Big passive OB project

jerome69

Member
2008-02-18 11:33 am
Lyon
Hi Everybody,

I would like to make an other OB but with a passive crossover.
I saw this "Panomaniac thread" one year ago http://www.diyaudio.com/forums/showthread.php?s=&threadid=110583&highlight=
This project seems to me to be an OB monitor. I wanted more sensitivity and more power handling. Thus I decided to add an other woofer and a 5" driver.

After a first version of baffle :

I made a second version geometry with the eleven version of crossover.

This project was very difficult for me because a lot of problems occurs but I managed to do something that sound good, right to my ears. One year to optimize the concept. I am very pleased to present this open baffle.

The photo of the baffle
[IMGDEAD]http://img8.imageshack.us/img8/6035/bpmk11.jpg[/IMGDEAD] [IMGDEAD]http://img8.imageshack.us/img8/bpmk11.jpg/1/w769.png[/IMGDEAD]

The dimension are 102cm height x 40cm large x 30cm deep. Weight 18kg.
The drivers are :
Peerless SLS135 830669
Peerless SDS134 830656
Vifa DX25TG05-04
The frequency response -3dB 50Hz to 25kHz.
Point of crossover 500Hz and 2500Hz.
Sensitivity 82.5dB +-2.5dB.
Impedance 4ohms. Minimum [email protected]

The response curve, subtract 3dB above 13kHz.
[IMGDEAD]http://img124.imageshack.us/img124/8092/reponsefine.jpg[/IMGDEAD] [IMGDEAD]http://img124.imageshack.us/img124/reponsefine.jpg/1/w512.png[/IMGDEAD]

The impedance curve :
[IMGDEAD]http://img208.imageshack.us/img208/8237/impedance.jpg[/IMGDEAD] [IMGDEAD]http://img208.imageshack.us/img208/impedance.jpg/1/w512.png[/IMGDEAD]

Distortion
[IMGDEAD]http://img124.imageshack.us/img124/6493/disto.jpg[/IMGDEAD] [IMGDEAD]http://img124.imageshack.us/img124/disto.jpg/1/w512.png[/IMGDEAD]

Raw measurements on the baffle
[IMGDEAD]http://img124.imageshack.us/img124/5562/rawdriver.jpg[/IMGDEAD] [IMGDEAD]http://img124.imageshack.us/img124/rawdriver.jpg/1/w512.png[/IMGDEAD]

The crossover schema
[IMGDEAD]http://img515.imageshack.us/img515/6602/filtrefinetune.jpg[/IMGDEAD] [IMGDEAD]http://img515.imageshack.us/img515/filtrefinetune.jpg/1/w671.png[/IMGDEAD]
The resistance of woofer inductors should be below 0.2ohms. Use film capacitors in series.

The plan
[IMGDEAD]http://img338.imageshack.us/img338/5854/schemarls907.jpg[/IMGDEAD] [IMGDEAD]http://img338.imageshack.us/img338/schemarls907.jpg/1/w527.png[/IMGDEAD]

Don't forget to mirror the midrange and the tweeter in the second baffle. Flush mount the front tweeter and just fix the rear tweeter.

The sound ?
Bass is very defined, fast and massive. Midrange is good, well defined. This 5" midrange does his job very well. The treble works as good as it does. The soundstage is very large. The sound seems to me natural like open baffles can do.

Have fun :)
 

ttan98

Member
2006-04-04 11:24 am
Melb
Designing x-cross for a project like this is a pain in the neck and lots of tweaking as well. On top of that a working synergy of these drivers is another matter, that the sound reproduction of these drivers working in synergy after the x-crossover is finalised. You may not like the sound, fortunately you like yours.

My project is similar to yours but I use DX2496 crossover hence I don't have to spend many hours tweaking and hundreds of dollars on passive components which you don't use after the project completion. Currently finalising my set up and may ultimately design passive x-cross for this setup and compare it to the DCX.

Congras to your successful completion of this project.
 

jerome69

Member
2008-02-18 11:33 am
Lyon
Many Thank for the congratulations :) !

There was a lot work to get the sound right (to my ears). Between the two geometry of this loudspeaker, time is spent. I had almost scrapped. The challenge wasn't so easy because I wanted a high level loudspeaker.

I didn't spend a lot of money for the crossover, fortunately simulations help a lot. I have also a stock of components, I have made different loudspeakers several years ago.

The slopes of the crossovers are LR4.
 

ttan98

Member
2006-04-04 11:24 am
Melb
What makes the x-over even more difficult is that your baffle is much wider for the mid-range, the FR for the mid is difficult to equalise.

My baffle is narrower and what I did was to introduce a notch filter around 600 hz(if I remember correctly) and 3rd order BW around 1.7KHz LP and 200Hz HP( 2nd order LR).

Like you I use twin 12" woofer, this gives me lower mid bass which sound more convincing.
 

Pano

Administrator
Paid Member
2004-10-07 6:05 am
Panama
Very nice Jerome! Felicitations.

That looks like a very good OB rig. Yes, I can understand why you had some much work on the crossover. It's not easy.

Good work and very well documented - merci!

I know that you enjoy them. And you probably learned a lot, too.



(just a note. you indicate 82dB/watt. That is probably about right for 4 ohms. But let's remember that it will be near 88dB @ 2.83V - for those who are counting).
 

Pano

Administrator
Paid Member
2004-10-07 6:05 am
Panama
Yeah Dennis, you may be right.

With the single Peerless on OB I was getting in the low 80's. That's after all the baffle losses, crossover, etc.
Normally adding a second driver like this should add 6dB at the same voltage. But considering the physics of the baffle, wavelenghts, etc. - there probably won't be that much gain.
 
All passive is much harder to do. These 5" HDS are superb. They have a narrow face so MTM is a good option. My planned next project will use a 93dB HDS tweeter, twin 5" HDS (94dB) in a MTM, and 4 x 8" HDS connected in parallel / series to make it WWMTMWW in OB. Hopefully the higher XO will be passive but the lower XO will be active. Then subs to fill the lowest octaves. I have all the drivers on hand except the tweeters.
 

Elias

Member
2003-05-28 5:27 pm
Suomi
Hello,

Passive full range dipole is very rarely seen. That makes your achievement even more remarkable. It's pleasing to see someone takes the hard way and goes passive.

What do you think is the inportance of the backside tweeter to the sound in your observations?


- Elias
 

jerome69

Member
2008-02-18 11:33 am
Lyon
Hello,

I always put a rear tweeter in my open baffle.
The improvements are in the treble. You double the surface of the treble and it seems more open, "bigger". You have a deeper soundstage and the instruments, the voices are more focused and more define in the space.
The level of the rear tweeter (0 to -6B) depends on the environment, for example, if the wall reflects a lot, you should have more attenuation.

Here in my design, I put 6dB, it 's discrete but enough.
In this passive design, I managed to use the same crossover for the tweeters. My first version used two crossovers, one for each tweeter.

I enjoy a lot with this design.

:)
 

jerome69

Member
2008-02-18 11:33 am
Lyon
Hi,

Regarding the rear tweeters, I'm concerning the distance to back wall. Wouldn't the rear reflections interfere with the front?
No it's a dipole, the panel is enough large, there is no wave cancellation in the treble. You will have interference between the direct and the reflected wave like all loudspeaker makes in a room.

How far is your rear tweeter to wall?
1m.
This loudspeaker is not very different from an other in room placement. You don't have the benefit of the rear tweeter if the walls are too far, i think if the distance is superior to 2m.
I tried an open baffle, not this one, in an auditorium and the wall was at 3m. To have a better sound stage in the treble, we placed an other loudspeaker behind the open baffle (0.5m), Just to reflect earlier the rear sound.

An important note
The crossover schema have a mistake, the real wiring of the rear tweeter on the panel is opposite. Like this
[IMGHTTPDEAD]http://img190.imageshack.us/img190/1255/wiringtweeter.jpg[/IMGHTTPDEAD] [IMGHTTPDEAD]http://img190.imageshack.us/img190/wiringtweeter.jpg/1/w249.png[/IMGHTTPDEAD]
;)