Do these exist?

[Davebassics]

I've had an idea, I'm hoping this i a known idea and already exists!

Do Amp Attenuators exists? for example taking the out put of a bass head into a 4 ohm dummy load/attenuator then into a 4 ohm cab giving a total of 8ohm impedance? Obviously this could be very beneficial for running a 4ohm min head into 2 4ohm cabs?

Any thoughts?

[waynepunkdude]

2 X 4 OHM loads would = 2 OHMS

[Davebassics]

But with an attenuator in line with each speaker bringing the over all impedance of each 4ohm cab to 8ohms, this would = 4 ohms total?

[ThomBassmonkey]

I don't see the point. You'd effectively be lowering the power that goes to your amp.

Take the GK 700RB-II for example, at 8Ohms it runs at 320w, at 4Ohms it's 480w. So if you ran an 8Ohm cab and an 8Ohm attenuator, you'd only get 240w into the one cab.

And as the others said, 2 4Ohm loads would be a 2Ohm load total. 2 8Ohm loads makes a 4Ohm load etc.

[EBS_freak]

Not quite sure why you would want to do that...

but... if I think what I think you are thinking, you want to change impedence of your cabs as seen by the amp? Then I guess something like Ted Weber's Z matcher would get you there? Although Ted's stuff is generally designed for valve amps so I don't know if you want to be doing this sort of thing with tranny amps.

[url="https://taweber.powweb.com/store/zmatch.htm"]https://taweber.powweb.com/store/zmatch.htm[/url]

I think what you want to do is as follows -

[codebox]
Z Match (head setting @ 8 ohm / cab setting at 4 ohm) -- 4 ohm speaker
Output (4 ohms) --<
Z Match (head setting @ 8 ohm / cab setting at 4 ohm) -- 4 ohm speaker
[/codebox]


Probably easier and wiser to buy 8 ohm cabs to be honest.

Edited March 28, 2011 by EBS_freak

[obbm]

OP, please explain in more detail why you feel the need to do this. Also what is the max output power of the amp?



ThomBassmonkey - "You'd effectively be lowering the power that goes to your amp." - power comes from the amp to the speakers.

[obbm]

[quote name='EBS_freak' post='1179596' date='Mar 28 2011, 03:11 PM']Not quite sure why you would want to do that...

but... if I think what I think you are thinking, you want to change impedence of your cabs as seen by the amp? Then I guess something like Ted Weber's Z matcher would get you there? Although Ted's stuff is generally designed for valve amps so I don't know if you want to be doing this sort of thing with tranny amps.

[url="https://taweber.powweb.com/store/zmatch.htm"]https://taweber.powweb.com/store/zmatch.htm[/url]

I think what you want to do is as follows -

[codebox]
Z Match (head setting @ 8 ohm / cab setting at 4 ohm) -- 4 ohm speaker
Output (4 ohms) --<
Z Match (head setting @ 8 ohm / cab setting at 4 ohm) -- 4 ohm speaker
[/codebox]


Probably easier and wiser to buy 8 ohm cabs to be honest.[/quote]


Without knowing a bit more detail (requested) I supect that he wants to be louder, in which case the amp will be running at a high output and would probably melt one of those things as they have quite a low power rating.

[bigjohn]

You can get attenuators. You use em for overdriving your valves whilst keeping the volume down... [url="http://cgi.ebay.co.uk/ATTENUATOR-TRAYNOR-ORANGE-VOX-AMPEG-MESA-GUITAR-AMP-/200559935676?pt=LH_DefaultDomain_0&hash=item2eb24dc0bc#ht_2598wt_905"]http://cgi.ebay.co.uk/ATTENUATOR-TRAYNOR-O...c#ht_2598wt_905[/url]

I don't really get why you'd want to do it for any other reason though.

You'd just be bleeding power.


In your example a 4Ohm minimum amp could run 2x4Ohm cabs if they were in series (=8Ohm). So what would be the point?

[ThomBassmonkey]

[quote name='obbm' post='1179597' date='Mar 28 2011, 03:12 PM']ThomBassmonkey - "You'd effectively be lowering the power that goes to your amp." - power comes from the amp to the speakers.[/quote]

Sorry, brain fart haha.

[EBS_freak]

[quote name='obbm' post='1179601' date='Mar 28 2011, 03:16 PM']Without knowing a bit more detail (requested) I supect that he wants to be louder, in which case the amp will be running at a high output and would probably melt one of those things as they have quite a low power rating.[/quote]

Agreed - Ted may build custom spec stuff as he has done for me. As I said earlier though, all this stuff is generally for valve amps and I don't think tranny amps like things like dummy loads/attenuators and the like...

[EBS_freak]

The last thing the OP wants is an attenuator.

If the OP wants to drive more speakers (but at the cost of output), he'll still be louder if he attached another 4 Ohm cab with a special diy series cable (to give 8 Ohm - I'm sure OBBM would make one up for you). I've detailed it in this post - [url="http://basschat.co.uk/index.php?showtopic=45810"]http://basschat.co.uk/index.php?showtopic=45810[/url]

[Davebassics]

My amp is 500 Watts at 4ohms and 300 at 8. I own 1 4ohm 2x10 400 watt cab at 4ohms.

My initial idea was by changing the 4ohm cab into 8 ohm I could run 1 cab at 300watts and 2 at 500. This would also mean there is no chance of overpowering either of my cabs.

If I was to run in series I would I still be putting 500 watts through a 400w max cab?

Does this make sense or am I talking rubbish?

[Salt on your Bass?]

I didnt think this would make much of a difference, or does it?

I'm probably well out of my depth here, but if its based on running say a 500W amp at 4ohms into a single cab, you (roughly) half the power by running at 8ohms (300W). You'd lose around 3db than you'd have running a single cab at 4ohms (assuming your cab is up to it of course).

If then you add a second cab, each would recieve half the power of the 8 ohm power output (300w), so 150W per cab. .....this is where I'm skethchy now... ....running two cabs moves more air, and reinforces some of the lows, and adds a speaker more at ear level, but I thought it only amounted to around 3db anyway...???

So the net gain isn't worth running 2 cabs in this senario, as you're better off running a single speaker at full power (again, assuming the cab is up to it....)

Is this right, or am I full of .....(Insert your preferred word here).

[quote name='EBS_freak' post='1179611' date='Mar 28 2011, 03:23 PM']The last thing the OP wants is an attenuator.

If the OP wants to drive more speakers (but at the cost of output), he'll still be louder if he attached another 4 Ohm cab with a special diy series cable (to give 8 Ohm - I'm sure OBBM would make one up for you). I've detailed it in this post - [url="http://basschat.co.uk/index.php?showtopic=45810"]http://basschat.co.uk/index.php?showtopic=45810[/url][/quote]

[Davebassics]

[quote name='Salt on your Bass?' post='1179642' date='Mar 28 2011, 03:44 PM']I didnt think this would make much of a difference, or does it?

I'm probably well out of my depth here, but if its based on running say a 500W amp at 4ohms into a single cab, you (roughly) half the power by running at 8ohms (300W). You'd lose around 3db than you'd have running a single cab at 4ohms (assuming your cab is up to it of course).

If then you add a second cab, each would recieve half the power of the 8 ohm power output (300w), so 150W per cab. .....this is where I'm skethchy now... ....running two cabs moves more air, and reinforces some of the lows, and adds a speaker more at ear level, but I thought it only amounted to around 3db anyway...???

So the net gain isn't worth running 2 cabs in this senario, as you're better off running a single speaker at full power (again, assuming the cab is up to it....)

Is this right, or am I full of .....(Insert your preferred word here). [/quote]

What about adding a second cab in parallel. would that give a total z of 4 ohms with 250 watts into each?

Don't worry, I think I have wondered out of my depth too!

[bigjohn]

[quote name='Salt on your Bass?' post='1179642' date='Mar 28 2011, 02:44 PM']I didnt think this would make much of a difference, or does it?

I'm probably well out of my depth here, but if its based on running say a 500W amp at 4ohms into a single cab, you (roughly) half the power by running at 8ohms (300W). You'd lose around 3db than you'd have running a single cab at 4ohms (assuming your cab is up to it of course).

If then you add a second cab, each would recieve half the power of the 8 ohm power output (300w), so 150W per cab. .....this is where I'm skethchy now... ....running two cabs moves more air, and reinforces some of the lows, and adds a speaker more at ear level, but I thought it only amounted to around 3db anyway...???

So the net gain isn't worth running 2 cabs in this senario, as you're better off running a single speaker at full power (again, assuming the cab is up to it....)

Is this right, or am I full of .....(Insert your preferred word here). [/quote]


The maths is right.

But you're assuming that the one cab scenario is actually drawing 500W, and that the 500W is being used as efficiently as 2x150W.

And that's before we even get to the surface area, sound re-enforcement stuff.

[obbm]

500-watt max amp into a 400-watt cab? I think you are worrying needlessly. You'll hear any problems before any damage is done.

[Salt on your Bass?]

[quote name='Davebassics' post='1179646' date='Mar 28 2011, 03:46 PM']What about adding a second cab in parallel. would that give a total z of 4 ohms with 250 watts into each?

Don't worry, I think I have wondered out of my depth too![/quote]

If you add a second cab in parallel, you're amp needs to be 2 ohm stable. If the amp only runs down to 4ohms, do not do it. Two 4 ohm cabs in parallel gives you a 2 ohm load and this will damage your amp. If you run two four ohm cabs in series, you will have an 8 ohm load and the amp will be fine.

Personally, I think I'd be inclined to change the 4 ohm cab for an 8 ohm cab, then get another 8 ohm cab, if you need/want to run 2 cabs. IMO .......

Edited March 28, 2011 by Salt on your Bass?

[markstuk]

Is not the master volume knob an "Amp Attenuator" in this context?

[obbm]

[quote name='markstuk' post='1179667' date='Mar 28 2011, 04:06 PM']Is not the master volume knob an "Amp Attenuator" in this context? [/quote]

Precisely.

[ficelles]

[quote name='waynepunkdude' post='1179566' date='Mar 28 2011, 02:46 PM']2 X 4 OHM loads would = 2 OHMS[/quote]

Or 8 Ohms if wired in series...

ficelles

[ficelles]

[quote name='obbm' post='1179658' date='Mar 28 2011, 03:58 PM']500-watt max amp into a 400-watt cab? I think you are worrying needlessly. You'll hear any problems before any damage is done.[/quote]

I used to run a 575W amp into a 600W cab. See the "free Eminence Gamma 10" post for the result!

Interestingly I now run a 160W head into the same (refurbished) cab and it doesn't sound significantly quieter... P=VI may be the maths but cabinet and speaker efficiency put a limit on effective output power...

ficelles

[Davebassics]

Another point I've came across is that putting a attentuator in series will means (give or take) 50% of the power will make it to the cab and 50% will be dissipated as heat from the dummy load.

Basically the moral of the story is get 8 ohm cabs!

[bigjohn]

[quote name='Davebassics' post='1179717' date='Mar 28 2011, 04:35 PM']Another point I've came across is that putting a attentuator in series will means (give or take) 50% of the power will make it to the cab and 50% will be dissipated as heat from the dummy load.

[b]Basically the moral of the story is get 8 ohm cabs![/b][/quote]

I reckon you'd be quite hard pushed in a blind test to to tell the difference between 2x8 Ohm cabs / 4 Ohm @ 500W and 2x4 Ohm / 8 Ohm @ 300W.

[watchman]

[quote name='obbm' post='1179658' date='Mar 28 2011, 03:58 PM']500-watt max amp into a 400-watt cab? I think you are worrying needlessly. You'll hear any problems before any damage is done.[/quote]

Exactly what I was thinking...

[xgsjx]

As far as I understand from the OP, he wants to be able to run 2 cabs from his amp to shift a bit more air. Unfortunately he's bought a 4Ω cab & the amp's min load is 4Ω.
The idea of an attenuator isn't ridiculous, but there's better options as other's have said. 1, get a series cable or 2, sell/swap the cab for an 8Ω jobbie.