Upgrade my amp again

I agree, interesting discussion with different opinions, so here’s mine.

No doubt a different speaker could be better suited for the room, however I think you definitely need more power on the current speaker.

they sound great with jazz or acoustic. With rock, they can sound a bit muddy

Since you said they sound great on jazz or acoustic implies the speakers are working OK in the room. Rock music is generally played somewhat louder than the others stated due to the tendency of “Let’s rock, crank it up!”, therefore requiring more power from the amp. The Marantz pm5004 is a good value, but with its rated power of 35w @ 8 ohms, and 45w @ 4 ohms, should be used on a less demanding speaker. Reviews and measurements on the PSB T6 indicate it should be used with a substantial 4 ohm rated amp. Also, considering the speakers’ measured sensitivity, average listening distance, and moderately loud listening volume for rock, it’s easy for me to see that the power requirement could exceed the Marantz pm5004.

And is the general issue about right amp for a speaker about the ratio (ie double the watts at 4 ohms) or is there an absolute number? Ie: ideally you would like 80 watts for a 4 ohm speaker?

Basic speaker/amp matching is generally done using the speakers’ sensitivity. Take a look here,

http://www.diyaudio.com/wiki/Loudness_and_Speaker_Sensitivity

This is all based on a 1 meter distance, and since you are probably further away, the reduction of perceived loudness at greater distances must be considered. The approximate reduction will be, 2M – 6db, 3M – 9.5db, 4M – 12db, 5M – 14db, 6M – 15.5db. Obviously, the greatest effect is the first 4 meters.

A 4 ohm speaker is more demanding than an 8 ohm. The amp should be rated for 4 ohm, or even better, rated for 2 ohm. It is definitely a big plus for the amp to double its power into a 4 ohm load, but not absolutely necessary, although you would want to see a substantial increase, much more than the 30% increase of the pm5004.

In speaker/amp matching, it is always better to err on the side of too much power than too little. With too little power, the desired sound cannot be achieved, and there is a greater risk of damage to the speaker, amp, or both. Since a double of power is only a 3db increase, I believe I would be looking at amps in the 100w range and above.

As Captain Kirk said, “Scotty, we need more power!”
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Point taken Bob, and thanks for stepping in Al. I’ll be the first to admit that technically speaking, I have a lot to learn. I hear what I hear but I don’t always know why I’m hearing it. I would actually like to be wrong on this issue because I've been operating under the premise that many of the efficient speakers that I am interested in are too big for my room. But I don’t know how else to explain the sensation that many of the smaller volume rooms, with big speakers, that I’ve been in were just overwhelming to me.

"I haven’t heard his speakers”

Mcanaday - Beg your pardon ma’am; I shoudn’t have assumed.

I always appreciate your contributions Bob... they're well thought out and I’ve learned by them.