Sub sealing

[NeX]

Can someone explain why sealing the sub is so important?

because from what i can work out, when the voice cone moves back it pressurises the sealed container and the pressure "pops" the cone back out giving a louder bass,

but i don't see why it's a certan size?

will any kind of box improve bass over one that is open?

Ta,

 

[Retepetsir]

It improves efficiency, it enables much better production of bass. A sub designed to be run in a box, being run out of one is not good at all.

The pressure created inside the box provides cushioning suspension for the cone, which helps increase power handling and avoids bottoming out.

Ported boxes, even though they appear open, work in much the same way. The back pressure from the subwoofer, and the design of the port still allows cushioning with air pressure. A subsonic filter is required, as when the box tuning frequency is hit, the sub will go mental and reach its excursion limits very quickly, which can cause it to break (pressure inside is incorrect).

i.e. my ported box is tuned to 33hz, with the subsonic filter set at 35hz.

Is yours not sealed then?!

 

[Ed]

Ok speakers that use sealed enclosures typically have fairly loose cones. The size of the box helps assist the suspension hold the cone in control. Too large a box and the speaker will flap about - too small a box and it will be too tight.

Now the other reason speakers need a box is to stop the pressure wave from one side of the speaker being cancelled out by the one on the other side. So the box does not allow this pressure to escape thus causing the speaker to work efficiently Ported boxes you may wonder work on the principle that certin size ports will slow the pressure waves, and what you infact do is design them to invert the wave so that it meets at the tuned point in phase with the speaker. This makes vented enclosures more efficient at their tuned frequency, but they are larger.

Thats a very rough summary

Ed

 

[Retepetsir]

What he said ^^^^^ :upside:

Basically 95% of subs are require a box for a good reason (unless they are infinite baffle subs).

Sub's that require boxes can have stiff cones, I know many of the DD and RE subs are stupidly stiff, and require a hell of a lot of time and power to break them in :devil:

 

[Ed]

Speakers like that in my opinion are pretty pointless. What AMAZES me is the very very poor efficiency of many car subs. Not many are above 90dB 1w/1m which is appauling. Decent PA subs can in some cases exceed 100dB 1w/1m which really is a very large difference.

 

[Retepetsir]

Very true......

But what I recently found out (and now know), is that for the maximum spl, its NOT best to go with the maximum effieciency......

News to me, but totally true according the the UK SPL competitors!

Some of the eminence subs are very high sensitivity, and good for nice SQ, they are derived from PA speakers afaik.

 

[NeX]

Thanks guys, that explains alot....

my sub is not really sealed. it is mounted on a board against the side of the boot and then the area behind is partly sealed with expanding foam and then muffled with toy stuffing,

but the air can still get out. what i did try for an experiment was covering the holes in the back of the sub with tape to seal it and it made alot of differnce....

i will have to make a fiberglass box, does it matter what shape the box is?
because i can use the inside of the C piller to get more space....


Thanks again guys

 

[Retepetsir]

No. shape doesnt really matter - just get it sealed!

 

[NeX]

ok,

what effect will it have becuse i don't want intense bass, the bass is ok but i'd like a little more kick. i don't want it to drown out everything else....

if i go for fiberglass does it have to be thick? because the distance between the back of the sub and the seatbelt restraint is about 10mm so it can't be 6mm mdf or anything like that.

also is there any damage of an unsealed sub?

 

[Ed]

Just so long as the box is not square, it will befine. A square box created standing waves that will not be ideal for perfect sound.

But what I recently found out (and now know), is that for the maximum spl, its NOT best to go with the maximum effieciency......

News to me, but totally true according the the UK SPL competitors!

Some of the eminence subs are very high sensitivity, and good for nice SQ, they are derived from PA speakers afaik.

The thing with SPL subs (as I remember) is they have a higher natural resonance near the SPL region like a tuned speaker to begin with (eurgh) and even more so when used in their ideal SPL enclosure. However out of this area I would say would not peform as well as a more efficient driver.

I would compare it to an engine with 100lb/ft torque at 6000 rpm as a high peak, vs one with only 90lb/ft across 4000-6000rpm. The first engine may make more power at 6K but the other engine would over all be faster.

I must admit though, that this is all based on my own assumptions without atually looking for any specifications on this gear.

Oh and finally as for PA subs, I think "Precision Devices" are my favoirite - anyone remember JAE a few years ago hhehehe

Ed

 

[quickdraw]

so what is the difference since the subject is on.
what about the inverted subs. that have the cones facing air bound?

and what problems and effeciancies etc does this cause if the wrong subs are done this way etc.

i know most of this issues but i have been asked this at least 3 times since the new forums were up. and i aint an ice person so whilst the thread is open . can you ice gods explain this also. you will explain it a hell of alot better than me

just an idea

 

[quickdraw]

also i think you are gonna be best top explain what each of the tech terms that yuo use. as again i also know alot of people get baffled at this. myself included some times.

sql =
SQ =
diffrence between the 2 =
etc etc etc.

cheers guys

 

[Retepetsir]

Inverting subs make little to no difference when run in a box, all you need to remember to do is reverse the phase of the speakers (swap the + and - around). Quite a few installs run inverted subs, or one inverted one not, etc. Just wire them correctly and its fine. I might consider inverting one in my new install (getting hold of a second JL sub).

Secondly, a quick explanation....

SQL = Sound quality install which can also go loud when required (mine is like this)

SQ = Sound quality install with great imaging, tone, staging, good response accross all frequencies, etc.

SPL = Pure 'loud' install with no sound quality. Tends to only occur under competition conditions where the highest dB's are required (world record is well over 170dB now........)

 

[Ed]

RE: RE: Sub sealing

so what is the difference since the subject is on.
what about the inverted subs. that have the cones facing air bound?

and what problems and effeciancies etc does this cause if the wrong subs are done this way etc.

i know most of this issues but i have been asked this at least 3 times since the new forums were up. and i aint an ice person so whilst the thread is open . can you ice gods explain this also. you will explain it a hell of alot better than me

just an idea

As Peter said, if one sub is inverted then you must reverse the polarity to the sub, however its my opinion that you will loose very slightly if you invert a sub within subs positioned the right way. Simply put the way in which a pressure wave is released from a cone on one side will be different to that on the other due to reflections from magnets and the speaker structure. It would also I believe affect the way in which a speak couples with the one next to it (which is what you want to happen, and is why on my old setup the two speakers were in a triangle formation, to enable both subs to couple nicely creating a much cleaner point source of bass sound