Pro ac dip

[Bam!]

hey guys!

Jon.....I mean guys....I wonder if you can help me out here....

here's tha ting :

I evaluated my pro ac 2.5 response for the timber's flatness....

We listened to many cds and found that the timbers coloration was...well a little off.....or different let us say...

So then...

Here's what we did.....We plugged a mike up at ran a pink noise cd at all frequencies...

We then noticed on the computer screen this pretty goos dip at 2.5 Khz and then a rise to 12 khz at 6 db....

Why is that....could the scan speak mid bass driver be pushed up a little to cover this gap ? The specs show that the mid bass driver can go higher....but according to the DIY recipe this setting is what they wanted...

Does this mean that that mid bass driver goes a little nuts when pushed up to those frequencies ? We noticed a rise of 2 dbs when pushed above 2khx with this driver...

Anyone tries to modify the x over to remove this dip ? And if you did what did it do the sound ? Good or bad ?

Thanks!

Fr

[ThomasW]

Just pumping pink noise into the room and measuring the output is not an accurate measurement of the speakers themselves

Unless you use a gated time/domain measurement = MLS, you're measuring what the room is doing to the sound.

[Bam!]

Just pumping pink noise into the room and measuring the output is not an accurate measurement of the speakers themselves

Unless you use a gated time/domain measurement = MLS, you're measuring what the room is doing to the sound.

Good point Thomas....

We did try 4 other pairs that were there with a pretty flat response....

Does that make any difference... ?

[JonMarsh]

Maybe you need to look for a crossover assembly error on the one pair that measures different. Of course, it coudl be a driver problem, too.

If you do a nearfield measurement of the speaker with pink noise (less than 1 meter, centered between drivers), it should give you a decent idea of the system response without much room interaction).

~Jon

[Bam!]

Maybe you need to look for a crossover assembly error on the one pair that measures different. Of course, it coudl be a driver problem, too.

If you do a nearfield measurement of the speaker with pink noise (less than 1 meter, centered between drivers), it should give you a decent idea of the system response without much room interaction).

~Jon

Hi Jon it was about 6 inches from the baffle......

Maybe I miswrote the thread......


I am not havig a problem really....more I was wondering if anyone tried adjusting the x ove differently from the original plans....

[JonMarsh]

We did try 4 other pairs that were there with a pretty flat response....

Well, if one speaker or set of speaker doesn't measure the same as the others, I'd look for the cause of that before adjusting anything! If they're supposed to have been built to the same DIY plans, then, if built per the plans, and if the drivers are OK from the manufacturer, you shouldn't be seeing what you're seeing.

First, double check the phase on the tweeter and woofer connections- if wired out of phase, this will result in a dip in the crossover region- in fact, it should be a very strong and deep dip.

You mention the response being 6 dB up at 12 kHz- this sounds like a problem with the wiring of the tweeter crossover, or the component values used.

Midwoofers are generally not pistonic much above 1 kHz, and pushing them up higher than the intended design crossover around 2 kHz will just bring out their faults more. (energy storage, smearing in upper midrange).

My best suggestion is to conentrate on finding out what is most likely "wrong" with how this one set is built compared with the others and the plans.

~Jon

[Bam!]

Thanks guys...

has anyone ever tried in the pro ac DIY ers to do a different cut off point from the one in the plans ?

.... the midbass driver can be cut off higher with a db rise though....I was wondering what that sounded like...

If anyone's tried this particular test please tell me! I'd be really surprised though...

Thanks Jon and Thomas!