Mazda RX8 Bose Head Unit + Polk Audio

VelocityVinnie

Hey Everybody

Ive just orderd a full Polk System for my car, which will replace the standard 9 speaker Bose system in my car.

However i will be keeping the Bose headunit to retain the cosmetics of the centre console.

The stock speakers are driven from 3 Bose amps located around the car which i would like to remove.

The standard headunit puts out Line level, which is flat EQ.

The problem i have is that the headunit gives out Balanced Differential output, which i metered at 1v, which meens if i use these to feed the Polk amps i will have to turn up the headunit gain to feed the amps with a substancial level, which inturn puts stress on the headunit, and increases line noise.

Is there a converter you can get which will take the differential outputs and convert them to normal RCA, with a better signal.

My other option was to use the signal POST Bose amps, using high to low level converters, the only problem i have with that is that the Bose amps add a rather 'crap' EQ curve to the sound, and wouldnt be Flat, so i would probably loose a lot of tuning aspects, and mid range. (Bose are known for there own unique sound:rolleyes:)

If anybody has any ideas then i would love to hear them!!

Oh and to wet your taste buds heres the car in question.

Thanks in advance
Vin

arun1963

Hi and welcome to CP.

If you're pulling out the 9 speaker Bose thing, I'm assuming you want good and realistic sound in your RX8. What all have you ordered? You can stay with the stock hu, no issues.

I would run the stock hu to a bit10 processor which will take speaker level inputs. Further it will flatten out any eq curve that is built in from the hu. The bit ten would let me run active and give me lots of tuning tools to tweak the sound. A bit ten without the 'digital in' should cost you around $300 or so. A car is a very different environment from a home. It is the worst environment for accurate reproduction of sound. It's almost impossible to have realistic sound in a car without dsp. I'd run a 4ch amp for the components and a mono block for a small 8-10" sub just to catch the 20-60hz range.

Speaker placement is very important. Can you post pics of the stock locations? I would also look at using sound deadening material to seal the doors for sure and maybe use a bit more elsewhere.

BTW nice car and which one of the two gents, is you?

VelocityVinnie

Hi Arun.

The HU actully gives out a flat line level signal, its not speaker level. My car has 3 seperate Bose amps, all the EQ ect is done by them, hense why i want to tap into the Pre amp signal.

The only issue like ive stated is that the HU uses a differential output to cancel out noise, thus given a 1v signal, if i attach the outputs to the normal RCA line ins on the amps i will have to crank the headunit up almost full to provide a suitible signal. This will inturn eventully Fry the head unit, + ill get loads of noise.

The bose amps convert the low differential signal into a higher one which is around 5-6v.

The only way i can see of doing it, is to use an active LOC on the HU outputs to maximise signal, and thus retain the smooth volume control rather than having to turn it up full.

the standard speakers are 2 x 9" mid/woofers in the front doors, 2 x 1" tweets on the A pillars, a small 5" mid/woofer in the centre dash, 2 x 6x9's on the rear deck, and 2 x 1" tweets on the rear deck.

I have already dynomatted the doors, and boot space.

I am a Sound designer, so do have an idea on what im doing, although im not fully at home with ICE.

arun1963

The gains on the Polk amps run from about 200mV to 5-7V depending on which amp you're getting. So you should be ok with a 1v signal. There's more to dsp than just an eq. I would definitely do this myself rather than depend on the curve set by the Bose amps.Keep in mind that curve was set to make the Bose speakers sound good and now you're not running them.

There's a reason why you're pulling out the Bose setup. You know what good sound is and chances are you are not going to be satisfied with something which is less than realistic. Else you would have have stuck with the Bose. The bit ten will let you set it the way you want to hear it. The reasons that the stock setup doesn't sound good are:
1. Too many speakers
2. Incorrect tuning
3. Bose speakers.

Even if you removed the stock speakers and ran only 1 pair of components, you would only have addressed two of the three. Chances are it still won't sound good.

VelocityVinnie

There wont be any EQ curve, the headunit gives out a flat signal, line level. The EQ is done within the amps, which im removing.

Will the Bit10 cope with differential line inputs?

arun1963

Yes it will.

VelocityVinnie

Thanks Arun

Have you got a link to this Bit10 you mention?

arun1963

http://www.audison.eu/index.php?page=product&id=42

Thats the product link on the Audison website.

VelocityVinnie

Thanks

It aint cheap is it!

arun1963

You should be able to get the non digital one for about 350-400. There's a guy here 'pentoncm' who bought it stateside recently. Send him a PM and he should be able to give you the price and place he bouoght it from. 400 bucks for what it does, is a decent price. Audison distribution though, seems to be weak.

VelocityVinnie

I can buy it here in the UK but its stupid money.

I could by it from the states, but once ive added shipping, handling, and taxes ect its really exspensive.

I have found a guy in the states that sells a LOC specifically for this type of application, and it also flatterns the signal and makes it full range/flat. Its only $40 so ill try that, hes used it on one of my head units before and he says its perfect.

Aslong as ive got a flat signal ill be ok, as i will be adding system management, PC controlled EQ anyhow

VelocityVinnie

Hopefully my first set of Polk comps will be here by the end of the week

ordered some DXi6500's to see what they are like.

Are the MM range the flagship of Polks car audio? and how better are they over the DXi range?

Also would you recommend 6x9's or 6.5 coaxials for the rear deck, i will be adding subs, so maybe the 6.5's maybe better??

arun1963

The Dxi are a step above the old Db series, but the MM's are better. Yes, as of now the MM's are the flagship. Although the best car speaker that Polk ever made were the SR's.

I'm not a fan of rears. I don't think anyone on this site runs rears. Try fronts+sub only and then see if you really want rears.

VelocityVinnie

Ill try just fronts and sub and see how it goes, although i dont want rear passengers to just hear the sub pounding them in the back and then getting no mids or highs, so ill probs end up putting some rears in anyway.

I may put 6x9's in as they tend to throw out a little more low end than the 6.5's.

The boot on my car is totaly cut off from the cabin space, so the sub sounds distant.

Ill see how it goes, the car is a show/stand car so ill probs need to add more to add a little more interest, i dont think a pair of comps and a sub would cut it. i may add two sets of comps to the front.

BeefJerky

You could do what I do. I have front and rear speakers, but leave the fader on my head unit all the way up front normally. I only fade the back speakers in when I need to (very rarely).

VelocityVinnie

Well my DXi6500's have turned up today, quality looks good, so we shall see how they sound.

Paid a fortune for them having had them sent from US to UK!, import charges ahhhh!!!

VelocityVinnie

Hey everybody,

Thought i would pop back as its been over a year since i last posted, and i got the car fully fitted out.

In the end i went for full polk speakers, and had to go with two Hifonics amps, as i had great difficulty getting hold of Polk amps here in the UK.

Heres how she finished up

And a pic of the car some time later since my last post, the car has won several comps since then, and shes still not finished.............although modified cars never are.

vin