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Author Topic: The O so impossible 20hz!  (Read 13607 times)

John Roberts {JR}

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Re: The O so impossible 20hz!
« Reply #40 on: March 03, 2006, 02:41:47 pm »

Tom Danley wrote on Fri, 03 March 2006 11:19

Hi Joe

You have hit on one of the more “sad” situations in audio, many of the largest companies seem to participate too (I.M.O.)
On the other hand, you have to understand, this isn’t like medicine where a life in the balance and you get in trouble for selling “BS” (alternately, Bad Sound).  
If you were a Madison Ave. type, knowing that the average buyer goes by numbers and reputation what would you do?  
I mean if by careful presentation, one could give the impression that your product were 10 or 100 or more times more powerful that it really was, would you present the numbers that way?  
Obviously artful presentation is cheaper than R&D or a new idea and that leaves more budget for building a reputation through advertising & image building etc.

A few common practices, which I think, are questionable.

For example, by measuring a subwoofer to several hundred Hz or even higher, one can get a much higher sensitivity than is present in the subwoofer range (where it is used).
This is a common practice.
By stating a 1 Meter sensitivity as an unqualified number, one is in theory providing the output of the speaker where its used, based on input power and response, yet this common practice essentially negates this possibility of this being accurate.
A similar situation is often true for what + - 3 dB and – 10dB means when you measure real products and compare to the data sheets.

By stating a sensitivity as above and using DSP or EQ to correct the response, one takes a step further from knowing how much the speaker can do.
Take the case of an imaginary speaker.
It has a sensitivity of 110dB 1 W 1M, (which is the figure at its highest at 400Hz).
At 40Hz, lets say it is really 95dB, a mere 15 dB less or 1/30 the output of what the spec would suggest.
So now one see’s a measured response flat to 40Hz and stated sensitivity of 110dB one assumes that with a rated 1000W, one could get to 30dB + 110dB = 140dB.
Most companies go on to assume that since the rated power pink noise signal has peaks that are +6 over the average level, that the peak output is 146 dB, see, all the math adds up.

In reality, assuming no excursion limiting or power compression, you really have 95dB + 30dB for a maximum output of 125 dB at 40Hz and if one actually measures the real SPL with a peak hold meter, one finds the actual peak SPL is usually around 1/100  the acoustic power one calcualtes.
Again, this is the common, if they are honest, they will say Max SPL “calculated”.

Your right too, room for these “errors” largely goes away “IF” a measured response curve is given, made in standard repeatable condition.  
It makes it easy to look at any frequency and say “the sensitivity at 40Hz is X” and the –3 dB point is Y.
The reason this is not the norm in what otherwise likes to think of itself, as a “technical industry” is pretty obvious, the room for this kind of monkey business goes away.

Tom Danley




At the risk of sounding like an apologist for the status quo or diverting the blame away from the merchandiser.... consumers by their buying behavior strongly reward such questionable marketing practices.

In most cases the consumers don't posses the skill set to properly evaluate raw specifications or much interest to acquire those skills. In general they will buy what they perceive is a good value based on a historical reputation and a superficial comparison of some presumably comparable specifications.

I believe all reputable (?) companies invest time and energy in trying to present meaningful, comparable specs. There is often a catch 22 where companies are afraid (for good reason) to look like they losing in a direct comparison to a major competitor. While a  salesman who is prepared with supporting explanations and a customer willing to listen can overcome such apparent but not real misses on a specification, in the larger flow of business the opportunity to educate and correct such flawed interpretations rarely presents.

The manufacturer to survive must both make an excellent product, and do make sure the product also "looks good" in spec sheet comparisons. This can become a circular finger pointing exercise with few willing to be the lonely, and sure to lose sales, honest man. This can be even harder for companies with solid engineering but a weaker reputation. In that case presenting specifications more conservatively than competitors will surely be interpreted as a lesser performing product.

In the case of transducers (speakers and microphones) being able to evaluate specifications is IMO rather important as these are the weakest link in SR. Even the best loudspeakers involve engineering tradeoffs or compromises to dial in the loudspeaker for a target application. i.e. a great studio monitor, is different than a  great FOH cabinet for solo use, vs FOH cabinets for arraying... etc.

Consumers are advised to invest what little attention span they are willing to spend on learning about loudspeaker tradeoffs and how to read specifications important for their applications. IMO this will be far better use of their precious (to them) time than yet another un-scientific power amp, or mic preamp shootout.

Stepping down from soapbox now.

JR

PS: BTW, a good start is to read every word written by Mr. Danley.        
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Joe Jones

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Re: The O so impossible 20hz!
« Reply #41 on: March 03, 2006, 03:15:11 pm »


Quote:

Joe, that's the idea of this forum. Most of us are interested in subs that don't require such radical processing. The idea is for the cabinet to do all the work, not the woofer. It's not difficult with today's technology to take any box with a woofer that can pass 20hz (even at 15db down) and smooth out the response to a +/-1db flat line, but you give up so much in dynamic range that it's not very practical for serious applications, not to mention the fact that you'll be beating the crap out of the woofer.


Duane, you should go back a ways and re-read the thread, especially this:
Quote:

Yes well you must have missed one of the replies where i said the bedroom its going in is about 14'x 16' haha


I agree that you do have to use the right tool for the job at hand, that's why I gig with four Tuba 36s, but I'm sure not going to use them in my livingroom, which is about the same size as his. I thought the idea of this forum was to offer advice, and I don't think that should be limited to telling the guy he has to put four Labs in his bedroom or that he can only get what he wants by spending two thousand bucks. Other options exist.    
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Duane Massey

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Re: The O so impossible 20hz!
« Reply #42 on: March 03, 2006, 04:37:40 pm »

Sorry if I missed the point of your post, Joe; I agree that a subwoofer in someone's bedroom is not the same animal as a touring system. Normally I'm the guy who suggest moderation in selecting the proper piece of gear.
I would agree that most manufacturers do go to a great deal of time and expense to document their products, but there has been a common tendency to omit the less-flattering numbers and "dumbing-down" the printed specs. There is no industry standard, and never has been. Even the 1w/1m is suspect, because there is really not a common way of measuring this.
That's one of the benefits I am gaining from this forum; I will be doing some testing on some cabinets in the next 3-4 weeks, and I will be asking for suggestions on what methods are preferred by most sound people.  Numbers don't mean a whole lot if you can't compare the same test results.
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Duane Massey
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