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Impedance etc

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[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 by Chienmortbb

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Same question alert -
Sorry about this but it's a new consideration for me and I cannot (as yet) wrap my head around this.

Can anyone help me out with this possible head/cab logic -

Aguilar TH500 (500 watts into 4 Ohms, 250 watts into 8 Ohms) into Ashdown Bentley 4x10 cab (600 watt 8 Ohm)
Am I right in thinking this isn't a great marriage? The cab will drain LOTS of power, really the head needs to be bigger/more powerful or the cab needs less impendence?

Heid is fried on this one.

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A TH500 is 350 watts into 8 ohms and you cannot damage an amp by running it into a cab with a higher watts rating. Cabs don't drain amps. Amps power cabs so IMO you would be fine with this gear as long as 350 watts is all you need. If you want more volume add another 8 ohm cab.

I have no idea what this Ashdown cab sounds like but I've used a TH500 for the last 3 years through several Bergantino cabs and several Barefaced cabs. It has sounded perfect to my ears in every situation.

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Hi guys, really useful thread here, nice one. I have read through and found some answers to a similar question but I'm just wondering if anyone could give me an answer on a specific scenario, I have recently acquired an SWR Goliath III 410 4-ohm cab that I was hoping to try out in series with my Ashdown 410 8-ohm, is this possible or not recommended? I know I can't run them in parallel as neither of my amps have 2ohm outputs, but if I ran from amp > cab 1 (4ohm) > cab 2 (8ohm) in series, would that create a total impedance of 12 ohm therefore could I run it from the 8ohm out of my amp?

Hope that question makes sense and I'm frustrated at myself for still not completely understanding all of this stuff. Maths isn't my strong point so I find it easier to get a second opinion. I'd also be interested to know if people think it's unwise to match different types of cab anyway, regardless of impedance.

Thanks guys.

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[quote name='Powertripper' timestamp='1489244126' post='3255441']
...if I ran from amp > cab 1 (4ohm) > cab 2 (8ohm) in series...
[/quote]

Unless you use special/custom speaker cables, the connections will be parallel.

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I have a question regarding my Trace Elliot AH500. on the back there are 2 outputs, a speakon and a 1/4" jack. The impedance information merely reads 'minimum load 4 ohms' can I use 2 outputs into 2 separate 4 ohm cabs or do I now need to use use 2  * 8 ohm cabs (or does it matter) ? 

 

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1 hour ago, Quilly said:

I have a question regarding my Trace Elliot AH500. on the back there are 2 outputs, a speakon and a 1/4" jack. The impedance information merely reads 'minimum load 4 ohms' can I use 2 outputs into 2 separate 4 ohm cabs or do I now need to use use 2  * 8 ohm cabs (or does it matter) ? 

 

For most amps, this means the minimum load you can hook up is 4Ω total.  So that would mean 2 8Ω cabs.  Doesn't matter if it's one to each out on the amp or daisy'd.

2 x 4Ω cabs = o.O

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3 hours ago, xgsjx said:

For most amps, this means the minimum load you can hook up is 4Ω total.  So that would mean 2 8Ω cabs.  Doesn't matter if it's one to each out on the amp or daisy'd.

2 x 4Ω cabs = o.O

I have one 4 ohm cab. can I use an 8 ohm cab on the other jack? 

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23 minutes ago, Quilly said:

I have one 4 ohm cab. can I use an 8 ohm cab on the other jack? 

No.

2 x 8 ohm cabs or 1 x 4 ohm cab. That's it.

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One 4 ohm cab and one 8 ohm cab would run at 2.67 ohms so no - and also the 4 ohm cab would draw 2/3 of the watts from the head so would be 50% louder than the 8 ohm. Complicated aint it!!

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On 26/04/2018 at 18:08, Quilly said:

Can a 4 ohm cab be converted to an 8 ohm cab without replacing the drivers ?

If there’s more than 1 driver, then you could make it 16 ohm. 

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I’m sure this may have been covered somewhere, but can you ‘trick’ an amp with a min load of 4 ohms into thinking it’s putting out to a 4 ohm speaker even if it’s actually an 8 ohm speaker?

 

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26 minutes ago, Deedee said:

I’m sure this may have been covered somewhere, but can you ‘trick’ an amp with a min load of 4 ohms into thinking it’s putting out to a 4 ohm speaker even if it’s actually an 8 ohm speaker?

 

no

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1 minute ago, Phil Starr said:

no

That’s that then 😂

I only ask as I have a clever cable made by OBBM of this parish that works the other way around - ie I can connect my head to two 4 ohm cabs, even though the min load for the amp should be 4 ohms

Edited by Deedee

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7 hours ago, Deedee said:

That’s that then 😂

I only ask as I have a clever cable made by OBBM of this parish that works the other way around - ie I can connect my head to two 4 ohm cabs, even though the min load for the amp should be 4 ohms

Yeah that lead will put the two cabs in series which is important as it keeps your amp safe. you'll get some extra efficiency by using two speakers but cancelled a loss of power into 8ohms. Assuming the speakers are identical you get double the power handling using that lead and excursion of the cones is reduced so your bass may be less distorted and the speakers are safer. 

If you use that lead with two 8ohm speakers you'll end up with the amp seeing a 16 ohm load so less power.

What you could do is use that combination as an 8ohm speaker and then add in an extra 8ohm speaker in parallel through your amp's second speaker outlet. That'd give you full power from the amp, buckets of power handling and high efficiency. No guarantees on what it would sound like but worth a try?

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Would the extra power to that 3rd cab be worth it?  It's likely going to be a different volume to the other 2 cabs.  What about putting it in the same loop as the other 2 cabs?

I know it means the full watts aren't coming from the amp, but if it's loud, what does that matter?  It'd certainly be kinder to the amp's circuitry than trying to get a 4Ω load.

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The question was if the full power of an amp can be drawn into a 8ohm single cab, without the need for further cabs.

Could for example a split cable be produced that uses both speaker outs at the amp end but with just one speakon at the other end?

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13 hours ago, Deedee said:

I’m sure this may have been covered somewhere, but can you ‘trick’ an amp with a min load of 4 ohms into thinking it’s putting out to a 4 ohm speaker even if it’s actually an 8 ohm speaker?

 

There's no point. You may think that there's an advantage to the proverbial 'getting all the watts out of my amp', but there isn't. If you did have a 4 ohm cab versus 8 ohms the greatest potential difference in maximum output would be 2dB, which is inconsequential. That's best case, with an amp that's rated no more than 1/4 the cab power rating. With a less skewed amp to speaker power rating, where the maximum output is likely limited by the driver excursion, there would be no difference.

Could for example a split cable be produced that uses both speaker outs at the amp end but with just one speakon at the other end?

The speaker outs are already connected within the amp. That cable would accomplish nothing.

Edited by Bill Fitzmaurice

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30 minutes ago, Bill Fitzmaurice said:

There's no point. You may think that there's an advantage to the proverbial 'getting all the watts out of my amp', but there isn't. If you did have a 4 ohm cab versus 8 ohms the greatest potential difference in maximum output would be 2dB, which is inconsequential. That's best case, with an amp that's rated no more than 1/4 the cab power rating. With a less skewed amp to speaker power rating, where the maximum output is likely limited by the driver excursion, there would be no difference.

 

The speaker outs are already connected within the amp. That cable would accomplish nothing.

Aha, that’s put that one to bed then.

Many thanks for clarifying for a certified technophobe 👍

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Question: I have a Trace Elliott 500W cab (500AH-7) and I have 2 x  4 ohm cabinets. The speaker outputs consist of a speakon connection and a 1/4"  jack output. If i daisy chain the cabs they will have 2 ohms right? . If I plug this combination into my head will I fry the output transformer?

Secondly as there are 2 separate outputs on my can I plug either one into each cab (i'e will it be 4 ohms into each head as normal). 

On the back of my amp it reads 'Minimum load 4 ohms'

 

      

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4 ohms on the amp means 1 4ohm cab or 2 8 ohm cabs. 2 ohms will probably damage the amp.

Either speaker output socket is fine as is daisy chaining the cabs.

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2 hours ago, Quilly said:

 If I plug this combination into my head will I fry the output transformer?

On the back of my amp it reads 'Minimum load 4 ohms'

If it says 'Minimum Load 4 ohms' that indicates an SS amp. Modern SS amps do not have output transformers.

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Class D amps will usually go into protect mode which is designed to prevent and damage to the amp. Current SS amps, I'm not sure if they have protection circuits.

Older amps?? Not sure, but probably don't have protection built in. If that's the case you'll be running them beyond their spec so I'd guess you're almost guaranteed to damage something.

Just be safe and never go below the stated minimum load for the amp.

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Having read through most of this thread and trying to understand how this works, am i right in thinking that all these combos we see which run at 300 watts at 8 Ohms and 500 Watts at 4 Ohms, will in all liklihood have two internal 16 Ohms speakers wired in parallel, or two 4 Ohm speakers in serial,which run at 8 Ohms, and then when the 8 Ohms extension cab is connected it runs as two 8 Ohm speakers in parallel at 4 Ohms giving the full 500 watts... ?

Edited by Creeper

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