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Old 16th May 2013, 07:22 PM   #1
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Arrow 2-way bookself xo point

Hi all

I'm building a 2-way bookshelf for my mom to use with the tv (subwoofer to be added later) and some light lounge music.

The system employs a 4" mid-woofer and a waveguide mounted tweeter.

Driver selection was based on what I had in hand and I'm considering Rod Elliot's Parametric and Sub-Woofer Equaliser to smooth out the tweeter response - would that be worth the effort?

I'd be bi-amping the speakers (TA2020's for the tweets and LM3886's for the mid-woofers) and am thinking of 24dB/oct LR xo. I am a bit lost on the XO point - I'm not too good at deciphering an optimum XO point form the graphs... would someone help me with this

I used Fabien Lefebvre's MESSON app on my iPhone 4s for the measurements, the graphs are done in Excel with the exported data. I forgot to use the same gain settings for the tweeter and the mid-woofer, however, as I would be adjusting the gain at the active xo, I figure it would not present itself to be much of a problem...

Click the image to open in full size.

I'd really appreciate guidance from the fine folks of this forum

Thank you in advance

Regards
Attached Images
File Type: gif MidWoofer in box.gif (13.7 KB, 63 views)
File Type: gif Waveguide Tweeter.gif (27.0 KB, 63 views)

Last edited by merajsalek; 16th May 2013 at 07:46 PM. Reason: Forgot to credit Rod :(
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Old 17th May 2013, 05:00 AM   #2
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re:"4" mid-woofer and a waveguide mounted tweeter" do you make & model number?
I don't really think it's worth bi-amping a 2-way like this.
The graphs are a bit hard to interpret, it looks like a crossover freq of ~3Khz would work
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Impedance varies with frequency, use impedance plots of your drivers and make crossover calculations using the actual impedance of the driver at the crossover frequency
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Old 17th May 2013, 05:22 AM   #3
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Location: Mar del Plata, a BIG seasonal getaway city, can see the Ocean from our residence.
It indeed looks like 3K for a crossover point will work just fine but you will have to dial back the mid-woofer by appx 8 Db to match the on-axis response of your tweeter.



-----------------------------------------------------------Rick............
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Old 21st May 2013, 06:57 PM   #4
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Default :hypno2:

Thanks for the replies guys

was out of town for a while, hence the delay in replying...

Quote:
Originally Posted by PeteMcK View Post
re:"4" mid-woofer and a waveguide mounted tweeter" do you make & model number?
I don't really think it's worth bi-amping a 2-way like this.
The graphs are a bit hard to interpret, it looks like a crossover freq of ~3Khz would work
Hi Pete

I'm not sure of the make and the model of the drivers..they are OEM units I purchased long time ago at a surplus sale...

One reason I've decided on the bi-amping route is because I don't want to use an L-pad for gain-matching the drivers. The second - I wanted to use the amps I already had, so I just needed an xo...

4KHz was my choice of frequency considering the FR of the drivers and Rod Elliot's articles on bi-amping...

However, I developed a vague notion about waveguides from my sporadic readings in this forum and was thinking - would choosing a frequency lower than 3KHz with a steep (24dB/oct) XO yield any benefit in terms of making the speakers act more like a point-source? Also, how does driver integration fit in to the equation?!?

Quote:
Originally Posted by Richard Ellis View Post
It indeed looks like 3K for a crossover point will work just fine but you will have to dial back the mid-woofer by appx 8 Db to match the on-axis response of your tweeter.



-----------------------------------------------------------Rick............

Hi Rick,

The gain settings for the mid-woofer and tweeter measurement were not the same. This was an oversight on my part...the sensitivity of the drivers are much closer in reality I'l measure again, just to be sure
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Old 21st May 2013, 07:05 PM   #5
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Third and main reason for active XO - tweaking is a lot cheaper than a passive XO
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