Pages: [1]   Go Down
Author Topic: Speaker help.  (Read 486 times)
0 Members and 1 Guest are viewing this topic.
Hampshire
Offline Offline
Jr. Member
**
Karma: 0
Posts: 77
Have a passion for electronics!
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Hello thanks for viewing.
Well my parents have been complaining about my bass. I have not been able to find a way to turn it off so within my 5.1 surround system I simply put a series switch with the bass speaker. For some reason the system now keeps cutting out and I have no idea what for.
I was wondering if I didn't have the speaker on I would need to emulate a speaker by putting some sort of resistor. But I have read that this will need to be a huge resistor because of the amount of power the speaker is. (it is a 25w sub woofer) I was hoping to eventually connect this to an arduino so I can remotely turn the whole bass off.

For some reason I always have bass and even if the knob is turned all the way down I still get a little bass which is enough for my parents to shout up stairs. It worked fine and it has cut out a few times and in order to get it working again I have needed to unplug and turn of the speakers. Could this be with the speaker not taking all the load of or is there something else causing the problem?
Thank you very much for your time
Trevor Boultwood!
Logged

TrevorB

Offline Offline
Edison Member
*
Karma: 34
Posts: 1318
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Quote
I simply put a series switch with the bass speaker. For some reason the system now keeps cutting out and I have no idea what for.
That's unusual...  Most power amps are happy with no load.

Do you know the speaker impedance?

Quote
But I have read that this will need to be a huge resistor because of the amount of power the speaker is. (it is a 25w sub woofer)
You can get high-power resistors, but I might be hard to find a 4 or 8 ohm resistor.   Here is a 5 Ohm 25 Resistor for about $3 USD.  Or, you can put resistors in series/parallel to get 4 or 8 ohms.   But since speaker impedance varies over the frequency range, the rated impedance is just the "nominal" impedance.

Some random thoughts...

You shouldn't need the exact-same resistance (impedance) as your woofer.  I think a higher value should work.  If the resistance value is too high, It will act like no resistor at all (or maybe about the same as your woofer with a series resistor).   But, a higher value resistance will also draw less current and therefore dissipate less power & generate less heat.

If the resistance is too low, too much current (and power) will be "pulled" from the amp, and you could damage the amp.   

Quote
. (it is a 25w sub woofer) 
You probably don't need a 25W resistor, but it's hard to say exactly what you do need.  Regular audio has peaks that are typically 10 times the average.   So, unless you are running full-power test-tones into your speaker, it's not seeing 25W continuously.   If you have the volume maxed-out (as high as you can go without distortion) you are probably averaging around 2.5W.    Less, if you are listening at lower volumes.    But to be safe, I'd probably try a 10W resistor.   It also depends on the music, and you can get the full amplifier-power continuously if you drive it hard into distortion.     But, if you can double the resistance (compared with the woofer) and the thing still works, you'll get half the current through the resistor, which means half the power.

Quote
...which is enough for my parents to shout up stairs.
If your sub is sitting on the floor, moving it to a shelf (or somewhere off the floor) should reduce sound transmission through the floor.   
« Last Edit: October 04, 2012, 03:47:00 pm by DVDdoug » Logged

Hampshire
Offline Offline
Jr. Member
**
Karma: 0
Posts: 77
Have a passion for electronics!
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Ok! That really cleared some of the stuff I was asking! I will try it out, I am not sure why it would 'time out' I wouldn't of thought it would. Strange... I would of thought the amp would just work as normal but without the sub woofer. If I had it on which I normally do, it has the lowest on the bass to begin with. So I guess I wouldn't need a huge resistor (Ill just turn the bass down when its off). One last question and that should have me sorted.

I have seen a video that I gentlemen did and simply measured the resistance with any normal volt meter. Someone said that this will give you an in accurate measurement. I guess Ill do the same and the values will either be 4 ohm or 8 ohm? Then Ill put the resistors in a configuration of series and parallel to get the desired 8 ohm and just monitor it for the time being.
Thank you for your reply, and ill look forward to seeing your next reply smiley Thanks
Trevor Boultwood
Logged

TrevorB

Left Coast, CA (USA)
Offline Offline
Brattain Member
*****
Karma: 361
Posts: 17294
Measurement changes behavior
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

The problem is best solved (at least from the parents perspective) with the knob labled VOLUME. Turn it slowly to the left until the parental units are happy with the results.  smiley-wink

Lefty
Logged

Hampshire
Offline Offline
Jr. Member
**
Karma: 0
Posts: 77
Have a passion for electronics!
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Hahahaaa! Ok maybe smiley-wink But that isn't the problem, even on low volume it kicks out bass. And I live above the living room so my parents here every step I take! Thank you! But Ill go with the hardcore way! smiley-wink smiley-razz
Logged

TrevorB

Anchorage, AK
Offline Offline
Edison Member
*
Karma: 42
Posts: 1176
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

No load is fine for any solid state amp unless maybe it's monitoring the load and trying to be smart.  Resistors will get hot quickly, so over-speccing will be better than under.  Make sure it's really in series with the driver, and check your wiring in case you shorted something or accidently wired it parallel.  Also look into L-Pads from Parts Express or similar.  They're made for controlling the volume between an amp and speaker.

Measuring with an ohm meter will give you DC resistance, but not AC impedance.  For this, it will get you close enough, but keep in mind it's common for an 8-ohm driver to have a DCR of 6 ohms.
Logged

Pages: [1]   Go Up
Jump to: