Speaker Spec's for dumbies

[theSeekerr]

Hi Philthy,

To be honest, most of what I know comes from pro audio (concerts and whatnot) rather than car audio. You're probably right that most car amp monoblocks these days are Class D - but that's a relatively recent development, since Class D has only been "mature" for about 5 years.

I think all the Jaycar "Response" amps are class D - and yes, they are, typically, an exception to the "you get what you pay for" rule. They sound fine, but I have heard reports of them failing from build quality issues - apparently the 2007 models were fine, the 2008 models broken. I haven't heard anything yet about the 2009 models, or whether they have even been updated this year.

The take-home message from most of my posts can be distilled to: It's never a bad thing to have too big an amp, and often a bad thing to have too small an amp, however, you probably don't need an amp as big as you thought you did in the first place, because you probably don't want to listen quite that loud. Put another way: 100 or 150 Watts RMS per channel is a good size to drive most speakers, and 500 Watts RMS is a good size to drive most subs.

Take the calculator I linked to a few posts back. Find a speaker, and plug in its efficiency figure. Then enter a quarter of your amplifier's RMS power, and a distance of 1m (which you'll have to convert to feet, sorry - I think it's about 3.28 feet). A 100 watt RMS amplifier, driving an ordinary speaker of 89dB/Watt sensitivity, will thus give you enough power for an average volume of 103dB, with peaks up to 109dB. That's pretty loud, and you can add another 3dB for the other speaker in the stereo pair.

 

[warney]

hope this helps :

General Information
*Terminology:
Impedance - The resistance of a load
Ohms - Main unit for Impedance
Watts - Main unit for Power
Amps - Main unit for Current
WRMS - Watts Root Mean Square (see below)
Hertz - Unit of measure of frequency
Frequency response (Hz) - It identifies the speaker bandwidth, the limits within which it can be used with a linear response
Decibel - Unit of measure of sound pressure
HU - Head Unit
AMP - Amplifier
THD (Total Harmonic Distortion) - Measured additional noise or interference induced into the system by the power supplies
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Amplifiers
Calculating WRMS:
From Max Power - Max Power / (Square Root 2)
Bridged Mode for a single 4 ohm speaker - 2*(AMP Power in WRMS @ 2 ohm):
#Eg. 2 Channel Amp; Power: 50WRMS/channel with 4 ohm load, 70WRMS/channel with 2 ohm load .:. Bridged WRMS = 2* 70 wrms = 140 wrms. Therefore the 4 ohm speaker is receiving 140 WRMS of power
Parallel Mode with 2 equal speakers of x ohm - Power = [Power @ (x/2) ohms]/2
#Eg. Mono block Amp; Power: 200 WRMS with 4 ohm load, 350 WRMS with 2 ohm load. .:. Parallel WRMS = 350 WRMS/2 = 175 RMS. Therefore, each 4 ohm sub would be receiving 175 WRMS of power
Series Mode with n speakers at x ohm - ?
*Terminology:
Stereo -A stereo system has two independent signals, each driven into its own separate speaker
Mono - A mono system sends the SAME signal to ALL of the speakers
Max. Power - The maximum power an amplifier can produce with no load
WRMS (Nominal Power) - The power that the speaker is actually receiving from the amplifier at a continuous rate
Bridging - Connecting the -ve from one channel and the +ve from a second channel to drive a single speaker with more power due to each channel seeing 2 ohm resistance. This does NOT mean that there is a resistance of 2 ohm in total, just that each channel see half the total resistance.
Parallel - Running two speakers off the one channel, in result halving the impedance
Clipping - When the volume is turned up past what the amplifier can deliver and distorts
Overload Protection - A protection circuit that eliminates component failure from impedance loads that are to low by shutting off the amplifier
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Speakers
*Terminology:
Power Handling - The power that a speaker can receive for short moments (Max) or for continuous programs (Nominal).
Efficiency (dB): Reference efficiency value of a speaker; it is measured in decibels and at a distance of one meter, with 2.83 Volts in the input
Tweeter - Speaker specialised in reproducing high frequencies
Midrange - Speaker specialised in reproducing mid frequencies
Woofer - Speaker specialised in reproducing low and mid frequencies
Xmax (mm) - Mobile voice coil excursion, in one direction
Voice coil - Wire (usually copper) winding around a cylindrical former that is glued with the speaker membrane. Alternate current passing through mobile voice coil generates a magnetic field that interacts with the one occurring into the gap; the vibrations that derive from this are sent to the membrane, generating sound
Speaker Size - The dimensions of the speaker given in terms of inches
Coaxials - A speaker which produces all three frequencies in one unit
Components/Splits - A set of speakers which seperates into 2 or 3 lone speakers, which is combined with a crossover so that each speaker only reproduces its specific frequency
Crossover - Filter used to separate frequencies to their appropriate speakers
*Resistance Calculations:
Speakers in Series = R1 + R2 + ... + Rn
Speakers in Parallel = [R1^-1 + R2^-1 + ... + Rn^-1]^-1
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Speaker Enclosures
*Terminology:
Sealed - Airtight enclosure suited to general applications
Ported - Enclosure with ports which can be tuned to certain frequencies to change SQ and SPL characteristics
Isobaric - Two speakers placed in an array as to act as one speaker in an enclosure design that requires half the air space that a single driver requires
Bandpass - Bandpass boxes are a special type of ported box designed for maximum bass. The woofer is mounted inside a dual-chambered box (one chamber sealed, the other ported), with the sound waves emerging from the ported side. The sound that comes out of the port is extra loud within a narrow frequency range
Dipole Passive Radiator - A sealed box with 2 subs running out of phase

Infinite Baffle - Infinite baffle enclosures are the simplest from a design concept. The principle of IB design is the seperation of the front output of the woofer from the rear output of the woofers. One of the advantages of this design is the low resonant frequency of the IB system. This low RF allowes the system to have a very good low frequency extension. Another advantage of an IB design is the little amount of boot space needed for this application. For this reason IB designs are popular in cars where the boot space is small but there is a need for big bass...

One of the main disadvantages of this application is the REDUCED MECHANICAL POWER HANDLING of the speaker. This is due to the fact that the enclosure is actually the whole boot volume and the air in the boot is not able 2 help the mechanical suspension system of the woofer, for this reason not all woofers are suited for IB applications.

It is a common misconception that IB enclosures are the easiest to construct, this is not true as maximizing performance in this type of enclosure is quite difficult and time consuming. Maximizing the performance in a IB system you must minimize leaks and maximize the sturdiness of the baffle....

Ok, so in short an IB enclosure is putting a sub in the parcel tray and using the boot as one big enclosure and attempting to seperate all the air either side of the tray, same principal is used when placing a sub in the ski-port in some sedans and using the back seats/parcle tray as the dividing wall and the boot as the enclosure.

Also this type of enclosure means u cant feed buckets of power 2 the sub cos its not being helped by the box and will be worked 2 hard if u do apply 2 much power.

You will be surprised how many installs come out of brisbane car sound like this, if u feel air leaking from around the plate ur sub is fixed 2 then this is the "box" that u have got... *Written by 'Ferdie'
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Head Units
*Terminology:
'Loud' Button - To prevent overloading on speakers i.e push into clipping, try and adjust system gain levels to prevent its use
Power Rating ( 45 x 4 etc.) - This is the Max Power of the HU, not the WRMS. However, this usually equates to only approx. 13 WRMS from each channel
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SPL and SQ
*Terminology:
SPL - Sound Pressure Level, measured in dB
SQ - Sound Quality, measured in ?
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Display Units
*Terminology:
LCD - Liquid Crystal Display
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Wiring Guide
*Terminology:
AWG (Gauge) - American Wire Gauge; Used to describe the size of a wire in relation to its current carrying ability. Smaller the AWG, Higher the current carrying ability
Earth/Ground Wire - The wire which is earthed to the chassis via direct contact; Drains excess electrons to create an equal balance in the system
Power (Memory) Wire - The wire running directly from the battery to the source unit i.e HU, AMP; providing the main source of power. Called memory wire in reference to its ability to provide power to the HU so that stored data is not lost when the car is switched off
Accessory Wire - The wire which only supplies power to the source unit when the ignition is turned over to ACC i.e car turned 'ON'
Speaker Wire - The wire which sends power and signal to a speaker
RCA Outputs - Dual wires which are specifically for sending signal to an amplifier, as they do not have a high enough output current to drive a speaker
Internal Wire Resistance - The resistance of the actual metal which the wire is made out of, usually small in relativity
*Guide to choosing what gauge wire:
AWG___Maximum Rated Current
00___ 400 amps
0___ 325 amps
1___ 250 amps
2___ 200 amps
4___ 125 amps
6___ 80 amps
8___ 50 amps
10___ 30 amps
12___ 20 amps
14___ 15 amps
16___ 7.5 amps
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FREQUENTLY ASKED QUESTIONS (FAQ'S)

Q: Will a blow off valvy thingy give me booste?
A: NO!

Anyways, here is a list of questions that seem to appear constantly in this forum:

Q: Is it safe to overpower a sub or speaker? Eg. 700W amp on a 400 W sub...
A: Yes, as a matter of fact, it is a lot more beneficial for the subs performance and safety that you use a overpowered amp and adjust the gain settings to suit your listening levels. Underpowering a sub, then pushing it to its limits (high volumes) can be harmful to both sub and amp due to clipping (see above)

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[theSeekerr]

'Loud' Button - To prevent overloading on speakers i.e push into clipping, try and adjust system gain levels to prevent its use

The "loud" button is a frequently misunderstood beast. It's simply an equalisation curve which is designed to compensate for the way the human ear works - at low SPL's, we're more sensitive to midrange frequencies than bass or high treble, and the "loudness" EQ crudely compensates for this by boosting the bass and treble.

It doesn't make your system louder, nor does it make your system "sound" louder. It just makes it sound a little bit better if you're listening at low volume.

Of course, a lot of people leave it turned on all the time, either believing one of the fallacies above, or, most often, because they like the bass boost.

Point is, it should only be used at low powers anyway, so the above advice is a bit silly.

 

[Philthy]

Amplifiers
Calculating WRMS:
From Max Power - Max Power / (Square Root 2)

Midrange - Speaker specialised in reproducing mid frequencies
Woofer - Speaker specialised in reproducing low and mid frequencies

Thats a good write-up, if maybe a bit long.
There's a couple things I wanted to pick up on though.

I see a lot of different amps where the RMS power isn't related to the max power as you stated above. Not to say I try calculating them, but for example I might see a 300wrms Kenwood amp advertised as 600w, but then an alpine 300wrms advertised as 500w.

And just to be picky, with the speaker terminology, I have always called midrange speakers woofers as well. There is confusion around where if you were to say the word woofer people automatically assume you are talking about a subwoofer

EDIT: Oh, and I agree with theSeeker on the LOUD button. If I'm listening to my stereo for a while with no sub and at low volumes (like when I wash my car) then I will turn loudness onto the low setting for that little extra kick that is hard to pick up when its so quiet

 

[theSeekerr]

Oh, cripes, I didn't even see the watts RMS thing the first time around.

That version is wrong, in two ways. Let's run the numbers:

Let's take an amplifier rated for 100W into 4 ohms. Since Power = Voltage Squared / Impedance, we can see that it's swinging a voltage of 20V RMS, or 28.28V Peak.

Since we also know that Current = Voltage / Impedance, we can see that there's a peak current of 7.07 Amps.

Finally, since we know that Power = Voltage * Current, we can see that the peak power is 28.28 * 7.07, which is 200W, or 2 times the RMS power, not Sqrt(2).

However, that's not how the amplifier makers calculate "Peak" power, or "Peak Music Power Output". That's done by a very technical method called "making **** up". Read some more about it here: Amplifier Power Ratings

 

[markER717]

Thanks for all your help guys!