Bd-15 frequency response (BD-Design)
by madprofessor 
, 27777 Ganderkesee, Germany, Thursday, April 19, 2007, 13:10 (6226 days ago)
Hallo Bert!
Are there any measurements of the frequency-response of Your BD-15 drivers, mounted in the Reference-set up, but without any crossover existent?
I'm intersted in using that system for bass up to 400Hz
Thanks in advance
Best regards
Stephan
Bd-15 frequency response
by Bert 
, Thursday, April 19, 2007, 22:01 (6226 days ago) @ madprofessor
Hi Stephan,
Are there any measurements of the frequency-response of Your BD-15
drivers, mounted in the Reference-set up, but without any crossover
existent?
I do not have any and making one would not be relevant as this will show you the interaction within my listening room...
The response starts to roll-off slowly at around 120-150Hz down to 30Hz at -9dB. Under room conditions the bass will roll-off less steep though...
Above 150Hz the respons is flat up to 800Hz (in all directions, no serious breaking ups) and from there starting to have less dispersion but still linear to where you do not want to hear them anymore as it then does not act as a piston anymore.
Crossing at 400Hz (minimal 12dB, better 24dB but depending on what you are going to use on top of that) is no problem at all.
Bert
--
BD-Design - Only the Best!
Bd-15 frequency response
by madprofessor , 27777 Ganderkesee, Germany, Thursday, April 19, 2007, 22:23 (6226 days ago) @ Bert
Hallo Bert!
Thanks for Your quick answer!
Is the roll-off You mentioned with the Oris 150 horns?
I want to use this bass-system together with a midrange/tweeter- hornsystem.
No problem to use two amps and a passive crossover.
Important is the flat response from 150 to about 600 Hz, to have a smooth transition and also to have the same dynamics and dispersion as from the midrange/tweeter system.
Best regards
Stephan
Bd-15 frequency response
by Bert , Thursday, April 19, 2007, 22:57 (6226 days ago) @ madprofessor
Stephan,
Is the roll-off You mentioned with the Oris 150 horns?
No, then the useable response is limited to 325Hz where it starts to roll-off due to the acoustical filter (the horn) in the higher frequencies.
It can be extended to 400Hz though by using a smaller throat for the 150 in front of the bass as used today.
Important is the flat response from 150 to about 600 Hz, to have a smooth
transition and also to have the same dynamics and dispersion as from the
midrange/tweeter system.
The response is smooth up to 800Hz acting as a piston (or 900Hz, can't remember exactly) and the dispersion similar to all drivers reaching the wave length limit that gives less dispersion (mother nature causing this!).
Bert
--
BD-Design - Only the Best!
Bd-15 frequency response
by madprofessor , 27777 Ganderkesee, Germany, Friday, April 20, 2007, 11:54 (6225 days ago) @ Bert
Hallo Bert!
Thank You very much for the information supplied!
Just to understand my project: I heard several speakers using the new Thiel ceramic chassis, like Kharma, Avalon or Lumen White. I was very much impressed by the reproduction of that chassis, especially the room-information achieved. But I was less impressed by the dynamics. So I started to build a project with sperical horns. for midrange I use the Thiel C 78/6 wit a 50 cm diameter spherical horn and a very good matched rear cabinet, to have at both sides of the speaker the same acousatical impedance ( I don´t know if that´s the right English term. The German term would be "Strahlungswiderstand). For tweeter I use the Thiel C12/6 also with a spherical horn, about 20 cm diameter. I´ ve build a stand, where I can set the distances of thespeakers in all three dimensions very accurate. The midrange/tweeter-section works very good. By lack of time I use at the moment a bass-enclosure of a Focal Utopia Klone. That doesn´t of course not match the other section.
TodayI did some measurements: the crossover-point should be at about 280Hz- 320 Hz. So I think the BD-15 with the Oris 150 would match perfectly.
For the midrage/Tweeter section I want use a S.E.T. rig, maybe based on 845 or 300B, which has still to be build. For the bass-section I´ve got a good solid-state amp.
Best regards
Stephan
Bd-15 frequency response
by Bert , Friday, April 20, 2007, 14:54 (6225 days ago) @ madprofessor
Stephan,
Thank You very much for the information supplied!
Thank You for your detailed description! Pictures usually show things more easy though... :wink:
Bert
--
BD-Design - Only the Best!
Bd-15 frequency response
by madprofessor , 27777 Ganderkesee, Germany, Friday, April 20, 2007, 15:12 (6225 days ago) @ Bert
Hallo Bert!
Of course You are right! Here is a picture of the speakers under construction.
Best regards
Stephan
[img]images/uploaded/image266.jpg[/img]
Bd-15 frequency response
by jw70 , Friday, April 20, 2007, 12:34 (6225 days ago) @ Bert
Hallo Bert and Stephan,
my name is Jürgen and Im from germany.
This is a interesting thread for me.
I have Altec 515 bassdriver in an reflex cabinet
and Altec 288 drivers with tactrix horns for mids and hights.
I cross at 500HZ with 12dB
My plan is to screw the BD 15 Horns in front of my bass driver
to get more efficiency and a better integration to the Altec 288 driver, so my bass
cabinet will look like the reference ultra. I will further close my bassreflexports, because I want the Altec just for 150HZ to 500Hz.
Below 150Hz I will take a subwoofer.
My question: will I get a flat responce from 150Hz to 500Hz
from my Altec 515 bass driver with the BD 15 horn in front of it?
Best regards
Jürgen
Bd-15 frequency response
by Bert , Friday, April 20, 2007, 14:59 (6225 days ago) @ jw70
Hi Jürgen,
My question: will I get a flat responce from 150Hz to 500Hz
from my Altec 515 bass driver with the BD 15 horn in front of it?
No, it will give a boost (about +9dB) in the lower midrange with a center frequency of 300-350Hz. This "peak" can be EQ-ed rather simple with a single notch to get a flat response from almost anywhere in the bandwidth. 150-500Hz should therefore be possible...
Bert
--
BD-Design - Only the Best!
Bd-15 frequency response
by jw70 , Friday, April 20, 2007, 15:50 (6225 days ago) @ Bert
Hallo Bert,
thank you for you answer.
To make it clearer I add a pic, where a frequence reponse of an
Altec 515G in different fronthorn enclosure can be seen.
there is always some peak between 200 - 400Hz,
Am i right you mean this peak?[img]images/uploaded/image268.jpg[/img]
Bd-15 frequency response
by Bert , Friday, April 20, 2007, 16:00 (6225 days ago) @ jw70
Am i right you mean this peak?
Yes, but more enhanced which is depending on the size of the throat. With the Oris 150 the throat is smaller compared to the standard Altec front horns which are not much smaller than their total cone area.
Bert
--
BD-Design - Only the Best!
Bd-15 frequency response
by jw70 , Friday, April 20, 2007, 18:24 (6225 days ago) @ Bert
Hallo,
with enhanced, do you mean more peak in a spezial frequency, for example 300Hz,
or more peak from 150-500Hz but relativ flat?
I can be wrong, but it seems to me that the throat size of the BD 15 Horn
is about 25cm in diameter, because you cut off a bit from the Oris 150 with 20cm throat size, and this is not much less than the throat size
of the original Altec 825 or 816 cabinet.
Here is a pic of the 816 cabinet
[img]images/uploaded/image270.jpg[/img].
Jürgen
Bd-15 frequency response
by Bert , Friday, April 20, 2007, 22:24 (6225 days ago) @ jw70
Jürgen,
with enhanced, do you mean more peak in a spezial frequency, for example
300Hz, or more peak from 150-500Hz but relativ flat?
A peak at a certain frequency (like a band-pass woofer enclosure).
I can be wrong, but it seems to me that the throat size of the BD 15 Horn
is about 25cm in diameter, because you cut off a bit from the Oris 150
with 20cm throat size, and this is not much less than the throat size
of the original Altec 825 or 816 cabinet.
It is about 23cm in diameter (415cm2) and the total area of the Altec is larger as far as I know and the horn is more straigth (less curved).
Bert
--
BD-Design - Only the Best!
Bd-15 frequency response
by jw70 , Sunday, April 22, 2007, 08:27 (6223 days ago) @ Bert
Hallo Bert,
yes you right, the altec horn throat is bigger, about 650-700 cm2 I think.
And it is straigher too.
So if I understand it right, this resultes in an stronger peak at about 300Hz.
Is it possible to calculate the needed notch without measuring,
because I have not such an equipment.
Bye the way there is a nice site from mr. vallieur,who built
a. midbass speaker with an frontloaded Altec 515.
He measured the same peak we are talking about.
http://www.vallieur.de
Jürgen
Bd-15 frequency response
by Bert , Sunday, April 22, 2007, 16:35 (6223 days ago) @ jw70
Hi Jürgen,
Is it possible to calculate the needed notch without measuring,
because I have not such an equipment.
That will be hard because of the many parameters influencing the filter. The impedance of the enclosed driver as major factor. You could make a correction in front of your amplifier (RCA input) which would be less depending on these impedance changes. Another problem is to know the precise location, width and amplitude of that peak so that you know how much you need to correct...
More easy and exact done with the help of some measurent tools (all speaker builders should have these tools to see what they are doing anyhow..)
Bert
--
BD-Design - Only the Best!
Bd-15 frequency response
by jw70 , Sunday, April 22, 2007, 16:57 (6223 days ago) @ Bert
Hallo Bert,
I think what you say, seperates the amateur from the pro.
If it dont go to far, can you say me or give me a link,
What kind of equipment do i need to measure such things.
regards
Jürgen
Bd-15 frequency response
by Bert , Wednesday, April 25, 2007, 17:32 (6220 days ago) @ jw70
http://www.kirchner-elektronik.de/
Cheap and useable if you have a PC with soundcard and a free USB port and a separate CD or DVD player to play the measuring signals.
Bert
--
BD-Design - Only the Best!
Bd-15 frequency response
by jw70 , Friday, April 27, 2007, 07:36 (6218 days ago) @ Bert
Thank you Bert!
So it isn´t expensive anymore to make you own measurements.
Thats good news!
Jürgen