[icnivad]

So, everyone keeps telling me that professional subs are preferred to car subs for dj systems, I'm trying to understand why that is. For the sake of this conversation, let's take the boxes out of the picture, as I understand that a bigger box will give you a lower tone, which is why a car box wouldn't work for a dj system.

It seems like the purpose of any sub is to move air, so the two most basic needs are surface area, and throw depth, combining to give you the maximum amount of air the sub can move with a single wave, and therefor the loudness. The other factors seem to be the rated wattage, and even more importantly the sensitivity, which will give you more movement of air for your wattage. Also the impedance comes into factor with a lower one letting you chain more speakers together for more bang for your watt.

It looks like car subs and dj subs have comparable SPL, volume of air pushable, with the car subs typically having a higher wattage, and lower impedance.

So, why, after all of this, is a dj sub with the same spl, wattage, and impedance better than it's car sub equivalent?

As a follow up question, why aren't pro subs then used in cars?

 

[tonyvdb]

It really boils down to quality of the driver, and as you mentioned box size. A good quality car sub driver will do just as well if placed in the right enclosure.

 

[Bill Fitzmaurice]

It really boils down to quality of the driver, and as you mentioned box size. A good quality car sub driver will do just as well if placed in the right enclosure.

The requirements to fill an 80 cubic foot car with bass are quite different than those for a 25,000 cubic foot club. Therefore not only are the cabs completely different so are the drivers used in them.

 

[icnivad]

The requirements to fill an 80 cubic foot car with bass are quite different than those for a 25,000 cubic foot club. Therefore not only are the cabs completely different so are the drivers used in them.

Yeah, I keep hearing this, but I'm not sure what needs to be different at the driver level. It seems to me that weather you're filling a 25,000 foot club or the 80 foot car, the goal of the drivers remains the same -- to move the most amount of air that it can for the least amount of watts. Certainly it's easier to fill a car, but you'd naturally use more speakers to fill the larger club.

The only real difference I can think of between a car and a club is that there's more space constraints in a car, so you're more likely to want to push a large amount of watts through a smaller number of speakers, whereas in a club you can spread out your watts to a greater number of speakers. This leads to the idea that max wattage is more important in a car, while sensitivity is more important on a stage. This seems to make sense that the average car drivers are rated for more wattage than the average pro driver, and is further enforced when you see that most car drivers have a sensitivity between 88 and 94 db and most stage drivers have a sensitivity between 90 and 100 db.

 

[Bill Fitzmaurice]

Yeah, I keep hearing this, but I'm not sure what needs to be different at the driver level. .

Model a driver in a 1 cubic foot sealed box and in an 8 cubic foot vented box and you'll find that what works very in one works quite poorly in the other, especially when cabin gain allows the auto sound cab to work best with an 80 Hz f3 while the pro-sound sub requires an f3 of 40 Hz, and 10dB higher sensitivity. Also note that autosound drivers tend to run 2 ohm coils, pro sound 8 ohm.

 

[icnivad]

Model a driver in a 1 cubic foot sealed box and in an 8 cubic foot vented box and you'll find that what works very in one works quite poorly in the other, especially when cabin gain allows the auto sound cab to work best with an 80 Hz f3 while the pro-sound sub requires an f3 of 40 Hz, and 10dB higher sensitivity. Also note that autosound drivers tend to run 2 ohm coils, pro sound 8 ohm.

Ah, you just hit on another question I've been having. Why is higher impedance better in a driver? Aren't two 2 ohm drivers in series the same as two 8 ohm drivers in parallel? From what I understand, with both setups you end up with a 4 ohm system where each speaker gets 1/2 the total wattage.

 

[tenzip]

Impedance differences don't make one driver better than another, you can get the same driver with different coils, so it's a matter of how you want to hook it up, and what your amplifier is capable of driving.

From what I understand, car audio drivers are usually rated at 4 Ohms so that the amplifiers that are being driven by a 12V system can use a lower rail voltage to produce more current, vs. home audio 8 Ohm using 120V can have a higher rail voltage in the amp.

 

[Bill Fitzmaurice]

Ah, you just hit on another question I've been having. Why is higher impedance better in a driver? Aren't two 2 ohm drivers in series the same as two 8 ohm drivers in parallel? From what I understand, with both setups you end up with a 4 ohm system where each speaker gets 1/2 the total wattage.

Autosound drivers run 2 ohms for maximum sensitivity with low voltage high current autosound amplifiers. Pro-sound uses 8 ohm drivers so that more than one can be paralleled on an amp channel.

 

[Ricci]

Also I'd say that the average car sub is not 88-94db sensitive. More like 84-90db. Also you see some car subs with 2" coils and 40oz magnet systems rated at 600w rms:rofl:. Where as a good pro audio driver might have a thermal rating of 1000rms with a 4" coil and much bigger motor, with better cooling. Car subs power ratings are inflated in general and all over the place. Don't get me wrong, there are some that will handle gobs of power that are rated accurately, but you have to excersize common sense. In general the thermal power ratings for pro subs are much tighter controlled and represent an amount of power that you can reasonably expect the driver to handle in a medium duty cycle.

As Bill mentioned many times the car sub will be optomized for the small confines of a vehicle and a small enclosure to save space. Many times this doesn't lend itself to a pro audio style enclosure. Another thing is that a pro audio bass bin may have decent response up to 400hz or more. The heavy high power handling car subs won't. Inductance is a factor here and is another difference between them in general as a good quality pro woofer will probably have much less inductance issues.

 

[dtsmucker]

Apoligies for hijacking the thread guys..

I've had the same argument with freinds over the years regarding subwoofers in cars.

Driver quality. The drivers available at component level for in car use are, at best average.
The "ratings" many manufacturers use are way over inflated, as stated earlier..
Unless you're talkin very exspensive or SPL competition stuff.

If you purchase a Subwoofer that claims 1000w PMPO.. You can half it and then half it and... probably half it again and then.......
In fact the term PMPO (Peak Music Power Output) was hi-jacked to make these bits of equipment appear to be better than they are.
In laymans terms, basically THE biggest "load" a driver can take before it dies.

Always, always look for RMS. It's the way forward..

As regard to the difference between "Pro" and "Car"... There are many differences, it's about application.

A 10" Sub in a sealed 10 litre cab will sound sweet in a Home Theatre bedroom set-up.

A twin 18" is going to sound horrid in the same set-up. Though some may prefer it..

But put these in a vehicle of any size and the math and physics capabilities change again.

The only differences I can think of regarding "Pro" and "Car" are marketing.. If you know what you are after then either could do.

 

[DrWho]

So, everyone keeps telling me that professional subs are preferred to car subs for dj systems, I'm trying to understand why that is. For the sake of this conversation, let's take the boxes out of the picture, as I understand that a bigger box will give you a lower tone, which is why a car box wouldn't work for a dj system.

Hoffman's Iron Law....a bigger box lets you go lower for the same efficiency, or gives you more efficiency for the same tuning point.

In the case of pro subs, the F3's are typically around 40Hz in the nicer rigs (usually more like 50Hz in the cheaper dj rigs). Also, the pro subs are typically around 6 cubic feet per driver, where in car audio you're looking at as small as possible (2 cubic feet perhaps?) while also digging as low as possible (like 20Hz).

It seems like the purpose of any sub is to move air, so the two most basic needs are surface area, and throw depth, combining to give you the maximum amount of air the sub can move with a single wave, and therefor the loudness. The other factors seem to be the rated wattage, and even more importantly the sensitivity, which will give you more movement of air for your wattage. Also the impedance comes into factor with a lower one letting you chain more speakers together for more bang for your watt.

Granted, more displacement will always yield more SPL, but at the higher frequencies you don't have enough power handling to take full advantage of the displacement. Also, higher frequencies require less displacement than the lower frequencies...so if you purposely don't make the system dig as low, then you're going to end up with more SPL.

For what it's worth, most pro subs aren't excursion limited. They're actually thermally limited, which gets back to the whole box thing where a larger enclosure allows for greater sensitivity. The increase in sensitivity means more SPL for the same power....but usually you'll still not be mechanically limited. It's almost like the engineers know what they're doing and put in just enough excursion for the desired F3 and maxSPL.


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Btw, the reason pro subs generally have higher impedance is that it improves electrical damping, which is another way of saying that it gives the amplifier more control over the motion of the driver. Car subs have to be low impedance in order to get high power levels from a small voltage.

Also, a higher impedance requires less current for the same power.
P = I^2 x R

800W into 8 ohms requires 10 amps.
800W into 2 ohms requires 20 amps.

Any series resistance (like the wire or the output stage in the amp or any lossy components in a passive xover) will result in significant power loss and excess heating. Keeping the current as low as possible also improves the power transfer.

 

[Bill Fitzmaurice]

For what it's worth, most pro subs aren't excursion limited.

Most pro subs are displacement limited, more often than to to well under 1/2 their thermal rating. A 500 watt Pe with a 5mm Xmax is common, being part of the price paid for the low Mms required for high sensitivity. But pro subs are also not intended for use below 35 Hz, and they are subject to a far higher input dynamic range than auto sound or HT sub drivers, so a higher Pe to xmax ratio is required. Pro-sound woofers with longer xmax values do exist of course, but they fall in the upper price ranges, are mainly neodymium magnet models that have been introduced fairly recently, and most still don't go beyond 10mm.

 

[E-A-G-L-E-S]

Car Subs = higher Fs(bad for movies)
Pro Subs, Commercial Subs = lower Fs(good for movies)
Both can be good for most music but some organs and such go too low for car subs.

 

[looneybomber]

Bottom line, it all revolves around efficiency. For a band playing at a bar, it's not like they have 8, 240v dedicated lines run just for amps, so you have to get the most out of your system.

If a "pro" sub required 200w to hit Xdb at Xhz and the "car" sub required 1600w, (negating any power compression and consequent distortion) that requires a much larger amp, increases costs and draws a lot more power, which may not be provided. I've been to events where we've tripped breakers and the volume had to be turned down.

It's as simple as that. Sensitivity rules.

Car Subs = higher Fs(bad for movies)
Pro Subs, Commercial Subs = lower Fs(good for movies)
Both can be good for most music but some organs and such go too low for car subs.

I think he was meaning pro audio and not HT. In which case, pro drivers have a high fs too due to the small mms.

 

[Blaser]

Most pro subs are displacement limited, more often than to to well under 1/2 their thermal rating. A 500 watt Pe with a 5mm Xmax is common, being part of the price paid for the low Mms required for high sensitivity.

Yeah, Bill! You're correct. Power handling is hardly an issue...

 

[DrWho]

Let's see, a 15" driver with 5mm Xmax is gonna do about 120dB, half space, down to 40Hz with a 40Hz tuning. That's fairly loud and low enough for a small SR rig. That would require 500W from a 93dB driver with no power compression (not gonna happen). 125W into a 99dB driver is still gonna have some power compression...

The JBL 2226H (a very common pro driver) is rated for 7.6mm of linear excursion and 20mm of throw with 600W of power handling. You can easily dump the full 600W before bottoming it out (and you'll be right around the 7.6mm of linear excursion depending on the cabinet alignment). However, you'll be running way into thermal compression before that...about 3dB of compression happening at 300W if I recall correctly.

Maybe I should rephrase to say linear power handling, or power handling before compression. A loudspeaker that makes a lot of heat is kinda pointless...

In the case of the JBL2226H, one could claim a 600W toaster rating, or 60W of clean output...60W is about 3mm of excursion (with a 40Hz tune) yielding ~115dB after ~1dB compression. That's well within the mechanical limits of the driver, but still limited by the thermal capabilities.

 

[Bill Fitzmaurice]

The JBL 2226H (a very common pro driver) is rated for 7.6mm of linear excursion and 20mm of throw with 600W of power handling.

The 2226H and other drivers with its capabilities are premium models which won't be found in the entry level subs that make up at least 80% of the pro-sound market, especially in the DJ genre.

 

[Ricci]

I'd just like to add that many of the pro-woofers that seem to have very limited excursion based on their less than stellar xmax rating will physically travel 15mm to 25mm or more each way before any damage is done. They do not run out of output or get damaged because the 5mm or whatever xmax was reached. The output may get increasingly more distorted though. Also the amount of xmax is really only useful for gauging the potential amount of output below 30hz. Above 30hz a large xmax is not really needed or of much importance. This is where Pro style woofers excel.

Car subs are designed with different goals in mind. Small boxes, tons of power, pressure vessel gain, repeated abuse by often times careless owners, etc.