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chris661 14th November 2011 06:00 PM

Small and loud guitar amp?
Hi guys,

Smurfing around on a couple of music 'sites, I've come across the ZT Lunchbox guitar amplifier. They claim 120dB @1m peak output from a single 6" driver.

ZT Amplifiers - Support - Technical Data

Now, I realise there has to be some limiting of lower frequencies to get anywhere near this output from such a small driver - I've done a proof-of-concept that works to limit the bass independantly of the mid/highs.

I'm thinking of using an amplifier of say 200w into a driver like this. I know that such a small driver does have limited power handling and efficiency, but would prefer to use a 6" over an 8" to keep with the idea of a tiny guitar amp that'll keep up with drums and another guitarist.
That particular speaker (running at 200w) will hit 117dB. I've never done anything I'd consider high powered before, so I'd like to know if I'm likely to cook such a driver.

The design criteria is similar to that of ZT's - portable, and able to go really loud.

What do you guys think? Am I insane trying something like this, or is there a chance it'll work?


firechief 14th November 2011 06:12 PM

Power Rating**
Watts 100W
Music Program 200W

Worthy expairment but -- you still have to move air to make a loud noise. Just because a speaker can handle a lot of power without blowing apart, dosen't mean that it can convert that power to acoustic energy. Im trying to not be too much of a doubting thomas but don't get your hopes up that you are going to achieve that SPL.

bunkie 14th November 2011 08:03 PM

And, you have to dissipate heat which is much harder to do with smaller voice coils, pole pieces, etc. If your plan is to keep up with loud drums, the heat soak from the power dissipation is going to have some negative effects. Aside from the obvious one of cooking the driver, as the voice coil heats up, it's impedance will rise leading to lowered output. What about using two of the 6" drivers? If ultimate size is an issue, you get better packaging efficiency this way.

Nanook 14th November 2011 08:13 PM

here's some numbers...
if 200W amp and one driver, then using:

dB(Max):=dB(sens) + 10*log (P2/P1)
where dB Max is based on the power available
dB(sens) is the sensitivity at 1W@1m.

Substituting dB(sens) of 93.6, and P1:=1, P2:=200, then the result is 116.6 dB. If you use a stereo amplifier (class D again), and 2 of these drivers, then you can get (close to) the 120 dB(Max) target you are seeking. If you place the drivers as close together as possible (without touching each other), a 3dB gain can be had, so then you could get +3dB (doubling the electrical power) and +3dB (by spacing the 2 drivers as close together as possible). Otherwise I'd look for a driver with something closer to 96-100 dB @ 1W@1M sensitivity. Using the same equation, with a dB(sens) of 97dB would get you to 120 dB(Max) @1W@1m if thermally capable...

Thermal capability is probably one of the limiting factors. You could look at some of the small "Orange" amplifiers, etc. Behringer sells a few efficient combination amps that could fill your needs at a very low cost.

have a look here for a very easy to use calculator

chris661 14th November 2011 09:47 PM

Hi guys,

Thanks for the quick replies.

Sounds like multiple 6"s will be the way to do this. I'm heading toward something like this

Given 100w per speaker at pretty much 94dB efficiency, that'd be 120dB@1m. Think that'd be enough.

I'm going to buy just one of the drivers, knock up a quick test box and give it a good thrashing - 117dB might be loud enough after all.

Pictures to come when things actually happen.


firechief 14th November 2011 09:49 PM

Nice drawing. Is that sketchup?

SemperFi 15th November 2011 07:36 AM

If you play country twang or screachin blues I bet that little combo works great, but try a down-tuned chugga-chugga riff and I suspect it doesnt do even for bedroom practice levels.
Not that it's a bad idea, just that it probably only suits some styles of playing.

Nanook 15th November 2011 04:40 PM

is it loud enough?
What's your application (specifically)? Small gig amp? Practice amp?

For this example I am assuming 100 watts "music power"(basically I guess from the driver's lowest available output to it's natural highest), and that SPL (in dB) reduces by 1/rČ in a "field". I am not concentrating on peak power as it is for very short durations.

So 117dB@100W@1m becomes 114db@100W@2m and only 110.5 dB@100W@3m. So if playing balls out, and your listeners are more than 4m away, you'll need a lot more power and/or more small drivers and/or larger driver(s).

chris661 16th November 2011 08:34 AM

Nanook, my application is, primarily, band practice. That is, unmiked drum kit, other guitarist, bassist, vocalist.
The practise mainly occurs at college, so being able to transport the amplifier room to room easily is priority. Despite my efforts (beefed up PSU & output stage), my 1x10" 40w combo doesn't have enough oomph, and gets annoying to move around when there's other stuff to be carried, too (I tend to be the techie that sets stuff up, so the fewer trips I have to make, the better.).
The 1x10" combo will do 111dB before clipping (calculated - 95dB speaker, 40w input). It won't keep up with a drum kit, even if I run everything wide open and drive it into square waves.

I have no problem with DIing out to a PA system at gigs, so long as I can hear myself onstage: the small size of these amps mean I can put it where I like and still hear it - that could easily be at head height instead of blasting away at my feet.


Nigel Goodwin 16th November 2011 09:56 AM

I'm very dubious about those ZT amps?.

Volume is simply about moving air - you can either move a large cone a small distance, or a small cone a large distance, either will move the same amount of air, and give the same volume.

The problems arise though that cones can only move so far - so small cones are limited in the amount of air they can shift.

I can only imagine that the ZT filters out all low frequencies, which limit the cone movement required, allowing higher powers to be used.

I would suggest getting a 1x12, 60W or 100W - if you can stand the weight (and the cost), get a valve one, which will be far louder because of it's distortion.

I've used a 1x12 Fender 60W transistor keyboard amp for guitar and bass (at the same time - it has two inputs) at a gig, and it coped fine with rock drums played hard.

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