Hello all,

I have just had a 'no direction' mini spending spree, and am a bit unsure what to do with it all

I have a 4dr classic with a Sony mini disc unit MDX C7900R, JBL 6.5" components in the fron doors.

I bought an Alpine V12 FRV-F400 (40wx4) amp 2nd hand, with the aim of powering the fronts and a pair of 6" subs off the other 2 channels. I have not fitted this yet.

Today, in a moment of madness, I bought a Rockford Fosgate 100.2 amp and 1 boxed 10" RF sub (RFZ2410), all new for the princely sum of £149.....bargain.

So then...to the equestions.

1. What is the best way to install 2 amps.
2. Am I best bridging the alpine amp to 2 channels and just using for the 2 fronts.
3. Do I need a different head unit, as this one doesn't have a sub out...just 4 speakers.

Anything else I should consider before I get the soldering iron out

Cheers

Andy Holmes

MY99 Royal Silver WRX, STi4 spoiler, 18" Radius R3's, SS mid and back, 4pots, hopefully a nice audio install !

 

If it were me, I'd start by ditching the rear speakers completely!

From memory, that Alpine amp has built-in crossovers? If so, wire up the front components separately, so you get the mids on one pair of amp channels and the tweeters on the other pair. That way, you can set crossover points at the amp, and alter the gains to suit your taste. You can then use the rear channels to drive the other amp, for the subs

 

Thanks very much, didn't think I could do that !?!?!

So I would just break the link between the mid and tweeter, basically ditching the inline capacitor thingy ma jig.

Sounds like a plan.

With having 2 amps, I presume the boot is the only place to put these.?? The WRX seats do not fold down (no jap spec 2 or 4 dr cars do), is is an idea to mount a carpeted piece of mdf or something up against the rear seat backs, and mount the amps to them, hiding the wires behind. ???

Cheers, and already getting good tips.

Andy

 

Note, the crossover point on the amp needs to be set to match the crossover point of the passive crossovers - this'll be around 5,000 Hz. As long as your amp'll do it, I'd go with that suggestion

 

Sorry to annoy but,

From what I have found on the net, it appears I can cable the RF amp straight from the alpine amp..... bonus

I don't think I understand what you are saying chairk, 5,000hz ?!?

cheers

Andy


I found these comment on the net :-

MRV-F400 has built in x-overs with constant level line out for
subwoofer. So you can use the Alpine amp to drive the components and connect the RF amp to the Alpine. This will eliminate the need of a x-over.

And additionally for the amp....

• 4/3/2 CHANNEL OPERATION-Can be used in a 4-channel mode providing 40 Wx4 into 4 ohms or 50 Wx4 into 2 ohms, or in a two channel mode producing 100W x 2 into 4 ohms (all power ratings are from 20Hz to 20 kHz at 12V DC). • MULTIMODETM CAPABILITY- The MRV-F400 can operate in 2-channel stereo and bridged mono modes simultaneously. • ACTIVE DIVIDING NETWORK-A built in variable electronic crossover network form 50 - 200 Hz (12 dB per octave)is independent for channels 1/2 and 3/4 and can be used to set up the amplifier for low pass or high pass applications. This network can also be switched off to allow full-range operation • DUO-ß FEEDBACK CIRCUITRY-Supplies low negative feedback throughout the audio frequency bandwidth and very high negative feedback at DC. This stabilizes the amplifier, removes the DC offset, offers excellent total harmonic distortion (THD), and provides low transient intermodulation distortion(TIM). • NO CURRENT LIMITING - Absence of current limiters in the audio section ensures low TIM, excellent transient response and superb sound quality. • S.T.A.R. CIRCUITRY - Alpine-developed Signal Transient for Accurate Response circuit topology improves sonic properties by reducing interaction between different sections of the circuitry. • INPUT MODE SELECTOR-CH1 Mono;Stereo; Left + Right • CONTINUOUSLY ADJUSTABLE GAIN CONTROL • FULLY DISCRETE, COMPLEMENTARY OUTPUT CIRCUITRY • GOLD PLATED RCA INPUT CONNECTORS AND SCREW-DOWN POWER AND SPEAKER TERMINALS. • HIGH PERFORMANCE, LOW NOISE, AUDIOPHILE QUALITY ACTIVE AND PASSIVE COMPONENTS • PULSE WIDTH MODULATED (PWM) DC-DC POWER SUPPLY- Alpine developed a new type of PWM power supply that maintains rated power output down to 12 V DC and allows for an approximately 40% increase in output power at higher, real world, battery levels. • LED STATUS MONITOR • NON-FADED PRE-AMP OUTPUT- A set of non-fading preamp outputs are included which can eliminate the need for RCA "Y" connectors and allows for greater system flexibility

 

Okay, so what you're saying is "Can I have that in English please"?
So, here goes:

You've got a set of components at the front of the car (mid-range drivers and tweeters) and a sub in the boot. What we're suggesting is that you dedicate one Alpine amp channel to each front speaker, and then use the RF amp to drive the sub. This much you know.

Trouble is, mid-range speakers use (typically) a frequency range between 80Hz and 4KHz. Tweeters use (again, typically) frequencies from 4KHz upwards. Any frequencies below their typical just distort the sound, and those above are lost.

So, the crossover that's built in to the Alpine amp can be used to cut down the frequency range given to each speaker. Chiark is suggesting (correctly) that the channels dedicated to the tweeter should have the crossover set as a high-pass filter (only pass frequencies higher than X) with the crossover (X) point set to about 4-5KHz.

In the case of the mid-range drivers, you _could_ leave the crossover off (as in, give the speakers a full range of signal) but you'd probably be better off using it as a low-pass filter (only pass frequencies below X) with the crossover point set to about 4KHz.

Now, as for how you send signals to the two amps.

The Alpine amp has 4 RCA input channels, one per speaker. It also (I think) has a pair of "repeater" outputs, which pass the signal it receives on the first pair of RCA inputs out again. So, you _could_ drive the sub amp from the Alpine. But, that wouldn't be the best option.

You would be better off using the FRONT output from your head unit to drive the Alpine amp. I'm sure there's a switch on the amp, to allow the first pair of inputs to drive the other pair of channels too, so that channel 1 and 3 get the same signals, as do 2 and 4.
You can then use the REAR output from your head unit to drive the sub amp. This then allows you to control the level of the subs, in relation to the front speakers by simply winding the fader forwards or backwards.

Hope that makes sense?

Richard

 

Sorry to go against the grain, but I wouldn't recommend running the components actively unless you're able to bandpass the signal to the mids - they'll sound bad when you start cranking the volume if they're trying to play all the way down to 0Hz !

Unless you've got an active crossover, or the headunit has built-in filters, I think I'd bridge the four channel amp down to two channels for the front and keep the regular crossovers.

Steve.

 

Thanks, I think the penny is dropping a bit now (unless it has a keyboard attached, I usually don't understand !!! )

The Apline amp is arriving in the next few days, I shall try and figure out what adjustment on the filters is available.

I have two possibilities, both of which use the front 2 channels from the HU to input to the apline amp, the rear two channels to the RF amp, which will be bridged to a single channel for the sub :-


1. Bridge the alpine amp to 2 channel only, 100w RMS to each component set. leaving the crossover in place. (sounds the easiest)

2. Amp adjustment allowing, split the components up, and use each channel seperately to each component. 45w channel each.

Thanks very much for your time and wisdom

Just got a couple of dynamat packs, hair drier in hand, the install begins.

Andy