Box venting help requested for Ultimax 18"

[mkellym]

Hello all. It's been quite some time since I have been on the board. I have had the honor the last few weeks to share my love of building an auto sound system with my 17 year old son. Reminds me so much of when I developed my passion in the mid '80's. I have retired from that life for several years so this has been a new learning experience, or re-education.
Anyhow we have decided to put the Ultimax 18 in his truck. We have the enclosure designed and mostly built. All 3/4 MDF, double walled on the large panels and internally braced. The net internal volume NOT counting driver displacement (I can't seem to find it listed anywhere) is 9,807 cu ", or 5.67 cu'. Again, this does NOT include speaker displacement, but does include all internal bracing.
He listens primarily to hard rock, current and classic. Will be feeding right at 1000 watts to the driver. Amplifier has an adjustable subsonic filter on it.

I would GREATLY appreciate some assistance in properly tuning this enclosure. Preference would be to use 4" PVC. I have some techniques to get a nice roundover on both ends.
I am somewhat familiar with Winsd, but I just don't trust myself enough to depend on my own results.
Thank you in advance for any and all help in helping me look like super Dad ! ;o)

[billfitzmaurice]

At roughly 5 cu ft leave it sealed, the UMax 18 needs a really large box to go ported, and you'd only do so if you wanted F3 well under 25Hz.

[mkellym]

At roughly 5 cu ft leave it sealed, the UMax 18 needs a really large box to go ported, and you'd only do so if you wanted F3 well under 25Hz.

Thanks for the reply! I know this statement is likely true for home use, I believe it may not be for mobile audio. The description page, as well as Dayton website, suggest 3 cu' sealed and 4 cu' vented for auto use.

[Face]

I too would recommend sealed. I have a few UM18s in 7CF enclosures. I played around with ported and sealed and sealed sounded much better. Ported, in that small of a box, in a car will result in a large peak.

[Millstonemike]

And you get cabin game in the low end, more than in a room.

Also, you should educate him on hearing loss. It's rea. l as I now struggle with phone calls, group conversations and certain accents.

[mkellym]

And you get cabin game in the low end, more than in a room.

Also, you should educate him on hearing loss. It's rea. l as I now struggle with phone calls, group conversations and certain accents.

thanks for the advice

[guitar maestro]

Superdad, what kind of out-of-car alignment are you looking to achieve? That is all a WinISD model will show you, after all. Maximally flat? EBS? Peaky response?

Also, don't take the PE/Dayton Audio description pages as Gospel when it comes to low frequency "designs". Most are simply generated from BB6 software as it's one and only suggestion.

[billfitzmaurice]

The description page, as well as Dayton website, suggest 3 cu' sealed 4 cu' vented for auto use.

I can't imagine why. With the cabin gain in a car there's no point to an F3 lower than 40 Hz. For that matter 50 Hz is usually sufficient. That's why most car subs are small and sealed. The charts in this link show the effect of cabin gain:
https://www.google.com/url?sa=t&rct=...9MPaYQ6m3XoBVu

[Chris Roemer]

If you want any kind of sound quality, then sealed is the only way to go.
In YOUR box (which will give "boom" around 40Hz, but not much lower - 'cause the box is too big , which is probably what WinISD is showing you, and it's NOT wrong), you'd need at least a pair of 4"id PVC vents, 2ft to 2-1/2ft long. THREE would be much better, but then they'd each need to be about 3-1/2ft long.

[mkellym]

If you want any kind of sound quality, then sealed is the only way to go.
In YOUR box (which will give "boom" around 40Hz, but not much lower - 'cause the box is too big , which is probably what WinISD is showing you, and it's NOT wrong), you'd need at least a pair of 4"id PVC vents, 2ft to 2-1/2ft long. THREE would be much better, but then they'd each need to be about 3-1/2ft long.

Thanks for the helpful reply! I assume you are meaning the box is big for sealed? And I'm not sure that a peak at 40hz would be a bad thing with the type of musice he listens to. His amp has a bass knob which I believe is centered around 40hz so could tame down pretty easily.
The enclosure is not finished and could be cut down a bit if necessary.
We purposely made it that size thinking we would be porting it. I was already planning on two 4" vents about 2' long, which will not be a problem with our design.
What kind of output difference would you assume between this enclosure sealed vs vented?
Thanks again.

[billfitzmaurice]

The only reason to port the UM18 is for home theater, to realize an F3 of between 15 and 25Hz. There's no point for it in a car, and for that matter in a car I'd put it in a 2 cu ft sealed cab.

[mkellym]

Wow that seems like a REALLY small enclosure for an 18! May have to do a complete redesign if we're going to use something that small. I'm use to big drivers needing big enclosures in vehicles. Most of the 18's for auto use require a minimum of 3 cu' sealed and at least double that for vented. I'm at a bit of a loss as to what to do from here...
One additional bit of info, the vehicle is a Silverado 4 door pickup. We removed one of the rear seats for placement of subwoofer..

[billfitzmaurice]

I saw that you said it was a truck. If it was a regular size car I'd have said 1.5 cu ft was enough. Did you look at the JBL chart I linked? The size box it takes to handle a 1500 cu ft or larger room isn't required in a 150 cubic foot truck.

[guitar maestro]

Wow that seems like a REALLY small enclosure for an 18! May have to do a complete redesign if we're going to use something that small. I'm use to big drivers needing big enclosures in vehicles. Most of the 18's for auto use require a minimum of 3 cu' sealed and at least double that for vented. I'm at a bit of a loss as to what to do from here...
One additional bit of info, the vehicle is a Silverado 4 door pickup. We removed one of the rear seats for placement of subwoofer..

Well Superdad, this is why you really need to sit down and learn WinISD. All this back-and-forth can be avoided. It's not all that difficult.

[mkellym]

Well Superdad, this is why you really need to sit down and learn WinISD. All this back-and-forth can be avoided. It's not all that difficult.

thank you for you kind and helpful comments.......