[dreadknot]

im new to custom speaker building so i need some advice

iv chosen a 12" Woofer, Poly Mica Cone, 4 Ohm, W-1244

with these specs Steel Frame
Poly Mica Cone, Rubber Surround, Vented, Bumped Backplate
Size: 12"
Hole cut-out: 11"
Depth: 5-3/16"
Voice Coil: 2"
Magnet: 40 oz
Impedance: 4 ohms, Re: 3.6 ohms
Power: 150 watts RMS, 300 watts max
Response: 18-5000 Hz
Sensitivity: 87 dB, 1 watt, 1 meter
Le: .60 mH, Fs: 33 Hz, Vas: 4.22 cu. ft., Qms: 3.30, Qes: .86, Qts: .68, Xmax: 5mm

for my 5 surround speakers center, fronts, sides

along two tweeters per

Dayton Audio AMTPRO-4 Air Motion Transformer Tweeter 4 Ohm

an too be run off a 2 Way Crossover, 12 dB/Octave, 2000 Hz, A-1300

powered by a set of Crown XLI800 Two-channel, 300W at 4Ω Power Amplifier

for the center, fronts, sides

my problem is the software im useing box port design 2 says for optimized sealed profile system q 500 -9cubic resonant fq 24hz -3dbs at 37hz an i have no idea how to make -9cubic feet for a box but i do want the system q value of 500 for tight response

my custom profile is
system q 1009
3.52cubic air volume
resonate fq 48hz
-3dbs at 38hz

is that bad or good
12.75 wide 48tall an 15deep

i plan to have 2 Dayton Audio RSS315-PR 12" Aluminum Cone Passive Radiator
for low end tuned at 17.7hz

is this good or bad

any advice

 

[fusseli]

Re: what does it meat when

I am not on my computer at the moment so I can't verify, but that box size seems way too big than necessary for a mains or surround speaker, especially for a sealed design.

I can't compare parameter this second, but for the sake of vague comparison, my mains have 12" woofers in 3cuft. They are on 4 or 5mm xmax also, and handle loads of amp power in a 3way speaker design.

My second question is, why two tweeters? Two drivers playing the same freq range can produce a lobing effect. And, you may not need the very high sensitivity you would get from two. Most designs end up attenuating the tweeter just to get it down to the same level to balance with the woofers.

 

[DqMcClain]

Re: what does it meat when

Yeah, I'm not 100% certain what it is you're proposing here... are you thinking a 2-way design with a single 12" woofer and 2 AMTs per box? If that's the case, I'm having a hard time imagining that working out well. First, the AMTs have almost comically high sensitivity on their own, and compared to the 87dB sensitivity of the woofer you've specified, you're going to have significant balance problems on the high end. And if you're thinking what I think you're thinking, and planning on two of the AMTs against a single 12, you're going to have to spend a lot of time and energy padding those down to a workable level.

(Side note, I built a 2-way MMT tower design for my brother using 2 5" woofers and a planar tweeter, and still had to pad that tweeter by 6dB to make the system sound good)
Another thing is attempting to have passive radiators tuned all the way down to 17.7Hz and getting that kind of response out of a full-range design isn't a good idea. The big issue here is that the crossover point of 2Khz might work with the woofer, and the tweeters will probably be happy with that... but now you're asking the woofer to deliver signal from 17.7Hz all the way up to 2KHz. That's just shy of 7 octaves. That can be done, but it's a very tall order for any driver to handle. It is best accomplished by a small-ish (3"- 8" or so, depending on Stuff) full range driver that has a decent bottom end and a cabinet designed to augment the response down low, but where they really shine is on the high end... and it is usually unrealistic to expect high performance below about 100Hz out of these designs. (I'm generalizing, and there are plenty of exceptions... but those are top of the line drivers, implemented by expert designers). The thing that tends to happen is that if a driver is tasked with delivering critical mid-range content, it will either be at the expense of low-end response... OR the low end response will muddy up the mid range. You're pretty much stuck with one or the other, unfortunately... which is why most good designs with large woofers (10"-15" in a full-range box) will either roll off around 80Hz (and supplement low end with a dedicated subwoofer), or employ a 3-way design with a dedicated mid-range driver. Another issue is an effect called "beaming". When the wavelength of the frequency a driver is reproducing is less than or equal to the diameter of the driver reproducing it, that frequency (and those above it) will become disproportionately directional in it's dispersion. This means that while lower notes will behave as you expect them to, higher note will become significantly more directional than you would expect given their frequency... so while you expect a certain amount of directionality in your tweeters, you should be able to treat mids and woofers as having a more even axial response. But in the case of a 12" woofer, this effect takes place nomially at 1132Hz (the speed of sound at sea level, 68F, 14.7psi) and get progressively worse up to your crossover point. Unfortunately, the range from ~1KHz to ~2KHz is right where you want the cleanest response possible for purposes of speech intelligibility and instrument articulation. In the end, it means that anyone sitting even a little off-axis will experience diminished response in a range that matters.

The next issue is the one mentioned in the previous response... if you are talking about two tweeters, there can be issues with comb filtering as their respective outputs interact with each other in the airspace between the cabinet and the listener. This effect is almost always avoided whenever possible... very rarely does anything good come from comb filtering.


Also, on a separate note, having a width of 12.75 with a 12" woofer is going to put the edge of the basket on the woofer very close to the edge of the box. This might not be a structural issue, but it could look weird in the end.

 

[fusseli]

Re: what does it meat when

So, we are suggesting that you consider a 3-way design, by adding a midrange, and only use one tweeter per speaker.

 

[DqMcClain]

Re: what does it meat when

Or, we are suggesting a smaller woofer and a single tweeter with a 2-way design, and getting the bottom octaves from a dedicated subwoofer. Either approach would yield a workable result.

 

[dreadknot]

Re: what does it meat when

on that note an my own thinking i've

revised my design to have a Dayton Audio

XO3W-500/4K 3-Way Speaker Crossover

500/4,000 Hz and 1 Dayton Audio RS270-4 10" Reference Woofer 4 Ohm

to be used as low fq friver an the Dayton

Audio AMTPRO-4 Air Motion Transformer

Tweeter 4 Ohm as midrange an 1 Pyle

PDBT19 3.75" Aluminum Bullet Titanium

Horn Tweeter for the highend

mid above the tweeter an the low range

below with a singal Dayton Audio RSS315-

PR 12" Aluminum Cone Passive Radiator

tuned at 17.7

box designs for a
1.54 cubicfoot box

with two baffels 1 an inch above the

woofer an one below between the woofer

an rad 11.25 wide 1.5in thick an 6in deep
dims are (outerdims)
12.75 wide
31.75 tall
12 deep
the the top bottom front an back are 1.5in

thick the sides are .75

 

[fusseli]

Re: what does it meat when

If you proceed with this design, I recommend adding a zobel circuit (just use an online calculator) for the woofer, and possibly also the midrange, since you are using "textbook" pre-made crossovers. This will help the crossovers perform as best as they can. Then for the midrange and tweeter, use online calculators to size an L-pad circuit to try and match the sensitivity all to the same reference at around 84-85 dB @ 1W/1m. I suggest this as a simple means of balancing levels so the speaker sounds right, and a way of incorporating some baffle step compensation rather then referencing the woofer's full 89 dB @ 2.83V/1m sensitivity.

On the baffle, space the drivers close together without intentional gaps, this will acoustically aid the crossover frequencies as well.

 

[dreadknot]

Re: what does it meat when

THANK ILL TRY THAT

HEY DO YOU KNOW HOW TO MAKE 60HZ LOWPASS 4 Ohm CROSSOVER FILTER WITH 500WATTS INPUT THE CLOSEST IVE FOUND TO WHAT I WANT IS THIS

Parts Express 80 Hz Low Pass 4 Ohm Crossover

 

[robbo266317]

Re: what does it meat when

Why do you need 60 Hz?
The low pass filter you mention is also only a first order design so it will have a lot of overlap.

 

[dreadknot]

Re: what does it meat when

Its for a sub

 

[robbo266317]

OK, so the sub should be able to go up to 80Hz and you set the mains in your receiver to crossover at 80 Hz.