Saabscene Saab Forum - Saab Technical Information Resource banner
1 - 20 of 29 Posts

·
Registered
Joined
·
1,592 Posts
Discussion Starter · #1 ·
I should be getting my fat stezza installed in the Aero soon - Max Power, here we come
.

Only joking! However, I want to establish whether to go for free air or a sealed enclosure subwoofer. I already have a really good JL 12" free air sub that is currently residing in my loft that could be installed. If used, I guess that this would save me around £250. This sub came out of my RS2000 (fitted to a modified, strengthened parcel shelf) and worked very well indeed, giving powerful, but very well controlled and tuneful bass.

I am intending to mate this to a bridged 3 channel amp, then drive the 4 satellites (Boston fronts, courtesy of Scrappy) from a second 4 way amp. Again, these bits are also sitting in the loft.
 

·
Registered
Joined
·
14,305 Posts
I've put 2 x 10" free air subs in the parcel shelf. They fit comfortably without mods (other than two holes, obviously
). They're connected via a Speakon 4 pole connector so I can easily unplug them to take the shelf out. I have also been meaning to get around to putting a "dummy" fabric covered panel above them to hide them... that was at least 18 months ago


They are Alpine type SWS1041; not cast chassis but pretty well made and for about £70 each good value.
 

·
Registered
Joined
·
2,263 Posts
Air (acoustic) short circuit = woofage from the rear of the cone coming round the baffle (your parcel shelf) and, being 180° out of phase with what's coming from the front, will cancel, meaning less overall woofage .

However, (acoustically) loading the driver into the boot rather than a box could mean more woofage, provided the driver is designed for it. Do you have the spec sheet? Let me know the fo, Qts, Qes and Vas (I think that's all I need
) and I'll let you know.
 

·
Registered
Joined
·
360 Posts
If the air can get directly from the front of the speaker to the back (and vice versa) much of the audible power is lost because less pressure builds up ("short circuited").

With a good baffle board (aka parcel shelf) there is no short-cut for the air to take so the speaker pressurises/depressurises the cabin as the cone moves in and out - and that's what your ears detect as sound.

HTH

Mike
 

·
Registered
Joined
·
2,277 Posts
As the Saab parcel shelf is quite well made and friction fits into the solidly built metal brackets either side the only tweak required would be to add some dense foam between the rear of the shelf and the hatch to prevent the 'short circuit' and increase 'Woofage'!!

Nick.
 

·
Registered
Joined
·
14,305 Posts
The 12" will just fit in the non-hinged section of the parcel shelf but won't shift as much air or sound as good as 2 x 10".

Most car subs are specified for either free air or enclosure use. Just make sure you do have the right type. The free air is a bit of a compromise as it assumes i) infinite volume which is not quite correct and ii) no leakage which is practically unachievable

If I was being a perfectionist then I would put mount a speaker specified for enclosure use on the parcel shelf and build an appropriately sized enclosure behind it, and tune it to a QB3 alignment... however that requires an awful lot of messing about to get it dead right, especially as the volume and damping of the car comes into play, effectively giving you an overall tuned bandpass enclosure (you still with me here?)

But being a realist, the easiest way to get a sub sounding OK in a car is to get one designed for "free air" use and mount it in the parcel shelf...

PS Martin it's more useful to have Qms and Qes from which most programs calculate Qts. Mms also helps.
 

·
Registered
Joined
·
1,592 Posts
Discussion Starter · #11 ·
That all sounds very complicated to me. The JL sub is a specially designed 'free air' type and as long as the phase is the same as the satellite speakers, surely it will all work nicely? It certainly did in my RS and I will be running exactly the same amps. Might find specs on JLs website.
 

·
Registered
Joined
·
2,263 Posts
Martin it's more useful to have Qms and Qes from which most programs calculate Qts.[/b]
Qts = 1/(1/Qms + 1/Qes) - ie parallel sum. Therefore any 2 out of three will do .

BTW, you can download a free Excel vented box design routine from http://www.fatcityaudio.com/audio/vented.zip. I'm sorry that it's a bit basic. I've updated it recently but haven't uploaded the new version. Still works though and I've checked it against commercially available programmes. NB: to do a sealed box, just set the port frequency to a low value, eg 0.01Hz.

enjoy!

Martin
 

·
Registered
Joined
·
1,592 Posts
Discussion Starter · #17 ·
OK - I'll try switching phases - shoudn't be too difficult.

I am usually a supporter of smaller bass units, but the JL does give a quite amazingly tight sound for the size. It has been driven by a Caliber amp, which I think does have a fair current delivery. I very much doubt that Alpine subs would better it for quality - after all, they are more of a budget model. My local specialist (Huet Car Radio - see http://www.huets.com/ ) reckoned that JL made the best free air models when I purchased mine.
 

·
Registered
Joined
·
14,305 Posts
Originally posted by Woofage:
[qb] QUOTE
The 12" will just fit in the non-hinged section of the parcel shelf but won't shift as much air or sound as good as 2 x 10".[/b]
Hhhm, the jury's out on this one. However, one thing is for sure, a single 12" still has more cone area than 2 x 10"'s! [/qb][/b][/quote]Nope, typical Sd for a 10" is of the order of 330-360 sqcm, so two is 660-720 sqcm. For a 12" it's 510-540 sqcm, thus you get about 33% extra for 2 x 10".

A 12" will fit- I know 'cos I measured it!!
 

·
Registered
Joined
·
14,305 Posts
Originally posted by Woofage:
[qb] QUOTE
as long as the phase is the same as the satellite speakers[/b]
It's actually worth experimenting with the sub both "in"-phase and "out-of" phase. Car audio isn't always straightforward! [/qb][/b][/quote]If it's working as a true sub, phase shouldn't matter that much as it will only start being "useful" below the present system -3dB point...

However, it'a always worthwhile swapping phase on an LF device in any listening environment in case there's particular nodal behaviour present
 
1 - 20 of 29 Posts
Top