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qingcong 8th January 2011 04:09 PM

Thiele guitar cab vs. ported guitar cab
I've been doing some research in preparation for designing my own 1x12 guitar cabinet. Part of my design goal is to do bass enhancement, and I see that there are two types of designs for guitar cab bass enhancement out in the market - thiele and ported. I understand the concept of ported cabs and cavity resonance, but what about the thiele cab? To me, it just looks like a tuned vented cab with 3 ports. I don't exactly get what makes it so special vs. a traditional ported cab.

A look inside a thiele guitar cab -
The Boogie Board • View topic - Thiele 1x12 cab build!! (Mini stack of doom content)

Genz Benz ported cab -

Inside a Bogner cube ported 1x12 -
another closeup of bogner 112 cube rear pictures from music photos on webshots

Keriwena 8th January 2011 05:58 PM

The so called "Thiele cab" is a ported cab. It was actually designed with an alignment by Don Keele, so the "Thiele" name is just marketing bull. The original plans are here:

The TL806 works with EVM12s because they were designed to be used with a ported cab. All other guitar speakers I know of are designed to be used in 'free air'. The difference is mostly in the compliance of the suspension - guitar speakers are very stiff, stiff enough to withstand the output of a highly distorted amp even if you snap the string (hifi guys - think of dropping a needle on an record with your volume control all the way up), and trying to control them with lightly compressed air isn't going to work.

This is quoted from the Celestion site:

Thiele-small parameters

Thiele Small parameters are useful for controlling the low frequency response of sealed or ported cabinet systems by changing the cabinet internal volume, and port dimensions. However they are of limited use when designing a guitar speaker cabinet.
  • Electric guitar speakers do not reproduce 'low' frequencies (the low E string of a lead guitar has a fundamental of 82Hz) and so the frequencies at which Thiele Small parameters have significance are mostly below the operating range.
  • Also, the parameters are measured at very small signal levels. Guitar speakers become non linear at very low levels compared to other types of speaker, greatly reducing the significance of Thiele Small parameters in actual speaker use. Using the Thiele Small parameters of a typical guitar speaker, you will find that halving or doubling the cabinet size makes minimal difference to the response.
  • They have no relevance to open back cabinets.
  • Care should be exercised designing ported (or reflex) cabinets for guitar speakers as the increased cone excursion below the tuning frequency can cause speaker damage.
The cabinet size, shape and construction are of far higher significance than the internal volume. Cabinet design using Thiele Small parameters ignores these most fundamental aspects. Important factors include the material you make the cabinet from, the panel sizes and shapes, how they are joined, how the cabinet is finished, the mounting of the speaker, etc. These, not Thiele Small parameters are the critical factors in the design and ultimately the sound of a guitar speaker cabinet.
If you want to design a ported cab for an EVM or Delta Pro it will work, but otherwise you're better off with a closed cabinet. Remember, musicality is in the overtones; strong fundamentals are boring. A guitar cab should be -3dB to -9dB down below 200Hz.

PS: before worrying about the cab's low end, make sure your pickups aren't doubling the low notes like humbuckers do.

qingcong 9th January 2011 04:32 PM


Originally Posted by Keriwena (
PS: before worrying about the cab's low end, make sure your pickups aren't doubling the low notes like humbuckers do.

What do you mean by this?

I want extended bass capabilities because I eventually plan on playing some 8 string guitar which will be tuned down to an E at 41Hz. I understand that it is not necessary to recreate the fundamental, but at the same time I don't want too much roll off. How much roll off is too much? I'm not sure.

Speakers I'm looking at such as the Eminence Governor have the resonant freq at 101, but list that a vented enclosure is acceptable. They give the thiele-small parameters right on their site, so it appears they want people to use them.

Eminence makes a 15" guitar speaker with the Fs at 55Hz and I think Scumback makes some 55Hz speakers as well. I guess with these I won't need to worry about porting since the speaker takes care of the low freqs already, right?

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