Can someone explain something (Hi-Fi vs Car audio)

[Barks]

I just bought a Wharfedale SW150 subwoofer (150W RMS) which genuinely does shake the house down.

What I don't understand is you can buy subwoofers for cars which are rated at 800W RMS. How on earth can it possibly get enough power to do this? I cannot imagine something in a car putting out the same bass as the SW150.

Could someone clear this up for me?

Cheers,

 

[chameleon]

Car speakers are generally rated at 4 ohms so are half the load of household speakers. Also, bear in mind, car hifi runs off 12v or thereabouts so the current can be considerably higher hence why large auto setups require much bigger cabling.
It is very possible to get car amps that run at 1kw+.
Oh, and you get some bloody hoooooj car speakers!

 

[Mr_Sukebe]

Also bear in mind that most indoor kit tend to measure stuff using RMS (root mean squared), whilst most car kit uses "peak" power. Peak as a rule is around double the RMS power for most kit. That's even before you take into account the distortion at it's power handling capabilities. Again, indoor kit tends to be somewhat more conservative.
In short, most car "hi-fi" is not going to get close to a good home system.

 

[pby]

not uncommon for car manufactures to quote their rms with a 2/4 ohm load. the power is typically doubled when you half the load so take that into consideration.

 

[daz]

What I don't understand is you can buy subwoofers for cars which are rated at 800W RMS. How on earth can it possibly get enough power to do this? I cannot imagine something in a car putting out the same bass as the SW150.

Cars are very strange acoustically. There's no reason why you'd ever really need 800W RMS going to a car subwoofer, although it really depends on a number of factors, main the design of the box it's going into, the sensitivity of the sub (e.g. 89db/W @ 1M), and finally the acoustics of a car.

Most rooms in most houses are very good at reflecting bass around the room, and filling the room sufficiently. You'll find this isn't the case in a lot of cars, and as such you need more power to achieve a the equivalent perceived volume.

 

[WantoN]

Cars are very strange acoustically. There's no reason why you'd ever really need 800W RMS going to a car subwoofer

People with 800wRMS subs are doing it for acoustic perfection. They're doing to get bass so slamming it makes you soil yourself

Ant

 

[PistolPete]

I assume you meant to say that they AREN'T doing it for acoustic perfection!!

 

[Barks]

I'd like to think that money was invested in a sub of good quality and not something which booms the house down with distorted bass, much like the crap I hear in most chavmobiles.

 

[james.miller]

Also bear in mind that most indoor kit tend to measure stuff using RMS (root mean squared), whilst most car kit uses "peak" power. Peak as a rule is around double the RMS power for most kit. That's even before you take into account the distortion at it's power handling capabilities. Again, indoor kit tends to be somewhat more conservative.
In short, most car "hi-fi" is not going to get close to a good home system.

virtually all speakers are RMS rated, whether they are meant for home use or automobile


its easier to pressurize a car than it is a living room - smaller space. in reality, the same speaker would need far less power in the car than it would in a 15' x 15' room of some description. if you want to go for a well balanced system in a car, a single 10/12" and 150w RMS of clean power is almost always way more than you really need in reality. big numbers are for competition runners and the type of people who drive down the street with EVERY window down just so everybody in a 5 mile radius can hear them. fools, everybody (except them obviously) knows it would sound better with the windows up :/

Most rooms in most houses are very good at reflecting bass around the room, and filling the room sufficiently. You'll find this isn't the case in a lot of cars, and as such you need more power to achieve a the equivalent perceived volume.

i have found completely the opposite to tell the truth, though its not an exact science. saloons can be a problem if the car is well soundproofed between the back seats and the boot

 

[MikeHunt79]

I just bought a Wharfedale SW150 subwoofer (150W RMS) which genuinely does shake the house down.

What I don't understand is you can buy subwoofers for cars which are rated at 800W RMS. How on earth can it possibly get enough power to do this? I cannot imagine something in a car putting out the same bass as the SW150.

Could someone clear this up for me?

Cheers,

Which car audio sub is rated at 800W rms? It would probably melt or go into power compression, unless you're using one a PD 1850 which is one of the few drivers that will be able to deal with 800W rms... Even then it starting going into a small amount of power compression.

 

[james.miller]

JL audio 13w7 for one 1000w RMS rated, and they build a HT subwoofer with two of 12" drivers

JL audio Fathom.

there's also the infamous cerwin vega stroker 18-d2, which if you believe the tales could be wired directly to the mains and still come back wanting more. they were rated at 3200w rms and were responsible for the first 160db+ audio 'drag races'. the new stroker PRO 15" is rated at 2500w RMS

 

[daz]

I've seen people plug RE XXX subs straight into the UK mains (not recommended)

And they take the power

 

[WantoN]

JL audio 13w7 for one 1000w RMS rated, and they build a HT subwoofer with two of 12" drivers

JL audio Fathom.

there's also the infamous cerwin vega stroker 18-d2, which if you believe the tales could be wired directly to the mains and still come back wanting more. they were rated at 3200w rms and were responsible for the first 160db+ audio 'drag races'. the new stroker PRO 15" is rated at 2500w RMS

Now THAT'S soil-yourself bass

Ant

 

[MikeHunt79]

JL audio 13w7 for one 1000w RMS rated, and they build a HT subwoofer with two of 12" drivers

Nice, it does look like it has a well cooled voicecoil, but they don't actually give the diameter. I guess it would have to be around 6" to deal with that amount of power.

Not the most efficient driver in the world, but has plenty of xmax and a pretty strong motor so is begging to be horn loaded. A 20Hz horn is gonna be huge however...

EDIT: Just noticed they £900 each tho, lol.

 

[james.miller]

so, build it outside the room then, infinite baffle style

 

[MikeHunt79]

so, build it outside the room then, infinite baffle style

I was going to try modelling the 13w7 but the TS specs are incomplete, still I'm sure it would work well tho... I could get 3 PD 1850's tho for the price of 1 13w7, I know which I'd rather have!

Here's what a PD 1850 will do when in a corner of a room

The only downside is it's 22 cubic feet!

I've seen people plug RE XXX subs straight into the UK mains (not recommended)

And they take the power

Are you sure? 13,225W is too much for any voice coil unless there is some crazy high impedance around 50Hz with this driver or the enclosure...

The 13w7 does this with 120v:

 

[Edinho]

I just bought a Wharfedale SW150 subwoofer (150W RMS) which genuinely does shake the house down.

What I don't understand is you can buy subwoofers for cars which are rated at 800W RMS. How on earth can it possibly get enough power to do this? I cannot imagine something in a car putting out the same bass as the SW150.

Could someone clear this up for me?

Cheers,

A bit like how a midi system from Argos can be rated at 250W. fiddle the figures to give the largest number. More powa init.

 

[daz]

Are you sure? 13,225W is too much for any voice coil unless there is some crazy high impedance around 50Hz with this driver or the enclosure...

Is that how much it would draw? I'd have thought there would be a 13A fuse somewhere limiting the current draw to ~3k RMS? Maybe not.

What's better the top end JL subs or RE?

 

[Nick1881]

That JL sub enclosure turns me on.

I used to have a JL12w6 in my car years ago driven by a Phoenix Gold 300w amp and my god it was good.

 

[MikeHunt79]

Is that how much it would draw? I'd have thought there would be a 13A fuse somewhere limiting the current draw to ~3k RMS? Maybe not.

If you plugged it directly into the mains then there would be no fuse.

If they used a cut up kettle lead with a 13a fuse then yes there would be a 13a fuse, but the fuse would not limit the current to 3Kw, the fuse would just blow when the power goes above 3Kw.

Now even if no fuse was used I think most house sockets use 20amp MCB's, but I've heard of some being 40amp (cooker feeds, etc.), I'm not a qualified electrician tho so don't take this as gospel.

The claim isn't far fetched tho, I've heard that some 80's PA cabs could be plugged into to the mains, but the reason they took the power was because the speaker (and enclosure) produced a high impedance (50 or 100Ohms maybe) around mains frequency (50Hz). Even at 40 amps, you can "only" pull around 10kw, so 13Kw would trip the MCB regardless...

I'll assume 50 ohms and 230v:
P = Vsquared / R
230 x 230 / 50 = 1058W so a lot of power but nothing crazy. Bloody loud tho I bet!

So if a 13 amp fuse was used and the sub still gave out sound after a few seconds, then it must have been pulling less than 3kw, meaning there is quite a high impedance at 50Hz... Still impressive tho, I imagine it must have a 6" voicecoil at least to deal with that amount of power...

What's better the top end JL subs or RE?

I'm not clued up on car audio, I'm more into PA. The JL specs look a little more believable but they are stupidly expensive... If it were my money I'd go for a PD 1850 driver, one of the only drivers to have thermal compression given on the spec sheet.

I did put a horn in my car with 2 x 8" drivers tho, they get around 30W rms each and this makes things shake as it's a high efficiency system...