Strange port calcs, Focal P25 subs

Hello,

First time poster, long time reader and enjoyer of the site.

I came across a good deal on a pair of Focal P25 subs (loose, not in the Focal cabinet) so I scooped them up to put in my work truck. Nothing special, but I like good clean loud music. So I am building a custom cabinet for them and I noticed that the port length recommendations are really short - like 1" - 1.375". I tried to validate this using the calculator here using their box volumes and it says ~15" long. Something is not adding up.

Any thoughts?

I suspect a typo. Instead of "mm" it should be "cm"

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At first I thought the same thing, but they also include the fractional equivalent as well.

Additionally I researched the cabinet that this sub came with as a kit and it uses a slot port, that on face value doesn't make sense either...




I sent an email to Focal, I guess I will wait see what they have to say.

The QTS doesn't support it, but I may try an IB set up with these, for grins.

the tuned frequencies that they show are the overall peak frequency of the sub and box,(f3) your box calculators are giving you just the peak frequency of the box itself(fb). thats why its not adding up

I had a feeling that this was the case. It makes sense that the driver has its own properties that would dictate the resonance.

Maybe a better calculator? Is there one online that you might recommend?

Thanks for your reply, btw.

So, as a follow up, I went a ahead and built a box based loosely on the lower end recommendations. Finished up the install yesterday and played around briefly for initial tuning. So far it sounds pretty impressive in the low end, but definitely needs some more tuning.

System details-

Alpine CDA-117
Eclipse 3640
Morel Maximo 6 comps
Orion XTR 600.4
Focal P25's

It's a work truck, this was about all I was willing to do for it.

I might talking to myself at this point but I will keep this updated for those like me who found little to no info for a similar setups.

First let me say that I built a very similar box like this over a decade ago for another work truck, same model. It was a pair of PG something or other 12's with some JL fronts and Blaupunkt HU, and a Lanzar optidrive something or other - 800w. Allegedly. It loving pounded, and the hits were tight crossed all of the genre of music I listen to, everything.

That's what I was trying to recreate here, maybe a little toned down, cause I am 40 and been into audio my whole life, work in a shop, underwater, in construction, and otherwise high level sound environments. My golden ear is a bit of gilded donkey.

That said...

This bass system, with two tens, nearly matches my two 12's for deep bass. It's not even funny below 35hz. Like break doodie hard.

Currently, above 42~hz it falls flat on its ass.

I will get back here with updates and specifics as I move towards a good sounding all around system for the work truck.

Thanks to the12volt forums for all their helpful input.

J

Shortened the port length today by 3", lost the heavy resonance at 30ish hz gained punchy hard hitting 50-60hz like crazy.

Foreigner, Eagles, White stripes all sound convincing now. Kinda miss those low hits for Thievery corp, Aphex Twins etc. Will work some more on port length next week, for now super satisfied.

Keep it loud, bitches.

yea that is the general trade-off when shortening your port, you raise the tuning frequency of the box. the same is also true with the internal box volume. im not on this site much these days but im glad it worked out for you. as far as box building programs theres really not that many out there and they arent real cheap either. ive built enough boxes in my life so far that i can do without a program to get me good results with sealed and ported boxes. since you have so little space availiable in your truck i would definitely recommend that you try going sealed or if you really want to go ported then maybe try just a single 10 or 12 but still using the same general size box because ported boxes do better when they have more airspace to work with.

i want to ask how long was your original port and what was the internal airspace?

To answer your ?'s - internal box volume is - 1.137 sq ft - Slightly less than the 35l recommended (32.20) - plus about a pound of polyfill per sub. The ports were sold as 4.5" x 3".

Originally, I actually kept the port as purchased (4.5") just because I knew that the id was an 1/8" smaller than the spec (3 1/8") and because I knew that I would run into some in resonance. Still, the port shortened to 1.25" seems to offer the best SQ with zero signal conditioning. That leaves me with plenty of wiggle room for equalizing and such.

I actually built a very similar box about 12 years ago with a pair of PG 12"s, it was sealed and over powered, sounded great. The sealed boxes are predictably nice, I just wanted to try a ported box this time.