Why do I have to set my SR6500 Crossover Freq. So High?

psykod

Greetings.

I've just finished installing a set of Polk SR6500's for my front speakers along with an Alpine PDX-4.150 amplifier in my 2006 Corvette and I'm in the process of trying to tune the system.

The rear speakers are currently still stock but will be replaced with a set of SR5250's soon.

I'm using my factory head unit with a PAC AOEM-GM24 adapter to send the low level signals to the amp.

The amp is fed straight off the battery using 4 gauge power and ground.

For some reason, I can't seem to set the high pass crossover below about 110hz without the speakers starting to overdrive with the dreaded 'blap' sound on bass notes when playing music any more than moderately loud.

The amplifier is rated at 150 watts X 4 and has no bass enhancements.

Can anyone think of a reason why I would have to set my high pass filter so high? I love the sound of system at low volume with a lower crossover point but the vette isn't the quietest car around when it's in motion so I do need more volume.

I'm not a Bass freak (There isn't even a subwoofer in the car yet). Most of my listening revolves around older rock and jazz.

Thanks for the help.

RuSsMaN

What is the current slope of the crossover (db per octave)?

More power.

psykod

The crossover slope is 12db/octave.

Do you really think I need more power? I figure with the way I have the gains set now I'm not giving it more than 50 watts or so.

I was thinking maybe the SR6500's rated power is not accurate for infinite baffle installs like door panels.

I was also thinking that perhaps since the Alpine PDX-4.150 is a Class D amplifier it might not be mating up well with the crossover. Maybe the damping is too low or something.

Thanks...

psykod

Let me re-phrase that power response.

It seems that if I turn the gain up to deliver more power than about 50watts or so, then the severe distortion starts showing up even at the 110hz crossover setting.

(Of course, I didn't measure the power so I'm just guessing based on the gain settings).

1996blackmax

The damping on the amp is around 80 or so....

I would suggest that you readjust you gains. I would start with a setting of 80Hz while adjusting the gains.

MacLeod

You DO NOT need more power, thats your problem right now. Youve already got more than those speakers are rated to handle. The SR's are very effecient speakers and do not require a ton of power to push them to their limits. Those PDX amps do slightly exceed their rated power so youre geting close to 160 watts out of your Alpine. This will be plenty of power to bottom them out but if you set your gains right then youll be able to get plenty of output from them without overdriving them.

What you need is to set your gains properly. My SR's had the exact same problem but after some gain tweaking I now run my SR's down to 65 Hz with an 18 db/oct slope and have no problem with them bottoming out and mine are mounted IB in the doors too.

Also, give them some time to break in properly. After a week or so theyll be good and limbered up and ready for dialing in.

The damping is not a factor nor is the Class D structure of the amp.

Adjusting the gain doesnt mean making more power. If you turn the gain all the way to the bottom or all the way to the top, your amp is still making 150 watts per channel. What the gain does is match up the input voltage of the amp with the output voltage of the HU so that when your HU is at 50% your amp is at 50%. If you set your gains wrong, when your HU is at 50% your amp is at 80% and it would be easy to overdrive the amp.

Here is a basic tutorial on gain settings.

http://www.andrew.cmu.edu/user/dhuston/audioindex.html

PoweredByDodge

another class D full range - i'd like to see the spec sheet on that thing...

MacLeod

A buddy of mine in MECA just bought 4 for his system. He seems to like them a ton over his old V12 amps.

Thom

As Mac said, you probably need your gains lowered. At what volume on the head unit does the bad noise start? For example, an Alpine head unit goes up to 35. It starts to clip at 32 or 33. So you get the maxmum clean output at 30 or so. You wouldn't want the system screaming at 15 or 20, you should have to turn it up to 28 or 30 for the loudest listening. Any idea how high your OEM head unit goes up to? With a line level converter you've probably got pretty high voltage so if your gains are up on a powerful amp you'll have problems.

I recently installed a Zapco DSP- 6 in my car and have a head unit with average voltage output. The Zapco has an input gain as well as output level. When I was first playing around with settings I swore something was wrong with the Zapco piece until I realized that the input gain needed to come down. But it was a noise like you descibe, bass notes just crack and it sounds like the speakers are blown...

Thom

psykod wrote:

The crossover slope is 12db/octave.

Do you really think I need more power? I figure with the way I have the gains set now I'm not giving it more than 50 watts or so.

Thanks...

Is there any way to select an 18- or 24- db/ octave slope? At a lower frequency, of course.

1996blackmax

I think those are set.

psykod

I will definitely try to reset the gains to see what I can do. Looks like it might be time to drag out the o-scope.

One thing interesting is that when I was searching for info on Google I came across a review on caraudiomag.com and he stated that he had to set his crossover at 100hz to protect his speakers (whatever they were).

"First up was “Snowbound” from Kamakiriad by Donald Fagen. The front separates were popping a little at high volumes, so I raised the crossover point to 100Hz to protect them."

http://www.caraudiomag.com/0607_cae_alpine_pdx_4150_amplifier/

Thanks again for the help.

MacLeod

Yes, it is easy to overdrive these speakers I suppose due to their high effeciency and the fact that they dont distort easily. But trust me, once you get the gains set right and everything tuned youll be fine. Again, mine are at 65 Hz and play like a champ.

psykod

Well I popped in my IASCA test CD and ran thru the frequencies. I turned off the HP filter completely while testing.

What I discovered is that below 50hz and above 80hz, everything sounds fine, but between those frequencies, the "blap" 'ing occurs.

I'm beginning to believe my factory head unit has some built in bass boost around the 60hz level.

1996blackmax

Some OEM units actually do have this "EQ-ing" built in.

psykod

Here's a link to some install pics just in case someone might see something obviously wrong.

Install Pics on CarDomain.com

Thanx...

Greg Peters

In looking at the wiring job on the SR crossover in the picture, it seems you have them wired for biamped mode (but you've left the jumpers in place). If you are using all four channels of your amp to run each SR tweeter and mid off a seperate channel of your amp (biamped), I believe you are supposed to remove the red jumpers on the right side of your crossover as per the manual. Your first post didn't really say whether you are powering just the SRs with your amp or are using it to power your stock rear speakers as well. If you are powering the rear speakers with the same amp, you only need to connect +/- leads from amp channel to the SR crossover terminals marked "woofer +/woofer -" and leave the jumpers in place.

While that's an enterprising place to put your amplifier (judging from the pics), it must be a bugger to have to go back and adjust gains after the fact . I hope that area is well sealed from the elements, as it would suck for a downpour to take out your amplifier. It appears that the OEM speakers were much larger than the SRs you replaced them with. I wouldn't be surprised if the OEM built-in EQ was designed to optimize performance of the factory speakers and presents a very different curve to your SRs than optimum.

Most factory head units do have some type of built in EQ, designed so that you don't roast the OEM components and have issues to be dealt with under warranty. Often the OEM system is not giving a boost to certain frequencies, but is actually cutting some in the bass and midbass area as volume is increased.

There are a number of systems designed to bypass/defeat the OEM EQ curve for aftermarket speakers and amplifiers, like the JL Clean Sweep, RF 360.2, and others that aren't springing to mind right now. While they're not cheap, they may be something to consider if adjusting gains or checking correct jumper setting on the SR crossovers doesn't fix the problem.

Your SR speakers should be more than capable of clean output from 50-80hz, and shouldn't require you to cross them over at 100hz. I'm assuming that your amplifier has no boost turned on around that frequency spectrum, so it may well be that something unique to your GM source unit is causing some boost or distortion when used with something other than the OEM speakers.

Beautiful equipment, elegantly installed in a beautiful car by the way.

psykod

My apologies for the crossover pictures, they were done prior to the current amp when I was using the original factory amp, which had high and low outputs so I was using the bi-amp mode of the crossover. They have been set to the standard single input mode now.

The factory used an 8" woofer and a 3" mid/tweet arangement (ala Bose).

You are right about the amp install. I wanted to completely hide everything and make it almost impossible for a thief to steal anything. They're pretty much gonna have to steal the car to steal that amp! I did a lot of testing for moisture and because of the location high up in the fender, It was almost impossible for me to get water near it and I sealed up the wiring as best I could. I'm hoping that since the car's computer is in the same location, it should stay fairly dry.

You are correct again about the settings, which is why I originally came here to ask the questions. I don't want to have to remove my fender every time I need to make a crossover adjustment!

Thanks again.

Greg Peters

The OEM computer is usually made to stand up to a little bit of moisture. Many are under the hood, and can usually take a very gentle engine compartment shampoo if you don't go directly at them with high pressure.

Amplifiers aren't quite so water resistant- it may be a good idea (if you have to pull that fender to adjust gains) to put a zip lock bag around it or something- zip portion facing up, open for some air circulation. Those PDX amps cost a pretty penny, and even a remote chance of frying it with some stray droplets would scare me. I'd personally be tempted to mount it inside, under a seat- the low profile might fit under there.

psykod

You might have a good idea with the zip lock baggie. I might give that a try.

So far I haven't had any problems (only one shower though). I know the factory computers are supposed to be sealed (I found out the hard way in my WS6 Trans Am one day after I cleaned my engine compartment that they aren't as sealed as they seem!).

This is kind of like a grand experiment, I really want to find out how this is going to work out.

It's a no-go for mounting it under the seats as the amp is small but quite thick at more than 2.5 inches and I have maybe 1 3/4 inches under the passenger seat and even less under the drivers seat. The only other place I could put it would be in my storage pockets back in back. I know of one other person who has mounted one there but then I lose my storage.

Thanks again!