Impedance etc

[dincz]

[quote name='spectoremg' timestamp='1427099182' post='2725629']
Have I seen some cabs with a series option on the backplate?
[/quote]

Hartke HX112 is selectable 4/8 ohms.

[spectoremg]

Cheers.

[matt-bass-sparkes]

Hi all.

Apologies for starting another question here, but I was rather hoping for some advice from people who have experienced this rather than problem solving as such:



I have a 300 watt head at 4 ohm minimum.

I now have the choice of either a 4 ohm 1x12 cab

OR

an 8 ohm 1x15 cab.

The 1x12 will recieve full power from the head whilst the 1x15 will probably receive about 180 or so watts.

I know that difference in wattage means a very small amount in perceived volume, but have any of you had experience of this kind of speaker set up?

I only want one cab to keep my rig to as small as possible, but I want the best sound out of the amp.

Many thanks.

Matt

[chris_b]

Are you sure it's a 4 ohm 112?

You mostly see 8 ohm 112's because 2 [i]always[/i] sound better than 1.

I don't see a single 112 sounding big enough even at 4 ohms. It just can't move enough air on its own.

[matt-bass-sparkes]

Yeah I bought a 4 ohm 112 speaker to go in an old combo that I have.

But was thinking of using it with the more powerful head as a cab, and selling the amp inside the combo.

I guess I'll just have to play both side by side and see the difference

[thelowend77]

Hey bass peeps, I've been following posts for quite some time, but haven't posted in ages ( mostly because I forgot my log in details! ) but now have a question of my own relating to cabs and ohms that I'm hoping you could help me with. A lot of the replies here are great, but there's still stuff I don't get, particularly with running multiple cabs in series or parallel, so thought it just best to ask my own particular question.
I've recently upgraded my head to a Markbass little Mark tube which is rated at 500w @ 4 ohms.
I now fancy upgrading from my heavy old Ashdown ABM 410 to something more modern and lightweight.
I tried out the Markbass 210 and it was lovely, but someone literally round the corner is selling 2 TC Electronic K210 cabs which are rated at 400w @ 8 ohm each.
There's only the one speakon output on the back of the head and there doesn't seem to be any switch on it to change the output from 4ohm to 8ohm.
So, if I daisy chain the cabs, head to cab then cab to the other cab, is this what's known as running them in series? And if so, do I then get a power handling rating of 800w @ 4 ohm? Or would this only be the case if the head had two outputs and I was running each cab from its own output on the amp ( which is not a possibility on this head ) is this what's known as parallel?
I was also considering this pair of cabs as I thought I could just use the one for small rehearsals or jams, but I guess if I did that I would have to be very careful with the volume. Am I going to do any damage to either the head or the cabs if I had this set up?
Cheers in advance for any help guys. Keep it low. Peace.

[Dad3353]

[quote name='thelowend77' timestamp='1465583771' post='3069513']...
Cheers in advance for any help guys...
[/quote]

Yes, you're confusing a couple of issues here, but let's clear them up.
Firstly, the twin sockets on the cabs (and, indeed, on almost all amps...) are wired in parallel. One can use either; it makes no difference. If an amp has two outputs, one would usually plug a cab into each, and the amp would 'see' the total impedance in parallel, just as if there was only one cab. For the two 8 ohm cabs mentioned, the amp would see 4 ohms.
Your amp has only one output, so you would plug instead one cab into that, and the other into the second output on the first cab. The result, electrically, for the amp is identical; it will see 4 ohms just the same.
The power handling question is also slightly askew. Each cab has a rating of 400w. Its impedance is of no importance for that; it just 'is'. The amp has a power output dependant to some extent on the impedance presented. It will give a certain power at 8 ohms, and a bit more into 4 ohms. The power rating of the two cabs combined is 800w. The amp will be able to supply 500w into that load (4 ohms...). The cabs are therefore 'safe'. One single cab can handle 400w, but the amp, into 8 ohms, will be able to supply only around 300 or so, so, again, the cab is 'safe'.
A word of warning, just the same. The manufacturer's rating of 400w doesn't mean that much in real terms; it basically means that the speaker (probably...) won't burst into flames before that wattage. In reality, it may very well sound bloomin' awful well before then. Use your ears to judge if the cabs are being over-driven (and wear ear protection, if you value your hearing...). Don't wait for the magic smoke to appear.
There; does that help at all..?
Subject to completion, correction and/or contradiction from others.

Edited June 10, 2016 by Dad3353

[thelowend77]

Brilliant. That really clears it up for me. Thank you.

[Dad3353]

[sharedmedia=core:attachments:167485]

[sebowden]

I have just bought a Selmer PA 100, not actually picked it up yet, but it has an Ohm Selector, and you can chose between [color=#282828][font=helvetica, arial, sans-serif]3.75 (4), 7.5 (8) and 15 (16) Ohm speakers. There is also a 100V option, but I don't know what that means.[/font][/color] I have a Peavey 410TX which is 8Ohm, does anyone know if the selector enables the amp to run at 100W with any selection? i.e, if I wire it through my cab, will it be running at 100W?

I understand that most amps halve the wattage if they are 8Ohm but are being played through a 4Ohm cab, but does the Ohm selector change this?

Edited June 29, 2016 by sebowden

[obbm]

The PA100 is a valve amp and uses a multi-tap transformer to match the output stage to the speaker load. It always gives the full output. You must never run a valve amp without a load connected.

The power output of Solid State amps however varies depending on the connected load as you say in your last line. Solid-state amps can be run with no load connected.

[sebowden]

[quote name='obbm' timestamp='1467228609' post='3082165']
The PA100 is a valve amp and uses a multi-tap transformer to match the output stage to the speaker load. It always gives the full output.
[/quote]

Cheers!!

[Dad3353]

[quote name='sebowden' timestamp='1467226639' post='3082141']
I have just bought a Selmer PA 100...
[color=#282828][font=helvetica, arial, sans-serif]...There is also a 100V option, but I don't know what that means....[/font][/color]
[/quote]

The power of an amp is partly dissipated in the cabling resistance, which is why speaker cables are better if they're quite 'chunky'. When cabling over greater distances than just to a cab, however, it's very expensive to use chunky cable. Your amp, you say, is a PA amp; as such, it was designed to be able to power speakers laid out across a field, or all around a village hall. For these distances, it's more efficient to 'up' the voltage (and thus reduce the current, for the same power...), which enables long cable runs of lighter cable. The downside (there's always a downside...)..? The speakers have to be able to cope with this high voltage, either by having special windings, or having a 'drop-down' transformer built-in.
Do not use this 100v tap, ever, unless doing specialised, long-distance cable runs with adequate speakers, such as those quaint Tannoy horns that used to be dotted around village fairs.
Hope this helps.

[Chienmortbb]

[quote name='Dad3353' timestamp='1467230082' post='3082191']
The power of an amp is partly dissipated in the cabling resistance, which is why speaker cables are better if they're quite 'chunky'. When cabling over greater distances than just to a cab, however, it's very expensive to use chunky cable. Your amp, you say, is a PA amp; as such, it was designed to be able to power speakers laid out across a field, or all around a village hall. For these distances, it's more efficient to 'up' the voltage (and thus reduce the current, for the same power...), which enables long cable runs of lighter cable. The downside (there's always a downside...)..? The speakers have to be able to cope with this high voltage, either by having special windings, or having a 'drop-down' transformer built-in.
Do not use this 100v tap, ever, unless doing specialised, long-distance cable runs with adequate speakers, such as those quaint Tannoy horns that used to be dotted around village fairs.
Hope this helps.
[/quote]100V line systems ate high impedance. A 100W speaker at 100V is 100R (ohms note the the international symbol for ohms has been R for years). If you try to put 100V across a 4R or 8R speaker it could be very expensive.

Chunky cables (if the conductors are chunky) are better but if the cable length is from Head to cab, where the Head is say 1 metre for less does not need a massive cable. PA cables go much further and can do with being quite big.

Edited June 29, 2016 by Chienmortbb

[icastle]

100V line systems were dependant on two transformers.

The one at the amplifier end stepped the voltage up to 100V.
In a speaker designed for 100V usage, there is another transformer in there to drop the 100V back down to a usable level.

The 100V is used purely as a 'carrier' for the audio signal.

[jeigenbass]

Apologies for a question that's probably already been asked 100 times but at least this is the right thread...!

Will a 350W 4ohm Aguilar DB210 cab work with a Markbass 500W @ 4ohm head?


Thanks!

[chris_b]

Yes it will.

You'll be capable of putting the full 500 watts into it which, at 4 ohms, means you can't add another cab.

I wouldn't turn the amp up to the point where it could damage the cab or run the bass frequencies flat out but with those limitations you can run this cab with this amp.

I prefer 8 ohm 210 cabs because then you can add another cab if you need more volume and IMO more speakers gives you a better tone.

Edited July 4, 2016 by chris_b

[jeigenbass]

[quote][color=#282828][font=helvetica, arial, sans-serif]Yes it will.[/font][/color]

[color=#282828][font=helvetica, arial, sans-serif]You'll be capable of putting the full 500 watts into it which, at 4 ohms, means you can't add another cab.[/font][/color]

[color=#282828][font=helvetica, arial, sans-serif]I wouldn't turn the amp up to the point where it could damage the cab or run the bass frequencies flat out but with those limitations you can run this cab with this amp.[/font][/color]


[color=#282828][font=helvetica, arial, sans-serif]I prefer 8 ohm 210 cabs because then you can add another cab if you need more volume and IMO more speakers gives you a better tone. [/font][/color][/quote]

Thanks!
So does that mean I would never be able to add another cab safely? not even another 4 ohm one or in parallel (my amp has two outputs)?

[obbm]

[quote name='jeigenbass' timestamp='1467666044' post='3085278']
Thanks!
So does that mean I would never be able to add another cab safely? not even another 4 ohm one or in parallel (my amp has two outputs)?
[/quote]

If the amps spec says no lower than a 4-ohm load then that is it. You should not any lower regardless of how many spare sockets there are.

[bigjimmyc]

I'm looking at buying an Ampeg Svt-2 all-valve amp. I believe the output selector is 4R or 2R only. However my main cab is a bf410 at 8R.

Other than buying a second cab, will I be able to match this head with the cab without causing damage?

[AndyRoo]

[size=4][font=Arial, sans-serif]Hi all, [/font]

[font=Arial, sans-serif]So I think I've got most of this and apologies if this has been answered already but there's one piece that's not quite clear/I haven't found the answer yet on this thread/the web.[/font]

[font=Arial, sans-serif]My setup (picked up through the BC for-sale boards) is as follows:[/font]

[font=Arial, sans-serif][url="http://usa.yamaha.com/products/musical-instruments/guitars-basses/amps/bbt500h/"]Yamaha BBT500H head[/url], 500W at 2ohm, 250W at 4ohm, class D amp.[/font]
[font=Arial, sans-serif]Cab 1 is a matched Yamaha BBT210S (250W handling at 4ohm). So far so good and one happy customer.[/font]

[font=Arial, sans-serif]I'd like to add another cab for bigger venues and the obvious thing is to keep it simple and get a 250W (or greater) 4ohm cab (so 500W total at 2ohm = happy days). However let’s say I want to [hypothetically] use an 8ohm 250W cab instead...[/font]

[font=Arial, sans-serif]The overall impedance is going to be 2.667ohms (still fine for the class D head).[/font]
[font=Arial, sans-serif]I understand the power will be split unevenly between the two cabs with 2/3 going into the 4ohm and 1/3 going into the 8ohm cab.[/font]

[font=Arial, sans-serif][u]My question is[/u]: is this one thirds/two thirds power splitting based on the max head power (i.e. 500W, which would put 160W into the 8ohm and be fine but 333W into the 4ohm cab and ultimately shred it subject to “Alex’s first rule”) [u]OR[/u] is this power splitting based on the power at the overall impedance (i.e. 500 * 2/2.667 = 375W) in which case the power nominally going into each cab is essentially fine (250W into the 4ohm and 125W into the 8ohm)?[/font]

[font=Arial, sans-serif]Thanks![/font][/size]

Edited January 6, 2017 by AndyRoo

[Bill Fitzmaurice]

[quote name='AndyRoo' timestamp='1483712605' post='3209463']
[size=4][font=Arial, sans-serif]is this one thirds/two thirds power splitting based on the max head power (i.e. 500W, which would put 160W into the 8ohm and be fine but 333W into the 4ohm cab and ultimately shred it subject to “Alex’s first rule”) [u]OR[/u] is this power splitting based on the power at the overall impedance (i.e. 500 * 2/2.667 = 375W)[/font][/size]

[/quote]It's based on the impedance. The problem here is that the 210 will be doing most of the work. Depending on what you're adding it might not be all that worthwhile. A second identical 4 ohm 210 would be the best option.

[AndyRoo]

Hey Bill, that's great, thank you!

Yes I'm keeping my eyes on the boards for a 4ohm 210 (or even something like a 110 or 112) for when payday comes around but good to know that I can play with 8ohm options (caveat it might sound awful) but without risking instant cab damage.

Cheers!

Edited January 6, 2017 by AndyRoo

[Bill Fitzmaurice]

An 8 ohm 110 would keep the same power in all three drivers. If you were going to a 112 or 115 it would probably be better for that to be 4 ohm.

[Chienmortbb]

[quote name='Bill Fitzmaurice' timestamp='1483722451' post='3209605']
An 8 ohm 110 would keep the same power in all three drivers. If you were going to a 112 or 115 it would probably be better for that to be 4 ohm.
[/quote]Bill is quite right here but there are no easy answers. I have rewritten this answer several times as it is complex. [size=4]In my opinion the best way forward is for you to find a second identical cabinet OR find two other identical cabinets whether 4 or 8 Ohm. The reasons are complex (as are the impedances but unless you want a physics lesson we will leave that alone).[/size]

Most Class D heads have a tuned circuit on the output that takes into account the speaker impedance. The speaker is part of the amp's output circuit. Change the speaker impedance and the amp behaves differently. I suspect that the Yamaha amp is optimised for 4 ohms so two 8R cabs would work well. Two identical 4R cabs will also work well although I don't like running at 2R. The reason is that amplifiers with short circuit or current limiting protection (most class D and class A/B, solid state amps have this) can get confused with 2R operation as it is getting close to zero ohms. So in a nutshell either get a second identical 4R [color=#282828][font=Arial, sans-serif]Yamaha BBT210S[/font][/color] or buy two identical 4R or 8R cabs.

Edited January 31, 2017 by Chienmortbb