Odd problem: Decent bass output only at very high gain. - diyAudio
Go Back   Home > Forums > General Interest > Car Audio

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 12th November 2006, 08:22 AM   #1
diyAudio Member
 
Join Date: Jul 2005
Location: Southern California
Default Odd problem: Decent bass output only at very high gain.

I just got an Alpine MRP-M450 subwoofer amplifier. My head unit is a Pioneer DEH-P4800MP which has a 2.2V preouts. Initially, I set the amplifier gain to what I thought was 2.2V according to the scale on the dial. This was too low. I could hear very little bass. My head unit EQ was set to Flat. I had to turn the gain very high to get a decent bass output. Right now im temporarily using some old noname 8" subwoofer in a vented box. I plan on replacing it with an Alpine Type-R 10" subwoofer (SWR-1042D) once I build the box for it.

I called Crutchfield (where I bought the subwoofer amp from) and the first guy i spoke with said that the gain should not have to be set so high. He suggested connecting the front and rear preout RCA cables to the subwoofer amplifier to make sure that it wasnt the sub RCA cable that was at fault. I tried both the rear and front RCA cables and it was the same thing as before.

I called Crutchfield again and this time the guy said that the gain depended on the output of the head unit and that I should set the gain to its lowest setting and set the head unit volume to the highest volume I listen at and then increase the gain until subwoofer distortion is heard and then back off a little bit.

I am thinking the amplifier is defective because it doesnt seem logical that I have to set the gain on the amplifier lower than 0.5V (close to Max) in order to get decent bass when the preout voltage of my head unit is 2.2V. Doesnt having a high gain lower the sound quality? The specs say that its input sensitivity is 0.2-4.0V so since my headunit's output voltage is 2.2V, my way of thinking tells me that the gain know should be in the 10 to 11 o'clock position.

I have an Infinity 7541a 4-channel amp for my front and rear speakers and in that amp, the gain is set to less than half; clearly nowhere close to the max.
  Reply With Quote
Old 12th November 2006, 02:26 PM   #2
diyAudio Member
 
Lothar34's Avatar
 
Join Date: Sep 2006
Send a message via AIM to Lothar34
Do you have a digital multimeter?
  Reply With Quote
Old 12th November 2006, 04:50 PM   #3
diyAudio Member
 
shallowfu's Avatar
 
Join Date: Aug 2006
Is there anyway you can swap out the sub with another?Maybe a lower watt sub and see if sounds different.It sounds like you are on the right track but, i didn't see you try another sub.Did you try to bridge the amp and see if it was just the alpine didn't have enough power?Maybe the no name sub is a 4 ohm and the amp you have is pushing it at 4 ohm and that would cut the music lower.At 2 ohm you would here a difference and it would be louder.Get some more info on the sub for me and even if it is a .I can tell you the type-r 10 is going to want some power and maybe more than what the alpine can give.It all depends on how loud you like it and i'm sure you like it loud!LOL!I have my share of type-r 12's and they are nice subs.
  Reply With Quote
Old 12th November 2006, 08:13 PM   #4
diyAudio Member
 
Join Date: Jul 2005
Location: Southern California
Quote:
Originally posted by Lothar34
Do you have a digital multimeter?
Yes, I do.

Quote:
Originally posted by shallowfu
Is there anyway you can swap out the sub with another?Maybe a lower watt sub and see if sounds different.It sounds like you are on the right track but, i didn't see you try another sub.Did you try to bridge the amp and see if it was just the alpine didn't have enough power?Maybe the no name sub is a 4 ohm and the amp you have is pushing it at 4 ohm and that would cut the music lower.At 2 ohm you would here a difference and it would be louder.Get some more info on the sub for me and even if it is a .I can tell you the type-r 10 is going to want some power and maybe more than what the alpine can give.It all depends on how loud you like it and i'm sure you like it loud!LOL!I have my share of type-r 12's and they are nice subs.
I first tried the 8" sub.
The noname 8" subwoofer has an internal crossover and it also has two satellite outputs (L+R). The sub box is in my car right now but im pretty sure its only rated somewhere around 100Wrms. The subwoofer has dual voice coils and it says on the sticker that its impedance is 6 ohms. The subwoofer box has 2 inputs (L+R) and I wired them in parallel, so I am also powering the subwoofer in parallel. Im not sure if the 6ohm impedance takes into account the parallel wiring or not, so I may be really wiring it at 3ohm. I'll have to use my DMM to test the voice coils.

I then tried the Alpine Type-R sub.
It hit harder than the 8" sub even though it doesnt have a box, so it may be fine when I put it inside a sealed box around 1.0 cu.ft. (minus the volume of the subwoofer). The gain was still at the very high level close to max.

Since you mentioned the Alpine amp may not be enough for the Type-R subwoofer since it only provides 400W at 2ohm, do you think I should get a higher rated amplifier? I was thinking it would be ok since it will be going in a sealed box and I read somewhere that sealed box lowers the power that can be given to a subwoofer. I am still within the 30 day Crutchfield satisfaction warranty so I can still return it and get a better amp.
  Reply With Quote
Old 13th November 2006, 01:43 AM   #5
diyAudio Member
 
Lothar34's Avatar
 
Join Date: Sep 2006
Send a message via AIM to Lothar34
Quote:
Originally posted by jaimegmr
Yes, I do.
Have you checked the amp's output voltage?
  Reply With Quote
Old 13th November 2006, 02:27 AM   #6
diyAudio Member
 
Join Date: Jul 2005
Location: Southern California
I got some more info about the 8" ported subwoofer:

Vector Research
VRP-375 Bass Module
38-150Hz
25 Watts Minimum
125 Watts Maximum

I verified that it is 6 Ohms per coil and I was wiring it in parallel.
  Reply With Quote
Old 13th November 2006, 06:23 AM   #7
diyAudio Member
 
Join Date: Jul 2005
Location: Southern California
Quote:
Originally posted by Lothar34


Have you checked the amp's output voltage?

I have not done that. Are there any specific settings I should set the head unit and the amplifier at before testing? Should I use a sine wave test tone? Do I set my DMM to VAC or VDC?
  Reply With Quote
Old 13th November 2006, 05:30 PM   #8
diyAudio Member
 
Lothar34's Avatar
 
Join Date: Sep 2006
Send a message via AIM to Lothar34
Well if your Alpine sub sounds OK, then the amp probably isn't the problem.

I can't find the page with the instructions I used, but IIRC it goes something like this.

Turn off all EQ and loudness setting on the HU
Use a CD with 0db sine wave test tone. Something around 60Hz for the sub
Unplug all the speakers from the amp
Turn the HU's volume up to around 80% (shouldn't clip at that point)
Set the multimeter to VAC (if it's not an auto-ranging multimeter, use the range that goes higher than 50V)
Stick the positive lead into the positive output from the amp and the negative lead to the negative output.

(Volts * Volts) / Impedance = Watts

So for your 3ohm sub, you'd want about 19V. (19 * 19) / 3 =~ 120W

That's assuming the amp can put out 120W at 3ohm.

If you have an oscilloscope, you can check to see just how high the amp can go before it clips.
  Reply With Quote
Old 15th November 2006, 06:43 AM   #9
diyAudio Member
 
Join Date: Oct 2001
Location: Brisbane, Queensland
Send a message via ICQ to junglejuice
Instead of running it in parallel try just usin one channel of the speaker at a time and see if that changes anything, with the internal xover etc maybe there is an out of phase issue......
  Reply With Quote
Old 15th November 2006, 04:26 PM   #10
diyAudio Member
 
Join Date: Jul 2005
Location: Southern California
I tried one input at a time and it is louder with both voice coils powered, so it is not a phase issue.

I am going to build the box for the Type R subwoofer next week and then ill post again to tune it. If even after having everything set up, I still have to turn the gain almost to max, then I think it will be the amplifier that is defective and ill have to exchange it.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Monica 2 + gain stage; High pitch noise problem spacemen12 Digital Line Level 0 27th October 2008 03:00 AM
Tuning 604 Project - High Q and High Output Impedance? Seadweller Multi-Way 20 18th February 2008 07:49 PM
high gain 2nd order high pass active filter topology sreten Solid State 21 23rd March 2006 01:26 AM
high output sub bass mart34 Subwoofers 1 13th July 2004 04:06 PM
looking for some decent bass speakers bonsai171 Multi-Way 19 19th December 2002 11:24 PM


New To Site? Need Help?

All times are GMT. The time now is 06:06 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2