Big passive OB project

[Rudolf]

Jerome,

what made you mount the rear tweeter NOT back to back with the forward tweeter? As done, I would believe the tweeter dipole axis will not be in line with the woofer and midrange axis'.

Rudolf

[jerome69]

Hi Rudolf,

I mount the rear tweeter not back to back because it's easier to fix, there is only wood on this part.
The rear tweeter "makes reflect waves", I think its position is not very important if the rear and the front have similar response. The choices of placement are very limited in this case : two !. This is why I only keep the symmetry to the middle axis of the baffle.

Rodolphe.

[jerome69]

The correct link for the linkwitz presentation is : http://www.youtube.com/watch?v=VC-sx...=TL&playnext=1

[jerome69]

Now the price of this project :

Loudspeakers : 400€ ~ 568$

Crossover : 170€ ~ 241$
Note 1 : woofer inductors should not have more 0.2 ohms resistance. The cheaper inductor I found in Europe, is Monacor transformer LSI-xxxT model For example 10mH/0.19ohms = model LSI-100T price 22€ ~ 31$.
Note 2 : The resistance of the other inductors should be near 0.3/0.5ohms.
Note 3 : You can use electrolytic capacitors in the woofer section.

Wood/finish/connectors/screws etc. 80€ ~ 114$
Only 1.5m²of wood is necessary

Total price : 650€ ~ 923$

For a big loudspeaker the price is not high.

[jerome69]

An update of this project, a new crossover more simple.
C1 could be an electrolytic capacitor. I recommend for C3, C5, C6 to be films capacitors.


The crossover frequency changes 400HzLR4 instead 500HzLR4 and still 2500HzLR4. The sound is not better, not worse, perhaps a little less clean. The principle advantage of this new design is you use less components, have a little more level.

The new response curve :


Comparison of the old (green) and new response (brown). Hard to see a real difference in the area 300Hz and above.


I am still happy with this speaker, it works very well for a passive OB.

[jerome69]

Hi All,

A new session of update begins, i play with the concept again. This is the second variant. I will come again on the first update later.
It is possible to make a lower cost OB with one 12" woofer. This variant use the mid-tweeter of the big one. An advantage of this version is its impedance higher than 5 ohms and very easy to drive for a lot of amplifier. The big version is much harder to drive.

This is a manipulated photo of this version. Just use the two woofer plan and remove the woofer in the bottom.


The crossover schema with one woofer


It is possible to keep or to remove the rear tweeter. The crossover frequency is 400Hz and 2500Hz. The sensitivity is always the same near 83db/2.83V but F3~75Hz is higher than the two woofer version. Don't forget the impedance is higher, and it is easier to drive.

Now the sound, i am not very objective but it can help to make an opinion. One woofer means less low-bass, it have less definition in the low octave but i like this version a lot. The mid and high bass extension is good, the mid-tweeter is very open like its big brother. I think it works very well and can be satisfying.

Have Fun

[jerome69]

Hi All,
Just a word about the 2 crossovers for the big version (2 woofers)
The first

This crossover is done with an amplifier with a lot of control in the bass (high current capability). Notice R9/C9 are optional and could be suppress.

The second

It is better for an amplifier with low control in the bass, should be the more versatile version. The explanation I think is there is a lot of bass reinforcement with the floor, The crossover doesn't compensate this. For an amplifier with low control in bass, it works well. Perhaps in a large room, it will work with all amplifiers ? I don't test the loudspeaker in a large room (>30m²).

Hope this is clear

Have fun

[grantnsw]

Hi Jerome,

Fantastic design, I wish I could hear them. I really like your low-cost version with 1 woofer and 1 tweeter and the 830656 of course. Thanks for posting such detailed information. May I ask please:

(In your post #13):
"I don't know ? Next Year ? I will not use a 5" on an open baffle, too much tricky. Perhaps make something with a 7" ? a much smaller OB, perhaps an active system ?"

The 830656 sounds good? But why is it 'too much tricky'.. your mid c/over looks excellent. It looks like it has a great usable range. Zaph says cross-it high, but you chose 2500Hz. I'm just intrigued why? please. The 30deg off-axis is ok out to 4000Hz?

What 7" mids would you consider? Eminence 6A and Beta 8A are the only other larger mids that I know of that get good reviews, but need eNABLing to fix ringing problems?

In the one woofer version, would there not be more bass if the woofer was in the lower position? Closer to the floor. Please excuse my naiivety!

Any thoughts on active system etc most welcome! Is it ok to email you re your impressions of the 830656? thanks Grant

[jerome69]

Hi Grant,

Thanks for your comments. I like a lot these loudspeaker because it works very well, can play a lot of music in a very natural way.

The midrange The 830656 sounds good ?
The answer is a little subtle. I evaluate this driver in a set-up with the 12" and the tweeter. The overall sound of the loudspeaker depends on the quality of integration of the drivers with the crossover. Yes it's sound rather right instead good. The sound is not as clean as more expensive loudspeaker but the sound is natural. The listening impression is the music comes from a little more far.

I had some trouble in the midrange with the 5" driver because it exhibits a dipole dip (see green curve) in the 1500-2000Hz area. The 830656 wasn't the worse case.



I choose 2500Hz for crossover frequency because the distortion of the 830656 is high and the tweeter can handle easily. The 830656 is not usable above 4.5/5kHz. I don't have off axis measurement because I cannot make good measurement below 250Hz without gating.

I would not consider a 7"/8" driver because a 5" do better the area 500-2500Hz. The eminences seem to be good candidate but the spider seems to be not well ventiled.

About the loudspeaker with one woofer...
I prefer this position of the woofer for two reasons, far from the floor. I don't want to have floor enforcement (till 200Hz), not very good if I want a smooth response. This woofer reproduces the midrange till 400hz and I want it near the midrange.
This loudspeaker is very easy for a lot of amplifier and work very well .

This loudspeaker is passive and will stay passive. I don't like the SLS 12 with active correction, too slow in the mid bass but excellent in the low bass.

Ok if you want to email me

[grantnsw]

Jerome,

Wow, thank you very much. You answered all my questions in detail.
I think I need to re-read Zaph's 5.5" driver IMDistortion plots, because,
to me, the 830656 initially looked OK. Obviously I'm wrong!

Also, congratulations on your mini-Manzanita variants. If I have more questions I'll email. Grant