I might be buying a pair of home made Altec VoTT and Peavey

[VolvoHeretic]

How does port sizing work? I don't want to cut the port out larger to experiment, If I build a bunch of .125"wood plates with 11x3 holes and start stacking them will it increase the port size eventually equaling a 12x3? Is port volume in any way relevant?

[cradeldorf]

So, I have been googling "Adding weight to lower Fs on a woofer". I can find no definitive answer, but did read that the woofer really can't play any lower than Fs since above Fs, the port is in faze with the woofer, and at Fs, the speaker stops moving and all of the energy is vibrating in the port, and below Fs, the port is out of faze with the speaker and any low frequencies are canceled out. (?) I don’t understand how the port can be reproducing in faze and out of faze frequencies at the same time, but I don‘t know much.

So, back to lowering the Fs of the 418-8H by adding weight, I know that the differences between the 418-8H and 416-8B are many, but how are they the same? Same frame, surround, cone, motor? That only leaves the voice coil and dust cap?

I can live just fine with this sound with out reconing these things, but am just curious. I just want my cake and eat it too, even though there is no such thing as a free lunch.

I need to build an adapter plate and mount my one good 416-8A in one of these and see what the difference is.

(Calling GM?)

PS; I have a low cut button on my EQ, and have no idea how it works, but I know I don't like the sound of it.

I added 6 of those brick paving stones to my cabs, they hit hard now. The low cut button cuts out the lowest frequencys. I stopped using mine too.... when I had one.

[Altec Best]

How does port sizing work?

The longer the vent,the lower the tuning I think.When GM was helping me with my custom cabs we came to a length of 4" with a 6" diameter PVC pipe for a 25 Hz tuning.

[VolvoHeretic]

Playing with WinIST Pro, to equal the graph of a 3x12x.75 inch port, the 2x11 would have to be 9/16" or .5624" thick, which seem counterintuitive, but I am not ready to drag out the jig saw just yet.

I have not opened up the back yet because I am too busy enjoying these things to go to the trouble of trying to take out the 32 slotted screws and replace them with Philips head screws. I can find no information on the 32B horns which I assume have 802 drivers. It has been mentioned that they probably have symbiotic diaphragms, and frankly, they sound pretty good, but I do have a Piezo super tweeter helping them along...

[GM]

So, I have been googling "Adding weight to lower Fs on a woofer". I can find no definitive answer, but did read that the woofer really can't play any lower than Fs since above Fs, the port is in faze with the woofer, and at Fs, the speaker stops moving and all of the energy is vibrating in the port, and below Fs, the port is out of faze with the speaker and any low frequencies are canceled out. (?) I don?t understand how the port can be reproducing in faze and out of faze frequencies at the same time, but I don?t know much.


(Calling GM?)

You rang?

A good article with animations on port action: Essay

As much as me and Ron E have posted the theory/math and his simplified math routine over the last 15 yrs or so, I?m surprised you didn?t find it Googling.

Since I currently can?t access my ?library?, I Googled to get Biro?s ?long hand? explanation for the math savvy folks and Ron E?s ?mass loading for dummies? for the rest of us: Biro Technology

how to lower the Fs of a driver - diyAudio

mr = (Fs/Fs')^2

Qes' = Qes*mr^0.5

Qms' = Qms*mr^0.5

then: Qts' = Qes'*Qms'/(Qes'+Qms')

where:

mr = mass ratio
Fs' = new, lower Fs

New, lower effective efficiency:

n0? = ~ [9.6352*10^-10*Fs?^3*Vas]/Qes?

SPLeff? = ~ 112.018+10*log10[n0?]

GM

[GM]

The longer the vent,the lower the tuning I think.When GM was helping me with my custom cabs we came to a length of 4" with a 6" diameter PVC pipe for a 25 Hz tuning.

Correct, the vent area [Av] sets the minimum [highest tuning] Fb for a given box volume [Vb] and the longer the vent, the lower its tuning, ergo making it longer won’t make it any bigger [higher power handling].

GM

[VolvoHeretic]

You rang?

A good article with animations on port action: Essay
GM

Thanks GM, evidently my google search engine sucks.

Those pendulum diagrams sure explain the relationship between the woofer and the port very well and explain why there is nothing going on below Fb and why no matter how I manipulated the box volume, port area or depth, starting with tiny changes and increasing to drastic ones, I could change the slope and amount of low frequency roll off, but every time, it always intersected F3 at 44 Hz. (And never for the better.)

Can those 'adding weight' equations be solved for Fs? I can sic them on my ‘much smarter than I’ sons, the engineer, or the physicist.

WinIST pro has a box for adding weight to the cone, but no matter what I input, it makes no difference, but I could be doing it all wrong. I also need to input the parameters for a 416-8B and see what they look like compared to the 418-8H and 421-8H.

Cheers

[GM]

You?re welcome!

It?s a long story, but no, not really, you just needed to go through one or pages of Google finds to locate them plus it helps to know what to look for. They were spit out first for me because Google ?remembers? everything ?you? have searched/browsed for in the past.

It?s starting to get spooky, I mean I do a search and usually within the day and sometimes the hour, my yahoo mail, on-line TV guide, etc. ads reflect it plus pertinent new recommendations, so the info is apparently being shared universally. Haven?t/won?t try it, but have to wonder what ads would pop up if I browsed for porn????

Yeah, I love those animations; you wouldn?t believe how many folks I?ve alone ?educated? since the article was originally posted.

Correct, for a given cab net Vb, Fb [alignment], all you?re doing is trading HF efficiency for a lower F3 until you?ve reached the alignment?s limit, so to get the full benefit of mass loading requires recalculating the requisite alignment using the new Fs, Qts, which normally will be a larger cab tuned lower.

This is a ?piece o? cake? using WinISD Pro since you can highlight the ?volume?, ?tuning? inputs and use the keyboard?s arrows to scroll up, down the values, changing the various plots in real time to find the desired response. Ditto with most of the other design variable inputs.

Yes, rearranging the formulas is beyond trivial for your sons, but I have to resort to an on-line computer program to do it for me: http://www.quickmath.com/webMathematica3/quickmath/equations/solve/basic.jsp#v1=%28x%2Fy%29^2%3Dz&v2=y

mr = (Fs/Fs')^2 must be converted to this: z = (x/y)^2

then:

solving for Fs? [y] = Fs*(1/mr)^0.5

solving for Fs [x] = Fs?*mr^0.5

Regardless, why would you want to? I mean Fs you have to ?know? to find out what amount of added mass is required to achieve your new Fs, Qts, eff..

Anyway, since Qts dominates speaker alignment design, its increase along with decreasing power handling with decreasing frequency is what you want to watch.

GM

[VolvoHeretic]

GM, it has taken days for what you have said to sink in. Sorry, I'm dense. I guess I want to solve for added weight with an arbitrary Fb? …And hope that I don't overload with watts, but maybe the good thing is these woofers are rated up to 150 wpc? Sorry for the ignorance, but I‘m and ignoramus, I am just now, after 35 years, trying to figure out this audio stuff. I will see my son, the engineer tomorrow and sick these formulas on him, and see if he was paying attention in Calculus class.

[VolvoHeretic]

Ok, I don't have a clue how to run a stereo, so at the end of playing my reference CD; Return to forever; "Romantic Warrior", I disconnected the EQ and ran it flat at about .625 volume of 100 wpc. Wow, other than being a little top bass heavy, they were crisp, loud and nice.