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Strange....use of two 4x10s hardly made any difference to using one!

Musicman20

By Musicman20,
in Amps and Cabs

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Musicman20 Veteran

Musicman20

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The room we use just outside of Newcastle centre is always my first choice. Nice staff, warm, plenty of room, and full PA/backline available.

To my surprise, this time when we arrived they had 2x Ashdown 4x10s. I am not sure of the model, but they were carpet coated, with plastic corners. Both were 8 ohms. They werent even heavy if im honest. If I think about it, they looked like these:

[url="http://www.ashdownmusic.com/bass/detail.asp?section=legacy&ID=195"]http://www.ashdownmusic.com/bass/detail.as...gacy&ID=195[/url]

They also had an Ashdown amp. Again, I didnt take the model down, but im sure it was a 300 Watt version.

Anyway, I plugged both cabs in, to see what the tone was like. I set the amp as flat as I could.

You know what, pretty damn good sound. Very punchy, and not 'wooly' like Ive heard. It wasnt amazing, but it was very decent.

I used both, then decided to just use the bottom one. I actually could barely tell the difference between one or two cabs. Sure, having two meant much more ommphh down low...in fact there was a lot, but no huge differences.

Boring observation over!

Edited by Musicman20
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Ghost_Bass Proficient

Ghost_Bass

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Using just one cab the amp (set at the same volume) will put out a little more in that cab than having to split the signal in two cabs (the same way we say a amp is 180W@8ohm / 300W@4ohm for full power... don't know the techs on this... but i think you get my point). Adding to this you used the bottom cab alone who benefits of floor coupling.

So, if we see this in perspective we have two situations:

A - Both cabs running - each will recieve less signal than a single one.
B - Bottom cab running solo - the cab will recieve an increase in signal and the floor coupling will increase in the same progression thus giving the feeling of having almost the same volume of two cabs.

You may find interesting next time you're in a reharsal to try with the top cab running solo. I believe you'll then notice a big drop in volume. Try to A-B all the possibilities (two cabs vs top cab vs bottom cab) if you find the time and post your results. It'll be an interesting expirience and we'll all learn something mores about cab placement and coupling :)

Cheers

edit: correction of my portuglish...

Edited by Ghost_Bass
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Musicman20 Veteran

Musicman20

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[quote name='Ghost_Bass' post='1041073' date='Nov 29 2010, 12:52 PM']Using just one cab the amp (set at the same volume) will put out a little more in that cab than having to split the signal in two cabs (the same way we say a amp is 180W@8ohm / 300W@4ohm for full power... don't know the techs on this... but i think you get my point). Adding to this you used the bottom cab alone who benefits of floor coupling.

So, if we see this in perspective we have two situations:

A - Both cabs running - each will recieve less signal than a single one.
B - Bottom cab running solo - the cab will recieve an increase in signal and the floor coupling will increase in the same progression thus giving the feeling of having almost the same volume of two cabs.

You may find interesting next time you're in a reharsal to try with the top cab running solo. I believe you'll then notice a big drop in volume. Try to A-B all the possibilities (two cabs vs top cab vs bottom cab) if you find the time and post your results. It'll be an interesting expirience and we'll all learn something mores about cab placement and coupling :)

Cheers

edit: correction of my portuglish...[/quote]

Cool, good idea. Next time, top cab only.

I actually realised how much I quite like 4x10s. Id love a Berg/Genz/Aguilar 4x10.

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Musicman20 Veteran

Musicman20

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[quote name='umph' post='1041110' date='Nov 29 2010, 01:23 PM']should be a noticable increase in volume, did you try doing that in a band setting?[/quote]

It was the band rehearsing, and to be honest, the levels are pretty much as we do them all the time. Not ridiculous, but I wear ear protection.

There was a difference, just not HUGE.

I did try it with/without ear protection as well.

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Bill Fitzmaurice Veteran

Bill Fitzmaurice

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[quote name='Wil' post='1040946' date='Nov 29 2010, 06:25 AM']Probably a case of the head not being powerful enough to give any real volume increase when its output was split between the two cabs.[/quote]
Adding the second cab halves the load impedance, doubling the current flow and therefore power. Another 3dB of sensitivity comes from the mutual coupling of the two cabs, so with the same amp the total volume increase is 6dB, which is the equivalent of four times the power. Then figuring in the greatly increased intelligibility of the mids and highs from the top cab versus the bottom and there would have been a huge difference between both cabs and the bottom cab alone if everything was working correctly. Conclusion: something was AFU, perhaps a blown driver or two in the upper cab.

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51m0n Mentor

51m0n

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[quote name='Bill Fitzmaurice' post='1041199' date='Nov 29 2010, 02:30 PM']Adding the second cab halves the load impedance, doubling the current flow and therefore power. Another 3dB of sensitivity comes from the mutual coupling of the two cabs, so with the same amp the total volume increase is 6dB, which is the equivalent of four times the power. Then figuring in the greatly increased intelligibility of the mids and highs from the top cab versus the bottom and there would have been a huge difference between both cabs and the bottom cab alone if everything was working correctly. Conclusion: something was AFU, perhaps a blown driver or two in the upper cab.[/quote]


+1, or more simply a duff speaker cable/output/input somewhere was not douing what it should.

No way can you get more power from a single amp running into a single cab than same amp running into two of the same cab, impedance just doesnt work like that chaps!

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Mr. Foxen Veteran

Mr. Foxen

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[quote name='51m0n' post='1041217' date='Nov 29 2010, 02:41 PM']No way can you get more power from a single amp running into a single cab than same amp running into two of the same cab, impedance just doesnt work like that chaps![/quote]

Can if the amp outputs are series. Won't lose much volume though, since the sensitivity will compensate. Ashdowns are generally parallel, but knowing the shonky repairs that practice space rigs have, or possibly cunningness knowing people borrowing gear can be d!cks about impedance, not impossible it was wired series.

If you were in a dinky practice room, could just me all the room effects messing with ya. I've taken to leaning against the wall to check how much low is coming from my rig, because quite a lot of a small room can be pretty lacking

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Ghost_Bass Proficient

Ghost_Bass

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[quote name='51m0n' post='1041217' date='Nov 29 2010, 02:41 PM']No way can you get more power from a single amp running into a single cab than same amp running into two of the same cab, impedance just doesnt work like that chaps![/quote]

If you're writting this because of my post then you didn't understand me. What i tried to say is that (if you don't touch the head settings or volume) when you connect one single cab it'll get a certain amount of signal (let's call it S). When you connect another cab, lowering the impedance, the signal from the amp will be bigger than "S" like BFM explained but this signal equaly divided to both cabs will be less than "S" in each cab. But adding to this we have the floor coupling fenomena happening, the higher a cab is more coupling you have.

So [b]my theory[/b] (feel free to correct me on this, í'm here to learn :) ) is:

[u]With two identical cabs, stacked, with the same setting on the amp (this includes the volume knob being untouched) we have[/u]:

- Two cabs running at the same time will have more volume than each of them soloed;
- The bottom cab running solo will have more than half of the the volume of two cabs;
- The top cab running solo will have less than half of the the volume of two cabs;

My main variable is floor coupling.
If anybody with knowledge could do the math with a simple example to try and find if i'm very far from the truth i'll appreciate.

Cheers

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warwickhunt Grand Master

warwickhunt

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Could the cabs be out of phase with each other?

I may have been in the rehearsal rooms you speak of with this rig (I actually had mine with me as I don't trust/rate rehearsal room gear even though it was actually the singer from my old band who runs the rooms... sorry Marti! :) ), though it was a 2x10 + 1x15 when I was in. I moved the gear out of the way and tbh the cables that were used to connect the cabs to the amp looked distinctly 'pants' so if this was the same rig with cabs swapped for newer ones (or from another room) then I'd be suspecting some issues with the cables!

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Mr. Foxen Veteran

Mr. Foxen

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[quote name='Ghost_Bass' post='1041262' date='Nov 29 2010, 03:21 PM']If you're writting this because of my post then you didn't understand me. What i tried to say is that (if you don't touch the head settings or volume) when you connect one single cab it'll get a certain amount of signal (let's call it S). When you connect another cab, lowering the impedance, the signal from the amp will be bigger than "S" like BFM explained but this signal equaly divided to both cabs will be less than "S" in each cab. But adding to this we have the floor coupling fenomena happening, the higher a cab is more coupling you have.

So [b]my theory[/b] (feel free to correct me on this, í'm here to learn :) ) is:

[u]With two identical cabs, stacked, with the same setting on the amp (this includes the volume knob being untouched) we have[/u]:

- Two cabs running at the same time will have more volume than each of them soloed;
- The bottom cab running solo will have more than half of the the volume of two cabs;
- The top cab running solo will have less than half of the the volume of two cabs;

My main variable is floor coupling.
If anybody with knowledge could do the math with a simple example to try and find if i'm very far from the truth i'll appreciate.

Cheers[/quote]

Top one is closer to ear height for the mids/highs. Acoustic coupling will mostly affect lows, and lows are affected by loads of other room effects. Since most of the 'sound' is in the mids, that would be a more signifcant factor to perception.

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Ghost_Bass Proficient

Ghost_Bass

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[quote name='Mr. Foxen' post='1041277' date='Nov 29 2010, 03:35 PM']Top one is closer to ear height for the mids/highs. Acoustic coupling will mostly affect lows, and lows are affected by loads of other room effects. Since most of the 'sound' is in the mids, that would be a more signifcant factor to perception.[/quote]

I see your point and you're most certainly right but i used to play with a TE stack (300W head+2x10H+1x15 - it's not the same situation, i know) and when i went from using the single 15 to the full stack i didn't find much increase in volume. In fact i only lowered my volume pot from 3.5/10 to 3/10 - i know! TE's volume pots aren't linear... - i don't think it would be such a small difference if some external factor wasn't kicking in!...

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LawrenceH Rising Star

LawrenceH

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[quote name='Mr. Foxen' post='1041277' date='Nov 29 2010, 03:35 PM']Top one is closer to ear height for the mids/highs. Acoustic coupling will mostly affect lows, and lows are affected by loads of other room effects. Since most of the 'sound' is in the mids, that would be a more signifcant factor to perception.[/quote]

Both you and Ghost have a point I think...most of my preferred tone's certainly in the mids but a fair number of players I've heard with rockier bands have a lot going on between 80 and 500 and comparatively little above. A lot of rooms I've engineered and played have nodes that make them very lively in this upper-bass/low-mid region. In a smallish rehearsal space all sorts of weird and wonderful (or more likely terrible) things can happen.

Acoustic coupling between single 10" speakers won't do much above 500Hz anyway - the main advantage of vertically stacked 4x10s, or 8x10s, over the 2x10 is going to be a little bit of coupling to boost the low mids and then getting the upper mids closer to your lug 'oles!

There could well be something wrong/unusual about the cab setup here but I wouldn't discount a quirky combination of the room's acoustics, cab and listener placement.

Edited by LawrenceH
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Bill Fitzmaurice Veteran

Bill Fitzmaurice

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[quote name='Ghost_Bass' post='1041262' date='Nov 29 2010, 10:21 AM'][u]With two identical cabs, stacked, with the same setting on the amp (this includes the volume knob being untouched) we have[/u]:

- Two cabs running at the same time will have more volume than each of them soloed;
- The bottom cab running solo will have more than half of the the volume of two cabs;
- The top cab running solo will have less than half of the the volume of two cabs;

My main variable is floor coupling.
If anybody with knowledge could do the math with a simple example to try and find if i'm very far from the truth i'll appreciate.

Cheers[/quote]The volume of a cab is not related to watts, it's related to voltage. At a given gain setting the amp output voltage is constant, irrespective of the load impedance. Two cabs parallel wired both receive the same voltage as one, so if identical they will each run at the same volume. Floor 'coupling' in terms of a mechanical connection does not exist. Boundary loading from the floor does exist, and will be the same with two cabs stacked as with one on the floor, as the two cabs are acoustically coupled in the low frequencies where boundary loading occurs, acting essentially as one.

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LawrenceH Rising Star

LawrenceH

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[quote name='Bill Fitzmaurice' post='1041539' date='Nov 29 2010, 07:40 PM']The volume of a cab is not related to watts, it's related to voltage. At a given gain setting the amp output voltage is constant, irrespective of the load impedance. Two cabs parallel wired both receive the same voltage as one, so if identical they will each run at the same volume.[/quote]

This is only true in practice at lower output levels. Amp power supplies are rarely capable of providing the maximum voltage at all impedences, otherwise our amps would all have watts ratings that doubled with every halving of impedence. So if you're running an amp close to maximum then adding another speaker cab will result in a volume drop per cabinet.

Another confounding factor might be the higher resistance-associated losses from increasing the current, cos that's exponential, so the more speakers you add the worse it gets.

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LukeFRC Grand Master

LukeFRC

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ashdown heads.... how were the speaker cables plugged in? I found this too.

Plug both cabs into a socket on the amp..... and the volume drops.

Plug one speaker into the amp, then daisy chain the other cab in, and it will be louder. (presuming the in/outs on the cab and wired in parallel.



No idea why but I doubled the volume and clarity of my old church's rig by realising

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Musky Proficient

Musky

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[quote name='LukeFRC' post='1041797' date='Nov 29 2010, 11:11 PM']ashdown heads.... how were the speaker cables plugged in? I found this too.

Plug both cabs into a socket on the amp..... and the volume drops.

Plug one speaker into the amp, then daisy chain the other cab in, and it will be louder. (presuming the in/outs on the cab and wired in parallel.



No idea why but I doubled the volume and clarity of my old church's rig by realising[/quote]
Now that is distinctly [i]odd[/i]. :)

Something tells me there might have been some problem with one of the sockets (like the phase), but it'd be interesting to find out if anyone else has experienced this.

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