Midbass

[bdavies11 10+ year member]

I understand what your saying but your also implying that anytime you double the impedance for any driver your also increasing the sensitivity by 3db's which doesn't always hold true.

 

[helotaxi 5,000+ posts]

All I've ever said is that if two drivers have the same sensitivity rating @ 2.83V/m, the driver with the higher impedance is actually more sensitive watt for watt. As a result it will usually get louder than the lower impedanc driver off the same amp and the amp will place less of a strain on the car's electrical.

 

[MiniVanMan 10+ year member]

It's a generalization, and no different than saying you get double the power going from 4 ohm to 2 ohm with an amplifier. There are variables in every situation, but they're exactly that, variables. Variables affect everything. There's no magic product that takes all variables out of the equation. The same variables that affect an 8 ohm driver, will affect a 4 ohm driver. There are certain constants though, and they can be planned for. With those constants we can come to some fairly valid conclusions. It's an exercise in compromise when dealing with audio drivers. So while it may not be always true that a 3 db gain in efficiency will be realized, there will be a gain. If only 2 db, or whatever.

Unfortunately, marketing departments have too much say in how a speaker will be presented to the public, and how it should be engineered. An 8 ohm speaker will not sell on the general market because of the fallacies, and myths surrounding car audio. Even though it has definite advantages.

It's much more lucrative to put a girl in a bikini in front of a car holding a speaker and have a caption saying "MORE POWER", than having a fat, sweaty engineer holding a speaker and a tube of KY saying, "MORE EFFICIENCY".

There are advantages to 4 ohm drivers, they're just not the advantages that car audio marketing departments really care if you know. Nor do they want to explain them.

So, the argument, is, and what started this, was not to look at power, and impedance, but rather efficiency. That just because it would take 200 watts at 2 ohms wouldn't make it louder than a 4 ohm driver at 100 watts, or 8 ohm at 50 watts. That is doing the basic math. Yes there are assumptions in there, and I've explained those assumptions, but the basic point is to get away from thinking in the terms of more power, less impedance.

 

[squeak9798 5,000+ posts]

So, the argument, is, and what started this, was not to look at power, and impedance, but rather efficiency.

You keep saying that....but so far all I've ever seen you mention is impedance....

Let's go back to some of your first comment;

That driver ran at 200 watts won't really be any louder than a 4 ohm driver at 100 watts,

YOU DO NOT KNOW THIS.

Where is your reference to efficiency? All I see is assumptions based solely on impedance.

You are assuming that another 4ohm driver will have a higher sensitivity....THIS WILL NOT INHERENTLY BE TRUE.

You can't say "well I meant if all else was equal" because that driver is not available in 4ohms, so you WILL NOT have the opportunity to compare the two different drivers "with all things equal".

You CAN NOT make an assumption of efficiency or output level of driver A vs driver B based solely on impedance, as you are obviously attempting to do.

Carrying on;

Not to get too technical, but an 8 ohm driver running off of 100 watts will have roughly the same output as a 4 ohm driver running off of 200 watts. Given all other things being equal.

You are again making the HUGE assumption that "all else will be equal". This will happen....hmmm......hardly ever. Especially when comparing two completely different drivers.

Generally (key word again) speaking, an 8 inch driver with a higher overall sensitivity, will a lot of times have lower low end capability.

Hoffman's Law dictates that in order to increase efficiency while reducing low frequency extension, the driver would require a substantially larger enclosure.....not practical in most applications. Most times a higher efficiency driver will lack in low end compared to a driver with lower efficiency.

I'm on a personal mission though to debunk this myth that to get louder you need lower impedances, and more power.

Great!

But you need to provide more thorough information and stop making so many assumptions, especially when they are based solely off of impedance.

Take an example like the RS180. It comes in both a 4 ohm and an 8 ohm version.

Lets.

Using the T/S parameters listed on PE's product page;

4ohm:

SPL = 112+10*LOG(9.64*10^(-10)*40^3*22.9/.48) = 86.69db

8ohm:

SPL = 112+10*LOG(9.64*10^(-10)*38^3*24.9/.47) = 86.48db

Only .2db difference, and that's actually in favor of the 4ohm driver.

If you use the T/S parameters listed on the "Exported CLIO" page;

4ohm:

SPL = 112+10*LOG(9.64*10^(-10)*38.32^3*22.59/.49) = 85.98db

8ohm:

SPL = 112+10*LOG(9.64*10^(-10)*40.26^3*24.35/.49) = 86.95db

Only 1db difference in favor of the 8ohm driver.

And if you use the T/S Params Zaph measured for the 8ohm driver;

SPL = 112+10*LOG(9.64*10^(-10)*40^3*20.06/.5153) = 85.8db

Take an amp that does say 100 watts at 4 ohms, and 50 watts at 8 ohms.
Take both drivers and run them subsequently on the same amp. Both drivers will have relatively the same output.

Looking at the above, I fail to see any sign that the 8ohm driver is actually 3db more sensitive than the 4ohm version. At best, so far, it has a sensitivity that's 1db greater......and that's only if we use the parameters that best suit the point you are trying to make.

Just a few more examples, lets check out madisound a little bit here too....

Vifa MG18WK09 using manufacturer stated parameters.

4ohm;

SPL = 112+10*LOG(9.64*10^(-10)*36^3*41/.32) = 89.61db

8ohm;

SPL = 112+10*LOG(9.64*10^(-10)*34^3*45/.41) = 88.19db

Scanspeak 7" Revs using manufacturer stated parameters.

4ohm;

SPL = 112+10*LOG(9.64*10^(-10)*33^3*42/.38) = 87.83db

8ohm;

SPL = 112+10*LOG(9.64*10^(-10)*28^3*59/.44) = 86.53db

Vifa PL18W using manufacturer stated parameters.

4ohm;

SPL = 112+10*LOG(9.64*10^(-10)*37^3*25/.33) = 87.68db

8ohm;

SPL = 112+10*LOG(9.64*10^(-10)*38^3*25/.4) = 87.19db

First three I could find that were offered in both 4ohm and 8ohm, chosen at complete random.

Stop thinking in terms of impedance, but rather sensitivity.

Practice what you preach ?

That just because it would take 200 watts at 2 ohms wouldn't make it louder than a 4 ohm driver at 100 watts, or 8 ohm at 50 watts. That is doing the basic math. Yes there are assumptions in there,

Very large assumptions, especially when comparing two completely different drivers and even apparently when comparing the same model driver in both coil configurations looking at the figures I calculated above. So many assumptions that the statement alone doesn't really hold true at all in reality. You must compare the two drivers in question and NOT be making assumptions based off of theory, impedance and/or generalizations.

The units above would need some pretty large (and I would say unacceptably large) variances in stated vs actual T/S parameters to come even close to having 3db higher sensitivity.

 

[MiniVanMan 10+ year member]

I keep mentioning impedance in context of the argument. If you're going to base your opinion on which driver to choose, and you choose a 4 ohm driver, or lesser impedance driver because it has a lower impedance, and you can deliver more power to it, that is not making an educated choice, and you're making that choice for the wrong reasons.

Doing the math helps, and I appreciate that. At least you're making valid arguments, and they're pretty hard to argue with. You've also taken many of my statements out of context. If I don't mention impedance, then people don't know what the argument is.

Hoffman's Law states basically what I said, but you seem to quote me to refute me. You just wrote it in the inverse of how I stated it.

I don't care what driver you choose. I'm just tired of hearing the same comments about 8 ohm drivers.

I can do the math, and I can get the same sensitivity numbers you get. They're irrefutable. However, I know, when I put both the RS180-4 and -8 into my vehicle running off the same amp, the audible difference is negligible. Even metered, the difference is only around .5 db on average (I've done a couple of vehicles). I did that because I had a hard time in the beginning believing that an 8 ohm driver would do that. Now that's while delivering a good amount of power though, 150x2 @ 4 ohms. If it were just a 75 x 2 @ 4 ohms, I'd be hesitant to suggest an 8 ohm driver for reasons I stated before.

So, while, I have been overgeneralizing, I've been trying to debunk myths. Oversimplifying is also saying that a 4 ohm driver running off of double the power of an 8 ohm driver will be 3 db more sensitive. That's the argument I'm debunking.

So, yes, I have been making references to impedance, but that was in the context of the argument that for some reason the lower impedance will create a louder driver. It very well might. But YOU DO NOT KNOW THIS!! I can make the exact same argument the other way for every time somebody says I'm generalizing. Why is it okay to generalize with a lower impedance driver and not a higher one?

Maybe I should not have said, "will not". I should have taken the road of "not necessarily".

Even sensitivity numbers don't tell the whole story. They're a bit more accurate than impedance numbers. Zaph consistently shows T/S parameters to be quite a bit different than advertised in his testing.

So, you're right, I'm wrong. I should have just kept my mouth shut, and not even brought up the argument. I should just accept that those that don't want to know don't need to know. Making argument against generalizations with generalizations is not very scientific I admit. I am wrong on that. However, I find that when trying to reverse a line of thinking, throwing out equations, and a bunch of facts, figures, and technical data is not the best way to do that.

To show that generalizations, and arguments can be made for both sides promotes curiosity and critical thinking.

I can go on and on about various "gross" generalizations in car audio, and misinformation. Baby steps though.

Thank you for the equations, but even you must admit that they don't tell the whole story. It's car audio. It's very hard to predict how anything will react from car to car. We have to go on generalizations at times.

In other words, I don't know why we're arguing. Unless you have stock in 4 ohm drivers.

 

[squeak9798 5,000+ posts]

I keep mentioning impedance in context of the argument. If you're going to base your opinion on which driver to choose, and you choose a 4 ohm driver, or lesser impedance driver because it has a lower impedance, and you can deliver more power to it, that is not making an educated choice, and you're making that choice for the wrong reasons.
Doing the math helps, and I appreciate that. At least you're making valid arguments, and they're pretty hard to argue with. You've also taken many of my statements out of context. If I don't mention impedance, then people don't know what the argument is.

It's not hard to state it properly.

Such as;

"Using a 4ohm w/ a sensitivity of 87db w/ 100w is the same as using an 8ohm driver w/ a sensitivity of 90db w/ 50w"

Had it been stated in that manor, I probably wouldn't have even responded in the first place //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

Hoffman's Law states basically what I said, but you seem to quote me to refute me. You just wrote it in the inverse of how I stated it.

Mmmm...then I must have misread what you typed.

After reading this comment, I have come to realize that by "lower low end capability" that you may have meant "less low end capability".

When I originally read the statement, I read it as "lower low end" referring to the driver extending "lower" (deeper, etc) in frequency and not "lower" as in decreased low end capabilities.

However, I know, when I put both the RS180-4 and -8 into my vehicle running off the same amp, the audible difference is negligible. Even metered, the difference is only around .5 db on average (I've done a couple of vehicles). I did that because I had a hard time in the beginning believing that an 8 ohm driver would do that. Now that's while delivering a good amount of power though, 150x2 @ 4 ohms. If it were just a 75 x 2 @ 4 ohms, I'd be hesitant to suggest an 8 ohm driver for reasons I stated before.

Then state it more closely to those statements.

So, yes, I have been making references to impedance, but that was in the context of the argument that for some reason the lower impedance will create a louder driver. It very well might. But YOU DO NOT KNOW THIS!! I can make the exact same argument the other way for every time somebody says I'm generalizing. Why is it okay to generalize with a lower impedance driver and not a higher one?

I don't recall anybody doing so in this thread //content.invisioncic.com/y282845/emoticons/confused.gif.e820e0216602db4765798ac39d28caa9.gif

Original poster commented about the decent power handling of the driver...which 200w is a pretty high rating for any midbass driver regardless of impedance. That's when you came in with the "200w to that driver = 100w to a 4ohm driver"....which isn't necessarily true and is the statement or theory I think most of the people responding took issue with. You hadn't used the driver to make the same comparison you did above, and you made no reference to efficiency (which it's realistically around 87db, no more or less efficient than the drivers I listed previously).

So, I guess I'm not sure of how "that myth" was even an issue until you brought it up?

 

[MiniVanMan 10+ year member]

So, I guess I'm not sure of how "that myth" was even an issue until you brought it up?

Because I'm overly sensitive (or my impedance is too high, and my coils are wound just a bit too tight) //content.invisioncic.com/y282845/emoticons/hide.gif.2d479cfd917eedfe201353b91522ceab.gif

This has been a good thread. Like I said, it's promoted critical thinking, and very much so on my part. Knowing something, and articulating it, in a manner that is understandable and correct can be difficult. Especially in a situation that has SOOOO many variables to begin with.

I'm reluctant to use hard data, as it doesn't tell a whole story. I'm reluctant to use personal experience, because it may not apply. I'm reluctant to use personal opinion, because as with anybody your opinion does not dictate truth. So, basically, you're screwed. It also leaves the subject WIDE open for the perpetuation of myths, that are, in the end, extremely difficult to debunk. Generalizations become the rule, especially in a forum that leaves communication as an exercise in patience. However, I'm not reluctant to jump right in, and throw myself to the wolves.

I guess the initial argument was that throwing more power into a 2 ohm load doesn't necessarily mean you'll get more output than a similar 4 ohm driver ran off of 100 watts. There are much cheaper options.

Oh and the reference to impedance was based, once again, on an assumption due to the OP posting a driver with a 2 ohm coil. The OP never stated that, but if he didn't see that to begin with, it's definitely something he should be made aware of.

 

[HCCA 10+ year member]

Okaaaay....not what I was looking for, but good info, none the less. BTW, is minivanman also known as Jim Fultz? If not, nevermind. //content.invisioncic.com/y282845/emoticons/rolleyes.gif.c1fef805e9d1464d377451cd5bc18bfb.gif I just made a guess by the vehicle listed.

OK, in reference to my original post. I will be running about 275w to my mid comps B/A Pro 60's. I will be running about 900w to a single B/A SPG555 sub. I was considering a midbass that would bridge the gap, and play down to 60hz. What power would you guys recommend I put to this driver, and what driver? Thanks to minivanman for your recommendations for drivers. (I have room for an 8" driver, with depth to 3 1/2". Well, sort of...I would have to make a baffle plate of 1" MDF to bush it out away from the door card.

One more thing, I had trouble with phasing on my last system running 3-ways up front. I used an Audio Control 24xs crossover (18db slopes). The midbass was in the factory door location, and the mid/tweets were mounted in the kicks. 50w/ea channel to all front drivers. I tried switching phasing of the wires in every conceivable way, but I had a major null in the 125-250 hz region. I couldn't equalize it out. It makes me worried about trying a 3way system up front, when a mid/ tweet combo did great in an earlier system. I know I F*ed up something in the installation, but could not figure it out before I sold the car. Still, I want good midbass in this install. //content.invisioncic.com/y282845/emoticons/suicide.gif.a649d21efc0d1fd4890a6428166586c1.gif

 

[MiniVanMan 10+ year member]

Nah, Minivanman is not named Jim.

Anyway, not really sure what your problem was last time. It could be any number of things. If your midwoofers were wired out of phase, that may have been the problem. That or they just didn't have enough power. Phasing between 2 woofers wouldn't normally account for a 1 octave loss, but stranger things have happened.

Anyway on to the future. That is an AWFUL lot of power you plan on sending those Boston comps. I'd say do the 275 watts to a midbass driver, and send 150-200 to your comps. That's still a ton of headroom. Especially considering the frequencies you're going to ask them to play. The less you ask them to dig deep, the less power you'll need to get good dynamics out of them. Bass takes power. At about 250 hz on up your power requirements dramatically decrease to get good dynamic sound.

What kind of vehicle is this going in?

A couple of ideas that come to mind for midbasses have been stated before. The L18RNX by Seas is a 7" driver totally capable of that given your doors are properly treated.

Nobody has anything bad, or even neutral to say about the Peerless SLS 8". They are some of the best midbass drivers available. They're not overly expensive, but they are deep, coming in at a little under 4".

The Dayton RS225 is wonderful midbass, and cost effective too. Comes in either a 4 ohm or 8 ohm version. The 4 ohm comes in at 3 1/2" deep. So that may be your best solution. They're under $50.00 a piece, and are really a nice detailed, and dynamic midbass.

Usher makes some fantastic extremely low distortion drivers. They're 8" 8955A would do very well, but has a HUGE magnet and is about $120.00 a piece. It's hard to say that you'll hear the distortion differences in a car, but I thought I'd throw it out there.

Personally, I think the RS225 will be fine for what you're asking them to do. For a few dollars more, if you can get the Peerless SLS to fit, then rock on with that bad boy.

 

[HCCA 10+ year member]

Thanks for the reply. I forgot to mention that I tried crossing them at 250, 325 & 500. I settled on 250. As I said, I tried every conceivable combination of phasing, to no avail. (On the old system)

I am installing my new system in a 2002 Explorer. Actually, the power rating that I WAS going to be sending the comps was from a B/A GT28 amp, but I am going to use that for the subs. I am going to use a GT 24 amp for the mids. That should be closer to 200-250w/channel. They are rated to 150W, but I was told that they will handle 250W, all day long. We'll see. I can run a either of the two amps for the midbass, but it sounds like another GT28 should handle those. At 4 ohm (MB driver not yet known, I should be able to send it 200-250W, to match the mids. I can keep the gains down on the mids if needed to balance the system.

I will be adding ensolite to the whole vehicle, and some egg crate foam to the back of the speaker location as well. Just wondering how the MB's will work in freeair, at thhat power level.

 

[helotaxi 5,000+ posts]

You had a pathlength suckout or a standing wave in the car in that freq range. That's pretty common and most every car will have a spot like that. Only real fix is to start playing around in the time domain.

 

[HCCA 10+ year member]

Heliotaxi, I was suspecting a standing wave, but did not know what to do about it. I will be using an Apline 7909 for the head unit. I don't have much control over the time domain without getting into a whole other source unit, that incorperates a time alignment feature. Any suggestions?

 

[MiniVanMan 10+ year member]

It's hard to do, but just angling the speakers as little as 15 degrees towards you can help dramatically. Some cars have nothing in between the two door mounting locations.

It's just another option, if you can make it work.

 

[helotaxi 5,000+ posts]

It's hard to do, but just angling the speakers as little as 15 degrees towards you can help dramatically. Some cars have nothing in between the two door mounting locations.
It's just another option, if you can make it work.

If ii's a phase suckout rather than a standing wave though, aiming doesn't do anything to address the arrival time difference that cause the issue.

HCCA- try moving your head round a bit. If the sound changes noticably and fills in that void, you have an arrival time issue.

 

[envengineer 10+ year member]

Not to fuel the fire in this debate, but often you do not need an 8 ohm driver to be 3db more sensitive in order to achieve the same output as a 4 ohm driver. This is because many (most?) amplifiers produce greater than 50% of their rated 4 ohm power at 8 ohms. (I'm not making an driver argument, rather an amplifier argument)

An example just to clarify my point: Take an amp rated at 200w @ 4 ohm, hook it up to an 8 ohm load, it may very well make 140w rather than 100.

You can see this in many amplifier ratings when comparing the 2 ohm and 4 ohm rating. Again using a 200w @ 4 ohm rating, often the 2 ohm rating is around 300w, not 400.

The doubling of impedance does not neccessarily mean halving of power.

BTW, I went with the SLS8s myself.