Sub woofer sound

[The Vee]

Know some of you are gurus on this so a few thoughts would be appreciated. Fitted a sub in the rear shelf today (saloon) and my queery is this. How much do I lose by not cutting a grille hole in the shelf cover. I know bass isn't really directional and that stand alone subs in the boot just rely on volume as they have no direct porting to the cabin area. I've tried it with and without the shelf and no real discernable difference in quick tests. My thoughts though is that it must restrict it a little as when the shelf is there it must to a degree have to compress the air between the sub face and the shelf although it's not air tight of course.
Am I losing much, maybe the higher end of the cross over range?

[Turbo_Steve]

Is it a bit of carpeted hardboard? If so, you're probably losing more than you think. And start turning the volume up, or listen to something seriously bassy (think Pendulum or Fuel Records etc) then you're going to notice that board flapping about and farting a lot. If there isn't enough clearance for the cone, it may actually be fouling the board....sounds rubbish and not at all good for the speaker.

The problem you have is that a bass speaker is trying to make good long wavelengths. If anything is in it's way, these are going to be either malformed or at least attenuated at a specific frequency.

At the end of the day: can you hear the difference? If you're happy....why change?

[The Vee]

Tbh my thoughts are to cut the hole. Just wanted opinions. Really you're saying what I thought must be the case. As an aside though, thought about the cone hitting the board, its well clear of that as I have mounted it on the underside of the shelf with a nice thick bit of MDF!
Thanks for your comments Steve

[VR4WGN]

it will be fine even if(i suggest)mounting it from the top instead,prolonged bass could cause it to fall,um keep eye on the sound quality of the rear speakers as the sub may cause them to deteriate FAST

[MarkSanne]

In my subwoofer setup we've cut away the lower layers of the shelf around the place where the factory subwoofer-gap is. Just left the toplayer intact which is fairy thin. However... when played hard and the subwoorfer-amp crancked up the whole shelf, cabling on there and other stuff starts to make vibrating & rattling sounds. If you want to keep the shelf such as I, you'll want to dampen all that stuff around there (which I need to do someday).

[The Vee]

Yep that's more or less what I've got. Not cut the metal shelf but mounted the sub under the factory hole with MDF. Certainly I've heard things rattle if I turn it up but have indeed fastened a few things down. TBH don't play it very loud, it just finishes off the sound quality better. Think I will cut the hole in the shelf cover though as that must be muffling it a little and should also stop it flapping as others have said. Have also put an MDF spacer around the hole on the top of the metal shelf so can fasten the cover and grill to that

[Spirit]

Well done mate.......after how many years ? /Devil5

[The Vee]

Well done mate.......after how many years ? /Devil5


Oh pooh....thought you'd be along soon:D Thought you might be asking why fit a sub when I still have drive shaft boots, bumper, rear lights, cat, dump valve, poor running and MOT to sort before September /pan. But yes the sub about 6 years. Maybe the bullet cam by 2013............

[Spirit]

Thought you might be asking why fit a sub when I still have drive shaft boots, bumper, rear lights, cat, dump valve, poor running and MOT to sort before September /pan. But yes the sub about 6 years. Maybe the bullet cam by 2013............

At least you're learning to prioritise :d

Now, that bullet cam......hmmm, I would say it would be nice to have it fitted for some RT action.......but the odd glimpse of my ass as I overtake you ain't gonna fill a movie is it :P

[The Vee]

At least you're learning to prioritise :d

Now, that bullet cam......hmmm, I would say it would be nice to have it fitted for some RS action.......but the odd glimpse of my ass as I overtake you ain't gonna fill a movie is it :P



PMSL you naughty boy. Anyway, you put the front seats back in yet? your arrrrrsssssee on the back shelf is a bit much to "bare" . Had any more Ivors recently? ;)

[Spirit]

Damn how did you know my arse won't fit in those damn Recaros anymore......too many bloody Ivors /megawoot

[The Vee]

Well, I'm just jealous on the Ivors front

[psbarham]

do you want a spare shelf to practice on?

[Wodjno]

PMSL you naughty boy. Anyway, you put the front seats back in yet? your arrrrrsssssee on the back shelf is a bit much to "bare" . Had any more Ivors recently? ;)


Ydna.. Best i come round and Set that E-01 up for you properly /yes

[The Vee]

PSB cheers mate - should be ok with the one I have - got it all marked up - but if it goes wrong, will give you a shout.
Nnelg not sure there's a prob with the E-01 but you're always welcome to come round. On early turn Sat

[Wodjno]

Nnelg not sure there's a prob with the E-01 but you're always welcome to come round. On early turn Sat

I agre /yes

There's not a problem with the e_01!

It's the Numpty setting it up :D :p

[The Vee]

I agre /yes

There's not a problem with the e_01!

It's the Numpty setting it up :D :p


Didn't know you did it?? /pan:jester:

Anyway to get back on topic, sort of, I have got claims to numpty of the year award. If you put back seats back up (therefore completing the boot enclosure) then having a hole for the grill in the back shelf makes a world of difference. Can't believe how thick I can be at times - must be my age or over tired or or or . Anyway yes it needs the hole!!

[White Lightning]

/pan

[Turbo_Steve]

er...yes. Having the seats down certainly counts as a "ported enclosure" though I am not sure what frequency it'd be tuned to?

[The Vee]

er...yes. Having the seats down certainly counts as a "ported enclosure" though I am not sure what frequency it'd be tuned to?


0.1 Hz @ 32DB sensitivity. "the numpty sound"

[Turbo_Steve]

LMFAO @ "The Numpty Sound"...one for the "Audio Engineers Handbook" there.

[CANDEE]

Nice work. :)

You are lucky in having the V6 and having metal backed seats... In the VR's we only have the foam seats, therefore getting a "proper" enclosure is hard...

I think that my old levin had a Fs of 25Hz with my old "open air" set up.

Did you get any pics of the set up that you have done?

Also as mentioned before, your rear speakers wont last long with a sub in there, with the backpressure from it. :) I havent run rear speakers in a car for about 5 years and dont miss them at all. :)

J

[oldgit9]

it also depends on what type of sub you are using...you can't just throw any sub in and hope it will give you the best results.

there are different types of subs. ones for sealed boxes, ones for ported boxes and (as CANDEE mentioned) open air subs. the best sub for your sub placement, is the open air type. these subs use the boot space as an enclosure.

im sure that there are web sites or stores out there that can tell you exactly what type, power rating and make to get for your system.

if you have fitted a different type (one for a box), then it would still work, but no way as good as it should.

[Turbo_Steve]

Actually, that isn't strictly true - It's a good broad guideline, but essentially the only property of the sub that is significant is the dampening factor of the suspension. This only really starts coming into play above certain powerlevels / below certain frequencies.

So if you're putting a 1000WRMS badboy in there, running it on a 150Watt amp and never going anywhere near clip, you're unlikely to encounter problems with over-excursion, under dampening etc. Of course, it's not going to be especially efficient, but then your average car subwoofer isn't exactly the most sensitive of devices.

In fact, most seem to list sensitivities around 89db/1wM, which is pretty lossy. Most of this loss is in the suspension!

I can't imagine it sound especially brilliant, but as Vee says, he isn't going for Max SPL.

The sort of frequencies where the box really starts to come into play are usually at wavelengths bigger than the space inside the car, and totally inaudiable inside the car. Stand 4 foot away from it, and you'll probably notice the lack of amazingly deep bass bouncing off the buildings.

However, if you're trying to go proper loud, you are correct, the speaker needs correct dampening to stop it destroying itself.

[MarkSanne]

All true Steve. I myself have a sort of hybrid open/boxed sub mounted to the rear shelf. It's a very, very small enclosure that houses a 10" Atomic sub powered by a very powerfull Earthquake Class J mono amp. The secret lays in the bottomside of the enclosure: a 'semi-open' (or closed, whatever you prefer) membrane. It's carefully balanced/tuned/adjusted to deliver a great of punch and low frequency sound level because of the pressure that builds up inside the enclosure. In a normal closed or ported enclosure the pressure would be too much for such a small enclosure, but because of the special constructed membrane it sounds very very good. Very nicely balanced to the rest of my audio setup.

You can see it's construction on the site of the builder:
http://www.zx-audio.nl/?target=g&item=4

And some more pics on our dutch forum:
http://www.galantfans.nl/viewtopic.php?t=19

For those who want to add a sub in a much more easy and cheaper way: DLS has an 8" open air subwoofer that should be plug & play (assuming you have an amp ofcourse). There doesn't seem to be that much open air subwoofers available, or at least I could hardly found any 2 years back when I was doing some research for this.

[Turbo_Steve]

Still pretty thin on the ground today from what I have seen.

The setup you describe is called a "passive radiator" over here and as you say can be a very effective way of tuning a speaker. I've tried to do it, but made a total shash out of the maths....VERY interested in yours!

Just had a look and OMG that is very neat!

[ZX-Audio]

Small correction... MarkSanne's subwoofer is not a "passive radiator" system but an aperiodic membrane.

A passive radiator or sometimes called a slap is airtight. Think of it as a speaker but without the motor (magent and coil). The passive radiator acts in the same way a helmholtz resonator (bassreflex port) does. It acts as a resonating mass with a surface area. Although with a slap the material is the mass where in a helmholtz resonator the aircaptivity in the port is the mass.

An aperiodic membrane like MarkSanne's subwoofer has is not airtight. Also the volume of air inside the enclosure should be as small as possible. The membrane is used to dampen the subwoofers impendance by selecting a specific membrane density and surface area.

[Turbo_Steve]

It's not airtight!!!!? Goodness me, how on earth do you calculate the permeability of the membrane?

[Nutter_John]

It's not airtight!!!!? Goodness me, how on earth do you calculate the permeability of the membrane?


ffs steve everyone knows that :D

Pish on it and measure how much goes through the membrane over a period of one hour :anxious::thumbsup:

[Turbo_Steve]

Cor, John, can you do my next stereo? :D

[The Vee]

He He didn't realise this thread was still going.
It is as Steve said earlier. Modest amplifier 2/300 watts rms and the sub is capable of 500 rms and 1000 peak. It is an inphase 8 inch which I was assured was ok for open air use. TBH it's not driven that hard as I'm using the standard head unit to power the other speakers. Appreciate what you say about the rear speakers, but if you disconnect them and watch the cones, at the general levels I play it they hardly move. The boot of course is far from air tight. What it has done though is given me a much more powerful sound with a decent dynamic range. While not earth shattering or real Hi Fi it's a vast improvement. Also put infinitys in which for mids and highs are so much better than the old stocks. Thanks for all your comments peeps. Oh and pics..........errr I'll see if I can get some

[White Lightning]

Yeah, some pics would be good mate /yes

Sounds like one of the front speakers is blown in my purple car and I have been reading old threads around what to buy/not buy. I was thinking about getting some Infinity Kappas for the front.

Didn't realise you could drive a sub seperately off an amp ... interesting, definately need to see some pics now ... and how much do you charge for fitting :D

[The Vee]

Yep Kappas for the front too. May not be fitted just yet!!
Charges would probably involve a burger or two, a pasty or three or even a cheese toastie on tiger bread. Of course all three options would secure the deal:D ;)

[White Lightning]

Sounds like a deal /lol :thumbsup:

[Turbo_Steve]

IF you're heading up in this general direction, I'd be happy to attend, I expect?

Do the kappa tweeters fit behind the factory grilles, then? Tempting......

[The Vee]

Don't know yet /pan But the rear speakers are too tall so have made mdf spacers to fit under the grills on the parcel shelf. Lovely stuff to work with a jig saw

[ZX-Audio]

It's not airtight!!!!? Goodness me, how on earth do you calculate the permeability of the membrane?
ffs steve everyone knows that :D

Pish on it and measure how much goes through the membrane over a period of one hour :anxious::thumbsup:

Unfortunately John was not so far from the truth. An aperiodic membrane is created by trial and error. Doing impendace measurements after every iteration you make (change density and thickness of the membrane).

Most calculations do not bring you anywhere in car-audio while these calculations are static and only theoretically based upon unreal environments. None of these calculations nor software tools like WinISD/BassBox Pro take account of the actual environment where you are going to use your subwoofer... a car!

As Turbo Steve said before, wavelengths of subwoofer frequencies do not fit in a common car. But it is not true that you cannot hear the because of that! In fact why the hell would earphones even exists if that really is the case?! In large areas like outdoor live performances acoustical wave development and coverage are big issues. However in a car there is not enough space to contain the full wavelength which causes just to compress and decompress all the air in the car instead of creating a waveform. Exactly the same was what happens with earphones in your ears. So basically the car is a cavity chamber with a specific shape and air mass which is also loaded to your subwoofer unit just like the enclosure itself.

At the end the functionality of an enclosure is not the spare the subwoofer unit to destroy itself, this is the suspensions (spiders etc) job. The main functionality is to couple the subwoofer unit to its environment (your car). To be able to design for this goal you need to know your car accoustically and you need to know your subwoofer parameter-wise (not just use the factory numbers, they can easily be 15% off).

Ofcourse poorly designed reflex enclosures can tear a woofer apart due to unloading poorts but that is just a side effect of that poorly designed enclosure.

[Turbo_Steve]

In large areas like outdoor live performances acoustical wave development and coverage are big issues.

Indeed, and this is where most of my experience comes from these days!


But it is not true that you cannot hear the because of that!

I see: I'd never thought of the headphone analogy before, but you're saying that because you're in a sealed enclosed with the subwoofer, your eardrum and the transducer (headphone) or subwoofer (car) directly couple?

That would make sense, as you do get bass fundamentals within the car environment, but they generally sound louder outside than inside when you open the window. I did a lot of experimentation trying to recreate 33.3Hz within the vehicle environment, and kept finding that it needed inordinately large amounts of power to get equivalent SPL inside the car compared to that measured outside, and no amount of port tuning seemed to change the effect inside the cabin. It got to the point where there were more harmonics/resonances from the speaker itself, the chassis and various bits of plastic rattling then there was pure sine-wave in the car. Shortly after that, the whole lot was stolen, and I totally lost interest.