Help in cab design ideas please:-)

[Bassmec]

Righto! so if an original Vintage Hiwatt 4x12 cab is only 4.8 cu ft internal volume. so I want to make a 1x12 at 1.2 cu ft internal volume for studio use with the loudspeaker in the far left hand column the std.
Link Removed
with metal dome anybody want to have a look at a graph from cabinet design software for me please, as I only have an Ipad to hand at the mo
The cabinet is actually 25% smaller than that, I have built, but I have calculated to have it stuffed with polyester batting and am told that is going to increase the effective volume by up to 30%
Link Removed

 

[will33]

On a phone here too. Be a while before I can do any real modeling. Couple things I can say though....

Though it was believed for a very long time that stuffing sort "made the box bigger", it has since been measured and accepted as not true anymore. That is to say, low frequency extension does not shift lower as it would by using a larger box. LF response fell off in the same/similar place before and after the stuffing. That's ok really, the stuffing does a bunch of other good things for the sound.

So....LF response may roll off a little bit higher than the full size box, and also may have a small hump in response just above where it falls off. Whether that's good or bad is just a tone preference.

I say just try it with various amounts of stuffing and pick an amount that sounds good. You could record examples in your studio with various amounts of stuffing to get a picture of the various changes in tone it causes.

Played live, the smal box will obviously lack some of the heft of the 412, not only because it's quieter and may roll off slightly higher, but also because it will have a higher baffle step from the now much smaller baffle. The recorded sound may likely not sound like as big a difference as the live sound between the 412 and 112.


Interested in how this goes. Keep in touch and I'll plug this stuff into modeling when I can.

 

[DukeLeJeune]

That's not a woofer I'd ever recommend for bass guitar.

The information given indicates an X-lim (damage-limited one-way excursion) of only 4 mm. Eminence's bass guitar speakers start at 8 mm X-lim and go up from there.

X-max (one-way linear excursion) isn't given but we can make an educated guess that it's probably no greater than 1/2 of X-lim, so a cab using this 12" speaker will probably fartout at a lower SPL than most 110 bass cabs.

 

[will33]

Good point there ^^

I guess I glossed over that. Peak to peak would mean 4mm each direction. It may have a nice sound pushed non-linear, but watch the power. Without modeling, I just can't tell if your box will have enough of an "air spring" effect to prevent mechanical damage, and just cook the coil instead. Watch the power levels. Begin testing at very low volume and increase gradually.

 

[Bassmec]

That's not a woofer I'd ever recommend for bass guitar.

The information given indicates an X-lim (damage-limited one-way excursion) of only 4 mm. Eminence's bass guitar speakers start at 8 mm X-lim and go up from there.

X-max (one-way linear excursion) isn't given but we can make an educated guess that it's probably no greater than 1/2 of X-lim, so a cab using this 12" speaker will probably fartout at a lower SPL than most 110 bass cabs.

I think the danger of fart out is very unlikely to be a big problem with this particular project, as I will be driving it with a whole 6 watts Duke.
If I play bass through it it's going to be a sort of "Stranglers" Peaches dirty 4 string bass track thing, re amped via the little labs phase tool just to down to the right of the RCA OP-6 in this photo:
Link Removed
What is it, it's a 60's Elpico as used by the "Beatles" and "Kinks". A Jolly British version of the original RCA circuit used in the Fender Champ C1 6sl7 single ended into 6v6 with 5y5 tube rectifier, all point to point minimal signal path.
Well smoke me voice coil!s

 

[will33]

I figured there had to be some sort of hijinx with this...

Just stuff the cab and play it.

 

[Bassmec]

I figured there had to be some sort of hijinx with this...

Just stuff the cab and play it.

It's a paper edge pulsonic cone with only 35 grams of un sprung weight.
Should be nice and bright for a big ribbon mic to get at.
A 3012ho is 46.9 grams a bit too sluggish for my liking, for this purpose.

 

[bgavin]

Though it was believed for a very long time that stuffing sort "made the box bigger", it has since been measured and accepted as not true anymore.

Sorry, but that is not accurate.
This has been done, Qtc measured and fully documented by Tom Nousaine in 1995.
The 30% increase can be obtained rarely, under ideal circumstances of a particular driver and box combination.
More realistic is a 20~25% increase.

The concept is isothermal vs adiabatic operation of the air volume inside the box.
The stuffing concept applies primarily to sealed boxes, because it is easier to fabricate with consistent results.

If this concept is intended for a vented box, much experimentation is required for accurate tuning.
The stuffing material is confined to the internal volume space, and kept clear of the effective vent and its correction factor length.
You will have to use nylon netting, etc, to control the stuffing placement.

OP, if this project is for your enjoyment, go for it and learn.
If the driver is unacceptable as noted above, you will find this out, and then learning will take place.
However, these projects normally require a huge amount of time, and expense, that is otherwise better spent playing your bass.

If you just need a decent cab, buy one, or build an established and well tested DIY box such as fEarful, or the Bill Fitzmaurice boxes.

 

[Bassmec]

This cab Pair is another of the extensive set of cabs that I will add to my guitar isolation room in my studios.
The drivers I have chosen are the vintage ATC's on the floor one has a paper cap, the other has an alloy voice coil cap.
I already have a pair of the very rare and extremely bright and agile EV12S short baskets and an Altec 417 series two, a la mode R Rhodes, Carlos Santana etc. and a JBL D120f a la mode Pete Townsend, Dicky Betts.
Link Removed
I am hoping that the ATC drivers and single ended amp will add yet another interesting colour to my very extensive re amping pallet.
My bass gear is mainly next door in the live Drum Room.

 

[will33]

Sorry, but that is not accurate.
This has been done, Qtc measured and fully documented by Tom Nousaine in 1995.
The 30% increase can be obtained rarely, under ideal circumstances of a particular driver and box combination.
More realistic is a 20~25% increase.

The concept is isothermal vs adiabatic operation of the air volume inside the box.
The stuffing concept applies primarily to sealed boxes, because it is easier to fabricate with consistent results.

If this concept is intended for a vented box, much experimentation is required for accurate tuning.
The stuffing material is confined to the internal volume space, and kept clear of the effective vent and its correction factor length.
You will have to use nylon netting, etc, to control the stuffing placement.

OP, if this project is for your enjoyment, go for it and learn.
If the driver is unacceptable as noted above, you will find this out, and then learning will take place.
However, these projects normally require a huge amount of time, and expense, that is otherwise better spent playing your bass.

If you just need a decent cab, buy one, or build an established and well tested DIY box such as fEarful, or the Bill Fitzmaurice boxes.

Geez.....I'm batting 0-2 here?.... Time to dig up more stuff. There's measurements out there somewhere that do not show a lowering of LF extension (like you get with a bigger box....within the capabilities of the driver of course).

 

[will33]

Was in a paper by G.L. Augspurger. Have to sift through all his transmission line stuff to find the sealed box stuffing stuff.

 

[bgavin]

Geez.....I'm batting 0-2 here?.... Time to dig up more stuff. There's measurements out there somewhere that do not show a lowering of LF extension (like you get with a bigger box....within the capabilities of the driver of course).

First, don't worry about your batting average.
If you get ragged by a TB armchair quarterback, just blow it off.

In normal adiabatic (unstuffed) mode, the air particle velocity is faster than in a fully stuffed (isothermal) cab.
Because of the slower velocity in the isothermal environment, the cab appears acoustically 'larger' than the adiabatic.

In the sealed box, larger does not necessarily mean more LF extension.
The sealed B2 Butterworth alignment (Qtc = .707) provides the lowest F3, most area under the curve, and a steeper rolloff.
As the box volume increases, the Qtc drops, but this raises the F3 somewhat.

The next larger volume is the sealed D2 Bessel alignment (Qtc = .577).
D2 provides the tightest transient response (critical damping), at the expense of a higher F3, less area under the curve, a more gentle rolloff, and decreased power handling than B2.
These can be demonstrated using any of the sealed Qtc graphing calculators.

It gets much more tricky in a vented box.
The stuffed volume around the driver is isothermal, and the unstuffed volume around the vent is adiabatic.
Vented isothermal projects require many iterations of trial and error.

Sealed B2 is analogous to Vented Flat.
And D2 to SBB4.

Refer to Leo Beranek, "Acoustics", 1954~1986, ISBN 0-88318-494-X
Edward Villchur, patent Acoustic Suspension, 1954

 

[Bassmec]

The real old boy at celestion Frank Knights sadly long gone RIP, said to me as far back as the mid seventies, "if you stuff a Marshall 4x12 you up the apparent volume of the cab" apart from the tonal changes.
He knew more than god about speakers, I think between him and a bloke called Stan Whitworth who made the test cones and voice coils, he probably invented a good deal of the ones Marshall lovers like best.
I have Marshall 4x12's a plenty in the drum room, I just want something a bit tighter sounding and no cab back rattles or boomy problems with downtune guitars. Thus power soaked smaller cabs in the guitar isolation room.
Suits nice ribbon mic's not being too loud too

 

[will33]

Forgot one of these ----> after the batting average thing. Was a reference to an earlier discussion.

I wouldn't even worry about this cab for guitars, downtuned or not....or with 6 watts of bass for that matter. I'd just mess with it until I liked it, whatever that ends up being. If it sounds good, it is good....especially in studio. If that HiWatt is pretty much unlined like the Marshalls, that stuffing is going to change a whole lot more about the tone than just the bass.

 

[Bassmec]

Forgot one of these ----> after the batting average thing. Was a reference to an earlier discussion.

I wouldn't even worry about this cab for guitars, downtuned or not....or with 6 watts of bass for that matter. I'd just mess with it until I liked it, whatever that ends up being. If it sounds good, it is good....especially in studio. If that HiWatt is pretty much unlined like the Marshalls, that stuffing is going to change a whole lot more about the tone than just the bass.

This is a good excuse to stuff one and not the other then, good I was kind of thinking that, with the more raged upper mid of the metal domed
version unstuffed might be mad in a good way