WATTS DON’T DO WHAT YOU THINK!!

Kind of a bold statement, don’t you think?  But do you ACTUALLY know what watts are???  Watts (at least in audio) is voltage across a load. AC volts to be specific.  And the load, in our case, is a speaker.  But ya know speakers AREN’T resistors.  Speakers are actually a complex circuit that is called an “inductive/capacitate/reactive load”.  (SEE BELOW)

Speaker as a Circuit

You’re going “Come on they’re just a speaker”.  Trust me it is way more complicated than that.  I wish it was that simple, but it’s not.  The best way to learn and understand is too see (read) about REAL stories REAL-WORLD and how to all “plays” out.

So here is a true story.   This is WATTS and BASS in REAL-WORLD, and how why having MORE watts doesn’t fix the lack of bass (The “It DON’T Hit” syndrome !!! …… more on that later):

How many times have you, a friend or a customer complained that they have TOO MUCH BASS in their car audio system!!!!!

NEVER! Or Once? Maybe twice…in your lifetime.!!

And how many times have you, or any of your friends or customers complain that they don’t have ENOUGH bass??

1,000’s of time (millions of times!!!  )

Add to that all the cars now that have SUPER sealed trunks, MBZ, BMW, Lexus, etc.  With these types of vehicles we have some REAL issues

In MOST vehicles if you want MORE bass you either add LOTS of power, OR lots of woofer(s).   Not a little more – (remember the 3dB rule.  The MINIMUM power increase is DOUBLE (3dB) to hear ANY level difference, so you really need more like 6-10 dB more power (or roughly 4-10 times!!!) to REALLY hear any level difference especially below 100Hz,  and, of course, ya gotta use those BIG A#S woofers that can handle that power (that’s all pretty cheap? right???.)

BigA@#Woofer

$3,400.00 and 82 pounds worth of BIG A#S Woofer!!!

Think you’r gonna drive this woofer with 500 watts or 1,000?  Or even 2,000 watts? Don’t think so!!!  Unfortunately energy is NOT FREE!! For every 1,000 watts of D class sub amplifier it will gobble up 116 amps of current (or within 5% of those 116 amps). Based on 30 yrs of dealing with car audio amplifiers and testing thousands of them (go here to the Everyday Formula page).

So…let’s take a REAL world situation. Consumer has a BMW 535. Cool car, dealer does an Audison LRx5.1K. (my favorite amplifier of all time!!) Our dealer put in a JL12w3 into a small sealed enclosure and built this really cool fiberglassed molded enclosure into the side of the trunk. Looked great. Sounded great.

Issue was the customer came back a month later (stop me if you’ve heard this before) and said “…it just doesn’t HIT like it use too!” (I think the correct term he used was it “lost bass”)

The dealer/installer told me this story and of course I responded with “OK…I’ll bite…how hard DO IT HIT???” (i.e; how much bass WAS there and how much was “lost”???) Do we know how much it had when it left?  In other words do we have ANY scientific information other than “It used to have more bass”.(this is part of the It DON’T Hit ” syndrome I keep speaking of)

NOOOOOOOO!!!!!!! Of course not!

So I asked him to go measure how hard it hits. He’s like? huh!??  What does that mean?  And how do I do that?

I said, just go measure the peak AC volts coming out of the sub channel with your handy dandy DMM (fancy name for a volt meter). Just use the most vicious bass discs the
customer has (I am SURE he has something, just a guess )

AC Voltage Test

SIMPLE AC VOLTAGE TEST

He called me back and said ” this can’t be right??”. I said “How many volts out peak did you get??   He said “63 Volts into a 2 ohm load” (just a note this woofer has dual 4 ohm voice coils, hence paralleled it is now a 2 ohm woofer).

I said, “yep that is what I have seen before.” He goes “that’s crazy! That’s 63 volts squared divided by the impedance ( 2 ohms) to calculate power. Right??”

I said YEP!! That it is. So, once you do the simply calculation,  that means the sub channel is making peaks of 1984 watts. (remember the formula for calculating power is AC volts squared divided by impedance)

He’s like “wholly Shit Batman! Shouldn’t it be louder?”  My response – Ahh NOT in a BMW it won’t!

That trunk is SO.oo sealed you’re lucky you get any bass out of it at all.  It isn’t simply that it is a BMW, it is the trunk is SEALED is the problem.  Doesn’t matter the “make” or model of vehicle.  SEALED is the issue.

The consumers issue is he wants MORE than a small sealed box will give. In other words he does NOT have realistic expectations!!   Actually he doesn’t care what the problem is.  He spent good money and he FEELS it should have more bass.     And his car is the REAL problem (how sealed the trunk is)  Not the amplifier…NOT the woofer

Again. I know that NONE of you have ever experienced that…EVER..in your own car or if you’re a retailer in your shop with your customers.

Yeah…Uh Huh!! (liar liar…pants on fire!!!)

Somehow someone thinks that thru magic (or pixie dust) this amplifier and sub woofer combo in this BMW trunk are going to defeat physics.

Don’t think so!!

How much SD (surface area) does this driver have? And Xmax mechanical (meaning how far can it move in the magnetic “gap”? That and the thermal dissipation of the voice coil will limit the output. No matter HOW MANY WATTS you shove into it! Check out the video below for XMax (mechanical limits of the driver)  notice the little white dot on the cone of this woofer?  Watch how far it moves with bass put into it.  Now remember that this woofer has no enclosure so it will travel quite far.  This little woofer can really move.  BUT…its a 6.5 inch woofer.  It ONLY has some much surface area (SD)  If we would put a DMM on this woofer and test the AC volts in when it goes to maximum excursion we will know the limits of the woofer.  PERIOD.  It will ONLY play so loud because it can ONLY move so far…AND it ONLY has some much surface area.  Its like drag racing.  There AIN’T no substitute for cubic inches, There AIN’T no substitute for cone area!!  A 15 inch woofer plays louder than a 12  inch woofer, assuming all things equal. And a 12 inch plays louder than a 10 inch, and so on and so forth.

My guess is at about 600-800 watts we are at X mechanical on this driver. And probably the thermal limit of the driver. So sticking more power (and how much would we need to make ANY difference, theoretically??- 3 dB. MINIMUM!! Right? )

 

Or double power… so that would be 3800 watts. We really need 6 dB to have any REAL audio difference or 7,600 watts which equals about 886 amps of current draw. So now you need double maybe triple alternators and more batteries. Yeah that was cheap..on a brand new BMW 535.

Plus it wouldn’t do anything! Just burn up the woofer because the current power output (1984 watts) is already at double the thermal dissipation of the voice coil and we were at Xmax already. There isn’t any more to be had.  You’re at XMAX and THERMAL limitations of the driver.

So he asked me “what do I have to do to get more bass output?”

I responded with “4th order BandPass and load all the energy INTO The cabin of the car.  That way you’re NOT just beating up the trunk with bass, the bass is going DIRECTLY into the cabin area (interior)”.

So I designed him a box, he built it and called me back.

“WHOOLY F$#K! This plays WAY louder” he tells me.

OK I said…how much harder Do it play ( How HARD do it hit!!!) 10 dB more output he said

WOW! Not a little louder. 10 TIMES louder!!!! 

So keeping the same amplifier, and just changing the type of enclosure bought this consumer 10 times more output!  Or like going from a 1,000 watt amplifier to 10,000 watt amplifier!!!

Same car, same amplifier, same woofer…different enclosure!!

(Physics!!….. ain’t it a wonderful thing!!)