What is a "Tuned Speaker Cabinet" ?

Bud Harger · From: Belton, Texas by way of Baton Rouge, Louisiana

I have seen references in several posts to "tuned" cabinets. What does that mean?

Thanks,

bUd

Glenn Uhler · From: Trenton, New Jersey, USA

The simplest explaination, Bud, is a "tuned" speaker cabinet is usually a closed-back cabinet that has a hole (or port) somewhere in the cabinet to either increase or decrease the bass response of the cabinet. The relationship between cabinet size, speaker size, speaker response, and port size and location is, unfortunately, very complex. I'll let other posters go into more detail.
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Fred Justice · From: Mesa, Arizona

Glen & Bud, there used to be a website with the formula there in of building a closed back/tuned spk cabinet. I don't have the link any more, it was really complicated as I recall.
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Mike Schwartzman · From: Maryland, USA

Yes...Fred has it. It's called "Thiele Parameters". You can google that phrase and get the equations.

And I remember a "Cabinet Calculator" that helps determine dimensions and porting depending on the specific driver (speaker) that is to be used in the cab.
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Don Poland · From: Hanover, PA.

http://www.webervst.com/spkrcalc/port2.htm
This is for 2 speakers

http://www.webervst.com/spkrcalc/port1.htm
This is for one speaker

Donny Hinson · From: Glen Burnie, Md. U.S.A.

"Tuning" a cabinet simply means you're altering the frequency response by some feature of its physical design. In hi-fidelity speaker cabinets, this can help to flatten the frequency response curve, and make the sound less "colored". And in musical instrument speaker cabinets, it allows you to enhance or reduce certain frequencies to get a desired sound or response curve, such as enhanced bass response from a smaller cabinet.

It's very important to differentiate between the two different applications, as the desired result (and how it's attained) is often quite different for each.

Les Cargill · From: Oklahoma City, Ok, USA

A way to get a feel for this is to play with it, and there is software called WinISD ( Interactive Speaker Design ) and it works.

It's very valuable for *buying* speakers; if you know roughly what drivers are in a box, you can get the Theile-Small parameters for the driver ( maybe ), measure the box and make a highly educated guess about how good the design is.

I bought G&K electric bass cabinets based on the fact that they appeared to use a variation on an Eminence Delta 15" and the boxes measuring-taped to be good.
They're great cabs.

They won't tell you if the box has a lousy midrange, but they'll help you keep the amount of weight you have to tote down if the cabs are efficient. 'Course, these days with switchmode power amps, it's less of an issue.

Bill Dobkins · From: Rolla Missouri, USA

The Greatful dead used stacks of tuned cabs. They were 12X12 Cubes 18X18 Cubes and 24X24 Cubes. You may want to research them.
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Dave Grafe · From: Hudson River Valley NY

All speakers suffer from uneven frequency response - and associated impedance curves - and all have a natural resonance at which the impedance is lowest and the driver delivers the highest SPL per watt, as well as frequencies that are relatively weak and produce higher impedances and lower outputs.

Tuning a cabinet is the process of adjusting the volume, internal absorption, and porting to even out this response. If this is done correctly the "hot" spots in the response curve will be diminished, the weak ones will be amplified, and the speaker itself presents a more even load to the amplifier across the frequency spectrum. There are a number of methods available, including simple ports, ducted ports, and horn loaded bass reflex ports.

It's not just about adding bass, it's about tuning the cabinet to optimize the speaker across the entire tonal spectrum, and a box tuned for one model of speaker will not necessarily couple well with another. GO get you some good books at the library, meanwhile here's a couple of quick reads...

http://en.wikipedia.org/wiki/Loudspeaker_enclosure

http://www.duncanamps.com/technical/speaker_cab.html

Doug Palmer · From: Greensboro, North Carolina, USA

If you have heard a Bose Wave Radio you have heard a ported cabinet. They get a lot of bass from two small speakers by porting the sound off the back of the speaker through a long chamber inside the radio.
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Dave Grafe · From: Hudson River Valley NY

Don Griffiths · From: Steelville, MO

Dave Grafe knows his stuff...

Original Wall of Sound speaker formula...
QUOTE from another Forum:
Postby Rick Turner Â» Wed Jan 02, 2013 11:22 pm
FYI,

When I worked up a lot of the Wall of Sound speaker cabinet dimensions, I used the cube root of 2 (1.25992105) as the multiplier to determine the ratio of depth to width to height of the cabinets. Take your smallest dimension and multiply it by that, then take that result and multiply it again by that constant. The idea (for better or worse...) was to spread any standing waves out equal distant from one another in the audio spectrum. There are other formulae that some folks use...Golden Mean, etc.

We also used heavy rug padding with horse hair in it to damp internal reflections.

We went with closed boxes because the transient response is better than with bass reflex designs, and the deep low end extension is better way down there, though they start rolling off a bit sooner than the bass reflex. But then when stacked in the tall array, that low end comes off better because it's better directed."

So, I'm not sure excactly what Rick Turner is saying here, but I just got some 15" JBL D130's that I'm planning some cabinets for.I am clear that a perfect cube,square or measurements with even multiples are not good as they will allow sound wave reflections to muddy things up.So I am going to keep things simple and go with something like a 17"x19"x11" partially covered open back.
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Ken Metcalf · From: San Antonio Texas USA

I know from experience that if you take a crappy Fender amp cabinet made from press-board masonite and have a cabinet built from solid wood like pine with finger joints.
It does improve the sound.
Is it worth it... ?? up to you but I like it.

Godfrey Arthur · From: 3rd Rock

A cabinet needs to consider the speaker to be used, its specs, its free air resonance, its volume, its spl's and a host of other specs per a given speaker.

My understanding of a tuned cabinet is one that is made for a specific model of speaker to do a certain task. Whether it is sealed or ported does not by itself mean it is "tuned" as the speaker's specs need to be part of the equation in constructing said cabinet. And different speakers are made for sealed and/or ported, or even free-air, at least that is the extent speaker technology has gone, over the decades.

What Rick Turner found was that a sealed cabinet was easier to predict than a ported one, while speaker specifics and cabinet/speaker/woofer/tweeter construction back then was in its infancy to do with musical instrument amplification.

People today are presented with different hearing.

Gone are the typical hi-fi stereos in the home and most all music is now ear buds or a single speaker on a laptop or a smart phone, lucky if it is even stereo and not just mono, only hearing large box speakers at a concert or a club.

You will notice that today the wall of sound is not a popular system as FOH has come around reducing the number of speakers on stage and their wattage/coverage/volume. Back in the Dead era it was all experiment. Today, a lower stage volume is preferred over the 60's 70's 80's blast-o-rama that went on simply because the PA/FOH system was under-powered and the whole line of gear associated, from the cabs to the speakers to the amps were not as developed as today's offerings.

The Dead were into using expensive McIntosh amps that are audiophile grade upper class items. They used them not only for PA but for instrument amplification and with accompanying Alembic preamps in their hi-tech multi laminated guitars. It was clearly the jet sound for the jet-set.

Them were the days.

But here is a recent opinion of Rick's and I tend to agree with him that arrays today are not as good as they are touted to be. Turbos, if properly aimed are a better overall sound than arrays. But since most artist riders request the arrays, that is what is provided.

Arrays have the computer interface to adjust cross over points, at the mixer using a laptop, but it's not perfect. And today most younger people can't tell the difference as they grew up listening to a different set of speaker systems than some of us did with A7's and rows of Marshall stacks.

Re: Original Wall of Sound speaker formula...
Postby Rick Turner Â» Sat Jan 05, 2013 12:48 am

"Bear in mind (pun intended) that we were doing the best we could with what was commercially available at that moment in time, and it was damned good. I've still never heard a system that comes close to what the WOS could do on a good day. The use of line arrays that were based on actual wave length theory really worked. Many modern line arrays ignore that whole thing...stepping down the height of the columns as frequencies go up...and too many are done with nearly full frequency cabinets with mid and high frequency horns in each cabinet. Now that will give you some comb filtration! And you cannot really project good controlled low end without going to at least a 30 foot tall line array. The way most subs are used is utterly wrong; they are effectively point sources splattering low end all over the venue and making everything sound muddled.

All frequencies can be directed if you pay attention to wave lengths and the size of arrays. The idea that lows are inherently non-directional is rubbish. Dispersion from a source is completely wave length dependent...until you get into some of the sonic holography technology, and that's just not practical yet in concert settings."

Economics dictates everything. Not only is the gear important, the venue is as well as many are not tuned themselves to produce music. Also not all in an audience can be in the sweet spot between the speakers. There will be those disenfranchised in the listener seats and it's based on economics or late ticket buying.

Hence, if the audience is not aware of what a better sounding system is, producers will not spend for it.

To its credit, a modern line array in a better FOH sound-person's hands can sound better than the giant Bose system that it is today. And depending on the expected draw of the artist, the producer will only order enough arrays to just suffice.

The best you can do for your own DIY speaker project is study the specs of your given speaker, check out similar installs for your given purpose. For what size and shape cab is your speaker optimized? Some speakers sound better open back like in a Fender Twin than they do in a box. Be careful of construction quality and materials used. A good speaker can sound soggy in a cheaply made cabinet, more over if the cabinet did not address the specs of the speaker, it will sound constricted. Some speakers are made for larger boxes while some can handle smaller volume boxes. You have to know what you have in your hands,

And then what will the function of that cab be on stage? Just to hear yourself? Or to play out into the audience? If you play through a PA, the sound guy, if you have one, will want all low end to be reserved for the low end instruments, while shelving all the low end off of instruments not needing those frequencies in a mix.

And if you use IEM's then is your amp cab that critical?
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Don Griffiths · From: Steelville, MO

Anyone care to explain what comb filtering is?
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Bill Duncan · From: Lenoir, North Carolina, USA

I like birds eye/quilted maple for guitar cabinets. I try to use a good mix of quilted/birds eye grain. Quilted is for those lush flowing notes and chords. The birds eye is for the quick staccato runs. To help accent the really fast "hot" notes and licks you can add some flame maple grain in the mix.
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Dave Grafe · From: Hudson River Valley NY

Comb filtering is the result of wave interference when two or more sources are producing waves simultaneously at different distances from the listening point. Because sound consists of vibrations moving through space in time, as the distance between the listener and each of the two sources changes the time between the sound being reproduced at each speaker and the same sounds arriving at the listener changes, and unless the listener is the exact same distance from both speakers, the sound from one will arrive earlier than the sound from the other and generate comb filtering.

Since audible sound consists of frequencies in the 20Hz to 20kHz range, and as it moves through air at approximately 1100 feet per second, we find that the wavelengths of these frequencies are between roughly 55 feet at ~20Hz, 1 foot at 1.1kHz, and a bit over 1/2" at 20kHz. Thus if the difference in distance between the listener and the two speakers is 6" then at 1.1kHz the sound from one speaker is arriving exactly out of phase with the other, i.e. the two waves cancel each other at that frequency AT THAT POINT IN SPACE, while sound at 550Hz - where the waves line up perfectly - will be boosted AT THAT SAME POINT as the two waves coincide. If the listening point is moved the same boost-and-cancellation will occur but at different frequencies, again depending on the difference in source distances. The same sort of interference will be generated if two speakers in the same cabinet are not properly aligned or if the crossover is improperly designed.

The resulting pattern of boosts and cancellations is called "comb filtering" as the pattern looks somewhat like a comb, alternating narrow bands of darkness and light, or in this case boosted sound and diminished sound. A good visual aid is to draw a series of concentric circles on two pieces of film and put them together to reveal a secondary pattern of lines and spaces where the two circle sets interact, as this stationary image demonstrates, the two speaker sources being represented by the green and purple dots...

Godfrey Arthur · From: 3rd Rock

Glenn Uhler · From: Trenton, New Jersey, USA

In answering his question, I hope we have throughly confused Bud by now. Laughing

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Herb Steiner · From: Spicewood TX 78669

I was an English major...
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Godfrey Arthur · From: 3rd Rock

Bud Harger · From: Belton, Texas by way of Baton Rouge, Louisiana

I never dreamed this was such a complicated subject. You guys are incredibly generous to give us all the time you all put into it. Thank you very much.

I use two G D Walker cabs...wedges...closed back, ported and loaded with JBL 130's. They sound great like they are...they may even be "tuned". I don't know.

G D probably thought about all of this and came up with an effective design. I think I'd best leave well enough alone.

I really appreciate everybody's contribution.

bUd

Godfrey Arthur · From: 3rd Rock

Dave Grafe · From: Hudson River Valley NY

The easiest way to experience comb filtering for yourself is to set up two identical speakers in a large room and play the same program through both of them - not stereo, but true monophonic content, so that each speaker reproduces exactly the same wave-form at exactly the same time.

If you then stand in the middle of the room, i.e. the same distance from each speaker, and then move slowly a few feet to the left or the right (skewing the distance between them), you can hear the shift in tonality as you move from side to side, the bass becomes boomy, then not, then weak, then boomy again; the mids can be smooth, then honky, then not, then honky again, then not; and the highs will shimmer, then screech, then shatter, then shimmer again, all because of comb filtering.

You can do the experiment with your two identical guitar speaker cabinets by tilting them back with your guitar in the middle. As you move your playing position from side to side, nearer and farther from the exact center of the speaker pattern, you will hear subtle changes in the tone, not much in the practice room, but sometimes enough to impair hearing yourself on stage. The same principle is why open backed cabinets cancel bass that closed back cabinets reproduce.

This is also why a vertical array distributes sound more accurately to an audience than side-by-side setups, and why two speakers don't always sound louder than one at a given position.

This is also, also, why some areas of certain rooms develop low-frequency standing waves, and why simply re-directing the PA stack can eliminate such reflection issues.

Don Griffiths · From: Steelville, MO

Thank you Dave and Arthur. Absolutely fascinating stuff!
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