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

[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.

[GM]

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.

Correct and just like with any speaker alignment, you don?t want to over drive it into damaging excursion, which the lower it?s tuned, the lower in SPL this will occur.

Then there?s the issue of how much added mass referenced to the driver?s moving mass [Mms] the suspension can safely handle, which only the manufacturer will probably know, but FWIW I?ve loaded down drivers up to 4x Mms [mr = 4] which cuts Fs in half and doubles Qts, though power handling is severely compromised unless it has a lot of Xmax, which prosound drivers typically don?t have, especially MI drivers such as the 418, 421.

Really, except for turning a burned out driver into a passive radiator [PR, AKA drone cone], I only recall adding mass to raise Qts.

No need to apologize, unless you?re a math/physics wiz, you don?t pick this type of info up real quick; for sure I didn?t. Oh well, better late than never, right?

Actually, I think it?s just high school Algebra, but I failed it, so not sure. I had to learn this stuff experimentally and it was only much later I was given the ?long hand? math and even then had to have yet someone else program it into Lotus 123 originally and later into MS Excel.

GM

[VolvoHeretic]

I've been doing some thinking... Just how does Altec use the same frame and wind up with speakers that have such a wide difference of Xmax? 416-8B; .13", 418-8hII, 421-8HII; .05" (?), I could go on, but how do they accomplish this? I am going to cut my 416-8a in half before I send it to GPA for reconing in the year 2016. Just wondering and wanting to learn.

[VolvoHeretic]

OK, just hooked up my new Behringer CX2310 crossover. Right now I am sending >80hz to a 100wpc Sherwood receiver to the Altecs (418-8H II, N501-8A, 32B horn w/ 808-8A/pascalite compression drivers, and one Piezo supertweeter) and <80hz to a Soundcraftsmen pre amp to a Crown DC300A to my pair of Alpine 10" box-O-subs in .75 cu. ft. boxes crossed over at 80hz.

Sounds a lot better than when I was running everything full range and using a graphic EQ to filter down the high frequencies to the subs. I also am not using any EQ and like it.

I have another Sherwood amp lying around and will bypass the N501-8A's after I find some more speaker wire and try tri-amping. Doing so, the Altecs will be receiving a full signal w/ F3 at 44hz.

So, I'm thinking I would like to get a Crown 75wpc D150A and 35wpc D75 for the Altecs and find a sub amp that has either 300wpc @8ohm stereo or 600wpc @4ohm mono.



Does everybody's wiring look like this?

[GM]

Xmax approximation = [Hc-Hg]/2

Where:

Hc = coil height
Hg = magnetic gap height

So assuming a constant Hg, the VC must get shorter to decrease Xmax, ergo the 421 would theoretically have a much shorter Vc than a 416. That said, there may be more at play here WRT each motor's design, but never bothering to learn about any detail differences across a 'family' of drivers or do any re-coning, I've no clue what the reality is.

GM

- - - Updated - - -

Very belated reply

Not nearly belated as me, his post just popped up earlier today in my email, so thought I was making a timely response for a change only to notice yours after I uploaded mine.

GM

- - - Updated - - -

(418-8H II, N501-8A, 32B horn w/ 806-8/pascalite compression drivers...........

Does everybody's wiring look like this?

32B? 800 Hz horn that wants a >1 kHz XO point coupled to a 'textbook' 500 Hz/2nd order? 'Careful with that axe [volume control] Eugene'!

GM

[Old Guy]

I've been doing some thinking... Just how does Altec use the same frame and wind up with speakers that have such a wide difference of Xmax? 416-8B; .13", 418-8hII, 421-8HII; .05" (?), I could go on, but how do they accomplish this?

Very belated reply, but xMax doesn't really address the frame. It is how far the coil can travel without leaving the magnetic gap. Altecs are underhung, meaning the coil is shorter than the gap Just for the sake of argument, assume a gap length of one inch and a coil 1/2 inch. Past 1/4 inch in either direction the coil leaves the gap.

Overhung OTOH uses a short gap and long coil...attempting to keep a constant number of turns in the gap. Most consider overhung not as linear.

[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.