Question about baffle placement and box volume

[piro]

Hi
I'm in the midst of building my very first speaker system, and I'm not quite sure about the enclosure.

I'm mainly uncertain about whether should the baffle be on the outside or on the inside, or in other words, should the baffle dimentions be the actual HxW or larger on each side by twice the thickness of the MDF?

Is there any general acceptation as to how it's best to construct the enclosure in that aspect? Which sides are to be in, out or on top of which?

And lastly, would sinking the entire baffle (about 0.7 cm), affect or distort the response?

TIA,
Jonathan

EDIT CONCERNING BOX VOLUME:
My drivers are SEAS 27TDFC (http://seas.no/seas_line/tweeters/H1189.pdf) and
L18RNX/P (http://seas.no/seas_line/woofers/H1224.pdf). According to my caculations the Volume is to be 10.8 Liters, and this, taking the drivers' diameters into account, calls for a 25x43x11(cm) box. Are my calculations correct? could it be such a small box?

Jonathan

 

[piro]

Another thing I've been meaning to ask (although I'm sure it will show me for the newbie that I am): inductors, as I know them, are large gauged copper wire things. Yet what I was given when I went to buy some for my original design of crossover were tiny objects, very much like small resistors, marked with that color code. Am I missing something here? could it be due to the values of those inductors (0.5mH and 2mH)?

thanks,
Jonathan

 

[simon5]

You probably got iron core inductors instead of air core inductors.

Iron core are much smaller, but you don't want iron core in audio, except for a subwoofer.

 

[simon5]

And lastly, would sinking the entire baffle (about 0.7 cm), affect or distort the response?

Yes, not recommended. The baffle should be flat.

 

[piro]

O.k thanks. I was getting worried about those inductors.
Any clue about the volume of the box?

 

[wintermute]

Just use simple math W X D X H = volume of the box... this should be the internal dimentions. Rule of thumb is to add 10% to the volume to allow for displacement of drivers, bracing etc.

so once you have the internal dimentions just work out which way you are going to join your cabinet sides, top, bottom back and baffle, and add the necessary amount for the thickness of your MDF. Do a drawing it will help

Tony.

 

[piro]

Yes, as I have said, I alredy have the dimentions of the box. My question was whether these dimentions appeaer reasonable considering the drivers' parameters.
And I gather there are is no general consensus as to the the way the box should be constructed?

Jonathan.

 

[wintermute]

Sorry Piro I misinterpreted your first post, probably should go to bed I had a late night last night, and going back and re-reading your first post it shows

With respect to how to do the baffle (and a completely non scientific approach), probably whatever way you find easiest to get it to seal well how accurately you can cut your MDF will influence this the most.

Tony.

 

[piro]

Okay.
How about the drivers' locations? (their distance from each other and from the edges of the baffle).
Also, I've determined the width of the baffle as 5cm more than the width (diameter) of the woofer. Again, is this o.k or is there special importance to the baffle's dimensions?

thanks again,
Jonathan

 

[wintermute]

Okay.
How about the drivers' locations? (their distance from each other and from the edges of the baffle).

summary put the drivers as close to each other as possible, and try to mount them a little off center (both height and width wise) for more info check out this recent thread http://www.diyaudio.com/forums/showthread.php?s=&threadid=61364

Also, I've determined the width of the baffle as 5cm more than the width (diameter) of the woofer. Again, is this o.k or is there special importance to the baffle's dimensions?

thanks again,
Jonathan

baffle width will determine at what freq baffle step (do a search lots of info in here) starts to happen at, also the width is (supposed) to effect the imaging with narrower widths supposed to image better. There are differing oppinions on this last point. I think that the above thread has mention of the edge and the baffle diffraction simulator in it both of which can be used to simulate baffle step, and the BDS being able to simulate difraction effects as well..

Tony.

edit: the edge wasn't linked, here it is http://www.tolvan.com/edge/

edit2: oh and one other thing, you shouldn't have any of your dimentions (W D H) the same, or it will tend to cause problems with standing waves.

 

[piro]

Thank you very much for your thoughtful response. I think that's about all I need to know.

Jonathan

 

[lynchingacers]

Okay.
How about the drivers' locations? (their distance from each other and from the edges of the baffle).
Also, I've determined the width of the baffle as 5cm more than the width (diameter) of the woofer. Again, is this o.k or is there special importance to the baffle's dimensions?

thanks again,
Jonathan

well one way of joining sides i did was a rabbat i think it was so strong i stood on it and no internal bracing just need a router or dato set tho

 

[piro]

whats a rabbat?

 

[piro]

Now that I think about it, if the tweeter and woofer arn't aligned (I mean their centers aren't on the same vertical line), wouldn't that cause discrepancies between the responses of the two drivers?

 

[wintermute]

If you are using 1st order crossovers then yes it is (I believe) really important (due to the large freq overlap of drivers). If you are using higher order then it isn't so critical.....

post five by rabbitz in the thread I linked to before ---> http://www.diyaudio.com/forums/showthread.php?postid=689379#post689379

has a link on exactly this subject

Tony.

 

[piro]

right.
Here's another one:
My baffle is the outer-most sheet of MDF' meaning that it's larger than the inner dimensions in both it's hight and it's width.
When I work with BDS or Edge, should I use the inner or outer dimensions for simulation? The reason I ask is that I'm pretty sure the margins do not vibrate (at least not to the same extent as the rest of the baffle), yet the sound wave dosent "break" till it reaches a physical edge.

thanks
Jonathan

P.S
It might be worth mentioning that I intend to chamfer the edges of the baffle.

 

[wintermute]

yes your feeling is correct Use the outer dimention as this is where the diffration occurs.... BDS from memory allows you to model with a chamfered edge

Tony.

 

[piro]

well, I have modled my enclosure using BDS and Sketchup (a trial of which may be found here).
I'd be greatful if you could take a look and give me your c&c (comments and critique).

TIA
JOnathan

Edit:
in BDS;
Load the profile, basic and advanced freq support, then:
set to quadruple sampling,
edge to Chamfer,
source to Combined, and type as Separate.
Only then press "Recalculate".

 

[wintermute]

Hi Jonathan,

Looks like you have BDS under control Only suggestion would be to try increasing the size of the chamfer. 2.5cm would probably be a good starting point... will tend to reduce that initial dip in the woofers response.

I didn't look at the enclosure because I don't like having to put details in to download a trial version of software.... but I think you are on the right track

Tony.

 

[piro]

The details are just fine being bogus...
The chamfer is 1.9 because that is the thickness of the MDF so it's easier to get a 45 degrees angle.

Jonathan