Different Sized speakers?

[kiwicano]

HI All. I'm new to the forum and about to build my first amp with the baby Will kit in my old epi valve junior. This amp will be for me mostly but will also be used for one of the guitarists in a band i tour with as there guitar tech. My question is this. I have seen in my travels there used to be amps that had a combination of different sized speakers. I am keen to build a cab wityh a fully closed back 12 inch speaker on the bottom and tilted back open back 10' speaker on the top. this way we can mike both on stage and get a blend of the 12' push and the break up of the more smaller 10' I have a jensen speaker to use in the top and an old Eminance 12' for the bottom. The band are all on In Ear monitors so the guitars don;t need to be up loud so the small wattage set up should be perfect for that search for great tone. has anyone else had any experience with taking 2 sized speakers and mixing them? the cab will look like a standard tilt top cab sliced top to bottom.

[StarGeezers]

Kiwi, it should work fine as long as the ohms are right !!!

[kiwicano]

awesome, I was hoping with the same homage it would be fine sadly I can't get the Baby Will Pcb now due to the sad circumstances, so I have to try find an alternative amp kit thats not too $$$

[Daviedawg]

This is spooky. I was sitting last night planning just the same speaker layout with a built from scratch EL84 SE amp much like the EVJ. I plan a tag board layout based on info from the SEWatt forum which is linked above left.
Loads of stuff there.

Dd

[FlyingV74]

I combined a 12" speaker and an 8" speaker. I connected them in parallel and the sound was horrible! The sound was extremely muddy. So then I decided to try them connected in series. Connected in this manner they sounded much, much better.

I wondered why the sound was muddy when the speakers were connected in parallel. I just happen to own a WT3 impedance tester sold by Parts Express. So I set out to measure the impedances of everything and try to make sense of this. First I measured the impedance of the 12" speaker. Big peak at 55Hz or so (resonant frequency) and your typical woofer impedance curve. Then I measured the impedance of the 8" speaker. Medium sized peak at about 100Hz (resonant frequency) and pretty typical looking woofer impedance curve. Then I measured both speakers connected in parallel. Both resonance frequency peaks were almost eliminated! This took me back to basic Ohm's Law stuff. Needless to say I learned that it isn't always best to connect speakers in parallel, at least as far as tone is concerned.

Final thoughts:
1. When connecting speakers in parallel, speakers with very similar resonant frequencies (i.e. within a few Hz of each other) produce more predictable results.

2. I found that with series connected speakers that the tonal qualities of each speakers kinda morphed with the other speaker to produce a composite sound. Parallel connected speakers sound more like the individual speakers as far as volume level and tonal quality is concerned. My 8" and 12" actually sounded pretty good together when connected in series and the 8" was only slightly lower in volume than the 12".

3. I have questioned using a crossover of some sort between the two drivers. Either a LPF on the 12" and/or a HPF on the smaller speaker. I never got around to experimenting with this to see if a crossover filter could help to improve the sound of the speakers when connected in parallel. A simple capacitor on the smaller speaker may be the ticket to getting rid of the muddy sound that I experienced.

[Daviedawg]

I was encouraged by a trial I did yesterday with two spare 8 ohm speakers a 10 and a 12 which are in old combo cabs robbed of anything of value. Neither is a very good speaker but for the purposes of research I set them up in series and got a nice sounding result. I don't have a 4 ohm output wired up so did not try them in parallel. As it was the volume was good for both. The tone with my Les Paul was better than the 12 alone, providing more high mids but keeping the rich bass, so sounding fuller. The highs were not too sharp.
My tests were purely aural. But enough to encourage me to start considering this as the next project after the SE amp.

Dd

[kiwicano]

Well I have an Ironsounds Traveller on route down here to new zealand where I am. So hopefully I'll get onto that in a couple of weeks when all my shows finish for a break. and I'm just bidding on a Jensen 10inch so hopefully I'll win that auction and can make a start on the cab while amps on route..! thanks for all the info,. this site is a wealth of information and very helpful people!