Enclosure Modeling

[RonSSS]

Using the shareware program "BoxPlot", I modeled the following drivers: (box size after the model #):

416-8B___________12.21 CuFt...-3dB@35hz
416-8C___________5.01 CuFt....-3dB@45hz
515B_____________1.21 CuFt....-3dB@90hz
515-8G___________2.97 CuFt....-3dB@70hz
604-8H___________5.55 CuFt....-3dB@50hz
604-8K___________1.71 CuFt....-3dB@75hz
411-8A*__________16.22 CuFt...-3dB@25hz

* 411-8A is really a closed box driver.

T/S parameters direct from the Unnoficial Altec web site.

This might give at least a little insight into what speaker could (should) be used in what box.
Looks like a 515 isn't a very good fit in the model 19 cabinet.
Also makes me wonder just how different the 416-8B and 416-8C are going to sound in the 19, since it doesn't appear to me that Altec changed the cab when they went to the ferrite driver.

From the shareware program:
"The particular alignment used is the QB3-B4-C4 series of responses based on the work of R.H. Small, A.N. Theil and others.
Most of the credit for taking the black magic out of speaker design belongs to A. N. Thiele and R. H. Small, whose work on modeling a vented enclosure has made predictable speaker enclosure design possible. By modeling a speaker and its enclosure as an electrical circuit (hi pass filters) and using network analysis, a set of equations were produced. From these equations, they developed a set of procedures that make designing excellent sounding enclosure more science than art. The model takes in to account all of the significant factors that influence the overall performance of a vented loudspeaker enclosure. Their work resulted in what they called alignments. An alignment is a combination of loudspeaker and enclosure parameters that result in a particular frequency response. Thiele and Small developed tables of alignments that narrow down the literally unlimited combinations of loudspeaker and box parameters to a few easily managed combinations."

Comments?

Ron

[joyspring]

Back again after a nearly fatal bicycle vs. inattentive-Lexus-driver-auto crash... thank goodness for Vicodin Hopefully the coming global oil peak will resolve that (and suburban sprawl) in due time...

Actually, there are many others who contributed; Thiele and (particularly) Small synthesised and codified sealed- and vented-box design methodology.
Benson, Locanthi, Olson are also names that figure prominently as well.

The shareware program description is quite accurate; the creation of electrical analogues to the mechanical attributes of loudspeaker drivers / enclosures allowed the use of network analysis and greatly decreased the amount of time (and greatly increased the likelihood of success) of loudspeaker system design.

Prior to the publication of Small's JAES series of papers in the early 1970s, loudspeaker enclosure design was largely a matter of trial-and-error.

So, looking at the results you received from BoxPlot, how was it that Altec was able to achieve much more impressive specifications?

First of all, most of the pre-1970s (and pre-Federal Trade Commission) Altec literature did not specify half-power (-3 dB) points, or an amplitude range ( i.e. +/-3 dB) for frequency response.

That's BTW how an Altec 604D has a frequency response of 20 - 22000 hz; what's not stated is that the driver may be down -40 dB at those frequency extremes or the driver may have a +6 dB peak centred about 3 kHz ;-)

The second reason is that Altec (and Tannoy and JBL and other manufacturers of low fs / low Qts / high compliance drivers) often used `too large' enclosures moving the -3 dB point lower than a nominally flat QB3-Butterworth-Chebychev (depending on driver Q) filter alignment would allow.

That results in a drooping passband that is augmented at the lower frequency range by a tuned-too-low (by Thiele-Small analysis) vented port.

In my opinion, these alignments typically sound `wooly' but that's my subjective assessment. There is no `right' way to design an enclosure really.

Anyhow, you would be quite correct in determining that a 515 wouldn't work well in a Model 19 enclosure. All 515s have exceptionally high Bl and low Q. They're really intended for horn loading and mid bass loudness.

However, I would not fret so much over the 416-8B vs. 416-8C. It's very likely you'll hear that much of a difference, and it's very highly unlikely that the Thiele-Small parameters quoted on Todd's site will be close to those of your drivers - particularly if they've been reconed.

As an aside, my 605As reconed with GPA kits do not measure anywhere close to the original cones nor do a few GPA-coned 604Es and 604-8Ks that I've recently measured, and that's to be expected - the exact composition/weight cones and other parts (spiders, coil formers, etc.) that Altec once used are probably no longer available.

This isn't a criticism; this is simply reality. Actually we owe a lot to Bill at GPA and Todd for the opportunity to even purchase as-close-to-original-as-practicable replacements.

Anyhow, enough ranting. I'll wait until the pain killers subside before replying to your loudspeaker efficiency vs. amplifier power question in the other thread...

BobR

[bfish]

Ron,
Do you have the port data (size and tuned freq.) for the alignments you ran? I'm particularly interested in that for the 515-8G, as the 2.97 CuFt is very close to what is left in an A7 with the horn flares and reflex area sealed off.
Thanks!
BFISH

[RonSSS]

BobR,

I suggest OxyContin as a pain reliever. Same magic stuff as the Vicodin, minus the acetaminophen. Rush Limbaugh really liked it!
And Lexus owners always drive like that...don't they? Usually on the phone and in a hurry.

"However, I would not fret so much over the 416-8B vs. 416-8C. It's very likely you'll hear that much of a difference, and it's very highly unlikely that the Thiele-Small parameters quoted on Todd's site will be close to those of your drivers - particularly if they've been reconed.

As an aside, my 605As reconed with GPA kits do not measure anywhere close to the original cones nor do a few GPA-coned 604Es and 604-8Ks that I've recently measured, and that's to be expected - the exact composition/weight cones and other parts (spiders, coil formers, etc.) that Altec once used are probably no longer available.

This isn't a criticism; this is simply reality. Actually we owe a lot to Bill at GPA and Todd for the opportunity to even purchase as-close-to-original-as-practicable replacements."

I agree about this completely. I also measure my own drivers and adjust the box accordingly. I imagine the T/S "specs" are nominal anyway, and there is probably quite a wide variation even for brand new drivers.

I'll measure my 416-8C's when I get them back just for grins.

Hope you get to feeling better and collect many $$$$ (For audio stuff of course) from the Lexas driver.

Ron

[RonSSS]

Bfish,

I can do that, what diameter would you like the port to be? I suggest 6".

http://www.diamondcut.com/boxplot.htm

Or, just go here and download BoxPlot and play yourself.

Ron

[bfish]

RonSS,
I've been playing w/Boxplot (literally), but I'm not proficient enough to have confidence in the results.

What I had in mind is the old dead horse.....in particular, with a 515-8GHP in the forementioned, sealed, (approx. 2.2 cu/ft effective) A7 horn, actively x'd at 120hz (24db/octave) with a pair of ducts from the back chamber to the upper corners of the sub baffle. 2 - 3" round ports (say 23" long, ea.) are about all that fit....small, I know, but with the higher tuning, shouldn't whistle. Or would everything be better to just leave the 515 sealed up, without a port tuned to xver, muddying things up? I've read all the dead horse discussions many times without getting a clear picture of this one point.You know how us dumb hillbillies is....

[GM]

Greets!

>Back again after a nearly fatal bicycle vs. inattentive-Lexus-driver-auto crash...
====
Been there, done that on motorcycles more than once so I 'feel your pain'. Anyway, glad you 'dodged the bullet' and hope you don't wind up feeling it all over again as you get older (as I do).
====
>The second reason is that Altec (and Tannoy and JBL and other manufacturers of low fs / low Qts / high compliance drivers) often used `too large' enclosures moving the -3 dB point lower than a nominally flat QB3-Butterworth-Chebychev (depending on driver Q) filter alignment would allow.
====
Hmm, you're forgetting the impact series R has on the FR, not to mention that in a prosound app, VC heating further increases the effective Qes, so all this must be accounted for in the cab's Vb/Fb. For HI-FI use, adjustable damping was incorporated into the amp to 'dial in' the speaker's in-room response, which often requires a somewhat roll offed response to keep it from sounding 'boomy'.

Indeed, extreme efficiency was required due to the amp's impact on speaker performance and why when hooked up to SS they sound lacking in both the bass and HF, leaving only a 'shouting' mids/lower HF, hence the need for higher Qts, lower Vas, wider BW drivers to compensate for an SS amp's virtually zero output impedance if no series R of consequence is added.
====
>Do you have the port data (size and tuned freq.) for the alignments you ran? I'm particularly interested in that for the 515-8G, as the 2.97 CuFt is very close to what is left in an A7 with the horn flares and reflex area sealed off.
====
FYI, for best performance use a sealed compression chamber and reduce the Vb as required to get the best blend to the sub. Using some averaged measured specs in a sim, I get reactance annulling (no high pass required for HI-FI apps) with ~684"^3 net so this is what I would start with and add/subtract as required to get a 4th order roll off, or use 2580"^3 if a high pass is used (Probably won't need to adjust it).

GM

[bfish]

Thanks GM, I finally "got it".

I just kept getting hung up envisioning such a large driver that was supposedly suited for BR apps being sealed up in such a small area. I was equally bewildered as to the effect of having a port tuned to XO, instead of low Fs or somewhere down the rolloff slope. If I consider the 515-8GHP as the mid it becomes in this app, instead of the LF driver it's normally used for, my weak brain accepts it much better.

Now my only problem is keeping my nose to the grindstone, since Spring has hit full force in the Ozarks, with mushrooms poppin' and crappie bitin'. Ain't life grand?!

Lookin' forward to meeting some of you at the GPAFest!

[GM]

Greets!

>This might give at least a little insight into what speaker could (should) be used in what box.
Looks like a 515 isn't a very good fit in the model 19 cabinet.
====
Per my comments in the '416 Vs 515' thread, it depends. Adding some series R increases Qes/Qts, so without changing any other specs, increase Qes and then hit the 'align' button to see how much the cab's Vb increases/Fb decreases. At 3 ohms (Qes = 0.479 for the 8G), the response is similar to the 416-8C and with a better impulse (AKA transient) response. At 6.5 ohms (Qes = 0.656), it's still better damped due to the shape of the roll off slope and has a significantly more tonally balanced response overall once the room's effect is factored in.

Note that I'm using an 8.622152778ft^3 Vb/36 Hz Fb in a much more elaborate/accurate program so you can't 'see' all this, but BP gives you a general idea of how changing Qes will affect an alignment. Indeed, I use it for all my initial sims to get the Vb, Fb and vent area I need, then plug them into the more elaborate programs to get the vent length (BP and all other 'freebie'/shareware programs calc a too long vent in most cases) and fine tune the driver, vent locations.
====
>Also makes me wonder just how different the 416-8B and 416-8C are going to sound in the 19, since it doesn't appear to me that Altec changed the cab when they went to the ferrite driver.
====
The 8B 'fills' the cab much better so should sound 'fuller'/better damped, while the 8C should be somewhat 'peaky', with more 'sizzle' (AKA West Coast 'sound'). Of the two, I prefer what I 'see' with the 8B, but then I've never been a big fan of the 'WCS' that has such a strong following here.
====
>"Most of the credit for taking the black magic out of speaker design belongs to A. N. Thiele and R. H. Small, whose work on modeling a vented enclosure has made predictable speaker enclosure design possible."
====
This is true to a great extent WRT the 'rank n' file', but Bell Labs/WE/Altec/RCA was designing drivers/speakers using Fs/Re/B*L/Cms/Mms, etc. from the get-go so this doesn't apply to the original major players in audio. Anyone who doubts this need only peruse the various early compression driver, microphone, and Thuras' 1932 bass reflex patent applications, which BTW is the design that inspired Jensen's Ultraflex, which in turn inspired the 'Onken'. Plagerism is indeed the sincerest form of flattery.

It was a boon for all the speaker designer wanna-bes though, and with the advent of cheap computers/software and the internet, anyone who has access to these and can read can do a decent job without having to learn/experiment much.

GM