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Open Baffle Epiphany!

BHamm said:
I am waiting to build some OBs as soon as I find a complete plan that documents everything. I want to go passive 2-way though. I read the plans for a nice looking build by MJK, but the Fostex driver used is no longer available.
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I have a new "small" OB speaker design, just finished building it a couple of weeks ago. I am using a Fostex FF85WK and an Eminence Alpha 15A on an 18" wide by 24" tall OB. The OB is tilted back 15 degrees so when standing on the floor they fire at the listener. This is a 2nd order passive crossover design and the in room response is smooth with a slight downward slope at high frequency (I have some really nice measurements to show). The bass and mid bass is good getting down to almost 40 Hz. The phase also is very linear without any major wiggles or reversals.

The speakers were designed and built as a request from a co-worker, they were put together quickly as a prototype. He wants to build something so I have loaned him these for a few weeks to try out. I think there will be a tour of other friend's homes over the next few months so I can gather some feedback (so far all positive). Eventually I will build something a little nice looking and fully document the design. Initial details and results should be up on my site in the next couple of weeks.
 
MJKing said:
I have a new "small" OB speaker design, just finished building it a couple of weeks ago. I am using a Fostex FF85WK and an Eminence Alpha 15A on an 18" wide by 24" tall OB. The OB is tilted back 15 degrees so when standing on the floor they fire at the listener. This is a 2nd order passive crossover design and the in room response is smooth with a slight downward slope at high frequency (I have some really nice measurements to show). The bass and mid bass is good getting down to almost 40 Hz. The phase also is very linear without any major wiggles or reversals.

The speakers were designed and built as a request from a co-worker, they were put together quickly as a prototype. He wants to build something so I have loaned him these for a few weeks to try out. I think there will be a tour of other friend's homes over the next few months so I can gather some feedback (so far all positive). Eventually I will build something a little nice looking and fully document the design. Initial details and results should be up on my site in the next couple of weeks.
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That sounds exactly what I want for my first OB project. I will keep checking your website for the details. Thank you MJKing.
 
^^^

Very interesting. :yes:

What's the approx cost for drivers and networks?

And if one could accommodate a wider baffle or, better yet, add wings would there be any worthwhile gain in LF performance?
 
I have not done the detailed cost roll up yet, I think it will come in around $400 a pair. The crossovers are expensive (around $180) due to large inductor and capacitor values required for the low frequency crossover points. I did run them with my active crossover but the passive set up performed better.

If the baffle is made wider or wings are added the bass might extend a few Hz lower. The down side is that the efficiency of the woofer will drop a little and the crossover may need to be tweaked due to a shift in the frequency of the dipole hump. These OB speakers produce plenty of bass and a big open sound.

The design is probably not tube amp compatible due to the crossover location (based on feedback about my other similar OB designs), if you build them think about a SS amp with > 50 watts of power.
 
Looks very promising. I think I can start buying the drivers, and I have plenty of 1 inch birch ply on hand. I look forward to this new project and new direction for me. :thmbsp:

MJKing said:
I have a new "small" OB speaker design, just finished building it a couple of weeks ago. I am using a Fostex FF85WK and an Eminence Alpha 15A on an 18" wide by 24" tall OB. The OB is tilted back 15 degrees so when standing on the floor they fire at the listener. This is a 2nd order passive crossover design and the in room response is smooth with a slight downward slope at high frequency (I have some really nice measurements to show). The bass and mid bass is good getting down to almost 40 Hz. The phase also is very linear without any major wiggles or reversals.

The speakers were designed and built as a request from a co-worker, they were put together quickly as a prototype. He wants to build something so I have loaned him these for a few weeks to try out. I think there will be a tour of other friend's homes over the next few months so I can gather some feedback (so far all positive). Eventually I will build something a little nice looking and fully document the design. Initial details and results should be up on my site in the next couple of weeks.
Click to expand...

MJKing said:
First info just added to my site.

http://www.quarter-wave.com/Project12/Project12.html
Click to expand...
 
MJKing, I realize your prototypes are making the rounds for feedback, but is there a chance you may be tweeking the crossover design based on what people think. Or, are they finalized? I will hold off on parts if they may change.

BHamm

MJKing said:
I have not done the detailed cost roll up yet, I think it will come in around $400 a pair. The crossovers are expensive (around $180) due to large inductor and capacitor values required for the low frequency crossover points. I did run them with my active crossover but the passive set up performed better.

If the baffle is made wider or wings are added the bass might extend a few Hz lower. The down side is that the efficiency of the woofer will drop a little and the crossover may need to be tweaked due to a shift in the frequency of the dipole hump. These OB speakers produce plenty of bass and a big open sound.

The design is probably not tube amp compatible due to the crossover location (based on feedback about my other similar OB designs), if you build them think about a SS amp with > 50 watts of power.
Click to expand...
 
BHamm said:
MJKing, I realize your prototypes are making the rounds for feedback, but is there a chance you may be tweeking the crossover design based on what people think. Or, are they finalized? I will hold off on parts if they may change.
Click to expand...

So far the feedback has been very positive. I may have a tough time getting them back and am considering building a second pair.

Based on my measurements, SPL nice and flat through the crossover with smooth phase, I do not see the crossover changing. I do need to double check my wiring and the driver's polarity to resolve my phase question, the Fostex should be wired out of phase.

I thought I had it right but needed to swap the Fostex leads, swapping plus and minus connections is easy and the difference was obvious.
 
Okay, thank you. Fostex should be wired positive lead to negative terminal.

MJKing said:
So far the feedback has been very positive. I may have a tough time getting them back and am considering building a second pair.

Based on my measurements, SPL nice and flat through the crossover with smooth phase, I do not see the crossover changing. I do need to double check my wiring and the driver's polarity to resolve my phase question, the Fostex should be wired out of phase.

I thought I had it right but needed to swap the Fostex leads, swapping plus and minus connections is easy and the difference was obvious.
Click to expand...
 
The Tang Band W8-1808's have arrived. Eminence Alpha 15's to follow. I'll start a separate thread when the build commences.

My gut tells me to use a large baffle, JE Labs Quarter Wave width - just taller to accomodate the two 15's and the 8" FR.

In general, does a larger OB provide better performance?
 
TubeHiFiNut said:
In general, does a larger OB provide better performance?
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Drivers, crossover, and OB size are all important and work together as a system. If you change the baffle size you will also need to adjust the crossover to account for the change in the frequency of the dipole hump. If you change the baffle size you will also alter the bass performance from the woofers, it will go deeper and not start to roll-off as soon. Doing the detailed design work is critical to getting an optimum result.
 
MJKing said:
Drivers, crossover, and OB size are all important and work together as a system. If you change the baffle size you will also need to adjust the crossover to account for the change in the frequency of the dipole hump. If you change the baffle size you will also alter the bass performance from the woofers, it will go deeper and not start to roll-off as soon. Doing the detailed design work is critical to getting an optimum result.
Click to expand...

Thank you for the guidance.

My plan is to biamp and stay away from passive crossovers. I also have a SAE Parametric to tweak things in the frequency domain.

This pair, like my 6201 Quarter Wave based pair will be 'proof of concept'. Larger size is OK - i have the room.

If I can get better extention by going with a larger baffle, I would like to explore that path.

Your thoughts?
 
IMO, doing the detailed design work ahead of time will get you to your goal faster. What kind of active crossover are you planning on using? I don't have any measured T/S parameters for the Tang Band W8-1808 but I believe a passive crossover is probably also possible.
 
MJKing said:
IMO, doing the detailed design work ahead of time will get you to your goal faster. What kind of active crossover are you planning on using? I don't have any measured T/S parameters for the Tang Band W8-1808 but I believe a passive crossover is probably also possible.
Click to expand...

I have a Dahlquist DQ-LP1 and a pair of tube Heathkit active crossovers.

Planned to use a Crown X1000 on the two 15's per side and whichever of my SET amps sounds best on the single TB per side.

I am not an engineer and do not claim to be one so much of this journey will probably end up being 'by gosh and by golly' and tweaked by ear. The 'general' OB comments I have read seem to indicate that the larger baffle will aid LF extension and that I should position the TB so that none of the center of the driver to baffle edge measurements are the same or multiples of one of the measurements.

This may or may not be germane to a good result.

So....this is kind of where i am right now. Poultrygeist recommends the use of the H-frames for the 15's and then smaller OB's for a variety of FR or coaxial drivers. I like PG's OB builds and the results he gets so this also has good potential.

What to do...what to do. :)
 
What drew me to the open baffle was the simplicity of the design.
HA!...so much for simplicity :rolleyes:
 
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