2 ohm stable amp recomendations please

[whoaru99]

As you boost frequencies, especially low frequencies/bass, it markedly increases the power demand on the amplifier.

The Crown CE-series has pretty loud fans, IMO, but quieting them down is usually only a replacement fan or a resistor to slow it down.

FWIW, I have a CE4000 and while it is great subwoofer amp, I perceive the QSC PLX amps to be better sounding on mids and highs.

 

[Patrick620]

I may hold out for a QSC PLX series but they are a bit high for my budget. Not out of the question, just high. Maybe I could get a part time job for a few weeks to pay for it, hmmmm.

 

[titanstats]

Could it be that your interpretation of loud and Patrick's interpretation of loud is two different things?

I'm going to guess that this the problem, and not your amp. The Infinity manual suggests an amp to 250W, so it doesn't look like you are underpowering them. I couldn't find anything stating what the max Spls are for these speaks, but it probably just isn't enough for you. Perhaps you'd be better served auditioning a pair of higher efficiency speakers that can generate some more dB of sound. Some JBLs, Altecs, etc. might be more to your taste, and may give you that level of sound you are after with your current amp.

 

[cbrworm]

As an aside, a friend had a set of speakers - either the Infinity SM150 or the cerwin vega equivelant - with a 100 wpc @ 8 ohm fischer amplifier from the same vintage (late 80's) that would play so loudly and clearly it was like a concert. Didn't sound as good as my infinities, but went much louder with about a quarter the power. And sounded great if you weren't listening critically. Needless to say his speakers and my amps were frequently paired for parties. But the point of this is that an efficient speaker will play really loudly without much juice. These less efficient speakers require a lot of juice to just get going.

I remember being amazed that with his speakers hooked up to my SX-1250 you could not get the volume knob near straight up unless you were behind the speakers. That same level and source with mine would just be moderately loud. As I recall his were rated at 100+db/w and mine were high 80's.

I now have an Adcom GFA-555ii driving my RSIIIa's. They sound great and get pretty loud, but not super loud before the clipping indicators start to flash on the amp. Certainly not loud like my friends speakers did on half the power.

 

[Elliot Thompson]

LOL, I think that the rest of my household would go along with that statement. BTW, Elliot, I can really appreciate your comments and concerns. I do not want to overpower these speakers. I guess my goal would be to find the maximum safe level.

Patrick,

I hate to give you the bad news but none of the amplifiers you are considering is going to make a difference in terms of volume.

Adcom GFA 555 MK II

SPECS
- Power Ratings:
200 watts continuous average power into 8 ohms
325 watts continuous average power into 4 ohms


Soundcraftsmen PCR 800/Pro Power One

SPECS
- Power Ratings:
205 watts continuous average power into 8 ohms
300 watts continuous average power into 4 ohms
450 watts continuous average power into 2 ohms

Peavey CS 800

SPECS
- Power Ratings:
240 watts continuous sine wave power into 8 ohms
400 watts continuous sine wave power into 4 ohms


Decibel Difference amongst the three:

Adcom –Vs- Soundcraftsmen @ 4 ohms: 0.3 dB Gain

Peavey –Vs- Soundcraftsmen @ 4 ohms: 1.2 dB Gain

It takes a minimum of 3 dB to hear a noticeable difference in SPL. That means you would need an amplifier that delivers 600 watts per channel @ 4 ohms.

As I mentioned in my previous post those Infinity Speakers are very inefficient. It could be one of the reasons I cannot find a 1 watt/1 meter SPL measurement listed anywhere in the manual. The speakers offer a very wide bandwidth, which leads me to believe that the box is a sealed design based on achieving 18 Hertz.

Infinity then, marketed their speakers to the very rich who listened to classical and, at times Jazz music.

Try connecting one box of your Klipsch on one channel of the Soundcraftsmen while leaving the other channel on one Infinity.

This will tell you what is the weakest link in your chain. I actually own three of those Soundcraftsmen PCR 800s. Everything you mentioned confirms the amplifier is operating correctly.



Best Regards,

 

[Patrick620]

Wow, Elliot!You shouldnt have gone to so much trouble, but I do thank you very much. I thank you, too, cbrworm. I will try my Klipsch and see the difference. I do beleive what you are saying is true, and it is actually good and not so good news. The good news is that the amp is fine. The not so good news is that my super bargain CL beast speakers wont crank up like I wish they would, BUT they do sound amazing and I am in no way dissapointed in them. They are just a "different animal" and will by all means have their place with me.

 

[Elliot Thompson]

Wow, Elliot!You shouldnt have gone to so much trouble, but I do thank you very much. I thank you, too, cbrworm. I will try my Klipsch and see the difference. I do beleive what you are saying is true, and it is actually good and not so good news. The good news is that the amp is fine. The not so good news is that my super bargain CL beast speakers wont crank up like I wish they would, BUT they do sound amazing and I am in no way dissapointed in them. They are just a "different animal" and will by all means have their place with me.

No problem. :thmbsp:

I own a good amount of amplifiers so I generally know off the top of my head what are the wattage measurements at the given load.

The Adcom is the only one I needed to research whereas the Peavey I own close to a dozen of those CS 800s.

Please keep us informed on the results.

Best Regards,

 

[jstang]

SAO..... Safe Area of Operation....

 

[Jon_Logan]

......not to nit pick, but isn't it SOA?

 

[whoaru99]

And generally related to transistors/semiconductors?

 

[Tedrick]

Did you read the Infinity Manual in which they state 75 - 300 watts? The Soundcraftsmen falls within Infinity's optimum recommendation to power these speakers.

Can you guarantee Patrick will not lose his speakers once he exceeds the recommended wattage from Infinity?

Based on the wattage figures they more than likely follow these measures;

75 watts RMS

150 watts Program

300 watts Peak

The Soundcraftsmen delivers 300 watts per channel @ 4 ohms from 20 - 20,000 kHz with no more than 0.05% THD.

Where are these speakers being underpowered?

Could it be that your interpretation of loud and Patrick's interpretation of loud is two different things?

Best Regards,

I do not argue the capabilities of the Soundcraftsmen amp. I was only implying that with these speakers, its as much (if not more) about current than watts. IF the amp is capable of meeting the current demands, then it won't clip and the speakers will play cleanly with minimal fear of damage.

I agree with you that the RS-II's are not "party speakers" and should never be expected to produce the sheer volume levels that much more efficient designs can do with a mere 5 or 10 watts (such as the C-W's and Klipsch's mentioned elsewhere).

 

[Mark B]

I was hoping that someone would chime in on the "loudness" issue, thanks, guys.
Here is what I have to say about this. These RS-II's....I couldnt be happier with these speakers' sound quality. They are probably the best sounding speakers that I have ever owned, but I could be happier with the volume. So, is it the amp or the speakers? Well, I have not swapped out these pieces of equipment with other pieces to determine that, yet. This PCR-800 amp (sticking with the forum topic) powers them in a way that is not bad. What I mean by that is the experience that I get when using this combo is unlike any that I have had. The volume may not be "in your face" but it seems that the volume level is nearly the same if I leave the room and listen from a whole other room. The sound really seems to carry. I think the amp has some power to it. Maybe not enough, but a fair amount. I know that the overhead lights dim just a bit with the beat of the music so this indicates that its USING a good amount of power (newer home on a regular 15A circuit). It's probably not the most efficient amp ever made, but it's probably not the worst either. Having said all of that, I think the overall sound from this combo is not bad, it is more unique than bad. Not what I am used to. I have a Proton AM-455 hooked up to a pair of Klipsch KG-2's for my bedroom setup that really cranks it out. Granted the speakers are pretty efficient and the room is smaller, too. My gut tells me that these speakers would handle more power. I think a more powerful amp would be safer for the speakers, too. I'm considering a Crown (not sure which model), an Adcom 555 MKII, or even possibly and old boat anchor Peavy CS800. I am in no huge hurry to get a new amp, but I will be getting one sooner rather than later. In the meantime I have decided to restore the speakers and continue researching what I will use to power them. I also want to thank everyone for informing me and educating me. I am learning a lot and am enjoying the whole process a great deal. :thmbsp:

Patrick

How loud in dB's do the RS-II's get when you're running close to clipping? Do you have or can you borrow an SPL meter to measure the dB's? With dual woofers there's a possibility that they're wired out of phase. Being wired out of phase will greatly diminish the volume.

 

[whoaru99]

I do not argue the capabilities of the Soundcraftsmen amp. I was only implying that with these speakers, its as much (if not more) about current than watts. IF the amp is capable of meeting the current demands, then it won't clip and the speakers will play cleanly with minimal fear of damage.

Tedrick, the point is though that watts(power) and current are interrelated. These properties are tied together through the impedance of the speaker and the voltage output of the amplifier.

One cannot get more current without more power, one cannot get more power without getting more current.

If one wants more current you have to get more watts. The amplifier that produces more watts at "X" impedance is the more high current amplifer.

 

[SoCal Sam]

Tedrick, the point is though that watts(power) and current are interrelated. These properties are tied together through the impedance of the speaker and the voltage output of the amplifier.

One cannot get more current without more power, one cannot get more power without getting more current.

If one wants more current you have to get more watts. The amplifier that produces more watts at "X" impedance is the more high current amplifer.

If you are driving a test tone, impedance stays the same. However, musical transients will cause impedance to dip so I still would want an amp that can deliver more power at 4 ohm than 8.

BTW, your last comment on massaging the specs is unlikely with Yamaha in the Pro arena.

 

[cbrworm]

Tedrick, the point is though that watts(power) and current are interrelated. These properties are tied together through the impedance of the speaker and the voltage output of the amplifier.

One cannot get more current without more power, one cannot get more power without getting more current.

If one wants more current you have to get more watts. The amplifier that produces more watts at "X" impedance is the more high current amplifer.

Right - A high current amp could be identified by having very high wattage at 1 or 2 ohms. A high power amp rated at 4 ohms may or may not have the current required to not fall on its face when confonted with a 2 ohm reactive infinity. Some modern 'high power' 4 ohm capable, high current recievers actually drop to below 60 watts output before clipping when tested with hard speakers to drive (I am referring to the Onkyo TX-SR806). A true high current amp with the same rating of 150wpc @ 8 ohms and 2xx watts at 4 ohms would not produce less power into a hard to drive load. That Onkyo is sold as a 4 ohm capable amp with 320watts of dynamic power @ 3 ohms, yet . . . Interestingly the previous version did produce more power into low impedance loads, and weighed 20 pounds more.

A true high current, high power amp rated at 4 ohms I would expect to be able to run a 1 or 2 ohm load without damage as long as heat is controlled. They may be not rated for 1 or 2 ohm load due to the inability to dissapate heat under test conditions, but actually perform very well in the real world.

There is always the question of 'well maybe it's really a 2 ohm amp and not an 8 or 4 ohm amp', which is really irrelevant if it gets the job done well which is why we need boards like this. To buy based solely on manufacturers specs is like driving with your eyes closed.

 

[whoaru99]

If you are driving a test tone, impedance stays the same. However, musical transients will cause impedance to dip so I still would want an amp that can deliver more power at 4 ohm than 8.

BTW, your last comment on massaging the specs is unlikely with Yamaha in the Pro arena.

I understand what you are saying, that's why I keep saying "X" impedance, where "X" is equal for both amps.

We wouldn't use information/specs from amp A at 8 ohms, but information/specs for amp B at 4 ohms or 2 ohms to draw a conclusion about "high current" between the two would we? I hope not.

Yes, I agree about the Yamaha amps. Generally, that type of specsmanship I referred to is only a concern where trying to show an amp "doubles down".

Case in point...one of my PLX 3402s. Below is the power per QSC specs.

700wpc @ 8 ohms
1,100wpc @ 4 ohms
1,700wpc @ 2 ohms

QSC could have rated this amp as follows:

425wpc @ 8 ohms
850wpc @ 4 ohms
1,700wpc @ 2 ohms

and in doing so many people would think "Wow, that must be a great "high current" amp because it doubles down all the way to 2 ohms". However, QSC would never sell any into the intended pro audio market because the amplifier cost for the "double down" sandbagged watt ratings wouldn't be in the ballpark with the competition.

 

[rabbit]

This Harman Kardon PA2400 amp is what I use to drive my RS4.5's. Note the instantaneous current capability spec of +/-100 amps

SPECIFICATIONS:
Continuous Average Power (FTC) per Channel : 8 ohms - 170 watts @ < 0.08% THD 20Hz-20kHz
4 ohms - 170watts @ < 0.08%THD 20Hz-20kHz
BRIDGED MONO - 8 ohms - 340 watts @ < 0.15% THD 20Hz-20kHz
High Instantaneous Current Capability (HCC) : +/-100amps
Negative Feedback : 12dB
Power Bandwidth : HALF POWER - < 10Hz - 100kHz @ 8 ohms
Frequency Response : 0.1Hz-250kHz @ 1watt (+0, - 3dB)
Transient Intermodulation Distortion (TIM) : Unmeasurable
Damping Factor : 120
Signal-to-Noise Ratio : 120dB
Input Level/Impedance : 0.8V/33k ohms

 

[whoaru99]

I'm sure it's a fine amp Harman Kardons generally are, but that "high current" spec is just a paper tiger.

Unless, of course, your speakers present a 0.1 ohm load or essentially a dead short circuit to the amp.

Here is what 100A of current represents at typical impedances

8 ohms = 80,000 watts
4 ohms = 40,000 watts
2 ohms = 20,000 watts

Even at 0.1 ohm, that 100A represents 1,000 watts.

From an amp rated 170wpc? Well, you make up your own mind how valid that spec is.

Again, my point isn't to speak poorly about the amplifier, only about that "high current" spec that means essentially nothing for real world loads.

 

[SoCal Sam]

I understand what you are saying, that's why I keep saying "X" impedance, where "X" is equal for both amps.

We wouldn't use information/specs from amp A at 8 ohms, but information/specs for amp B at 4 ohms or 2 ohms to draw a conclusion about "high current" between the two would we? I hope not.

I don't think we are too far apart in our thinking. Agreed, there is no substitute for metal and by all means go for the bigger amp. However my line of reasoning is for comparing two amps with the same 8 ohm rating, which is what is commonly stated on spec sheets.

I'm sure it's a fine amp Harman Kardons generally are, but that "high current" spec is just a paper tiger.

Unless, of course, your speakers present a 0.1 ohm load or essentially a dead short circuit to the amp.

Here is what 100A of current represents at typical impedances

8 ohms = 80,000 watts
4 ohms = 40,000 watts
2 ohms = 20,000 watts

Even at 0.1 ohm, that 100A represents 1,000 watts.

From an amp rated 170wpc? Well, you make up your own mind how valid that spec is.

Again, my point isn't to speak poorly about the amplifier, only about that "high current" spec that means essentially nothing for real world loads.

Are these the correct figures for your example?

Here is what 100A of current represents at typical impedances

8 ohms = 1,250 watts
4 ohms = 5,000 watts
2 ohms = 10,000 watts

Your example assumes the amp is capable of doubling down.

 

[rabbit]

I'm sure it's a fine amp Harman Kardons generally are, but that "high current" spec is just a paper tiger.

Unless, of course, your speakers present a 0.1 ohm load or essentially a dead short circuit to the amp.

Here is what 100A of current represents at typical impedances

8 ohms = 80,000 watts
4 ohms = 40,000 watts
2 ohms = 20,000 watts

Even at 0.1 ohm, that 100A represents 1,000 watts.

From an amp rated 170wpc? Well, you make up your own mind how valid that spec is.

Again, my point isn't to speak poorly about the amplifier, only about that "high current" spec that means essentially nothing for real world loads.

Well we know that the RS4.5's and Kappa 9's can reach down to 1 ohm at certain low and high frequencies. For all intents and purposes if we assume a resistive load at these frequencies and a peak voltage across the speaker of 60 volts then this is a 60 amp peak current requirement straight off the bat But if the impedance is reactive and the signal is a much more complex musical signal then things can get a lot worse for the amplifier

For a more moderate impedance speakers the 8 ohm rating can be a bit misleading at times. You may want to read this which explains why

http://www.stereophile.com/reference/707heavy/index.html