DiyMobileAudio.com Car Stereo Forum banner

61 - 72 of 72 Posts

·
Registered
Joined
·
2,450 Posts
Something most people forget when designing ports. WE all mention chuffing but what most don't know is that above 20 M/S we are near or above 3db of port compression. This renders the port useless. You are running a leaky sealed box at that point along with the added noise/distortion that "that" leaky box is adding.

So maintaining that balance of port area under power is essential to having a bass reflex design that performs and sounds how you want it to.
 

·
Registered
Joined
·
7,203 Posts
question for fourthmeal, i also plan to run a pair of jbl w12mk II subs, but with a 4.5 cuft vented enclosure. My question is which port design is better for sq, slotted or ported? i was under the impression a slotted port design was better than the round ports. which is better for these subs? forgive me because i never ran a vented sub setup, always sealed. and the only reason i'm going vented because i have been reading as many older threads on this sub as i can and everybody who i know has a ear has stated that with this sub, going vented , you still keep the SQ of the sealed but adds the spl and efficiency of a vented box. BTW my music taste is fusion jazz and limited rap (roots/dr.dre).
Near as I can tell, and I'm not an authority on this, there makes no difference in how the port is constructed so long as it is made large enough and rounded over enough for it to not make noise that you can hear, thus something that would take away from the music. My gut says to use a heavily flared port for best SQ, and that seems to be the agreement in home audio as well. But slot or round, either can be flared. A ported box has more group delay near the tune freq, so I'd tune very low to minimize that effect in the listening range where your ears could pick up the delay.
 

·
Registered
Joined
·
7,203 Posts
Something most people forget when designing ports. WE all mention chuffing but what most don't know is that above 20 M/S we are near or above 3db of port compression. This renders the port useless. You are running a leaky sealed box at that point along with the added noise/distortion that "that" leaky box is adding.

So maintaining that balance of port area under power is essential to having a bass reflex design that performs and sounds how you want it to.
I wasn't sure it was around 20m/s but I knew that port compression is a real thing. I thought it was around .1 Mach, which is ~34 m/s
 

·
Registered
Joined
·
954 Posts
Discussion Starter #64
Happy New Year guys! Quick update. Everything installed and very basic tune using mic supplied with Pioneer 80PRS.

This setup has far exceeded my expectations. I'm sure the sheer size and volume of the box have much to do with the fact that I've got low end which far exceeds the output capability of my front stage... by a wide mile..

Sound is seamless, wide/tall imaging, nice detail, hits like a well balanced sledgehammer.. that's when listening to "normal" music

When I "uncork" the subs and throw some Bass Mechanik on there, bump sub level and EQ, they absolutely blow the roof off my minivan, it's absurd.. As a whole, the system for what it is, just wow..

I'm supposed to meet up with a member who happens to be local.. He's got the gear needed to optimize this setup which atm is probably operating at only 1/3 of it's actual capability..

Once it is properly tuned and I have some hard data, I'll be able to update with a bit more than "just wow"

Mannish, get it right and your ears will thank you for it.. Fouthmeal, thanks so much for all your help, it really made the difference..

I'm so glad no one took me up on these subs when I offered them for sale on this site..

THANKS FELLAS!!
 

·
Registered
Joined
·
954 Posts
Discussion Starter #65
I will update with photos and graphs when I am completely finished.. Now that my subs are rattling panels loose, I realize I'm only halfway there.. LOL
 

·
Registered
Joined
·
2,450 Posts
I wasn't sure it was around 20m/s but I knew that port compression is a real thing. I thought it was around .1 Mach, which is ~34 m/s
I have a pic I saved of a graph I got from DIYAudio I believe where it shows the compression vs port speed. It matches very closely with what John from AE told me. He said stay under 10 ideally. Realistically stay under 20 at full power. I need to find that pic!!

After taking his advice, I lost all interest in sealed enclosures. Ported and PR designs are the way I go mostly any more. Not counting Tapped and front loaded horns...:D
 

·
Registered
Joined
·
954 Posts
Discussion Starter #68
I have a pic I saved of a graph I got from DIYAudio I believe where it shows the compression vs port speed. It matches very closely with what John from AE told me. He said stay under 10 ideally. Realistically stay under 20 at full power. I need to find that pic!!

After taking his advice, I lost all interest in sealed enclosures. Ported and PR designs are the way I go mostly any more. Not counting Tapped and front loaded horns...:D
According to Winisd, the 8cf enclosure I modelled with dual 1.5" x 16" ports topped out at 26 with 1000 watts RMS (if memory serves correct)

In my real world application, the only chuffing I'm hearing is from some of the screw holes I missed with woodglue.. FWIW, I've never heard a sealed box which provided the type of low end response I'm getting from the ported box I "rigged" :D
 

·
Registered
Joined
·
954 Posts
Discussion Starter #69
Excellent, I'm happy the advice worked out.

Enjoy!
Thanks so much! "Enjoy" is an understatement in my case.. Pie eating grin every time my rear view mirror falls off..
 

·
Registered
Joined
·
897 Posts
@lust4sounds..thanks for the updates! sounds like your more than happy. And im going to take your advice and do it right.
@fourthmeal would you be so kind to point me to a person or yourself who could design and send me a cutsheet for a sub enclosure? and i right to assume that since one sub needs 2.25cft, that 2 would would be 4.5cuft?
i think since i have no real tools yet, previous tools was stolen, i should go for the round ports as i can make them with pvc pipes and use elbows if needed. and you mentioned flares, so i should look at some premade flared ports. actually, i eed to just find a really good box builder. anybody know of one?
 

·
Registered
Joined
·
7,203 Posts
@lust4sounds..thanks for the updates! sounds like your more than happy. And im going to take your advice and do it right.
@fourthmeal would you be so kind to point me to a person or yourself who could design and send me a cutsheet for a sub enclosure? and i right to assume that since one sub needs 2.25cft, that 2 would would be 4.5cuft?
i think since i have no real tools yet, previous tools was stolen, i should go for the round ports as i can make them with pvc pipes and use elbows if needed. and you mentioned flares, so i should look at some premade flared ports. actually, i eed to just find a really good box builder. anybody know of one?
I didn't design one in this case, we were just using WinISD Pro 0.7 to calculate stuff but I never made a 3D model of it. I don't use cutsheet programs, though. I always just make stuff up as I go, once I have a model or an idea in my head. :)

If you lack the tools, best to find someone that can do it and do it right for you for sure. Not sure who to recommend in your area, might want to post something in a fresh thread so people can suggest where to go.
 

·
Registered
Joined
·
954 Posts
Discussion Starter #72 (Edited)
I came here looking for that Winisd download link, figured while I'm here I'll provide an update.

The subs have broken in and I must say... the low end, detail and the riotous output from these 2 12s... absolutely insane! (using a smallish pair of JL 500/1 amps, 1 per sub)

I haven't had time to meet with a friend and have everything tuned properly with O-scope, proper mics/program EQ etc. For a baseline tune, the mic provided with the Pioneer 80PRS provided surprising results, did not expect this kind of performance from that mic .. I will definitely need to tune properly, will get that done soon..

Thus far I'm pretty impressed by what I have.. (especially considering the fact that I'm using D class power on subs, isn't there a raging debate for A/B vs D?) I have to say, I was never a fan of JL amps till I stumbled on the 3 500/1s which I now own.. Have always LOVED their subs, am now a fan of their SUB amps.. (never got into anything mid oriented by them)

When dialed WAAAAYY down, they blend nicely with the Hertz Milles. Subs, midbass/midrange detail is pretty awesome,

For a balanced sound, by default, it keeps setting my sub section to 63Hz w 12dB slope, sub level pulled way back down to -16. It keeps setting the 6.5" Hertz Milles (mounted in doors) to 100Hz with 18dB slope. I'm assuming that huge gap between sub and midbass is it's way of compensating for cabin gain as well as the output/capability of the subs?

When I turn the sub level way up for bass music (EG: Excision "swerve" streaming through "Tidal") the sub midbass experience is absolutely incredible. Jaw dropping output, bass hits hard and fast, really tight.

When I dial the subs back for balanced listening mode and listen to "Vadrum" (through Tidal) equally impressive. While imaging not quite there, the detail tone and impact of a masterfully tuned drum-kit accompanied by a full on orchestra is incredible. Can't wait to hear the same music once it's properly tuned with imaging and EQ.

I've never heard a pair of 12s hit this hard accurate AND LOUD with only 1000 watts RMS...
 
61 - 72 of 72 Posts
Top