ampeg b15n cabinet help

[danecho283]

Hello, i won an ampeg b15n head and am building a matching cab...does anyone know the size of the port at the base of the baffle? thanks[IMG][/IMG]

[CoolBlueGlow]

Based on my research, the porting changed between the original recipe fliptop and the later models. This happened at least once in the 1960's era B-15. The 1964-66 model had a complex port, the approximate design being available by looking at Jess Oliver's patent drawing. It is a very non-traditional port system.

The later model, beginning in about 1966, eliminated the more complex construction required for the original porting arrangement. It did this by entirely eliminating the floating port arrangment in Mr. Oliver's original design. This was apparently to save costs. Based on my personal discussion with him before he died, It seemed that Mr. Oliver was not happy about that modification.

I have one of each, a 64 and a 66. My stock 1966 model B-15 has no port. My stock 1964 B-15 has the original recipe port.

I am not familiar with other porting arrangements on later model flip tops, or if they differ from the second design non-ported fliptops which came into being in about 1966.

It would be fairly easy to calculate the required port dimension, using your desired speaker's performance, your cabinet dimension, your desired fundamental resonant fequency and one of the many online cabinet port calculators.

Cheers

CBG

[donh]

The B15 design I am familiar with is not a ported box, but a Helmholtz Resonator design. Whole different beastie, that!

[StephaninMelb]

With the lapped corner joints you've done consider drilling some holes and sink some screws. Glue in dowels to cover and chisel level. Otherwise the speaker vibration will probably loosen the box.

For porting I would just go about it as CoolBlueGlow has suggested. You could also run "side ports." I wouldn't try and clone the Ampeg design exactly as your are building a clone as you can buy complete cabs as seen below. There are various enclosure design tools that will help you calculate the port diameter and port length.

In the first photograph at the bottom of the page is a Ampeg 1966 B-18 cabinet interior shot. To left and right of the speaker, at the front are the "slotted: ports. You could use this as a design concept guide and make calculations for total port opening area using your "selected speaker" specifications and an online guitar speaker enclosure / port size calculator.

Also below is an exploded drawing of an Ampeg B-15 Double Baffle Cabinet. Note the following information "closely." In this design"

• Speaker is attached to the inside baffle panel
• Inside baffle panel has slotted ports
• Shims are used between the inside and outside baffle panels to create an air duct space
• The speaker is installed through the front of the inside panel
• Note the "four" diagonal shims, which must be present for this design to work properly (many are missing on rebuilt cabs!)
• Air is exhausted into the space between the two baffles and flows out the circular front panel grill cut-out

It is important to use a foam surround on your speaker so that it creates an airtight seal. This type of enclosure design will vibrate like crazy if not sealed properly or with if it has missing or loose parts.

You can get vintage Ampeg parts at:

Fliptops
They have proper speaker baffles, flip-top cabinet, extension cabinets, stacking cabinets, caster carts, tilt-backs, Ampeg Tolex, grill cloth

http://www.fliptops.net/

Tubes and More (Antique Electronic Supply)
Logos, cab corners, flip-top latches, latch tabs, Ampeg grill cloth, two types of Ampeg Tolex....

http://www.tubesandmore.com/

Vintage Amp Restoration
Ampeg parts & restoration services. I think they can provide the rubber cover gasket for the bottom vent in Portaflex cabinet.

http://www.vintage-amp.com/ampegpts.htm

American Musical Supply
Ampeg Portaflex Cabinets, including "scratch & dent" cabs (45% off)

http://www.americanmusical.com/Item--i-AMG-PF115HE-LIST

ZZSounds
Same Ampeg Portaflex Cabinets as American Musical Supply, including "scratch & dent"

http://www.zzounds.com/item--AMPPF115HE

Photographs top to bottom:
(1) Ampeg 1966 Portaflex B-18 Cabinet Interior
(2) Ampeq B-15 Double Baffle Cabinet Exploded View
(3) Ampeg Portaflex PF-115HE Cabinet Interior (New - Reissue type product)
(4) PF-115HE Rear (New - Reissue type product)

----> Click on pics to view (Full Size)

[StephaninMelb]

I will just throw this bit of information here about the Ampeg B-15 tray cover material as it is generally NOT known. The B-15 trays were covered with black imitation leather, Black Levant material with 100% cotton base that is traditionally used in the book binding industry. The cover material is pyroxlin, which provides a durable surface. It is still available from vendors supplying book printers.

Below is an example. Also included is a link to one supplier (Hollanders):

http://www.hollanders.com/supplies/V...d-0b3fc3e308ff

[StephaninMelb]

I will just throw this bit of information here about the Ampeg B-15 tray cover material as it is generally NOT known. The B-15 trays were covered with black imitation leather, Black Levant material with 100% cotton base that is traditionally used in the book binding industry. The cover material is pyroxlin, which provides a durable surface. It is still available from vendors supplying book printers.

Below is an example. Also included is a link to one supplier (Hollanders):

http://www.hollanders.com/supplies/V...d-0b3fc3e308ff

[CoolBlueGlow]

Thanks to Stephan! Great info on B-15 cab and other info as well.

My 1964 Fliptop is built per the exploded diagram - JO's original design. My 1966 has the slots shown in the interior photo provided by Stephan. I would not call them "ports" in the traditional sense. Based on my direct measurement of their area and length, it is clear to me that they are not tuned to the cabinet volume in any logical way. Someone at Ampeg was guessing, methinks. :-)

re: Hemholtz resonators - In fairness to DonH's post, it is the the principle of the HR which makes a ported cabinet work...so I am neither trolling Don nor flaming him. :-)...but to be precise, most ported musical instrument cabinets are more loosely tuned, to avoid excessively lumpy resonant peaks. You'll want to take that into consideration as you port your homebrew bass cabinet. If you don't, you'll have one or two notes sticking out like a sore thumb, while the ones right above them on the neck practically disappear.

A little info below on Dr. Hemholtz, who was a true renaissance man. (Yes, I own and have actually read "On the Sensation of Tone" :-) HvH was incredibly influential, and every serious student of sound should read this work. Even a quick trip to wiki will reveal a tiny bit of just how influential this intellectual giant was. It was Dr. Hemholtz who did the first proper and serious exploration of how the human ear works, including dissection and drawings which became the standard reference work for the anatomy of the human ear. He did this "on the side" because of his interest in acoustics. :-)

It was also Dr. Hemholtz who coined the term "resonance" as we now use it. He did this in his seminal work on acoustics, called "On the Sensation of Tone" and published in Germany in 1863. In that work, he was using narrow necked glass bottles tuned to sympathetically vibrate air at a very specific pitch. These were, in effect, very high Q ports attached to a sealed space. He called them "resonators", from whence the term Hemholtz resonator derives. You can make one yourself, by blowing across the opening of a glass jug or even a pop bottle. If you do it right, it will make a distinct pitch. This is a Hemholtz resonator.

Besides using his "resonators" for acoustical amplifiers to discern fine upper harmonics in complex acoustical signals, Dr. Hemholtz also used them as acoustical transducers. He stretched India rubber skins across the opening of specially blown glass resonators. On that thin membrane, he distributed fine sand. When excited by acoustical energy, the sand formed visual patterns of that acoustical energy - in effect an acoustical oscilloscope. Dr. Hemholtz published drawings of these patterns in "On the Sensation of Tone". They were, I believe, the first directly observed and published visual representation of pure tone sine waves. This was in the middle of the 19th century, mind you!

So, with regard to "Hemholtz resonator" ported cabinets - you've probabaly heard a few pass through your neighborhood from time to time in certain vehicles so equipped. Car stereo builders call them "bandpass" cabinets, since they are tuned in more nearly Hemholtz like methodology to a fairly high Q. This matches them to the bass/kick drum fundamental pitch of popular Rap and R&B artists. I call them a "nuisance". :-) I think Dr. Hemholtz would be horrified.

Cheers,

CBG



v

[danecho283]

i posted really quickly to see if someone would post a pic of a b15n baffle that i could base my port on. i should have let everyone know that i have done plenty of homework before this point and understand the different baffles through the years. i have seen a lot of pictures of the other baffles but have not found a pic anywhere of a b15n (mine is a 1968). i am putting an altec 421a in the cab and i am making my build to exact measurements found on the talkbass portaflex thread. thank you for all the info and if anyone owns one of these amps and can "feel" the port through the speaker cloth or even has a pic it would be greatly appreciated. i am staying away from the calculators and want to try the vintage "mojo" thing that worked for ampeg back in the day. thank you.

[danecho283]

Hey guys, i got this pic when i posted at the talkbass portaflex thread. it is the info i was looking for, thank you all for your info.[IMG][/IMG]
i also got all the info on the inside of the cabinet from this discussion
http://www.electricalaudio.com/phpBB...hp?f=5&t=47105

[CoolBlueGlow]

Hi danecho,

Great! Glad you found what you were looking for. Sorry it took a bit. We weren't very helpful were we? Pontificating on Hemholtz, et al.

Cheers,

CBG

[StephaninMelb]

Gee he could have just said he wanted a picture of an early Ampeq B-15N "cat guard" single baffle with the lower water drain holes.

[danecho283]

anybody have another picture of an early Ampeq B-15N "cat guard" single baffle with the lower water drain holes? i only have one but its not the greatest, thanks.