2 way stand mount build

[Janus77]

Quick progress, felt arrived today so I’ve glued it up using vinyl adhesive which was recommended by Troels for attaching felt on my first build.  
 

cutting acoustic bats is a long tedious process.  Anyone have any suggestions? Scissors seems to work best, but they leave you feeling sore.   

 

Edited April 1, 2022 by Janus77

[Sub Sonic]

 What sort of material are the acoustic batts? Is it the felt?  Would it be possible to post a pic?

Cheers,

 

SS

[Janus77]

[davewantsmoore]

10 hours ago, Janus77 said:

Scissors

 

 

Is usually what gets me the most results  .... that or a very sharp blade/scalpel.

[Janus77]

12 minutes ago, davewantsmoore said:

 

 

Is usually what gets me the most results  .... that or a very sharp blade/scalpel.

 

Yep - the scissors might need to be sharpened..

[Janus77]

In trying to reduce internal reflected waves as much as possible, would it be worthwhile applying some felt to the braces too?

[Maz4bz]

I only cut the bat to half it's depth on the first pass. Go back for a second to cut through the remainder.

[Janus77]

Yep I’m doing 3 passes with tin cutters.  A bit easier than scissors

[Janus77]

First box glued up.  

[Janus77]

I need to add 100g per passive radiator.  Anyone able to recommend what I can use as weights?  100g is a LOT of M8 washers..

almost needs to be lead or something to be heavy enough and fit.

 

**Edit: https://www.wagneronline.com.au/sb-acoustics-50g-weight-for-passive-radiators/sba-drivers/sb-acoustics/speaker-drivers/audio-speakers-pa/dw-50-69100/991298/pd/ These will do the trick - $65 worth of weights is a little steep though.

Edited April 2, 2022 by Janus77

[davewantsmoore]

10 hours ago, Janus77 said:

In trying to reduce internal reflected waves as much as possible, would it be worthwhile applying some felt to the braces too?

No, it will be too thin and not porous enough to absorb sound. 

[Janus77]

Waiting on my 4 x mono amplifiers to arrive before i can do more work.

As can be seen in the photos, i've lined the internals with 8mm felt.  I left the inside bottom panel without to allow me to attach the crossovers, and i'll then felt around them. 

 

For stuffing i'll just try a few different amounts, from zero stuffing through to quite a bit and see how the response looks.  There doesn't seem to be a way to calculate this out too well, though i believe i can model different amounts of stuffing in WinISD to see how it should perform:

 

"It's not just your O, it's fact. Stuffing lowers Q, which can help tame a midbass hump, but it doesn't lower F3, and it reduces overall sensitivity. You can model it in WinISD 0.7 in the Box tab, clicking on 'Advanced' to reveal Ql and Qa. Ql is leakage losses, Qa is absorption losses. The default Qa of 100 is a bare box, 50 is a lined box, 10 is stuffed but not compressed, 5 is stuffed and compressed. The effect of lowering Qa is seen on the SPL and impedance charts and in the box Qtc. It by no means is the same as making the box larger. Stuffing a ported cab upsets the box tuning, lowers sensitivity, and if sufficiently stuffed effectively changes the alignment from ported to sealed."

[davewantsmoore]

8 hours ago, Janus77 said:

There doesn't seem to be a way to calculate this out too well, though i believe i can model different amounts of stuffing in WinISD to see how it should perform:

Different types of stuffing has different properties, and will affect those quoted box Qs differently.

 

It's best to do it empirically.

 

Looking at the electrical impedance of the driver, is better at looking at the SPL for this.

[Janus77]

Cheap solution for passive radiator weights.  From Bunnings $0.40 and 30g each:

 

I will need to grind the corners off so they don’t hit the back of the passive radiator frame, probably need 4 per PR.   I'll also epoxy a few M6 washers to the side touching the PR suspension to avoid it hitting the weights when at xmax, and another washer on the other side to ensure they're held centered firmly.  $6 worth of parts vs $65, it all helps

Edited April 5, 2022 by Janus77

[Janus77]

Amplifiers are with the delivery driver today, hopefully they make it.  Once received i'll need to get to Jaycar to pick up a few bits and pieces to assemble the testing rig, after that i'll start measuring.  Easy part of the build nearly completed...

[Janus77]

Amps!!

[BuzzzFuzzz]

On 04/04/2022 at 6:19 PM, davewantsmoore said:

Different types of stuffing has different properties, and will affect those quoted box Qs differently.

 

It's best to do it empirically.

 

Looking at the electrical impedance of the driver, is better at looking at the SPL for this.

Hi Dave.

 

Could you please expand on some types and their qualities?

Also, how the impedance affects stuffing the cabinets, or vice versa?

Thanks, as always.

 

Ant.

Edited April 5, 2022 by BuzzzFuzzz

[Janus77]

Ant, I think all he means is different types of stuffing will have different levels of absorption/density, so you need to measure the box with whatever stuffing you use to determine the optimum amount. 
And stuffing will effect Q of the box meaning it impacts resistance on the voice coil which changes the electrical resistance when you measure it.  Q is resistance, most speaker drivers quote electrical and mechanical, but then obviously a sealed box would impart different resistance to a ported as the air compresses and pushes back, so stuffing will have an effect too, but quite a bit less than a port vs sealed.  

 

Dave correct me if I’m wrong?

[davewantsmoore]

13 hours ago, BuzzzFuzzz said:

Could you please expand on some types and their qualities?

It depends on how much "flow resistance" the stuffing has.... like how hard would it be to blow through it.    The soundwaves need to be able to move into the stuffing, so something like "felt" doesn't really absorb sound (as you can't blow air through it) .... but acts more as a mechanical damping of the wall.

 

13 hours ago, BuzzzFuzzz said:

Also, how the impedance affects stuffing the cabinets, or vice versa?

Imagine you have sound reflecting around inside the cabinet..... the sound retruns to the back of the cone and puts a force on it.

 

If you look at the electrical impedance of the woofer.... both in free air, and mounted in the cabinet.   You can see differences, and some of those differences can be due to the reflected sound on the cone.

 

If by stuffing the cabinet, you are trying to prevent sound from doing that to the cone.... then this is how to see (firstly, is there a problem at all, and secondly, how does the stuffing change it).

 

12 hours ago, Janus77 said:

And stuffing will affect Q of the box

Yes... above I am talking about "specific (big) unwanted reflections returning and hitting the cone".

 

But more generally the entire pressure inside the box (unavoidably) causes the driver movementr to becomes stiffer at certain frequencies.    Stuffing can impart a certain amount of loss (Q is loss) .... as can port stuffing or turbulance, or enclosure flex.

[Janus77]

Close to testing.  
 

 

[Janus77]

A mate with a proper workshop is going to round off the PR weights i've glued together for me so they don't hit the frame during excursion (and to bring them down from 126g to 100g as modelled).

Also designing a box to 3d print to hold the stacked 4 x 30w mono amps, cables and miniDSP.  it'll have speaker binding posts on one end and minidsp inputs and power input (bridged) for the amps at the other end.  Should be a tidy little solution in the end, assuming the amps don't heat up so much they melt the box  - can always install a fan if required.

4 way DSP amplifier for $480 - Bargain.

 

 

Edited April 7, 2022 by Janus77

[Janus77]

Looks like i'll be waiting till next week before i can start measuring and testing.

 

Wordle 293 3/6

 

So addictive..

 

 

 

 

[Janus77]

PR weights done. 
 

 

[r3x]

On 02/04/2022 at 12:58 AM, Janus77 said:

 

cutting acoustic bats is a long tedious process.  Anyone have any suggestions? Scissors seems to work best, but they leave you feeling sore.   

 

 

Late i know, but for future reference, grab a wide piece of something straight and heavyish (like a wide 1m steel ruler) and something to cut against (like a square of hardboard), place the hardboard on the ground, batting on the hardboard, steel ruler right along where you want to cut, squish down and cut with a nice sharp stanley knife (or i've used a sharpened machete for those bigger bits).  Keep your fingers away from the cutting action...

[Janus77]

DSP tuning rig up and running.  
stuck a 1400hz crossover on 1 speaker just to see, they sounded pretty decent.  Looking forward to testing!