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THD measurement in Logitech Z680 and Klipsch Promedia 5.1s?

L

Lore

Diamond Member
Hey all:

I was reading the specifications on the Klipsch Promedia 5.1s and noticed that they have less than 1% THD @ the maximum burst power of 500watts (Yes, I know, this is not the same as the RMS measurement used by Logitech but this question has nothing to do with that).

The Logitech Z680s, on the other hand, state in the manual that they have a 10% THD @ 450 watts RMS (if I remember correctly). I also remember someone mentioning that the Creative 510 speakers also have the same amount of THD @ full power.

My question - why is there such a discrepancy with the specs? Why is Klipsch listing only 1% when their competition is listing 10%? Are the Klipsch speakers _really_ that clean?

Thanks!
 
Yeah, I've got one. I don't think your manuals are telling the truth. THD above .1% is audible and unacceptible in current amplifiers. I have a set of Klipsch 4.1's, and they say 0.1% under THD in the manual. I have a buddy with a set of Klipsch 5.1's, and his say 0.05%. I have a Sony surround sound receiver, and it's rated 0.09%.

It looks to me as if somebody misplaced a dot. If you bought an amp that had 10% THD, it would sound like crap!
 
I was kind of hoping that someone here would have the Z680 manual on hand to look at the specifications... I'm not sure why they would be so different, and I'm pretty sure it would sound like crap if they were at 10%!!

So, if anyone has the manual handy, please quote the page for us!
 
I checked the manual, and this is what it says:

Subwoofer amplifier power: 185 watts at 10% clipping THD at 100Hz long term RMS into 8 ohms
Satellite amplifier power: 5 x 53 watts at 10% clipping THD at 1KHz long term RMS into 8 ohms

Interesting ... is there a difference between normal THD and clipping THD?

edit: OH WAIT... at the bottom of that it says: "System Distortion: Better than 0.01% THD before clipping" --> how is this measurement different than the other stuff?
 
Actually, THDs below 1% are quite inaudible, and some people can't even tell much of a difference up to 10%. Still, most decent audio electronics today have THD way less than 1%, more in the range of 0.1% or less. However, it depends on how you measure it. THD can be measured in such a wide range of environments that it can't really be compared directly unless you know exactly the conditions of measurements. Some of the factors include frequency range of measurement, any weighting done(A-weighting being the most common), power output when measuring, whether at peak, burst or nominal, load(speaker impedance) during measurement, etc...
 
Sure, but why are there two different THD ratings? One for "before clipping" and one for each of the speakers?
 
When amps clip, the signal is modified dramatically(higher THD). Not because of the quality of the components but because of the power output capability.
 
They probably measure the power when it clips 10% to increase the power rating of the speakers. Clipping is what happens when you drive your amplifiers beyond what they are capable of producing. Instead of the amplified signal, when you get is a clipped signal where the amplitude is cropped off at the top and bottom. So, if you were to amplify a sine wave beyond what an amp is capable of, the signal will clip and what you end up getting is something resembling a square wave. This is very harmful to your speakers especially since they'd have to move like crazy to produce the square wave and might just blow.
 
Originally posted by: Goi
They probably measure the power when it clips 10% to increase the power rating of the speakers. Clipping is what happens when you drive your amplifiers beyond what they are capable of producing. Instead of the amplified signal, when you get is a clipped signal where the amplitude is cropped off at the top and bottom. So, if you were to amplify a sine wave beyond what an amp is capable of, the signal will clip and what you end up getting is something resembling a square wave. This is very harmful to your speakers especially since they'd have to move like crazy to produce the square wave and might just blow.
Click to expand...

So let me see if I got this right.

THD is essentially clipping, and the percentage that they state is the amount of clipping that occurs. Therefore, at full "rated" power it's clipping at 10%. However, that still doesn't explain why there's a 0.1% rating for total system distortion. What level of playback is that at then?
 
Not quite. There is always THD, but not necessarily clipping. Most quality manufacturers state the maximum amount of RMS power the amplifier will produce while keeping the amount of THD a constant. (clipping shouldn't even be a factor here.) Adding in the value for clipping is kind of a trick (at least in my book.) And I really don't see why it's nessecessary for Logitech to state it this way since the speakers are so powerful anyway. My Klipsch's are so darn loud I have never heard clipping from them. Not saying they won't, I just never turn the volume up that high.
 
THD stands for "Total Harmonic Distortion". Harmonic distortion is one kind of distortion, there are other kinds, such as Inter Modulation Distortion(IMD), but THD is just the most popular one to list. Harmonic distortion occurs because no amp is clean enough to reproduce exactly the signal it receives. If you supply the amp with a clean 1KHz signal, it will amplify that signal, but the final amplified signal will consist of mostly 1KHz, but also some other frequencies, or "harmonics", at 2,3,4,5,6,...KHz. These values will be comparatively much much lower than the 1KHz amplified signal, but they are present. The total value of these harmonics, in comparison with the 1KHz signal, is measured by Total Harmonic Distortion(THD), either as a percentage or in dB. It has nothing to do with clipping, though clipping does increase every sort of distortion by a large degree due to the change in the final signal to a clipped one resembling a square wave.
 
Well, now I am thoroughly confused.

So those two specs that the manual lists, 10% THD at full power and 0.1% THD before system distortion - which one really counts? Should we only be concerned with the one that says 0.1% THD before system distortion, as that seems much more in range with the other speakers in this class.
 
So those two specs that the manual lists, 10% THD at full power and 0.1% THD before system distortion - which one really counts? Should we only be concerned with the one that says 0.1% THD before system distortion, as that seems much more in range with the other speakers in this class
Click to expand...

The "full power" rating probably means when its running at its max power, i.e. peak ratings, rather than continuous power. You should be more concerned about ratings taken at max continuous power(RMS power) rather than peak/burst power. Both count, but they count to different things.
 
since ur interested in that, guess u might want to know more😛

"The second piece of marketese in the Z-560 specifications has to do with the abovementioned power output issue. Logitech make a big deal about the Z-560 system having 400 Absolutely Genuine Federal Trade Commission Authorised Totally Real RMS American Watts Baby. 188 watts for the sub, 53 watts for each satellite.

This is not true.

Well, OK, it could be true. If it is, though, the speakers should all blow up.

Point one - not enough amp power. No way is that a 400VA toroidal in the corner of the box. It'd have to be a bit beefier even than that, of course, because the amp isn't 100 per cent efficient. If it were, it wouldn't need a heat sink.

Point two - insufficiently chunky drivers, with embarrassingly low power ratings printed on them.

Such things as almost-200-watt eight inch drivers exist. If you want to cheat then you can make a zillion watt speaker by putting a crowbar across its input wires; now you can pump vast amounts of power through that speaker (if you define the crowbar as being part of the speaker...), and it won't make any more noise than it would from far less power without the crowbar. In other words, its efficiency is now astoundingly poor.

That's not what Logitech are doing; it's not what any sane speaker builder does. The drivers in these speakers have perfectly OK efficiency for their size. If the eight inch bass driver had an ultra-humungous magnet around a similarly huge voice coil and a unit retail price up around $AUD200, then it'd be plausible for it to have better than 150 watt power handling.

That's not the kind of driver that's in there, though. The back of the sub driver hides behind the huge bent port, but you can peer through the gap to see the mere hundred watt rating.

Similarly, I suppose it's possible to make a three inch mid/treble driver, like the ones in the Z-560 satellites, which can handle 53 watts. I don't know whether any such product actually exists on the retail market, but I'd be happy to learn otherwise.

Once again, though, that's not what Logitech have actually used. 15 watts, people. A Tangband Speakers W3-665SC, to be exact. Which isn't listed on the Tangband site; I just linked to that site out of malice.

Exceed the rated power handling by a significant margin for a significant period and you'll kill the driver. Unless the sticker ratings are very conservative, therefore, one 100 watt sub plus four 15 watt sats is 160 watts. QED.

The driver-peering also revealed that none of the Z-560 speakers contain any resonance-reducing damping material at all.
http://www.dansdata.com/speakersets.htm
 
You're confusing the specification. Since this is an amplified speaker product, THD specification is moot. Why? They're giving you the THD specification of the AMPLIFIER. You never see THD specifications on speakers because they are tenfold sometimes a HUNDRED times worse! Particularly in the bass range. Most woofers produce 10% HD and that's considered acceptable. A speaker system that can keep THD levels below 5% at full output is quite costly due to its design. Cheap cabinets colour the sound because they're inadequately braced. That folks, is just the beginning. 🙂

Cheers!
 
It's true what they say, that hearing is totally subjective and my contention is that, like used car salesmen, manufacturers and their marketing cohorts are capitalizing on the lack of object, clear, concise knowledge.

Example: I could read a book all about cross frequency components active, passive whatever. I like this aspect because it would allow me to adjust which drivers are covering which range of frequencies.. semi-infinite experimentation.. well, it'd keep me entertained for a while. [Search "how to build speaker..."]

Boston acoustics (captalized only because it's at the beginning of a sentence) uses one set of specs, another manufacturer uses another. I see all sorts of information from individuals that believe they have the key to helping everyone understand.

I submit a question in this foray; why do our purveyors of hardware, most especially speakers, refuse or demonstrate themselves to be so reluctant, in providing information. Clear, comparable specs, white papers, etc, and why do they refuse to communicate when queried? Like tell me what the advantage is in using 1 cubic foot of resonating space in a cylindrical aluminium enclosure have to do with sound quality. I just read that for a 10" subwoof it's suposed to be 10 cubic feet, and that the dimensions are important too, (it can't be 2" x 2" x 8'). And if you're reasonably serious about sound then you'll wonder why your box woofs and your neighbor's sings. [Musta been a sale on aluminium] what possible advantage is there in using an aluminium 'core' on a paper cone? money money money money...

Yall are showing me that when "joe" goes shopping for speakers, he believes he has to look for 'x' & 'y' stats. "Alfonsoe" thinks he should be priortizing "k" & "t" info.

Manufacturers totally capitalize on this by blurbing out their "high" points... "titanium...", "burnished and brushed anodized admantium...", "rectilinear parathorazic, burst buffering...", .000378% RFUS...., 10K input impedences, yadayadayadayada.

I've seen resellers put up the rinkydinky speaker displays but what about the more expensive systems? I'd like to hear 'em. I'd like to see exactly what pinning or input/output panels are available on some sets, but do they have the close up pictures or stats on web sites?

Why are you guys yacking yourselves to death rather than asking the manufacturer to explain why they do things this way or that. Make them accountable for your $$$ or why bother.

Brain dead and totally passive,
Rico
 

Why are you guys yacking yourselves to death rather than asking the manufacturer to explain why they do things this way or that. Make them accountable for your $$$ or why bother.
Click to expand...


Oh but I have... and gotten no response.

 
MY good person; In fact all good people...

Be you wolves in sheeps clothing, be you sheep in wolves clothing, be you scallywag, ursuper, poodlefaker or charlatan. Whether you are a gamer, fashion designer, hunter or web addict, who cares, whatever. You, we, deserve more respect and attention than this.

The callous negligent nature of a lot of vendors and manufacturers, the incomplete and disinformation; the intentionally missleading implications of compliance, superiority and certification, and perfection that fall short; the obvious halfaxed efforts, the pretence, the refusals of admission, the ommissions, or [heaven forbid] failures; the ongoing bullbit and pandering pacifications with intentions to quell the dissatisfaction,...

... instead of spending inordinate amounts of time to make sure we're not getting screwed, (a lot more time required if we want to make sure we get a good deal), and constant reminds to ourselves "buyer beware", ......

..why not reserve the right to refuse to spend obliviously, the right to question vendors, resellers and manufacturers endlessly and persistently and the rights to have easy and timely remedy if resistance is perceived. The rights to change and modify any of this and escalate as we see fit. We demand the rights of respect.

Are we allowed to exchange information about business entities and decide on action?

Eg. I just noticed that logitech can not afford the effort or space to offer technical specs of their old speaker lines....

"hurry, hurry, hurry up and upgrade, before we not only stop supporting it, but deny we ever made it"....

Sorry I am still so amazed at the ridiculous pricing of the z680's, the lack of useful features and most of all their concerted, contrived, mean-spirited lack of any response for questions (some technical others very general) I've had or ideas and suggestions.

It's Christmas ... hold those dollars back

Lock and load, ("pucker" don't work at mach2)
Rico
 
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