High SPL @ 60hz

colinbg

Member
2008-01-23 8:08 am
Hello all,

I thought I would get some feedback as I am looking to build a HIgh SPL application that is far away from the norm. Basically I am building a test application to test indutrial equipment by using sound. Specifically, I need to move air, quick bursts of air that will trigger sensors to be exact. My current plan is to use car 10" subs since they seem to have good cone travel to actually "move" the air at 60hz (best guess at what gives the most punch). I realize that 60hz is low and may not give as much punch as say 120hz, but I can always change that later. I figure since car stereo SPL competitions are popular they would have the best range of products for my appilcation. Anybody want to chime in about what would work best? I am sure this is a bit diffrent from the normal "help me" question... I thought you guys might be intrigued and lend me your expertise in choosing what would work best.
 

MaVo

Member
2006-01-07 12:40 pm
you could tune a resonant system, so that its most efficient point is your 60hz. tapped horns for example have a few frequencies, where the driver excursion is so minimal, that a lot of spl could be produced, but those points are small in bandwidth, sine tones with long envelopes could be fine. short tone bursts on the other hand will have a broad spectrum.
 
Hi,
a vented box tuned to the desired frequency resonates at that frequency and the driver excursion is very low, allowing enormous SPL over a tiny bandwidth.

Look up WINisd and try some numbers.

But, you must monitor cone movement to check you don't overstroke your driver!!!!!!

Alternatively, build a bass horn for High SPL.
 
simon5 said:


You have a 30 Amps line at your job ? That means 7200W to me !

We paralelled two 16A lines to be sure.
At the tuning frequency of a BR box you get an impedance peak, we didnt measure how high the peak was, so how much power it really was I don`t know.

We started first with four boxes in series- then three, then two, then one. Three was louder than four, two was about the same as three but a bit more distorted. One was less loud, but still crazy loud :hot:
 
At the tuning frequency you get an impedance DIP and the thermal power handling is the lowest among all frequencies, while the excursion limited power handling is the highest. It's quite easy to burn voice coils by applying a continuous tone near port resonance, not only due to the low impedance but because null cone displacement results in no air movement inside the pole piece and no voice coil cooling.

On the other hand, a high-Qts high-cone-excursion big driver in a small enclosure will result in gentle impedance and SPL peaks around 60Hz and plenty of cone displacement to cool the voice coil. In these circumstances, direct connection to mains is not a problem at all, impedance at 50/60Hz may be 50 ohms if the system is tuned properly. Four series/parallel drivers may be used for 230V.

BTW: Wow, now the formula to win car SPL contests is public domain :D:D:D
 

colinbg

Member
2008-01-23 8:08 am
MaVo said:
you could tune a resonant system, so that its most efficient point is your 60hz. tapped horns for example have a few frequencies, where the driver excursion is so minimal, that a lot of spl could be produced, but those points are small in bandwidth, sine tones with long envelopes could be fine. short tone bursts on the other hand will have a broad spectrum.

This is what my original plan was... The enclosure seems to be hugh though and I really just need to move air, not at a specific sound per se. THe real question I have is at this point: How can I capture the air from teh driver efficiently without impeding the driver itself? I need to channel the air pulses it creates and by doing so it seems to me the enclosure design is then rendered useless or ineffective.


Peter M. said:
Hi,
Are you using just a sine wave?

A BR box tuned to 60hz can get you maximum powerhandling at that fequency.

At my previous job we used a Cerwin Vega stroker 18" in BR box tuned to 50hz, and connected it straight to the wall.
240V 50 hz :yikes: Great fun :devilr: and it survived :devilr:

I am using a sine wave, But I dont have to if need be. I just need to create a pulse and a sine wave seemed the cleanest way to do this. I tried a kick drum but the wave was to long (time wise) and I am really tring to get one solid burst of air.


AndrewT said:
Hi,
a vented box tuned to the desired frequency resonates at that frequency and the driver excursion is very low, allowing enormous SPL over a tiny bandwidth.

Look up WINisd and try some numbers.

But, you must monitor cone movement to check you don't overstroke your driver!!!!!!

Alternatively, build a bass horn for High SPL.

How would I go about building a bass horn, I liked it up briefly and it refers to low brass instruments... I like the idea, but how do you go about this?
 
How loud do you need it, and for how long? How close can the equipment under test be to the moving cone? Is vibration a concern?

120db at 1m is a piece of cake at 60hz. A pair of 10" subs and 1000 watts will do it.

How big are the things you are testing? You can get much much louder by placing whatever you are testing inside the subwoofer. [email protected] is within reach.

Dan
 

colinbg

Member
2008-01-23 8:08 am
Re: compressed air....

moray james said:
and a valve to modulate the release of the air in the tank. That has been done before. You might ask Tom Danley directly.


ACtually. this is what we currently do. however, the control of the PSI and valave release and such are done by a custom system which is too costly to rebuild or re engineer. The beauty of loudspeakers si sthat they provide a control of pressure via volume. The other beaty is that instead of speding 20k to develop a system, I can do it for under 2500.00 if I use off the shelf audio components and editing softwrae to create mt testing solution.

I am 95% sure I can get this to work, its just finding the best way to approach it first. Thanks.
 
Since you only want to channel air, might as well use a vented subwoofer and only use the port at the maximum air velocity frequency to trigger your sensor. Just put the sensor just in front of the port.

Also, ain't 60 Hz too fast for your sensor ? I mean you'll have positive pressure then negative then etc. You might as well use 10 Hz ?
 
Try here too

http://www.realmofexcursion.com/


At my previous job we used a Cerwin Vega stroker 18" in BR box tuned to 50hz, and connected it straight to the wall.

:D I wired a 6vac output from a mains transformer to the speaker output of my Amstrad Midi system, when I was young. With music playing, I switched on. The driver survived, for some reason the music stopped and I didn't make my Midi any louder!:hot: :hot:
iUSERTLO72p:ashamed: :headshot:
 

colinbg

Member
2008-01-23 8:08 am
simon5 said:
Since you only want to channel air, might as well use a vented subwoofer and only use the port at the maximum air velocity frequency to trigger your sensor. Just put the sensor just in front of the port.

Also, ain't 60 Hz too fast for your sensor ? I mean you'll have positive pressure then negative then etc. You might as well use 10 Hz ?


This is what I am thinking. By making a tuned enclosure and then using the port to provide my air output. With 10hz though its actually to slow and most loudspeakers cannot reproduce this frequency. I suppose I could just feed a DC pulse to the driver to activate the full range of the magnet but I believe the driver would not last long in that capacity.
 

kelticwizard

diyAudio Moderator Emeritus
2001-09-18 2:33 am
Connecticut, The Nutmeg State
One suggestion is to use a fourth order compound box, back chamber sealed, front chamber ported to 60 Hz or whatever you choose. The larger the front chamber compared to the back, the greater the SPL and the narrower the bandwidth. If all you want is one note bass for short duration, this would seem to be the way to go.

You can model this on WinISD or any of a number of freeware programs.
 
colinbg said:
This is what I am thinking. By making a tuned enclosure and then using the port to provide my air output. With 10hz though its actually to slow and most loudspeakers cannot reproduce this frequency. I suppose I could just feed a DC pulse to the driver to activate the full range of the magnet but I believe the driver would not last long in that capacity.

Several drivers can do 10 Hz in a large box.

Anyway, maybe you could record a signal with only the positive half of a 60 Hz sinewave, and play that. I would also bias the driver with DC so it's always at its negative Xmax point, trying not to cook the coil. That means you could use a really loud half sinewave and be able to use the full forward stroke of the driver, starting at -Xmax to end at +Xmax.

You could do it like something in that example, 8 drivers with single centered port, something like a 4" Precision Port tuned to 60 Hz.