40th Birthday present

[Forcefed2002]

Would really like that hump 10 cycles to the left!

 

[hispls 5,000+ posts]

Would really like that hump 10 cycles to the left!

You saw for yourself it won't happen in your airspace. Do play with port length and compare what you hear to what you see on that program. The lines you see on the software (doesn't much matter which, the math is long established and the formulas the same). You'll find that the line you see is going to be more accurate with the box outside or in a very large room. Reflected sound waves add peaks and nulls when you put it in the car. These vary of course but are somewhat predictable, all of the low end will be exaggerated and you'll typically get a bump around tuning (regardless of the predicted curve) and a bump somewhere between 45 and 60hz wherever your vehicle resonates.

I can tell you what you explained when you first made this post is consistent with the 2 humped camel I explained and what that green line you plotted will actually sound like in-car.

 

[Forcefed2002]

You saw for yourself it won't happen in your airspace. Do play with port length and compare what you hear to what you see on that program. The lines you see on the software (doesn't much matter which, the math is long established and the formulas the same). You'll find that the line you see is going to be more accurate with the box outside or in a very large room. Reflected sound waves add peaks and nulls when you put it in the car. These vary of course but are somewhat predictable, all of the low end will be exaggerated and you'll typically get a bump around tuning (regardless of the predicted curve) and a bump somewhere between 45 and 60hz wherever your vehicle resonates.
I can tell you what you explained when you first made this post is consistent with the 2 humped camel I explained and what that green line you plotted will actually sound like in-car.

I hear you loud & clear hispls.

I was fixing to ask why I didn't SEE the camel hump I HEARD. Great explanation...learning more by the hour.

Is there a way to culminate a large enough sample in order to look at the amplitude response after a specific/generic vehicles transfer function is applied?

Or is it still at a point that those that have been in the industry long enough, with many builds under their belt can say something like "expect an X-db bump around xx-hz in that type of vehicle?

This company says that when they hit 3000 members they will activate the transfer function parameters to be used by clients. Is that hogwash or something that is attainable?

I will play with the port some more as u suggested if nothing else than to get a feel for things.

You've been indispensable to my learning curve & want you to know I do very much appreciate it.

 

[hispls 5,000+ posts]

I hear you loud & clear hispls.I was fixing to ask why I didn't SEE the camel hump I HEARD. Great explanation...learning more by the hour.

Is there a way to culminate a large enough sample in order to look at the amplitude response after a specific/generic vehicles transfer function is applied?

Or is it still at a point that those that have been in the industry long enough, with many builds under their belt can say something like "expect an X-db bump around xx-hz in that type of vehicle?

This company says that when they hit 3000 members they will activate the transfer function parameters to be used by clients. Is that hogwash or something that is attainable?

I will play with the port some more as u suggested if nothing else than to get a feel for things.

You've been indispensable to my learning curve & want you to know I do very much appreciate it.

To some degree I think you can predict your main peaks via measuring corner to corner front to back dividing that into the speed of sound then dividing by 1/4 and 1/2. Expect standing waves around those points, predicting nulls may be more difficult as would be predicting overall gains. It's really a matter of wavelength. Low frequencies have a very long wavelength and are subject to interference from their own reflections coming from all directions. Most of this interference will be constructive (make it louder). You can use generalizations to get a ballpark idea what to expect but beyond that you need to test and ideally own an RTA or SPL meter to really quantify and see what's happening.

Then again, I could be wrong and with enough data perhaps you could get a lot more accurate predictions than I expect? Again this is something you can easily see for yourself and have seen for yourself just by flipping the box upside down making a dramatic difference. Play the box outside the car and see what it sounds like, take it in your house and use it on your home theater. The differences should be clearly audible.

Anyway, there's plenty of generalizations we can make from experience, but plan on being surprised and mystified when your best predictions fly right out the window when you try to put them into practice.

 

[Forcefed2002]

To some degree I think you can predict your main peaks via measuring corner to corner front to back dividing that into the speed of sound then dividing by 1/4 and 1/2. Expect standing waves around those points...

Could you elaborate a little on this?

I know the speed of sound is based off of temp,humidity,elevation & such. And I could find an average number for my climate. But what of the corner to corner measuring & dividing by x amount, then by x again...I dont follow.

Also, when dealing with modeling software in the vent section where it asks for:

Square/round

# of ports

#of flush ends count

Options are "No" "1" "2"

What are flush ends?

 

[hispls 5,000+ posts]

Could you elaborate a little on this?I know the speed of sound is based off of temp,humidity,elevation & such. And I could find an average number for my climate. But what of the corner to corner measuring & dividing by x amount, then by x again...I dont follow.

Also, when dealing with modeling software in the vent section where it asks for:

Square/round

# of ports

#of flush ends count

Options are "No" "1" "2"

What are flush ends?

Corner to corner being the farthest two points in your vehicle. Corner up where you put your feet and the opposite corner in the rear of the passenger side for example. Speed of sound divided by the frequency is how long the wavelength is so your peaks will be at 1/2 and 1/4 of the wavelength. Wavelengths are pretty long and you'll get some gain above and below the frequency, and a car interior is such an oddball shape that you'll get ballpark at best, but it's a good estimating tool for what frequencies to watch.

If you ever played with a wave pool/generator in physics class it's easier to picture how reflected waves build or cancel each other out.

I believe flush end would be the port opening into and out of the box as opposed to sharing a side with a side wall, I haven't used a program that asks that in a while don't they have an illustration? Check the FAQ or "help" section to confirm.

I find if you're off by a couple hz or a 5% margin of error you'll never hear the difference so I wouldn't get so hung up on precision. See for yourself by throwing numbers at it how little the curve changes with small variation in frequency or volume...bear in mind 1dB is the minimum audible change you'll notice.

 

[Forcefed2002]

The Mysterious Loudness Control: What Does It Do? | Extron

Found this interesting.

 

[Forcefed2002]

You saw for yourself it won't happen in your airspace. Do play with port length and compare what you hear to what you see on that program.

Again, your absolutely right...so I added 3cu/ft.

Maybe ill see that shift to the left near 40hz that I wanted.

I also have a few boards cut to change port length to see how a lower tune will sound.

I managed to get 1.5cu/ft behind each seat without giving up much cargo capacity.

 

[Forcefed2002]

Also, each "wing" had enough downward facing real estate to mount a 12" sub. Either common or seperated (made the inserts & they are on standby should I decide to)

 

[hispls 5,000+ posts]

Be careful you don't over-drive those subs now. Smaller box = less mechanical control over the woofers.... it'll take less power to push them to excursion.

Box looks pretty wild now. Hopefully the extra volume gives you the results you're after, looks like a lot of work transforming it.

 

[Forcefed2002]

Dropped this in today. It's a cheap 250amp unit.

Have yet to fire up after box mods & alt, maybe sometime this upcoming week.

Will keep an eye on the power.

Wasn't too terribly bad to mod the box. I guess I'm enjoying the learning curve. Thx for the pointers & will let you know how this experiment unfolds.

 

[Forcefed2002]

Also, Hispls, if this doesn't sound good it will be entirely your fault!

J/k

 

[Forcefed2002]

Short of REAL sound deadening down the road...

Does this paneling that was installed by prior owner help or hurt (in even small ways) the audio environment in which I'm working?

It's a panel side (no windows) cargo, of which you see the extent of the interior. Thinking of expansion foaming the little cavities that are scattered around (near sliding door) and such.

If the answer is to keep the paneling in favor of bare sheet metal, would increasing the material to 1/2 ply be better than this cardboard like crap you see drooping from headliner?

 

[Forcefed2002]

Side note:

Grew up in northern Pennsylvania Allegheny mountains where from age 8 to 16 helped grandpa in a sugarshack nestled in his prized maple stand...good times.

 

[Forcefed2002]

Be careful you don't over-drive those subs now. Smaller box = less mechanical control over the woofers.... it'll take less power to push them to excursion.
Box looks pretty wild now. Hopefully the extra volume gives you the results you're after, looks like a lot of work transforming it.

It gave me something that I didn't know I wanted.

A flat response from as LOW as possible.

You mentioned from the beginning that those subs model great in 6 or 7 cu/ft & you were correct.

I will, from here forward, aim to build this way, even if it costs spl elsewhere. There is just something to being able to not just feel, but also hear down in the 30s...

I think I'm addicted to alot of the slowed & rebassed stuff coming out.

I realize I'm not loud down there, but for the 1st time, with this big box tuned low, I'm feeling a whole 'nother world.

Currently, it sounds like the green line looks (short of a small cabin gain bump).

I also re-ran the big 3 (big 5 in my case) with 1/0 instead of 4g & now voltage drop is much MUCH better. It surprised me actually, I didn't think much about it until I committed with the big stuff & WOW. People need to give that portion of their build more attention.

Anyway, here's some pics.

Thinking about adding another pair of 12's or selling it all & running 2 15's across the back panel area of that box. (In a different enclosure of course)

Pretty sure I can snitch some more room - lol