Turn Your Bass Reflex Speakers to Passive Reflex




Introduction: Turn Your Bass Reflex Speakers to Passive Reflex

passive reflex speakers are higher quality and have much faster responce exept they are hard to find and expensive so why not change all of your bass reflex speakers to dipole passive for extremely cheap.

-Note this will not improve all speakers (mine were very cheap and as pointed out by Arx the enclosure was not tuned to the maximum and adding the diaphragm improved the tuning)

-I also would like you to know that the sound produced by adding this will be different.  I recommend that you compare your two options to see what sound you prefer. 

Step 1: Materials and Supplies

-latex (balloon, glove, ext.)

Step 2: How to Do It

Cut a flat strip of latex big enough to cover your bass reflex air port.

Tape it tightly over the hole and be sure there are no leaks

Fire it up with these tests:http://www.stealthsettings.com/woofer-bass-subwoofer-sound-test
       Number 10 is best

My mod took about 5 tries for best quality, you want the smallest square possible and as little latex contacting the tape as possible, tell me if it improves your speakers.

Step 3: Alternate Ways

 if you want even better quality hot glue an old speaker of the right size into the hole or use a piece of poster board with a latex ring around it.



    • Tiny Home Contest

      Tiny Home Contest
    • Furniture Contest 2018

      Furniture Contest 2018
    • Metalworking Contest

      Metalworking Contest

    15 Discussions

    There is no tube for reflex in the passive radiator speaker you are just adding blockage to the reflex of your speaker to make its worse. you should remove the tube first and then add acaustic spring of same frequency response as the active radiator to make it work better. There is some calculation for the size of the spring. Do some home work on that and then inform me if it is doing well.

    This will actually make your speaker perform worse. Air reflex ports are what allow the diaphram to move faster. the air from the diaphram moving is going through the port. this allows the sub to move faster and therefor better response. Covering the port will give you harder hitting bass since the air can not escape.

    this isn't going to really do very much. and it's not a dipole. it may help with the loss of control of the cone below resonance, but at the expense of a change in port tuning frequency, and non-linearity. I think it'll do more harm than good. That howstuffworks link (where you snagged the picture from) is totally off base. A passive radiator actually works under pretty much the same principle as a "bass reflex" vented box. The only difference is that the air mass in your port is replaced with a second non driven speaker cone(with tunable weight). It's not a dipole, as the passive radiator is tuned to operate in phase with the speaker cone. for a dipole, you would have another cone (or the exposed back of the main speaker) which is playing the reversed phase signal. The HSW pic could be a dipole if the 2nd "passive" cone was an active driver wired backwards from the 1st (I think the radiation pattern would be a bit odd, though, with them offset so far vertically)

    6 replies

    Yea, I know it can do more harm than good but when I stretch the latex just right it actually resonates correctly and my base notes come out much stronger.

    Well, whatever works for you. The majority of speakers tend to be badly tuned anyways, so it could well be that you're actually improving the tuning. Or possibly you just like a little more peak in your bass that what your speakers were originally tuned to. Even if it is "worse" from a technical standpoint, if you like how it sounds that's what matters.

    The name of the article is still wrong though. It's still a "bass reflex" speaker really. You could even go so far as to call it a "passive radiator", but it's not a dipole. And the HSW description is wrong too. That description would be correct, except that air is compressible, so a passive radiator won't act as a dipole unless the box volume is extremely small (in which case you would be better off just running an open baffle.

    The latex is an interesting way of changing your port tuning though, and may have the added benefit that your port won't unload the cone quite as badly below resonance.

    Normally, the port is tuned such that the box and port will resonate such that it damps the cone motion at the frequency where it would otherwise resonate the most. At resonance, pretty much all of the sound is from the port, and the speaker itself will barely be moving. (Though it'll be just as much work for the amp to move it)

    unfortunately, below this frequency, the port will fairly quickly go out of phase and the already flappy unloaded cone will actually get pushed even further by the out of phase port.
    At that point, you're throwing the cone around like crazy, and almost all of the sound is getting cancelled anyways.

    The latex over the port might help it behave somewhere between a sealed and ported (bass reflex) enclosure. It'll still gain some cone damping from the port, but won't let the cone get quite as far out of control when playing too low. It's going to be a bit of a tradeoff, but it's cheap to try if you don't like the way your speakers sound, and if you don't like it, just peel it off. :)

    I've never seen a passive radiator with a port too., That seems to defeat the purpose of the passive radiator.
    It looks more like a design flaw &/or a bass reflex/passive radiator hybrid.

    I wouldn't worry to much about it, just next time spend a little extra cash, you'll really be surprised on how much better better speakers sound.

    well, it would be sort of like having multiple ports at different tuning frequencies, which is rarely done.

    The "spend a little extra cash" mentality I don't necessarily agree with. Several times in the past I've bought moderately cheap speakers, and rebuilt or modified them to sound better than anything I could get at several times the cost. (I'm not saying you can turn junk to gold, mind you)

    The description in this instructable is not a ported passive radiator. It is more of a hybrid. It's using the air mass, as in a standard port, but might have the advantage of limiting excursion at frequencies where the port falls out of phase below resonance.

    The images taken from howstuffworks are kind of crap. It says Dipole, but it's not any more of a dipole than would be a bass reflex with its port on the back. Their article really oversimplifies all of the enclosure explanations too.

    For it to be a dipole, it needs to be radiating a back and front wave which are out of phase at the frequencies of interest. A free-air woofer has a dipole radiation pattern, as does an open backed speaker.

    The passive radiator "dipole" described in the HSW article will have its PR in phase at the frequencies of interest, and will act to damp the active woofer's motion.

    At resonance, unlike what their diagram suggests, the passive radiator will be moving outward at the same time as the active woofer. It acts as a monopole over all frequencies that matter, and only becomes dipolar at frequencies below resonance where the wavelength is so long that most of the wave will be cancelled anyway. At those low frequencies the cone becomes unloaded leading to high excursion with little useful output.

    As far as making the speaker sound better goes: If there's an improvement by adding the membrane, the tuning of the port is probably wrong. Just changing the port length to optimize its tuning would probably give much better results than the non-linear component which you create by adding an elastic membrane.

    Yep, I will change that title and thanks for your input, I rarely get so much professional knowledge and I am very happy to learn that what I understood was wrong. ☺

    Cool. It's actually interesting to see that someone has had some luck with it. I actually tried this when I was first learning about how speaker ports actually worked, but it didn't really go that well on mine. I think I was using a piece of rubber from an old balloon. In hindsight, it was probably both too thick, and not flat enough to work at all. It was either loose enough that it was flapping (probably partly because the tension was uneven), or it was so tight that it mostly made the port completely ineffective (and rang like a drum).

    Some other tweaks worth trying, which may give similar results with less distortion, is to experiment with the box size, or port length.

    You can try different box sizes by filling part of the box with a non-compressible non-resonant material, like sand bags, chunks of scrap mdf or 2x4, bricks, etc. to make it smaller, or by stuffing more or less pillow stuffing into the speaker (more stuffing actually makes the box act larger, up to a point)

    Port length you need to get a little bit more creative with to get something non-permanent.

    Experimenting with the volume of a sealed speaker box is definitely worthwhile, and much easier to get right than a ported system. Making the box smaller will give you more peak in the bass, but at a higher frequency, and making it larger will make the peak smaller and lower in frequency, giving a smoother overall response, and more _low_ bass.

    In many cases, a ported box is larger than an appropriately sized sealed box, so sometimes a badly tuned ported speaker can be made to sound better by fully blocking its ports, and then tuning the box size for the sound you want. You'll get lower efficiency, but in some cases you can make a mediocre speaker sound pretty good.

    Keep up the experimenting anyways. Even the "failed" experiments can teach you a lot if you're paying attention. ;)

    In order for this to work ,the passive driver should be large enough. What you're doing is that you're clogging the port.

    Please be more explicit, the matter is very interesting. I understand almost nothing here...

    1 reply

    Thanks, latex is hard to work with sometimes, your taping is very tidy on that.