[anku94]

Originally Posted by DerAlte

Perhaps it would be better to read up available physics / engineering text on the subject beforehand, otherwise this thread could do well without 'time-pass'.

Perhaps you're right. Evidently, my Class 12 physics isn't enough to understand all this stuff.

Originally Posted by DerAlte

No. An 'AC Power Source' is expected to PRODUCE a significant amount of energy converted from energy in another form, e.g. heat from fuel (steam-fed turbo-generator, auto alternator), potential energy (hydro-electric generator), stored energy (batteries -> Inverter) etc. An 'amplifier' USES energy from a source, e.g. alternator / batteries to increase the amplitude of the sound signal. The sound signal itself has very little energy to be of any practical use.

What got me the idea of driving an AC device through an amplifier was a video by Sam showing someone using an amp to power a saw which, in turn, was used to cut another amp into two.

I was thinking that a 400W output from an amp was as good as 400W power supply.

Originally Posted by DerAlte

So, if bad music makes you run away, the amplifier is not feeding energy into you to provide you energy for your locomotion - your body's (chemically) stored energy does.

[diesel_maniac]

Quote:
Originally Posted by Pr_007
If you want some Good amp with excellent musical output and at a very very competitive price you can try the Focal Solid 4. Very good and VFM product. Gives out 75x4 at 4 ohms.

You can even go for the alpine PDX-F4, gives out 100 x 4 at both 4 and 2 ohms.

Since you already have a mono from alpine it will be a great match.

But I do not know much of it's tuning options, you can do a research.

Solid 4 is out as its only as good as my RF400-2 with respect to SNR and THD values.

DM: Gurus I came across this discussion between Pr_007 and Mi10 going on in one of the threads in ICE section. Please Shed some light on the meaning and importance of SNR and THD values while selecting an Amp.

[anku94]

Originally Posted by diesel_maniac

DM: Gurus I came across this discussion between Pr_007 and Mi10 going on in one of the threads in ICE section. Please Shed some light on the meaning and importance of SNR and THD values while selecting an Amp.

While I'm nowhere near a Guru, here's what I know about these two.

SNR (Signal To Noise Ratio) : It's basically the background noise in a signal. Like if you're in a big hall and someone's delivering a lecture, all the people speaking in the background will affect your capability to hear the lecture, and constitute noise.

THD (Total Harmonic Distortion) : It is the measure of harmonic distortion in a signal. A harmonic is an integer multiple of the frequency that was actually meant to be played (Called the fundamental frequency).

Let's hope I'm right.

Wikipedia has a lot of info on these two.

Total harmonic distortion - Wikipedia, the free encyclopedia
Signal-to-noise ratio - Wikipedia, the free encyclopedia

[diesel_maniac]

@anku94: Thanks for the insight Anku. That is a very simple explanation and easy to understand for what I though was some out of the world Term. Thanks again.

What should be ideal range of both of these factors in a Good quality or SQ Amp ? Also few examples like Make and Models will help in comparison and assist in further learning of Laymen like me.

[anku94]

Originally Posted by diesel_maniac

@anku94: Thanks for the insight Anku. That is a very simple explanation and easy to understand for what I though was some out of the world Term. Thanks again.

What should be ideal range of both of these factors in a Good quality or SQ Amp ? Also few examples like Make and Models will help in comparison and assist in further learning of Laymen like me.

Now you just went beyond my area of expertise. Although as far as I know, a THD of <1.5% is considered good.

No idea about make or models or anything.

[navin]

Originally Posted by anku94

Now you just went beyond my area of expertise. Although as far as I know, a THD of <1.5% is considered good.

A THD of 0.1% is easily achived by most amplifiers. However loudpspeakers often have much higher THDs (1% is common and a very audible 10% is also easy to achieve) especially at low frequecies where their suspension system is being taxed.

[anku94]

I was looking at the tech-specs of an amplifier for the first time (The JBL GT5-S644) and I found the following two lines:-

Crossover type (12dB/Octave, 20 Hz-320Hz, rear) - LP/HP/Flat
Crossover type (12dB/Octave, 20 Hz-320Hz, front) - LP/HP/Flat

So, from this, it seems that amplifiers have crossovers. What I also know is that crossovers are used in components to split the sound signal into high and low frequencies for the tweeter and the..umm...it's midbass, right ?

Here are my questions

1. So why are crossovers there in an amp ?
   
2. And what does the 'LP/HP/Flat' part mean ? Does that mean that there are both High Pass and Low Pass crossovers in it ? What does 'flat' mean ?
   
3. Also, what does 12dB/Octave mean ? I know that an octave consists of frequencies between a given frequency and its double. Like 400Hz-800Hz would be an octave. Does that mean that the SPL of a frequency 800 Hz is 10^1.2 times the SPL of 400Hz ?
   
4. Lastly, what does the 20Hz-320Hz part of the specs mean ? Is it the frequency range that can be controlled using the crossovers, meaning you cannot control output of frequencies above 320Hz, and every speaker connected to the amplifier would play those ?

I think that's enough questions for one post.

Thanks a lot for answering.

[navin]

Originally Posted by anku94

Crossover type (12dB/Octave, 20 Hz-320Hz, rear) - LP/HP/Flat
Crossover type (12dB/Octave, 20 Hz-320Hz, front) - LP/HP/Flat

1. So why are crossovers there in an amp ?
   
2. And what does the 'LP/HP/Flat' part mean ? Does that mean that there are both High Pass and Low Pass crossovers in it ? What does 'flat' mean ?
   
3. Also, what does 12dB/Octave mean ? I know that an octave consists of frequencies between a given frequency and its double. Like 400Hz-800Hz would be an octave. Does that mean that the SPL of a frequency 800 Hz is 10^1.2 times the SPL of 400Hz ?
   
4. Lastly, what does the 20Hz-320Hz part of the specs mean ? Is it the frequency range that can be controlled using the crossovers, meaning you cannot control output of frequencies above 320Hz, and every speaker connected to the amplifier would play those ?

I think that's enough questions for one post.

Thanks a lot for answering.

Crossovers are put in amps when one uses the amp only to drive a part of the audio range and not the full audio range. In this case the front and rear channels of the amp can be independantly used to drive either the full audio range (in which case you set the crossover to flat), the bass under 320Hz (or any frequency between 20 and 320Hz) in which case you set the crossover to LPF, or the higher freqencies over 320Hz (or any frequency between 20 and 320Hz) in which case you set the crossover to HPF.

So say for example one wants to use the front channels to drive small 4" front speakers from 120Hz to 20kHz and a subwoofer from say 20Hz (or Fb whichever is higher) to 120Hz. One would then bridge the rear channels. set the rear crossover to LPF mode and keep the knob in approximately the 12 o'clock position. Then one would set the front crossover to HPF mode and keep the knob in approximately the 12 o'clock position.

All crossovers have a slope (how fast they roll of the frequencies they are not supposed to allow through). 12db per octave means that if the crossover was set at HPF and 120Hz, the frequency of 240Hz would be 12db lower than the reference at 120Hz, and 480Hz would be 24db lower than the reference of 120Hz. In this case 120Hz is also called the "turnover frequency".

I hope this helps. For a better explanation you can ask the gurus like Bass & Trouble, Sam Kapasi, Low Bass (GoogleMeister) Maker, etc,..Sam can simplify things , LBM will give you every link the internet can throw up. I wish had either of their skills.

[low_bass_makker]

Crossover Slope

Passive Crossover Slopes

These links might help !!!

[anku94]

Originally Posted by navin

Crossovers are put in amps when one .....skills

Thanks. Made perfect sense.

One would then bridge the rear channels. set the rear crossover to LPF mode and keep the knob in approximately the 12 o'clock position.

What would be the advantage of bridging ? Is it that by bridging, the sub will be able to use power meant for both rear left and rear right ?

All crossovers have a slope (how fast they roll of the frequencies they are not supposed to allow through). 12db per octave means that if the crossover was set at HPF and 120Hz, the frequency of 240Hz would be 12db lower than the reference at 120Hz, and 480Hz would be 24db lower than the reference of 120Hz. In this case 120Hz is also called the "turnover frequency".
.

Originally Posted by low_bass_makker

Crossover Slope

Passive Crossover Slopes

These links might help !!!

Thanks for the links sir. I haven't studied them in detail yet but they seem like something I can understand.

One more question : What is good, steeper slope or flatter ? In the links provided by LBM, more complex arrangements give steeper slopes. But wouldn't steeper slopes mean that, say if the XO was set to HPF, very high frequencies would have very low SPL ?

Wouldn't that be bad ? I mean, in a song, you would want to hear the whole spectrum and not just some particular frequencies, would you ? Or have I got it all wrong ?

Thanks again.

EDIT : Just revisited the links. Makes sense now. I was thinking along the lines of a tuner in a tv/radio which allows the resonant frequency only and all other frequencies have low amplitude. The crossover has a flat slope in the desired range of frequencies.

You don't need to answer my second question now.

[navin]

Originally Posted by anku94

What would be the advantage of bridging ? Is it that by bridging, the sub will be able to use power meant for both rear left and rear right ?.

Exactly. It allows for a small 2 channel amp to produce enough drive to drive speakers than need more power.

Disclaimer: Not all amps can be bridged so please always adhere to the manufacturer's recomnedations and instructions.

[Astleviz]

Coming back to navin's post about stuffing cotton socks into a basstube/ ported box to reduce the boom associated with ported boxes, I just tried it with my bass tube. To be honest, it's still boomy. Am I doing something wrong? Is it because the volume of the basstube is too big for the sub? I believe that ported boxes need a lot more volume as compared to sealed boxes, could this be the reason? That the volume is too high for the sub to be used in a (speriodic) sealed enclosure? Will it help if I completely seal the port with mdf?

[navin]

Originally Posted by Astleviz

Coming back to navin's post about stuffing cotton socks into a basstube/ ported box to reduce the boom associated with ported boxes, I just tried it with my bass tube. To be honest, it's still boomy. Am I doing something wrong? Is it because the volume of the basstube is too big for the sub? I believe that ported boxes need a lot more volume as compared to sealed boxes, could this be the reason? That the volume is too high for the sub to be used in a (speriodic) sealed enclosure? Will it help if I completely seal the port with mdf?

Most probably the box is a bit big. Do yo have the T/S (Theil / Small) parameters of the woofer?

BTW it is "aperiodic" not "speriodic" - I must have made a typo. An aperiodicbox is just a lossy sealed box. A lossy box damps the peak in the bass response which occurs if the box is too small. The trade of is sensitivity. There is no free lunch.

[Astleviz]

Unfortunately T/S parameters are not available for this sub, even the blaupunkt website doesn't offer much info.

Just found this for another blaupunkt sub (mystic series) which is almost identical to the gt sub specs-
# Power rating (Watt): 200
# Impulsbelastbarkeit (Watt): 900 Power handling (Watt): 900
# Frequenzgang (Hz) -10 dB: 35-1.000 Frequency (Hz) -10 dB: 35-1000
# Wirkungsgrad (dB / 2,83 V / 1m): 91 Efficiency (dB / 2,83 V / 1m): 91
# Nennimpedanz (Ohm): 4 Nominal Impedance (Ohm): 4
# Einbaulochdurchmesser (mm): 233 Mounting hole diameter (mm): 233
# Thiele-Small-Parameter fs (Hz): 35 Thiele-Small parameters fs (Hz): 35
# Thiele-Small-Parameter Qts: 0,61 Thiele-Small parameters Qts: 0.61
# Thiele-Small-Parameter Qes: 0,67 Thiele-Small parameters Qes: 0.67
# Thiele-Small-Parameter Qms: 6,8 Thiele-Small parameters Qms: 6.8
# Thiele-Small-Parameter Vas (l): 28 Thiele-Small parameters Vas (l): 28
# Thiele-Small-Parameter Xmax (mm): +/- 8 Thiele-Small parameters Xmax (mm): + / - 8

[navin]

Originally Posted by Astleviz

# Thiele-Small-Parameter fs (Hz): 35 Thiele-Small parameters fs (Hz): 35
# Thiele-Small-Parameter Qts: 0,61 Thiele-Small parameters Qts: 0.61
# Thiele-Small-Parameter Vas (l): 28 Thiele-Small parameters Vas (l): 28

this gives a sealed box of about 3 cu. ft. (80 liters) that is huge. A ported box would be larger ....in the region of 100 liters for a QB3 alignment.