where's its secret ?
Bert, I'm not asking for your secret recipe of course : I'd just want to know if there is actually one (so the BD15 cone wouldn't be just made of plain paper), or if there is not (and in that case I wouldn't understand how can a light membrane achieve such results without noticeable breakup problems).
Thanks for enlightening us all.
Jose
Choice of BD15 for our High-end Hifi project?
by Jose Hidalgo , Wednesday, May 02, 2007, 14:07 (6213 days ago) @ Jose Hidalgo
edited by unknown, Wednesday, May 02, 2007, 14:11
Still waiting for an answer... 
I have another important question : some friends of mine are trying to convince me that the BD15's Xmax would be only of 3.5mm ! :shame:
They are saying this :
Coil height - 7mm, Air Gap height - 14mm
So Xmax = (Air Gap Height - Coil Height)/2 = (14-7)/2 = 3.5mm
However, I say this :
Xmax = Vd/Sd = 513/855 = 0.6cm = 6mm
And Bert even says (if I remember well) that Xmax = 7mm...
so I'm asking : WHICH ONE IS CORRECT PLEASE ??? What is exactly the BD15's Xmax ?
Thanks.
PS : of course we're talking about Xmax (max linear displacement on a given direction - peak to peak divided by two if you prefer), not Xdamage.
Choice of BD15 for our High-end Hifi project?
by Bert , Wednesday, May 02, 2007, 14:25 (6213 days ago) @ Jose Hidalgo
Jose,
PS : of course we're talking about Xmax (max linear displacement on a
given direction - peak to peak divided by two if you prefer), not Xdamage.
7mm p/p (standard value as given by most loudspeaker manufacturers). Due to tolerances this migth be less in one direction hence the given safe value of the Vd.
Bert
--
BD-Design - Only the Best!
Choice of BD15 for our High-end Hifi project?
by Jose Hidalgo , Wednesday, May 02, 2007, 14:39 (6213 days ago) @ Bert
edited by unknown, Wednesday, May 02, 2007, 14:45
Thanks Bert. However, there's one last thing I don't understand. As far as I know, Vd = Xmax * Sd IF the considered Xmax is not the p/p but half of it. The official definition of Xmax is "the measure of a speaker cone’s maximum excursion in one direction while maintaining a linear behavior".
For instance for a TAD 1601a (Xmax = 0,8cm on a given direction - or 1,6cm p/p if you prefer), Vd = 0,8 * 881 = 705.
For a Beyma 15LW30 (Xmax = 0,7cm on a given direction - or 1,4cm p/p if you prefer), Vd = 0,7 * 880 = 616.
So for the BD15 (Xmax = 0,7cm p/p = 0,35cm on a given direction), Vd should be equal to 0,35 * 855 = 299, not 513.
If we take the tolerances into accound, the safer value of your Vd should be equal to 0,3 * 855 = 256,5, not 513.
So saying that your Vd is 513 would be definitely incorrect.
Where am I wrong ? (I'm not trying to trick you, I'm just trying to understand things)
Choice of BD15 for our High-end Hifi project?
by Bert , Wednesday, May 02, 2007, 14:58 (6213 days ago) @ Jose Hidalgo
Jose,
Last answer regarding to the BD15 (as you do not seem to do your home work well).
For a Beyma 15LW30 (Xmax = 0,7cm on a given direction - or 1,4cm p/p if
you prefer), Vd = 0,7 * 880 = 616.
This driver (look up the PDF-file from Beyma so that you can check properly)
Coil heigth of 17mm minus Pole plate thickness of 8mm leaves 9mm peak to peak linear excursion. To my calculations this comes to:
BD15 - Xl (7mm p/p) times Sd equals 616 cm3
15LW30 - Xl (9mm p/p) times Sd equals 792 cm3
Did you ever wondered how little more output in dB's you get with the mentioned differences? Have you any idea how much (or should I mention little) +3dB sounds louder?
Start wondering about that first and you will fully understand my sentence below...
Bert
--
BD-Design - Only the Best!