I have finally gotten started on reviving the Big Old Coax OB speakers. My buddy John Busch left these Coax drivers to me when he passed away last year.
John had used them in a couple of different OB configurations, the version I knew - we had at RMAF 2008. It had just the 18s, on OB no helper woofer. They were amazing! John and I worked to fine tune the passive crossover while we were in Denver. We never got it perfect, but it was much, much better than 90% of what was on show that year. Extremely dynamic with amazing imaging.
Today I made a couple of crude test sleds to get these up and running again. I wanted 30mm OSB,for the baffle but that didn't work out. So I have 13mm MDF (yuck). Here's hoping that the 2x4 braces add some rigidity to the baffle. Might need to add a cross brace below the woofer. It will get wings once it's up and running.
These are the biggest coaxial drivers I know of, and no longer made. They have substantial frames and weigh 17 kg each! The 18" cone serves as a horn for the 1.4" compression driver. This allows an acoustical crossover point of around 750 Hz, which this compression driver can do on this cone/horn.
I'll be using two QSC pro audio amps with plenty of power, and DSP active crossover because I have it, and because it should be fast to implement. Crossover work will begin tomorrow.
John had used them in a couple of different OB configurations, the version I knew - we had at RMAF 2008. It had just the 18s, on OB no helper woofer. They were amazing! John and I worked to fine tune the passive crossover while we were in Denver. We never got it perfect, but it was much, much better than 90% of what was on show that year. Extremely dynamic with amazing imaging.
Today I made a couple of crude test sleds to get these up and running again. I wanted 30mm OSB,for the baffle but that didn't work out. So I have 13mm MDF (yuck). Here's hoping that the 2x4 braces add some rigidity to the baffle. Might need to add a cross brace below the woofer. It will get wings once it's up and running.
These are the biggest coaxial drivers I know of, and no longer made. They have substantial frames and weigh 17 kg each! The 18" cone serves as a horn for the 1.4" compression driver. This allows an acoustical crossover point of around 750 Hz, which this compression driver can do on this cone/horn.
I'll be using two QSC pro audio amps with plenty of power, and DSP active crossover because I have it, and because it should be fast to implement. Crossover work will begin tomorrow.
Who says it could? DSP can't change directivity either.
DSP is used to compensate for dipole loss and naturally for xo. Room eq is also possible but that's another story and applies to all speaker types.
Well OK, here you are!
This my first try at a crossover, no wings. Yes it has EQ.
Basics:
This is measured at 2 meters from the baffle. The corner you see behind is 4.4 meters from the speaker. Side walls about the same distance.
The room is very big, 16.5x9 meters, ceiling at 2.75 meters. I haven't listened in stereo yet.
This my first try at a crossover, no wings. Yes it has EQ.
Basics:
- Woofer LP @90Hz 1st order
- Woofer EQ -4dB@155Hz, +3dB@50Hz
- Horn HP @750Hz, 2nd order, polarity reversed
Horn EQ -5dB @1600Hz
This is measured at 2 meters from the baffle. The corner you see behind is 4.4 meters from the speaker. Side walls about the same distance.
The room is very big, 16.5x9 meters, ceiling at 2.75 meters. I haven't listened in stereo yet.
I've been listening in stereo for the past 3 hours (it went fast).
The speakers are 12ft (3.6m) apart and I sit the same distance back. The wall is 8ft (2.5m) behind the speakers
First listen was "OK" but with definite problems in the midrange. Rather congested with too much mid near or below the crossover, so I used EQ to pull out some 630Hz, which was better, but not perfect. Then I had a look at the crossover - I had not turned on the high pass for the horns!
The horns were running fullrange, no wonder the midrange sounded bad. The drivers survived, thank goodness.
After a lot of listening and tinkering and more listening and trying things, the crossover did not change, but EQ did change a little. The corner behind the speaker might have been adding some 150Hz boost. More properly placed in the room that range need to be added back in by about 2dB. I also brought up the 50Hz bump to give them a little more pleasant bottom end. The sound a little too flat without the bump.
Bass is good where there is bass on the recording, I listened to some bass heavy tracks with Victor Wooten, Ray Brown and a few others. Plenty of low end and it seems to go deep with no trouble, always very clean. Not the sort of slam you'd get out of a live PA, but it thumps nicely and can be felt in the chest. The image tends to be back behind the speakers, in the little alcove with the windows seen in the photo. On some tracks, there are layers from the speaker to the back and wider with symphonic works. The image is stable pulling only a little left or right as I move outside the horizontal footprint of the speakers. Center image stays in place.
On rock guitar they can really light you up, there is a lot of power and drive, on orchestral and opera works the venue is quite audible and changes per recording.
Today they are not perfect, but 90% of the way there. As we know, that last 10% is devilishly tricky. But overall I'm happy with them and they sound the way I remember from 2008. They probably need wings, but I'm kind of afraid to mess with what I have.
The speakers are 12ft (3.6m) apart and I sit the same distance back. The wall is 8ft (2.5m) behind the speakers
First listen was "OK" but with definite problems in the midrange. Rather congested with too much mid near or below the crossover, so I used EQ to pull out some 630Hz, which was better, but not perfect. Then I had a look at the crossover - I had not turned on the high pass for the horns!
The horns were running fullrange, no wonder the midrange sounded bad. The drivers survived, thank goodness.After a lot of listening and tinkering and more listening and trying things, the crossover did not change, but EQ did change a little. The corner behind the speaker might have been adding some 150Hz boost. More properly placed in the room that range need to be added back in by about 2dB. I also brought up the 50Hz bump to give them a little more pleasant bottom end. The sound a little too flat without the bump.
Bass is good where there is bass on the recording, I listened to some bass heavy tracks with Victor Wooten, Ray Brown and a few others. Plenty of low end and it seems to go deep with no trouble, always very clean. Not the sort of slam you'd get out of a live PA, but it thumps nicely and can be felt in the chest. The image tends to be back behind the speakers, in the little alcove with the windows seen in the photo. On some tracks, there are layers from the speaker to the back and wider with symphonic works. The image is stable pulling only a little left or right as I move outside the horizontal footprint of the speakers. Center image stays in place.
On rock guitar they can really light you up, there is a lot of power and drive, on orchestral and opera works the venue is quite audible and changes per recording.
Today they are not perfect, but 90% of the way there. As we know, that last 10% is devilishly tricky. But overall I'm happy with them and they sound the way I remember from 2008. They probably need wings, but I'm kind of afraid to mess with what I have.
From image I presume woofers first dipole peak is at about 400 Hz, so there is also reasonable to cut it with LP filter.
How did you settle on the height and width of the baffles? Commendably flat FR and with just a few days work, from the guy who has spent the better part of the past couple of years trying to get where you are. I'll tell myself it's the room..
Seriously though, awesome job, as a former Magnepan owner I totally get the appeal. I have also heard some really good OB in Montreal and upstate NY.
Seriously though, awesome job, as a former Magnepan owner I totally get the appeal. I have also heard some really good OB in Montreal and upstate NY.
Yes, it's the room I do believe Having over 1600 sq ft is very helpful.
These are similar to the Magnapan in many ways. Perhaps more efficient, and with more punch and dynamics. Also a wider sweet spot than the Maggies. But my old Magnapans had much cleaner vocals. That is work left to be done on these, I remember very clean and clear vocals on the 2008 version of this speaker we had at RMAF. I haven't got that, yet.
It's what I could find. The baffles where supposed to be 50" tall and 22" wide, with wings, as that is the original design. I went to buy lumber, there is only one store anywhere close, and wanted to buy 2 sheets of 15mm OSB that could be glued together to make a 30mm baffle and some wings. But alas, the saw at the store had eaten its own power cord, so there were no OSB cuts for me. I bought MDF 1/4 sheets and did what I could. My baffles are slightly wider and shorter than planned, but also much thinner.
These are similar to the Magnapan in many ways. Perhaps more efficient, and with more punch and dynamics. Also a wider sweet spot than the Maggies. But my old Magnapans had much cleaner vocals. That is work left to be done on these, I remember very clean and clear vocals on the 2008 version of this speaker we had at RMAF. I haven't got that, yet.
https://en.toutlehautparleur.com/br...-b-c-speakers-18htx100-8-8-8-ohm-18-inch.html
Here is a new 18 Inch Coax
Here is a new 18 Inch Coax
