Studio Monitor Tweeter Hiss (JBL LSR305, KRK Rokit 5 G3, Etc.)

[dimtsak]

I have KRK Rokit 5 G2 and they make the noise too.
Tried in different wall outlets and it's still there.
I can hear it from listening potition but i forget it once i start mixing.
Since it's normal, i guess you have to learn living with it.

[miketurn]

@dimtsak
Thank You for your response, so the KRK 5 G2 version does this as well.

(Overall I get it, but just to rant a little bit )
I obviously don't know a ton about electronics / power / manufacturing costs / etc. but it seems odd that most manufacturers would just allow this.
I know once you sit further back from the speakers and also get into listening to music it goes away but just not something I would expect from some of these big name companies. I know others have mention that they have to save money somewhere, so they provide cheaper amps, but come on it is 2017, most of these products have been being produced for a long time so the money isn't being spent on development of these products. Even though $300 isn't a lot compared to more expensive speakers, it is still quite a bit of money to be using cheaper parts on. 15-20 years ago the home studio market was obviously quite a bit less, but now that more and more people are purchasing monitors, I would think the cost of parts would be cheaper today, and with so many more monitors being sold they would also get better deals on purchasing them in higher quantities, so long story short, I don't want my monitors to hiss

If anyone else has any more monitors to comment on please do so, also still looking for people to comment on the Presonus and KRK 4s. I would imagine if the KRK 5s and 8s hiss then the 4s would be no different but still interested in hearing what people have to say.

Again I know this is not a huge deal, just something to discuss a little.

Thanks Again to everyone that has commented.

[JCJR]

(Overall I get it, but just to rant a little bit )
I obviously don't know a ton about electronics / power / manufacturing costs / etc. but it seems odd that most manufacturers would just allow this.
I know once you sit further back from the speakers and also get into listening to music it goes away but just not something I would expect from some of these big name companies. I know others have mention that they have to save money somewhere, so they provide cheaper amps, but come on it is 2017, most of these products have been being produced for a long time so the money isn't being spent on development of these products. Even though $300 isn't a lot compared to more expensive speakers, it is still quite a bit of money to be using cheaper parts on.

Actually I agree. It seems that nowadays they ought to be able to make at least somewhat less noisy cheap gear. Decades ago I did electronic work, designing and building gadgets and repair/modification and such. Nerded out rather heavy on it for awhile. It was hard to make low-noise gadgets. Then around the mid 1980's on, occasional not-expensive fairly low-noise gadgets got manufactured and it seemed to me amazing they could get low-noise at such a small mass-manufactured price.

I remember talking with Craig Anderton sometime back then at a NAMM show, about noisy products. 1980's or maybe 1990's. Dunno if he was correct, but he voiced the opinion that so many young engineers were specializing in digital that it was becoming difficult to find good analog designers. If it was anyway true back then, then perhaps it remains true today.

However, even if the breed is becoming rare, the big companies ought to be able to hoover up whatever top talent remains. I don't keep up with the field at all, but read on a couple of threads that some of the most-favorite low noise audio opamps are being retired by manufacturers with no "even more gooder" replacement designs. Some comments that those particular assembly lines are getting old and there isn't enough money in it to build new assembly lines for that relatively small niche. Which is all hearsay and I can't say whether it is true.

****

In a system you will have noise from instruments or the audio interface. If you use a mixer between sources and speakers, the mixer will add its own share of noise. And then finally the speaker amps will contribute some noise ontop of that.

When evaluating self-noise in an amp or powered speaker, the noise might come from different places inside the amp, or it might be fairly evenly distributed. When I test such thangs, I'll often insert a shorting plug into the inputs. Just a plug with a wire between input hot(s) and ground. Sometimes, especially with higher-impedance inputs, an amp with "nothing plugged in" can be noisier than in practice with a proper input cable plugged in. So a shorting input plug can give the amp or audio interface or mixer or preamp "the best case odds" of working as noise-free that it is capable. Sometimes a test with "nothing at all plugged in" would not be a fair test.

Then check whether the noise is modulated up/down by the amp input level controls. Level knob and possibly "hi/low gain" switches. If "most of the noise" is in the amp's input stages, then it will be noisier with a gain switch set to high gain and will be noisier with the level knob turned up.

If it happens that your mixer or audio interface might be lower-noise than the speaker amps, and if the mixer or audio interface can deliver fairly hot undistorted signal, then you might get the best noise performance with the source turned up about as loud as it will go without distortion, and then turn down the amp until the room listening level is about right.

If the amp has tone contour controls, does it hiss more with the treble boosted? In that case you might turn down the speaker's treble controls and then use an EQ to boost the treble feeding the amp, so you get a flat output with less hiss. Again, that would only be beneficial if your mixer and EQ are less noisy than the amp. Possibly in some cases could cause audible phase oddities.

On the other hand if the speaker makes the same amount of hiss with a shorted plug, regardless where you adjust the input level controls, then that might imply that most of the noise is in the driver/output stages, or that the noise might be fairly evenly distributed in the circuit. In that case maybe fooling with the source and amp gain levels can't diminish the quiescent hiss.

Often but not always, low impedance inputs have less noise than high impedance inputs, so if the amp will accept low impedance balanced XLR or balanced ring-tip-sleeve inputs, use them if possible.

[JCJR]

A practical example, building on BertKoor's earlier explanation of signal to noise ratio--

Voltage dBs are calculated dB = 20 * log10(VoltsOut / VoltsIn)
Power dBs are calculated dB = 10 * log10(WattsOut / WattsIn)

They are both the same in practice, it is just that power is the square of voltage, assuming a constant load impedance (such as speaker ohms or a preamp input impedance).

Nothing in the real world is completely linear, but some ballpark estimations--

Last year was building some cheap coaxial studio monitors, triamped subwoofer, 12" mids, 1" horn drivers. Crossed-over between mids and highs at 1 kHz. The ear is most sensitive to noise above 1 kHz. Therefore noise is most likely to be heard from the horn.

Found a real good used price on a good-condition single rack space Ashly SRA120 to drive the horns.
http://www.fullcompass.com/common/files ... Manual.pdf

Specd at 40 watts RMS per channel into 8 ohms, hum+noise less than 100 dB below the rated power. The new retail price of that amp was about $580 US so far as I know. About the same as an entire pair of LSR308. Though my used price was lots lower.

So, the homemade monitors' horn drivers claim to handle 60 watts and deliver 105 dB spl in a suitable horn, at 1 watt input, measured 1 meter distance from the horn.

OK, how many dB above 1 watt, is 40 watts? Unless I'm suffering a senior moment, it ought to be 10 * log10(40 / 1) = +16 dB. If 1 watt delivers 105 dB SPL, then 40 watts ought to deliver 105 + 16 = 121 dB SPL at 1 meter distance. Because no component is perfect, the actual output might be something else entirely.

OK, in theory how loud should be the hiss from the amp alone? If the amp's 40 watt rated output delivers about 121 dB SPL and the noise is 100 dB less than that, then the quiescent noise from the horn ought to be something like 121 dB - 100 dB = 21 dB SPL.

My home office is not real noisy but I'd be surprised if it averages much quieter than 30 dB SPL. My cheap SPL meter doesn't go that low, so all I can tell from the meter is that the office is probably quieter than about 40 dB SPL.

If environmental noise is about the same level, or louder than some signal, then the environmental noise will tend to mask the quiet signal and the ear will have difficulty hearing the quiet signal. Because my room is almost certainly A LOT louder than 21 dB SPL, then if the above rough math is about right, then it is unlikely that I would hear the horns hissing (from the amp alone) from 1 meter distance. And in fact I don't hear the horns hissing from 1 meter away, though i can hear them hiss if I put an ear close to the horns.

****

I do not see a specified SNR for the LSR308 here-- http://www.jblpro.com/www/products/reco ... r308#Specs

Maybe it is there and my eye doesn't find it, or maybe it is quoted somewhere else. Tis hard to compare without a spec. I tend to trust specs published by many of the Harmon companies, but who knows without a published spec?

My mids (below 1000 Hz) are driven by a crown XLS 1000. http://www.crownaudio.com/en/products/xls-1000

It is not as likely I'd hear hiss thru the mid speakers unless it is louder. But if I wanted to drive the horns with the XLS 1000-- It is specd 215 watts per channel at 8 ohm, A rated signal to noise ratio greater than 97 dB below rated 8 ohm power. So (assuming the driver is linear and doesn't blow) 215 watts would be about +23 dB more than 1 watt, and the theoretical SPL of our 105 dB sensitivity driver would be 105 + 23 = 128 dB SPL at 1 meter. If the noise is 97 dB quieter, then the quiescent hiss might be in the ballpark of 128 - 97 = 31 dB SPL.

Maybe the horn hiss would be about 10 dB louder, driven by the more-powerful amp, even though the rated signal to noise ratio of both amps is similar. 31 dB SPL ought to be more-likely heard from 1 meter distance, but dunno if I would hear it in my room. Maybe even 31 dB SPL would be masked by environmental noise, or maybe not.

[annode]

I have a set of original Mackie HR824. They are active and employ an AB Class amplifier. The hiss is very subtle. These days many active monitors employ the D Class amplifier because it has less parts, is lighter,dissipates little heat and costs less. It has a much greater efficiency for amplification but needs a great deal of additional circuits to compensate for inherent audio problems. The LSR305 is D Class.
If these designs are poorly made it will show up in it's performance.

All this i've found is very complex and I don't advise you read up on it.

[miketurn]

Thank You guys for the responses and examples.

[chk071]

I have a set of original Mackie HR824. They are active and employ an AB Class amplifier. The hiss is very subtle. These days many active monitors employ the D Class amplifier because it has less parts, is lighter,dissipates little heat and costs less. It has a much greater efficiency for amplification but needs a great deal of additional circuits to compensate for inherent audio problems. The LSR305 is D Class.
If these designs are poorly made it will show up in it's performance.

Yep. That's what i read about the LSR305's too, that they have D class amps, and therefor, there is some hiss. Anyway, got used to it, and i barely hear it anymore, TBH.

[EnGee]

Mine (HS7) have a very low noise I can only hear it if I put my ears near the speakers. In my seat (about 1 to 1.5 metres) I don't hear any noise

Edit: I think they are class AB (according to various websites and forums).

[JCJR]

My crown xls 1000 and 1500 are class D. As Annode mentioned they have advantages in price, weight, low heat dissipation etc. So far as I can tell they are low enough noise and distortion for my purposes.

If a class D amp performs good enough for the purpose then those weight, power and heat advantages can be very appealing.

Some class AB amps can be noisy, distorted and unreliable. Maybe statistically MOST AB amps are not very good. Until recently almost all audio amps were AB. Always seemed to me that there were more crappy amps out there than good ones.

Buying an AB amp you wouldn't want to buy a bad class AB amp. Buying a class D amp you wouldn't want to buy a bad class D amp.

It is one reason that powered speakers don't seem such a good idea to me unless the price/performance happened to be so good that you could consider them disposable bic speakers. It is easier to be selective if buying separate amps and speakers. You can't go to the store and say, "I want the LSR305 but upgraded with lower noise amps." Or whatever.

[annode]

JCJR sez;

Buying an AB amp you wouldn't want to buy a bad class AB amp. Buying a class D amp you wouldn't want to buy a bad class D amp.

That's not how it works here. It's not simple.

[JCJR]

JCJR sez;

Buying an AB amp you wouldn't want to buy a bad class AB amp. Buying a class D amp you wouldn't want to buy a bad class D amp.

That's not how it works here. It's not simple.

Thanks annode

Though not exactly nuclear physics, implementation details of any type of amp are not simple. With proper care, excellent amps can be made with many techniques. And crappy amps can be made with the same techniques.

Some folks believe that nothing but class A tube is "good enough". Then there is class A bipolar semiconductor or class A mosfet.

Class AB made with tubes, symmetrical npn/pnp bipolar output pairs, assymetrical "all NPN" output devices (All PNP is equally possible but all NPN's have some slight practical advantages, or did at one time), or Class AB mosfet.

It is possible to find folks convinced that one of the many strategies is "the only one that can sound good".

I could be wrong but am of the opinion that excellent amps can be made, and have been made, with any and all of the above. And that excellent class D amps can and have been made.

Some studio and mastering guys seem convinced that hypex-based class d and some other high end class d are among the best which one can use. Maybe an equal number of pros who think the only thing that will do is some kind of expensive tube amp.

On the other hand you can go to partsexpress.com and order little class d amps for less than $10 on up to $50 or $100, which probably don't sound very good and probably are not very reliable. Class AB costs maybe a few bux more for the same watts, but you can buy almost equally cheap AB amps which probably don't sound good and will probably go up in smoke the first time you look at em crosseyed.

Regardless of the design, you want to get one that is strong enough for purpose, low distortion and low noise enough for purpose, and as reliable possible considering the available budget.

[annode]

JCJR wrote;

I could be wrong but am of the opinion that excellent amps can be made, and have been made, with any and all of the above. And that excellent class D amps can and have been made.

Yes, I'll sort of agree with that. But, use of class D under 300watts makes me question ...why use it?
I see class D for near fields at 40watts or there about. Why? Not for any added features or quality.(maybe for heat safety if installed within the cabinet?) I've read how designers are not following the full path to quiet systems with good linearity. It's not a beef of mine but I have read ppls complaints about unknown noise from their NF monitors here at KVR and it seems to fit with bad grounding/shielding designs that are extremely necessary in class D.(as I understand) Those using switching supplies as well, are like RF transmitting stations and get into the audio section through cables.(so i've read)

It just seems like the manufacturer of a NF monitor doesn't really have a need to use a class D except to cut costs somewhere....and it doesn't seem they are giving the buyer a break.(or are they?)
They make 'simple' bass reflex ports so they can scale down the woofer size to 5" and claim response down to 43hz, when they could pay a bit more and use a tuned ducted system for a smoother bass response. But it appears they don't really care to.
Most of the monitors I saw with it's class noted in their specs are class AB. Many don't list the amp class.

page#2 is revealing; (concerning 'switching amps' [class D])
Scroll down to: "Further Comments on grounding and PCB layout from Bruno Putzeys:"
http://www.audioholics.com/audio-amplif ... ues-page-2

This article was well written and not overly technical.
http://www.audioholics.com/audio-amplif ... er-classes

[JCJR]

Thanks annode

Am not an expert, just what I think I know-- Circuit layout details are important for many applications. With microwave radio equipment, the frequencies are so high that rather than using tiny-value capacitors and inductors, sometimes parts are "emulated" just by the precise shaping of the circuit board traces. A certain shape of circuit board stripe behaving like a desired inductor, and another shape of circuit board stripe behaving like a desired capacitor.

Layout is also important in computers and high-clock-rate digital equipment. It was "challenging" to get a good layout decades ago when computer clock rates were much slower than today. Maybe some designers 20 years ago would have considered it "impossible" to lay out a computer motherboard for modern clock rates? Equivalent to laying out a microwave circuit board, but with lots more components and traces than a microwave circuit.

In some ways analog audio is easier to lay out but is an art. Long ago I built a little compressor and followed good layout practices as I understood it-- It used a simple opamp comparator to light up an LED when over-threshold. It was a regulated power supply, all the parts were power-supply decoupled and the circuitry related to the LED was isolated as good possible from the audio path. The audio output would click every time the LED would turn on or off. Took awhile to fix.

Except for fairly low-power devices, switching power supplies are so obviously superior that they just need to be built good enough to avoid possible drawbacks. As you say there are possible drawbacks but the advantages are huge. I never learned how to repair switching power supplies but maybe it could be learned. There are tricks to everything. Years ago when I fixed a few, they seemed built to throw away rather than repair. Components tightly crammed in a can with high voltage inside. Not pleasant to probe with an oscilloscope. But hey I was also too chicken to work on the high voltage parts of CRT TV's.

Long ago first time realization that switchers are great-- I had bought some synth that needed 12 volts regulated DC at something like 3 amps. And they didn't sell the power supply along with the synth. You had to buy the power supply brick separately-- Which was priced rather high, $50 or $75 or whatever. Maybe they were pricing the synth below cost and then making all the profit on the power supply brick. The synth needed more current than off-the-shelf cheap power bricks could deliver. Maybe it was a Casio CZ-1000 or maybe something else. Can't recall.

So at the time I kept lots of parts in stock, and said "I'm not gonna pay that much for a power supply. Will build my own instead". Had built many linear regulated power supplies up to 1 amp, but hadn't built a higher-current regulated power supply. So after I built the 3+ amp linear regulated power supply in a bud box-- My supply worked fine but was lots bigger and heavier than the factory switching power supply brick. My supply ran about as hot as a space heater. Fairly big heat sinks. The factory switcher brick would barely get warm.

Linear regulated power supplies take "somewhat smoothed" DC at higher voltage than you want, then drops the voltage thru a feedback-controlled transistor so that there is "excellently smoothed" output at exactly the voltage you want. Furthermore, the regulated voltage stays "exactly what you want" even if sometimes the device draws more current and sometimes it draws less current. An unregulated supply would have lots more ripple, and would change in voltage according to how much current the device draws at any particular time.

But the voltage drop thru the regulating transistor generates heat. For example if you have unregulated 16 volts and you turn it into regulated 12 volts, that is a 4 volt drop thru the transistor. If you need 3 amps, then the transistor dumps 3 amps * 4 volts = 12 watts of heat. Doesn't sound like a lot, but it will eventually get rather hot unless you use a pretty big heatsink. Even better to put a little fan on the heatsink. Seal up a small 12 watt incandescent light bulb inside an aluminum chassis and see how hot the box gets after awhile.

Also, only a 4 volt drop might be over-optimistic. I think if you want a linear regulator with very small drop, the transformer would need to be bigger, more expensive, over-spec'd so that heavy current draw doesn't drastically pull down the unregulated voltage. To use a smaller cheaper transformer you probably need to use a bigger voltage drop and generate more waste heat.

Switchers are vastly more efficient and also do not need as big a transformer. If I were to do any more electronics, would use linear regulators for up to maybe a half amp, but bite the bullet and use switchers for higher-current demands.

[miketurn]

Just typed a whole bunch only to have my browser randomly select a link or two and erased it all
Only happens to me when I type a ton, never when I just have a couple of words typed!

I get a little confused because I tend to be looking at amplifier classes as school grades.
The benefits of type D sound actually pretty nice (weight/heat/etc.) but if they are only benefits for larger wattage amps as @annode I believe is mentioning, then that would mean that those amps are chosen for more cost issues, that is disappointing, slightly understandable, but still disappointing.

@JCJR
Funny you mention about the possibility of using a separate amp and speakers.
I was going to make a thread about this, but in doing some research, figured a thread wouldn't be needed, at least for me.

As far as using two passive speakers and amp, I looked around and oddly couldn't seem to find any 5" passive studio monitors. Also I wouldn't know how to pair an amp with the speakers and would imagine that between the monitors and a pretty good amp, it would probably be pretty expensive for me.

Would be an expensive piece of gear, but it would be cool to have a all-in-one kind of a unit
preamp-audio interface-monitor amp.

[miketurn]

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