It Hertz!

[Brindle]

Been putting an an upgraded system in my van, mostly repurposed from stuff I’d had for years. Installed everything at the weekend and all was good and sounded great, really clean and powerful apart from the fan in the amp was rattling (been in the loft for 7 years or more) so I’m a typical state in manliness I couldn’t wait to do any research so went and locally picked up an Alpine BBX F1200 4 channel amp. The original amp was nothing special so I thought this would be an upgrade of sorts. It’s sounds bloomin awful, really boomy at the higher frequencies and I’ve got the filter turned down to 50hz, however, if I do a sine sweep the sub doesn’t drop off until 120hz or more, in other words the filter is doing naff all. I’ve tried both sets of channels bridged with the low pass filter switched across as well. Any thoughts? Crap amp? Faulty amp? Expecting too much from a budget amp (expected more from Alpine).

Arghhhhh!

 

[Brindle]

I think the main question I am asking, is that if the amp is set to 50hz, anything above that should massively drop off, or is it not that simple?

 

[Dellmassive]

post a few pics of the AMP settings. . . and wire connections

the 50Hz (adjustable) crossover would be a HPF or LPF depending on the switch position relating to the speaker output channels.

for example 80Hz LPF(Low Pass Filter) for the SUB

and 80Hz HPF(High Pass Filter) for the mids and tops.


post a few pics and well have a look.


FYI 50Hz is VERY low, you might need some serious EDM or Reggae music to drop that low.

SUB crossover is normally 80-120HZ down. (Then 80-120hz up for the mids and tops)

maybe try setting the crossover at 100Hz as a starting point.

 

[Brindle]

Will do, the witch is over to LPF not HPF. I’ve also tried it with a different sub and enclosure and it was the same. It’s defo wired up correctly but I’ll get some pics tomorrow.

I’ve played with the hertz adjuster knob from 50hz and above but it seems to make little difference to what it does or doesn’t filter out.

 

[Brindle]

My simple brain still goes back to thinking that if it’s switched to LPF and the frequency is turned down to 50hz (or even 80) surely when doing a sine sweep it shouldn’t be driving loads of power at 120hz? It should have dropped off well before that?

 

[Dellmassive]

The book for the amp shows -12dB/oct drop off at the cross over point.

so if you have it set at "50hz LPF" then you should only hear 50hz and below (mains hum) (for sub)

also make sure the BASS EQ is set to off/0


see here:

https://www.alpine.co.uk/fileadmin/user_upload/manuals//car_audio_manuals/BBX-F1200/OM_BBX-F1200_EN.pdf

 

[mmi]

Hmmm.... perhaps not really

Slope or Q-Factor – determines the rate at which the audio system’s volume will diminish as the frequency extends past the crossover point. It is measured in decibels (dB) per octave and the most common slope options used range between 12 dB per octave and 24 dB per octave.​

​

So setting crossover to 50Hz would mean a noticeable drop (6dB) would be easily even at approx. 3 x 50 Hz - depending on the amplifier....​

EDIT: Oops.. for 12dB/octave not quite that far but still almost 100 Hz.​

​

How To Set Crossover Frequency For Car Audio System

We teach you exactly how to set crossover frequency, with detailed explanations of the big three filters and various system configurations.

speakerchampion.com

Low-pass filter - Wikipedia

en.wikipedia.org

 

[Dellmassive]

eg . .





you wont see much bass bellow 50hz.





.

try these . . . to get an idea of how low 50hz is . . . you will need a decent audio setup to hear it. (so try 100hz as a crossover, thats easier to work with)

..


I was running 2x 15" KICKER L7 solarbarics in sealed boxes . . . and didn't cross over lower than 80Hz ever.

 

[Brindle]

eg . .

View attachment 114009View attachment 114010



you wont see much bass bellow 50hz.

View attachment 114011



.

try these . . . to get an idea of how low 50hz is . . . you will need a decent audio setup to hear it. (so try 100hz as a crossover, thats easier to work with)

..


I was running 2x 15" KICKER L7 solarbarics in sealed boxes . . . and didn't cross over lower than 80Hz ever.

Awesome stuff, really appreciate you taking the time to pull that together. I’ll do some more testing tomorrow.

What a bloody great forum!!

 

[Absolut5]

Been putting an an upgraded system in my van, mostly repurposed from stuff I’d had for years. Installed everything at the weekend and all was good and sounded great, really clean and powerful apart from the fan in the amp was rattling (been in the loft for 7 years or more) so I’m a typical state in manliness I couldn’t wait to do any research so went and locally picked up an Alpine BBX F1200 4 channel amp. The original amp was nothing special so I thought this would be an upgrade of sorts. It’s sounds bloomin awful, really boomy at the higher frequencies and I’ve got the filter turned down to 50hz, however, if I do a sine sweep the sub doesn’t drop off until 120hz or more, in other words the filter is doing naff all. I’ve tried both sets of channels bridged with the low pass filter switched across as well. Any thoughts? Crap amp? Faulty amp? Expecting too much from a budget amp (expected more from Alpine).

Arghhhhh!

Tell us what other equipment you are using, headunit, speakers, sub and it’s location, box etc

 

[Brindle]

All, thanks for the help and advice. In the end it seemed that I got given duff info about the enclosure sizing for the sub and it was well undersized. Ended up buying a new JL sub that needed a smaller box, built a new box mm perfect and to cut a long story short it’s phenomenal. So the alpine amp was fine all along. Thanks for the help and advice again guys, as always - what a great forum!!