Widerange Driver 2-Way project

[LageB]

Hello,

I hope someone here could have mercy and read through this “report” and give comments on my “In the Wall speaker project”.

My Questions are mentioned at the very end of this loong post, but first, you have to read through (AA), (BB), (CC), (DD) under.


(AA) First, some general important factors (as I understand it) Please correct me if I am wrong.
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(1) Cone excursion seems to start to increase drastically below the free air natural roll off for most Drivers. It is an exponential increase that starts before f3. Simulating with LspCAD indicates this is the case regardless whether you put the driver in a sealed or BR, although BR has the advantage of having a temporary “dip” of low cone excursion at fs.

(2) Sealed box has best transient response among all enclosures - but limited power handling and uncontrolled cone excursion at lower frequencies - thus higher distortion.

(3) In case of sealed, the larger box is the better as regards to transient response. But, larger box is worst in terms of cone excursion.

(4) The influence from any box design is in most cases “negative“ for midrange, namely reflections from inside of box disturbs the driver. As far as I understand it, this is one of the advantage of an open baffle where the driver can “breath freely”?

(5) The ability to extend Low frequency response from single driver with smallish Xmax is an art which I admire and obviously works fine in many designs. However for plenty “bass slam” I believe it is important to move some air. In this project I will simply let a woofer do that job.

(6) I do not want to use passive XO because I would not know how to do it well. Through answers here and elsewhere I realized that the complex interaction Driver-Enclosure-XO(passive) , especially in low frequencies is a no-no area for me. (To add super tweeter with Highpass cap is different matter though)

(7) Lately, the availability of flexible Active Digital XO including EQ, seems to me offer very exciting possibilities to address some of limitations listed above.


(BB) My idea, a 2-Way speaker with Full Range Driver + Woofer:
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(a) Basic concept in this project, is to take advantage of sealed/IB (excellent transient response, small group delay etc) and at same time making effort eliminating the problems of sealed/IB as much as possible.

(b) My idea is to use the FR driver ONLY within the limited frequency range where the driver has flat free air SPL.

(c) The supplementing woofer would not be stressed much lower than its f3 point.

(d) The Fullranger should however cover very wide frequencies range, if possible from 90Hz and above, eliminating crossovers in that fundamental range of voice and most instruments.

(e) I found one Full Range Driver capable of a+c above - and that is Fostex F200A.

(f) Digital High Pass XO for the Fullranger to effectively ”chop off” signals below 90Hz

(g) Since the F200A shall be relieved from all its bass duties, I will use the F200A in an Infinite Box, or rather an Infinite Baffle since this in Wall Speaker Project. I had for a long time been considering to make a small sealed enclosure for the Fullranger that would be hidden behind the wall. But, now I believe an IB is a better choice because the 2-way concept allows me to cut off low frequencies for the Fullranger.

(h) The woofer will be placed in a rigid sealed enclosure made of concrete, in order to eliminate Sound and Vibrations inside the wall. Woofer enclosure will have a Qtc somewhere between 0.5-0.7. I can not make an Infinite Box for the woofer due to space limitation inside the wall.

(i) The woofer will have both Low Pass XO as well as High pass, for the limited bandwidth only 35-90Hz

(j) The woofer is a Scan Speak 25W/8565-01 with fs=19Hz, Qts=0.34


(CC) Expected merits with my 2-way Wall Speaker targeted flat 35Hz-20,000Hz
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1.Infinite Box/Baffle for the FR
a) To avoid all ”Box influences” for excellent reproduction of bandwidth 90Hz-20,000Hz.
b) Best transient response
c) No need for complicated Box

2. Digital XO for both FR and Woofer
a) Very flexible XO for tuning & tweaking.
b) XO is no problem at 90Hz (compared to using passives)

3. Cut off Frequencies at 90Hz for the Fullrange driver F200A
a) Limit long cone excursion movement to enable superior performance for Midrange and HF
b) Very flat SPL whole bandwidth 90Hz-20,000Hz
c) High power handling
d) Highpass XO at 90Hz is low enough covering most sensitive bandwidth especially Voices
e) XO at 90Hz is low enough to make the positioning of woofer less critical

4. Highpass Cut off Frequencies at 35Hz for Scan Speak 10” Woofer (48dB/Oct)
a) Limit Cone excursion and distortion
b) Higher power handling
c) In my taste, sub 35Hz is not that critical in a majority of music I listen to. Plus, it is more difficult to tame room interaction in that lowest region. I think that steep Highpass XO at 35Hz may actually give an illusion of more ”tight” Bass.?
d) In future, I may add a subwoofer with XO Lowpass at 35Hz, to be used when listening to Classic or Organ music.

(DD) Wall Speaker system details:
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a) The infinite Box for the F200A is not really infinite. The space behind the driver (inside wall) is about 1000L which I will fill with insulation to avoid noise from inside the wall leaking out to the listening room. The space closest to driver will however be free from insulation.

b) The baffle will be the wall itself. However part of the wall around the Driver will be thick MDF, in which the driver is fastened. Measures will be taken so that Baffle/Wall shall be rigid enough to avoid any vibrations.

c) The fullranger F200A will be positioned on the wall at ear level, about 110cm above floor.

d) The 10” SS woofer will be placed in an sealed enclosure with Qtc somewhere between 0.5-0.7. The enclosure will be made by concrete (it will truly become a permanent part of the wall & house.) From the listening room it will appear as if both the F200A and Woofer are flush mounted on the wall.

e) The woofer will be positioned under F200A and as close to floor as possible in order to gain boost both from baffle/wall and floor. The c-c vertical distance between F200A and woofer will therefore be about 80cm.

f) I will use Digital XO which will be Behringer DCX2496 and biamping together with inexpensive multichannel digital amplifier, which will solve the problem of different sensitivity of F200A and the 10” Woofer. I will not describe this digital system here, but you can read about it in Newform Homepage here:

http://www.newformresearch.com
or
http://www.newformresearch.com/digital-amp-packages.htm (I am copying Newform’s concept as it is)
The Behringer has also some EQ possibilities besides its XO, which might be handy for in-room-tuning.


(QQ) Questions
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- Well, what do you think? Does my project makes sense? Have I overseen something important?
- I made an assumption that IB would be somehow superior for Midrange - but is it the case ?
- Do you see foresee problems with integrating F200A IB / Scan-Speak 10” Sealed woofer?
- Any other pitfalls ??

Thanks for reading this post. Looking forward to hearing any comments

Best regards
LageB

[leifislive]

It may be too late, but anyway...
looks like nobody read it...


basically correct sounding to me, some buts:
- 35Hz highpass 4th order might be audible group delay, but you will find out whether you hear it.
- !!!! GROUP DELAY IS WORST AT LOW FRQUENCIES!!!! our ear can tell very very short time differences between right and left ear, but whether you can actually hear a 4th order 300/3000 crossover (what I assume you would like to avoid)...? you should try www.winabx.com and find out in a computer simulated double blind test. fullranges might be prefered by folks because of their beaming at higher frequencies and therefore reduced room/baffle interaction... but with your kind of wall system you have a perfect solution for these problems anyway...

- do you like full ranges? I don't, they don't sound neutral to me... (I am a "part time" violoncellist) therefore, I would have thought about a at least three way project when thinking about such a extreme construction...


if you like them, have fun, digital xo, are an easy thing...

leif