110 Detuned Guitar Cabinet
a "detuned" 110 cabinet with tilt-back legs and built-in recording interface
last update: July 14, 2013

Copyright 2014-2020 by H. Gragger. All Rights Reserved. All information provided herein is destined for educational and D.I.Y. purposes only. Commercial re-sale, distribution or usage of artwork without explicit written permission of the author is strictly prohibited. The original units  with their associated  trade-names are subject to the copyright of the individual copyright owner. The Author is by no means affiliated with any of those companies. References to trade names are made for educational purposes only. By reading the information provided here you agree to the Terms of Use.
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Index


Gallery
The Detuned Idea
Recording With The Built-In Microphone
Sound Samples

Gallery
cabinet side/rear view cabinet side/front view cabinet tilted cabinet logo detail cabinet logo detail cabinet logo detailcabinet with guitar
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The Detuned Idea

This is my rendering of a 1x10" detuned cabinet (a.k.a. 110). The design goes back to a suggestion of Kevin OīConnor from londonpower.com in Canada. It is 40x60x40cm in size. Total weight ends up 22 kg.

The enclosure is made from 3/4 inch baltic birch with additional crossbracing. I used battens, heavy glue and screws. The cover is heavy quality tolex western style with fabric on the inside. It is glued with Ponal Express (white glue) and Pattex Transparent on the corners. Beware of Pattex as it contains solvents. This produced bulges that fortunately disappeared again, but they made me sweat.

The corner protectors are Fender style. Grille is Ampeg style. Hardware has been obtained from Tube Town, Germany. Power is connected via Speak-On combo connector (speak-on type plus standard 1/4" jacks), a second XLR connector serves as microphone output (see later).

The term "detuned" has been created by Londonpower to distinguish the design from conventional "tuned" cabinets, i.e. mostly closed cabinets with carefully tuned ports to enhance the bottom range. Basically it is an oversized cabinet that would otherwise take 2x10" speakers with one speaker omitted. The effect is similar to the more common "open back" designs most combo guitar amps have, except that the latter is heavily dependent on proper room placement and the detuned cabinet is not.

The detuned approach has several advantages such as its "big" acoustical appearance and extended bottom range. It also has disadvantages, some of which can be counteracted and some not.

One disadvantage is weight, one size. There is nothing that can be done about that, but this enclosure is not for the timid.  The speaker is lightweight, it has an Neodym magnet. Another disadvantage (although common to all big cabinets) is increased beaming (higher frequencies are concentrated to a small beam in front). This can be partially compensated by using a disperser (acoustical lens). I used vertical slots that also protect the speaker from mechanical damage. As all detuned cabinets, it has a port that is equal in size to the speaker cutout, which functions as a secondary source of sound. In this case the slots are made horizontal to help disperse sound in this plane too.

Through extensive simulation with my DAWīs parametric eq I preselected some 10" drivers of interest and finally decided upon a Faital Pro 10PR300, a real powerhouse P.A. midrange speaker with 600 W(RMS) rating. In times of speaker emulation devices a "neutral" speaker is advised. Simulation here or there, inside the enclosure it sounds different - but good.

Compared to my 12" design it makes the impression of less high-end, although it would be expected to extend further up.  Well, it has more prominent midrange and no peak on the high end; a well behaved neutral midrange.

A powerful speaker like that may appear oversized. Is it? You can easily blow out a 100W Speaker with a meager 20W amp running on its limits. Why? A distorting amplifier delivers near square-wave signals into a speaker, meaning the speaker gets flooded with enormous HF content. You wonīt hear that, but the speaker has to burn this energy. Also, an undersized speaker is always running close to its limits, far from being linear. Being capable of sheer power does not mean you have to run this enclosure at those levels. As one of the dealers mentioned, people are set back by the attribute "professional driver" and think they cannot use them for their projects.

The mounting is 8 bolts on a seemingly standard radius, so mounting a different driver should not present any problem.

Sound is incredibly big and very beefy for all styles. Bass range does not extended as far down as the 12" version, so for a bass guitar the enclosure is unsuitable.

Since the enclosure is typically sitting on the floor, the player might not hear what the auditory hear due to the inevitable beaming. This is not new and in the past many makers of guitar amp combos such as Fender have installed tilt-back legs.
I obtained short Fender legs, but unfortunately combos tend to be higher than deep, whereas the side profile of my enclosure is almost square. You can tilt combos back and they rest on the tilt legs, and they of course have a tendency to fall forward on their feet with the tilt legs leveling straight downwards. You cannot tilt the 110 back because it has a whole different center of gravity.

However I installed the tiltback legs horizontally.  They are held in their rest position with a strong Neodym magnet salvaged out of a hard disk which rests inside the enclosure and protrudes to the outside with a piece of iron.

If you tilt the enclosure backwards, the tiltback legs can be flipped forward. This position is rock-solid, compared to the conventional  combo arrangement, the enclosure can under no circumstances topple over.

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Recording With The Built-In Microphone

A company on the web offers an enclosure with built-in recording microphone. They uses a fairly big size dynamic unit.
Those tend to be expensive plus, being directional, suffer from low end inflation due to the proximity effect.
Being a fan of inexpensive, yet high quality omnidirectional capsule microphones, I installed one into the box.
It sits right in front of the speaker invisibly behind the front grille.

It is a Panasonic WM-60A electret microphone which I modded according to Linkwitz for greater dynamic range (described here, look at the very end of the document). For a microphone, mounted so close to a driver, there is no margin for wasting dynamic headroom. With this mod signals up to several volts can be produced by the microphone unclipped.

The microphone is fed with a phantom powered circuit that produces a standard impedance interface, which connects to an 3 prong XLR plug on the back plate. Any commercial microphone cable and recording hardware will accept this signal, however, even at moderate sound pressure levels a 10dB attenuation pad is in order to avoid clipping of the amplifier stage. The preamplifier inside the enclosure has been designed by ESP and works a treat. Since we are recording an instrument, the output caps donīt need as big as depicted. I uses 33 uF which produces a rolloff far below a guitarīs frequency of interest.

People have been totally astounded of how accurate the recordings are on fullrange playback compared to the original. No speaker simulation circuits needed - have the real thing!

Due to the high SPLīs expected the otherwise considered inferior noise performance of the WM-60A is not an issue, however care has to be taken to have a silent recording environment like with all microphone recordings. Nevertheless, due to near-field recording (note: omnidirectional mics are not subject to proximity effects) picked up background noise is sufficiently low despite the omnidirectional character.
For such a low price add-on the recording feature works phenomenal..,

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Sound Samples

Samples demonstrating a stompbox effect using the 110 as recording interface can be listened to at the sound section of the Overdrive Special document. Note that the built-in microphone is mounted on-axis with the speaker cone and thus "hears" what the guitar player might not hear, at least not if s/he is standing off-axis. To make the recordings realistic and not flattering, no further processing (such as treble roll-off) has been applied.


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Update History
  • July 14, 2013: small update
  • July 11, 2013: first release
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