hi guys,



iv just aquired bass box pro,



and for someone who doesnt think much of graphs, im actually intrigued into the difference a bax will make to the output and linearity of a subwoofer...





now, my question is, after putting in all the info of my lil qmax 6.5 inch sub,



it says that for two subs, in a sealed box, the optimum size to get .707, is 3 ltrs,





this cant be possible can it??





where have i gone wrong, and why is .707 so critical???





also, waht if you get the responce you want, but its not .707, which is more desirable??





thank you guys

charlie

just worked it out....

gonna sound liek anoob, but its quite fascinating,

it turn out i can tune 2 subs in 20 ltrs to 35 hz, and get a f3 of 36hz...

another question,

how can this box play to 36 hz, when my woofer fs is 43 hz???

get on messenger i need some assistance ..........cors

dead set dont f#ck around with programs like BB pro and XO pro unless you know what the terms all mean.

I have a shelf full of books on loud speaker design, sound reinforcement, cross over design, audio terms, speaker design, loudspeaker enclosures etc etc.

I've studied this stuff for years. I can do all the sums manually (i have excel spread sheets i've developed as well to help me too). It wasn't until i understood all this stuff that I decided to spend the coin on BB pro / XO pro and a Harris tech USB speaker tester.

These programs can, will and do cause more issues for you newbies than they solve.

your speaker will unload below Fs, essentially in theory it can play below Fs but the amplitude and port velocity will make it virtually null and void.

BTW if you know your sums you will find BBpro isnt always on the $ especially when aiming for superior SQ or extreem SPL. Only testing testing testing will achive the ultimate at either end of the spectrum.

Shrek.. Komodo called you a noob.


It's actually not THAT difficult (unless you're clueless!).
It all comes down to what programs you use Bass box pro, is simple.

.707 is critical for nice sounding bass - tight detailed not boomy and smooth, any higher or lower and it sounds off. Group delay becomes fuct etc.
The program isn't always right, its just a program making a hypothesis.

I wanted bass box pro for its data base on subs, I found it quite out dated, and now I have to type in the T/S specs myself... lazy

0.707 is a "Q" factor. Supposedly the best transient response.

0.577 is "critically dampened" and warrants serious consideration.



People have been arguing over this for years.



If your "serious" you will measure the driver for its "actual" specifications before proceeding. These programs are only as good as the data you input.



Group delay is a strongly effected by attenuation, IE the steeper the slope the greater the group delay. Passive radiators are approx 29 degrees, reflex 24, sealed 12 degrees and infinite baffle 6 degrees. You can change this by "packing" up to 6 degrees. IE a packed reflex could go from 24 degrees to 18 degrees.



In theory infinite baffle provides the least group delay. (least bandwidth)



I prefer high order slopes to reduce point sourcing problems. The main thought process is how your going to integrate the sub network with the mid bass network. (Clue, different order slopes for the sub and mid bass provide poor listening)

dudes, i simply asked for some help on bass box pro, i aquired it freely, and was wanting a push in the rite direction,

bit rough to say if your a noob dont fk with it??

how bout spending that post explaining in detail why a sub wont play below fs, and what all the t/s specs mean???


it would of been much nicer on the ear to say, hey charlie, bassbox pro is a rough guide, dont take it as gospel, if you want a hand, iv got some experience, i may be able to help you...


thanks ablomech, but i dont believe its worth it, if a sub cant play below its fs, then i wont bother, as the prefab box tuned to 50hz provides a f3 of about 45 hz,


either new sub, or just lump the lack of low end...


is there any way i can make two drivers with an fs of 43 play any lower???

thank again

Is this one of those "onion things"?



I haven't worked with bassbox pro specifically, but I can assure you these programs are accurate. The problem is the "generic" specifications of the manufacturer.



Fs is the frequency at which the cone resonance starts to become an inhibitor to motor. A larger cone diameter will naturally have more mass than its smaller sibling (all else being equal) and therefore its resonate frequency will be lower. You could increase the mass with "doping" etc and therefore lower the FS. There is another way (OK yes there are several but they all use the same mechanism)



This is where bassbox pro etc start to shine. How is it that it predicted a lower frequency response than FS? Well you can change the FS with "loading", in this case air. So the box is designed to support (load) your driver for lower bandwidth extension. Sneaky eh? This is the PRIMARY function of an enclosure, to EXTEND the usable lower bandwidth. Now there is no such thing as a free lunch, so the penalty is a steeper slope (higher order), in fact the more you extend it, the higher the required order.

So is bassbox pro right? Absolutely IF the data is correct.



How low do you wish to go?



You could confuse everybody and play up to the FS.

isobaric will do it

You can play below Fs but you cant play both above and below Fs (or atleast thats my understanding.

Aquiring freely would give one the assumption that it is not a "legal" licence that you are using. Thats none of my business however. Mr Harris may mot like it though.

I'm not paying you out I'm mearly suggesting that you spend more time reading the abundance of published articles on this topic and playing with gear you already own rather than playing with tools such as BB pro to make a decision for you.

As abmolech pointed out 0.707 is just one figure used - though probably one of the most popular there are many theories regarding the maths involved with developing boxes.

Personally I preffer a lower "Q" factor on my home audio subs (though probably not as low as 0.577) and I rely on additional power to give me 'more' a linear result. However in car where I believe mechanical transfer is about the only thing in our favour I would rather go after something higher like 0.85.

In all honesty in a car with wind noise, road noise, fan noise, engine noise and all the other noises that generate an extreemly high noise floor do you really think that you need to play anything below 45 hz...

What type of music do you listen to?

Coming from a backgound of working in live sound reinforcement mainly in the rock, indie, pop/punk & blues and roots scene I can assure you that its fairly common practice to drop 10 - 12dB on the graphics below 50Hz because of noise floor limitations and the ability that that gives us to drive loudspeakers and amplifiers harder in the more audible spectrum...


Just food for thought

your one of those 'haters"



Pipe organs forever.

LOL Pipe organs forever as long as your ceiling tiles can cope

Speaking of which how good will the opera house be when they do the refirb! hopefully they can let the bottom end open up properly. Then the rivalry between melbourne town hall and the opera house might become lively again

.

I have never been impressed with the Opera house, (except for their acoustic testing room, now THAT is impressive), our town hall is rated in the top ten in the world (Auckland NZ), the Sydney Opera house would be lucky to be in the top one hundred. Now the Melbourne town hall is another story, one of my all time favourites (OK I prefer the Carnegie or the Fisher). There is a reason they built Gothic cathedrals that way. You want to hear real bass(unequalled), spend some time in one them.





Sorry to say most people cant hear below 35 Hz. However that doesn't mean we cant feel it.

so, if i have two drivers working tohgether, it lowers the fs due to higher mass???

my next question, what would a good starting point be to build a nice sonding box for two of the qmax subs???

dont mind getting a bit fiddly, as long as its not like a wicked one or anything, have maybe 1.5-2 cubes room worth!


thank you guys...

It is easier to reduce the internal volume (packing blocks etc) than to increase it.



Make the largest volume box you can get away with.



Box construction for subs is a matter of providing the least baffle flex to reduce paradisaical energy loss, and a suitable resonant frequency outside of the expected frequency bandwidth.(MDF should be somewhere around 200-300 resonant range).



There is considerable force developed by the motor, I suggest bracing from the front baffle to the rear (Threaded rod can work well, if your not into wood bracing) Glue all joints. Radius all outside edges if your going to cover the box.



Possible over the top "solutions".

Support the motor and attach to the rear baffle.

Use 45 degree internal bracing on all the perpendicular joints. (Adds to rigidity and reduces internal loss to heat, yeah OK barely measurable )

Seal the inside with fibreglass resin to reduce loss through joints and the wood breathing. (Some driver glues are susceptible to fumes, so wait for a day or two before installing)

Make sure the front baffle is flat (They can warp the basket, and not perform a seal)

Consider using bolts instead of screws for "bolting" the basket to the box.(countersunk bolt and nut)

Use at least 25 mm thick MDF.

cool,

where would i start as to ports and such, would i use BBP as a rough guide,

also, does he port size get tuned to the box or the woofer???


thank guys