Hi David,
I don't think there is a right or wrong answer. The baffles are built in mirror image pairs. When I have had speaker like this, I always put the higher frequency range driver towards the inside edge of the baffle. But to try the other orientation all you have to do is swap right for left speaker positions. Whichever sounds best in your room is the right answer.
Hope that helps,
amt said:
Hi,
for the valve / tranny hybrid case probably the best way of doing it
is to retain the the mid/top passive high pass crossover. The low
pass feed is attenuated from the direct output of the valve amplifier
and fed to the tranny amplifier via an active 200Hz 2nd order filter.
(May be possible to mod a sub amplifier to go go this high.
All you need to know is the target Q for this 200Hz filter. For fully
active you also need to know is the target Q of the 500Hz filter.
Unless I've misread the paper this Q is 0.7 - classic Butterworth.
(Both the above result in an acoustic c/o point ~ 400Hz)
/sreten.
sreten said:
I have a similar setup at the moment. But I found that the 2nd order active low pass for the sub amp did not mate well with the open baffle FR driver. Had to add an inductor in front of the woofers to get it to mesh. So odd order on both passovers - 1st and 3rd. (No idea what the acoustc slope is).
Worth a try if you are doing the same thing.
One thing to keep in mind, if you go with some form of PLLXO or active crossover you are going to loose the added series DC resistance of the big coil in front of the woofer. The DC resistance was factored into the crossover design calculations so making this change is going to impact the low end response. Even if you switch inductor types, you will change this resistance value. I looked at air core inductors and they did not work as well as the ERSE Super-Q's I specified.
panomaniac said:
Hi,
Could be a phase issue, might not be the same with 2nd order highpass.
MJK said:
Hi,
Whilst this is true as I read your paper the electrical targets
described as "ideal" 2nd order filters at 200Hz and 500Hz
do not consider these factors.
Presumably it is the added bass inductor DCR causes the bass alignment
in figure 13 to be somewhat fatter than that shown in earlier figures.
As overall level is easily adjustable for an active bass end I
cannot see any real concern about this, unless I'm missing
something ? the bass end will match figure 6 more closely
than figure 13, which seems not to be a bad thing.
/sreten.
I looked at air core inductors, but then realized that Martin mentioned taking the resistance of the inductors into account when designing the crossover. That's why I went with the parts specified in the article. Sometimes it's just better to build the damn thing and be done with it.
I'll be finishing these things tonight and will post my impressions.
Of course. I've already warned my friend that Fostex drivers take a long time to break in. I'm more worried about the crossover point and in room bass response. I'm going to get phase plugs once the drivers break in and I get accustomed to the sound of the speaker. Then the tweakery will begin!
We'll be hooking them up to a pair of Atma-Sphere OTL's, Audible Illusions pre and Vacuum State modified SACD player. It should be interesting...
sreten said:
Hi,
I think you have missed the point. High resistance / air-cored
inductors are not good and will take the response off target.
Thanks. That is if you use Alpha 15A, as Martin recommended. But, if you use a Beta 15, then higher output impedance amp, or air core inductor may be better suited.
I hope there will be a new article about an active OB, and a new thread as well. In the meantime, I am very curious to hear the practical experiences with MJK's passive OB.
Regards,
Vix
Well, they're built and they don't look bad at all considering they're mock-ups. We worked on them all day Saturday, but didn't finish until 11:45 last night. My friend's roomie said no go to a test run, as he was going to hit the sack - but they're built!
We would have finished them earlier, but we were sawing wood in the basement hallway on Friday night (my friend has the only apartment in the basement of the building he lives in) and we set off the fire alarm. The fire dept. showed up, and that kind of put the kibosh on the whole thing for the evening.
I'm going to try to find my camera so I can post some pictures, and will post on the sound later.
We would have finished them earlier, but we were sawing wood in the basement hallway on Friday night (my friend has the only apartment in the basement of the building he lives in) and we set off the fire alarm. The fire dept. showed up, and that kind of put the kibosh on the whole thing for the evening.
I'm going to try to find my camera so I can post some pictures, and will post on the sound later.
A progress report:
Well, they're up and running (currently playing the Red Hot Chili Peppers).
First off, they sound MUCH better than I thought they would, and they're improving RAPIDLY. The bass is very fast and tight - not incredibly deep, but very fast and fleshing out. The treble at first simply was not there, you didn't hear cymbals decay - they just stopped at a certain point. That's changing as well.
Right now they LOVE three things:
Vocals
Electric Guitars
Kick Drums
I will say this, they are FUN to listen to. There is a bit of a "tinny" quality to the sound (as judged by my friend's non-audiophile roomie) but both he and his girlfriend were quite surprised at the sound quality. They have that very "alive" quality that you can hear from another room - very dynamic and rhythmic.
I built the baffles out of 1/2" birch plywood, all of the crossover components, wire and drivers are connected via terminal strips and crimped lugs and hard screwed to a wooden base. The height is as per the instructions, but the bottom width is 21" and the top edge is 19", this creates an angle on the outside of the baffles (think Apogees) this is to break up baffle resonances, but I think it looks better than the "plank" look. For the connections, I used only the finest Radio Shack solid core hookup wire. The baffle is connected to the "base" via a couple of L brackets. The front baffle is leaned back to aim more or less at our ears. There is hardly any movement of the baffle even though it is incredibly springy.
I was concerned that the bass would be boomy due to the fact that we're using Atma-Sphere OTL's with the speakers, but that fear proved to be completely unfounded. I can't say that these speakers would sound good on a SET, but I can hardly wait to hear them with the tubed Scott integrated amp another buddy of mine has. I bet it will sound absolutely great.
I can definitely say that I'm going to do a more "serious" build of these speakers, with 3/4" birch, a base that has solid braces to the main baffle, phase plugs, hardwired crossover components, enable and mamboni mods, etc... It will be worth it.
As far as building them, my friend and I were able to wire up the crossovers and drivers after, shall we say, a "few". If I can build these, ANYONE can. I simply cannot think of a better beginner's project.
Well, they're up and running (currently playing the Red Hot Chili Peppers).
First off, they sound MUCH better than I thought they would, and they're improving RAPIDLY. The bass is very fast and tight - not incredibly deep, but very fast and fleshing out. The treble at first simply was not there, you didn't hear cymbals decay - they just stopped at a certain point. That's changing as well.
Right now they LOVE three things:
Vocals
Electric Guitars
Kick Drums
I will say this, they are FUN to listen to. There is a bit of a "tinny" quality to the sound (as judged by my friend's non-audiophile roomie) but both he and his girlfriend were quite surprised at the sound quality. They have that very "alive" quality that you can hear from another room - very dynamic and rhythmic.
I built the baffles out of 1/2" birch plywood, all of the crossover components, wire and drivers are connected via terminal strips and crimped lugs and hard screwed to a wooden base. The height is as per the instructions, but the bottom width is 21" and the top edge is 19", this creates an angle on the outside of the baffles (think Apogees) this is to break up baffle resonances, but I think it looks better than the "plank" look. For the connections, I used only the finest Radio Shack solid core hookup wire. The baffle is connected to the "base" via a couple of L brackets. The front baffle is leaned back to aim more or less at our ears. There is hardly any movement of the baffle even though it is incredibly springy.
I was concerned that the bass would be boomy due to the fact that we're using Atma-Sphere OTL's with the speakers, but that fear proved to be completely unfounded. I can't say that these speakers would sound good on a SET, but I can hardly wait to hear them with the tubed Scott integrated amp another buddy of mine has. I bet it will sound absolutely great.
I can definitely say that I'm going to do a more "serious" build of these speakers, with 3/4" birch, a base that has solid braces to the main baffle, phase plugs, hardwired crossover components, enable and mamboni mods, etc... It will be worth it.
As far as building them, my friend and I were able to wire up the crossovers and drivers after, shall we say, a "few". If I can build these, ANYONE can. I simply cannot think of a better beginner's project.
Great to hear that they sound so good. They seem as if they have the strengths of the dipole format.
After the earlier discussion on damping factor, I wonder how they'd compare with a couple of ohms in series.
Have you considered running rails down and across the back of the baffle for strength? I realise that may inadvertently lift the bass a little by changing the dimensions. Just a thought.
Is your Fostex mounted in front of the baffle?
After the earlier discussion on damping factor, I wonder how they'd compare with a couple of ohms in series.
Have you considered running rails down and across the back of the baffle for strength? I realise that may inadvertently lift the bass a little by changing the dimensions. Just a thought.
Is your Fostex mounted in front of the baffle?
Yes, it's mounted on the front of the baffle.
These speakers are meant more as a mock up than anything else. I'm going to let the components break in, but to say that these speakers have potential is an absolute understatement. I'm not worried about the bass, it's already filling out. Remember, this is a brand new driver out of the box with only about four hours of playing time on it.
I will say that at this point there is definitely a point where the Fostex starts to "shout", but we're playing them pretty loud, plus that shouting point is higher now than it was four hours ago.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.