car acoustics

Post and discuss acoustic topics, Studio design, construction, and soundproofing here

Postby Philip de Haan » Sun Jul 25, 2004 4:01 pm

Sorry but something went wrong with the attachments.

Here they are.

Philip.
Attachments
windows.gif
windows.gif (9.55 KiB) Viewed 11417 times
mercedes.gif
mercedes.gif (9.13 KiB) Viewed 11417 times
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Postby bert stoltenborg » Sun Jul 25, 2004 5:15 pm

OK.
This settles it, we're only gonna perform in rooms the seize of a car. Finally we get rid of carrying PA-systems around. The standing wave can be treated with an dedicated EQ, or has anybody an idea for a basstrapp??? :-)

Eric, if you read this, you're the smilies-expert. Why can't I use the smilies? Or are dutchman excluded? :-)

Regards,

Bert
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Postby Eric.Desart » Sun Jul 25, 2004 5:17 pm

Philip de Haan wrote:Conditions:
Ampeg 4x10" enclosure (closed box) measured half space and calculated to full space.
This is the dotted line in mercedes.pcx..


Hi Philip,

MANY thanks.
Can you help me a bit? What do you mean with the above sentence?
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Postby Eric.Desart » Sun Jul 25, 2004 5:24 pm

bert stoltenborg wrote:Eric, if you read this, you're the smilies-expert. Why can't I use the smilies? Or are dutchman excluded? :-)
Bert


:-) Don't say this out loud or Dan listens to Scott....

Check your profile: There is a related setting.
Also check that smileas aren't disabled underneath the message entry window.

The dutchman until now, I think are seen as good and not dangerous, the belgians bit less ........ :?
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Postby Eric.Desart » Sun Jul 25, 2004 5:43 pm

Bert,

:) MAGIC ......
I can't get your smilies to work either (tried to edit your message).

This must be "BERT" related (whatever this means in computer notions, Bert BUG or BUG Bert or something)

:-) :-)
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Postby bert stoltenborg » Sun Jul 25, 2004 6:17 pm

:-) always the small guys......
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Postby Eric.Desart » Sun Jul 25, 2004 6:27 pm

Bert,

It was BERT related, but you didn't read my message :(

Your setting in your profile was set to disable smileys.
Changed it for you now.

:)
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Postby Philip de Haan » Sun Jul 25, 2004 9:42 pm

Hi Eric,

What I meant is, that I measured the 4x10” box via a groundplane measurement setup. This means that the 4x10" box is standing on the floor and the microphone is lying on the floor. This gives a +6dB rise in the sensitivity readout. In the graph this is corrected giving the 4pi or full space sensitivity@1W/1m. So the 4x10” box is showing a sensitivity of 96dB@1W/1m for frequencies higher than 100Hz.
The solid line of the box in the car represents the SPL at the driver’s seat for 1W input. At 50Hz the SPL is 106dB for 1W input meaning that you still need 2500W for 140dB (neglecting powercompression and excursion limits). A smaller car will be beneficial in getting a higher SPL at lower power/excursion.

Philip.
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Postby bert stoltenborg » Sun Jul 25, 2004 10:30 pm

Hello Eric en Philip,

probably you understand Philip, but a 4 x 10" means a loudspeaker cabinet with 4 * 25 cm (10 inch) speakers in it.
Powercompression relates to the fact that a speaker coil when you put more amplifier power in it heathens up, the resistance gets higher so that not all the power is converted in higher SPL. So you can put more amp power in it without getting more output 'till the gear starts to smoke. There are physical limits to what's possible concerning output.
Right, Philip?

:-)

(still no smilies?)
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Postby Eric.Desart » Mon Jul 26, 2004 8:38 am

Philip , Bert

Thanks,

The Philip part I understood now.
So with this setup is assumed that the signal at the mic is the pressure of a hemisphere where the reflected signal remains exactly in phase and then recalculated to a sphere.

If I'm wrong use the new smiley ......

Bert the compression part is for intelligent guys. But it's good that you explain so I know that part is out of my league.
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Postby Philip de Haan » Mon Jul 26, 2004 8:54 am

Bert, Eric,

You both are right.

Philip.
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Postby Brian Dayton » Mon Jul 26, 2004 7:57 pm

hey philip, thanks for the measurements.

it looks like they are at least broadly similar to what i had from so long ago, eh? a peak, and a rolloff at very low frequencies presumably due to non-perfect pressurization.

so the peak, then, in a room mode?

and lack of perfect seal for the lf rolloff. the return at 10hz in my graph... possibly an RTA artifact? this was not MLSSA but whatever RTA the local stereo store had.

thanks thanks

Brian
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Postby Philip de Haan » Mon Jul 26, 2004 10:12 pm

Hi Brian,

The roll off below 10Hz has maybe also something to do with my measurement set-up.
Microphone
Pre-amp
Power-amp
Normally I’m not so interested in frequencies below 10Hz, so I never checked this.
Maybe I'll do on another rainy Sunday afternoon.

Philip.
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Postby Brian Dayton » Tue Jul 27, 2004 1:48 am

i see i see

i guess it hadn't occured to me that the LF rolloff could be equipment. if it is, let's say, an equipment phenomenon, then it appears that you have low frequency extension to forever

in any case, you got more than i did in the Trans Am
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Postby Bob » Mon Aug 02, 2004 11:21 am

There's a couple of paragraphs on car acoustics here
http://www.saecollege.de/reference_mate ... stics1.htm
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Postby Philip de Haan » Wed Aug 04, 2004 9:50 pm

There's a couple of paragraphs on car acoustics here
http://www.saecollege.de/reference_mate ... stics1.htm

Hi Bob,

I think we all agree here that a car is not at all behaving as open space not even with 4 windows open. ( Then it is behaving like open space, only below 30Hz )
The saecollege article tells another story (with a lot of guesses).

But hey, I measured a Mercedes (not my own). Maybe all other cars are so floppy, that the do behave as open space.

Philip.
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Postby Philip de Haan » Wed Aug 04, 2004 9:51 pm

There's a couple of paragraphs on car acoustics here
http://www.saecollege.de/reference_mate ... stics1.htm


Hi Bob,

I think we all agree here that a car is not at all behaving as open space not even with 4 windows open. ( Then it is behaving like open space, only below 30Hz )
The saecollege article tells another story (with a lot of guesses).

But hey, I measured a Mercedes (not my own). Maybe all other cars are so floppy, that the do behave as open space.

Philip[/quote]
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Postby Brian Dayton » Wed Aug 04, 2004 9:56 pm

lol!

the all time repeated-post record

hey, thanks again for taking the time, Philip
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Postby Philip de Haan » Thu Aug 05, 2004 8:38 am

Brian,

Sorry, I had some trouble with the quote, and I got a error message while submitting the reply.

Philip.
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Postby Eric.Desart » Thu Aug 05, 2004 1:56 pm

This SAE description is almost a chidish one from somebody who does not seem to have an idea how to calculate with dB's and what they represent as arithmetic factors.

It strange that such a thing is on the SAE site.

And you don't have to be specialized in car acoustics.

Eric
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