Although I usually agree with GM, this is one place that I historically do not. I never heard the comb filtering and don't believe it's a problem in a well implemented Onken/Ultraflex bass cabinet.
The way to get this right and prevent the mids from coming out the vents is to use high quality, wide bandwidth damping material. 100% thick wool felt works wonderfully well, though the Bonded Logic denim insulation might be close. It works better than fiberglass in the low range.
Hang a curtain of felt behind the woofer about 1/3 of the way back. This is one of the best things you can do for the Onken. Cover the inside walls about 50% with felt. This will result in a very clean, neutral sounding box.
for what is is worth - I built the Mar-Ken trapezoid speakers with Dave's (planet 10s) design and the Mark audio 85 dollar drivers and I have to say they are a really impressive they hit way way way above their weight class. The enclosures are complex enough to keep the woodworking side interesting. no crossover - I have been working on other speakers for a several months now and just scratched the surface of speaker design. I have come to realize the order of skills in increasing difficulty maybe medical doctor, rocket scientist, particle physicist, speaker designer.
Just to be clear I mean no disrespect to any of the above skill sets. It is true that the more you learn about speaker design the physics and the math become quite difficult. measurement alone is a study onto itself as is what happens to the sound once it leaves the speaker. Not to mention that a speaker that measures well will not always sound good. To make matters worse there is a lot of conflicting information. I think that is why most people recommend a kit for the the first project. I do not mean to discourage you as it is a excellent hobby for keeping my mind occupied. I made the mistake of thinking how hard could it be? I mean it is only a box a couple of drivers a cap or two a coil and if needed a resistor. 6 months later and i am still scratching my head.
Just to be clear I mean no disrespect to any of the above skill sets. It is true that the more you learn about speaker design the physics and the math become quite difficult. measurement alone is a study onto itself as is what happens to the sound once it leaves the speaker. Not to mention that a speaker that measures well will not always sound good. To make matters worse there is a lot of conflicting information. I think that is why most people recommend a kit for the the first project. I do not mean to discourage you as it is a excellent hobby for keeping my mind occupied. I made the mistake of thinking how hard could it be? I mean it is only a box a couple of drivers a cap or two a coil and if needed a resistor. 6 months later and i am still scratching my head.
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in my mess, somewhere are Heath's version of the Jensen "Ultraflex" - that was a nice way to integrate a reflex into a corner.
http://www.audiofanatic.it/Piani_costruttivi/pic_piani/Jensen_Ultraflex.jpg
http://www.audiofanatic.it/Piani_costruttivi/pic_piani/Jensen_Ultraflex.jpg
Hmm. Issue as GM noted is vent harmonics combing with the driver output; the problem with a lot of Onkens is the large vent CSA requires considerable duct length in many cases to hit the target Fb. Since ducts are 1/2 wave resonators they have their own harmonic structure, so if they get too long, that's where you can encounter issues with audible pipe resonant modes. As a very rough & ready ROT, I try to avoid duct lengths > 6in to keep the 1/2 wave fundamental & its harmonic modes above c. 1KHz where for back loaded bass enclosures they usually are less problematic.
Internal damping to the box itself unfortunately can't do anything about this; if duct pipe resonance is an issue you either need a shorter duct length & smaller CSA (assuming velocity doesn't become excessive) or some damping in the duct itself. A good Onken design balances / accounts for all of these things & works fine; unfortunately, not all of them do so.
Dave's Mar-Kens & similar resemble Onkens, but are functionally somewhat different in that he's often pushed the aspect ratio of the ducts to quite high levels to increase friction & push the alignment in the direction of resistive-vent design.
Internal damping to the box itself unfortunately can't do anything about this; if duct pipe resonance is an issue you either need a shorter duct length & smaller CSA (assuming velocity doesn't become excessive) or some damping in the duct itself. A good Onken design balances / accounts for all of these things & works fine; unfortunately, not all of them do so.
Dave's Mar-Kens & similar resemble Onkens, but are functionally somewhat different in that he's often pushed the aspect ratio of the ducts to quite high levels to increase friction & push the alignment in the direction of resistive-vent design.
Worth nioting again that the miniOnken’s do not use a classic Onken alignment.
Really glad you are enjoying them :^)
dave
Well I can't say I understand that Scottmoose as I've never heard the problem in the 4 different size Onken cabs I've listened to. I understand the physics, but don't understand why I - nor anyone who's been standing next to me - has ever complained or noticed.
To me it's similar to all the stories of how multi-cell horns are so bad with comb filtering. I don't hear it - and I've asked other people to listen for it and they don't hear it. A mystery.
To me it's similar to all the stories of how multi-cell horns are so bad with comb filtering. I don't hear it - and I've asked other people to listen for it and they don't hear it. A mystery.
A relatively new one on me WRT multicell horns. Re the Onkens though, as noted
So it's possible you've only heard examples that do not suffer such issues. Alternatively, it is also possible that you simply like what they do, whether they have any issues with vent harmonic modes or not. Which is unlikely to factor as a great crime against audio or humanity at large.
As far as subjectivity goes though, as I've discovered, within certain limits, a touch of 'euphonic distortion' is frequently preferred by blind listeners to something lacking that. Depends on what and what's involved in the comparisons of course. But we often build a touch in, deliberately or otherwise; a lot of EQ curves for example come out of that (in this case linear rather than non-linear), and there are plenty of mechanical ways of generating various effects along those lines also, albeit in that case usually non-linear rather than linear. As always, name your poison. YouTube
So it's possible you've only heard examples that do not suffer such issues. Alternatively, it is also possible that you simply like what they do, whether they have any issues with vent harmonic modes or not. Which is unlikely to factor as a great crime against audio or humanity at large.
As far as subjectivity goes though, as I've discovered, within certain limits, a touch of 'euphonic distortion' is frequently preferred by blind listeners to something lacking that. Depends on what and what's involved in the comparisons of course. But we often build a touch in, deliberately or otherwise; a lot of EQ curves for example come out of that (in this case linear rather than non-linear), and there are plenty of mechanical ways of generating various effects along those lines also, albeit in that case usually non-linear rather than linear. As always, name your poison. YouTube
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For me, it's the other way around, I gave up on [pre] amp design long ago and this old fart is having problems just remembering what he once knew, so not much absorbing, etc., going on these days.
GM
The Onken only has some damping on the back plate, hence the well documented, audible, strong comb filtering, but if damped as I, and now you recommend, then any comb filtering will be minimal except possibly at high power at tuning [Fb] where it will likely be 'drowned out' and why I normally recommend using a single large vent [which has its own harmonics that comb filter, just not as high amplitude] damped to 'taste' unless one wants the Onken 'look'.
GM
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