Choice of BD15 for our High-end Hifi project? (BD-Design)

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 ?

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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 ). Wouldn't it possible to have a
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!

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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

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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.

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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:

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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

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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:

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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

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Hi Peter,

Hi Jose (José ?),

Jose without accent (my spanish origins).

You ended up in this forum, because of a BD15 driver. That's okay.
You should know though, that a few of us are after one thing only : 1:1
music playback. For us this means high efficiency (112dB) (DIY) horns like
the Orphean. Everything else is dull sounding ...

Yes, I can perfectly understand that. However for a lot of good reasons our project is a no-horn project. Please don't take it personally but we are not here to discuss that. :wink:

Maybe read the first post of this :
http://forum.bd-design.nl/index.php?id=13600
It shows that analythical sound can go too far. But if you want ... it
exists.

I must admit that I don't understand why you did all that hard and surely beautiful development work. We are currently using foobar2000 with its Kernel Streaming component, and it gives us what we want : bit-perfect playback (verified) under Windows XP (who needs Vista anyway ? ). We don't ask for more.

Then, although the BD15 is rated at 30Hz, you better anticipate on 26,5 Hz
(in-room) straight with the downfireing ported BD15 Ultra (includes horn)
cabinet (which I have as the so far only one I think), or a straight 25Hz
in Swing enclosure (containing two push-push / pull-pull BD15's) in a
small cabinet.

We will design our own cabinets, so that's another story. Thanks anyway.

Next I can tell you that *most* CD's have sub-low information. Whether you
want to hear/feel it is another thing ... I do. And, if you X-over the
sub(s) properly to the steep roll of of the BD15's, it just does not
destroy the very tight bass of the BD15's.

I believe that most CDs (well, most of the CDs *I* listen to) don't really have sub-low information. But you're right, some CDs do have it (we're not here to discuss how many of them, that would be useless). Anyway, the subwoofer will allow us to try to feel the difference with or without it. So in the end we'll always have the choice to turn it on or not. Don't worry.

Last for now ... if you guys are into time alignment, note that the
overall "construction" of a BD15 Ultra cab with an Orphean on top of it,
not only looks good, but keeps on looking good when you want to align the
both i.e. want to attack group-delay when you sense it is there. However,
also note that there is a "pure" solution for that on the horizon, by
delaying "channels" (bass / mid-high) in the digital domain without any
DSP stuff molesting the sound (data). My player will be doing that
eventually. It needs a pair of synchronized stereo DACs though.

Of course we are into time alignment. But it won't be a problem because like I said, we are using IZotope Ozone 3. You might think that it molests the sound (data). Actually it doesn't because it works internally in 64 bits. Check it out and give it a try, it's the best there is as of today IOHO : http://www.izotope.com/products/audio/ozone/

Regards,
Jose

P.S. : we are getting away from the subject which is and must remain the BD15. Thank you.

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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

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Ah, Peter, Peter...

If you are not open to THIS group of people just doing the same as you
claim you do ... that's okay. But as long as you state that Foobar is okay
for you, you just don't know about the basics yet.

1°) I'm a very open guy (want a proof ? I'm discussing with you right now ), so I don't see the point.
2°) You have absolutely no right to judge me. Come back to earth !
3°) foobar with Kernel Streaming activated gives absolute bit-perfect playback. We have demonstrated this from A to Z with a strict protocol, there is not a single bit difference between the generated output and the initial input. So I guess we know a bit (a bit... mwahahahaha ) about what you call the basics.
4°) Give IZotope Ozone a try. It's a professional software (the same kind as the studios use to master the CDs that *you* listen to), and you just won't get better than that by yourself alone. All right, it costs $249 which is much more expensive than your own player. But hey, there's an evaluation version, so what are you waiting for ?

Why I started working on that player ? because Foobar gives the most lousy
playback. Please think that over before you think you can judge any speaker
and state that listening is subjective.

Well, until you can objectively demonstrate that foobar with Kernel Streaming activated is really lousy, I will say that you are totally wrong. And unlike you, I can prove it : http://www.homecinema-fr.com/forum/viewtopic.php?t=29816403 (sorry if you can't speak french - the topic demonstrates in a certain number of scenarios that foobar doesn't change a single bit of the audio flow).

We can also take your software, make it pass the same scenarios, and see which one of the two is the more lousy (just kidding, we don't have time for that, and I'm sure your software is good, but again this is not the subject here)

If you think it's unrelated ...
Okay ... it is. Don't let me disturb you. :rolleyes:

I'm sure you are a very kind guy Peter (a bit harsh maybe, but kind :wink: ). But you are right : please stay within the BD15 subject. Thank you.

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Hi Jose,

I am very sorry, but I just was in the mood to delete my posts in your thread. Too much preaching.

Feel free to delete yours, which are right in the air now.

Again, sorry,
Peter

PS: Deleted the other thread as well.
Thanks for your support GC. Your post went with it.

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Hi Peter,

I'm not used to deleting my own posts, nor am I used to people deleting their own posts after a reply (here in France it is often forbidden to do that). I must admit I'm a bit surprised.

However, if you want to open another thread so that we can discuss *calmly* (!) about foobar, Ozone, your own player, etc., that could be nice and I would delete my post then of course. Up to you : maybe your player is really better than foobar, and in that case I'd love if you explained us why in another thread and in cartesian terms. Thanks in advance.

Regards,

Jose

PS : I'm still waiting for an answer from Bert to my previous questions about the BD15 (if he ever sees this post...). Thanks again.

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Hi Jose,

I'm not used to delete my own posts either. But I felt like teaching indeed. And since you didn't respond anyway ... So I thought it was silly.
Just as silly as deleting posts. I'll admit that.

Thanks,
Peter

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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]

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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

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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.

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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!

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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)

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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!

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