on Sale - $55/pr (drivers & XO)

[Chris Roemer]

Re: on Sale - $55/pr (drivers & XO)

Ok, I've purchased the drivers and XO parts and am starting my enclosure build. I'm going with .32 ft3 enclosures (after the XO, drivers and port tube is added I think it will be closer to .3) and am making it a little wider and not quite as deep to better fit my shallow desk.

My question is regarding driver spacing. I'm considering using a baffle cover using a 6" wide by .5" thick piece of solid red oak routed on the backside to allow for the surface mounted driver (going for a "rear mounted" look without actually rear mounding the drivers). I was wondering if the specified driver spacing is the furthest distance or if they can be moved a little further apart to accommodate the .5" round over I will be using on the driver holes.

At an Fc of 4kHz, you should TRY to not exceed a center to center spacing of 3-3/8" (sos 13,500 ips / Fc 4000 = 3.375" c-c). So there's a bit of room to wiggle.

[lostboy77]

Re: on Sale - $55/pr (drivers & XO)

At an Fc of 4kHz, you should TRY to not exceed a center to center spacing of 3-3/8" (sos 13,500 ips / Fc 4000 = 3.375" c-c). So there's a bit of room to wiggle.

Sweet! Setting driver spacing at 3-3/8" gives me 3/4" between driver holes on the facer. I am planing on using a 3/8" round-over on this trim piece so this is perfect.

BTW, is there anything bad that will happen by recessing the tweeter 3/8" with a 3/8" round-over or should i just simply flush mount the tweeter on the baffle cover.

[Chris Roemer]

Re: on Sale - $55/pr (drivers & XO)

Sweet! Setting driver spacing at 3-3/8" gives me 3/4" between driver holes on the facer. I am planing on using a 3/8" round-over on this trim piece so this is perfect.

BTW, is there anything bad that will happen by recessing the tweeter 3/8" with a 3/8" round-over or should i just simply flush mount the tweeter on the baffle cover.

Wolf says that if you used an npe cap on the tweeter, then it won't matter.





(just joking, and putting words in Ben's mouth) - Chris

[lostboy77]

Re: on Sale - $55/pr (drivers & XO)

If I NEEDED a smaller box (say, 0.15 cf), I'd vent it and use the ND90-8 for an F3 in the 40's.

Chris

Chris, what port length/dia. would you use for this? Also, can your XO be modified for this purpose. If so, wouldn't you use the ND90-4 (4 ohm) like you did for the MT?

[waaadef]

Re: on Sale - $55/pr (drivers & XO)

Sorry for the noob questions, but I'm baffled by the crossover component values.

It seems like a 4uF capacitor would result in a textbook 6,631 Hz crossover at a tweeter impedance of 6 ohms.

A 0.44mH inductor on the woofer would result in a 1,447 Hz crossover (assuming 4 ohms impedance).

I'm really perplexed by the Zobel values. Maybe the Zobel flattens the impedance at about 11 ohms? In that case, I think a 0.44mH inductor would low pass at 4,000 Hz.

Any insight would be most appreciated. Thanks!

[Wolf]

Re: on Sale - $55/pr (drivers & XO)

That's why Textbook Equations are not the best answer for xover values.

There are a lot more factors involved.
(If you read up on the 'Bible' thread at the top of the forum page, your mind will be invaded by tons of info...)

For example, if the tweeter has a peak before rolloff, then a smaller cap can be used to smooth that rolloff out for a lower xover point.
And that coil- is larger than normal to help faciliate baffle step losses to make the design sound more 'full' in the bass.

The transfer-function is what the xover parts are doing to the frequency response plots for the respective drivers. I know this example is for 12dB slopes below (and -6dB is typical xover junction for 12dB slopes), but it is easy to simulate and post. You can see how the woofer rolls off at 1k or so, and the tweeter very shallow. The actual xover point is about 3k in the transfer functions (which will be different from the actual acoustic xover point too I might add), but the tweeter is -3dB at 4k.

The formulae give you the -3dB points for the 1st order Butterworth equations you are using, and may not actually be where the xover exists.

Make sense?
Wolf

(PS- yes, I know I didn't give the exact example he was looking for, guys, but I tried to whip up an easy to see simulation.)

[Chris Roemer]

Re: on Sale - $55/pr (drivers & XO)

Chris, what port length/dia. would you use for this? Also, can your XO be modified for this purpose. If so, wouldn't you use the ND90-4 (4 ohm) like you did for the MT?

I'd have to check the box/tuning tonight.
No XO, the "Pico Neo" is a full range design.
If you compare the -4 and -8 (overlay) you'll see that the -8 is a bit flatter.

chris

[Chris Roemer]

Re: on Sale - $55/pr (drivers & XO)

Sorry for the noob questions, but I'm baffled by the crossover component values.

It seems like a 4uF capacitor would result in a textbook 6,631 Hz crossover at a tweeter impedance of 6 ohms.

A 0.44mH inductor on the woofer would result in a 1,447 Hz crossover (assuming 4 ohms impedance).

I'm really perplexed by the Zobel values. Maybe the Zobel flattens the impedance at about 11 ohms? In that case, I think a 0.44mH inductor would low pass at 4,000 Hz.

Any insight would be most appreciated. Thanks!

As Wolf said, "textbook" XOs just don't work.
The simple act of attenuating a tweeter will "slide" its point where it crosses a woofer's rolloff slope, thereby changing the system's Fc. You're not accounting for that fact whatsoever.

If you want the "bulb" to go on, you have 2 choices:
Download Jeff Bagby's "PCD" and dive in. You need Excel running on a PC to use it, OR
Google "FRD Consortium" (it's moved as of late) and download "XOverSim.exe" (it only needs a PC to run on). I can help you with that.

If NOTHING else, you can use it to design "perfect" Zobels (well, as perfect as they can be), and you'll be able to SEE what's going on here.

BTW, a "Zobel" doesn't have to be used strictly to flatten the rising impedance of a driver. When used with a coil, as you drop the resistor's value down (from typically near nominal driver impedance) to end at zero, you can shape an entire gamut of slopes and shoulder contours between a -6dB/oct filter and a -12dB/oct filter, which is what you get when the "Zobel" turns into just a cap.

If you want to play, get "XOverSim.exe" and get back to me. I'll show you how to run it.

Chris

[D, Rose]

Re: on Sale - $55/pr (drivers & XO)

anyone have more pics? Dave?

[kornphlake]

Re: on Sale - $55/pr (drivers & XO)

anyone have more pics? Dave?

Here's my attempt:

[waaadef]

Re: on Sale - $55/pr (drivers & XO)

Chris and Wolf, thanks for the responses and recommendations. Much appreciated!

[greywarden]

Re: on Sale - $55/pr (drivers & XO)

I did a 3d model of these lastnight because I want to use them in my Steampunk speaker build for a friend.

I'm planning on putting a clock face in the fron baffle, and I can either move the port up or down, and I decided to move it to the front.

Is there going to be any major differences in moving the port to the front and should it be closer or further from the woofer, vertically?

[Chris Roemer]

Re: on Sale - $55/pr (drivers & XO)

I did a 3d model of these lastnight because I want to use them in my Steampunk speaker build for a friend.

I'm planning on putting a clock face in the fron baffle, and I can either move the port up or down, and I decided to move it to the front.

Is there going to be any major differences in moving the port to the front and should it be closer or further from the woofer, vertically?

My advice is:

Don't try to skimp on the box and build it out of 1/2" or 5/8" stuff. Think of these little woofers as you would a fairly stout 6" to 6-1/2" woofer. They need 3/4" walls.

Front venting is fine, but:
Don't obstruct the airflow in front of the vent with anything.
Try your best to get the vent exit rounded over. A 3/8" "roundover bit" in a router will give great results.
I'd keep the vent the same distance up (from the cab bottom) as if it were on the back - just like on my drawing.

Make sure nothing rattles, and have fun with these.

Chris

[greywarden]

Re: on Sale - $55/pr (drivers & XO)

Oh yeah, I'm pretty sure it's going to be solid 3/4" Red Oak. And the brass "port" I'll be using has a decent flare built into it.

Hm. I had to move the port almost to the bottom of the speaker becuase of the clock face, the clock face needs to stay, becuase of the theme, and the rear baffle is going to be hinged and latched, so I won't be able to have it back there, really, becuase the "door", as it were, probably won't open correctly like that.

So, would you recommend the port be closer or further from the woofer?

[Chris Roemer]

Re: on Sale - $55/pr (drivers & XO)

Oh yeah, I'm pretty sure it's going to be solid 3/4" Red Oak. And the brass "port" I'll be using has a decent flare built into it.

Hm. I had to move the port almost to the bottom of the speaker becuase of the clock face, the clock face needs to stay, becuase of the theme, and the rear baffle is going to be hinged and latched, so I won't be able to have it back there, really, becuase the "door", as it were, probably won't open correctly like that.

So, would you recommend the port be closer or further from the woofer?

It can go right next to it w/out issue, but it seems like it would be restricted right at the bottom.