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Discussion Starter #1
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.
 

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Discussion Starter #3
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?
 

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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?
There is no problem with the driver; that's a superb driver. I'm sure it will give you good SPL with levels of THD that are well below audibility. But the problem is the frequency response curve. I don't care what quality of driver you use, if the FR curve is not to one's preferred shape, it's not gong to sound like the best quality. The FR curve is a massive factor in perceived sound quality - even if everything thing else is theoretically perfect - the FR curve will be the final determining factor. I would recommend using a DCX2496 with the Envision Electronics 12V PS module. This will let you shape the LF response to ANYTHING you desire; letting you get any degree of 'tightness' or 'extension' that fits your preference. In addition, of course, you get to have a great active crossover to control your system.

-Chris
 

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That's a good idea.

Is there no proper 12V parametric EQ that would do the job?
If you find one offering anywhere near the FR shaping possibility of the DCX unit, let me know. Most car audio 'parametric' EQs are not even parametric EQs. A true parametric EQ must have these variables for each band: Frequency, Q(bandwidth) and Gain. The DCX goes beyond this; it provides shelving functions, an the parametric bands can overlap each other for complex curves. It also offers dynamic EQ and limiters that can be programmed to protect speakers under specific conditions - to damage proof your system.

If ones goes with the DCX: Using a laptop to set up the DCX with it's GUI while listening in real time will be very useful.

-Chris
 

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Discussion Starter #7
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?
 

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Your results may vary of course, due to many factors but I'm getting greater than 30db gain in the lowest bass and basically flat response down to 3hz in my Jeep I assume roughly 12db octave gain.I'd go sealed for SQ in a car. Ported always seems to have a rising response with a big boomy peak around tuning. You could pad that down with EQ and have massive headroom. Sealed is smaller and simpler if you aren't worried about rattling other cars license plates as you go by.
 

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Discussion Starter #9
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?
 

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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?
The DCX has 3 analog inputs and 6 analog outputs. If you send the 2 main channels, and use the DCX for all controls, then yes, the DCX can take care of your entire system, if 6 channels is enough. The DCX allows you to independently apply xovers, filters and delays to each of the 6 channels. DCX units are cascadable. That is, you can connect a 2nd DCX to the 1st, and a 3rd, and so on... and the 1st unit will be a master controller and the other units slaves. If you need more channels. If you are using front seperates fully active, then this will consume 4 of your 6 channels. You can use one more channel for the subwoofer(s), then possibly the last channel for the rear midbass if you will not mind mono midbass units. Or you can use passive crossover on the tweeter to midrange on the front components and have enough channels from a single DCX to feed all speakers. I'm assuming you are using rear midbass units. If not, of course a single DCX will handle a front component set and a subwoofer with no passive xovers in full stereo.

There is a 12V PS unit for the DCX. It has no noise issues. You open the top cover of the DCX, unplug the 120VAC supply, remove it. Put in the new 12VDC supply and plug it in. Replace top cover.

As for signal routing... I would use an ART DTI or similar up front and feed the unbalanced RCAs to this. The ART DTI in turn will output balanced XLR lines. Run balanced to the rear of car - this will prevent any noise pickup from occurring.
 

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Discussion Starter #11
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.
 

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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?
Yes, each of the 6 channels can be independently EQed. You can treat each channel as a separate entity entirely, if you wish, or you can 'gang' channels together to adjust with each other.
Can I create a mono output from two inputs?
Yes. There is a routing screen. You choose to SUM channels 1 and 2 to MONO 'C'. You can then assign 1, 2 or SUM to any channel you want as it's input source.

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.
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.

-Chris
 

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Discussion Starter #13 (Edited)
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! :D

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?
 

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Sneaky! :D

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?
I don't have any specific suggestions on any current car audio amplifier models/brands. However, if you could find enough of the old ART series from PPI, I would recommend them. These are some incredibly high quality amplifiers and you can get some deals on them from time to time since they are long long since discontinued. Plus.. come on... they look so sweet. :) However, I will urge you to go for the most 'real' power you can afford, even for mids/highs. The inherent noise floor of a car is so high, that I would even suggest 150 RMS for each tweeter and 250 RMS for each mid range. Assuming average sensitivity drivers. This assumes you listen to dynamic music. If you only listen to TOP 50 stuff... not much point considering the pathetic level of dynamics in the overwhelming majority of modern album releases.

-Chris
 

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Mav... I have a brand new DCX I can let you have for $240 + shipping... still NIB.

Check out the Phoenix Gold Xenon amps... the 200.4 is a real 200+ watts x 4 and they are very clean amps. ebay is about the only place you can find them. I have it running my mids/highs active.

I also have the 1200.1 for my subs.
 

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So the AX606.2 is too weak to power my entire system? Even in 5-channel mode?
I am merely recommending an 'ideal' situation to allow for little to no compression/clipping when playing dynamic music at a satisfactory SPL level while driving(which presents to the listener a very high noisefloor that they will in turn increase the volume level to compensate and 'break through'). I am sure many would think my suggestion to be excessive. But if this is supposed to be a SQ system - I hardly consider clipping/compression of the signal due to insufficient amplifier power to be acceptable in this case.

I would power the subwoofer in question with an absolute minimum of 500 Watts RMS. If you want to minimize distortion to the absolute fullest extent, then as another poster suggested earlier, use it in a proper ported cabinet system. I would personally target no higher than a 25Hz tuning. Ideally 20Hz. Then use the DCX to flatten the response. This would give you massive headroom, and absolutely minimize non-linear distortion(s). Yes, it would be a sizable cabinet. Be sure to use a slot port and keep air speed well under 20 Meters/second at the target 500 Watts input power for ideal performance. Of course, I understand if you prefer to go sealed due to the substantial space savings and simplified cabinet construction.

I don't know what your car power supply system is like, but I would probably add a very large capacity battery on a battery isolator, and a low ESR 1 farad capacitor on this system.

-Chris
 

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Discussion Starter #19
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. :p

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! :)
 

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Chris... of all people I would have assumed you would have investigated capacitors. No need to waste your money... they do not help and there have been several credible tests completed that prove the same.

You can add a second battery, of which any would be superior than even a 100 farad cap. There is a company that actually make a product called BatCap (or something similar) that is actually a small battery for the purpose of extra power in a system. However, adding a battery is really only going to give you longer play time with the vehicle engine turned off. If you need more amps for the system, the only solution is adding a higher output alternator. I run right at 2000 watts in my car and use a Kinetik HC1800 (1900 Amps 81 Ah)... and I really need a HO alternator, but they don't make one for my vehicle at present.
 
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