porting a sealed cab

[stingray_65]

 I'm almost finished on a 1 x12 cab for my eminanece wizard.

dimentionaly it is very close to the AX-84 speaker enclosure project.

I liked the way they had different port sizes geared to the differnt tuning of your guitar (drop d =4.5 " port ,open E = 5.5" etc)

I was going to make several panels with different port sizes and swap them out accordingly.

then I got to wondering,

DO PORTS HAVE TO BE CIRCULAR?

could I for example cut a long oval port and slide a gate  to poen or close the port apeture?

[FYL]

The opening can take any shape.

I would suggest an internal volume of app. 50 liters and a tuning frequency of 75 Hz. A baffle won't be deep enough so you'll have to play with ports.

The attached pdf includes a quick BBP simulation.


 

[Frankenamp]

Stingray: What you are describing is the "classic" way to tune a bass reflex box using a port without a duct. Most period designers would cut a rectangular slot and make a sliding cover (just like what you drew) and slide it back and forth untill the bod sounded right. A poorly tuned classic reflex is the origonal 'BOOM BOX'. You can model this two ways: pick a diameter and vary the length of the duct, or set the length at 3/4" (baffle thickness) and change the diameter to change the response.

FYL's BassBox model lists the number of vents as zero so I assume it is a sealed box?

Xmax of .8mm is pretty short- more like a midrange driver. I'm concerned about the Xmech. Is it really 1.2mm? that is the one-way cone excursion before the VC former contacts the back plate (at high velocity) just touching the rear pole plate will make a nasty buzz and any more excursion will ruin the VC former.

[stingray_65]

well my volume came in pretty close to 3520 cui  (57.6 L)thats not including the cleats

LOL I got this thing screwed up alreadythen  :)

but she shore is purdy in blonde and wheat
I'll post pix tommorow

if I'm that big I should probably leave the back off

lol or maybe some 4x4 posts for cleats 

[PRR]

> DO PORTS HAVE TO BE CIRCULAR?

Not in the least. There are subtle reasons to slightly favor round-ish, nothing that matters on the band stand. Altec A-7 port was 8" tall 27" wide rectangle. Don't go to a slit, although one insider trick is to space the frame off the board and let the "port" be the gap around the speaker.

Sliding ports, removable plugs, etc are all old tuner tricks. In a final product, you want to KISS, no loose movable parts to rattle, fall off, add weight. But in shop and for the first few gigs, leave something to change.

>> suggest an internal volume of app. 50 liters

> (57.6 L) thats not including the cleats LOL I got this thing screwed up alreadythen  :)

No. Box volume is VERY un-critical. 10% changes are hard to discern in the result. 30% changes are plenty good enough, with maybe a half-inch adjustment to the hole. If you have 57L, use it, and FYL's port calculation for 50L will probably be "perfect" +/- your particular taste and need.

After skimming FYL's sim, I'm thinking that a 89Hz 41L driver, for guitar duty, in 50-56L, might ultimately work better sealed, and maybe like a smaller box. Sealed in 53L, resonance will be 119Hz, f3db around 95hz, Qt=0.62: a gentle shoulder with useful output at 82hz and a few semitones lower. Because of the low Xmax, the cone will slap with just a few watts electric power at the lowest gitar pitches. True, the vent significantly reduces excursion around 60-90hz.

Uhhh.... this sim is for a zero-impedance amplifier, right? Many gitar amps are high impedance. That means, roughly, that the zero-Z response curve is multiplied by the impedanace curve. That suggests a big peak at ~~130Hz, negating most of the effect of box tuning.

This speaker is really good for 180Hz on up. It has BIG midrange (no over 5%! BL > 14!!). While you can flatten it to 70Hz, to get that high efficiency, it has a short motor, and slaps at 5W 100Hz or 1W 50Hz. Its a helluva tenor. It's not a strong clean baritone. If you play with a bassist, that's good. But then you don't really want to "optimize" your bottom octave. That's the bassist's turf. I think what a guitarist wants is bottom-octave slap to colorize the tone and give an implied fundamental pitch splattered all up the mid-bass.

It would be killa on a 36" open baffle. Or on-floor, a 20"x36" baffle. Perhaps folded-back for 14"x24" front with 6"-8" sides. With a hi-Z amp, response to 82Hz is not bad, though still too easily over-driven by deep heavy bass. Be easy enuff to knock a hole in a 2'x4' handy-panel and try it at home, though an open baffle this large really needs a larger space to work into.

[Dynaflow]

 Anxious to hear how this works for you, the Wizard is my very favorite speaker, I've got a pair of them, one in my 18 watt tmb and I must say its probably the loudest 18 watter I've ever played in my life.

Regards,

Dyna

[stingray_65]

I'm very anxious too.

I'm finaly set to start on my AC30 ish build and this is my first higher wattage amp.

everything else I've built has been hi fi or fender.

odd thing though,

my son was home when the package arrived and he took the pigtail out of his cab with a Weber alnico sig series.

hooked it up to the speaker and just sat it on the floor. the Weber sounded SOOOO much better and louder , but then again he was playing a gibson SG with humbuckers into his 5E3 which sounds awful any how ( need to put a .6uf/22uf cap switch on that amp)

I hope they end up sounding at least good :)
I had plans of a 4 x 12 cab loaded with them.

[FYL]

FYL's BassBox model lists the number of vents as zero so I assume it is a sealed box?

I haven't entered enclosure or port data, so the BBP lists zero, but the sim is for a standard bass reflex.

Xmax of .8mm is pretty short- more like a midrange driver. I'm concerned about the Xmech. Is it really 1.2mm? that is the one-way cone excursion before the VC former contacts the back plate (at high velocity) just touching the rear pole plate will make a nasty buzz and any more excursion will ruin the VC former.

Most guitar speakers using a pleated paper surround show a ridiculously small Xmax. The Emi is typical.

[FYL]

After skimming FYL's sim, I'm thinking that a 89Hz 41L driver, for guitar duty, in 50-56L, might ultimately work better sealed

Sealed, open back, "detuned" or maybe using aperiodic loading (closed with a heavily resistive port).

Uhhh.... this sim is for a zero-impedance amplifier, right? Many gitar amps are high impedance. That means, roughly, that the zero-Z response curve is multiplied by the impedanace curve. That suggests a big peak at ~~130Hz, negating most of the effect of box tuning.

Of course. You can expect 2 ohms or more of source Z.

[Frankenamp]

FYL's BassBox model lists the number of vents as zero so I assume it is a sealed box?

I haven't entered enclosure or port data, so the BBP lists zero, but the sim is for a standard bass reflex.

Xmax of .8mm is pretty short- more like a midrange driver. I'm concerned about the Xmech. Is it really 1.2mm? that is the one-way cone excursion before the VC former contacts the back plate (at high velocity) just touching the rear pole plate will make a nasty buzz and any more excursion will ruin the VC former.

Most guitar speakers using a pleated paper surround show a ridiculously small Xmax. The Emi is typical.

Correct, I've built a few... and driving the speaker out of Xmax gives it another non-linear component to the sound. What worries me (if the Xlim isn't a typo) is hitting an open E with more than 7-10 watts and whacking the back of the VC on the frame. which won't sound good at all. Agree with PRR about the Bl product. most cheap speakers have a Bl of 3-5. 14 is phenominal- makes for a very strong motor. looks like it could be horn loaded even... but that's just crazy talk.  PRR's 1/3 watt amp (with that in a horn) would run you out of the room.  That speaker (to quote Paul W Klipsch) just needs a good 5 watt amp.