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Most guitar cabs designed poorly?
Most guitar cabs designed poorly?
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Old 21st October 2019, 09:15 PM   #61
Mario Pankov is offline Mario Pankov  Europe
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Most guitar cabs designed poorly?
Quote:
Originally Posted by Gnobuddy View Post

I was unable to find any Thiele-Small parameters for the G12-T75, otherwise I would have at least run a simulated frequency response (with and without an additional 10 ohms - 50 ohms in series).
Here, enjoy. When designing it I assumed 25 ohms which produce a bump at 150Hz but the intentionally designed wide baffle somewhat coincides this with the baffle step loss so the actual bump is less than 3db, in theory (haven`t measured it and will not). This is an old trick to make a speaker with higher Fsc sound more dynamic. The rise in group delay is very narrow in frequency and will affect one or two notes at best, however below the Fsc this tuning yields lower group delay compared to a conventional Qtc 0.6-0.7 design. Adding to this the rigid box and some absorption, compared to the usual 16mm particle board cab, I don`t see how it could be flabby. Turned out really nice and today went to have a bath in porcelain white paint
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Old 21st October 2019, 10:32 PM   #62
Gnobuddy is offline Gnobuddy  Canada
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Quote:
Originally Posted by Mario Pankov View Post
Here, enjoy.
Thanks for the data, and also for sharing some of the thoughts behind your design!


-Gnobuddy
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Old 22nd October 2019, 06:50 AM   #63
PRR is offline PRR  United States
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> backwave absoroption to reduce the smearing caused by the backwave wave leaving through the thin paper cone with a delay
- work out a cabinet where standing waves are reduced
- work out edge diffraction by offseting the guitar driver (roundeovers will be impractically large here) and reduce sharp edges
- use diffusors or irregular inner shape to further kill standing waves


Click the image to open in full size.

After your thoughtful thinking, I'm startled to see the driver rear-mounted. On my first "hi-fi" (hah!) cabinet I quickly heard the extra resonance from rear-mounting, switched to front-mount for all but low woofers (<200Hz) and horns where the cavity was part of the design.

Yes the cone is more exposed but there are stand-out grilles.
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Old 26th October 2019, 04:00 AM   #64
JMFahey is offline JMFahey  Argentina
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Quote:
Originally Posted by Mario Pankov View Post
Here, enjoy. .........
Thanks Mario, very useful
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Old 26th October 2019, 07:54 AM   #65
Mario Pankov is offline Mario Pankov  Europe
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Most guitar cabs designed poorly?
Quote:
Originally Posted by PRR View Post

After your thoughtful thinking, I'm startled to see the driver rear-mounted. On my first "hi-fi" (hah!) cabinet I quickly heard the extra resonance from rear-mounting, switched to front-mount for all but low woofers (<200Hz) and horns where the cavity was part of the design.

Yes the cone is more exposed but there are stand-out grilles.
Well, I don`t like backmounted drivers but here I had to work with the following constraints:

- protect driver without to have a grille extending on the front
- the Celestion has the gasket on the front and its thick which makes it a bit tricky to panel mount and keep some good look
- I didn`t have enough grill cloth for a full cover (rectangular one for the front baffle) and didn`t want to wait for new to be shipped

I totally agree, this is far from optimal but here had to do a sacrifice. The hole is rounded over with a 1" bit, however.
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Old 28th October 2019, 02:06 AM   #66
Variac is offline Variac  Costa Rica
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Most guitar cabs designed poorly?
Or: it’s got free extra resonance!
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Old 1st November 2019, 08:12 PM   #67
Mario Pankov is offline Mario Pankov  Europe
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Most guitar cabs designed poorly?
Where is this free resonance for a large 300mm hole that is 21mm deep and has a large roundover?
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Old 1st November 2019, 09:04 PM   #68
Gnobuddy is offline Gnobuddy  Canada
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Quote:
Originally Posted by Mario Pankov View Post
Where is this free resonance for a large 300mm hole that is 21mm deep and has a large roundover?
It's the "21 mm deep" that matters - you have a (short) organ pipe that's 21 mm long.

The big diameter will add some effective length ("end correction"). Usually the end correction is 0.6 times the radius, so in your case, it would be 90 mm, making the effective pipe length 111 mm. (But this end correction may not apply to such a short, fat pipe; I think computational fluid dynamics modelling might be required to get an exact answer for this one!)

The fact that your short fat pipe has a big roundover probably makes it act like a crude horn, which may make the organ-pipe resonance a little louder than without a roundover, because of better coupling to the air because of the horn.

Roundovers do reduce diffraction effects, so they're nice to have on the outer edges of a speaker cab. I don't think they help solve the problem of back-mounted drivers and thick baffles, though.

If we proceed on the assumption that the end correction is 90 mm, so that pipe length is 111mm, and we assume 20 deg C (68 F) room temperature, the first organ pipe resonance for a 111 mm long pipe is at about 1.55 kHz, with harmonics at 3.1 kHz, 4.65 kHz, 6.2 kHz. At least the first two of those are solidly in the electric guitar's frequency spectrum.

I really don't know if we can trust this simple approximation (end correction of 0.6 radius) when the pipe is so very short, and so very fat. But resonance frequencies predicted by the application of this approximate theory are low enough to colour e-guitar sound, which is interesting, and I think it may be worth some experimental investigation.

Someone has got to have done this already - maybe there are measured frequency responses out there, showing the effect of back-mounting in a 21 mm thick baffle (that's between 7/8" and 13/16" for our American friends.)

Edit: this shows up to 5 dB change in frequency response at 3 kHz, comparing front vs rear mounting: Should I front- or rear-mount a speaker onto the cabinet baffle?


-Gnobuddy

Last edited by Gnobuddy; 1st November 2019 at 09:08 PM. Reason: Add link
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Old 2nd November 2019, 03:13 AM   #69
PRR is offline PRR  United States
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Quote:
Originally Posted by Mario Pankov View Post
Where is this free resonance for a large 300mm hole that is 21mm deep and has a large roundover?
It is quite tiny.

At a different range of scale: in-ear monitor, when I compress the foam ear-tip to fit my small ear, the foam "swells" past the end of the sound tube, and forms a few-mm horn/resonator, with wicked gain above 10kHz.

A hole 300mm expanding to 340mm over 21mm will be a very small effect. In context of a Guitar speaker, negligible compared to all the paper resonances most g-speakers are riddled with.
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Old 2nd November 2019, 04:38 AM   #70
Gnobuddy is offline Gnobuddy  Canada
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Quote:
Originally Posted by PRR View Post
In context of a Guitar speaker, negligible compared to all the paper resonances most g-speakers are riddled with.
Celestion's data attached (from the link in my previous post.)

There's almost a 5 dB difference at 3 kHz in this particular example. Whether that is significant on top of all the other guitar-speaker peaks and valleys is up for debate.


-Gnobuddy
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