I need some help tuning the box for my Altec model 19 clones.
The speakers are built into an existing media room cabinet and use Great Plains Audio drivers. GPA recommends 8.8 ft.³ cabinet volume for the 416 drivers. I built the cabinets with 9.08 ft.³ volume to give myself a room for error. Dampening material is No-Rez, which Danny told me should have almost zero influence on the cabinet volume. The port is 6 inches diameter and 6.91 inches in length per the Precision Port calculator For a tuning frequency of 29 Hz, as recommended by GPA. Note, the baffled side of the flared port is fabricated from wood, but it is identical dimensions as the plastic PP unit.
Using Dayton Audio DATS V3, I am measuring a F(b) of 26.6 Hz. Working backwards using the PP calculator for this port at this frequency generates a 10.5 ft.³ volume cabinet. Inserting half cubic foot of material in the speaker to reduce volume results in zero change in frequency.
What am I missing? The volume may be off by a 0.2 ft.³, but I’m not off by 1.5 ft.³.
The speakers are built into an existing media room cabinet and use Great Plains Audio drivers. GPA recommends 8.8 ft.³ cabinet volume for the 416 drivers. I built the cabinets with 9.08 ft.³ volume to give myself a room for error. Dampening material is No-Rez, which Danny told me should have almost zero influence on the cabinet volume. The port is 6 inches diameter and 6.91 inches in length per the Precision Port calculator For a tuning frequency of 29 Hz, as recommended by GPA. Note, the baffled side of the flared port is fabricated from wood, but it is identical dimensions as the plastic PP unit.
Using Dayton Audio DATS V3, I am measuring a F(b) of 26.6 Hz. Working backwards using the PP calculator for this port at this frequency generates a 10.5 ft.³ volume cabinet. Inserting half cubic foot of material in the speaker to reduce volume results in zero change in frequency.
What am I missing? The volume may be off by a 0.2 ft.³, but I’m not off by 1.5 ft.³.
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Hope you made the horn/woofer ctc and offset spacing same as the M19 or the designed XO won't be perform as designed/proven.
Curious what the slot over the horn is for..........
Regardless, typical port calculators assume that the internal volume has a ~uniform particle density, i.e. no eigenmodes, which your high aspect ratio cab has, therefore complicates optimum woofer, vent locations that should ideally be at its 1/4 WL pipe odd harmonics, hence the lower than predicted tuning, net Vb gross change, so trust your measurements.
Curious what the slot over the horn is for..........
Regardless, typical port calculators assume that the internal volume has a ~uniform particle density, i.e. no eigenmodes, which your high aspect ratio cab has, therefore complicates optimum woofer, vent locations that should ideally be at its 1/4 WL pipe odd harmonics, hence the lower than predicted tuning, net Vb gross change, so trust your measurements.
Thanks GM,
I attached a file of the speaker drawings. The dimensional relationship between the horn and the woofer are identical to the Model 19. Only the box aspect ratio and port are different.
The slot below the horn is for the L-pad panel. I custom designed the panels to reflect the original design.
As a test I inserted one cubic foot of books in the cabinet to see the impact. The frequency only changed from 26.6 to 26.9 Hz. So achieving 29 Hz box tuning is impractical with out reducing the port length. I believe this leaves me only two options. Reduce the port length by 0.33 in, or accepting 26.6 Hz. Changing the port length at this time is possible, but a pain. So I am wondering, how much of an impact being 2.4 Hz low in box tuning will be?
For reference, below is the GPA data for the 416.
You're welcome!
Ah! The speaker is upside down........
Minimal sound wise, power handling a bit less if you actually listen to anything that goes this low at relatively high amplitude such as pipe organ symphonies and/or modern music with a continuous, strong (sub) bass beat and/or HT LFE without a sub or two to do the heavy 'lifting'. For instance, here's the sound power requirements for a 75 pc. orchestra from way back when and R&R's response was nominally flat from 300 - 80 Hz, rolling off at 24 dB/octave down to 40 Hz, hence the M19's ~45 Hz Fb.
Regardless, it's not an M19 clone per se, which is ~8.10615 ft^3 net tuned to ~45 Hz, so recommend tuning it to whatever works best in your app as opposed to somebody else's preference.
Ah! The speaker is upside down........
Minimal sound wise, power handling a bit less if you actually listen to anything that goes this low at relatively high amplitude such as pipe organ symphonies and/or modern music with a continuous, strong (sub) bass beat and/or HT LFE without a sub or two to do the heavy 'lifting'. For instance, here's the sound power requirements for a 75 pc. orchestra from way back when and R&R's response was nominally flat from 300 - 80 Hz, rolling off at 24 dB/octave down to 40 Hz, hence the M19's ~45 Hz Fb.
Regardless, it's not an M19 clone per se, which is ~8.10615 ft^3 net tuned to ~45 Hz, so recommend tuning it to whatever works best in your app as opposed to somebody else's preference.
Thanks again GM,
Your response will accelerate the completion of this long Fran out project. With an predicted efficiency of approximately 101 db, and in the size room they will be occupying, a minor drop in efficiency is no issue. I can now finish up both cabinets, and make a decision at a later date if I want to tweak the port length. Once I start enjoying the speakers however, I have a feeling I will lose any desire to open them up again.
I will post photos here are the final completion. But at the rate I’m going it may be around Christmas.