My Open Baffle Journey

So, in addition to my other thread in the Speaker forum on my Open Baffle Epiphany, I thought I would create one showing the build process of my open baffle speakers from start to finish.

My goal is to have a flat response across the audio spectrum using the open baffle concept. I have chosen Foster (fostex) FE103 alnico for the full range drivers and Eminence Alpha 15A for the low bass duties. There are a lot of projects online that utilize this driver arrangement with the newer Fe103, including the now famous Martin King version which I would imagine sounds terrific.

I've never been a fan of passive x-overs, mainly due to the fact that once in circuit, I always feel something gets lost to the overall transparency of the speaker. Also, having designed them for other speakers is the past, at least for me, they are hard to get right the first time and require a lot of tweaking. This usually ends up with a lot of spare parts and lots of $$ wasted.

This brings me to my x-over of choice - Active. More specifically, the miniDSP. I have not used one yet, but I really like the idea of a programmable xover that can be endlessly tweaked with a few clicks of a mouse. The idea of being able to tweak the x-over if I move speaker positions or move to different rooms is really a benefit. Also, with passive x-overs, you need to create a circuit to to specific jobs, eg. low pass, high pass, notch, etc. With the miniDSP, since it is digital there are no limits to what you can do to the slope - what corrections you want. No need to follow math or electronic formulas. Simply Measure and adjust!

I am planning on going with a flat panel open baffle, probably not much wider than the 15" woofer. I debated trying a "C" of "H" frame for increased low end response, but I should be able to boost this to flat no problem with the miniDSP. X-over point from the 15" woofer to the 4" full range will be determined with measurements once the baffles are built.

Cost break-down:
2x Eminence Alpha 15A $129
2x Foster FE103a $6 (goodwill)
2x Phase plugs for FE103 $18
1x MiniDSP 2in-4out $80
Wood for baffles $20

Total cost for project: $253

I also purchased the UMIK-1 microphone to go with the miniDSP so I can get accurate in room measurements. I haven't included it in the cost as you could do without it. We shall see how useful it is when the project starts coming together.

Another point is this will be a bi-amp speaker. The ultimate goal having a SET tube amp running the Fe103's and SS for bass duties.

Experimental stage

First experiment with open baffle - This is when I realized box speakers no longer do it for me. What an eye opener. Fe103's paired with paradigm sub.



Experiment #2 - Determine bass is possible with open woofers. These are 12" Eminence Special Design woofers out of my Fender Blues Deville. Bass is possible! And nice bass indeed!

Eminence Alphas Arrive

I picked up the Eminence Alphas from q components yesterday and have had a chance to install them in their cardboard baffles. They did not integrate at all with the Fe103's while using the sub amp for some reason. Very muddy and uneven frequency response. I ended up hooking up the woofers to the 130WPC Pioneer VSX-D1S and running the Fe103's off a small Realistic SS receiver. The result is the best open baffle sound yet. Very nice integration. Both speakers are running full range. I can't wait for the mini DSP to arrive to get these dialed in!!

Hey that's a good start. So you didn't like the plate amp? I'm going to look into the mini DSP. Sounds interesting. I have a OB thread here to. Waiting on parts.

MK

The plate amp I was using was pulled out of a paradigm sub and has a low pass x-over built in. It was adjustable from 50hz to 150hz but it just didnt sound right with the Alphas. They sounded waaay slow, like they were a few ms behind the top end. Maybe the Alphas needed some breaking in, but they seem to sound much better with the receiver amp driving them full range.

Watching your thread with interest too! :thmbsp:

Are you set up to run audio from a laptop/desktop through your rig?

tomlinmgt said:

Are you set up to run audio from a laptop/desktop through your rig?

Click to expand...

Absolutely!

cptnCanada said:

The plate amp I was using was pulled out of a paradigm sub and has a low pass x-over built in. It was adjustable from 50hz to 150hz but it just didnt sound right with the Alphas. They sounded waaay slow, like they were a few ms behind the top end. Maybe the Alphas needed some breaking in, but they seem to sound much better with the receiver amp driving them full range.

Watching your thread with interest too! :thmbsp:

Click to expand...

I wonder if the Alpha's response was caused by the cardboard. If they were solid mounted, the plate amp might perform better. :scratch2:

MK

It looks like you have a very nice project going. I was planning something similar a while back, but went with coaxial drivers instead.

Alphas definitely need some break in time. My speakers are based on Alphas and had very lean bass for the first hour or two. The next day, suddenly I had bass... a little boomy even. They smoothed out nicely over a period of 100 hours or so.

Im beginning to think they needed to break in a bit. The plate amp, even if it wasn't the cause, is only temporary as it is mono and I don't want my bass to be mono. I'm sure the cardboard isn't helping either, but im going to do a side experiment and wait until I get the miniDSP and measure them in cardboard vs wood just to see the effect. The cardboard sounds surprisingly good and doesn't vibrate much with the miniscule xmax of the Alphas.

MK, it will be interesting to see how your Alphas perform for the first few hours.

I should have them this week. I might power the Alpha's with a strong T or D amp. The Mini DSP might work great for that setup. I don't do loud volumes with SET amp.
I'll keep my thread posted.
Did you try to run the Alpha's with the speaker outs on the plate amp? I'm guessing there would be no x-over/volume adjustment that way.

Mark

Great project and what an inexpensive way to get high end sound that will rival megga buck systems. My Alphas are a few years old but I don't recall much of a break-in period.

The H-frame Alphas sing with two Yung SD300 plate amps but that's excessive power. Two SD200 would be better. On the flat baffles I'm currently driving double Alphas per side in parallel ( 4 ohms ) with a single SD300 but a SD200 would be more than enough.

FWIW - For max power with two plate amps use a Y cable ( one into two ) on each plate input rather than a single.

Poultry:

What is the benefit you are seeing with two Alphas? Is it helping with the really low stuff, or is it a SQ thing? I could always do two per side once I get the miniDSP if there is not a lot of low end extension on a flat baffle with one. Those Alphas are so cheap

Another question about multiple drivers...I have 4 of those Fostex Fe103 Alnico's. Do you think there would be any benefit going two per side running in 4 ohms?

BTW, currently listeneing to Miles Davis "Kind of Blue" on the cardboard OB's. Never been much of a jazz guy but had this LP lying around. Sounds like the band is in the room with me.

Doubling up the Alphas doesn't increase the depth but does increase the amount of LF.

Connecting the 8 Ohm Alphas in parallel gives a 4 ohm load which plate amps love.

It might be great fun mounting a front firing Fostex combined with a rear firing Fostex on the same baffle. I would run them in parallel but the 4 ohm load wouldn't make much difference in this case.

Out with the cardboard, in with particleboard!

Went to the local hardware store and got a scrap piece of 1/2" thick particleboard melamine. Not ideal, I know, but these are still in experimental phase. Dimensions are 18"x38". I also mounted the second set of Fe103's for some experimenting. So far I have only the one set hooked up and will experiment a bit later tonight with both.

They definitely sound better than the cardboard, especially at higher volumes. Still running both full range and Alphas wide open waiting for the miniDSP to arrive. The bass extends fairly low before it rolls off and there are some peaks I notice but over all sounding awesome.

When I get the measuring mic I am going to measure the response from the front of the baffle and the rear. I am expecting a roll off on the upper frequencies on the back baffle, so I may get a rear firing tweeter to match the top end to see how that sounds.

But for now, enjoying the tunes as is!

One thing I have noticed about open baffle bass, which is a big plus in our house with kids. The bass is contained to the room. With my old JBL speakers cranked, the whole house would be rocking. With OB, even the room above the system is useable, no booming bass from below at all. :thmbsp:

Both Fe103's hooked up per side in parallel. All I can say is WOW!

Looks good. When is the DSP going to arrive? I'd like to know what you think of it.

MK