Basic ported (my own) design (pics at end)

[MissileCrisis]

Hey so I am trying to design a ported home speaker for my school and was wondering where I should look for how to arrange and size 4 diagonal corner ports (like the Simplexxx lineup) based on tuning/whatnot. I've decided to try it instead of going with a 2'' flared precision port to cut down on material cost and to make it look cool. Any advice would be greatly appreciated and it will in no way be competing with any of Bill's designs .

I mainly mentioned it here because I noticed Bill mention that the 4 triangular ports balances some sort of air pressure or something along those lines.

Thanks Again!

[Charles Warwick]

For the tuning frequency you've chosen, calculate minimum port area necessary (using the calculator I've linked), and plug it back in to find the length needed: http://www.carstereo.com/help/Articles.cfm?id=31

That's about it. Play with the calculator and do some math. It's a good learning experience. If you have BassBox or WinISD consider doing some modeling first before choosing your tuning frequency.

Cheers

[MissileCrisis]

I'm using bassbox at the moment to model it. Seems like the drivers like a tuning of 40 Hz (for the box) to maximize their extension. Unfortunately that means a size compromise. Anything I need to know about vent air velocity or is their a target number below which is satisfactory?

I may end up making them sealed and living with 60 Hz extension. Otherwise it looks like 50 hz tuning will be what i go with.

[Charles Warwick]

http://www.eminencedesigner.com/EDTopic14.html

What's the speaker you're using? If the output/extension isn't critical sealed is certainly an easier route, but it's not that much work to add ports if the driver is good for ported enclosures.

[MissileCrisis]

As much as I would like to go sealed, for ease of design, it wouldn't attract many builders/kit buyers because most people want standalone bass. The ported design i'm working on gives bass to about 45 Hz (-3 dB) and roughly 110 dB max output per speaker (rms). Not bad imo. I'll upload a sketchup once I decide how to make the ports as I'm rather noob at this. I am using the following drivers

2: https://www.parts-express.com/peerless- ... --264-1146
It says it's optimized for sealed enclosures but bassbox seems to think that it could be used in either, and the modeling I've done seems to support that it can indeed do both. I'll post the file if anyone's interested.

1: https://www.parts-express.com/vifa-bc25 ... --264-1028

Question, will changing the given (calculated) dimensions of 22.4/13.9/8.7~ to something like 22/13/11 (even numbers) make a difference? Assume that they have the same internal volume after ports/driver/other stuff are subtracted. Mainly I don't want it to fall over and my dad, mech engineer, mentioned not making any dimension less than half the height...

Now, I know that the tweeter is 4 ohm, 93 dB at 1 watt and the pair of woofers (parallel) are 14/2 = 7 ohms at the crossover frequency of 1.5k with a sensitivity of 93 dB with 1 watt to each. Should I still consider putting in a series resistor with the tweeter to help match the woofers? and if so I assume I would just calculate the crossover with the tweeter resistance being the sum of the crossover impedance + that of the resistor I choose?

[Charles Warwick]

they have the same internal volume

That's your answer right there. Generally, people often say a 'golden ratio' of dimensions minimizes internal resonances the best, but realistically, just try to avoid making a cube and brace/stuff it well enough to dampen the rest. As long as the internal volume is same, that's all that matters. I don't know if you've factored this in, but if you stuff the enclosure with poly-fill it tends to make the box seem bigger to the woofer. Heavy fill is roughly 10% larger, and you can approximate down from there. e.g. for a 1 c.ft box with heavy stuffing you should make you models based on a 1.1 c.ft box. I think Bassbox might already have this built in with options for amount of stuffing, but it's been a while since I last used it.

Should I still consider putting in a series resistor with the tweeter to help match the woofers?

They're close enough that I personally wouldn't fret about it but 3-4db might be noticeable. You could always just put a L-pad on it if these are going to be for someone else since everyone's taste differs. I know I like my speakers a bit bright so I normally have a bit more high-end. Otherwise, yeah, just grab a few resistors and play it by ear: that's what I generally do.

Also, I think you may be crossing that tweet a bit low. I haven't used it personally, but unless you're planning on using a rather steep HP 1.5khz is probably pushing it's safety. I sometimes use 1.5-2X the fs for crossover as a rough safety margin. It certainly depends on the tweeter, but that seems low to me.

[MissileCrisis]

Lucky for me i've procrastinated on settling in on a crossover point, partly because its so expensive and partly because I want to nail the CAD design of the box/determine other design attributes before I settle on crossover, especially considering potential l-pad. I currently am sitting on 22/13/11 for dimensions and am designing it with the "no fill" setting on Bassbox because I don't have any polyfill and when I model light/heavy fill it doesn't seem to improve but actually seems to hurt max output (hard to capture in words, but it does seem to reduce the max output near the LF cutoff, rounding out the "max output graph, based on power handling". It does seem to reduce the group delay and air speed velocity, does anyone know if that would be an audible difference? I already designed the speaker such that the vent speed velocity is relatively low ~16 m/s and adding the fill drops it to a max of 13-12ish whereas the fill would decrease the delay a similar amount and remove the "dip" in cone excursion between 60 and the cutoff to make it look more flat in that section.

Question: How much bracing is "enough" I'm probably going to use 3/4 inch wood (solid) and use triangular 4 inch right angle braces or something along those lines. I could give it "ribs" which I've seen done before.

Seeing as l-pads don't effect the impedance in the crossover calculation I'll probably build the box using the given 4 ohm tweeter 7 ohm woofer numbers (may need to adjust woofer impedance if I change crossover freq) and then decide if L-pad is worth it after I measure it.

You're right, I originally wanted to use a more expensive 700 fs tweeter that would be fine at ~1500, I'll be changing the crossover to 2200 (3rd order butter) as the woofer falls apart above that, another reason its good to wait on buying crossover parts.

[MissileCrisis]

What I don't get is why they suggest 3.2 cuft. for ported when 1.2 cuft. ported looks like plenty fine to me (albeit 3 Hz less extension traded for power handling). I will likely aim for 1.2 cu.ft. ported.

[MissileCrisis]

So I went ahead and am in the process of building these speakers so this will be my unofficial non-bfm picture/build thread (short and sweet). If anyone is interested in specifics about the design process or the 3d model send me a p.m. I don't plan on selling this pair, it is for my own use but a similar set (1 woofer version) will probably become a club kit build, teaching sealed bookshelf basics.

Clamp efficiency

The sides are attached with biscuits, glue, and lots of clamps

This shows off a new set of bright orange clamps I convinced my dad to buy for the project!

The triangular slot ports aren't installed yet but the cutout for them is visible.

All that's left now is:
ports
cutting the back to fit the recess we made
wiring screw holes/ pre-mount.
prep-for finish,
finish, driver mount,
stuffing,
does it turn on test?
does it sound good test?

[Rick Lee]

Just saw this- looking good so far! Having used that tweeter before I will say that I like it. It is hot! You probably will find that you need to pad it. Some have used that tweet as a standalone in the middle of a line array and it worked well for them. And since you'll be padding it you might be able to get away with backing the xover down a little from 2200.

Also, I would damp the cab. Always good to cut down on internal reflections in the midrange.

[Rick Lee]

Ok, just saw your other thread on this. I've used this tweeter with 4th order active xover at 2k and it worked well. So..., might be best to keep it where you've decided since you're using 3rd order.

[MissileCrisis]

Bit late unfortunately, already built x-over, raised it to 2800 to play it safe. Hoping the beaming isn't too bad or I'll have to consider remaking the crossover $$$. Regardless they are drying their first coat of Danish oil at the moment so I'll get a pretty picture in soonish.

[MissileCrisis]

Just sealed one up using 1 pound of acoustuff in the speaker and I'm relieved to say it turned on, the first time. Oh and it sounds pretty sweet too. More on that later, when the second is assembled. For the record I used danish oil finish with a wax coat for protection. Pretty pics by tomorow.