What ohm for extensions speakers?

Frank Parish · From: Nashville,Tn. USA

I'm using an old Session 400 and have to use an extension speaker cabinet so the guys on the other side of the stage can hear me so what is the lowest ohm I can get by with? It has an 8 ohm speaker now and the amp has the typical 4 ohm speaker.

Jim Sliff · From: Lawndale California, USA

Im not familiar with Peavey's SS output stagews, but normally you want an extension speaker and stock speaker to be the same impedance if wired in parallel, or replace both with (the same) lower-impedance speakers if wired in series. Having one higher and one lower will cause an unbalance volume level if the speakers are similar in efficiency. Hooking an 8-ohm up to the extension jack, assuming it's wired in parallel, will result in a higher load than normal...so you'll lose a bit of power and tone, but gain air-movement.

I'm sure some Peavey guys can chime in on the best way to handle it - I'd simply use a stereo chorus or something as a "splitter" and put a second amp on the other side of the stage.
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional

Dave Mudgett · From: Central Pennsylvania and Gallatin, Tennessee

The Session 400 manual states

Output Power @ 1Khz @120VAC Line
Rated Power: 200 W RMS into Rated load: 4 Ohms
Power vs. Distortion:
120 W RMS @ 1% THD into 8 Ohms
210 W RMS @ 1% THD into 4 Ohms
80 W RMS @ 1% THD into 2 Ohms

My take is that I would prefer not to run it less than 4 Ohms nominal total parallel impedance, although it doesn't appear to be dangerous. In general I don't like to run solid-state amps below the rated impedance - they tend to run hotter and as you can see, you lose a lot of power going down to 2 Ohms. It would be ideal to put an 8 Ohm speaker in both the amp and extension cab for a total of 4 Ohms in parallel, and the power would be split evenly between the two, as Jim says.

Another option is to run what you have - 4 Ohms in the amp and 8 Ohm in the extension. That gives a total parallel impedance of about 2-2/3 Ohms, which closer to the optimum than 2 Ohms. The power will split roughly 2:1 between the amp and extension cab, so the other side of the stage will get about 1/3 of the total power, and you'll get about 2/3 at the amp. Of course, since you're running off the optimum load impedance, the total power may well be down from the nominal 200 Watts, but hopefully more than 80 Watts.

Similarly, if you run the amp at 4 Ohms and the extension at 16 Ohms, the power would split roughly 4:1 - you'd get around 80% of the power behind you and about 20% on the other side of the stage. The overall parallel impedance would be around 3.2 Ohms, which would be even closer to the optimum load impedance.

I think any of these would be better than running both amp and cab at 4 Ohms for a total parallel load of 2 Ohms. The power would be split evenly, but you'll be running far below the optimum load impedance and only get 80 total Watts out of the amp.

Robert Harper · From: Alabama, USA

Power vs. Distortion:
120 W RMS @ 1% THD into 8 Ohms
210 W RMS @ 1% THD into 4 Ohms
80 W RMS @ 1% THD into 2 Ohms
_________________
"Oh what a tangled web we weave when we first begin to deceive" Someone Famous

David Nugent · From: Gum Spring, Va.

Frank..."Tech 21" makes a great sounding little 60 Watt powered speaker cab that you can slave from your Session. I also use mine with a Profex in front for small gigs, very light and portable. It is not a "Furlong Split Cab", but it will certainly hold its' own.

Dave Mudgett · From: Central Pennsylvania and Gallatin, Tennessee

THD is Total Harmonic Distortion.

I agree with David that a powered extension speaker is a good way to go. I generally prefer not to go lower than the rated impedance on a solid-state amp, especially when I see a significant power loss like this.

Ken Fox · From: Nashville GA USA

Frank, if the internal speaker is now an 8 ohm then you can safely run an 8 ohm extension load or even a 16 ohm load.

8 + 8 = 4 ohm load total

8 + 16 =
1/8 + 1/16 = 1/R total
3/16 = 1/R Total
R total = 16/3 = 5.33 ohms

Dave Mudgett · From: Central Pennsylvania and Gallatin, Tennessee

Frank Parish · From: Nashville,Tn. USA

Thanks guys. I've been running this extension speaker cabinet for a couple of weeks and the other side of the stage is hearing me now but it's not overwhelming so that's about what I was looking for. I used to own about five of these Session 400's at one time but have sold off all but my favorite here and the only other amp I have is the FSK. About 8 years ago I got an SE 200 from Johnny Cox and I called Ed Buffington at Evans to see if I could run the extension speaker cabinet. He suggested that I used the 8 ohm speaker as it wouldn't hurt the SE 200 and that's what I did. What I'm discovering is the tone from the amp is not what I'm used to as it's a lot thinner now. Normally I'd run the lows at 8, mids at 3, treble and presence at 5 (great settings too!) for this amp and now I've got the lows all the way to 10, the mids at 2, the treble at 3.5 and the presence at about 3 so I lost a lot of lows by doing this. This old Session 400 has been my mainstay for amps for the last 25 years and the thing just takes a beating and doesn't give up. The only thing I've had done in all this time was get a new basket once when a bass player came in and jacked into my amp when I wasn't there and blew out the basket and about three years ago I order Brad Sarnos mod kit for it and had that installed so it's really honking even to this day.

Forum Index > Electronics		Next oldest topic :: Next newest topic

All times are GMT - 8 Hours	Jump to: