[atledreier]

Hello!

In home audio we figure room gain is about 6dB/oct below the lowest room node. How do I figure cabin gain for a small car?

I'm thinking of using an RL-p12 for a SQ setup. Nothing very fancy, but definetly no boombox. I'm thinking separates up front and a ported box in the boot.

The car is a Mazda 323 GTR, so it's an open cabin. I'll probably go for a cheap'ish amplifier, around 100W or so. Hard to tell, the ratings on the box are usually meaningless.

 

[atledreier]

Yeah. Kinda hard to read anything about rolloff there, with the gain being as it is. Big jump at 70ish Hz and then looks like a 6dB/oct increase as you go down. But there definetly looks like a 'base gain' of about 20dB! Wow! So I think output shoudn't be much of an issue. I' more concerned that I'll have no means of EQ in the car. That's out of my price range, I think.

I'll look into this some more.

Anyone have experience with the RL-p12 in car for sound quality? Any other drivers that would do a better job on a budget?

 

[atledreier]

That's a good idea.

Is there no proper 12V parametric EQ that would do the job?

 

[atledreier]

Modelling the RL-p12, it looks like sealed will be the way to go. Ported will give me a huge peak around tuning, and a steep dropoff below. The sealed has a rolloff that almost match the general cabin gain, and the RL-p12 will have incredible headroom for the power I plan to feed it.

Is there anything I should think about regarding the 12V->110/230V conversion? What about noise?

Could a DCX EQ the front separates as well? How about a BFD? Could that be used? Most amps have an analog crossover anyway, and all the bands of a BFD could emulate shelving and stuff most times, and it would be alot wheaper. Do the DCX have delay adjustment?

 

[atledreier]

Yeah, looks like sealed will be a winner. I'm more concerned with blending with the separates up front than with output, to be honest. Ridiculous levels of bass is easy in a car, so EQ and delay is more important, and infinitely harder to get right. With virtually all drivers at different distance, orientation and phase the soundfield gets really complex. I'm starting to think good EQ is the only way to go. I've heard of some automotive headunits have Audyssey built in. Now THAT sounds like a great application for Audyssey!

Edit: I'm currently looking at the Rockford T400-4 amp to drive the sub and separates. It's got very good reviews and the price is very good. Any thoughts?

 

[atledreier]

Awesome. I wasn't aware that the DCX was so versatile. I need to read up on that unit for sure! Is the 6 outputs independently EQ'ed as well as assignable to output?

Can I create a mono output from two inputs?

Going this route I may go for a 6-channel amp and go all active with a single DCX. Now THAT would be awesome.

I haven't thought about midbass yet. I don't have the car yet so I don't know how much room I have. If I do get midbass units, I might just use a single channel for those and a single channel for the subwoofer and still get good EQ for all. I guess mono midbass is much preferred to un-EQ'd midbass.

One concern, though. The midbass units will most likely be placed in the back, either all the way with the subwoofer, or in the rear seat panels. Would this pull the image rearwards? How high do you usually cross the midbass over? I'm not concerned with rear seat SQ at all, but both front seats should sound good.

 

[atledreier]

If the midbass will be hidden back into the car where it does not matter anyways, then you may as well go mono with it. One more option, to keep everything stereo... is to set up the last two channels on teh DCX to feed the midbass upper xover point(say 120Hz as example) with flat LF response. Now, use an inexpensive 2 way analog 4th order car audio xover and feed this signal to this unit. Split at say 80Hz - feed the high pass to the midbass amp and low pass to the subwoofer amp. Now you can still use the DCX to apply EQ and other things to the subs and midbasses - and control level gain to the midbasses and subs with the analog xover.

Sneaky!

The DCX definetly sounds like the way to go. Any tips on cheap'ish amps in the $500-$600 range?

Edit: Just found a used Precision Power AX606.2 on ebay fro $350. I have owned one PPI amp before and it was truly awesome. Is this the gem I think it is?

 

[atledreier]

So the AX606.2 is too weak to power my entire system? Even in 5-channel mode?

 

[atledreier]

I had a ZX475TI back in the day on a Boston Acoustics pro6.4/6.0/12.4 system and it totally rocked!

Found an X100.4...

 

[atledreier]

I am aware of the benefits of ported, I use two RL-p15 LLT tubes for my home theater. I was suggesting the sealed before EQ was brought to my attention.

I am also aware of the spl and dynamics requirements for automotive audio, and my opinion is that you can't really get good sound quality in a rolling vehicle anyway. I want to be able to stop my car and enjoy good sound while reading a book or having a snack or whatever.. yeah, I'm weird.

I'm one of those that truly love driving for the sake of driving, and music for the sake of it. With a good sound system I can do both, but not at the same time, usually. If my audio system can maintain enough SPL to break out of the road noise I'm fine.

I want the system to be able to wow my friends for sound quality, not be the loudest boombox in my street. That is easy, if not cheap. From modeling the RL-p12 with 100W of clean power it can do over 100db even without figuring cabin gain. For my budget I think that's enough. We'll see, I can always switch amps. Right now the car is on my priority list, then I'll build a system for it.

Thanks for the help so far, i'm sure I'll have many more questions once I get into this!

 

[atledreier]

did you get my PM sonnie?

 

[atledreier]

I'm with you on the isolated battery, but in this particular vehicle weight will also be an issue. The subwoofer enclosure needs to be removable for track use, and an extra battery is too much weight to lug around on track. There's enough of that as it is. I think I'll just exchange the normal battery for a high performance one. Is the Optima range still considered high performance?

The DSPower unit is sold out. Know anywhere else I can get something similar?

 

[atledreier]

Ok, I just bought a PG X200.4 amp to power the mid and highs. I may have to run the mid/highs off the analog crossover for now and have the other two channels drive the sub for about a month, as the car purchase depleted my bank account a little more than I'd hoped. Should be good for a while, though. The 1200.1 seems like overkill for a single 12" driver. I thought a 600.1 would be sufficient for a highpass filtered ported 12".

 

[atledreier]

Sonnie, you didn't warn me how incredibly HUGE this amp is! :unbelievable::yay2::rubeyes: