[Spadez]

Its a 50L Twin Passive Radiator Sub with Peerless driver and O-Audio 300W amp. Here is a link to my build information:

http://www.hometheatershack.com/for...7-passive-rad-build-good-idea-copy-build.html

At this current stage, all of the compoents are mounted in my sealed box. Currently the lid isnt attached but for testing I placed the lid on top and put a weight on it to get a decent seal. I then hooked the amplifer input up to my laptop with an RCA cable and played some bass heavy songs. I used the default amp settings, low-mid volume, 80Hz crossover, etc.

However, the sound wasnt great. There was decent enough bass, but there seemed to be a lot of extra noise made by the driver cone itself vibrating to produce the sound. With my bose speaker, all you heard was the solid bass sound, but this also has a sound a bit like flicking a tentioned elastic band. The speaker is secured well to the bass box, so what could be causing it?

The following things still have to be done in order for the speaker to be properly finished:

1. Glue the top on properly
2. Add 300g weight to each of the peerless passives
3. Add fiber baffeling

Can anyone give me some help please?

 

[davidburn]

I have seen in some Subs where the Speaker terminal wire going to the cone is hitting and makes a sound similar to what you are hearing. Im no expert but it sounds as if something is loose. Your build should yield great bass and looks well designed. Run your sub in free air and you will be able to hear if something is not right.

Cheers.

 

[Spadez]

Hi, im at work at the moment, but I will look at the terminal wire when I get home. Im not quite sure that is the route of the problem in my case however.

What could be loose so I know what to look for? When running it in free air, is there anything I should be listening out for?

 

[Spadez]

Ive been looking into this and something that came up is "speaker chuffing". Im not sure if this is what my speaker my be suffering of? Its hard to describe, its like you can hear the air moving as well as the sound the low tones sub is making.

 

[Chester]

chuffing is basically when the air speed exiting the port goes over ~25 ft/sec (If I remember correctly) and can basically cause a standing wave to build within the port; it sounds sort of like what you would get if you blow air fast over the top of a beer bottle (to make a sound) but is probably lower in freqeuncy... that is why it is important to use winISD to check the air velocity in the port and if it is too high, either use a larger diameter port (which would also end up being longer) OR get a passive radiator

Chuffing will 'commonly' happen when you are driving a ported subwoofer below its tuning frequency (so if you tuned the port to 30 hz, below that frequency there is no 'resistance' to the subwoofer and to the cone it appears to be in free air (not in a box) so the you will end up moving a lot more air (greater speaker travel due to the lack of pressure build up behind the cone at the lower frequency)

 

[Spadez]

Ok, I guess it isnt chuffing then because mine is a passive sealed sub. Any more input to help me fix this would be much appreciated.

 

[Chester]

but looking at your build pics you are using passive radiators... so its not chuffing; that only happens with ports

 

[Chester]

you had a rectangle cut out of one side, are you using a plate amp? that could be rattling some how possibly (I never use plate amps, just my intuition)

 

[Spadez]

Hi. The plate amp is installed but it is very secure. I think the sound is coming purely from the driver.

 

[Chester]

I would definitely hook the driver up in free air (DONT TURN THE VOLUME UP TOO LOUD WHEN YOU START TESTING IT ) and drive it with whatever was causing it to make the sound while in the box

 

[Mike P.]

Currently the lid isnt attached but for testing I placed the lid on top and put a weight on it to get a decent seal.

Test the sub in free air to verify that isn't the issue. My guess is the box is leaking air.

​

 

[Chester]

get some silly puddy and make a long line of it around the edges, then put the top down... be careful though, it can be difficult to separate if you put too much pressure on it

 

[Spadez]

Im a little happier now. I've come home and tested it some more. There is a 1mm gap on one side between the lid and one of the sides which I guess would allow air to travel quite freely. When sitting on the lid and running it, I could also feel a bit of air moving between the driver and front panel.

I think I need to get the top attached properly and figure out a way to get the driver fully air tight, then I can start worrying what it sounds like. It already sounds better just by putting a lot of weight on the lid and running it.
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[Endesereth]

What I did is that I used silicone to fill up the cracks inside of the box, I am also going to put some wood putty in the cracks before I stain it. I am pretty sure this will be a really good sealer.

 

[evilskillit]

it is most likely just because the top is not attached. I built a small sealed box for an 8" sub and tried it. In free air the sub sort of made a lot of noise, then I tried just resting the sub in the box but it still made a nasty sort of poppy noise, but then I got some gasketing and screwed the driver in and tried it again and it sounded great.

You may also want to give stuff some time to break in once the box is finished.

 

[Spadez]

I need to seal the driver into the sub unit because air is escaping between the two. I don't want it to be a permanent solution, just in case I do decide to take the drivers out of the sub unit in the future (if one breaks etc).

Can anyone recommend either a material or some kind of sealant which can be sandwiched between the two to make it air tight.

 

[Spadez]

When I run the sub in free air, even though it is very quiet, it doesn't make the twanging noise, however it may do when the volume is turned up, but I didn't want to do that in free air in case I damage it.

Im just going to get the sub properly sealed this weekend.

 

[Spadez]

One more thing! In addition to my question above about sealing the driver, can someone tell me if it is beneficial to have the sub slightly suspended off the ground with rubber feet. I don't mind having it sitting on the ground without feet if it sounds better.

 

[Spadez]

Final thing!

http://cpc.farnell.com/_/mdm-25/speaker-sealing-tape-3m/dp/LS00625

Would this sort out the driver sealing problem

 

[Mike P.]

Final thing!

http://cpc.farnell.com/_/mdm-25/speaker-sealing-tape-3m/dp/LS00625

Would this sort out the driver sealing problem

That will work. Window weather striping works well too. Seal the sub and both PR's. Placing rubber feet on the bottom of the sub will help decouple it from the floor. Subwoofer spikes would be better.