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Alpine DIY Subwoofer Build for HT
60 replies to this topic
Posted November 29 2012 - 05:25 AM
Find a similar sized driver and use it. Fi Car Audio has their driver displacement. For a port, use basic geometry. Measure the internal length, width and base that is taken up by both the port area and the wood that makes the port. FMOD is designed to work with a specific amplifier input impedance. So if you is designed to work with a 10k ohm impedance and your amp has an input impedance of 20k ohms then the filter will be halved (or doubled). I can't remember if change is inverse or proportional.
Posted November 29 2012 - 06:14 AM
Let's say the air volume in a slot port is 1 cu foot (1728 cu inches) and the mdf that forms the port has 0.75 inch thickness, 15 inches width, and 10 inches deep; the total port volume will be 1728 + (0.75 x 15 x 10)?? Am I correct on this or goofed it?
For a port, use basic geometry. Measure the internal length, width and base that is taken up by both the port area and the wood that makes the port.
Posted November 29 2012 - 10:00 AM
That's it. Basic geometry. Building speakers is the only thing that keeps my math skills sharp.
Posted November 29 2012 - 11:04 AM
According to Unibox, the Alpine driver works best in a sealed enclosure. I modeled it in a 42L box with 600w of input power. The Qtc is close to .5 which is what I shoot for in my subs. Xmax gets close to 20mm but never passes it which keeps distortion low as possible. If you go ported, anything from 80L to 120L tuned to 20hz is fine. The larger the box, the more gain you get at 20hz but not more than 3db max. I went with 120L tuned to 15hz and it looks exactly like a typical EBS (extended bass shelf) response.
Posted November 29 2012 - 09:43 PM
WinISD is totally opposite. It says Alpine works better in vented as compared to sealed with an EBP of 56.
According to Unibox, the Alpine driver works best in a sealed enclosure.
I modelled it in a sealed box in WinISD putting exactly the same net volume and 600 watts but Qtc is nowhere close to 0.5. Pls check the values of Xmax, Z, and Re. WinISD calculates Z at 6 ohms and Xmax 17 mm; whereas they should be 4 ohms and 20 mm respectively. Here is what I get; Which is correct; UniBox or WinISD?? Confused. Can you post the graphs u got in Unibox so I can compare??
I modeled it in a 42L box with 600w of input power. The Qtc is close to .5 which is what I shoot for in my subs. Xmax gets close to 20mm but never passes it which keeps distortion low as possible.
Posted November 30 2012 - 01:16 AM
Years ago, Dan Wiggins posted that Unibox modeled closer to the very expensive software he used daily when he owned Adire Audio. If you aren't familiar with his work, he has the patents on XBL low distortion motor technology. I have 7 different subs using that technology. It works. Also, when building my TC Sounds sub, Unibox modeled the sub almost exactly like I measured it. I'll double check my work this weekend. I need to check the filters section in Unibox. I may have had it set for a using a plate amp with a subsonic filter.
Posted December 04 2012 - 12:54 AM
I built a roughly 50L sealed box to test my sub and took the FR in REW. Pls have a look at the WinISD modelled FR and compare with the actual room response. They do not match at all. I am surprised at the low extension. The roll off starts at 16hz. I tripple checked it in rew. But this is how it is. Can someone tell me what wrong am I doing here?? I am skeptical coz Crown goes into clipping, which never happened before and listening experience is way below par. I mean looking at the room response, I feel elated but listening is just not good. Maybe crown doesn't have enough power to match the projected in-room response or God knows what. Can someone help. WinISD Modelled Response In-Room REW Response Edit: The sub doesn't bottom out at reference volume even with 20dB transients. The box is properly sealed
Posted December 04 2012 - 04:57 AM
Did you measure in your room our outside? The room makes a HUGE difference in the response. I did check my Unibox models and I had all settings correct.
Odd because that's very close to my in-room response and I love how my subs sound. Low volume or high, they sound great to me.
I mean looking at the room response, I feel elated but listening is just not good.
Posted December 04 2012 - 05:42 AM
That's an in-room response. I was actually surprised to see such depth. But the listening is far from impressive and seems anaemic and strangulated. The driver does not bottom out at full reference throttle, but Crown goes into clipping during transient bursts (For example, the last scene of Shooter when Mark Whalberg blows up the senator's hut in the forest) even at 10dB below reference. I am not using more than 4dB of gain on 2-3 filters in BFD, rest all are cuts. Do you think Crown XLS1000 is running out of steam?? One more thing, my wife is in DC these days. I was planning on getting Behringer iNuke3000 DSP Amp coz it has a floating point HPF and the lowest setting is 20Hz. I can use this amp for my ported builds. Is this amp any good??
Posted December 04 2012 - 08:42 AM
The guys at AVS like the iNuke models. I'll get one of those if my EP-2500 dies on me. It's odd that the Crown clips without providing the punch that you expect. I've run a TC Sounds Epic 12 with a 275w amp and it is great for normal listening levels. The Alpine has more excursion and the Crown more power so you should be getting some volume out of that driver. But I've never used Crown amps. In fact, the only time I've seen them in person they were being used for the sound system in a New Orleans bar.
Posted December 04 2012 - 01:32 PM
You described it well. There is no punch. My previous not-so-perfect pioneer/sub-12 duo setup was a scary knock-the-walls-down setup. This one just doesn't cut it. I think its the crown not living upto the sealed sub duty.
It's odd that the Crown clips without providing the punch that you expect.
Posted December 05 2012 - 06:01 AM
Can you please specify what port size and system input power yeild that? Can you please specify the slot port dimenions for this? Also, when you specify power, is it max power or continuous?? I need the port velocity and Xmax figures also. Btw, I have ordered Behringer iNuke6000 DSP model. I thought what the hec....let's get the max power on tap. It is best to have more and use less than to have less and crave for more later
If you go ported, anything from 80L to 120L tuned to 20hz is fine.
Posted December 09 2012 - 11:29 PM
Port = The equivalent of a 4" diameter port or 12.5 square inches. Here's your port length calculator - http://www.psp-inc.com/tools.html Power = I never thought of it. Since I don't worry about melting the coil which will happen if you use continuous power, I worry about bottoming the driver out and keeping distortion to a min. So that is probably max power that I am talking about. You never reached xmax with this design.
Posted December 10 2012 - 04:17 AM
This is a funny calculator that doesn't specify the units; nevertheless any sane person can guess the units based on what it gives against the entered values. I am more interested in slot port design coz its tons easier to build. Your belated reponse triggered a self engineered 4.8cu ft box with 43" slot port keeping in mind the Xmax and port velocity. The in-room response is bone shattering and gives -3dB point at 16Hz. Will post the response curve tomorrow.
Posted December 10 2012 - 08:19 AM
If you use 2 , 4" ports you will have 25 square inches of port area. A slot port 2.5" high and 10" wide will give you the exact same port area.
Posted December 10 2012 - 04:14 PM
In-Room Response That depth below 20Hz looks great on paper, but I think the sub is moving in free air coz that area is below the tuning frequency but the driver does not bottom out even at reference volume. Also, there is a null at 70Hz with two dips at 48hz and 55hz. The midbass looks very ruffled up. I will get iNuke NU6000 DSP this thursday. So, will check the FR with a 20Hz HPF. Although, the listening experience scares the hell out but I feel it is a bit crude. I mean it is not smooth bass. What could be the reason?? The box came out to be huge (my wife is gona hit the roof when she gets back from US) and I am not using any internal bracing in it coz it is a test box made from 0.75 inch chip board. May be that is the reason. I will do the final build with mdf.
I've read the ratio between slot port height and width is 1:8-9 to keep port velocity below 20 m/s i.e. port width should be 8 to 9 times the port height. I followed this to come up with 2 x 16 inches port.
A slot port 2.5" high and 10" wide will give you the exact same port area.
Posted December 10 2012 - 11:32 PM
Port area has an impact on port velocity, not the ratio. There may be some minor, very minor impact with the ratio due to friction on the air but if your ears can pick that up you have super hero hearing. Those dips are room induced. If you can't add a few dbs of boost and help them, then you will need to move your sub to a different location. I would try something as simple and rotating it 45 degrees. No bracing and chip board (official name is Oriented Strand Board or OSB) could be the cause of your sound issue. Other people have reported similar responses when they first hear a low distortion sub. They have been listening to normal subs for so long, they think they are missing something. Find a good acoustic concert with some bass. It should sound like the bass player is in the room with you.
Posted December 11 2012 - 02:44 AM
Ok Thanx Robert. I have re-run audyssey and it is bone-jarringly dreadful bass after tweaking the response in REW and adding some BFD filters. Very accurate with monsterous punch. I will start my final build with 0.75 inch MDF with full cosmetics. Any chance i can reduce the size to 3.5 cu ft max including driver displacement and port area with the same sonic impact as this one?? The current size (4.8 cu ft gross) is way too huge.
Posted December 11 2012 - 02:50 AM
Not that I have anything to add...as this sub is beyond anything I could build, on purpose(mine would be blind luck and maybe within 90% of your output goal)... But your bass curve is unbelievable. I'm jealous. And about "what people are missing". I have an M&K sub that bewilders people in how clean it is...and it is over 20 years old. The mass market crap that passes for subwoofers nowadays has people missing out on what they can really have... Anyway, great sub and the search for perfection...and then complacency....and the desire for better(vicious cycle isn't it...???)
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