1x12" Cab Design Diary

[redstriper]

Thanks Balcro, I don't understand a word of that, but that's my problem and I appreciate your effort, my brain's just not big enough

I'm happy to accept that for deep bass you need less sensitivity, without understanding the science.

[Phil Starr]

Balcro's car analogy is excellent. If you increase the weight of a car you need bigger springs. That's simple enough but if you just do this it is going to bounce around more, you need to change the shock absorbers to exactly match the increased weight and the stronger new springs to get the best out of your pimped vehicle. Mass, springiness and damping are all things which need to be calculated in speaker design and balanced out. You can't change just one thing you have to look at them together.

To get deeper bass you need to tune lower and move the cone further. Just as in your bass thicker heavier strings or cones do lower the tuning, as does slackening off the tension. Just as Balcro says increasing the weight means less cone movement for the same power.

Then to get the extra movement you have to have a longer voice coil. This also wastes power because most of the coil is out of the magnet at any given time and using power but not making the cone move.

You can put in a bigger magnet to get the efficiency up again but this will also increase the damping and the cost so you have to get that right too. Price for price you trade bass extension for efficiency.

[LukeFRC]

[quote name='stevie' timestamp='1391517491' post='2357961']
I can give you a list of the 12" drivers that are in our possession and that we may be trying out:

Beyma SM212
Ciare 12.00NdW
Celestion TF1225
Celestion TN1230
DAS Audio P12
Eminence Beta 12
Eminence DeltaLF
Eminence Kappalite 3012LF.

It's not a list of recommended drivers though. When we look more closely at these it will become apparent which ones are suitable and which are not - and why. This should help you choose your own drivers in the future.

We can't test every potential driver out there - so our list of recommendations will necessarily be limited to what we can get our hands on. However, there are a couple of drivers that we would like to test but which we cannot really justify going out and buying. These are the Celestion BL12-200X and the Faital Pro PR300. If anyone has one of these and wouldn't mind lending it to us when we reach the measuring/testing phase, that would be great.
[/quote] argh you've got me looking at fancy speaker specs again. Some of the BMS drivers look nice (though at the high end of the budget)

[LukeFRC]

interesting thread from the PA side. Looks a nice driver - I found a pre-fearful greenboy and bill fitzmaurice talking about that 12n630 over on talkbass, but they don't seem to have thomann in the us!

[LukeFRC]

mind you neither did we back then

[stevie]

[quote name='redstriper' timestamp='1391554584' post='2358641']
Why does a cab have to be less sensitive to be more bassy?
[/quote]

Good question. It’s because there is a direct relationship between cabinet size, low frequency extension and efficiency - as summarised in Hoffman’s Iron Law, which was a forerunner of the Thiele & Small parameters upon which all cabinet design is now based. There is a mathematical formula for Hoffman’s Law – just google if you want to know what it is.

The relationship of cabinet size with low frequency extension is fairly obvious. A 2 x 18” cabinet is going to go lower in the bass than your little transistor radio - and a double bass can produce more bottom end than a violin.

The third variable, efficiency, is not quite as easy to grasp, but Hoffman’s Law says that if you want lower bass extension *without* changing the size of the box, the only way to do it is to sacrifice system efficiency. To compensate (and get back to the same sound pressure level as before) you will need a bigger amp and a drive unit that can move a lot of air. Alternatively, you can also increase bass extension by increasing the size of the cabinet (and using an appropriate driver).

The easiest way to understand how this works is to look as some simulations. This is a simulation of the two 12" Kappalite drivers in the same 50-litre box. The Kappalite 3012LF (blue), a driver known for its good bass extension in this size of cabinet, has a sensitivity of about 94dB at one watt. The other is the KappaliteHO (white) - sensitivity (roughly) 98dB. The differences when you put them both in the same box are self-explanatory.



We can go down even lower in the same cabinet if we drop the system efficiency still further. Here we see the Kappalite 12LF and the BMS 12n630 (red), which Luke mentioned, in the same cabinet. Despite the fact that the BMS is 4dB less sensitive than the Kappalite overall, the BMS is 8dB louder at 30Hz.



Now, if we drop system efficiency *and* increase cabinet size, we get this (yellow):



Which is a 12" Scan-Speak hi-fi driver. The white curve represents the other end of the scale and is the Eminence Kappalite 3012HO again.

Maximum output and power handling are another matter.

Edited February 6, 2014 by stevie

[redstriper]

Thanks Stevie, things are becoming clearer now

With the knowledge of the iron law, it shouldn't be too difficult to design a small lightweight cab that goes very deep, whilst needing a lot of power to drive it.
And yet very few manufacturers provide such a thing to my knowledge, probably due to low demand - most bassists (not me) want high efficiency and extended treble response.
As you say, the charts don't show how loud each driver will go before distorting and I can see this is a complicated science with no single answer for every user.

My current solution is to use a Kappalite 3015LF in a very small lightweight Flite cab, which is a good compromise but I think the cab is too small to get the best out of the driver.
I would be happy with a slightly heavier, larger cab, (this one weighs under 10kg) if it increased bass response and volume, but no such thing exists AFAIK.
Hence my interest in 12" cabs, particularly the Acme Flatwound - I just can't bring myself to spend over £600 on a single small cab.

[stevie]

The 3015 will produce prodigious amounts of low end but it needs a cab between 100 and 120 litres to work properly. If you put it in a smaller one it will still work but you will lose quite a bit of output between 40 and 80Hz - exactly where the fundamentals of the bass guitar are. It's good old Hoffman up to his old tricks again.

Here are curves showing the 3015LF in 60, 90 and 120 litres. Notice how the bass efficiency drops as you reduce the size of the cab with the same driver. There is a point with every driver where you don't get much more bass by increasing the cabinet size and it's around 120 litres with that 15.

[IMG]http://i60.tinypic.com/2l6v6t.jpg[/IMG]

[LawrenceH]

[quote name='redstriper' timestamp='1391703519' post='2360426']
With the knowledge of the iron law, it shouldn't be too difficult to design a small lightweight cab that goes very deep, whilst needing a lot of power to drive it.
And yet very few manufacturers provide such a thing to my knowledge, probably due to low demand - most bassists (not me) want high efficiency and extended treble response.
[/quote]

Part of the problem is finding suitable drivers for a 1- or 2-way design; dedicated bass guitar drivers is already a very niche market. The lower efficiency 'true subwoofer' PA drivers are not designed to run above ~120Hz so you get fairly horrible midrange responses or at the least, a design where directivity narrows very quickly starting around a few hundred Hz thanks in part to the large diameter voicecoils employed. These in turn will cross to a midbass driver to deal with ~100-2/3k, which is what is used for many bass cab designs. Whereas for your application you would want a driver capable of running ~30-2500Hz and with decent off-axis presentation. The Acme driver appears to be based around a Kappalite frame, but presumably they have worked on the soft parts to eliminate a lot of the midrange spike from the LF design, likely at the further expense of mid-range efficiency.

[redstriper]

Thanks again Stevie.

The 3015LF loaded Flite cab sounds great at moderate volumes, but I fear it loses deep bass at higher volumes as you suggest.
I use it with another identical cab (different Eminence Delta non neo driver) for louder gigs.
This works well, but I think I'm sill missing the level of deep bass that a larger cab would provide.

I'm not sure how to work out litres but the outside of my cab measures 46 x 46 x 36cm, which is about as small as it could possibly be to fit the driver.

How much perceived increase in volume and depth of tone would be provided by a larger cab, is hard to know.
I tried the 3015LF in a larger Ashdown MAG cab and didn't notice any big difference in sound levels.
The Flite cabs are wonderfully light and sound good, whilst not giving me the kind of chest thumping depth of an old school 2x18 or 8x10.
This is a compromise that I am willing to accept for the reduced weight and size.

But I can't help wondering if there is a better way - hence my interest in this thread.
I've tried a lot of 12" cabs, but not found anything that sounds as deep or smooth as my Flite 15s.
I look forward to trying the Acme 12" cab soon, but I fear it may have a very costly outcome.

Apologies for derailing this thread with my personal situation

[attachment=154466:Flite cab.jpg]

[redstriper]

[quote name='LawrenceH' timestamp='1391707940' post='2360484']
Part of the problem is finding suitable drivers for a 1- or 2-way design; dedicated bass guitar drivers is already a very niche market. The lower efficiency 'true subwoofer' PA drivers are not designed to run above ~120Hz so you get fairly horrible midrange responses or at the least, a design where directivity narrows very quickly starting around a few hundred Hz thanks in part to the large diameter voicecoils employed. These in turn will cross to a midbass driver to deal with ~100-2/3k, which is what is used for many bass cab designs. Whereas for your application you would want a driver capable of running ~30-2500Hz and with decent off-axis presentation. The Acme driver appears to be based around a Kappalite frame, but presumably they have worked on the soft parts to eliminate a lot of the midrange spike from the LF design, likely at the further expense of mid-range efficiency.
[/quote]

Thanks for this.
I think I am a bit unusual in my tonal requirements.
I turn the low mids and upper mids EQ to zero on my LM11 and I use only the neck pick up on a Jazz bass with the tone rolled right off.
I find the 3015LF still has plenty of top end for my needs and I look forward to comparing it to the Acme.

[Roland Rock]

[quote name='redstriper' timestamp='1391709759' post='2360515']


I'm not sure how to work out litres but the outside of my cab measures 46 x 46 x 36cm
[/quote]

That's just over 76 litres :-)


I find the thread derailment really informative, thanks Stevie/Lawrence

Edited February 6, 2014 by Roland Rock

[redstriper]

Thanks Chris, that doesn't sound too bad, does it take account of the inset handle and the quite thick walls?

I have noticed it sounds deeper on a hollow wooden stage and I've considered placing it on an empty wooden box to extend the bass response - cheaper than a new cab, but would it work?

[stevie]

[quote name='redstriper' timestamp='1391711743' post='2360542']
Thanks Chris, that doesn't sound too bad, does it take account of the inset handle and the quite thick walls?
[/quote]

Exactly. It depends on how thick the walls are, Steve, but the internal volume of the Flite cab is probably around 55 litres. Have a look at the yellow curve in the diagram I posted for the 3015LF - that's how much bass you are losing because of the small cab. The Ashdown MAG cabs are around 85 litres internal volume - still not big enough for your particular needs and they have a problem with inadequate porting which limits maximum output (porting is a subject that the three of us have discussed at length and that Phil will talk about in detail later on in this thread).

If you could modify the Flite cab to take a 12 you would get better results. I don't know of a sound reinforcement 15" speaker that will produce reggae-style bass in a 55-litre cab.

Edited February 6, 2014 by stevie

[Roland Rock]

[quote name='redstriper' timestamp='1391711743' post='2360542']
Thanks Chris, that doesn't sound too bad, does it take account of the inset handle and the quite thick walls?
[/quote]

Erm...no. Well done, you've passed the test ;-)

[stevie]

[redstriper]

[quote name='stevie' timestamp='1391712675' post='2360552']
It depends on how thick the walls are, Steve, but the internal volume of the Flite cab is probably around 55 litres. Have a look at the yellow curve in the diagram I posted for the 3015LF - that's how much bass you are losing because of the small cab. The Ashdown MAG cabs are around 85 litres internal volume - still not big enough for your particular needs and they have a problem with inadequate porting which limits maximum output (porting is a subject that the three of us have discussed at length and that Phil will talk about in detail later on in this thread).

If you could modify the Flite cab to take a 12 you would get better results. I don't know of a sound reinforcement 15" speaker that will produce reggae-style bass in a 55-litre cab.
[/quote]

Very interesting.
The Flite cab walls are thick, being a foam filled composite and I can see from the diagram that I am losing bass response with such a small cab.
The problem with diagrams is that one can't actually hear the differences, so it is difficult to make judgements.
I guess it would be possible to modify the Flite cab [color=#282828][font=helvetica, arial, sans-serif]to take a 12, but it's hard to know exactly how much the sound would improve.[/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]I could get a larger cab for the 3015LF if I could find a suitable lightweight model - Flite do custom orders, so that is a possibility.[/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]Or I could start again with a new 12" cab from Acme or similar.[/font][/color]

[color=#282828][font=helvetica, arial, sans-serif] [/font][/color][color=#282828][font=helvetica, arial, sans-serif] [/font][/color][color=#282828][font=helvetica, arial, sans-serif]Or I could just forget all this and carry on quite happily as I have for the past few years [/font][/color]

[mcnach]

[quote name='redstriper' timestamp='1391709759' post='2360515']

I'm not sure how to work out litres but the outside of my cab measures 46 x 46 x 36cm, which is about as small as it could possibly be to fit the driver.

[/quote]

1 litre = 1 dm3

so 4.6dm x 4.6dm x 3.6dm = 76.176 dm3

or 46cm x 46cm x 36cm = 76176 cm3 = 76.176 dm3

... sorry, it's the only thing I can contribute to this thread

[redstriper]

Nice one mcnach

[Owen]

Yeah yeah yeah...... try the ACME.... yadda yadda yadda. The ONLY time you will ever have an obscure piece of bass kit (possibly the only one in the UK) within a 10 minute drive in this area and it has been months since you said you were going to!

[redstriper]

[quote name='owen' timestamp='1391722254' post='2360699']
Yeah yeah yeah...... try the ACME.... yadda yadda yadda. The ONLY time you will ever have an obscure piece of bass kit (possibly the only one in the UK) within a 10 minute drive in this area and it has been months since you said you were going to!
[/quote]

OK I'll be round in 10 mins........... just hope I don't like it

[Musky]

[quote name='redstriper' timestamp='1391709759' post='2360515']
Thanks again Stevie.

The 3015LF loaded Flite cab sounds great at moderate volumes, but I fear it loses deep bass at higher volumes as you suggest.[/quote]

That's a little odd as bass is perceived as more prominent as volume increases. Compare the difference in perceived volume of the bass at 30hz at 40db and 100db.

I really don't know enough about cab design to know whether the 3015 in a small cab would drop off at the bottom end as the volume increases though.

[quote]
The Flite cabs are wonderfully light and sound good, whilst not giving me the kind of chest thumping depth of an old school 2x18 or 8x10.
[/quote]
Would that be an Ampeg 810? They're not known for earth shaking lows but they are strong in the low mids (as are the matching amps). This might beg the question of whether what you're looking for is really lots of very low bass.

[LukeFRC]

[quote name='owen' timestamp='1391722254' post='2360699']
Yeah yeah yeah...... try the ACME.... yadda yadda yadda. The ONLY time you will ever have an obscure piece of bass kit (possibly the only one in the UK) within a 10 minute drive in this area and it has been months since you said you were going to!
[/quote] Regional High End Cab Hoarders - N Wales branch captain. (as awarded by the Scottish Captain Funkle)

[redstriper]

Good points Musky, truth is I don't know what I'm looking for and may well already have it

It was a Trace 8x10 and I think an Acoustic 2x18 that I remember sounding very deep and punchy, but it was a long time ago and may be rose tinted memories.
The problem with trying cabs at home is that they can sound great at moderate volumes, but quite different in a loud gig situation.

[funkle]

[quote name='LukeFRC' timestamp='1391723481' post='2360715']
Regional High End Cab Hoarders - N Wales branch captain. (as awarded by the Scottish Captain Funkle)
[/quote]

Ha!