Ported Apogee Centaur

This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Back in the 90.....I got my first pr of Minors....an called Apogee an spoke to Jason got the port mod kit sent to my shop....it took about two weeks...
all it was... 3/4"long...1 1/2" round peace... that was just a cover to make the 1 1/2" hole you cut look good ......it was just a flaired peace black plastic...1 1/2" hole was to be cut 1"up..1"in from the bottem right side...from looking the back.....there was no info in the kit...on removeing any stuffing...
I could have just cut the 1 1/2 hole....but I never did the mod...sold the Minors......I was moveing thought a lot of speakers then..
So move to last year when I got my last pr of Minors....an there is some info about the Minor port mod on the web.....I have never owned the Centaurs...an I never have seen any info on a mod for the Centaurs.....only the Minors
What I have done with my Minors ....is found on the web...were a guy just took the screws out of the input cover on the back ...an just let it hang open......but it makes a BIG diff in the sound!
I like it because I can go back to the sealed box vary ezey.....cant say what way is better.....if I had to have it just one way....I would not have the port!
All just one mans finding.............
Thanks for the responses.
Maybe there wasn't a factory mod for Centaur.
I have a pair of cabinets with all components removed.
The ribbons are being used experimentally elsewhere and the Vifa drivers have a significant amount of corrosion on the magnesium casting behind the cones. They seem to be quite functional and I have managed to clean some of the white powder off the castings and paint over the pitting with an enamel paint.
I was wondering if the Dayton RS180 might perform well in the 0.75cu.ft enclosure with a port mod. I would use a minidsp for crossover and EQ unless someone more skilled than I could tell me how to mod the stock crossover.
I would think ...that all the Centaur would have had the mod kit?....an if we look at all the Ribbon hybrids that came after the Centaurs.....all are ported....I well say night & day diff in sound....with a port!....with the minors it not more bass...it adds depth...diff type of bass...to my ears...
I was into the full rang ribbons....like the Stages...then I got the Duettas Sig ...then the buzzzzzzzing bass panels came up...even in the 1993-5 time frame...I got turned off...to the Apogees.....there was no web to get all the info we know today...
then I saw the big full ribbon as a dead end......now we know better...
I have been looking at a pr of Caliper....that would move me from the Stage-Minors 26" ribbon...to a 36" MTr.....10"more bass & MTr would..i think give better sound...maybe maybe not..an still drive ezey....but who knows.....
cost is vary low....freaks me out how people well not touch these old Apogees.....I found that it like...if the owner finds someone that has had the Apogee speakers...that well give them away...to get them out the door....
not all people are into Diy......not a nutjobs like me....life is short...I just like Apogee sound...
Joined 2014
Paid Member
Is the middle child really only 0.8cuft box? Quick guestimate on my minors is nearly that size.

Anyway time to confess. About to hit but on 8 woofers to OB mine and realised that I just don't have time, workshop or power tools to do that at the moment, but I DO have a pair of scanspeak 18W-8545 looking lonely. Cabinet volume is about right with a 2" port about 8" long to get to around 35Hz f3.

Will have to change packaging plans for the amps to drive it active though. Original idea to pack in bottom of speaker wont work so will have to fit them in the stand!

OB is still long term but I worry about the narrower stock baffle than PJB has used meaning a lot of EQ needed for a 2.1 solution. 3-way is better but with latest addition going to be crawling soon that will have to wait!
Joined 2014
Paid Member
Some rough numbers run this evening using my scanspeak TS parameters. Interesting one alignment pretty much is the size of the input cutout, so I can understand why tyu found that to work.

I need to remeasure and make sure that the 8545 isn't too wide for the box, but it looks a def possibility.

Given the issues with the minor X-over not sure the big brother will be any better. Anyway as you have found, pushing the ribbon lower has major benefits!
Slant ....an i think Cepheus.....were slot ports....No ports tube!...an I don't wont to say that the input cover opening.....was more than a taste of what the right port size may sound like....... but with the Apogee port kit.....there was no tube....just a flared cover...
I thought there was going to be a tube.....like your saying....but now are you saying the biger slot type well work fine?.....
as for the lowering of the x-over point of the 26" MT.... of the minor..has a 30mf cap look like 1khz.......an the Centaur has the same crossover that the Stages has on the 26"MT....70mf...like 500hz.........
I went to look at a pr of Centaur once on CL.......but one MT was just hanging lose from being over driven....I passed...
I well say I like the topend of the minors after living with the MT on all the Stages I have owned.........
Joined 2014
Paid Member
The 'right' port size is an interesting question. Really depends how you like your bass. I'll have an active X-over to a sub so can correct it however I want, but some of the sims suggest having a higher Q could reduce the BSC required. I'm more a Q=0.5 kind of guy. Once I am sure I haven't done something boneheaded will post up some numbers. Won't sound as good as PJBs open baffles, but as I said, those will have to wait.
As far as I remember, the volume of the Centaur cabinet is 0.75 or close. The crossover is in a separated portion of the cabinet, unlike the Minors.
I have the OB ribbon project on hold while I go through some health issues. The LXmini clones received a definite thumbs down from the CEO who thinks they should be on a boat somewhere.
So to further my enjoyment in this (frustrating?) hobby I have acquired the components to build a pair of Continuums using a nice piece of walnut I was given for the cabinets.
The last kit speaker I built was the LS3/5A clone from Wilmsow or Falcon, I've forgotten which, in the 1970s. They were really impressive in the midrange but suffered with limited power handling.
Keep us informed as you experiment.
Joined 2014
Paid Member
Hope your 'issues' are resolved quickly. My problems are all time related (babies eat all spare time, before the 3 teens are accounted for) and money.

I haven't remeasured, but a couple of references say 0.6cuft so I'm going to re-run my calculations on that and see what I get. I think its borderline sealed vs ported if I am going for a sub, but the idea of a low Q alignment is tempting me towards a port.

Still gutted to put my OB on hold, but I had to face that the chance of ending up with nothing working was higher than the chance of the speakers getting completed. Plus all the sums said that the plastic basket wonders I was looking at would be running at under 1W each at max so should have been fine but really need to build a test piece. Just have to swallow my pride for a bit and stick with line source dipole going to point source box.

I will be interested in seeing if I can tame the awful x-over dip the stock unit had. I suspect that in its own will really help. More news as I have it.
Joined 2014
Paid Member
I've done some recalculations about using the scanspeak 8545 in the stock cabinet and there are 2 choices:

1. Keep the box as is (sealed) and have F3 around 85Hz with a Qtc of 0.54 and use a linkwitz transform to go as low as I want.
2. 5cm by 20cm port to give an F3 of 45Hz

As you can put a blanking plate on a port there is a temptation to try both.
have you pulled the input plat ..an just let it hang?.........I wish you could.... tell me what you think about the sound....not sure I feel theres any lower bass....just a more depth..in the image...lot more....good...bad...?
thanks for the info..an your work
All this talk of ports......I had these Dynaudio bm5a for a while now...an I must say there sound with there mosfet active amps... an a old hhscott tube preamp ...there crossover is at 1500hz....6db .....give a big stage-image with the 1.1" Silk tweeters.. 6"mid-bass....with 3" voice coil...2 1/2" X 5 long tube port in the back....an my two 12" subs.....give these ribbons a run for there money......vary panels like sound....I say as good a sound as I have ever had....from piston type drivers.....kills B&W...mabe if the 801s had these seting in for that mid- an ringing tweeter.....
I Am thinking of droping one of these Dynandio 6" driver in the Minors......what do you think....


  • dynaudio-bm5a-compact-175040[1].jpg
    131 KB · Views: 113
Bill....Thanks for the kind words. The health issues seem to be proportional to the number of birthdays, and certainly would like a few more of those!
As far as ported speakers vs sealed, I have built several of both and almost always end up stuffing the ports with felt, socks or similar. I enjoy the low extension, and that can be impressive, but to my ears, the ported variety always negatively impacts the upper bass/lower midrange. Most evident in male voices, which become more "chesty". The minidsp has been a revelation for me and contouring the bass of sealed speakers is a cinch, plus the crossover capabilities are rather handy too. The negative effect of bass reflex in a small room is even more pronounced. Having said that, I'll probably continue to experiment with BR.
Joined 2014
Paid Member
exactly my conundrum. With MiniDSP I can bang in a transform to extend the bass as low as I want and just pump more power in. I think the problem is that most of the equations out there give a Q=0.7 alignment for ported and in fact a lower Q can be perceived as better. But a port is a few $ so won't cost me much to try!
I have been playing with the back plat port.....I got say I see what going now.....when I run my Stages.....the bass is so open an makes MRT-bass drive.... sound like one big sound image....with the stock minors... not ported...thay don't have the openness the stages dose an all full range ribbon speakers have.....porting much closer match....an they use a slot port....biger image
I actually have some of the ported Centaur Minors, and my first Apogee's about 20 years ago were the regular ones. The ported exceed the sealed by quite a margin, and the port is not elaborate at all - slightly tapered thin plastic actually! Calculating the correct port for the job and making it from something more substantial could yeild some benefits, though drilling for the port and routing the transition would be messy!
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.