# Stuffing and crossover design doubts.



## Guest (Feb 21, 2007)

Hi there everyone!! 
I've just finished building my first two way speakers. So far everything seems fine. But I would like some advice on how to stuff the interior and on the crossover network design. 

I calculated about a 10per cent oversize in volume to make up for some aditional bracing and the stuffing. At the moment I'm using a 40kg/m3 open cell foam I had lying around, and I've placed it on three interior walls, each corrensponding to x,y and z axis. Is this alright? The foam is about 50mm thick and isn't easy to cut thinner. The results are ok, but I still have some resonances I think might be due to lack of bracing or stuffing.

The other doubt I have is regarding the passive crossover network. I have used a digital mixing console to see and experiment how the speaker sounds best. In the woofer section I have a 4KHz cutoff and two notch filters, one at about 600Hz and another at about 1.2KHz. I thought that the resonance at 1.2KHz might be a harmonic of the first, but it still appears with the 600Hz notch filter so I added the second. With this configuration ther sound is alright. If I were to make a passive crossover with all that, including another notch filter required for the tweeter at about 8KHz to boost a small dip, wouldn't it seem to be a big crossover??


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## kano32 (Sep 14, 2006)

What are the drivers that you are using (brand, model and TS)? 

A lot goes into designing a set of speakers. If you want to continue, maybe check out all the free programs at FRD Constortium: http://www.pvconsultants.com/audio/frdgroup.htm


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## BoomieMCT (Dec 11, 2006)

eddiesubscription said:


> I calculated about a 10per cent oversize in volume to make up for some aditional bracing and the stuffing.


Someone correct me if I'm wrong, but I thought stuffing increased the effective box volume, not decreased it. So, you probably are okay



eddiesubscription said:


> The other doubt I have is regarding the passive crossover network. I have used a digital mixing console to see and experiment how the speaker sounds best. In the woofer section I have a 4KHz cutoff and two notch filters, one at about 600Hz and another at about 1.2KHz. I thought that the resonance at 1.2KHz might be a harmonic of the first, but it still appears with the 600Hz notch filter so I added the second. With this configuration ther sound is alright. If I were to make a passive crossover with all that, including another notch filter required for the tweeter at about 8KHz to boost a small dip, wouldn't it seem to be a big crossover??



I also just started with crossover design. I tried something simpler (2nd order highpass, 2nd order lowpass) and ran tests on it to see how it matches up with reality. I recommend starting simple and then working your way up - that way if you hit a SNAFU you can debug it easier. Maybe try building the pass filters first and add the notch filters if you need them. I believe there is no better way to learn then by just diving in and doing!

That being said, I also give a +1 to the FRD Consortium's tools.

As far as the crossover size, that will be determined by the size componants you use and the complexity of the system. If you are making a very complex crossover you proabably are using high quality parts which tend to be larger. So, yes, that will be a big crossover.


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## Prof. (Oct 20, 2006)

BoomieMCT said:


> Someone correct me if I'm wrong, but I thought stuffing increased the effective box volume, not decreased it. So, you probably are okay
> .


Depends on what you stuff it with...
If for example you lined the sides and back with 1/2" thick carpet, you will have effectively reduced the volume..
If on the other hand you lined the sides with 1" Polyfil, the effective volume would remain about the same..

I believe that there is an acoustic cotton material that is quite thick, and that can be used very effectively without substantially changing the volume of the box..


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## Guest (Mar 5, 2007)

Sorry!!! I've been a bit too busy lately to answer, please accept my apologies.

To be a bit more specific, the drivers I've employed are these:

TWEETER: P.audio PHT408 
http://www.paacoustic.com/Product_Detail.asp?CatalogID=0116&ProductID=PHT-408

WOOFER: beyma cm8b
http://www.elmuz.com.pl/sklep/index.php?p129,cm8b
http://elmuz.com.pl/beyma/cm8b.htm

At the moment, I'm about to implement a 18dB rolloff hipass for the tweeter at 3KHz for protection, as I have already burnt a tweeter in a rather clumbsy fashion. 
I'm also looking for some place I could go to test the speakers, as I'm trying to identify a resonant peak in the low mid- bass range that ocassionally appears, and I'm not sure if it's the speakers or the room acoustics. 
But so far, I'm pretty happy with the results. I'm still experimenting with different amounts of stuffing. The easiest solution so far is to stick with the biamped system and the digital mixing console. It makes fiddling much easier and quicker. It also maintains the xover frequency constant, without depending on impedance variations on the driver. I've even considered buying a dedicated digital xover like the behringer dcx2496. By the time I've constructed four or five quality passive crossovers I would have spent as much as the digital xover.
Thanks for your repplies, and I'm still open to more opinions and suggestions.


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## Guest (Mar 5, 2007)

Here's how things look at the moment:

http://img409.imageshack.us/img409/919/dsc4534he2.jpg

http://img72.imageshack.us/img72/7184/dsc5138qg2.jpg


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