Attenuator question

77custom · Post by **77custom** » Sat Oct 28, 2006 9:33 am

How does the load of an attenuator affect the amp? If your amp is set at 16 Ohms and your using a 16 Ohm attenuator, does it really matter if your going into a 4,8 or 16 Ohm cabinet?? Doesn't the attenuator's input load react with the amps output only or is the speaker connection part of that reaction? Does this make sense? What is the draw back of running my amp at 8 Ohms into an 8 Ohm attenuator then into a 16 Ohm cabinet??

Anyone have any idea??

77

908ssp · Post by **908ssp** » Mon Oct 30, 2006 11:01 am

It does make a difference but less then people believe. Just addressing the mismatch issue first. An attenuator has a voltage divider in it sending part of the signal to the speaker and part to the attenuator. Let's address this situation an 8 ohm attenuator and a 16 cabinet and the amp is set on 8 ohms. So if you have the attenuator turned almost off volume down 3 db then you have your amp feeding a 16 ohm load 50% of the power and the attenuator 50% of the power. But if you have the attenuator turned down say to minus 12 db then only 12% of the power is going to the cab which means the mismatch is extremely low. Generally this situation is considered safe.

This is really more important to sound quality. A speaker load fluctuates from 12 ohm to 400 ohm for a 16 ohm speaker that is what it means when people say reactive load. Most attenuators don't do this and that is why they sound different then a speaker their load if fixed at 4, 8, 16, or 32 ohms. A reactive load sounds better.

Now some people claim to hear a difference when running their amps at different output impedances. Some will tell you they like their amps set at 16 ohm output but not 8 ohm output. Well I can't say I can hear the difference and if I can the alternatives are worse. In other words I would rather use an 8 ohm Richter at 8 ohms then any other attenuator at any other output because I can hear the difference the Richter makes.

blfrd · Post by **blfrd** » Sun Nov 19, 2006 2:20 am

So is the Hotplate a reactive load? my guess is no, it's not.

908ssp · Post by **908ssp** » Sun Nov 19, 2006 10:46 am

They don't claim it is. They do say inductive load rather then resistive load honestly I am not sure what that is. They also claim to have volume frequency compensation. My experience is that it does not sound as good as the Richter. It also seems to be an often repeated refrain that the HP is good down about 8 db after that the tone doesn't cut it anymore. The Richter works very well at levels much lower then that.

BashCoder · Post by **BashCoder** » Sun Nov 19, 2006 11:10 am

908ssp wrote:They don't claim it is. They do say inductive load rather then resistive load honestly I am not sure what that is.

Reactive means that they use inductors instead of (or along with) resistors. Inductors exhibit inductive reactance in AC circuits (such as audio), where the impedance of the device is frequency-dependant (like a speaker is).

So an inductive load is a reactive load.

There's an old page out there on the web by Harry Kolbe which shows why reactive loads are better than resistive loads. On that page he claims the Hot Plate is resistive only. That may have been true at one time, but THD clearly say theirs is inductive. So I think that the old Kolbe site (and the included graphs) is no longer accurate.

Harry's load boxes and attenuators are excellent, BTW, and very hard to find. He uses a multi-tapped transformer to attenuate, which of course is an inductor.

Ted Weber uses an actual speaker motor in his systems, I believe, which is what makes his reactive as well.