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[Mark Wilkinson]

A standardized frequency response "target" would be nice. Say 35-100 hz +-3db curve? The Max output rating would have to stay within the window and below a certain threshold of distortion and however many decibels you can make with XXX sub is how loud it would get.  It wouldn't matter what kind of processing or how much power it takes to get there. Either it will do it or it won't.

Very much agree, Tim.  It would be great to at least have some kind of disclosed window in place.

[Ivan Beaver]

With all due respect, I think it gets alot easier than your example, if we just stick to measurements for discussing sensitivity and max output.
Besides, the second we start talking wattage ratings to determine max output, it's becomes all bogus anyway...

For sensitivity, I could live with a single number...if that number was simply SPL vs a reference voltage (like you guys do).....and if that voltage and SPL were time-averaged to get a stable look while using band limited pink. I'd also ask for measured average current over the same period, for a more meaningful nominal impedance spec.

I'd say let the manufacturer choose whatever bandpass he wants to claim for the intended use....just discose the exact HP and LP filters being used.
This would help keep the low end f-3 more realistic, as using an unobtainable f-3 would lower the measured SPL vs the reference voltage. The sensitivity spec would suffer from claiming too low a response.
If a manufacturer wants to include peaking or other filters in their processing, fine, just disclose them.
But even if they weren't disclosed, if sensitivity was simply measured as proposed,  a 10db boost like you mentioned, would require a corresponding drop in overall voltage level to keep the reference voltage intact. So again, the sensitivity spec would suffer, once again forcing the manufacturer to be a little more circumspect.

Max output could be measured using the exact same filters in place, for both short term max output and AES time ratings. 
Just measure average voltage, current, and SPL, ....cold, and then at the end of long term time trials. 
Comparing short term cold and AES, would give us real world compression too.

Take this relatively simple method for measuring both sensitivity and max output, and throw in raw magnitude and phase curves, along with cold and hot impedance sweeps....and damn, we'd have some really useful disclosure huh?  Who knows, distortion could possibly even make it to the specification's table someday if we could get off to a new start

So what if I just list some freq response I would like to claim the cabinet has.

Then find a point in the response that has an impedance peak.

Then put a nice big boost at that freq and drive the level up and simply use an SPL meter.

Then measure the voltage-and base the power on some minimum impedance.

That would give a really high MEASURED SPL.

Of course the freq response would not be anywhere near flat, but it WOULD measure that SPL.

The sensitivity and -3dB points and applied voltage MUST be all tied together or else non of them mean anything useful.

It is real easy to say "measure the peak SPL", but there are all kinds of ways to high numbers that are useless in actual usage.

There is one very well respected manufacturer who claims a very high SPL for one of their floor wedges.

But when you look at their data in EASE, you will see that the  "claimed SPL" is only around 1300Hz.  Above and below that, the level is 10dB lower.

So that "peak SPL" is nothing but a peak in the response and COMPLETELY USELESS for a floor wedge.

But yet I have heard many people say that the "XYZ" wedge is louder than others and quote that peak SPL number as "fact".

But in reality, it is right where other premium wedges are in terms of SPL.

But people let that "simple single MEASURED" number somehow dictate the "truth"-at least as far as they are concerned.

That peak is not a lie, but not the truth-as far as people would like to believe.

You simply CANNOT use simple easy numbers to give factual-useful information on a complex subject.

[Cesar Acosta]

I know how hard that is with the Alto as nobody seems to have them in rental stock. Sometimes you can find things like a PRX718xlf, or a QSC kw118 and use that. Then read online, first hand reviews to see how the Black would compare against those two subs.

I'm the only person in my town that is using Alto speakers (as far as I know). No one knows the brand here, they mainly only use JBL, QSC and Yorkville. Nobody wants to take a chance on anything else. It's also quite a small town and we don't even have any stores that sell pro audio equipment; I have to order everything online. So going to a store to try them out, or renting any equipment is not really an option for me :-/

I did read a lot of reviews, look at the specs sheet (which seems quite comprehensive, compared to others I saw) and watch as many videos as I could find before I decided to purchase these speakers. They have surprised me and everyone that has heard them. Especially since no one here ever heard of the brand.

I've seen videos of people comparing the Alto subs with QSC, JBLs and such, and they say they are right up there with them.

Just as clarification: I don't watch the videos to hear the speakers, just to hear what the people that actually use them think about them. Just thought I'd say it before I stir something up in here lol (like with the peak watts xD).

[Rob Spence]

I'm the only person in my town that is using Alto speakers (as far as I know). No one knows the brand here, they mainly only use JBL, QSC and Yorkville. Nobody wants to take a chance on anything else. It's also quite a small town and we don't even have any stores that sell pro audio equipment; I have to order everything online. So going to a store to try them out, or renting any equipment is not really an option for me :-/

I did read a lot of reviews, look at the specs sheet (which seems quite comprehensive, compared to others I saw) and watch as many videos as I could find before I decided to purchase these speakers. They have surprised me and everyone that has heard them. Especially since no one here ever heard of the brand.

I've seen videos of people comparing the Alto subs with QSC, JBLs and such, and they say they are right up there with them.

Just as clarification: I don't watch the videos to hear the speakers, just to hear what the people that actually use them think about them. Just thought I'd say it before I stir something up in here lol (like with the peak watts xD).

When watching reviews, pay attention to who is sponsoring them. If the vendor, they are only publishing positive ones.



Sent from my iPad using Tapatalk HD

[Mark Wilkinson]

You simply CANNOT use simple easy numbers to give factual-useful information on a complex subject.

I must still respectfully disagree....a simple number, if honestly produced, can have very useful information IMHO

The two examples you posed are both based on deliberate dishonesty.
 
The first example jacks boost at an impedance maxima, and then quotes specs built around impedance minima.
A honest measurement wouldn't boost like that to begin with, and would use measured nominal impedance to extrapolate specs from.

The second example, as you point out,  chooses single point peak, again deliberately providing misleading information.
Using the speakers' entire intended passpand would eliminate the possibility of choosing a single peak like that.
And pls note, I haven't used the term 'peak'...I've been sticking with 'max output'  in regard to continious output.

When I measured my subs sensitivity a few months ago, I asked myself
"what do i really want to know and is there a single number that lets me compare two different subs?"
 
I said sure, .....if I compare identical passbands of intended use.
So I came up with the time averaged SPL vs Vrms vs measured nominal impedance approach.

And that approach still makes good sense to me. It's the best single number I can think of wanting to have or give.

Recently I stumbled on a highly regarded speaker designer advocating the same approach for max output specs, a designer you're rather familiar with    I hadn't thought of using the bandpassed pink approach for anything other than sensitivity; it was nice to see some validation in the approach and learn how it could be used further.

Here's a snip specifically about measuring max output ....

"The logical approach (I would like to think
it is anyway) to rate a loudspeaker would be to present the speaker with a band limited
(limited to the actual frequency range of operation) pink noise signal.

Then (per AES) drive the system to the maximum level it can withstand (and lasts for the
required 2 or 24 hours) and then at the end, measure the average Voltage and average
Current. This equals the real Volt Amps the speaker was being driven with. Measuring
the difference in the V&I and SPL at the beginning -VS- the end of the test would also
show the effect of power compression. Such measurements do require a fancy integrating
volt meter (dealing with pink noise) but they are easy to get now days."

Here's the entire post for others interested in this stuff, buried somehere in the Lab Archives, that i found delightfully aboveboard...

"Subject:    Real power handling

hi
No, they take the same amount of heat, the electrical power is what is different.
In the last update I touched on the "power" rating of the system and the things which
change it. Mark went further but still there is more that should be said to put "power"
in perspective. In electronic engineering the word Watt has a specific meaning, 1 Watt
is 1 / 746 horsepower, 1 Watt is the heat dissipated in a 1 Ohm resistor connected to a
1 Volt source. Wattage is a specification of power and both have a specific definition
in the electronics world which is unambiguous.

Loud speakers unfortunately also use the term Wattage and power but unlike everywhere
else, these figures have only an ever so slight relationship to the Wattage and power
terms as they understood and used in every other area. The AES amd other technical
groups have established measurement standards in an effort to eliminate the ridiculous
figures that manufacturers had been using in marketing back in the 70's-80's which
allowed say an amplifier that actually put out 40 Watts RMS. to be rated at "800 Watts
peak integrated music power".

While those standards did reduce the fully imaginary numbers that many marketing depts.
used (more is better you know), the tests were still not very good at describing the
loudspeaker. The typical woofer has 2 main limits, one being the limit of linear
excursion which is the point that the harmonic distortion rapidly increases and reflects
the motor non linearity as the coil begins to leave the gap. The second is thermal set
by the maximum temperature the VC can handle without failing over the test period.
I believe I have allowed for sufficient excursion that distortion / excursion limits
will not be an issue on the lab sub.

The heating of a driver is set by the current flowing across the "loss" part of the load,
this is the DC resistance in a speaker motor. The logical approach (I would like to think
it is anyway) to rate a loudspeaker would be to present the speaker with a band limited
(limited to the actual frequency range of operation) pink noise signal.

Then (per AES) drive the system to the maximum level it can withstand (and lasts for the
required 2 or 24 hours) and then at the end, measure the average Voltage and average
Current. This equals the real Volt Amps the speaker was being driven with. Measuring
the difference in the V&I and SPL at the beginning -VS- the end of the test would also
show the effect of power compression. Such measurements do require a fancy integrating
volt meter (dealing with pink noise) but they are easy to get now days.

It is obvious however to anyone who has studied the curious situation in loudspeaker
specifications that loudspeaker mfr.'s are not interested in "Actual" numbers, the "more
is better" mentality is hard to shake especially since the public has been taught to see
it that way.

Rather than the direct logical measurement I described, loudspeakers are measured in a
rather different way. The impedance is measured with the driver "cold" and the lowest
point found, this becomes the "reference impedance". The speaker is driven with a pink
noise signal, band limited, starting at the low cutoff (usually) and extending to 500 Hz
or a decade depending. For a subwoofer, measuring a couple octaves above the actual upper
frequency limit can result in higher sensitivity
figures and higher power handling numbers even though they can be way off in the
frequency of actual operation. This has been one of Barry's rants, if one wants to
compare subwoofers, one must be comparing measurements at the same frequencies,
sensitivity at 300 Hz does not tell anything about what happens at 30 Hz. When comparing
the LAB sub to others, compare it only at subwoofer frequencies.

As for the "power" remember the heating is current squared divided by Rdc, the current
flowing is set by the voltage input divided by the impedance with total being that
integrated over the entire frequency range. Going "up high" in frequency then includes
the inductive roll off, where the impedance of the driver climbs, reducing the current
flow and power delivered. Using R minimum as the reference impedance also does not
include that fact that at ALL other frequencies, the impedance is higher so less current
(and power) is flowing at all other frequencies.

Not only that, but as soon as the Coil heats up at all, the resistance rises and then the
current falls, at maximum power it is not uncommon to have had the DC resistance well
more than doubled at "rated power". After raising the voltage to the point where the
driver has survived intact for 2 Hr. (or 24 depending who's rules you follow) the final
input voltage is divided by the reference impedance and then times the input voltage to
get "power".

As one can imagine this figure may be 2,3,4, 5 times greater than the "REAL" Wattage but
alas this is the custom. Like distortion, they figure "you can't handle the truth" or
something silly.

You will notice also that most amplifier mfr.'s have adapted to the imaginary Wattage
scheme loudspeakers use by eliminating anything that would indicated the output power or
voltage except to say "blink" you are clipping or that you are within 1/100 of rated
power. With electronics being so cheap, it would be easy to go back to having power
meters on amplifiers, even real peak and average indicators are easy. Ask your self why
there is nothing to indicate the real power?

The problem is, even if you use a more realistic method (like we did on the BT-7) and are
willing to accept the lower numbers, the problem remains that the rated power is still
going to depend on what one does with the driver, this governs its impedance curve.

For example for a sub woofer, a driver in a vented box will measure a lower electrical
power capacity than the same driver in a sealed box because in the vented box the
impedance is lower on average and so draws more current at a fixed V input (assuming
both had enough excursion capacity).

In an efficient horn, the load impedance may be 2 times the driver resistance so the
current is cut in half for a given voltage and since it is current squared divided by
R, the heating is reduced to 1/4 the old value. With the LAB horns, like all other bass
horns, the measured power capacity, efficiency and response will change depending on the
number of units used. The predicted impedance for 6 units for example suggest that the
power capacity will be several times the normal rating for the drivers.

I have been honest about what I see here, in real life, until a system is set up and
driven to its death, the actual power capacity will not really be known.

Cheers,

tom "

[Marjan Milosevic]

Mark, real problem is that most of todays spec are misleading. Not to say false.
Was just checking the spec of one of the lastest releases of the M-force based sub.
It says in the spec, operational bandwidth 25-90hz.
What does that means?
Then i checked the graph, 25hz is at -16db point.
So, one simple number is pretty much useless data in todays spec war.

[Ivan Beaver]

I must still respectfully disagree....a simple number, if honestly produced, can have very useful information IMHO

The two examples you posed are both based on deliberate dishonesty.
 

Agreed.  I was just pointing out some things that can be done.

One of the little issues that I have with using pink noise as the stimuli is how to measure a dynamic signal.

The integration time of the meter used will affect the reading.

Choose a meter and read a pink noise signal.  Now choose a different brand meter and another.

You will most likely get different readings.  They should all be "in the ball park" but different.

The same thing goes with both analog and digital SPL meters.

So when you compare the differences in volt meters and SPL meters, you have a decent size of variables.

Unless different loudspeakers are measured with the SAME MODEL test gear and under the same circumstances, the results will be different.

And let's say you "band limit" the signal.  Unless the same freq band is used, the voltage and SPL will be different.

The one with the wider band will produce greater voltage/SPL.

But it also produces more heating on the voice coil.  So it is advantageous to use a narrow freq range for power capacity and a wider freq range for SPL output.

And I see no way to you would be able to get all loudspeaker manufacturers to use exactly the same gear and methods.  They will argue that the particular test does not represent what their particular product does.

Let's say that one sub can legitimately go 10Hz lower than another.  Does the test allow for a lower HP filter?  Knowing that it will produce greater SPL?  That is "not far" when comparing to a speaker that doesn't go as low.

Where is the HP filter set?  At the -3dB point?  How is the -3dB point determined?  Is that with processing or without?

3dB down from WHAT?  A peak in the response (that gives a higher sensitivity number)?   An average in the response?  How is that average determined?

Or (as in some cases)  the -3dB point is 3 dB down from the +/-3dB "window" that means that the manufacturer can choose a point that is -6dB down.  So the "-3dB" is actually 6+3=9dB down-NOT 3dB down.

It is a very difficult subject with no simple answers.

Or it is pretty simple-as long as you don't look at other possibilities.

[Mark Wilkinson]

Mark, real problem is that most of todays spec are misleading. Not to say false.
Was just checking the spec of one of the lastest releases of the M-force based sub.
It says in the spec, operational bandwidth 25-90hz.
What does that means?
Then i checked the graph, 25hz is at -16db point.
So, one simple number is pretty much useless data in todays spec war.

Hi Marjan, yes, agree and understand.

I think a big part of what makes sub specs misleading is that operational bandwidth, sensitivity, and max output are all usually quoted independent of each other.  There's no common denominator tying them together to keep the specs relative to one another.

That's where I think using the same bandwidth pink for all three specs would provide much greater reality.

For instance, if sub manufacturers had to show sensitivity as determined over the claimed operational bandwidth that was -18dB in the low corner, the sensitivity would no doubt look pretty shitty.

Likewise, max spl couldn't be cherry picked by either out-of-band or even in-band frequency selection. It would have to represent the entire band of intended use.

[Mark Wilkinson]

Agreed.  I was just pointing out some things that can be done.

One of the little issues that I have with using pink noise as the stimuli is how to measure a dynamic signal.

The integration time of the meter used will affect the reading.


So when you compare the differences in volt meters and SPL meters, you have a decent size of variables.


But it also produces more heating on the voice coil.  So it is advantageous to use a narrow freq range for power capacity and a wider freq range for SPL output.



Where is the HP filter set?  At the -3dB point?  How is the -3dB point determined?  Is that with processing or without?

hi Ivan,

As far as the integration time of the meter, there I think you just take an average of V,I, and SPL over a minute or two.

Variability between meters ?  I have no experience here, but I take Tom's comment that integrating meters are pretty easy to come by as evidence variability isn't too big a deal..  But again, I sure as hell don't know..

I completely agree with you about manufacturers wanting to use different frequency ranges to make sensitivity and max output each look their best.
That is exactly what I'd suggest is most misleading about the specs, and would be elimnated by making the frequency bandpass be the same for both specs.


Last, I'd say let each manufacturer choose whatever bandwidth they want for each individual product.....I mean, products are made for different operational bandwidths. 
ONLY they have to use that bandwidth for both sensitivity and max output, and disclose the actual HP and LP filters in place.

If they want to show specs with additional processing beyond just HP and LP, fine.  Just show another set of sensitivity and max output numbers, along with the exact filters used.

The nuts of it is....using the same band-passed pink of the intended range of operation and making all specifications is not that hard,
and would provide orders of magnitude better information, even in the form of a single number.
This gets closer to real world,.... intended operational bandwidth, filters being used, and specs that tie together.
At a minimum, using band-passed pink for the specs is certainly a giant step forward from the willy-nilly  methodology commonly being used.

IMHO, sometimes simplicity is very valuable, despite all the unaddressed variables...... 

[John Roberts {JR}]

In an ideal(?) world we would measure all speakers with this one standardized test criteria. This would indeed give us comparable numbers (for that specific test criteria).  Next the loudspeaker designers, using that single test criteria as the benchmark, would target their new designs to rock that one test......  But, the reason there are different speakers is because customers have different needs, or different criteria they want optimized.

The major sin is of omission, not fully documenting the sundry qualifications. As you can imagine to fully and accurately describe these test procedures is more than a few words in passing.

I have long advocated, not second guessing the design engineers, but buying already engineered systems, designed by people who understand what the specs mean. For the small fraction who must stand with one foot in that world (you know who you are), it is worthwhile investing the effort to understand the specification qualifications.

Lacking a full understanding of how to read specifications, we can read anecdotal reports from people who bought these different boxes and used them for similar applications.

JR

PS: In this modern internet age there is no reason why specifications could not link to a full detailed specification with documented test procedures. That said I doubt today's customers will ever invest the time and effort to understand (I'm still waiting for marketers to fully understand). So this returns to the classic "trust me, I wouldn't lie to you"  .

 

[ProSoundWeb Community]