Using WinISD to Design a Proper Sub Box [LONG]

[StereoInstaller1]

Just gotta get the ability to do waterfall plots...but no mic, no PC card, no high dollar software, just a beat up old man with a tabelsaw and a calculator from the dollar store.


<sniff>

[Schnitzer318is]

As always... wealth of information in here. Loving it. Keep up the good work gentlemen.

I, like you, opted for a sealed enclosure (custom built ~1.2ft^3) with more power for as good an SQ as I could get. It sounds really clean on all forms of music (important to me since I have a VERY wide taste). I'm sure it could benefit from some form of active Xover setup, but I am pretty pleased with it as is.

I also run a 12" Luke box in my wife's car, and it sounds awesome as well. I prefer my 12" sealed box in my turbo car, but I am pushing 5 times the power to a much more expensive sub and amp setup. Luke's box is the best compromise of Power/$$$ to SQ I have been able to find. I hope he continues to build these sort of boxes and offer them to the community. His box saved me mucho time and $$$ in doing my wife's car and she couldn't be more pleased.

[bmwman91]

Theoretical Luke-Box performance with various drivers...

[StereoInstaller1]

Hey man, post up those graphs...they show exactly why my boxes sound so damn good in these cars.

Big fat peak at 50Hz with a mellow drop down to 0db at about 80...let the cars acoustics do their thing below 50 or so.

[StereoInstaller1]

All of the above, bro.

Thanks!
Luke

[bmwman91]

You should run one of my boxes through WinISD.

Using a gross volume of 1.5ft3 & 2x3"ID pipes ot 17", the box tuning frequency is 36.6Hz. I also tried it with 1.35ft3 (accounting for port volume & a guess at rough driver volume) which raised it to 38.3Hz. it sounds like your calculator is pretty accurate. Good work with the dual 3" pipes too, that really really helps to keep the port air velocity down, so your boxes probably don't add too much "port flavor" haha.

[bmwman91]

You should run one of my boxes through WinISD. I do not build to "spec", as I know the marketing department has more to do with specs than engineering does.

My gross internal volume is 1.5 cubic feet (gross as in not accounting for port or driver displacement) and the porting is 2) 3" ports with a length of 17" each. My calculator shows that as a 35Hz tuning, but I do 30Hz as standard on the 2 cubic foot (gross) 12" box. As peaky and lumpy as the cars response is (12db down at 80Hz compared to 40Hz) the compromise is as good as I can get until I do a serious build using FFT analysis on the IDMax 10" setup I plan.

BTW: I do not build "what fits" (and I do know MOST installers do, but most SUCK!)...I do however, use my 30 years experience in building subwoofers for demanding customers, then design and build so it is the best possible compromise I can achieve...but I will not compromise sound quality for SPL, nor for space...so I go a more difficult route and build for fit and SQ...but at the expense of my time/effort.

I think it is funny...lots of people see this guy as some kind of "threat" (like what, do I have some kind of Kingdom that needs guarding?) to me, but 99% of the time, he only posts data that completely validates my engineering...even though I am a retarded 9th grade drop out.

I am SO glad he is here, having someone who knows the engineering side and can actually DO the stuff he does is fantastic to me.

Soldier on, boys!
Luke

I hope you didn't think I was talking badly about any of your work. I have no personal experience with it so I certainly won't make any big claims. Based on what I have seen, I would guess that it is top-quality stuff, and you are obviously one of very few honest people trying to make $ in the audio world. I may have the engi-nerd side, but that probably isn't as valuable as 30 years of hands-on experience. I hope that some of my ramblings will be useful to you & your projects/products.

And yes, I get treated as a hostile somewhat frequently in certain parts of certain car forums (or just largely ignored). A lot of people make a living peddling snake oil, and while I really want nothing whatsoever to do with them & their livelihoods, passing information on to people can potentially interfere with the cash flow lol. This is true almost everywhere in life though...consumption is fueled by those with knowledge making money from those without it, or with the wrong knowledge. I just enjoy sharing things I have learned since it feels really good to learn & understand things. A few years ago I was one of the usual, "well if I want a good system I need 2000W & big-name expensive gear to get results," types. The feeling of, "holy shit, no f'ing way," I got when I heard my friend's DIY back-loaded horns that made deafening SPL of amazing clarity from a 1W tube amp with 5% THD was definitely one of those "revelations" in life lol (the whole system probably cost him $200 in parts & materials). It is a feeling I would like to try to pass on to others.

BTW, r3v has been the best place for car audio discussions, by far. Maybe it is because there are not gobs of "supporting vendors" in here or something, but this just about the only car forum where I have been able to have good discussions.

[StereoInstaller1]

You should run one of my boxes through WinISD. I do not build to "spec", as I know the marketing department has more to do with specs than engineering does.

My gross internal volume is 1.5 cubic feet (gross as in not accounting for port or driver displacement) and the porting is 2) 3" ports with a length of 17" each. My calculator shows that as a 35Hz tuning, but I do 30Hz as standard on the 2 cubic foot (gross) 12" box. As peaky and lumpy as the cars response is (12db down at 80Hz compared to 40Hz) the compromise is as good as I can get until I do a serious build using FFT analysis on the IDMax 10" setup I plan.

BTW: I do not build "what fits" (and I do know MOST installers do, but most SUCK!)...I do however, use my 30 years experience in building subwoofers for demanding customers, then design and build so it is the best possible compromise I can achieve...but I will not compromise sound quality for SPL, nor for space...so I go a more difficult route and build for fit and SQ...but at the expense of my time/effort.

I think it is funny...lots of people see this guy as some kind of "threat" (like what, do I have some kind of Kingdom that needs guarding?) to me, but 99% of the time, he only posts data that completely validates my engineering...even though I am a retarded 9th grade drop out.

I am SO glad he is here, having someone who knows the engineering side and can actually DO the stuff he does is fantastic to me.

Soldier on, boys!
Luke

[bmwman91]

Wow. Great work! - I think I got yelled at when I suggested that I wanted to do something other than a Luke box. :(

So you don't mention anywhere about box dimension - unless I missed it. So it really is all about volume then - and the box shape can be what ever you want, you just need to take port design into account? Correct?

And if that is the case, why is it that people don't pick the woofer first, and then just go off the specs they give you to get/make/buy the box? I assume the "better" woofers would give you some design specs that would include volume, port length/size? No?

Also - I was surprised by you wanting to go sealed box. I guess for you, power efficiency - and turning limited power into as much bass as you can't isn't what you're doing. You're looking to control the woofer as much as possible with the sealed box and using a larger amp to over come the problems of the car's interior? Is that the short version of it?

Dimension ratios are important, but as Luke kindly noted, a car is far from an optimal environment for a number of reasons. Space is super limited in a car, so basically just "make it fit."

I think a number of people do use the box dimensions suggested by some driver sheets. I think that most sealed box recommendations are probably going to work fine, but I would double-check any ported box suggestions. Lots of car-brand stuff is crap & aimed at people who want loud boom-n-doom. It is pretty simple to get a rough idea of ported box performance for a driver, so it is wise to check.

Sealed boxes have many technical advantages. Sound quality wise, they are superior to ported ones in every way. However, it is also not necessarily something that one will ACTUALLY hear depending on the design. Porting is a way to get audible output at lower frequencies at the expense of technical sound quality, and depending on the application this trade-off may be well justified.

I don't REALLY have a sealed box in my car. The trunk is the "enclosure" with the driver mounted through the rear bulkhead, but the trunk is not sealed from the cabin by any stretch of the imagination. Still, it sounds good and hits clean and hard, so I am happy.

Efficiency was sort of important since an efficient driver will make more noise with less power, thus reducing the chances of clipping & distortion in the amp and speaker. A sealed box gives better group delay, which may or may not be a big deal (probably not so much when under 50Hz). It also yields far better cone control, which is good for 2 reasons: 1)driver protection...helps reduce the chance of damage from over-excursion, and 2)you can run more power to the woofer and keep it in its linear operating range. Think of it like this:
A driver has an x-max of 10mm. This means that by 10mm, the cone will be (for example) 10% out of its linear operating range, which means 10% distortion or something along those lines.
1 Newton of force = 1mm excursion
2N = 2mm
3N = 3mm
4N = 4mm
5N = 4.9mm
6N = 5.7mm
7N = 6.4mm
8N = 7mm
9N = 7.6mm
10N = 8mm

You see that you get a nice linear ratio of force to excursion for the first 5 or 6N, but after that it is no longer the case. As the driver moves, the foam surround & spider stretch & will eventually start acting on the driver more. So, in short, if you should try to get your target sound level with minimal cone excursion.

[george graves]

Wow. Great work! - I think I got yelled at when I suggested that I wanted to do something other than a Luke box. :(

So you don't mention anywhere about box dimension - unless I missed it. So it really is all about volume then - and the box shape can be what ever you want, you just need to take port design into account? Correct?

And if that is the case, why is it that people don't pick the woofer first, and then just go off the specs they give you to get/make/buy the box? I assume the "better" woofers would give you some design specs that would include volume, port length/size? No?

Also - I was surprised by you wanting to go sealed box. I guess for you, power efficiency - and turning limited power into as much bass as you can't isn't what you're doing. You're looking to control the woofer as much as possible with the sealed box and using a larger amp to over come the problems of the car's interior? Is that the short version of it?

[StereoInstaller1]

BTW, I am getting closer to sending you those amps.

[accident]

badass

[bmwman91]

Oh yeah, absolutely.

The E30 is not a good environment, either.

Haha yeah, tell me about it. I wish I could weld in E34 kick panels...

[StereoInstaller1]

Oh yeah, absolutely.

The E30 is not a good environment, either.

[bmwman91]

Yeah, there are about a million of them.

The big issue is that while the math is good, it simply does not work in a car. Near field acoustics are a big part of that, but primarily transfer function and vehicular anomalies make that nice smooth graph look like a dragons mouth.

For sure. Cars are big, poorly sealed enclosures, and sitting that close to a driver also changes things a lot. Still, I would have to assume that having a box that isn't boomy would be a helpful starting place so you could focus on improving the car response (sound deadening) and maybe do a little less EQ work.