My DIY speaker problem

[psin3t]

I am an audio producer on limited cabbage. For the first time I am launching into building my own monitors (with a little help from my friends). Unfortunately I am an electronics noob - but I do know these prosumer monitors (M-Audio/Behringer etc) are ballz and I can do better for less.

I have watched and learnt on this site on and off for years, but never needed practical help. Here's where I have gotten to, and then I will explain my problem:

I have purchased B&C 6NDL44 6.5" mid/woofers and a pair of Vifa BC25SC06-04 1" Textile Dome tweeters. They are on their way here and should arrive in a week. My friend is building an internal crossover for them at somewhere around 3000hz (exact calculations and experiments yet to be investigated) with an impedence match workaround.

They are to go into simple vented enclosures, powered by a 138w@8ohm/220w@4ohm per channel amp, fed by my crossover with a HPF at somewhere around 100 - 150hz?, with the remainder of the bottom end going to my 188w active 10" sub (already purchased).

So here is my problem:
I installed WinISD to calculate the enclosure volume. To my suprise - it came out as 4.3ltrs. I thought that was rather small for such a driver. After investigating the recommended vent sizes, I saw that it in an effort to keep the Vent mach down (the speed at which the air passes through the vent), it suggested a port of 68mm diameter and 329mm in length.

I do not see any feasible way to build an enclosure as small as 4.1ltrs, with a port that big, in any format that resembles any speaker cabinet I have ever seen - let alone something that would stand up by itself. A very similar driver from B&C recommended a 9.1ltr volume, but I can find no enclosure designs for this driver.

What am I missing here? I sense the clue is in the high Qms rating of the driver...but I am a little lost. Any advice would be much appreciated.

[psin3t]

Anyone? From what I can gather - a driver with a high Qms is more "rigid" and therefore requires a smaller volume of air to perform correctly, as larger volumes of air have more spring. So, after running MANY various calculators (I thought there was some guy called Thiele who had already sorted this out....?...no calculators give the same answers..?...) I have come to the conclusion that something around 5lts is correct for this particular driver.

HOWEVER (and thats why I would love a response from someone who knows this stuff...) when following the "Golden Ratio" (1:1.618 :0.618) for minimizing internal resonance an enclosure of this size has an internal base depth of only 11.2cm (@18.13cm wide and 29.33 high)!!! This provides for a 4cm diameter port @ 9.71cm long...

.....but that is a TINY enclosure. I new they were for compact design, but that's more compact than I suspected.....do my calc's seem fine?

[psin3t]

Should I alter the ratios to get the driver around the "front" by reducing the height and increasing the "depth"?

up all night nutting this out......considering shotgun mouthwash for breakfast

[Brett]

The 6NDL44 doesn't model well as a bass driver, more like a mid, but that comes down to terminology in it's intended use.

For a max flat 4th order at 68Hz, I also got about 5L. Using your suggested 68mm diameter port, I got it's length as 41.6cm or a port volume of 1.5L. And it 's possibly still too small depending on the levels you want to use it at.

Looks like you picked the wrong driver for a small ported enclosure. Seal it, use it as a mid >150hz and put another driver suitable for the role under it. Or return them for a refund.

[planet10]

This driver really doesn't look like it makes a practical midbass. It is a moderate efficieny mid that can be XOed low.

Trying to get anything reasonabley shaped in a vented box leads me to the same issues you modeled. Means the port needs to be external... but the port becomes long enuff to need to be modeled as a TL, so your modeler & mine aren't and can't tell the story. You'd need the MJK modeler.

IMHO these want to be in 4-6 litre sealed and XOed to a pair of woofers just below 200 Hz (with 1 woofer your XO should be below 80-100 Hz)

Did you order the drivers before doing your homework?.

dave

[psin3t]

I really could shoot myself in the face after all that.

What about this as the reserve of the desperate:

Considering I have the 10" sub that is good up to at least 250hz, and these are basically going to be used for 2.1 playback at the computer, could I just make the vented ports as described (everything will certainly fit - i have a new design with a 40mm port @ 97.1mm) with the drivers on the broad side of the enclosure, and tune the sub to pick up the rest??

I have even come around to the compact idea....

Would it be workable?

[psin3t]

Yes I am feeling very humble. Any suggestions on suitable replacements for the desired application using the range at parts-express as a guide...?

I guess I need to get onto this quick smart before they ship.............

[planet10]

Maybe one of the multi-way guys could help... i don't pay much attention to midbasses (except for use as helper woofers that only need to reach 500 Hz.

I'd probably try to get away with a Mark Audio Alpair 7 (or a 12 if the 7 didn't have enuff headroom)

dave.

[planet10]

I must say that B&C aren't very honest when they say woofer 70-6000 Hz....

dave

[niss_man]

I would have bought a Madisound RB Kit. All the hard work has alreafy been done. Crossovers pre made, box design and using beautiful Euro design vifa drivers you wouldn't have needed your sub either.