Tower Phase question

[ThSpeakerDude88]

Hey there,

Ok I have a phase question.


Ive got a fisher ca857 amp. 100 watts RMS per channel into 8 ohms with < 0.09% THD

it has A and B speaker outputs.


I have 4 floor speakers I have stacked on top of one another in a pair I want to run off of this amp.

On the bottoms, Sansui Sp-1500's
On top of those, Marantz sp-1200's

I have no idea how many ohms my amp is stable at. Does anyone know if it will do either 4 ohms or 16? because if so, I can paralell/series each tower and run on 4/16 ohms.

Currently I have them running off of a and b, and you can turn on a and b at the same time.

I was wondering if with this set up, what should the phase be? I had it with the bottom ones normal and top normal and the bass seemed reduced when running in a/b mode.

I reversed the wires on the bottom ones ( + to - and - to +) and the bass was improved.


Whats up with this? What is the best phase reccomended?

And finally, since my amp is running the same wattage, only into more speakers, does this affect the bass? how should it be set up properly to counter act this? and finally, how many ohms is my amp running at when set to a/b mode instead of one or the other? Please help me! thanks!

TSD88~

[ThSpeakerDude88]

heres a pic of my setup. You can see the amp lurking under the monitor.

[ThSpeakerDude88]

amp.

[bakh]

Most amps are stable at 4-8 ohms. If Bass increases by swapping only the bottoms out of phase(180 degree) then you may actually have a impedance problem, ie.. one or both sets of speakers are out of phase. Does the amp increase base when switched from one channel to another with only one set running at a time? Also, with the speakers stacked as they are the upper set will not produce the noticable bass that the lower ones will. This is due in part to accoustics. If both sets were placed about 4" away from a wall or in corners there would be a more noticable increase in the lower end. I would suggest placing all speakers on the floor , evenly spaced, and change between your a and b channels with only one set playing at a time. If the bass is equall in this manner I would then turn all speakers on. If the bass decreases then set your balance to one side. If there is a noticable increase in bass on only the left or right channel only and it weakens when you go to center your problem lies in the way the speakers are wired.If this is the case the fix is simple but these steps must be taken first.

[ThSpeakerDude88]

Well actually the way my room is designed it doesnt much affect bass when their on top. I gotta weird room


anyways the marantz's ( top ones) put out more bass than the bottom ones when switched to only them. Keep in mind I have one bad woofer in one of the bottom ones ( the one closest to me) so the bass isnt going to be phenominal out of the bottom ones. I was able to recoil it and get it aligned and "working and making bass" so it could be in there untill I get replacments. I'm going to go for some sp 2000 woofers on ebay.

I did find out I had one wire reversed at my amp ( stupid me!)

I'm wondering if maybe one set is wired differently than the other due to age? Like say the sansui's. Maybe their wired backwards from modern ones? just a silly though, correct me if I'm wrong.


So do you think its safe to just paralell the whole system to make two 4 ohm channels on my amp and run 120 watts ( or how ever much more it makes into 4 ohms, it does 120 into 8) into each tower without hurting my amp?

another thought-- is that basically what I'm doing when Iam useing a/b? I know on my onkyo amp it says combined a/b systems should be 8-16 ohms. But when in normal ( a or b ) it is only 4-8 ohms. This is only a 30 watt per channel reciever though, thats why Im useing my fisher. Just dont wanna blow an output darlington or something due to under-loading the fisher.

[bakh]

It would seem easiest to wire the two sets together by wiring the lower set to the upper set and then run the upper set directly to your A channel on the amp(in series). If both sets are 8 ohms they should remain so in this configuration.
I have a set of Cerwin Vegas vs15 and had a similiar problem once when replacing a blown crossover in one. It appears that Cerwin Vega wires their mids and tweets out of phase (reversing polarity) and the woofers are wired in phase. I didn't realize this when I replaced the crossover and wired all speakers in phase. The out come was a noticabaly deeper bass when the speakers were balanced left to right and weak bass in center. Once I rewired to the original config. I could once again "feel" the bass.
I would suggest checking the wire on each component from the crossover to be sure yours aren't similiar to these. If so, you could actually be running one, two, or all speakers out of polarity. This will substantially decrease bass. If you do decide to wire parallel then you would drop your impeadance to 4 ohms. Home amps aren't like auto amps, ie.... you will not double power output. You will increase efficiency which causes the speakers to play somewhat louder with the same amount of power.
If your Fisher Amp is class A/B I wouldn't worry about underpowering it. These are very durable amps. They normally aren't as efficient as H class amps but are much more tolerant. They don't normally produce the heat that kills the H class amps.

[bakh]

By the way, it looks as though(in your picture) that your cat may have eaten your mouse.lol