Very efficient speakers (100 dB), how important is amplifier power?

[Flavio]

According to @amirm's measurements there is a very narrow vertical listening window. It is expected to affect people at different heights or at different seating, upright or laying back. How is it in your experience?

There is a noticeable difference between sitting upright and half lying on the couch.
I have aimed the speaker as best as I could.

 

[Holmz]

No center speaker, I always sit in the middle.
I was offered the 70J's as a complete set and they fit nicely wall mounted on the sides of my projection screen.
Because of space and money concerns I chose the 50's for surround and Atmos ceiling duty.

You’re not alone in that a 4.x or 6.x system can be good.

and with the remote mono amps…

Because I like them and they …

You are also not alone here.

What about the Niachrome amps?

 

[Flavio]

You’re not alone in that a 4.x or 6.x system can be good.

and with the remote mono amps…

You are also not alone here.

What about the Niachrome amps?

What are Niachrome amps? My search engine can't find them.

 

[restorer-john]

What are Niachrome amps? My search engine can't find them.

He means Neurochrome. @tomchr is a member here. Nice bloke.

DIY Audio Engineering Gear for Audiophiles | Neurochrome

Neurochrome is your go-to source for audio engineering gear and consulting. We make it easy for audiophiles to get the gear they need to get the sound they want.

neurochrome.com

 

[HighImpactAV]

I have a pair of JBL CBT 70J-1 / 70-JE1 as my main speakers and four JBL CBT 50-LA1 as surround speakers . . .

According to JBL they are 8 Ohm, have a sensitivity of 100 dB/1m and can take 1000 W low-Z (whatever that means?).

Where do you get that spec? The CLF file (Common Loudspeaker Format) that JBL provides shows an average sensitivity of 90.3 dB and their spec sheet shows 92 db (300 Hz - 18 kHz). Maximum input voltage is 63 Vrms, which is 500 watts at 8 ohms.

Note: when actually viewing the CLF file, you can scroll over all the way to 20k.

 

[kemmler3D]

Where do you get that spec? The CLF file (Common Loudspeaker Format) that JBL provides shows an average sensitivity of 90.3 dB and their spec sheet shows 92 db (300 Hz - 18 kHz). Maximum input voltage is 63 Vrms, which is 500 watts at 8 ohms.

Note: when actually viewing the CLF file, you can scroll over all the way to 20k.
View attachment 261614

The JBL site https://jblpro.com/products/cbt-70j-1 says anywhere from 98 - 92 depending on settings. 98 is pretty close to 100 I guess.

Even at 92 most amps will blow your hair and your neighbor's hair back, any of the NCORE units that came up are more than enough for that.

 

[Killingbeans]

Benchmark ABH2 should solve your hiss issue.

Or Topping LA90. (Although a bit anemic in power)

 

[Blumlein 88]

How do you calculate from 20uV and 4 Ohm to - 100 dB?

Never mind, I already figured it out.

8 ohm rating for 1 watt is 2.83 volts. 4 ohms is close enough to 2 volts. So ratio of the two voltages taking the log and multiply by 20.

 

[benanders]

FWIW I’m running a ~5.3 ohm line array with a Musical Fidelity A3.5 integrated stereo amp. MF factory specs say the amp will deliver below 240 wpc max. The monitors I’m using (6 per stereo channel, homologous to coupled woofers) to comprise the LA will handle max continuous power of 150 w… each. That = 900 w continuous per channel max, and that covers ~100 Hz up; bass is powered separately.
Sensitivity calculates to 99.5 dB, but the tweeters aren’t coupling so that value’s an overestimate. The individual monitors are rated 90 dB sensitivity.

Never, ever any hiss

>> Edit: that is to say, hiss audible to my ears or those of other listeners; not measured / mic’ed. Hook a tube amp up, and that changed a little, at very close range (within inches) <<

unless it’s part of the recording (which can be heard clearly on some vinyl digitizations, home recordings with guitar amp hiss, etc). Between the two channels, there’s over 60’ of speaker wire. I don’t know enough about the topic to dismiss “max possible amp overhead” advocacy, but despite my speakers’ list of design atrocities, I haven’t seen heard any need for amp overhead.

I would think those JBL LA’s would be flexible, modeled more for decent HT/multi-channel receivers than massive mono blocks, no? Have you at least tried a chip amp x switching power supply per channel? It would be a cheap (albeit not properly controlled) test of suitability for “makeshift mono’s” in your case.

 

[Holmz]

…
Never, ever any hiss unless it’s part of the recording (which can be heard clearly on some vinyl digitizations, home recordings with guitar amp hiss, etc).
…

Let’s not confuse the master tape hiss and think that the vinyl is hissing.
It is only pressed into the vinyl as it was presented.

 

[benanders]

Let’s not confuse the master tape hiss and think that the vinyl is hissing.
It is only pressed into the vinyl as it was presented.

Ha! That’s a fair clarification.
I should’ve specified the low-level snap-crackle-pop on vinyl that can resemble a slo-mo hiss, of sorts.
As you’re correct - what vinyl may cause is generally quite a different form of noise than the hiss mentioned by the OP. But I did simply mean whatever noise is coming from the source, whatever it’s ultimate cause may be

 

[Holmz]

Ha! That’s a fair clarification.
I should’ve specified the low-level snap-crackle-pop on vinyl that can resemble a slo-mo hiss, of sorts.
As you’re correct - what vinyl may cause is generally quite a different form of noise than the hiss mentioned by the OP. But I did simply mean whatever noise is coming from the source, whatever it’s ultimate cause may be

I think it is cool to hear the stylus touchdown, and then a few seconds later the mater tape hiss start… just before the music… and it dies again after the song ends… and starts before the next song…
(yet we worry about 120 vs 125 dB SINAD)

 

[benanders]

I think it is cool to hear the stylus touchdown, and then a few seconds later the mater tape hiss start… just before the music… and it dies again after the song ends… and starts before the next song…
(yet we worry about 120 vs 125 dB SINAD)

Agreed. Main reason I do not prefer noise-removal on digitized vinyl tracks. That software’s a sentiment hissassinator

 

[voodooless]

The JBL site https://jblpro.com/products/cbt-70j-1 says anywhere from 98 - 92 depending on settings. 98 is pretty close to 100 I guess.

Even at 92 most amps will blow your hair and your neighbor's hair back, any of the NCORE units that came up are more than enough for that.

Good somebody did the fact-checking! I thought the 100 dB was bogus from the start. You'd probably want to run in "broad" mode with the "music" setting. The actual sensitivity is then closer to 90 dB.

So now you'll need a 10x bigger amp and don't need to worry about hiss as much

 

[Flavio]

The sensitivity of 100 dB and power handling of 1000 W are straight from the JBL brochure and are for the 70J1/70JE1 combo.

 

[restorer-john]

The sensitivity of 100 dB and power handling of 1000 W are straight from the JBL brochure and are for the 70J1/70JE1 combo.

They are at least a 13 year old design- I wonder what, if anything they have updated/improved on since May 2010 brochure date?

 

[restorer-john]

I'd say realistically anything in the high 80s, low 90s SNR at low power should be good. Once you are in the 100s, there's a good chance you will never hear any noise at all under any circumstances.

I have several power amplifiers here with 123dB S/N. Some at 120dB S/N. You will hear residual noise in tweeters, even with those numbers, even on 87dB@1W/m speakers in a quiet situation or at close range.

 

[voodooless]

The sensitivity of 100 dB and power handling of 1000 W are straight from the JBL brochure and are for the 70J1/70JE1 combo.

Ah, so you also have the bass extension. Still the sensitivity spec is nonsense as can be seen in the datasheet:

This looks more like 95 dB in bass. But at 1 kHz it’s just above 90. Funny enough, the sensitivity spec in the datasheet is indeed 90 dB for the extension. That seems a few dB too low.

Better looks at the actual frequency response, and not just a silly number in the spec sheet.

 

[Bob from Florida]

I would propose that the speaker sensitivity does not really matter in the context of the issue - audible hiss. The OP needs an amp without hiss.

 

[fpitas]

I would propose that the speaker sensitivity does not really matter in the context of the issue - audible hiss. The OP needs an amp without hiss.

It matters because some amps are much quieter than others. There's no such thing as "no hiss". Just degrees. It's measurable just like everything else.