-Please move if in wrong category, its been a while since ive been on here-


ok, here's the scenario,

CAR, 94 toyota corolla hatch
SUB, Rockford Fosgate P3 15" dual 4Ohm Coils
BOX, Ported, 2.5 cubes, 9" X 4" Port (round)
AMP, Rockford Fosgate P4002, bridged 2Ohm Load
0awg cable, no cap.
Alpine Cda9815 HU


when playing any up beat music, dance techno etc sub has a huge delay from the front stage, not so noticable whilst playing rnb/hip hop style, have tried to rectify problem using Time Alignmet in hu, but still no fixy the problem... Not happy Jan...

Front stage consists of Alpine SPX-177a Splits driven off another P4002, and they sound really good, lots of mid bass, very good vocals.

Any Suggestions much appreciated.

Cheers,
Blade

I had the same problem in my car.

when I reversed the phase of the sub, the problem was reduced, also resonances in the car were "blurring" the sub's response.

lowering the crossover frequency of the sub was able to push it below the resonance. I was fortunate that my splits would play low enough.

Also try increasing the xover slope of your sub, around 18-24db/oct

What is the low pass point set at? Try it around 40hz-80hz depending on the rest of your setup.

edit:double post

^^ What he said You beat me to it Pulse-R Just a question - did your sub sound kinda weird when you reversed the phase? I tried that, for the same issue Blade has, but it sounded 'hollow', even though it was more in time with the splits :huh:

yes, sounded hollow, then fiddled the x-over frequency & slope

Its called group delay. Basically theres a delay between the sound emanating from the woofer, and the sound emanating from the port. When the group delay goes up...this "laggy" sensation also increases.

Its affected, i THINK, by
port design
port length
tuning frequency
box design (ported, bandpass, etc etc)

So, did you design the sub-box specifically to suit that sub? Did you model the group delay?
Its possibly the main thing thats turned me off ported boxes. A well designed port, and box, wont suffer from it much, if at all...but a badly designed one...well....

15s in a big a$$ ported box equals high group delay. Try a smaller sealed box. Id go smaller subs too but definatly go sealed first and see if that more how you like it
peace
Cyberpunky

*smacks head*
Why didnt i recommend that. DUH.

Try blocking the port with a towel or somesuch and see if the delay dissapears.

Ow, but i wike my port, pulls 139db on new meter.

I have thought about fiddling wit the port length, but i cant really do much about the box size without re doing ALOT of the install, and that, ISNT going to happen any time soon.
I think i may be getting some box flex, in between where the sub hole and the port is, its quite thin, would this be adding to my problem?

I was thinking more power may also be a fix for it, Maybe running one 2004 into each coil, but then each amp would only be seeing a 4ohm load (which its designed for) and not really getting an increase in power...

just another thought, would the fact that the rockford amps have so little capacitance in them, and im not running an external cap maybe play a part in the delay, i know its hard to actually say, but im trying to cover all my bases...

cheers,

Blade

Technically, sub wall flex would cause sound that was, well, crapper. Ditto for a leaky box. But it wouldnt cause the big group delay your experiencing.
That said, interior box bracing is never a bad thing (taking into accoutn volume changes)

Changing ohm loads affects power and, before anyone jumps on me again, damping factor. While changing your damping factor *can* help with cone control, in my opinion its minimal. I dont think its responsible for the large lag your describing.

The amps internal capacitance probably has jack-all to do with it, but i'm not the expert on that. I DO know, however, that external caps have been shown to actually drop SPL on most systems, i wouldnt be suprised if they adversely effected sq as well. Your better off spending your money upgrading the STOCK engine bay power/ground wires to/from the battery and alternator...but again, this wouldnt be responsible for the laggy bass your describing.

KEep the ports, fine, but if you can block them off just as a test to see if the bass delay dissapears.
May as well troubleshoot, starting with the easiest step.

15" woofers arent the best choice for extremely rapid cone control in a ported box, generally. The best subs with the best amps in a good box will soudn great, but for tight punchy bass you'd want a 12", for mid-spec components. And a sealed box, generally.

edit : *looks down and sighs* I still maintain the easiest first port of call, and probably the problem, is blocking the port for a minute.

9815 has alot of features. switch off ur eq's and TA and have a good play aroudn with crossovers and slopes and phase etc. if u cant rectify it then look at blocking port, rebuilding box, box positioning

Good luck! how much power is the sub getting?

Well, as you can see, I wont really be changing the install any time soon,

Click to view attachment

So i guess doing the old port blocking trick wit a towel or something is on the agenda...

I guess the sub is probly getting bout 400 to 500wrms, i havn't got the birth cert on me atm, the amp is rated at 2 x 200rms but it exceeds its ratings like a good amp should.

Is 2.5 cubes too big for a sealed box???

I have this bass delay trouble too and I have just installed a new Head Unit, an Alpine CDA-9847. I've looked in the owners manual but I can't find anything about Time Alignment. Does anybody know if the Alpine CDA-9847 has Time Alignment?

thanks

(by the way, my new HU has made a marked improvement in SQ)


Doug

Seriously, your on the internet. Try www.alpine.com.au

But to answer your question, no, it doesnt. Not according to the website, at least.

Time alignment is a fairly subtle thing. It cant cure the aformentioned group delay.

9847 doesnt have it 9851 has bass engine plus which has 4chan TA 9853 and 9855 have bass engine pro. which has the more sofisticated crossovers, TA, and eq's

Dude your delay is caused by box type and subs...if all you care about is pulling 139 then learn to live with it
Im pullin at least that with 2 12s in a sealed box with 300 per woofer so its not like your a big hitter
anyway google group delay and you may understand what we are talkn about
peace
Cyberpunky