Has anyone used a combination of speaker+ dummy load ?

[bakerlite]

I dont see this done much if at all so there is probably a pretty good reason why it doesnt work -

Probably to do the way the speaker interacts with the OT,

But why not say:

 a 30watt 16 ohm speaker with 3 x 16R 30watt wire-wound + heatsink resistors in Parallel? (4R load)
or
 a 30 watt 4 ohm speaker with 3 x 4R 30watt wire wound +  heatsink resistors in series? (16R load)
or whatever combination you like once the load matches the OT

Is there a way to ensure the "watts" would be equally delivered to both the speaker and the 3 resistors?

I appreciate I may be missing a few fundamentals here but just curious as to why it is not done.

[sluckey]

Is there a way to ensure the "watts" would be equally delivered to both the speaker and the 3 resistors?

POwer will be distributed equally just due to the fact that all resistances are equal.

I appreciate I may be missing a few fundamentals here but just curious as to why it is not done.

It's very wasteful, unless you need an amp/hand warmer. 

[bakerlite]

Thanks Sluckey

So theoretically - my DR103 only sounds good when my ears start to bleed so I have to use it at lower volumes, I could  rig one of these up and run the amp at high volume settings getting the tone I like without the sore ears?

And have warm hands :)

[jeff]

Is there a way to ensure the "watts" would be equally delivered to both the speaker and the 3 resistors?

POwer will be distributed equally just due to the fact that all resistances are equal.

I was wondering that the other day and this question came to mind.

A resistor is a straight resistance where the speaker is an impedance, meaning that it's resistance varies depending on frequency. If the speaker and resistors were all 8 ohm resistance then the power would be equally shared but what happens when the resistance of the speaker rises at certian frequencies? Now instead of 4 8ohm resistors in series parallel you have 3 8 ohme resistors and one higher resistacne to that frequency. Doesn't that shift the power distrubution between what each resistor dissapates and the speaker?

In other words if you have a 100W amp and use three 8ohm 25W resistors and one 8ohm 25W speaker, then when the speakers restance is 8 ohms each gets 25W but what happens in the range where the resistance of the speaker rises to 25+ ohms?

[sluckey]

but what happens in the range where the resistance of the speaker rises to 25+ ohms?

The power dissipated by the speaker drops. Now you need to plot a freq response curve. I was just trying to keep it simple. I thought bakerlite had a speaker with a flat freq response, or was only gonna play one note songs.   

[jjasilli]

I've been thinking of doing this for testing purposes.  It is very useful to hear what an amp under load is doing; a dummy load, also very useful, defeats this.  E.g., things to listen for:  horrible hums, noise or squeal.  Clicks when meter probes are touched to tube pins confirm the signal path, etc.

[jeff]

The power dissipated by the speaker drops. Now you need to plot a freq response curve. I was just trying to keep it simple. I thought bakerlite had a speaker with a flat freq response, or was only gonna play one note songs.   

My main concern for asking was is there a risk of damage? 

I'm not sure how to calculate it but if you have 100W going into an 8 ohm resistor and a 8 ohm speaker in parallel and the speaker rises to 24 ohms at 82Hz when you're playing an E, how much is the speaker dissipating and how much is the resistor dissipating? Will a 50W resistor be in trouble?

I imagine this is why the sound suffers too becasue where the impedance rises on the speaker the power is unevenly distributed. So even though you have a 8 ohm speaker and an 8 ohm resistor you're not splitting the power in half for all frequencies.

[bakerlite]

maybe I should really let you guys talk this one out as you have more knowledge than I but are you saying that because the resistors don't react like the speaker as the ohms go up and down then the method I have suggested can only really be tweaked to a given frequency at a given volume? not much use!
Could inductors be used instead/along with resistors to give you some of that rise and fall that you don't get form a  resistor?

In a nut shell the problem is that resistors have a fixed resistance? (just making sure I havent lost you totally)

[sluckey]

http://www.tedweber.com/atten.htm

[bakerlite]

A 16 Ohm:




and Also an 8ohm


I think bluestone amps are out of business so hope its cool with doug's posting rules having the seller on a picture

[kagliostro]

To have a quick idea of what happen having parallel or series (or parallel + series) speakers connected

look to this useful calculator by Duncan's Amps

http://www.duncanamps.com/technical/impedance.html

http://www.duncanamps.com/software.html

K

[HotBluePlates]

A resistor is a straight resistance where the speaker is an impedance, meaning that it's resistance varies depending on frequency.

Be sure to be very careful with terms.

The speaker has impedance, so its reactance varies with frequency. As reactance increases, the impedance will also increase, as impedance is the vector sum of resistance and reactance.

So what I'm saying with this is the resistance itself doesn't change, even though the total impedance will.

... but what happens when the resistance of the speaker rises at certian frequencies? ...

The total impedance will rise somewhat, which will be less apparent if all loads are in parallel. Try it out: calculate the total load of four 16Ω resistors in parallel, and four 4Ω resistors in series; recalculate for each situation assuming one of the resistors is now 4x as big.

My main concern for asking was is there a risk of damage?

If you want to go down this road, you'll need to research "real power" vs. "reactive power" (and the related term "power factor").

Bottom line: heat dissipated only results from the "real power" dissipated, which is related to current and resistance. While total impedance will increase, it is due to increased reactance of the speaker at some frequencies. Because voltage and current are out of phase in a reactance, heat dissipated is not what you'd think it would be (and is quite a bit lower than in the case of a resistor).

Regardless, this effect is happening all the time to every speaker you play through, but you never notice issues result. So you need not worry about damage to the load resistors or speaker, but know only that the reflected primary impedance will be higher when the speaker's impedance increases. As noted earlier, you might minimize this effect somewhat by placing the speaker/load resistors in parallel.

And, as Sluckey pointed out, if the speaker's impedance increases, it will dissipate a little less power than when its impedance matches load resistor resistance. But you don't really care, because you were gonna select resistors rated for at least double the anticipated power for safety and cool operation, right?