Why loudspeakers should all be rated at 1W/1m

[///M5 2,833]

As most of you know, I do measurements for a living. So I have a few pet peeves about how things are done in this industry. Nothing is standardized and the accuracy of everything is questionable and typically quite subjective. In this thread, I would like to address something I would like to see standardized and that is the sensitivity of loudspeakers. There are a lot of you car audio nuts that are afraid to run home audio drivers in your car due to the fact they are 8ohms, but you really shouldn

[helotaxi 46]

You're also assuming that the amplifier is capable of providing only half the output power into 8 ohms compared to 4. This is rarely the case. The difference might be enough to squeeze another dB out of the 8ohm driver.

[///M5 2,833]

Thanks for clarifying, I was trying to err on the conservative side.

[CBFryman 2]

pfftm 0.5ohm pwnz you guys.

Very nice write up sean.

[DevilDriver 28]

Just a few thoughts of my own here.

Yes, increasing the length of the coil will increase efficiency; it increases BL. However, it can also increase Mms, which will decrease efficiency. There is a point of diminishing returns where you are much better off to increase BL and, conversely, efficiency by adding to the "B" portion of that equation. A positive effect of adding length to the coil is increasing Mms (yes, it is positive as well). Increasing Mms will also lower Fs, which is very handy for those who dig their low frequency response. The last negative effect of increasing L is the increase in inductance, which impacts your high frequency response and your transient rise response.

For subwoofers in general, I hate efficiency ratings. If I'm using a subwoofer, I want something that can produce low frequencies adequately in a small enclosure, and here comes Hoffman's Iron Law to trounce on my dreams. I would love to increase BL or drop Mms to increase efficiency, but this will also be damaging to my Fs. If I'm buying a subwoofer, I honestly don't care how efficient it is; there are several high efficiency subwoofers that sound awful from the inherent damage that a low Q subwoofer can audibly produce.

Good stuff all around!

[helotaxi 46]

Agreed on all the subwoofer stuff, but this post was specifically talking about midranges and tweeters and the confusion caused by the ratings when trying to match them in a DIY setup.

[bdawson72 0]

Twas a good read......

[Aaron Clinton 2,372]

These are the topics that are making SSA a better place.

[PaulD 0]

a big amen to that one ....

[PaulD 0]

well, it wouldn't let me edit .....

When the FTC laid down the law about stereo specs (1974 I think), they were asked about car stereo equipment. Their response at the time was - car stereo is car stereo. Meaning the best you could get was a cassette or 8 track player and a 12.5 watt/channel amp. Not much there to regulate.

I would also like to see more standardized spec ratings but the problem is what you saw with the new CEA rating scheme. The cheapo companies so watered down the way ratings are done that many of the specs are nearly worthless.

[helotaxi 46]

Comparing 4 ohm and 8 ohm drivers is bringing "home audio" speakers into the equation, so this isn't really car audio specific. 4 ohm drivers aren't just for cars, 8 ohm aren't just for the home. What about 16 ohm drivers, too? The point is that it should be industry wide, not just car audio like CEA, which as you mentioned is pretty well pointless anyway.

[Fi Car Audio 64]

Oh so true. 1W/1m is infinitely more useful than 2.83V and it is always fun to see a 102dB at 2.83 V 12" sub from some companies. Creative marketing at its finest when it is a dual 1 Ohm coil and you only know they measured the driver in parallel with 2.83 V. Looks much nicer to measure things at 16W vs 1W...lol Nevermid the fact that the tolerence factor for overall TS params is huge with such a low DCR as well (how many of you have meters that read to .001 Ohms let alone measure "0" when you cross out the leadwires... now you can see how even .1 Ohm makes a HUGE difference when you are measuring a DCR of .5 Ohms for TS param calculation. 20% error... vs 5% if measured in series at 2 Ohms.... or about 1% on an 8 Ohm driver.

Now from a little different viewpoint...

Id love to buld 8 Ohm drivers. I can make an 8 Ohm driver do the same thing as a .5 Ohm driver, but with a smaller motor and often more overall efficiency which translates into less cost to the customer. Why dont I? Well because the market keeps heading in the direction of ultra low impedance amps and setups. The problem with this is that you are moving into a much higher current than voltage and you need to use heavier AWG wire to handle the current... which in turn makes the gaps larger/reduces flux density, increases moving mass, and requires larger motors and heavier duty parts in general. At 8 Ohms, you have signifcantly more voltage than current which means that you can reduce the wire AWG, tighten up gaps, and often shrink the motor down to maintain overall specs. I have hi-pot tested coils to over 1000V with no arcing or shorting between turns. But try to run 100 A through 20 awg wire and things tend to get mad.

You do have increase inductance with a higher impedance coils of the same winding height, but relative to the DCR, it is often better of a ratio than the inductance vs dcr on the .5 Ohm coil which translates into better high frequnecy extension.

As for the other stuff of interest... a higher impedance driver is not always higher efficiency with the above formula in real world practice either. Looking at a 3" coil that has 2" of windheight of round aluminum wire for coils of DCR 6.13 Ohms and 3.07 Ohms. If we jockeyed the B to be the same between both motors (by either keeping the same motor and gap for both coils, or by shrinking the motor and tighening the gap on the higher DCR coil because we can) we can knock that out of the equation. Same goes for SD since both drivers will use the same soft parts... so what we are left with is L^2 / (R * Mms^2) Since this is a normalized number we only look to see the higher value as being more efficient...

For the 6.1 Ohm coil we have a wire length of 74.44m and a moving mass of 80g. Looking at it with only coil mass will yield a value of .1417 for the 6 Ohm and .111 for the 3 Ohm coil. And indeed the higher impedance coil is more efficient. But... now add the balance of the soft part moving mass of say 100g and the 6 Ohm coil is now .0280 and the 3 Ohm is .0284... 3 Ohm becomes more efficient then. Or by the example above keeping the wire Awg the same and decreasing wind height to drop DCR, you have a 3.07 Ohm coil with the same wire as the 6.13 Ohm coil with a wire length of 37.84m. Adding in the same soft part mass, you end up with a value of .0234 which is lower than both other drivers... but I would think that having half the windheight would have other drastic implications depending on how the gap height to wind height ratio is as well... with a gap of 1", you got to an even hung setup where you are not even using the balance of stray field either... resulting in more issues. At .500" gap height and even stray field both sides, you might get all of the useable B over the L of the wire with the shorter coil, but no where near the linearity of the the other two options. Keep in mind that the "l" in this equation is not the overall length of wire on the coil, but what portion of the wire is being acted on from the flux in the gap (plus stray field out of the gap).

With a 4 layer coil you have an Le of 8.34 mH for the 6 Ohm and 5.25 mH for the 3 Ohm... first glance looks like the lower Ohm coil is the winner due to reduced inductance, but when you actually calculate it based off of DCR/2Pi * H for the corner frequency, 6 Ohms is 116Hz and 3 Ohms is 92. Looks like the higher inductance/DCR coil will play up higher as well...

There are several other ratios and relationships between gapping, coil, B, wire and other factors that really come into play in driver design. Bl in and of itself isnt always the key either.

So at the end of the day, I am forced to keep pushing in the wrong direction... Oh well, it seems that 40 lbs speakers that can do the same thing as a 90lb counterpart just dont look as cool

[Typo_Knig 0]

Nice little read, Fi dude (it's Scott, right?). Sometimes I wonder why I don't just throw a pro sound woofer into my car.

What I notice about his thread, and discussions about measuring efficiency in general, is that no one mentions that a lot of manufacturers seem to get their number outside of their product's useable bandwidth. Don't even get me going on companies that state "in-car SPL".

Any thoughts?

[JimJ 11]

Sometimes I wonder why I don't just throw a pro sound woofer into my car.

If you have the space for a pretty large enclosure, that's not a terrible idea...basically where the old Stroker got its origin from

This fetish for smaller boxes, more power and lower impedances really seems to be self-defeating.

[mrray13 30]

Sometimes I wonder why I don't just throw a pro sound woofer into my car.

If you have the space for a pretty large enclosure, that's not a terrible idea...basically where the old Stroker got its origin from

This fetish for smaller boxes, more power and lower impedances really seems to be self-defeating.

unless your chasing tenths on a meter.

scott, my question is this. you say you can take a higher impedence woofer, tighten up the motor and it'll do the same thing as a low impedence/big motor sub. would that mean much of a change on box design, other then the obvious sub displacement? and would less power then yield similiar overall displacment? meaning cone movement.

i mena, don't most people say efficiency is pretty much a useless parameter, in car anyway? i can see where in home is different, and i also now understand why pro audio speakers have much smaller asses, lol. but in car, why is efficiency not a big deal? is it because of the amplifier companies building for such low impedence?

my god, i actually learned something today, lol

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

[///M5 2,833]

Scott, thanks for filling in your thoughts on subs. The original intent of this thread was to stop the disillusioned ones from thinking they need low impedance mids & tweets in their car, when usually in a driver that size it is a completely useless thing to purchase.

[DevilDriver 28]

scott, my question is this. you say you can take a higher impedence woofer, tighten up the motor and it'll do the same thing as a low impedence/big motor sub. would that mean much of a change on box design, other then the obvious sub displacement? and would less power then yield similiar overall displacment? meaning cone movement.

Tighten up the gap, you increase B, which decreases Qes, which decreases Qts. I think I'll take some time to post about this later this weekend, but the lower Qts will lead to a smaller enclosure, assuming other parameters like Qms, Vas, and Fs (all inter-related) stay the same. When it comes to thiele/small parameters, there are only 5 that really matter, and all other parameters are derived from those. They are: BL, Mms, Cms, Re, and Sd.

i mena, don't most people say efficiency is pretty much a useless parameter, in car anyway? i can see where in home is different, and i also now understand why pro audio speakers have much smaller asses, lol. but in car, why is efficiency not a big deal? is it because of the amplifier companies building for such low impedence?

It's considered useless in a vehicle because of the extremely affordable high power amplifiers available. In a vehicle, consumers want a ton of output in a tiny box. How do you achieve that? Well, based on the Hoffman's Iron Law thread, we know we would probably be best to give some efficiency, keep your low end and small enclosure, and pack a ton of power on. Of course, that might also explain why car audio users damage so many speakers!

Honestly, I think efficiency can be a good thing in any listening venue. Why do we need to pack on kilowatt after kilowatt when we're already getting diminishing returns? Well, it's what the consumer wants, so what's a guy to do? If only people realized what you can do with an efficient design (remember how excited people were when 95Honda from CSo did the 8 RE8's on 150W and nearly cracked 150dB?).

[mrray13 30]

scott, my question is this. you say you can take a higher impedence woofer, tighten up the motor and it'll do the same thing as a low impedence/big motor sub. would that mean much of a change on box design, other then the obvious sub displacement? and would less power then yield similiar overall displacment? meaning cone movement.

Tighten up the gap, you increase B, which decreases Qes, which decreases Qts. I think I'll take some time to post about this later this weekend, but the lower Qts will lead to a smaller enclosure, assuming other parameters like Qms, Vas, and Fs (all inter-related) stay the same. When it comes to thiele/small parameters, there are only 5 that really matter, and all other parameters are derived from those. They are: BL, Mms, Cms, Re, and Sd.

i mena, don't most people say efficiency is pretty much a useless parameter, in car anyway? i can see where in home is different, and i also now understand why pro audio speakers have much smaller asses, lol. but in car, why is efficiency not a big deal? is it because of the amplifier companies building for such low impedence?

It's considered useless in a vehicle because of the extremely affordable high power amplifiers available. In a vehicle, consumers want a ton of output in a tiny box. How do you achieve that? Well, based on the Hoffman's Iron Law thread, we know we would probably be best to give some efficiency, keep your low end and small enclosure, and pack a ton of power on. Of course, that might also explain why car audio users damage so many speakers!

Honestly, I think efficiency can be a good thing in any listening venue. Why do we need to pack on kilowatt after kilowatt when we're already getting diminishing returns? Well, it's what the consumer wants, so what's a guy to do? If only people realized what you can do with an efficient design (remember how excited people were when 95Honda from CSo did the 8 RE8's on 150W and nearly cracked 150dB?).

jesus, you guys make me realize just how much i don't know about the inner working of a subwoofer. lol. thanks for making me inferior.

in anycase, while i understand what parameters are important, what i'm getting at is this. if one does all the right things to make the sub that much more efficient, ie:8 ohms and whatnot, and now the motor is smaller, and just as strong, we can then build smaller enclosures, use less power and have the same output as the larger motored, less efficient, more power getting, low impedance driver? or am i way the hell off?

as far as the speculation on why they aren't building things like that, it is indeed mostly marketing. teh re8 getting loud was extremely cool, but then again, tuan got damn near as loud with just rl-i 8s and a bunch more power. so we have what i'm talking about. many efficient subs with less power vs few inefficient (in comparision) subs with a bunch more power, similar results.

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee

[JimJ 11]

If messing around with 70 year old amplifier and speaker designs has taught me anything, it's that...chances are, somebody's tried it, and there are a lot of ideas out there that shouldn't be discarded in today's world Altec used 16 ohm drivers in cabinets the size of 'fridges, and they'll still rock your skull out to this day. Because amplification wasn't - and still isn't, for the non-mass market stuff - cheap. Or easy to move for that matter

[Aaron Clinton 2,372]

I need to read what Scott wrote a few times so I fully grasp everything he said.

[pimpedout97x 4]

interesting read.

my eminence are 8 ohms

[helotaxi 46]

interesting read.

my eminence are 8 ohms

Still doesn't make them good

[Aaron Clinton 2,372]

Posted and cited on CA-F.

[The enD 467]

I am really confused about this. Should I get D2 for 1 ohm or D1 sub for 0.5 ? Or maybe 2 ohms ?

At 0.5 it requires more juice(more batteries, alternator, wires) and it stresses the system.

I understand it that way- when you are playing at 0.5 it is more resistant and you have to throw more power to have the same output in sound. Then why shouldn't I wire to 1 ohm, having less resistance than 0.5, thus resulting I don't have to throw so much power at the subwoofer to make the same output in sound, and not so much stressing to the amp and my electrical installation?

I am a Please someone explain to me.

[Jay-C76 333]

One of the best articles I've read on here to date!

Very nice write up from the Staff.

I just wanted to say good job guys!

Looking forward to more quality information like this!