Luke

Guys
I have a JL 8W6 in my legacy. its in a sealed box behind passenger seat. I love it. But have heard that putting the speaker into a really good bandpass box will help produce a bigger/louder sound.
If this is correct ,I would live some help to design one. I will build it myself ( cause i love doing things!!)

So please help with info/views

Thanks

john banks

AHA - my favourite subject!

Well, I think I'm the only regular poster in the ICE forum with a bandpass setup, but I think it is fantastic. There is a trade off between sensitivity and low frequency extension which can be altered by adjusting the relative volume of the ported and unported sections of the box. Note that it is worth putting overload protection into a bandpass design as distortion is very difficult to perceive and the first sign can be a dead driver. One advantage is the natural top end roll off of a bandpass design which means you can get away with 12dB/oct LPF rather than 18dB/oct as most sealed systems need to avoid contamination of the mid bass. Mine is 18 litre box with dual ports, only 20cm (8") paper cone sub makes unbelievable amounts of bass and goes as low as I could wish for. I bought a prefab Pioneer TSWX205. The sub is only rated at 250W max 100W continuous, but it claims to kick out 129dB. It certainly is the loudest sub I have ever heard. I think I got lucky with this one as bandpass boxes have a reputation for being one note wonders - I'm sure the dual ports help. I think it would need several times as much power to get the same performance out of a sealed/ported box. And I find it is wonderful for jazz/classic/rock/pop/chill out all of which I listen to regularly. Folk who sit in my car cannot localise the bass and believe it all to be seamless from the fronts. It is a modest and cheap bit of kit which makes it all the more satisfying. However, box design is all important with bandpass more than just about any other design. With such a quality and high powering sub as the JL you COULD get fantastic results, but the difference between a good bandpass box and a crap one is very little in terms of dimensions. Obviously prefab bandpass boxes that are not matched to a specific driver just sound hopeless.

Car Stereo Cookbook (from Amazon) by Mark Rumreich has a good section with some helpful graphs on bandpass box building. But trying a dual ported one would involve more complex calculations.

[This message has been edited by john banks (edited 13 August 2001).]

Luke

John

Cheers for reply
I am up for it !! Eventhough it will be a large cabinet,I still want it to fit in the rear passengers foot wells !!!!

I would much rather take my time get the best advice and get it right???!! first time . It will be controlled by a Nakamichi active sub control fitted in armrest consol.
Amp is R/F punch 40. bridged. The JL is a great speaker,and I really want to use it.

I understand I will have to use fibreglass as well as top birch ply.

I also know that i will run into trouble with the equations etc. This is where i will really need support.

Again thanks for a positive start.

Maybe I should listen to yours at a meet???

john banks

Well if you are anywhere near Scotland!?

I really don't think the rear passenger footwells is an option! It sounds fine in the boot. If in the footwells you would not be able to put someone in that seat and would only attract toe rags. It works quite well in the boot believe me!

Luke

John
Thanks!!!!!!!(Scotland...Jesus!!!)
I have a Legacy turbo estate and I always need the boot. I never carry passengers much.
I just fancy the idea.also if it is about 18.ltrs it will fit easly.

I spent years watching "Blue Peter"!!!

cheers
Luke

rockin'Ru

I agree with John 100%.Dude knows his shiznits.
If he put his sub box in the creature cabin,it could and WOULD be localized,destroying his "seemless" sub-to-midbass interface.That one sub will be on one side of you,either left or right,which will totally screw your imaging and sq of the system.
If you don't have rear passangers,could you use the rear seats as your boot space?You'd still have original boot space anyways because the 8" sub wouldn't require a very large box anyways.
No bigger than Johns anyways.
Thoughts?

Luke

John , do you have any drawings /plans etc you could fax me??

0208 362 8246 Cheers

john banks

Luke, sadly I bought a prefab box with sub as I knew how difficult it was to get a bandpass design right. The book I mentioned is really good, but would be a bit tricky to scan as it has quite detailed graphs and is bound.

Chris.Palmer

I have a similar Pioneer Bandpass box to John (Quasi-Sixth Order series tuned dual ported to be precise ) with a Rockford driver!

Of all the sub enclosures, bandpass are the most difficult to build, not physically, that’s the easy bit - just mdf (must be very well sealed recommend fibre-glass & silicone sealant) plus and a bit of carpet to make it look pretty. The difficult bit is calculating the size of the enclosure(s) and the size/length of the port(s) so your box is appropriately tuned for the parameters of the driver and your sound requirements.

I would recommend you take a look at the Car audio FAQ – it gives a pretty good overview of sub enclosures and the pros and cons of the different types. The sub-woofer bit is here:

rockin'Ru

Also worth a look...

rockin'Ru

500 watts...

Scooby Doc

Luke

Have a look at

Luke

Ok Ok Ok Ok guys I give up!!!
I will try the ported route!!!. I have the details for size etc. How much of a sound difference will it make ie will it be louder and that much lower.?? I will realy make it well,I have the use of a joiners work shop.

Thanks for great help so far guys

Will do it one day ......