Box-tuning magnet-to-magnet construction

[Mr_Oasis]

Hi,

I'm building a boombox on a set of wheels for Roskilde Festival. I'm using two amp6-basic from 41hz.com, and four 6x9" fullrange drivers.

In order to maybe gain a little extra sensitivity, I'll be doing a magnet-to-magnet solution (flipping the stereo-image on one side in order to get the same signal on both drivers facing each other).

Does anybody know anything about the dimensions of the box, and the diameter of the reflex-port? How far should the magnets be from each other?

Cheers!

[planet10]

Can you draw a picture?

dave

[Mr_Oasis]

Sure I will!

http://img34.imageshack.us/img34/4370/boxg.jpg


The barrow I'll be using is 45x74 cm - so the box has to fit to that size, og maybe be only a little bigger or smaller. I think the depth has to be smaller in order to have the magnets close enough to each other - but it can't be smaller than 35 cm minimum in order for the battery to fit in.

Does anyone have an idea of the measurements of cabinets for 6x9" drivers, and maybe the best diametre of the reflex-port.

It's just some quite cheap drivers - they're rated to play 30-22kHz but I do not believe in that.

Any ideas?

[richie00boy]

I suggest you just make the box sealed, those kind of drivers are not really meant for boxed use and if ported will be peaky.

[planet10]

What you have is a bi-pole... the wider you can make it vrs the depth the better. Actually getting the magnets touching will have little effect on the sensitivity, but will kill off any issues with baffle step. To get the most from the push-push arrangement you do want to mechanically couple the magnets.

dave

[planet10]

Originally posted by Mr_Oasis
Does anyone have an idea of the measurements of cabinets for 6x9" drivers, and maybe the best diametre of the reflex-port.

We'd really need T/S parameters to be able to give a real answer.

Ritchieboy has the best guess without such, more often than not these are for IB use, in a smaller box aperiodic might actually be best.

dave

[chrisb]

I suspect these are car audio drivers, and the 6x9" size generally get used in a rear window deck or door panel of van, etc.

Leaky "enclosures" and very small "rooms" would describe the normal operating conditions for which these driver's parameters were most likely "optimized" .

At the risk of sounding elitist, also bear in mind that it's probably safe to suggest that for at least the past several decades, more engineering has gone into durability of car audio drivers for the harsh environments and extreme power handling to which they are frequently exposed than to refined sonic performance.

Having said that, I think you'll find that Dave's advice on driver mounting, particularly the inclusion of some type of cabinet wall bracing that also rigidly couples the magnets is well worth the efforts

[Mr_Oasis]

Thanks for all of your comments.

It is car speakers, but i'll mount the box on a set of wheels so it's almost a car anyway :-)

I won't be able to have the magnets physically touching each other, as the box then won't get deep enough to store my battery. The closest I'll be able to mount the magnets to each other is approx. 15 cm.

I'm sorry, but I won't be able to give you the T/S parameters as I don't have them.

When I can't get the speakers touching - and need to make the cabinet as wide as possible compared to the depth, would it then be worth the effort to omit the magnet-magnet solution and instead divide the cabinet into two between the drivers? Even thought they probably are intented for 'leaky' enclosures in a car, the reflex-port won't be a good idea?

[col]

I have played a bit with some JBL GTO937 6x9". I even made an attempt to measure the TS and design a ported box. That went out the window though when the software was wanting a stupid port that was something like a 100m long!

I ended up putting them in a sealed box with a cap to cut out anything below 200hz. I then ran subs via a active crossover, all being powered off a 41hz amp9. I'm quite amazed by the sound I get out of the GTO937 as mid-high and they really take a thrashing! I play them flat out for hours at festivals and parties.

Iv'e been contemplating trying them in an open baffle.

Mr Oasis you could try running them in a sealed box and sticking a 400uF cap on each driver, if they are 4ohm that would cut them off at 100hz. If you run them without the cap you might get a lot of distortion. I did.


col.

[planet10]

Originally posted by Mr_Oasis
Even thought they probably are intented for 'leaky' enclosures in a car, the reflex-port won't be a good idea?

No it isn't... any port would be a wild A*^ guess and much more likely to make things worse than better ... and if they are hi Q for mounting on the back deck, there is likely no reflex port that would do the job.

dave