Gauging amp's RMS output to speakers for optimum or best sound

For a newbie like me, I always go with the recommendations by friends and vendors (subject to the respective price tags!) and bought my very first hi-fi system (RMS rating 45W 8ohms/60W 4ohms) together with a set of bookshelf speakers.

Was happy at first until I bought another amp (RMS rating 70W 8ohms/100W 4ohms). Wow! What a difference, significantly better on the bass "solidness" and slightly higher clarity. Switching between the two amps confirmed my statement.

Recently, i'm toying with another set of speakers, a floorstander with a rating of max 250W and although using the higher RMS output amp (100W 4ohms), it sounded much better but still lacking. Unfortunately, I do not wish to spend on another set of amp that put out much higher than 100W.

So here's my question. How would you gauge when shopping for a new set of speakers, that you will know that your current amp have enough juice to bring out the optimum sound? Is there a sort of formula? Let's put aside the hardware and accessories compatibility and our "feel good" hearing.

I hope my curiosity would not spark any hot debate (i.e. a speaker with a RMS rating of max 200W need to have a corresponding amp output of 200W), just an understanding to be a more careful buyer in future.

Cheers

Jack




In case you need to know my set up

Marantz PM6003 (RMS rating 45W 8ohms/60W 4ohms)

Marantz PM7003 (RMS rating 70W 8ohms/100W 4ohms)

Rogers LS7 floorstander specs
Three way reflex system
1 X 28mm soft dome (ferro-fluid cooled)
1 X 65mm Polymer Cone Mid
2 X 222mm Polymer Cone Sub
Frequency Response 63Hz~20KHz (+/-2.5dB)
Sensitivity 92dB
Nominal Impedance 8 ohms
Crossover frequency 3.5KHz
Recommended amplifier 5~240W per channel

Mordaunt-Short Mezzo 2 (bookshelf) specs
6.5" aluminium CPC mid/bass driver
1" ATT aluminium dome tweeter
Frequency response 48Hz~22kHz
Sensitivity 89dB
Nominal impedance 4~8 Ohms
Crossover 2nd order with DVP
Recommended amplifier power 15~120W per channel

Hey Jack,

good post. My own experience is that this is not as easy as it seems. There are several different parameters that i look at.
1) The size of my room. I have a tiny room for audio, so i am not expecting the speakers to move as much air, so the out put will be less, needing less watts.
2) The sensitivity of the speakers. My first speakers of any worth were the Vienna Acoustics Haydn stand mounts, they were very sensitive and went loud with a few watts. My next pair, Celestion SL700s were not so sensitive, and demanded nothing less than 250w rms to shine, my old Accurus DIA 100 amp could not drive it well. A pre power combo of old Perroux 250w per channel drove them very well. Strangely enough, later i bought a Tube integrated amp putting out 30watts per channel, and it sounded very nice with the Celestion. Of course it could not go too loud, but in a small room, it sounded decent enough.

My biggest challenge was when i heard the sound of Magneplaner. I fell hopelessly in love with them, but these speakers demand that i understand their needs first before they will sing. I walked thro 2 pairs of very old Magneplaner speakers before i finally understood that these speakers demand a lot of watts, a lot of current, and an amplifier with a very high 'damping factor' and low 'output impedance'.
I am not at all sure what these 'damping factor', is, perhaps someone could explain it to us in simple english without the math. But i had to understand the needs of the speakers, respect this need, and then only was i rewarded with wonderful sound, and more importantly, wonderful MUSIC. i had to let the tube amp go, and with the financial restraints i have, only managed a NAD C270, but to my very pleasant surprise, this amp partners well with the magnepan speaker. perhaps because it does indeed put out a lot of watts, and delivers high current. Perpaps one day i will be able to afford that Krell power house to drive my wonderful magnepans.

By the way, there is nothing wrong with having a 'hot debate', even a passionately heated one. Just as long as everyone maintains dignity, and does not resort to cheap name calling and hitting below the belt, i feel it is fine. We audiophiles are a strange bunch, and passionate about our music and sound. Nothing wrong with expressing ourselves strongly within the boundaries of civil decorum, still being ladies and gentlemen through and at the end of the debate.

Cheers!
Bal.

Hi Bal,

You may read this 'Damping Factor' in Wikipedia.

Jacky,

Is that a typo ? The Rogers has a sensitivity of 92 dB ?

jackyuen wrote:
How would you gauge when shopping for a new set of speakers, that you will know that your current amp have enough juice to bring out the optimum sound? Is there a sort of formula?

Unfortunately in hi-fi there is no formula. you just hv to audition to find out.

the power rating of the speakers has no bearing on how well they can be driven by an amp. the power rating e.g. "50W to 200W" just means that the manufacturer recommends any amp tubed or solid-state which can output from 50w to 200w rms.

how well a speaker can be driven by an amp depends very much on the design of the speaker and also the design of the amp. some speakers are power hungry; some are easy to drive. some amps have sturdy output stages; others have useless ones. some amps can handle complex loads; others can't. some speakers offer complex loads; others easy-to-drive ones.

generally, you can tell if an amp is suitable for the speakers by checking the speakers' sensitivity. higher sensitivity like 90 db and above shld be easier to drive and u can use a lower powered amp. lower sensitivity like 85db and below would require u to use a more powerful amp.

what u can do is take yr amp to the showroom and ask to demo the speakers with yr amp. that's the best way to find out if they match well.

Hi Bal

Thanks for sharing.

WongKN wrote: that a typo ? The Rogers has a sensitivity of 92 dB ?

As per the specs sheet included with the speakers.

sflam wrote:generally, you can tell if an amp is suitable for the speakers by checking the speakers' sensitivity. higher sensitivity like 90 db and above shld be easier to drive and u can use a lower powered amp. lower sensitivity like 85db and below would require u to use a more powerful amp.

Thanks for the clarification.

sflam wrote:what u can do is take yr amp to the showroom and ask to demo the speakers with yr amp. that's the best way to find out if they match well.

Good advice. Will remember that when I go shopping in future.

Update -

Was given a chance to test my amp (Marantz PM7003) with MS Mezzo 8 (200W RMS). The owner of the Mezzo 8 uses NAD C375BEE amp (150W RMS). Using my favourite test CD (Folks Song by Tsai Chin - HD Mastering CD) for the demo.

To cut the story short -

Marantz PM7003 with Mezzo 2 (my existing setup) - "excellent"
Marantz PM7003 with Mezzo 8 - better bass but not that solid
NAD C375 with Mezzo 8 -

Conclusion :- Hands now very itchy!!

Moving up to bi-amping.

Marantz integrated amplifier (70W RMS @ 8 ohms) for HF
Marantz power amplifier (140W RMS @ 8 ohms) for LF

Additional gadgets : Noise filter, upgraded power cords, new speaker cables & new hifi rack. Nearly bought the Pearl Lite CD player (credit card maxed out!!)

Bi-amping really sounds better than bi-wiring.

#cheerful note - have to stop visiting KLIAV liao. All these superb systems and settings really beh tahan. Now my bank account suffering....

jackyuen wrote:



Nearly bought the Pearl Lite CD player (credit card maxed out!!)

#cheerful note - have to stop visiting KLIAV liao. All these superb systems and settings really beh tahan. Now my bank account suffering....

welcome to the club...

You don't have to spend a fortune to get to musical nirvana. The ideal word is " MATCHING". Even if u buy expensive gears but if they are no match to each other, u won't get the sound u want. Matching here involve interconnect cables, speaker cables jumper cables, power conditioner and etc. A lot will take count. My advise is "Do not afraid to experiment". trust me it worth the effort. But get the sound that u like not other people like, after all u are going to listen to it every single day.

don't forget to "match the room" as well.
Room factors are always literally, the elephant in the room that everyone seems to just ignore.

Yes, our room will determines the speakers, equipments and the power required to fill the room. Room acoustic is the most critical part and will make or make for a system.

Time to consider doing room acoustic treatments eh?

Adcomer - My advise is "Do not afraid to experiment". trust me it worth the effort.

Experimenting is a very expensive affair. But will take it slowly.

mugenfoo - Don't forget to "match the room" as well. Room factors are always literally, the elephant in the room that everyone seems to just ignore.

Mikapoh - Our room will determines the speakers, equipments and the power required to fill the room. Room acoustic is the most critical part and will make or make for a system.

uncle_vic - Time to consider doing room acoustic treatments eh?

Definitely. But need to wait till I move to my new house in Subang (due to collect keys next month). Converting a bedroom (9’ by 12’) for HF/HT purposes. However, it is still a bedroom, so my finance minister would like something more of a bedroom than a studio.

Hi Jackyuen,

So much compromise to live with ah. Initially, I was about to reply telling u to ignore the elephant; because I took for granted that u would have stuck ur system in the living room. Now that u will have it in the 9x12 ft room... that's the paramount matter to start with. there will be a lot of echo from such a small room, if u have no intention to play moderate to loud, it will still be bearable. Fear not, a lot of guru here will offer help when u ask for it.



If you really quest for more power, do look into audio gd punya power amp~ 1 of the best bang for buck stuff~

Mean time, matching doesnt mean interconnect, speaker cables and equipments.. it can be isolation feet, vibration control, fuse and so fore.. which is much cheaper~

ok, I thought that there was a mistake into saying amp output rating at RMS for majority of the hifi amp, but it seems correct. As majority of the brand is now complying to FTC standard.



Power in very important, not for loudness but for dynamic. There is a fact that to achieve an audible loudness u need to double the wattage instead of getting 10~30% increase of watt. Music is dynamic, for milisecond there might be a demand of full watt even when ur volume is at 10 o clock. So the additional watt we look for got not much meaning into loudness but into dynamic and control...



Now I realized, that what WongKN cakap before that someone with JBL 100++ dBW sensitive speaker get a very good match with a monstrous power Krell. It must have make music a very close to live experience~

Actually power is everything thrust me, u can drive a tiny bookshelf with a monstrous amp and the sound will be better than driving a hard to drive speaker with a puny amp. I've tried once a bridge Bryston 8B amp and the sound is the most enjoyable that i have ever heard from my Xavian.