Schiit SYN -> Adcom 555, bridge? -> LS50 as center + L/R

[john61ct]

Hi, building a 5.2 HT in a pretty big room, based on Schiit SYN and OG KEF LS50s

I have three now, and want to get max SPL from them, within safety limits ofc, already planning on HP filtering to them, getting the subs to cover up to say 300-400Hz (those details best discussed elsewhere)

I'm looking to use two of the LS50s as the main L/R pair driven by a stereo Adcom 555 power amp, also OG model from Nelson Pass.

I understand from Schiit, the SPL of the simulated Center should be quite higher than the main pair, so now I'm looking at getting another Adcom 555 to run the third singleton LS50 in bridge mono mode.

At 4-8 ohm 300+W in stereo, supposed to go up to double that (!) bridged mono. No danger of overloading even if the LS50 gets down under 4 ohm, very unlikely anyway with the HP filtering. Some say LS50 never goes under 4 ohm anyway no matter what?

So, first off feedback on the above is most welcome, I realize the 555 amps are overkill but headroom is A Good Thing™ amirite?

My initial explicit Question is: will I actually get significantly higher SPL on my center compared to the main pair?

Plan B would be get LS50 #4 and run a pair in the center, feeding the center mono output from the Schiit SYN Wye'd to BOTH channels of 555 amp #2.

The reason I don't just do that in the first place, I know from years of watching, it's very rare for even singleton well-used LS50's to go for reasonable prices :-(

so far I'm under $1,200 and this might delay me many months

I could go for a cheaper and louder rig for Center, but I really like the idea of the SQ signature matching all across the front.

Thinking KEF Q150s for the rear satellites...

Again, feedback on any of this, or new ideas would be most welcome, TIA

 

[Wayne A. Pflughaupt]

The rule of thumb with amplifier power is that doubling it only gets you an additional (IIR) 2-4 dB in SPL. So no, bridging the 555 won’t get you “significantly” higher SPL.

KEF claims the LS50’s maximum output is 106 dB. Will you ever be playing it that loud?

The nail in the coffin is that KEF recommends amplifiers between 40-100 watts for the LS50. Thus, a 555 in stereo mode is enough amplifier for the LS50s.

Regards,
Wayne A. Pflughaupt

 

[john61ct]

Thanks for that.

With the LS50's I'm told that it's not Watts power so much as massive Current output and damping factor that counts, keeping voltages high when the load impedance gets low.

Many respected members state that in order to get max SPL (safely) with high SQ, a much bigger amp is required for LS50s than one would think.

If the 555 in stereo mode does truly get them there, that's a good thing of course, so I will start looking for LS50 #4 to bump up the center

unless meantime the brain trust has other ideas for me to consider...

 

[EPICURIOUS007]

Pardon Our Interruption...

 

[john61ct]

That looks like a good deal, thank you!!

However, it does not have the same depth of raving reputation as the Nelson Pass OG GFA-555 - which is likely the reason for the more reasonable pricing

The fact that the 125W into 8ohm turns into175W into 4ohm is I think A Good Sign wrt **CURRENT** delivery when LS50 impedance drops, same also with Damping Factor ~400

and that these ratings are for Continuous power, apparently conservative as verified by reviews' measurements.

So, given that my goal is Maximizing LS50 SPL within the "safely" qualifier, there seems to be plenty of headroom capacity,

right?

The higher output of GFA-555 would be entirely wasted wrt LS50s,

is that also correct?

Finally I am looking for reco's on ways to protect the LS50s from getting blown out by my partying teens when I'm away from home.

Ideally an OTS pre-built solution, not DIY...

 

[john61ct]

I also see Hafler DH-200, lots of mod/restore HowTo's, even kits available

any remarks comparative to these Adcoms would be appreciated.

Also wrt new-school Class D - 3eA7 and Wiim Amp Ultra, also near the top of my lists these days...

 

[EPICURIOUS007]

i would not get class d unless it's purifi or hypex or you know the amp has no or little load dependency

 

[DVDdoug]

Finally I am looking for reco's on ways to protect the LS50s from getting blown out by my partying teens when I'm away from home.

Lock the amplifier in a box. Or collect a security deposit. Speakers are usually blown by "kids", drunks, or just "testing" to see how loud you can go.

There's no easy solution to that other than using a way-underpowered amplifier or speakers with extra-high power ratings. The problem is that speakers are rated for peak power an music, and other program material is dynamic... The peaks are a lot higher than the average. It's the short-term average that burns-out voice coils.

A 100W speaker is supposed to be safe with a 100W amplifier hitting 100W on the peaks and not clipping, but it's "statistical". If you push the amp into clipping the average goes up even though the peaks are clipped/limited. For the same reason, you can fry 100W speakers with continuous 100W test tones. And high frequency test tones are more dangerous because the tweeter can't handle as much power as the woofer.

There is a popular myth that an underpowered (but overdriven) amplifier is more risky because clipping creates harmonics that go to the tweeter. It's true that clipping creates higher-power harmonics, but you're getting more power either way and you can burn-out a speaker either way. And you are more likely to turn down the volume of the smaller amp if you hear distortion. If the sound remains clean you might turn it up more...

 

[john61ct]

I bought an Alesis 3632 with adjustable peak limiter circuits on each channel.

Shouldn't I be able to establish the voltage point on the amp's line-in side that produces "max safe" power/current to the speakers?

 

[MPod]

Hi, building a 5.2 HT in a pretty big room, based on Schiit SYN and OG KEF LS50s

I have three now, and want to get max SPL from them, within safety limits ofc, already planning on HP filtering to them, getting the subs to cover up to say 300-400Hz (those details best discussed elsewhere)

I'm looking to use two of the LS50s as the main L/R pair driven by a stereo Adcom 555 power amp, also OG model from Nelson Pass.

I understand from Schiit, the SPL of the simulated Center should be quite higher than the main pair, so now I'm looking at getting another Adcom 555 to run the third singleton LS50 in bridge mono mode.

At 4-8 ohm 300+W in stereo, supposed to go up to double that (!) bridged mono. No danger of overloading even if the LS50 gets down under 4 ohm, very unlikely anyway with the HP filtering. Some say LS50 never goes under 4 ohm anyway no matter what?

So, first off feedback on the above is most welcome, I realize the 555 amps are overkill but headroom is A Good Thing™ amirite?

My initial explicit Question is: will I actually get significantly higher SPL on my center compared to the main pair?

Plan B would be get LS50 #4 and run a pair in the center, feeding the center mono output from the Schiit SYN Wye'd to BOTH channels of 555 amp #2.

The reason I don't just do that in the first place, I know from years of watching, it's very rare for even singleton well-used LS50's to go for reasonable prices :-(

so far I'm under $1,200 and this might delay me many months

I could go for a cheaper and louder rig for Center, but I really like the idea of the SQ signature matching all across the front.

Thinking KEF Q150s for the rear satellites...

Again, feedback on any of this, or new ideas would be most welcome, TIA

I have an Adcom 555 that I don't use anymore if you are still interested.

 

[john61ct]

PM sent

 

[john61ct]

There's no easy solution to that other than using a way-underpowered amplifier or speakers with extra-high power ratings.

Thanks so much for that clear explanation.

So, I am willing to research solutions that are not easy - can you (or anyone?) help point me in the right direction?

A box that I can set a dB SPL threshold or ideally two, so when "too loud" flashes a red strobe at one level, and then cuts the power out a couple dB higher? would be ideal, only partially tongue in cheek

Of course I would need an accurate way to safely judge the limit to set.

Is using a measurement of voltage, power or current at the speaker terminal better than SPL?

At some point I will gather the gear to measure for room correction, maybe even DSP if that is relevant.

...

I bought an Alesis 3632 with adjustable peak limiter circuits on each channel.

Shouldn't I be able to establish the voltage point on the amp's line-in side that produces "max safe" power/current to the speakers?

Is there anyone out there can answer this ELI5 ?

 

[Everett T]

Hi, building a 5.2 HT in a pretty big room, based on Schiit SYN and OG KEF LS50s

I have three now, and want to get max SPL from them, within safety limits ofc, already planning on HP filtering to them, getting the subs to cover up to say 300-400Hz (those details best discussed elsewhere)

I'm looking to use two of the LS50s as the main L/R pair driven by a stereo Adcom 555 power amp, also OG model from Nelson Pass.

I understand from Schiit, the SPL of the simulated Center should be quite higher than the main pair, so now I'm looking at getting another Adcom 555 to run the third singleton LS50 in bridge mono mode.

At 4-8 ohm 300+W in stereo, supposed to go up to double that (!) bridged mono. No danger of overloading even if the LS50 gets down under 4 ohm, very unlikely anyway with the HP filtering. Some say LS50 never goes under 4 ohm anyway no matter what?

So, first off feedback on the above is most welcome, I realize the 555 amps are overkill but headroom is A Good Thing™ amirite?

My initial explicit Question is: will I actually get significantly higher SPL on my center compared to the main pair?

Plan B would be get LS50 #4 and run a pair in the center, feeding the center mono output from the Schiit SYN Wye'd to BOTH channels of 555 amp #2.

The reason I don't just do that in the first place, I know from years of watching, it's very rare for even singleton well-used LS50's to go for reasonable prices :-(

so far I'm under $1,200 and this might delay me many months

I could go for a cheaper and louder rig for Center, but I really like the idea of the SQ signature matching all across the front.

Thinking KEF Q150s for the rear satellites...

Again, feedback on any of this, or new ideas would be most welcome, TIA

More importantly is where you cross the KEFs over. You need to be higher the 100hz if you plan on reference levels.

 

[john61ct]

Yes I figure 120Hz, maybe 200 or even higher