Speaker Cabinet design: Interpreting Thiele-Small data, using sofware, and tuning

[SoulFetish]

Over one shoulder I hear "just buy an existing cabinet. These projects always involve more research, money, and time than you anticipate." Over the other shoulder I hear, "So what, you always get yourself into these kinds of projects and always end up better for learning something you didn't know in the process. Besides music is an ultimately an acoustic event, you know much less about acoustics than you do audio electronics. Plus, the voice over your other shoulder underestimates just how cheap you are." Both these imaginary voices make cogent points, but the second one is right. I am cheap. But, I also do think speaker enclosure is important and traditional guitar speaker cabs do little to compensate for the beam type focus of upper middle and high frequencies.
Some people choose the best speakers for their cabinet design. I am approaching the cabinet design using brand new Eminence speakers I got at a great price. I have two 12" Eminence Red Fang 8Ω/50W speakers I've been wanting to use. I have 4Ω,8Ω, & 16Ω outputs on my amp, so I have flexibility in load impedance. Clean sine wave output is no more than 18W, but it clips early and relies on the guitar volume for cleaning up the signal. So doubling the power output still gives me some headroom with one speaker, so I would like to build a 1X12" cabinet, but I'm open to building a 2X12" if there is a good reason to.
I'm looking for some advice to get started. Does anyone have any expertise in this area who can help me interpret the Thiele-Small data and perhaps advise on some helpful software available, etc.?
Here is the relevant data:



here are the specs and Thiele-Small parameters:

Specification
Nominal Basket Diameter 12", 305 mm
Nominal Impedance* 8 Ω

Power Rating*
Program Power N/A
Watts 50 W
Resonance 97 Hz
Usable Frequency Range 80 Hz - 5.2 kHz
Sensitivity* 102.5 dB
Magnet Weight 35 oz.
Gap Height 0.31", 7.9 mm
Voice Coil Diameter 1.75", 44 mm

Thiele & Small Parameters
Resonant Frequency (fs) 97 Hz
DC Resistance (Re) 5.72 Ω
Coil Inductance (Le) 0.39m H
Mechanical Q (Qms) 13.39
Electromagnetic Q (Qes) 0.74
Total Q (Qts) 0.7

Compliance Equivalent Volume (Vas) 39.4 liters / 1.39 cu.ft.
Peak Diaphragm Displacement Volume (Vd) 24.9 cc
Mechanical Compliance of Suspension (Cms) 0.1 mm/N
BL Product (BL) 11.1 T-M
Diaphragm Mass Inc. Airload (MMs) 26 grams
Efficiency Bandwidth Product (EBP) 131
Maximum Linear Excursion (Xmax) 0.48 mm
Surface Area of Cone (Sd) 519.5 cm2
Maximum Mechanical Limit (Xlim) N/A

Mounting Information
Recommended Enclosure Volume
Sealed Acceptable
Vented Acceptable
Driver Volume Displaced 0.079 cu.ft. / 2.24 liters
Overall Diameter 12.03", 305.6 mm
Baffle Hole Diameter 11.07", 281.2 mm
Front Sealing Gasket Yes
Rear Sealing Gasket Yes
Mounting Holes Diameter 0.25", 6.4mm
Mounting Holes B.C.D. 11.59", 294.4mm
Depth 6.2", 157.5 mm
Net Weight 8.8 lbs, 3.99 kg

Materials of Construction
Coil Construction Copper voice coil
Coil Former Nomex former
Magnet Composition Alnico magnet
Core Details Non-vented core


ps. if I were a betting man, I would think my man JM Fahey has old school tuning tricks and done some cabinet design over the years. Yes?

[Mike Sulzer]

I have two 1X12 cabinets, each with a Red Fang. One is an old Line six open back cabinet that came with a not so good Celestion. I tried various speakers, including a Celestsion Blue. The Red Fang sounds better, sounds louder, takes three times the power, and costs less. Line 6 now sells a closed back 1X12 with a front port instead. So apparently they think there is a reason to design carefully. I do not agree since I do not like a lot of bass in a guitar speaker cabinet, but prefer the uneven response you get with an open back.

My other cabinet is a closed back, not really designed, and a bit small for the job in any case. Some casual experimenting with from ports did not make it better IMO. I like the open back.

[J M Fahey]

Thanks for the confidence vote

Thiele Small parameters are very interesting and useful, tell **a lot** about the speaker ... specially to a competitor who might be trying to clone it

Notice Celestion for ages avoided supplying TS parameters for their Guitar speakers ... among other things they allow a competitor guess how close he actually is

That said, when designing a cabinet, where they really shine is in (vastly) improving the lowest octave, or even narrower 1/2 octave or so.

VERY important in a Bass or PA cabinet, hardly so in a Guitar one, and might even backfire providing *less* perceived Bass
Incredible, huh?

What I found:

* TS tuning gives you an extra half octave, *flat response*
Excellent for Bass/PA/Hi Fi .
Hardly noticed in a guitar.

* open back gives you an up to 6 to 9dB peak at speaker resonant frequency ... if you drive it with a terrible damping Tube Guitar amp, even worse if overdriven because then NFB disappears and Pentodes reveal their true self: pure current sources.

Not when Triode connected of course, that´s why that mode lacks bite/punch/balls.

"Single note boomy Bass" which was the curse of the Wurlitzer coin operated machines in the 40´s to 60´s is a Godsend for Guitar players.

It´s not so overwhelming only because small portable open back cabinets attenuate *all* bass, but even so the resonant peak is noticeable (think Twin Reverb and all other open back cabinets).
Notice in speaker above resonance is 97 Hz, smack in the middle of lowest Guitar frequencies (82 Hz and up).

* Large closed back cabinets rise the natural speaker resonance which in classic Celestions is around 75Hz (there are also a few 55Hz ones) to around 90/100 Hz so again in the best area for Guitars.

There is a reason both configurations became **Classic* , and in a way reach similar ends with very different means.

* now suppose you want to "Thiele" your Guitar speakers:

- classic Jensens will *lose* apparent Bass because proper tuning kills the resonant peak, go figure.

- classic Celestions will reach flat to 50 something Hz ... pity is that Guitars have nothing there, at all.

Now I can understand a Modeler amp cabinet being tuned lower: I guess they want to include dropped tuning "Guitar players" , who actually venture into Bass territory.

Personal experience: when TS methods appeared and became fashionable in the late 70´s , I became very excited.
Then I got dissappointed, they seemed to work but I didn´t hear what I was expecting.

FWIW old Bass cabinet designs (Fender for certain, maybe Ampeg or SUNN) used a tried and true formula: built a large cabinet and tuned it around 40 Hz (lowest Bass frequency is about 41/42 Hz), period.

Notice exact same cabinet (Fender Bassman 215, Ampeg Portaflex, etc.) was loaded with CTS/Jensen Oxford/Altec/JBL as regular or Premium version, yet nothing else was changed to adapt it to SO different speakers.
Thiele must be revolving in his grave, but old cabinets seemed to work well.

And they were loud and efficient, driven with meager 100W tube heads whereas today I see myriads of young players with a perfect tuned 2 x 10 cabinet driven by a 350/500W Class D amplifier struggling to be heard over a loud drummer.

Small World: just NOW I am finishing an "old style" 2 x 15" Bassman style cabinet for a customer who self built a Bassman 100 clone

[Mike Sulzer]

There is another thing about TS parameters and alnico magnets. Alnico is a permeable material that changes significantly along the hysteresis curve. Thus the "effective" TS parameters shift with changes in applied power. So a careful attempt to design to the parameters might give unexpected results. Sure, they change when it used in an open back cabinet, but that seems like part of the fun. I think that would apply also if you make a closed back cabinet large, rather than attempt to tune to the parameters.

[bob p]

my experience is that TS parameters tend to work best with drivers that have bigass ceramic magnets. they don't work so well with alnico magnets, though I never knew exactly why. thanks for explaining that, Mike.

TS tuning is a dual edged sword. It definitely has advantages and disadvantages. Some examples:

You have to be aware that voice coil excursion increases dramatically when you hit the port frequency and tends to increase beyond Xmax if you go below it. There have been a lot of TS arrays that have destroyed their drivers when someone tried to use the array outside of it's intended design parameters. Examples of this are those numbskulls who tried to use something like an EV TL-606/EVM-15L combination, which was designed for 4-string bass, with a 5-string. The low B on a 5-string causes a tremendous increase in excursion which tends to kill an otherwise robust woofer. The same thing happens when some of the metal guys try to use the TL-808/EVM-12L system with a de-tuned guitar. Pow! Xmax gets exceeded and drivers take the hit. The lesson from that is that you need to understand the performance limits of the system and obey them.

Then there's the problem that T-S parameters describe small signal performance, not large signal performance. That's a bit of a dirty little secret. The frequency response of T-S arrays is great when they're measured in anechoic chambers with small input signals, but the truth is that with large stage-level signals, the performance gains of the TS array seem to drop off. There are some good papers about this in the EV PA Bible and the EV TL-series design guides, which I think EV still maintains online.

To answer your question about which types of speakers tend to perform well in TS type enclosures, as a general rule of thumb you can get a lot of information by looking at the total Q of the speaker (Qts). In general, speakers that have a low Qts tend to work well in vented enclosures, speakers with a medium Qts tend to do well in sealed boxes, and speakers with a high Qts tend to do best in infinite baffle configurations. There's some helpful info on this at the Eminence site:

Understanding Loudspeaker Data | Eminence Speaker

When it comes to a manufacturer not publishing their TS parameters, I'm not sure that they withhold that data to impede their competitors from copying their designs. TS parameters aren't difficult to measure, and any speaker company would have no problem obtaining a competitor's speaker and taking measurements. More likely, I think, is that Celestion resisted publishing their TS parameters for so long because they didn't want anyone to know how bad their drivers' TS specifications really are.

[bob p]

The Qts that was mentioned int he first post is on the high side. According to Eminence a Qts of 0.7 is high enough that the speaker would be expected to perform best in an open back enclosure. that number goes along with Mike's experience.

[Leo_Gnardo]

my experience is that TS parameters tend to work best with drivers that have bigass ceramic magnets.

Coincidentally, it was ElectroVoice that first promoted Thiele aligned cabinets in the mid 70's. I still have a folder full of blueprints & design specs EV sent me. Back then it was either free for the asking, or almost - maybe 75 cents for postage. At that time EV had left behind their alnico SRO series and were making "big ass ceramic magnet" EVM woofers. I wonder if EV's engineers had noted the strange behavior of alnico magnet speakers and decided to change materials. It wasn't until late 70's that cobalt started to become scarce and expensive, forcing a move to ceramic magnets by all the major speaker manufacturers.

Comedy time: around 1980 I was pricing out components for a PA system, and the salesman told me the price of alnico was soaring "because of all the trouble in the alnico mines." Had a hard time not laughing at him over the phone. I waited until after we rang off. Alnico mines, indeed! Wonder where they are?

[bob p]

In the mid-70s I was ahead of the curve with the T-S thing. We were using EV drivers for pro sound apps back then, and one of my buddies was using the ST-350 tweeter in both his pro-sound apps and in his DIY home speakers, which were 3-way horn arrays with T-S woofers that were covered in what can only be described today as horribly ugly looking green velvet. It was the 70s, after all. He drove his home rig with a big Marantz power amp, and he was always blowing the tweeters. He had a number of spares, and when he ran out of spares we'd take a drive up to Buchanan with a box of ST-350 to get while-you-wait repair of the drivers under warranty. My friend Jim was the reason that EV designed the tweeter production circuit that used the light bulb limiter. EV got tired of repairing his tweeters, so they designed the tweeter protection circuit and gave them to my pal Jim so that he wouldn't come back so often.

It was at one of those visits to EV that I had my first introduction to the TL series cabinets. While Jim's teeters were being fixed we took a tour of the plant, and in the anechoic chamber they were testing a prototype TL-606/EVM-15L. I thought that was interesting, having just replaced the 15" eminence in my Acoustic rig with the 15L. So they gave me a copy of the cabinet plans and I built my own TL-606. I was the first kid on my block to have one of the compact 15" TS rigs by EV. And when Mesa later came out with the Road Ready 2x15 cab, which was just a TL-606D, I had to get one of those too. 40+ years later my original EVM-15L/TL-606 is still going strong. The funny thing about it? I built it out of plywood, and wiped some stain on it, and I was done. 40 years later it still hasn't been painted or covered in tolex, it's just stained plywood without any finish on it.

[Leo_Gnardo]

It was at one of those visits to EV that I had my first introduction to the TL series cabinets. While Jim's teeters were being fixed we took a tour of the plant, and in the anechoic chamber they were testing a prototype TL-606/EVM-15L. I thought that was interesting, having just replaced the 15" eminence in my Acoustic rig with the 15L. So they gave me a copy of the cabinet plans and I built my own TL-606. I was the first kid on my block to have one of the compact 15" TS rigs by EV. And when Mesa later came out with the Road Ready 2x15 cab, which was just a TL-606D, I had to get one of those too. 40+ years later my original EVM-15L/TL-606 is still going strong. The funny thing about it? I built it out of plywood, and wiped some stain on it, and I was done. 40 years later it still hasn't been painted or covered in tolex, it's just stained plywood without any finish on it.

Kool! Somewhere about 25 years back I scored a single 15 Mesa cab, copy of a TL606 nicely covered in black Tolex. I think they called it "The Diesel Series." What I didn't realize, the previous owner, a pro bass player, had beaten up the speaker to the point its spider & surround had little springiness left to them and I could bottom out the voice coil (KLACK!) with only a 40 watt Bassman head. A wise recone man pointed this problem out to me, I had it reconed by him, and all has been well, in fact outstanding, for the last couple decades. It's been my livingroom test cab ever since, and rented out a couple times for studio & stage use. Early on I swapped the steel grill out & made a regular black grill, no more klank klank klank especially with a mic nearby. The steel grill has been put to use properly, sifting rocks from garden soil, it's perfect for that.

Some friends built their own TL606's from plans I copied for them. Plywood with stain or black paint, they all came out well.

Then there's a PA company from around Trenton NJ, "Joe's Sound and Salami Co." I guess Salami because they're always slicing wood? In the 70's & 80's they had a truck full of TL cabs they made. Smart because they could use as many cabs as necessary for a gig, and their rig always sounded good. Plus you could order cabs from them and a few of my friends picked some up.

[Justin Thomas]

And they were loud and efficient, driven with meager 100W tube heads whereas today I see myriads of young players with a perfect tuned 2 x 10 cabinet driven by a 350/500W Class D amplifier struggling to be heard over a loud drummer.

Small World: just NOW I am finishing an "old style" 2 x 15" Bassman style cabinet for a customer who self built a Bassman 100 clone

^^^THIS^^^THIS^^^THIS^^^THIS^^^THIS^^^THIS^^^THIS^^^
"Meager?"
Rant Mode ON: all these "bass players" and "bass amps" and "bass speakers" piss me the $&@# off! "Bass" is an INSTRUMENT, a part of an orchestra, a VOICE in and of itself, <NOT> some "set of frequencies" to be felt and not heard. I'm so sick of all this subsonic mush bullshit where you can't tell what notes are even being played, even though you have "1000W" pushing all these "speakers" with horns and crossovers and extra BS... your "speakers" suck and your amps sound like the love child of an earthquake and a garbage disposal.

Efficient, lower-powered speakers are an absolute secret to great bass TONE. Amplification is the EASY part; making it sound aesthetically pleasing is where nearly every single modern "bass amp" falls short. In my not-so-humble opinion. Yeah, it's "loud" - painfully so. But you wonder why bassists are the butt of so many musical-incompetence jokes? Because they can't HEAR what they're actually playing.

I get more bitching from sound guys about being too loud with my 50W Bassman w. its 2x15" CTSes. No horns, no tweeters, no active electronics, no kilowatts, no "Sub-Bass" knobs... no "tube preamp" gimmicks... go figure. First they laugh, then they whine. And I slice through a rowdy drummer and a PA mix straight to the back of the hall, where my friend (whose father put himself through college by playing bass in the Army Band during WWII, so she knows and LIKES bass) could hear every note. And with no help from the PA.

Boys & Girls: stop falling for the tricks and trappings of the purveyors of "rap bass." Go out, get a 100W OLD tube amp with as few knobs as possible, hook it up to some nice vintage or vintage-style EFFICIENT speakers, and get ready to rip off some heads.

Rant Mode OFF.
Have a nice day, everyone.

Justin

[bob p]

or better yet, just drive your stack of 15 with a pair of SVT. too much is never enough.

[Justin Thomas]

I would. But it's only a 100W cabinet. My first REAL experience with a Bass Amp was a matching 1972 SVT & 8x10". I'm spoiled and will never be able to look back.

Justin

[eschertron]

Rant

I hit 'like' because there's no ROFLMAO button

[Dave H]

In my not-so-humble opinion.

You can say that again

I used to play bass through two 15" speakers, wife said it was the only time I moved the earth for her.

[Justin Thomas]

@ The Dude: can you put up that little rolling on your side crying-laughing smiley-face guy emoji?

@ Dave H: yes, but are those efficient paper&glue speakers, or plastic&rubber "speakers?" Lots of bass players play through 2x15" whatsits...

Justin