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-   -   Can someone explain the theory behind "sound reinforcement drivers"? (http://www.diyaudio.com/forums/pa-systems/26328-can-someone-explain-theory-behind-sound-reinforcement-drivers.html)

Cal Weldon 18th January 2004 11:20 PM

Can someone explain the theory behind "sound reinforcement drivers"?
 
I don't mean what they are used for, I mean why is there a 15" driver that is down 3dB already at 45 Hz. What is the advantage in building this over a driver that completes the bass spectrum.
Thanks
Cal :confused:

BAM 18th January 2004 11:27 PM

In the large rooms that sound reinforcement systems are used, it would be extremely difficult to pressurize the space below something like 40 Hz. The LAB Horn Subwoofer only accomplishes its 32 Hz by causing a slab of air to move 3" in either direction. It would require a huge amount of displacement. Instead, sound reinforcement engineers focus on getting the most response from the least amount of power, and this has the advantage of requiring sound guys to spend less money on amplification. It is an OK tradeoff because live music doesn't have that much sub-bass content anyway.

kelticwizard 18th January 2004 11:38 PM

Quote:

Originally posted by BAM
Instead, sound reinforcement engineers focus on getting the most response from the least amount of power, and this has the advantage of requiring sound guys to spend less money on amplification. It is an OK tradeoff because live music doesn't have that much sub-bass content anyway.
It should be pointed out that the lowest note on a normally tuned bass guitar-the instrument which often provides the "bottom" on most popular music-is 42 Hz.

Also, when it comes to moving air, 6 dB=1/2 octave. So all other things being equal, you can design a box that delivers down to 30 Hz with 91 dB@1W/1M sensitivity or one that delivers 42 Hz with 97 db@1W/1M sensitivity.

Put another way, it takes the same amount of air moved to produce 30 Hz at 91 dB as it does to produce 42 Hz at 97 dB.

Most 3 Ft³ DJ cabinets with 15 inchers have an F3 around 60 Hz, so by experience that seems to be low enough for popular music, and allows the designer to turn his attention toward sensitivity.

Talking to some cyber friends who are DJ's, it often occurred to me how fine a thing it would be to design a 3 Ft³ cabinet with a 15 incher that had an F3 of 42 Hz and a sensitivity of 97 dB@1W/1M. To my knowledge, there is no such beast presently, (if someone knows of one, please post). :)

The 15 incher with the closest Thiele-Small numbers that I know of that might get close is the McKenzie C15 400lr. I don't even know if that is sold in North America.

Stephen D 19th January 2004 02:00 AM

Quote:

Originally posted by kelticwizard


It should be pointed out that the lowest note on a normally tuned bass guitar-the instrument which often provides the "bottom" on most popular music-is 42 Hz.


That was then but this is now. ;)

What I mean is these days the 5/6 string bass guitar (at one time rare) has become quite common place if not the norm. Lowest note for them is normally a B approximately 31.5 Hz! This is why I recommend port tuning no higher than 36 Hz for PA /Home music subs or bass guitar cabs, because of the increasing risk of over excursion damage do to port unloading. I've known a few 5/6 string bass players to rip the drivers right out of the spider using a cabinet tuned to high (41 to 50 Hz range). Most older cabs are tuned to high (following the old 4 string bass standard) & I'm surprised how many newer ones are still. I had one guy bring his 2x15" spkrs into the shop that were ripped totally out of the spiders. He was playing a 5 string bass through a sub octave box that adds a note an octave below what's played!!! :smash: :smash: :eek:

OMNIFEX 19th January 2004 02:36 AM

Re: Can someone explain the theory behind "sound reinforcement drivers"?
 
Quote:

Originally posted by Cal Weldon
I don't mean what they are used for, I mean why is there a 15" driver that is down 3dB already at 45 Hz. What is the advantage in building this over a driver that completes the bass spectrum.
Thanks
Cal :confused:


There is a Huge difference from playing music in your
home, and, providing sound reinforcement in a venue.

1. Turntable Rumble And The Launching Of Cones

Turntables, and, vibrations don't mix. Especially when you
have 10 - 10,000 party goers jumping to the beat. You
will have a greater chance of destroying your woofers
if you don't use some kind of cutoff frequency to prevent
uncontrolable excursion.

2. Sub Frequencies That Are Just Not There.

Rock, Dance, and, Hip Hop generally don't have any low
frequencies under 50Hz. The rare few, are so low (In
SPL) it can easily be rolled of without being noticable.

3. Home Speakers -vs- Pro Audio Speakers Requirements

Pro Audio Speakers are designed to not rely
on room gain to get the necessary bass under High
SPL usage. When the object is to achieve lower bass,
you generally add more subs. Thus making the cabinets
couple, and, having the Lower Bass increase. So, you
can achieve 20Hz by merely adding more subs, instead
of fighting with one box to cover the lower notes accurately.
For the home Audiophile, room gain is welcomed. For
the Soundguy, it is the biggest obstacle we need to
overcome.

4. Screaming Fans, And The Need For Volume

Keep in mind that efficency is the key, when you are
required to cover a large area. PA speakers are designed
to play loud to overide the screaming fans when they
hear their favorite song. This is why home speakers,
and, car speakers cannot be used for PA Requirements.
They are just not loud enough. PA Subs are designed
to perform with only one boundary........ The Floor.
Home Subs are designed to use with more boundaries.
(Floor, Corners, Wall)

The frequency response needs to stay within the Flat
range, and, rolloff to the desired f3. Using an Equalizer
or Room Gain to make up the declining rollof like home
subs........... Not Possible

GRollins 19th January 2004 04:40 AM

Just thought I'd throw in a note here, so to speak. I'm a bass player, usually 4-string, but I do own a 6. While it's true that if a 6-string bass is tuned low, i.e. to a B (the tuning on 5 and 6-string basses cannot be taken for granted, some tune for a higher pitch), you'll get a low pitch out of the instrument. But...the actual--and I mean real-world--response of most bass rigs is pathetic by hifi standards. As an example, the specs frequently quote low end response as being down 10 dB. "Usable?" I don't think so! That simply won't do for home use, and I question its validity for bass rigs and PAs.
Setting aside questions of efficiency, reliability, and so forth, most people (bassists and synth keyboardists included) wouldn't know true low end if it bit them on the ***. They, like the boom-boom car stereo guys, think that if it vibrates their chest, it's deep. Nope. Just loud midbass. We're talking 60-80Hz.
Also, like many foolish stereo users, musicians sometimes have really destructive ideas about how to match a head (the amp) to a cabinet. Yes, it's quite possible to rip a cone loose from the basket. But that's not necessarily saying that it was playing a deep note at the time--just a loud one.
Playing through an effects box that synthesizes sub-harmonics can be thought of as an IQ test. Anyone who blew their drivers failed the test. If you're going to pull stunts like that, plan your rig accordingly. Spend lots of money. Lots. And still you should live in fear.
To answer Cal's original question in the vernacular, you can't have loud and low at the same time without spending a really, really huge amount of money. Given that choice, most people would choose loud over low every day of the week, cuz money don't grow on trees.

Grey

P.S.: Wanna scare the hell out of a bass player? Get him to play through his stereo at low volume. Ninety-nine out of a hundred bassists will have a heart attack--they never knew that much low end was available from their instrument; their bass rig just couldn't cut it.
I take no responsibility for what happens if they start trying to crank up their stereo once they've had that revelation.
Dynamics are a whole 'nother thread. Most 300-500W bass rigs have enough capacitance in their power supplies for a 30W home stereo. If that much. 'Nuff said.

synergy 19th January 2004 10:06 AM

Hi guys first post here (nice site btw! hope the server issues get sorted!)

kelticwizard you asked for some 15"ers with a low Fs and high sensitivity

here's some at Precision Audio Products

they'll all do the job some better than others

i use the PD 154's in a dozen short folded horns i've got - kick *** punch around the kick drum

the PD 1550's are 99dB with an Fs of 31Hz - that do ya?

dunno if you can get them in the states but Eminence have just bought the company so there is every possibility

laters
dave

mikee12345 19th January 2004 11:09 AM

the jbl2226 goes well in 3cubes= efficiency is 97db/1watt

at 100hz :D ;)

there will never be a free lunch. my miniature basshorn for 40hz-of which you would require a stack of 4 outside, is 150L each... and ~104db efficiency..

GRollins 19th January 2004 02:38 PM

Low Fs looks good in simulations, but does not equate to flat response in the real world, witness the Shiva/Titanic/et. al. Fs for these drivers is typically in the teens to twenties, depending on driver and version, yet not one of them can reproduce anything like flat bass without eq. You'll invariably find that a driver of that nature will, like most bass and PA drivers, give a lot of output in the 60-100Hz range, then begin a long, slow rolloff, leading to response in the 20-30 Hz range being 10-20 dB less. Cabinet design choices do not cure the problem. The best you can do is put the driver in an undersized cabinet, thus raising the Q, which will flatten the response down to 40Hz or so, yet with a dip-bump before rolloff. Surprise! We're back where we started. Getting response anywhere near flat down into the 30 Hz and below range is not easily--or cheaply--done.
Trust me. Been there. Done that. Got a drawer full of T-shirts to show for it. Still there, for that matter. Good tweeters and midranges aren't hard to come by. It's 150Hz and below where you hit the hard rocks and start running into serious problems.

Grey

phase_accurate 19th January 2004 03:09 PM

Fellow bass-player GROLLINS wrote:

Quote:

They, like the boom-boom car stereo guys, think that if it vibrates their chest, it's deep. Nope. Just loud midbass. We're talking 60-80Hz.
Unfortunately thats also what guitar-players, drummers, soundmen etc prefer our instruments to sound like ! :mad:

One of my next experiments will be two ELF subs (using RCF L18P300 drivers).
And yes, I prefer the sound of an uncompressed bass over the mainstream bass-sound even if it doesn't get as "loud" using an 1 kW amp as some 200 Watt instrument amps go.

Regards

Charles


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