Quote:
Originally Posted by greenhorn  I'll join in the party as well 
Even I've got a few sub doubts floating around in my head. I'd like a sub with SQ, but a brawny monobloc isnt my idea... Its just the sheer wattage of these amps that overwhelms me. .. What tangible benefits does a monobloc amp give as opposed to a bridged 2 channel amp of approximately the same power output..I listened to redfire's 2 ch blau amp driving a sealer blau sub, and it was more than adequate, how would a monoblock improve on that ? |
Fantastic question. To think I was just this morning lanmenting to a friend on why we dont get quality questions like this posted often enough on TBHP. My friend told me "Relax navin, TBHP is a car forum; go get your fix on diyudio/audioasylum/etc...". To that friend I say "Boooo we are not engine-vengine types only! Ha!"
To produce bass one needs to move air, lots of it. To move air one needs a large cone with suffcient mass. To move that large cone one needs electrical power in the form of watts. Class D amps give you this power in smaller packages. In most cases they are very adequate.
All things remaing equal lets consider 2 amps. Amp A is a 2 ch. amp that puts out 50W rms/4ohms, 100W/2ohms or 4 ohms when bridged, 200W at 1ohms or 2ohms when bidged. Amp B is a monoblokc that puts out 100W at 4ohms, 200W at 2ohms, and 400W at 1ohms. Now both these amps are great amps. Both will drive a sub well. The Monoblock might be a bit more stable at lower impedance and that means if the sub's impedance curve is complex (most siubwoofers have inductive impedance curves that can peak at resonance and fall fast mkaing them to be quite complex) the monoblock will have an edge.
Also when you bridge 2 channels on a stereo amp you also half it's damping factor and the higher the damping factor the better the control the amp has on the speaker.
Usually when an amp is not able to control the speaker properly the speaker will sound a bit woolly.
Also remember the example of the stereo amp I have given is of a very good stereo amp. Most plain jane stereo amps are not stable at 2 ohms when bridged. Now a speaker's impedance is not constant (if t were we'd call it resistance) but varies with frequency. So a speaker that is rated at 4homs nomial impedace can see it's impedance drop to 2ohms for a small frequency band. If there happens to be music in that small band the amplifer will loose control (albeit temporarily) and once cna hear this loss of control.
many years ago a company called Wilson Audio designed and produced a 2 way speaker using a 6.5" SEAS woofer and 1" focal tweeter (the same speaker is in it's 8th generation today) the speaker sounded great (I only got to hear versions III, 5, and 6 the last in 1997) but had an impedance curnve that included a dip to under 2ohms. A friend who heard these speakers tried to listen to them using his 200W Adcom GFA555 amp and the amp balked. A lesser rated amp (Krell KSA50) however had little problems. It was as clear an example i needed to understand the need for speaker-amp matching.
I found a good primer on amplifier basics here. Hope it helps.
Lenard Audio - Education - Amplifiers. Quote:
Originally Posted by nishantgandhi Last I remember, either B&T or Navin had said that Blaupunkt GT4, Kenwood 840x and JBL GT5 are more or less the same.
So to put in it another way, which sealed subwoofer would run happily off that kind of power? EDIT: Also, does a sealed sub require more power than ported/BR/IB/free air?.. Hence, I thought a 10 inch sub would be less 'dominating' than a 12 inch one.
I dont know when I will ever get to install ICE in my car. It has already been 4 months of research!  |
The "60x2, 120W bridged" amps listed (Kenwood, Pioneer, JBL, Blau etc...) are more similar than different. When looking at paper specs of amplifers try to keep the following in mind.
1. THD/IM distortions at rated wattage
2. How stable is the amp at low impedances?
3. What is the function of the power output with respect to (nominal) impedance?
4. Over what frequency range has the amp been measured?
Amps ratings should really read something like this: 50W rms/4ohms (stereo) / 100W/4ohms (bridged) 20-20khz, THD < 0.01% at rated output. Another indicator (more ture for Class AB amps than Class D amps) is the weight of the amp and the size of it's power supply (usually rated in VA and not Watts).
If you have a small amp it will in all probablity be able to drive a lighter 10" woofer better than a heavy 12" woofer. The reason why I mention light and heavy is that today you find 10" woofers with a Mms of 100gms and 15" woofers with a Mms of 60gms so it is cone weight (and the strength of the magnetic circuit the voice coil is in) that matters along with woofer diameter.
Yes with a small amp and a lighter woofer one wont get the last 1/2 octave or so of bass (especially if the box is small) but what bass is there will be better defined and the subconcious mind will fill in the rest.
Ever hear a good small 6" woofer (like the Dynaaudio 17W75 or ScanSpeak 18W8xxx series) in a small monitor speaker style box? Notice that even with such a small speaker Stanley Clarke's bass is very discerable and one can actually hear the impact of when his fingers hit or slide on the strings? This is what you need to look for. Indian acoustic music is very demanding. Listen to the instruments live and you will hear what you need to listen for when you listen to them over a stereo.
I have heard good quality bass from ported, sealed, transmission lines, horns and even speakers that dont have boxes (Jamo R909 for example) dont fret about the design. Listen, feel, and listen again - to every instruemnt, loudspeaker, amplfier , CD player you can find. Every listen even if it to a pair of Pioneers powered by an Xplod amp can be a learning expereince.
23rd April 2009, 18:13
