KEF question

[Steve81]

So, what do you make of all this "power hungry" business? And what would be the easiest way to figure this; let's say your speakers dip to 3.9Ohm at certain freq. is it enough to just check how your amp deals with 4Ohm. For example, if it can handle 4Ohm, dips shouldn't bother it. Is this all there is to it? Does this cover all the "transients" stuff?

You didn't ask me, but I'll give you a couple pennies worth of my thoughts. The three main factors I'd look at are voltage sensitivity, impedance, and phase angle.

I think voltage sensitivity is pretty well understood, X dB for 2.83V input. Impedance relates to that, as 2.83V into an 8 ohm load is 1W, and into a 4 ohm load is 2W given that the speaker is drawing more current. Phase angle is also a factor, not because it makes a speaker more or less power hungry, but because a reactive load will cause the amplifier to have to dissipate more heat than a purely resistive load.

Given its relatively low voltage sensitivity, low impedance in the meat of the audio band, the LS50 isn't the easiest speaker to drive on the block. Electrical phase isn't too bad for the most part, but there is a spot around 150Hz where it approaches the - 45 degree mark where the impedance is relatively low (135Hz, 5.3 ohms, -41 degrees per Stereophiles reckoning), making for another difficult combo for an amp.

All that said, one should look a little closer at the distortion graph from Soundstage before going too nuts. The input there was 10.6 volts, or ~14W into 8 ohms, and ~28W into 4 ohms. Given the amount of distortion already present, one wonders just how much more juice you would want to actually feed them in the first place.

 

[shkumar4963]

Thanks @PENG.

Not saying that we could play ls50 at this volune, but just to calxulate max power, 200 watts will get us 107 dB at 1 meter. Now to handle 20 dB transuent peaks we would need additional voltage/current. Ate these amps voltage limited or current limited?

Is that correct?

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[PENG]

You didn't ask me, but I'll give you a couple pennies worth of my thoughts. The three main factors I'd look at are voltage sensitivity, impedance, and phase angle.

I think voltage sensitivity is pretty well understood, X dB for 2.83V input. Impedance relates to that, as 2.83V into an 8 ohm load is 1W, and into a 4 ohm load is 2W given that the speaker is drawing more current. Phase angle is also a factor, not because it makes a speaker more or less power hungry, but because a reactive load will cause the amplifier to have to dissipate more heat than a purely resistive load.

Given its relatively low voltage sensitivity, low impedance in the meat of the audio band, the LS50 isn't the easiest speaker to drive on the block. Electrical phase isn't too bad for the most part, but there is a spot around 150Hz where it approaches the - 45 degree mark where the impedance is relatively low (135Hz, 5.3 ohms, -41 degrees per Stereophiles reckoning), making for another difficult combo for an amp.

All that said, one should look a little closer at the distortion graph from Soundstage before going too nuts. The input there was 10.6 volts, or ~14W into 8 ohms, and ~28W into 4 ohms. Given the amount of distortion already present, one wonders just how much more juice you would want to actually feed them in the first place.

Thanks, you summarized pretty much everything I wanted to say in my post but I chose to go point by point and got carried away in the process.

 

[PENG]

Thanks @PENG.

Not saying that we could play ls50 at this volune, but just to calxulate max power, 200 watts will get us 107 dB at 1 meter. Now to handle 20 dB transuent peaks we would need additional voltage/current. Ate these amps voltage limited or current limited?

Is that correct?

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KEF specified 8 ohm nominal, min. 3.2 ohm, but looking at the graph I would guess they are closer to 6 ohm nominal. The specified sensitivity was 85 dB 2.83V/1m, based on 6 ohm nominal, I would subtract 1.25 dB, so your 83 dB seems reasonable to me.

If you punch in 2 speakers, you will end up with approx 106 dB for 100 W X2 amplifier, same difference!!

 

[KenM10759]

I no longer obsess about measurements, specifications, graphs and calculators.

My preference is to hook up speakers to music I like and listen at whatever volume I'm feeling. If it sounds good, I'm happy. If it doesn't sound good, I change whatever is wrong.

And I like a lot of KEF speakers, but not all.

 

[shkumar4963]

KEF specified 8 ohm nominal, min. 3.2 ohm, but looking at the graph I would guess they are closer to 6 ohm nominal. The specified sensitivity was 85 dB 2.83V/1m, based on 6 ohm nominal, I would subtract 1.25 dB, so your 83 dB seems reasonable to me.

If you punch in 2 speakers, you will end up with approx 106 dB for 100 W X2 amplifier, same difference!!

Now thinking more about it, since we need sufficient power for each frequency to achieve 107 dB, shouldn't we use 3.2 ohm as worst case? So 85 dB sensitivity at 2.5 watts per meter. Or 81 dB per watt per meter sensitivity (give or take)?? So would need more than 300 watts per channel for sustained 107 dB output.

And then we still need to accomodate 20 dB transients. ??

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[PENG]

Now thinking more about it, since we need sufficient power for each frequency to achieve 107 dB, shouldn't we use 3.2 ohm as worst case? So 85 dB sensitivity at 2.5 watts per meter. Or 81 dB per watt per meter sensitivity (give or take)?? So would need more than 300 watts per channel for sustained 107 dB output.

And then we still need to accomodate 20 dB transients. ??

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If you want to be more conservative than just realistic, take a good look of the impedance vs freq graph again and you will see that 5 ohm would be a good number to use, so go with 83 dB like you did in the first place. It is not reasonable to use the 3.2 ohm unless you listen to tones all day. For me, yes I would definitely use 3.2 ohm, and no wonder I have much more amps that I need.

 

[killdozzer]

All that said, one should look a little closer at the distortion graph from Soundstage before going too nuts. The input there was 10.6 volts, or ~14W into 8 ohms, and ~28W into 4 ohms. Given the amount of distortion already present, one wonders just how much more juice you would want to actually feed them in the first place.

You understand graphs better than me. Does the cited graph show distortion from pushing them too loud? Could the registered distortion come from the amp clipping?

Loud is actually not my goal. I don't want them gagging for it during the crucial passages.

Thanks!

 

[killdozzer]

@PENG I think I'm getting the hang of it. So, even a 60Wpch into 8 that can handle 4ohms easily is more than enough and KEF's proverbial hunger should be catered to with the amp behaving nicely at 4Ohms?

As I said to Steve81, I'm not looking for full 106 decibel SPL, I want them as clean as possible between 85 and 90.

Also, would you than say that the active version of these are a pure example of overkill for marketing purposes? They are 200W for mid/bass and 30W for the tweeter.

I admit, I was secretly taking a hint from those bc I thought the engineers knew what they were doing and I would be crazy not to take that as an advice.

Albeit, I wasn't going for 230. I wanted a 100 into 8 with a stroll of 150 into 4, like this:

This is something I wouldn't mind sticking to and passing it on to my nephews. They seem to be taking into listening to music.

These measures are taken in accordance with EIA Standard RS-490

 

[PENG]

@PENG I think I'm getting the hang of it. So, even a 60Wpch into 8 that can handle 4ohms easily is more than enough and KEF's proverbial hunger should be catered to with the amp behaving nicely at 4Ohms?

If you are going to be using those speakers in a small (say by THX standard) room sitting 6 to 8' from them, a 60/100W 8/4 ohm amp should get you 100 to 103 dB of spl. That means you can listen to spl of 80 dB and still have clean power on hand for peaks of up to 23 dB above the average spl. 103 dB is getting close to the speaker's maximum output capability of 106 dB. So an amp rated for 60/100 W, 8/4 ohm could in fact be more than enough, depending on your spl requirements, room size and sitting distance.

View attachment 23116

This is something I wouldn't mind sticking to and passing it on to my nephews. They seem to be taking into listening to music.

These measures are taken in accordance with EIA Standard RS-490
The 100/150 W 8/4 ohm integrated amp specs you attached is impressive. It should be capable of pushing the passive LS50s very close to their 106 dB limits.

That integrated amp has very good specs, it should be powerful enough to push the LS50 close to their 106 dB/1m limit.

As I said to Steve81, I'm not looking for full 106 decibel SPL, I want them as clean as possible between 85 and 90.

If the 85 and 90 are average spl then that's very loud already. I can't withstand such spl for more than a minute. Also, if you allow for 20 to 25 dB for peaks, you will be pushing the LS50 pass it's maximum spl capability. If those numbers are for peaks, then just use the previously linked calculator to figure out the power you need, use 83 for sensitivity to be on safe side.

Also, would you than say that the active version of these are a pure example of overkill for marketing purposes? They are 200W for mid/bass and 30W for the tweeter.

No I would not say that at all. There is not enough information as their literature simply says 200 W class D, and 30 W class AB. If they meant peak power, than the average would be 100 W and 15 W. There's no mentioning of distortions and anything else that could be useful.

I admit, I was secretly taking a hint from those bc I thought the engineers knew what they were doing and I would be crazy not to take that as an advice.

I am sure they know what they are doing, but the power specs they provided are simply too brief.

Albeit, I wasn't going for 230. I wanted a 100 into 8 with a stroll of 150 into 4, like this:
View attachment 23116

This is something I wouldn't mind sticking to and passing it on to my nephews. They seem to be taking into listening to music.

These measures are taken in accordance with EIA Standard RS-490

That integrated amp should be just about capable of pushing the LS50 to their limits.

 

[little wing]

Maybe why class A is expensive, the way it works in the first 30 and heat.

Curious to know how these speakers stack up to your Raal towers for..........for obvious reasons

 

[Steve81]

You understand graphs better than me. Does the cited graph show distortion from pushing them too loud?

Correct.

Could the registered distortion come from the amp clipping?

Negative. It's a loudspeaker bench test done at the Canadian NRC. I assume they have access to devices that won't clip driving a loudspeaker at a whopping 10V

 

[ematthews]

The reviewer also said the Polks were "neutral to warm", so his subjective observation was in line with yours. By the way, I do think the LS50 needs to be placed on stands, good quality ones, instead of sitting on some book shelves. The Polk LSiM703s, being larger and 3 way, may be a little more forgiving but should be put on proper stands too for optimal performance. So how did you place them?

Both are on stands.. A few weeks later and I still haven't warmed up to them. I am going to try them in a different room.

 

[shkumar4963]

Both are on stands.. A few weeks later and I still haven't warmed up to them. I am going to try them in a different room.

Do you have a sub as well when you audition them. If not, try with one.

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[ematthews]

Do you have a sub as well when you audition them. If not, try with one.

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Oh yeah. I have tried both my Outlaw and SVS sub with it. A must for me.