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Ohms and Gain

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Jack1991 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jack1991 Quote  Post ReplyReply Direct Link To This Post Topic: Ohms and Gain
    Posted: 25 January 2024 at 1:02pm
I have a amp for a portable speaker. It will do ~35w @ 8Ω  or  ~70w at 4Ω

So if I buy the 4Ω version of the driver I want to use. If the battery drains too quickly would turning down the gain, essentially give me the 8Ω driver difference? I was thinking that way I can always test it out and dial it down if so, but I can't dial it up to get more if I get the 8Ω version.

Does that make sense?

Cheers


Edited by Jack1991 - 25 January 2024 at 1:03pm
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Xoc1 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Xoc1 Quote  Post ReplyReply Direct Link To This Post Posted: 25 January 2024 at 1:11pm
Efficiency is measured in decibels per watt so as long as the 4 & 8 Ohm drivers have comparable efficiency the 4 ohm should just allow you more dynamic headroom. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Conanski Quote  Post ReplyReply Direct Link To This Post Posted: 25 January 2024 at 4:19pm
Originally posted by Jack1991 Jack1991 wrote:

So if I buy the 4Ω version of the driver I want to use. If the battery drains too quickly would turning down the gain, essentially give me the 8Ω driver difference?
The 4ohm vs 8ohm thing is something you need to look closely at, just because the 4ohm driver will consume more power does not mean it will create more SPL than the 8ohm version. Loudspeakers are voltage sensitive so look at the rated sensitivity... this is the spl generated with 2.83v input, if they are the same for both drivers then there is no advantage to using the 4ohm version.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jack1991 Quote  Post ReplyReply Direct Link To This Post Posted: 25 January 2024 at 5:19pm
Cool cheers guys. Yeh I ran a load of drivers through hornresp and this one came out best. The 8ohm version of it looks very similar on hornresp but around 2-3db quieter at points. So was mainly concerned for battery life.

Edited by Jack1991 - 25 January 2024 at 6:27pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jack1991 Quote  Post ReplyReply Direct Link To This Post Posted: 20 February 2024 at 10:24am
I thought I understood this, but using hornresp im not sure I do now.

I am comparing 2 of the same driver in a Tham10, the 4ohm and 8ohm version. The driver is the Faital Pro PR300 

Here are my results if someone could confirm or explain to me which is correct would be great. I assumed at first that hornresp would take into consideration the driver and 'know' what impedance it is from the TS parameters.

Anyway here's the photos to show. There is quite a big difference, so I need to know which is the best choice to choose from and what way is correct in simming on hornesp please.











Here is the results compared to one another. Clearly the 4ohm is the better choice here by roughly 2-3db at points.



Now I went back to the 4ohm Faital Pro input. Here i double clicked 'Eg' this box comes up and I changed the 'Load impedance in ohms' from 8 to 4. (the Eg box itself did change from 2.83 to 2.00 after I clicked 'OK'.



Here's the comparison outcome again with just the 4ohm driver Eg load changed. And now the 4ohm is slightly worse than the 8ohm.


So I'm confused if the Eg should be kept at the same 2.83 when comparing the 2 drivers. Or if it's something else I'm doing wrong. 


Edited by Jack1991 - 20 February 2024 at 10:29am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 20 February 2024 at 12:38pm
You're not doing anything wrong, just finding out the difference between modelling voltage vs power. 2.83V is the equivalent of 1Watt into an exact 8Ohm load, so is the same as 2Watts into an exact 4Ohm load. That's why the 4Ohm version of your 1st comparison was louder. When you chenged to 2V for the 4Ohm you modelled 1Watt into an exact 4Ohm load. The difference in output now is because the 2 versions of the driver do not have exactly matching parameters (aside from the impedance).

The way I would decide between the 2 is to think about how likely it is that I might want to double up the rig later. If so, I'd start with 8Ohm drivers so that when more boxes are added later the amp can still drive them relatively easily. That wouldn't be so easy if starting with 4Ohm drivers as doubling up would result in a 2Ohm load which is not ideal for many amps. 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jack1991 Quote  Post ReplyReply Direct Link To This Post Posted: 20 February 2024 at 12:52pm
Ah right ok I see, thanks very much that explains it perfectly.

This is for a 2.1 portable Bluetooth speaker. So it will only be 1 sub. The 2x midtops are both 8ohm Faital pro 4FE32 and are on 1 channel each of the amp and the remaining two channels bridged for the sub.

Im trying to get as much bass as I can. It will run off Makita battery's, I have a fair few of them for work and have made a MK1 speaker and they lasted a good while with that. 

My thinking is if I use a 4ohm driver this time I could draw a bit more power for the sub. But, at the same time it's why I was wondering about ohms & gain in the first place as I was thinking if I use a 4ohm driver which is more powerful than the 8ohm equivalent, and it does end up draining the battery too quickly, I could perhaps reduce the subs gain to save some battery, and hope that reducing the gain would then end up being roughly what the 8ohm version output would have been anyway.



Edited by Jack1991 - 20 February 2024 at 12:56pm
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Xoc1 Quote  Post ReplyReply Direct Link To This Post Posted: 20 February 2024 at 1:18pm
As you have discovered both the 4 & 8 ohm will give the same output per watt.
So if you use the 4 ohm it does not use any more power (Watts) - but you turn the amp gain down a little as you need less volts.
When you reach a dynamic peak, hopefully the amplifier can deliver a higher power transient in to the 4 ohm load. Therefore you can achieve more dynamic headroom.


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Jack1991 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Jack1991 Quote  Post ReplyReply Direct Link To This Post Posted: 20 February 2024 at 1:38pm
Ah right cool cheers Xoc1 that makes more sense to me now then too.

I am hopeful I made the right choice in the 4ohm driver now as I already bought it a few weeks back, haven't used it at all yet though as the enclosure itself isn't ready just yet. Should be Friday I'll get a chance to fit everything and test it out.

Thanks again guys👍🏼


Edited by Jack1991 - 20 February 2024 at 1:38pm
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