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Old 27th January 2014, 01:37 AM   #11
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Actually, it is the Behringer DCX2496 Ultradrive Pro Digital Crossover. I didn't make that clear.

I hate to ask yet another newb question, but is the TPA3116D2 available already assembled and ready to use?

Sorry for learning at your expense, but I do appreciate your willingness to coach.
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Old 27th January 2014, 01:42 AM   #12
xrk971 is offline xrk971  United States
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Yes, it comes pre-assembled. You need to connect the audio input to a small connector or solder directly onto the 3 pins.

TPA3116 Amplifier Board(50W+50W ) D Class Amplifier Board-in Amplifier from Electronics on Aliexpress.com

This could work too but I have not been able to verify the gain and input impedance.
http://www.aliexpress.com/item/TPA31...629195683.html
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Old 27th January 2014, 01:49 AM   #13
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Quote:
Originally Posted by xrk971 View Post
Yes, it comes pre-assembled. You need to connect the audio input to a small connector or solder directly onto the 3 pins.

TPA3116 Amplifier Board(50W+50W ) D Class Amplifier Board-in Amplifier from Electronics on Aliexpress.com

This could work too but I have not been able to verify the gain and input impedance.
TPA3116D2 amplifier board 50w +50 w digital two channel amplifier board 24V-in Amplifier from Consumer Electronics on Aliexpress.com
Holy cats, its like they are giving it away!

Wow.

And, again, thank you.
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Old 27th January 2014, 12:56 PM   #14
xrk971 is offline xrk971  United States
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Default Sim of OB response

I put together a model of this speaker and it is instructive to see it predicts the bass extension quite accurately and also predicts a bump at about 270 Hz due to the baffle size effect. This is well known and typically, the XO freq should be set below this point. I was able to EQ this bump out in the DSP but if you are going with a PLLXO route, the XO point will need to be lowered. The Vifa can handle a XO point as low as 200 Hz and that will help to keep the distortion lower as more of that is played through the Vifa.

Here is the predicted response for the 300 Hz XO freq (-24 dB/oct):

Click the image to open in full size.

Here is the predicted response at 200 Hz XO freq:

Click the image to open in full size.

And here is the problem with using only 1 woofer as I suspected - the cone has to really move to displace the air needed for the low frequencies and will hit the 3.5 mm xmax within 2 watts of power at 40 Hz (if you have content there). Here is cone displacement at 2.83 volts:

Click the image to open in full size.

My initial guess that you need a 15 in woofer (like a Manzanita) makes sense and if you have 6 drivers then the xmax will be cut by 1/6th and be only 0.58mm instead of 3.5mm. So the way to do this is to use 6 woofers - and I plan to keep the profile of the baffle slim by going with slot loading like the Nelson Pass design. Using a 7 in tall x 7 in deep x 2 in wide box/slot will provide the recommended 30% slot area for two drivers. Stacking 3 units vertically will be 21 in tall. Adding another 9 in on top for the Vifa baffle will make it 30 in tall. A perfect height for 30 in foam core. The slop loading will provide a forward bass boost of about +2dB at 3 meters away.
Attached Images
File Type: png Cardboard-OB-Sim-200Hz-Freq-1m.png (26.0 KB, 858 views)
File Type: png Cardboard-OB-Sim-200Hz-Displ.png (24.0 KB, 849 views)
File Type: png Cardboard-OB-Sim-300Hz-Freq-1m.png (26.7 KB, 852 views)
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Old 27th January 2014, 03:52 PM   #15
xrk971 is offline xrk971  United States
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Default 6 Driver Slot Loaded Woofer

Here is the simulation with 6 drivers pushing a 21 in tall x 7 in deep x 1.5 in wide slot for the bass located from the bottom up to 21 in. The total speaker height is 30 in and width is still a svelte 12 in wide. Vifa is located 5 in from top and 4.5 in from edge as before. I am now running a 210 Hz XO frequency (-24 dB/oct).

Here is the xmax at 15 volts drive (3-series/2-parallel wiring) for both the woofer and tweeter:

Click the image to open in full size.

This is the max SPL corresponding to 15 volts rms:

Click the image to open in full size.

Here is the impedance for both woofer and tweeter:

Click the image to open in full size.

This is the impulse response which looks pretty clean and tight:

Click the image to open in full size.

This is the air velocity at the slot exit which is well below 10 m/s to avoid chuffing:

Click the image to open in full size.

It looks like the baffle-induced bump is now at 217 Hz and will need to be EQ'd out. Although it is not a bad bump to have as peaks go.

Edit: it looks like playing with slot box dimensions is an important knob to smooth the response. Here is a 10 in deep box (allows higher drive voltage) and gives reduced bump at 217 Hz:

Click the image to open in full size.

Last edited by xrk971; 27th January 2014 at 04:15 PM.
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Old 27th January 2014, 04:00 PM   #16
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Can you explain why you have a chunk of foam wrapped around you mic? Doesn't that muck up the HF? I have a boom mic stand I use, I've tried a few things like dangling it from the wire, foam, etc. I have found just mounting it on the boom stand to be best. And I've read comments from other members that mic stands can affect HF. I can't remember where I saw it, but someone on here used a very long perfectly shaped pipe that transitioned smoothly onto the mic body. They went to great lengths to minimize HF reflection off the mic.

I'm surprised you're getting output down to 40hz with that driver / baffle. Any chance you've got off axis measurements? It would be interesting to see how that driver beams and how the OB with side walls affect the dipole behaviour. That's a nominal 3" driver?

One last thing... A FR chart on a 5db scale and 12/oct smoothing would be nice
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Old 27th January 2014, 04:22 PM   #17
xrk971 is offline xrk971  United States
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Tux,
Very perceptive of you - the mic is set in a piece of foam that cradles the larger body and allows the velcro to hold it well. The foam doesn't extend to the tip and is about 3 inches behind the microphone tip - and apparently, it doesn't seem to cause any problems with the HF measurement as you can see. It is open cell foam so really doesn't cause reflections (similar foam is sometimes used to cover mic for wind noise suppression). If I were doing near field (within inches from driver face) maybe I would be concerned but the pistol grip tripod mount would be more of a concern then. I will try to get you the 5 dB scale at 1/12 oct later.
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Old 27th January 2014, 08:10 PM   #18
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Ok I see, so just to grip the mic in there securely. Open cell foam is probably a good idea, nice.
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Old 27th January 2014, 08:25 PM   #19
xrk971 is offline xrk971  United States
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Tux,
Regarding your question about the bass extension: I was surprised that I am getting such good extension in such a narrow OB - but then I do have 8 in deep wings that gradually taper off to 3 in deep wings - forming almost a rear H-frame. If you extended the wings and added it to the front you have 12+16=28 inches which is a pretty respectable width for an OB. Note that to get 40 Hz the driver is basically hitting its xmax which is not good. I think I am going to change the high pass filter to a 45 Hz rather than the 30 Hz. Having a Qts of almost 1 makes a big difference in ability to get deeper extension in an OB. A more pricey 6.5 in driver with a bigger motor and Qts of 0.35 will have a hard time getting to 50 Hz. My big problem is that these drivers are out of stock and more will not be availabel until April. The cost of 6 of these drivers is about the same as a single 15 in GRS used in the Manzanita. I think having 6 smaller drivers will have an improvement in the dynamics and impulse response (plus it provides an asymmetric throw that enhances forward SPL over backwave SPL, and it looks more compact and cool as a slot loaded woofer). The full range driver is a nominal 3.5 inch unit - no beaming at all with this driver as it is small.

Last edited by xrk971; 27th January 2014 at 08:29 PM.
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Old 27th January 2014, 11:15 PM   #20
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xrk,

I think I'd take the multiple smaller drivers over a larger one as well, but mostly for flexibility of tackling room placement. I'm not sure it would affect the impulse response. The impulse response is going to be largely dictaded by the Vifa full range. Don't forget that IR is just what the mic hears, which then describes the frequency response and CSD via the Fast Fourier Transform. The woofers are only working up to 300hz, so you're looking at the 4ms and longer range. I bet if you measured the woofer alone, you'd have a very flat looking IR. Then measure the full range and the IR will look very similar to both drivers combined. The full range dominates.

Will you arrange the woofers vertically to get an array effect? Is that what you mean by "asymmetric throw that enhances forward SPL over backwave SPL"? I'd agree this will tame any vertical room issues you might have. Nice woofer choice for this app. Obviously it payed off. With multiples you won't have your xmax problem either.

How do you like your minidsp? I love mine for trying FASTs. They're really slick. I have mine tied up in my subwoofer system right now. I gotta either get another, or buy an amp with built in DSP to free up my mini.
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