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Multi-Way Conventional loudspeakers with crossovers

Guitar cabinet as a OB?
Guitar cabinet as a OB?
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Old 26th February 2017, 08:36 PM   #1
erkki1 is offline erkki1  Germany
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Default Guitar cabinet as a OB?

Due to non-existent woodwork facilities/tools in my present apartment, I just came with idea to use a standard quitar cabinet for OB. For example Thomann sells those 1x12" cabinets even without loudspeakers.
There are three versions, closed box, fully open from backside, and partly open.
Any opinions, how that kind of open/semi-open cabinet would work as OB, in bass/low mid application?
I don't need /cant use high SPL levels, this is a German apartment.... so I believe even one 12" per channel might be enough. Room size some 25m2
Amp: hopefully 50W/4ohm would be enough.

Of course the driver shall then be some decent one suited for general PA, not a quitar driver.

For mids/tweet, there is still some mindwork to do. Maybe TC9FD or something else.

Last edited by jazbo8; 27th February 2017 at 12:22 PM. Reason: Typo
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Old 27th February 2017, 07:40 AM   #2
mikey_audiogeek is offline mikey_audiogeek  New Zealand
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I like your idea. It will be more like an "H" baffle for the bass.
You will still need equalisation. And you will need to be careful of reflections behind the mid/tweeter.

Maybe this will provide inspiration? The curious case of my new "Boffle" speakers | Audiokarma Home Audio Stereo Discussion Forums

Cheers,
Mike
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Old 27th February 2017, 09:34 AM   #3
Sonce is offline Sonce  Macedonia
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For OB, use fully open back cabinets.
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Old 27th February 2017, 10:07 AM   #4
keithj01 is offline keithj01  United Kingdom
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The open-back version would give you an H-section baffle, as already mentioned. Crossing over at, say, 120Hz, you should be able to avoid problems with resonant modes. Hopefully, the cabs will be of heavy construction - they'll need to be.

I fully understand your need for a ready-made solution - I'm just the same, and did indeed consider cabinets from Thomann! However, my solution was to use 2 12" drivers per channel, and to mount them without any baffle, using Thomann's cheap but sturdy acoustic guitar stands:

https://www.thomann.de/gb/millenium_gs2001a.htm

The drivers sit perfectly on the stands, and the magnetic field from the large magnets hold them firmly in place - even when supplying thunderous bass (using an amplifier capable of 40W into 4 ohms). Obviously, the usual heavy EQ is necessary. I suspect you could manage with single drivers if you don't want to go too loud, though obviously the solution involving a cabinet will go significantly louder.

Choice of driver is the other consideration. I used cheap QTX drivers, with Fs=30Hz, Xmax=6mm, Qts=0.5, and about 88dB/W. However, they may not be currently available, and maybe other drivers have a weaker magnetic field?

Wish you luck, anyway, and I'm sure you'll end up with more than enough loudness.
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Old 27th February 2017, 10:40 AM   #5
keithj01 is offline keithj01  United Kingdom
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Correction: more like a U-frame actually.

Thinking a bit more, the cabinet solution may need steeper crossover slopes in order to avoid possible resonant modes - in that respect, the baffle-less solution would represent the ultimate in terms of ease of use. Could use 15" driver too.

I've looked around for the QTX drivers, but they don't seem to be around any more (type 902.184 for the 15", 902.222 for the 12").
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Old 27th February 2017, 11:02 AM   #6
erkki1 is offline erkki1  Germany
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Thanks for your comments. I already thought that it should work as U-frame, now I have confirmation.
Have to make some calculations about the quarter wave resonance, to have idea what is the suitable XO frequency. EQ is needed for sure, in any case.
As it is a U-frame, I think even 1x12 would be enough.
I was most concerned how sturdy the cabinet will be, but yes, they have been made to withstand some heavy handling. So, maybe ok.
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Old 27th February 2017, 12:51 PM   #7
Rokytheman is offline Rokytheman  Denmark
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Guitar cabinets are made thin and made to resonate - IMO that would not make it a good option. - Maybe MAX 7-8 mm?
I would say a good sturdy baffle should be at least double that or 3 times that => if you choose wood like baltic bitch sheets.

Sheets of would cut into the dimensions that you like, is not that expensive.

How would you make the holes for the drivers, if you have no tools available?

For a 25 sqm room, I would choose minimum 15" drivers. It requires BIG drivers to get any decent bass out of dipole. I can get the same or more amount of bass from a 6" driver in vented cabinet vs 15" in dipole. (yes that is true!) There is of course a difference in quality. Also how a dipole loads the room IE how one feels the bass, is IMO a lot diffrent than closed or vented cabinets. I would say - Some like it, some dont.
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Old 27th February 2017, 07:26 PM   #8
erkki1 is offline erkki1  Germany
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Hard to find info about cabinet thickness. Some discussions mention values 1/2"..3/4" (12..18mm) but manufacturers don't specify anything.
And the resonating cabinet, I understand very well that quitarbox maker might use that to give their own distinct sound.
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Old 27th February 2017, 08:16 PM   #9
AuroraB is offline AuroraB  Norway
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Panel resonance is mostly an urban myth in guitar speakers, - although it has some minor relevance. Same situation about choice of wood for electric guitar bodies, - sustain effect, yes, but tone is almost all due to pickup choice.

Nobody in theur right mind would build a guitar speaker cab out of 8mm ply..... 3/4" or 18mm solid wood or ply is the usual choice.
BTW - I looked at Thomann, but could not find any empty cabs??

EDIT: If you find a local supplier of ply or gluelams, they might cut it measure for you for a reasonable price. The all you need to do is screw and glue....
That should be possible in an apartment....
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Last edited by AuroraB; 27th February 2017 at 08:19 PM.
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Old 27th February 2017, 08:33 PM   #10
keithj01 is offline keithj01  United Kingdom
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Quote:
Originally Posted by erkki1 View Post
Hard to find info about cabinet thickness. Some discussions mention values 1/2"..3/4" (12..18mm) but manufacturers don't specify anything.
And the resonating cabinet, I understand very well that quitarbox maker might use that to give their own distinct sound.
Do try the baffle-less solution. Virtually no cost - you may be surprised.

Though it has to be said that four 12" speakers in fairly close proximity will be much louder than a couple of isolated naked 12" speakers.

I recommend you experiment. If you get the right drivers, very low bass is easily achievable, and loudness levels compatible with apartment living easily achievable.

With OB speakers, it's just a matter of diaphragm size, really. A given motor will drive a small or large cone. Who cares if it's 6" or 15"? The former will need a box, and have attendant problems. The box will need all sorts of tricks to get decent bass in a room environment. The OB will need a longish room with a decent amount of rear space. Given that, will sound better.
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