Sensitivity

[J_Dunavin]

A friend of mine tried to boast his brand X speaker as being superior than some other brand of speaker because of it's high sensitivity and therefore doesn't need as much power to sound as loud as some other brand of speaker. So... i looked up the specs

Please correct me if i am wrong, as i really do want to know.
The specs for his speaker say it is 89db...at 2.8V
Take the competitor which is 82db at 1W
If i figure right....2.8V squared over resistance is power, so if the voice coil is rated at 2 ohm that should equate to about 3.9W, depending on the impedance, right? (whatever freq they are inputting and weather or not its free air or in an enclosure)
So... isn't the 82db at 1W way better?

[Bill Fitzmaurice]

2.83v into a 2 ohm load is 4 watts. That makes it 83dB at 1W.

[J_Dunavin]

Ah ha! Inflated numbers! How dare they

[MissileCrisis]

For the record, all of Parts express driver sensitivities are given as 2.83 V. So If it is a 4 ohm driver, you know that the actual sensitivity is 3 dB less than the 2.83 V given one. But at least they are transparent/consistent about it (saw them mention this in their magazine/online).

[Charles Warwick]

Ah ha! Inflated numbers! How dare they

Lots of car audio folks do that type of thing. They use low resistance drivers and amplifiers to get more amperage out of the equipment. If it's actually stable at that level I guess it's okay, but it's certainly a little misleading to the rest of the audio community especially since you need a 2 ohm stable amp to use it. Recently I've been seeing really stupid things like 1ohm dual voice coils so you can wire for .5 ohms. Maybe I'm missing something, but I just don't see the point.

[J_Dunavin]

Marketing. I did car audio (in an actual shop) for 5 years and everyone just about had an aneurysm when i suggested an 8 ohm driver from PE that would be a good fit for some project we were working on.

[CoronaOperator]

Ah ha! Inflated numbers! How dare they

Recently I've been seeing really stupid things like 1ohm dual voice coils so you can wire for .5 ohms. Maybe I'm missing something, but I just don't see the point.

In car audio we are working with 12v /13.8v power supplies with car batteries that can handle 650 CCA. Amperage is a lot easier (and cheaper) to come by than higher voltages in car audio. Highest voltage car audio amp I ever measured was about 39v at the speaker terminals, after that all you have left is amperage. Gotta get your power from somewhere (P=VxA).

[Charles Warwick]

Highest voltage car audio amp I ever measured was about 39v at the speaker terminals

Isn't that mostly a transformer issue? I don't work with car audio often, but if line in for the amp is 12V, doesn't that mean the lack of high-voltage output is mostly by design?

[Rich4349]

"Cheater amps" of the 80s, some of them (claimed to be) stable to 1/16 ohm...that's practically a dead short! But if that lets you run 16-32 speakers off of one channel...

[CoronaOperator]

Isn't that mostly a transformer issue? I don't work with car audio often, but if line in for the amp is 12V, doesn't that mean the lack of high-voltage output is mostly by design?

Totally, however the power supply is the most expensive part of the amp and in car audio it is unnecessary as amperage comes easy. $500 in car audio can buy you a solid 2500 watt amplifier (into 0.5 or 1 ohms) if you have the power to run it (hi output alt, 0 gauge cabling, yellowtop battery, etc). What would that cost into 8 ohms? Probably 4-5 times the price. In my car I have a 30amp circuit for hibeam, lowbeam, for fog lights and another for cigarette lighter. How many venues have 4 30 amp circuits just sitting around?

Marketing plays a part too. Who would buy the markets 8 ohm speakers when you can buy my 2 ohm ones and get 4 times the power? Don't forget the shiny $5/foot welding cable with x company brand name on it to hook everything up. They (car audio companies) had a niche to fill and made a profitable business out of it.

[Bill Fitzmaurice]

Isn't that mostly a transformer issue? I don't work with car audio often, but if line in for the amp is 12V, doesn't that mean the lack of high-voltage output is mostly by design?

Transformers don't work with DC.

[byacey]

In the early days of car audio before switching supplies and inverters, nominal 12 volts was the operating rail voltage available for the power amps; actually around 14.1 with the engine running.

This means with a non-bridged complimentary output topology you could realize a whopping 8.9W RMS across an 8 ohm load, or 17.98W if you had a 4 ohm speaker available.

Bridged output ICs became the rage in the 1980s. With your eight ohm load, you could now realize 35W under ideal conditions, and with a 4 ohm load, 70W! Unfortunately most vehicles didn't have sufficient wiring to supply the current draw, so there would be some losses there when trying to impress the potential girl friends.

In an attempt to get even more power, GM was using 2 ohm speakers (I think made by Bose). Unfortunately, power losses in the amplifier, the speaker and power supply wire losses become a significant factor, and it all became a point of diminishing returns.

When switching inverters became reliable and cost effective to manufacture, the 12V rail could now be raised considerably higher, and +/- split supplies could be used to simplify the power amp output circuitry. It all culminated in the super power amps available today.

In the real world though, how much volume do you really need in a car? It's not like it's the ideal listening environment for high quality audio. If you really want to listen to top notch audio in the car, buy some good headphones, a 500mW amplifier to drive them, and your done.

[Bill Fitzmaurice]

In the real world though, how much volume do you really need in a car?

IME the level in dB is inversely proportional to the IQ of the driver.

[CoronaOperator]

In the early days of car audio before switching supplies and inverters, nominal 12 volts was the operating rail voltage available for the power amps; actually around 14.1 with the engine running.

This means with a non-bridged complimentary output topology you could realize a whopping 8.9W RMS across an 8 ohm load, or 17.98W if you had a 4 ohm speaker available.

Still holds true today for modern Head Units. Regardless of what the box says your aftermarket HU only puts out ~12.5 watts RMS/channel give or take depending on how much THD you want in your measurement.

In the real world though, how much volume do you really need in a car?

You need all that power so you can hear those 83dB/W speakers talked about in the beginning of the thread . Seriously though you ideally would want at least 20 dB above the noise floor of your vehicle. Loud car on highway would need a louder system to overcome road noise.

It's not like it's the ideal listening environment for high quality audio.

Totally disagree if its done right. Car audio is the one place where I can guarantee the listeners ears to within a few inches. Time aligning each driver to the millisecond and balancing 28 bands of left/right EQ not only for tonal balance but for left/right positioning can make for a near perfect soundstage. Hearing your favorite tunes with the band at eye level and spread left/right across the hood of the car as they are on stage is as awesome as your first time at a concert with decent seats.

IME the level in dB is inversely proportional to the IQ of the driver.

Uh Oh . My system goes to 128dB @ 50hz and I still use tube driven preamps . I however blame the designer of the sub box for that

[Charles Warwick]

Isn't that mostly a transformer issue? I don't work with car audio often, but if line in for the amp is 12V, doesn't that mean the lack of high-voltage output is mostly by design?

Transformers don't work with DC.

Ah, is the term I'm looking for DC converter or a step-up converter? I really don't know much about how most electronics work so