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Permalink Reply by Ron "Oily" Sprague on January 13, 2012 at 10:46pm

GH,

 

Don't skimp on speaker size; generally, the more air it can push, the better your overall sound will be. Based just on that criterion, use the 8" 4-ohm. Check the frequency response on both 8" speakers at your disposal; the subwoofer will most likely have an attenuated response geared to the low end. It could work if you want to use this as a bass practice amp, but I'd be inclined to just slap the 8" standard in a box with the amp guts, if you want a guitar amp. A 10" or 12" would sound even better; I have a Crate 15w V16 Palomino with a 12" speaker that sounds so much better than, respectively and progressively in size, the 2", 2.5", 3.5", 4", 4" stereo and 8" speakers in my small amp collection. The only exception is the 6" speaker in the ZT lunchbox: the circuitry pushes up to 200W, which means this little sucker can hang with a Marshall half stack in a club setting (I know this to be true - it's my main stage amp when I play with pickup bands).

 

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Permalink Reply by GARAGE HERMIT on January 13, 2012 at 10:56pm

thanks oily,

if moving air is the main thing, would'nt the 2 - 7" + the 2 - 6" speaker's be the best combo, ?

i'd use a 10" or bigger speaker, but i dont have one, and i'm not going to buy one, too expensive, just for home use,

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Permalink Reply by Printer2 on January 14, 2012 at 4:52am

Since you do not give the model of the amp I could not look up what the amp wants to see as a load. Having two 7" speakers does not do you much good if it wants to see 4 ohms but you are giving it two ohms. I would say the the two ohm speaker is out from the start. Being a transistor output amp I would say it is safe to use a 8 ohm speaker.

I have a number of speakers and they vary greatly in terms of how they sound and how loud they are. You could try them all and decide which sounds better (keeping in mind the load rating on the amp), I would not even bother with the sub. Also what is the power ratings on the speakers? Do they all handle the power the amp puts out.

Just listing the size and impedance of a speaker does not give much in the way of how suitable the speaker will be.

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Permalink Reply by GARAGE HERMIT on January 14, 2012 at 7:05am

printer2, thanks for your input, but, just done a bit of reading on the subject and i can use the 2- 7" + the 2- 6" together if i wire them in a parallel series circuit, total load would then be 4 ohm, which is the max loading of my amp, all i have to do now is find some old floorboard's to make a little 4- speaker cab,,

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Permalink Reply by GARAGE HERMIT on January 14, 2012 at 7:51am

meant to say total speaker load would be 6 ohm's, which is ok for my amp which has a minimum loading of 4 ohm's,

no idea what the power rating's of the speaker's are, if they blow it's no great loss, they cost me nothing,

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Permalink Reply by Ron "Oily" Sprague on January 14, 2012 at 5:38pm

GH,

 

The problem with smaller speakers is that 1) they don't move as much air as the next size up, and 2) they can have different frequency responses, usually sacrificing the low end. ONe thought I had, after realizing that you had 2 of each (sorry, Iddin;t notice the numbers, was focused onthe size and impedances) was that you could take an 8" and a 6" and do a "2 x 7," or even, as you suggest, a real 2x7 using the two you have. Sorry, my brain was fogged when I wrote the first response. It should work. Why not do this test?: hook up both 7s, see how it sounds (record it, even)
, then hook up the 8. You could even do this with all the speakers you have available, and do it to your taste. Understanding the electronics is necessary, but your ears will be the  determining factor as to how you think it sounds. Also, you may want to build a test box to mount the speakers in; they'll sound different than unenclosed.
GARAGE HERMIT said:

thanks oily,

if moving air is the main thing, would'nt the 2 - 7" + the 2 - 6" speaker's be the best combo, ?

i'd use a 10" or bigger speaker, but i dont have one, and i'm not going to buy one, too expensive, just for home use,

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Permalink Reply by GARAGE HERMIT on January 14, 2012 at 10:49pm

oily,   thanks,

yes, the speaker's will sound different in an cabinet, closed back, open back etc, really only want to build the final cab i will use, have some dimention's, spec's, cubic volume, etc that will suit the 4- speaker's,

cab i'm going to build is loosely based on the early "crate" amp's cab, beat up packing crate look,

 think i'll wire the 4- speaker's, parallel + parallel first, then swap them to parallel + series, and see if there's any difference, although the 1 ohm difference in the total loading wont make much of a difference to the sound/volume, or will it, ??

 

 

 

 

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Permalink Reply by David L. on January 15, 2012 at 6:16am

I work this out to be 3.333 ohms not 7ohms - not sure if this would be good for the speakers/amp?

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Permalink Reply by GARAGE HERMIT on January 15, 2012 at 8:39am

david,,

  3.333 ohm's,   how did you work this out, ??

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Permalink Reply by GARAGE HERMIT on January 15, 2012 at 9:10am

david,

 

your right,

i thought 2 - 4 ohm speakers in parallel was just 1/2 the total, but it's not,

it's, 4 x 4/4+4,

       16/8

      = 2 ohm's

should have read up a bit more on the subject, but i'm getting there,,

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Permalink Reply by David L. on January 15, 2012 at 9:36am

Hi GH,

I worked it out this way

 

I usually am lazy and use an online calculator such as this one http://www.speakerimpedance.co.uk/?act=two_series_two_parallel&... :O)

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Permalink Reply by Ron "Oily" Sprague on January 15, 2012 at 3:35am

GH,

No, I doubt 15 watts (which may be more like 12 watts RMS) will overload speakers wired in parallel the way you're going to. Most amps can drive speaker loads that have impedances 1 level above and below the amps nominal rating, so for example you could use a 2 ohm or 8 ohm total load with no actual damage to the speakers or the amp. You shouldn't run the amp flat out on a 2 ohm load, and you won't drive an 8 ohm load at its optimum performance running at 15 watts flat out. So wiring for a 6 or 7 total ohm load is doable. Be interesting to see how it sounds. You may surprise yourself, and hey, if you blow one speaker, you have others. If it were me, I'd still do the test using various speaker combos, including the 8" 4 ohm.

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