Gpa 416-8c

The Fed Ex truck brought a pair of nice boxes yesterday.
Inside are my factory-new 416-8Cs from Great Plains:

http://imageshack.us/a/img541/4016/i4fq.jpg

http://imageshack.us/a/img13/7816/z9w6.jpg

Here is the impedance plot: (not broken in whatsoever)

http://imageshack.us/a/img22/7323/y6qz.png

If you can't make them out, here are the (non-broken-in) 416-8C T/S parameters:
Re = 7.46
Fs = 24.22
Qts = 0.305
Qes = 0.321
Qms = 6.904
Le = 1.478
Mms = 68.56
Vas = 21.19
Zmax = 149.3

Got them in my 816 enclosures right now breaking in, then I'll re-run the TS sweeps and do some FR measurements.
The cones are incredibly light; I'm not sure about the Mms and Vas numbers (I used the delta mass method), so I am going to build a test box to test them out that way. What size box would work?

Here's the default WinISD box sim for the (non-broken-in) driver:
http://imageshack.us/a/img826/7980/a2mj.png

It's indicating an 8.6 CF vented box tuned to 24 Hz. This will get re-measured as well after a healthy break-in period.

Normally, the specs change in complementary ways, so short of Vas being off a lot, the cab size/tuning should stay the same.

GM

They look nice Mike ! Let us know how they sound/perform...

However did they survive in that flimsy box when the FedEx driver threw them over your fence?

http://www.youtube.com/watch?v=D7Sb_r7BKTc

Isn't the zmax saying 5 inches? 149.3? Isn't that MM? or is it thousands of an inch?

Edit: never mind I was thinking xmax... I'm getting too old for this stuff.

The 24 Fs is pretty impressive though. They ought to dig pretty deep with that.

Yeah, the published Xmax is 3.8mm.
The Fs I measured right out of the box is pretty close to what GPA publishes (within 5%), which is good to see. The Qts and Qes are pretty far off though, enough to change the EBP considerably (the published specs yield a box size of 4.7 CF tuned at 23 Hz). Does anyone know if Qes will change much as the speaker breaks-in? I would expect Qms to move some as the suspension loosens a bit.

The beefy Le is probably due to the beefy voice coil and no shorting rings, so a zobel will likely be in the new XO...

I can tell you that the speakers sound amazing even on the current crossover (designed for my old 416As). It's going to be fun designing a 2-way using these drivers!

Altec published Xmax is very conservative. They have probably 20% higher if you used typical ratings.

Here's an FR plot from a measure I did. This is taken with the driver mounted in an Altec 816 bass horn, 1' from the horn front, on axis.

http://imageshack.us/a/img34/1365/pe8.png

As good as this plot looks, the driver sounds even better. It has quite an extended range; and the mid-bass sounds absolutely gorgeous.
Next up is to put one into a 1.5CF test box to zero in on the Vas number, then build a ported cabinet for it. I'll probably start with a 2-way waveguide design.

That's interesting. There's a 10dB slide starting at 900Hz and ending around 2300Hz. That's understandable. I wonder what accounts for the 9dB bump from 2300 to 2700?

Was this measured inside?

Quote:

---

Originally Posted by Alien_Shore

It's indicating an 8.6 CF vented box tuned to 24 Hz.

---

GM - how do you think these would play in that big GPA 604 box that you simmed for Jay that I built?

• L = 42.5"
• CSA = 422.04"^2
• vent = 6" diameter x 2"
• Driver center point down 19.625" from top interior.

It is illegal to put a 604 in a 1.5 cu ft box!

Quote:

---

Originally Posted by alancohen

That's interesting. There's a 10dB slide starting at 900Hz and ending around 2300Hz. That's understandable. I wonder what accounts for the 9dB bump from 2300 to 2700?

---

A little phenomenon called beaming, and perhaps a bit of cone breakup overtones thrown in.

Quote:

---

Originally Posted by gortnipper

GM - how do you think these would play in that big GPA 604 box.....

---

Using the measured plus derived specs [attached], it will need to be tuned lower [Fs] to get a 'close enough' similar response, so will probably need at least a 6? long vent.

GM

Quote:

---

Originally Posted by VolvoHeretic

It is illegal to put a 604 in a 1.5 cu ft box!

---

10 cf box...

Quote:

---

Originally Posted by GM

Using the measured plus derived specs [attached], it will need to be tuned lower [Fs] to get a 'close enough' similar response, so will probably need at least a 6” long vent.

GM

---

Thanks. And keep the 3.5R or no?

sorry, last time I checied, 42.5 liters equealed 1,5 cubic feet.

Quote:

---

Originally Posted by gortnipper

Thanks. And keep the 3.5R or no?

---

Hmm, IIRC, the 3.5 ohms was due to Jay's tube amp, so was tuned to the Iconic/GPA's Fs to maximize power conversion and you used it too.

Anyway, as a general rule for HIFI apps, I prefer/recommend an Fs or lower tuning and EQ if necessary to flatten it out in-room, but if you’re using a typical SS or tube PP amp, then try the cab as is first without any added resistance.

GM

Quote:

---

Originally Posted by VolvoHeretic

sorry, last time I checied, 42.5 liters equealed 1,5 cubic feet.

---

Sorry, I copied out of GM's doc to Jay and L=Length of the internal longest dimension of the cab, not Liters. So, ~10.3 cu ft.

Quote:

---

Originally Posted by GM

Hmm, IIRC, the 3.5 ohms was due to Jay's tube amp, so was tuned to the Iconic/GPA's Fs to maximize power conversion and you used it too.

Anyway, as a general rule for HIFI apps, I prefer/recommend an Fs or lower tuning and EQ if necessary to flatten it out in-room, but if you’re using a typical SS or tube PP amp, then try the cab as is first without any added resistance.

GM

---

OK, thanks again.

BTW - with the 604s in that box and my SE valve amp, I tried first w/o any added R and it sounded flat and thin. I then used a variable and found ~3R works very nicely so I added a fixed r.

You’re welcome!

OK, then tune to Fs and experiment with up to 3 ohms if required.

GM

Quote:

---

Originally Posted by alancohen

That's interesting. There's a 10dB slide starting at 900Hz and ending around 2300Hz. That's understandable. I wonder what accounts for the 9dB bump from 2300 to 2700?

Was this measured inside?

---

Yes, measured in my garage. This weekend, I'll take them outside, refresh the imepedance and T/S plots, and take another FR measurement.
That crazy FR rise at the end of the range is pretty typical woofer cone breakup; from what I've read*, paper cones and dustcaps (particularly lightweight ones) have exaggerated peaks like that.

*Some interesting references:
The Art of Speaker Design Part II
Cone Breakup Simulation
Woofer Design Tutorial

shouldn't you measure them where they're gonna sit and then tune them to a flat response?

Quote:

---

Originally Posted by cradeldorf

shouldn't you measure them where they're gonna sit and then tune them to a flat response?

---

Yeah, but when you're going to design an enclosure, how should you measure for that? I don't have anechoic chamber or anything so I was thinking just do it outside to get the best "raw" FR measure I can to import into my design tools.

So I did re-measure these after they've broken in for a while and the numbers did change a bit:

Here are the revised T/S:
Re = 7.46
Fs = 24.22
Qts = 0.303
Qes = 0.319
Qms = 6.003
Le = 0.582 (*)
Mms = 85.31
Vas = 17.03

(*)I think my initial value for Le was improperly inflated. I believe this is the accurate number.

I still don't trust the Vas number or the Mms. I still plan to build a 1.5CF sealed box to test Vas that way, but have not yet gotten to that.
But if you believe this new Vas, WinISD is saying to use a 6.82 CF vented box tuned to 24Hz.

I took the 816 cabinet outdoors this weekend and measured. Here's the plot comparing the first (brand new driver, measured indoors) with the new measurement:

http://imageshack.us/a/img571/6231/dl27.png

Quote:

---

Originally Posted by Alien_Shore

But if you believe this new Vas, WinISD is saying to use a 6.82 CF vented box tuned to 24Hz.

I took the 816 cabinet outdoors this weekend and measured. Here's the plot comparing the first (brand new driver, measured indoors) with the new measurement:

http://www.hostboard.com/forums/

---

I'm sorry I didn't realize you were trying to design cabinets, I thought you were just trying to tune them. I think 6.82 is a good size cabinet. Don't you?

Hmm, typically Fs drops, Vas increases, Qts remains ~ the same, ditto measured efficiency, so something seems amiss. FWIW, the most accurate way to measure Vas [and the most tedious] is to find the sealed cab net Vb that raises Fs 1.56x, then divide it by 1.44.

Don?t currently have access to my collection of measured specs, but Le @ the 1 kHz reference is ~1.2-1.5 mH IIRC. A traditional 15? with 0.582 mH would need a shorting ring, which Altec never used AFAIK on any of its woofers, relying on its inductance rise to extend the driver?s HF response, especially when driven by a high output impedance.

You can check it though by working off an impedance plot:

Le = 1000*SQRT[[Zxo^2-Re^2]/[2pi*1000]] where Zxo is the resistance @ 1 kHz = 1.4954 mH Vs DATS?s 1.478 mH just ?eyeballing? Zxo = 12 ohms off your original plot, so it was accurate enough for me originally since it falls in line with my faded memory. ;)

GM

Quote:

---

Originally Posted by GM

Hmm, typically Fs drops, Vas increases, Qts remains ~ the same, ditto measured efficiency, so something seems amiss. FWIW, the most accurate way to measure Vas [and the most tedious] is to find the sealed cab net Vb that raises Fs 1.56x, then divide it by 1.44.

Don?t currently have access to my collection of measured specs, but Le @ the 1 kHz reference is ~1.2-1.5 mH IIRC. A traditional 15? with 0.582 mH would need a shorting ring, which Altec never used AFAIK on any of its woofers, relying on its inductance rise to extend the driver?s HF response, especially when driven by a high output impedance.

You can check it though by working off an impedance plot:

Le = 1000*SQRT[[Zxo^2-Re^2]/[2pi*1000]] where Zxo is the resistance @ 1 kHz = 1.4954 mH Vs DATS?s 1.478 mH just ?eyeballing? Zxo = 12 ohms off your original plot, so it was accurate enough for me originally since it falls in line with my faded memory. ;)

GM

---

Yep, you're right on, GM. John Murphy (DATS designer) let me know that DATS has selectable ranges and units for several of the t/s parms. My first Le readings for this driver (~1.5mH) were at 1kHz, while the second readings (~0.5mH) were at 10kHz. For others using DATS, you simply double-click on the units box to toggle (you can see which parms have selectable units because of the little box drawn around them).

I'll try to get that test box done this weekend. I'm not trusting my delta mass technique :rolleyes:

FWIW, here are the T/S params in free-air, cone vertical, before and after break-in (sans Vas added mass that was skewing the data):

GPA 416-8C	new	after break-in
Re	7.77	7.59
Fs	23.55	22.88
Qts	0.294	0.293
Qes	0.308	0.309
Qms	6.638	5.931
Le (@1kHz)	1.51	1.47

Quote:

---

Originally Posted by Alien_Shore

I'm not trusting my delta mass technique

---

Why not?

Not familiar with these types of programs, so can you post all specs it spits out when no attempt is made to measure Vas other than inputting the 12.75" piston diameter?

GM