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Old 20th July 2009, 10:28 PM   #1
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Smile Big passive OB project

Hi Everybody,

I would like to make an other OB but with a passive crossover.
I saw this "Panomaniac thread" one year ago Fast, fun, Inexpensive OB project
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 :
Click the image to open in full size. Click the image to open in full size.
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
Click the image to open in full size. Click the image to open in full size.

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 2.9@43Hz.

The response curve, subtract 3dB above 13kHz.
Click the image to open in full size. Click the image to open in full size.

The impedance curve :
Click the image to open in full size. Click the image to open in full size.

Distortion
Click the image to open in full size. Click the image to open in full size.

Raw measurements on the baffle
Click the image to open in full size. Click the image to open in full size.

The crossover schema
Click the image to open in full size. Click the image to open in full size.
The resistance of woofer inductors should be below 0.2ohms. Use film capacitors in series.

The plan
Click the image to open in full size. Click the image to open in full size.

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
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Old 20th July 2009, 10:41 PM   #2
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Congratulations! I can appreciate that it would take a very significant amount of effort to get it this far. I consider it a well designed budget OB.

Regards,
Bill
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Old 20th July 2009, 10:53 PM   #3
ttan98 is offline ttan98  Australia
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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.
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Old 20th July 2009, 11:22 PM   #4
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That's an impressive crossover work. I wouldn't know where to start with these passive xo.

What are the slopes of 500 and 2.5kHz?
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Old 21st July 2009, 12:40 AM   #5
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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.
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Old 21st July 2009, 01:41 AM   #6
ttan98 is offline ttan98  Australia
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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.
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Old 21st July 2009, 01:58 AM   #7
Pano is offline Pano  United States
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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).
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Old 21st July 2009, 04:09 PM   #8
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Good work, Jerome!

Panomaniac, 82.5dB/2.83V sounds about right for a 5" consumer mid with 4 ohms in series. That's what Jerome's graphs show, assuming the measurements were done at 1m.
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Old 21st July 2009, 04:24 PM   #9
Pano is offline Pano  United States
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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.
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Old 21st July 2009, 10:16 PM   #10
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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.
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