Large Advent Specs

[Guest kevemaher]

Does anyone have the specs (Fs, Qes, Qts, Qms, Xmax (one way), Le, Re, and the rest, but especially these) for the Masonite Advent woofer? Mine are stamped, Dec 1974 on back of magnet.

Thanks!

[Carlspeak]

I recently refoamed 4 masonite Advent woofers dated a few years later than yours. One had a bad VC but I WT3 tested the other 3 and below are some nominal T/S averages you may find useful.

Fs = 17.5

Re= 4.45 ohms

Le =1.2 mH

Qes=0.34

Qms=5.7

Qts=0.32

Vas=13.5 cu. ft.

Sens = 89.5 dB/w/m

Not sure about xmasx. VC windings are 5/8 inch long and pole plate is 5/16 thick if that helps.

P. Basel has also posted some of his measurements here. Do a search.

I'm not aware of any original mfg. t/s specs being available.

[Guest kevemaher]

Carl,

Thanks so much. The large Vas makes for a Q=1 in the box. WinISD shows small 1dB peaking between 50-100 Hz and a -3dB at 47 Hz. Not a bad way to go. The large inductor on the LPF was there because of the high woofer impedance (23-50 ohms) at the 3-7KHz xover point (xover depends on where the switch is). So I'm finally understanding their design which was to boost the HF response for "older" program material ("Decrease" position). With today's program material the tweeter should probably be in "Extended" position to move the tweeter xover up in freq in order to tame its output. But this also depends on individual taste.

Of course, the project described in my previous post removes the tweeter and inductor. But at least I now know what the LF performance should be. It should be fine for my experiment which was to fill in the low end of the Dynaco A-35s.

Again, many thanks. You've saved me many hours of impedance measurements.

And boy did they tightly stuff the box with fiberglas!!!. I used a much looser polyamide fill when I restuffed and tore the pieces up into small chunks. Can't safely do that with fiberglas. Ear check confirms the LF performance is still there. I had great success with loose poly fill in my previous 3-way tri-amped 120 liter box, where I achieved -3dB at 30Hz with a 10" Scanspeak woofer. But that's another story for another forum.

Kevin

[Pete B]

Carl,

Thanks so much. The large Vas makes for a Q=1 in the box. WinISD shows small 1dB peaking between 50-100 Hz and a -3dB at 47 Hz. Not a bad way to go. The large inductor on the LPF was there because of the high woofer impedance (23-50 ohms) at the 3-7KHz xover point (xover depends on where the switch is). So I'm finally understanding their design which was to boost the HF response for "older" program material ("Decrease" position). With today's program material the tweeter should probably be in "Extended" position to move the tweeter xover up in freq in order to tame its output. But this also depends on individual taste.

Of course, the project described in my previous post removes the tweeter and inductor. But at least I now know what the LF performance should be. It should be fine for my experiment which was to fill in the low end of the Dynaco A-35s.

Again, many thanks. You've saved me many hours of impedance measurements.

And boy did they tightly stuff the box with fiberglas!!!. I used a much looser polyamide fill when I restuffed and tore the pieces up into small chunks. Can't safely do that with fiberglas. Ear check confirms the LF performance is still there. I had great success with loose poly fill in my previous 3-way tri-amped 120 liter box, where I achieved -3dB at 30Hz with a 10" Scanspeak woofer. But that's another story for another forum.

Kevin

Your simulation does not sound quite right. You want to increase the enclosue volume to

simulate the effect of the enclosure filling so that the simulated Fc matches that measured

which should be about 41-42 Hz. Then you should lower Qm of the driver so that the Qtc

matches that measured which should be around .8, not 1. Lowering Qm simulated the

effect of the fiberglass behind the driver as an acoustic resistance. A Qtc of 1 should have

peaking above Fc and should cross the passband level at Fc, - 3 dB should be below Fc.

Are you talking acousti-stuff for the polyamide fill? Or what exactly did you use? I've found

that it has to be very tightly packed to come close to the original fiberglass stuffing in the

Advents.

[Pete B]

Xmax calculations:

http://www.classicspeakerpages.net/IP.Boar...ost&p=75006

The driver has a huge mechanical Xmax as compared to the linear or even

50% limit which I see as one of the advantages of this driver.

[Guest kevemaher]

I am using Acoustastuff. On my big speakers, I've actually seen a larger Q and a lower Fc with a light stuff rather than heavy. I can't quantify as I haven't actually measured the weights.

I really don't mind a little bump in the 50-100 Hz range from the higher Q. It moves the Fc to a lower freq relative to the 200-500Hz range.

I love the sound of the A-35 mid and woofer. The 250Hz-5KHz range is laid back and smooth, perfect for my taste. I know my hearing rolls off above 10KHz, so I'm not too concerned about the 87H driver lacking an extended high end.

The intent is to fill in the low end with the Advent woofer, rolling off with a 12dB/octave active LPF at either 90 or 180Hz. An Fc between 40 to 50 Hz will be fine. I'm simulating the Advent woofer using Carl's TS values and WinISD Pro. In that model, I have played around with the absorptive and leakage loss parameters and seen little variation in Q (0.8 to 1.0) with large variation in absorptive losses, so I think the stuffing is not terribly critical. That being said, I don't want to make it boomy. So I should do some impedance vs. freq measurements to obtain the actual Fc and Q.

Leakage losses should be very small. The boxes are tight and I've used AR putty to seal the woofer (great material!).

Thanks Pete B. for your informed comments. It helps to have a reality check. I'm sure I'll have more questions and problems as I continue with this project.

Kevin

[Guest kevemaher]

Your simulation does not sound quite right. You want to increase the enclosue volume to

simulate the effect of the enclosure filling so that the simulated Fc matches that measured

which should be about 41-42 Hz. Then you should lower Qm of the driver so that the Qtc

matches that measured which should be around .8, not 1. Lowering Qm simulated the

effect of the fiberglass behind the driver as an acoustic resistance. A Qtc of 1 should have

peaking above Fc and should cross the passband level at Fc, - 3 dB should be below Fc.

Are you talking acousti-stuff for the polyamide fill? Or what exactly did you use? I've found

that it has to be very tightly packed to come close to the original fiberglass stuffing in the

Advents.

I did an experiment with very heavy Acoustastuff fill and a lighter fill of about half (I did not measure the weights). I measured impedance vs. freq using the method referred to in Wikipedia (under Thiele/Small parameters). Attached is a graph of my results.

The Fc is about right at 40 Hz. The lighter poly fill raises the impedance. Qtc is 0.60 and 0.68 for the light and for the heavy poly fill respectively, so lighter is preferable. Using WinISD with the bare driver data from Carl, I modified the model box volume to get Fc at 40 Hz. I had to double the physical volume to 92 liters. I then adjusted the absorption losses due to the the poly fill to get the desired Qtc. According to WinISD, even the fill I call light is on the "heavy" side. The light fill has less Acoustastuff material than the fiberglas I pulled out.

So a light poly fill will produce a nearly ideal Q. The -3dB point for heavy and light stuffing is 49Hz and 41.5Hz, which is a real difference. I have not verified these results with SPL measurements. These are tricky to do without an anechoic chamber.

Now I'm off to mate these with the A-35s. The line level active xover I bought does cause a variable phase shift in the xover region (line level input/output measurements with an oscilloscope). I will see how audible this is as it will combine with the A-35 running full range. The 12dB/octave roll-off may be fast enough to eliminate any audible effects.

[Pete B]

I did an experiment with very heavy Acoustastuff fill and a lighter fill of about half (I did not measure the weights). I measured impedance vs. freq using the method referred to in Wikipedia (under Thiele/Small parameters). Attached is a graph of my results.

The Fc is about right at 40 Hz. The lighter poly fill raises the impedance. Qtc is 0.60 and 0.68 for the light and for the heavy poly fill respectively, so lighter is preferable. Using WinISD with the bare driver data from Carl, I modified the model box volume to get Fc at 40 Hz. I had to double the physical volume to 92 liters. I then adjusted the absorption losses due to the the poly fill to get the desired Qtc. According to WinISD, even the fill I call light is on the "heavy" side. The light fill has less Acoustastuff material than the fiberglas I pulled out.

So a light poly fill will produce a nearly ideal Q. The -3dB point for heavy and light stuffing is 49Hz and 41.5Hz, which is a real difference. I have not verified these results with SPL measurements. These are tricky to do without an anechoic chamber.

Now I'm off to mate these with the A-35s. The line level active xover I bought does cause a variable phase shift in the xover region (line level input/output measurements with an oscilloscope). I will see how audible this is as it will combine with the A-35 running full range. The 12dB/octave roll-off may be fast enough to eliminate any audible effects.

Your sims do not sound right, and I suspect that Carl's parameters are off,

particularly Vas which combined with Fs determine the moving mass used

by the sim program. Carl's data indicates far too low of a moving mass.

You're having to increase the simulated volume far too much and your Qtc

is low.

Here's just one set of my measurements, note the much lower Vas:

>Fs = 18.23 Hz

>Vas = 250 liters or 8.82 cu ft

>Re = 4.83

>Qe = .364

>Qm = 2.93

>Qts = .324

>Mms = 42.28g

>Cms = 1.80 mm/N

>Bl = 8.02 Tm

>no = .400 %

>SPLref = 88 dB

[Guest kevemaher]

Your sims do not sound right, and I suspect that Carl's parameters are off,

particularly Vas which combined with Fs determine the moving mass used

by the sim program. Carl's data indicates far too low of a moving mass.

You're having to increase the simulated volume far too much and your Qtc

is low.

Here's just one set of my measurements, note the much lower Vas:

>Fs = 18.23 Hz

>Vas = 250 liters or 8.82 cu ft

>Re = 4.83

>Qe = .364

>Qm = 2.93

>Qts = .324

>Mms = 42.28g

>Cms = 1.80 mm/N

>Bl = 8.02 Tm

>no = .400 %

>SPLref = 88 dB

[/quote

Thanks for the updated info, Pete. The impedance measurements I reported are not simulations. They are real measurements with a 6.6 ohm test resistor in series with the woofer w/o inductor driven by sine wave test tones. Voltages are measured across the amp (constant at about 1.2V) and the test resistor. I obtained Fc and Qtc from these measurements. The WinISD simulation was tweaked to get these values. I then read the -3dB values from the resultant FR plot. The out of box values are irrelevant because I have the real in-box values.

[Carlspeak]

The 3 MMS's I got included with the prior averaged data were 34, 37 and 40 gms.

I have a cone assembly (cone, VC, DC, Spider and foam surround) apart now for repair, weighed it and got 42 gms.

[Guest kevemaher]

Pete,

I've entered your T/S parameters into the moded I use - WinISD. This is freeware, readily available. I think it is really good. I have played around with the modeled box volume in order to obtain Fc near 40Hz. There is a loss parameter that is related to the absorption of the stuffing and affects the box Qtc. Attached are the results for FR and Impedance.

The orange FR plot has a Qtc = 0.8, a value you've referred to for fiberglas. The loss parameter is low.

The red FR plot has a Qtc = 0.7, near the optimum Butterworth value. The loss parmeter is low (same as the orange plot).

The yellow FR plot has a Qtc = 0.68, the value I've measured with a "medium" Acoustastuff fill. The loss parameter was tweaked in the model to obtain this Qtc. The value is medium.

The corresponding Impedance plots are also shown. The peak impedance of 30 ohms matches my measurements, which could be taken as a validation of the WinISD Sim.

All three FR plots predict nearly identical performance, with Fc approx 40Hz. This indicates that the proper Acoustastuff fill can achieve performance similar to the original fiberglas fill.

Do these modeling results match results you'd get with your model?

(By the way, for a Qtc = 1, the model predicts an Fc of 58Hz and a box volume of 30 liters. The FR plot passes the passband level at Fc.)

Kevin

Your sims do not sound right, and I suspect that Carl's parameters are off,

particularly Vas which combined with Fs determine the moving mass used

by the sim program. Carl's data indicates far too low of a moving mass.

You're having to increase the simulated volume far too much and your Qtc

is low.

Here's just one set of my measurements, note the much lower Vas:

>Fs = 18.23 Hz

>Vas = 250 liters or 8.82 cu ft

>Re = 4.83

>Qe = .364

>Qm = 2.93

>Qts = .324

>Mms = 42.28g

>Cms = 1.80 mm/N

>Bl = 8.02 Tm

>no = .400 %

>SPLref = 88 dB

FR_plots_from_WinISD.bmp