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Balancing Speaker Cab levels

Postby pitchwest » Tue May 07, 2019 10:16 am

I have a question for this community:

Odd Speaker Over Powering

I have a 2x10, 1x15 guitar cab but would like to turn the volume down independently on the 10's. Is there a way to do that without installing some sort of PowerBrake or other attenuator? The 2x10's are obviously louder than the 15 and I'd like to just turn their volume down.
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Re: Balancing Speaker Cab levels

Postby Sam Spoons » Tue May 07, 2019 10:28 am

No is the short answer, sorry,

The longer answer is that you can use a power brake or attenuator to reduce the volume but you may need to consider impedance mismatches if you driving them with a valve amp.

If it's solid state than at the simplest attenuator would be a suitably meaty (probably wire wound) resistor but you'd need to experiment to find the right value and so you'd probably be better getting a variable speaker attenuator (again, to be safe, this would need to be rated for at least ½ the amps output power).

Hopefully Dave ef34a will be along soon as he has much experience in the field.
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Re: Balancing Speaker Cab levels

Postby ef37a » Tue May 07, 2019 11:52 am

Hmm? Tricky!
There is much we need to know before a solution can be finalized. On the face of it, easy. Just buy an "L pad" to connect between the amp input jack on the cab and the 2x10s, leaving the 15 to receive the full amplifier power. L pads keep the impedance fairly constant at all attenuation setting so no amp loading worries, IF you know the impedances in the system!

1) How are the various drive units wired? All in parallel? 15 straight to jack but the tens in series? All in series? (very unlikely) Have you had a varder inside the cab? Might be a crossover network.
2) What is the power rating of the amplifier and yes, is it a valve or transistor output stage?
3) What are the individual impedance ratings of the speaker units?
4) What is the power rating of the speaker as a whole?

And finally (for now) do you own a digital multimeter and have a rough idea how to use it? You will need one to check DC resistances and IF you do the work that you have not made a wiring boob that will destroy the amplifier. (not likely if valves but transistors do NOT like shorts!) Oh, and a PP3 battery and croc leads to check speaker phasing (sorry H, POLARITY!)

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Re: Balancing Speaker Cab levels

Postby pitchwest » Tue May 07, 2019 12:15 pm

ef37a wrote:Hmm? Tricky!
There is much we need to know before a solution can be finalized. On the face of it, easy. Just buy an "L pad" to connect between the amp input jack on the cab and the 2x10s, leaving the 15 to receive the full amplifier power. L pads keep the impedance fairly constant at all attenuation setting so no amp loading worries, IF you know the impedances in the system!

1) How are the various drive units wired? All in parallel? 15 straight to jack but the tens in series? All in series? (very unlikely) Have you had a varder inside the cab? Might be a crossover network.
2) What is the power rating of the amplifier and yes, is it a valve or transistor output stage?
3) What are the individual impedance ratings of the speaker units?
4) What is the power rating of the speaker as a whole?

And finally (for now) do you own a digital multimeter and have a rough idea how to use it? You will need one to check DC resistances and IF you do the work that you have not made a wiring boob that will destroy the amplifier. (not likely if valves but transistors do NOT like shorts!) Oh, and a PP3 battery and croc leads to check speaker phasing (sorry H, POLARITY!)

Dave.

The 10's are Warehouse 75w 16ohm in series and the 15 is Legend 1518 150w 8ohm. The cab is 16ohm. I'm running a 100w tube amp right now but moving to a 120w tube amp soon. The other half of this full stack is a 4x12 cab 16ohm.

I do have a multimeter and am very competent with wiring and such.

The 15 sounds amazing but the 10's really drown it out. I've thought about flipping the baffle so the 10's are on the bottom and putting defuser cones in front of the 10's as well but would rather fix this electronically.
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Re: Balancing Speaker Cab levels

Postby BigRedX » Tue May 07, 2019 12:58 pm

Is this rig for live use? Studio use? Or playing for your own enjoyment in your bedroom?

Are all the cabs running at the same time?

Can you provide a clear diagram showing how everything is connected up?

Basically you appear to have at least two problems affecting this set up. The different driver cone sizes and the impedance mis-match between cabs. You may also have additional factors involving the efficiencies of the various drivers and cab designs.

Generally running different sized drivers simultaneously without crossing them over electronically is not recommended, as they will give unpredictable results depending on where you are in the room. The rig might sound awesome form where you are standing, but others in the room will have a totally different tonal experiences depending on where they are in relation to your rig.

My initial advice would be to go for a single cab solution that delivers the tone you require, and if you really need more volume (although unless you are after super-clean guitar sounds 100W is already overkill IMO) get another cab exactly the same.
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Re: Balancing Speaker Cab levels

Postby ef37a » Tue May 07, 2019 1:40 pm

Wow! So you have two tens in series at 32 Ohms that are still beating a 15 incher?

Ok, let's deal with the impedances (Zs) here which are neither cakehole nor breakfast time for the amp!

The 2 10s+15+4X12 come out at 4.6 Ohms so the safest tap for the amp is 4R but I doubt it would mind being on 8R in any case, low is the way to go with valves.

You could indeed just put an L pad in the tens circuit (leave them in series. VERY verboten for hi fi but gitists are weird!)
Now these L pads are rated very optimistically! Typically a "100W" rating means for a 100W SYSTEM and the pad intended to handle around 20W of tweeter power. This should not matter however for your application since I doubt the speakers will absorb more than 15W or so from the amp on 4R tap. You do however need a 16R pad and I think that might be a problem. Not insurmountable, just get an 8R plus a 20W 8R resistor to put in series in the amp side.

I shall have a look for thee....https://www.parts-express.com/parts-exp ... m--260-261
Easier than I thought!

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Re: Balancing Speaker Cab levels

Postby Sam Spoons » Tue May 07, 2019 1:55 pm

I have to say I agree with the others, bigger speakers are usually more efficient than small ones so that your two 10" in series are overpowering a single 15" is unusual. A quick google reveals that the 15" is very efficient at 103.4dB 1w/1m, the 10's only rate 96dB so a lot less efficient........ Something odd going on I think?
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Re: Balancing Speaker Cab levels

Postby ef37a » Tue May 07, 2019 2:34 pm

You are right Sam, something odd there but, loudspeaker sensitivities are notoriously fickle things, just defining what is a watt going in is tricky!

Tolerances mean the figures could be at least 2dB adrift. Then, subjective loudness depends hugely on what part of the spectrum is hitting the ear. The tens might be of lower overall sensitivity (on pink noise?) but several dBs hotter at say 1kHz where it matters? This of course also applies to amp ratings, loudness depends upon the "voicing".

We also have no idea of the "MO" used to measure the sensitivity in each case? I have also read that it is very difficult to make a direct radiator speaker with a genuine sensitivity much higher than 100dB/W/mtr?

I also wonder how the 10s are disposed? If in a vertical line they will gain a dB or two from the tighter radiation pattern...And ALL that before we suspect massaging by the adpuff department!

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Re: Balancing Speaker Cab levels

Postby pitchwest » Tue May 07, 2019 3:07 pm

ef37a wrote:Wow! So you have two tens in series at 32 Ohms that are still beating a 15 incher?

The 2 10s+15+4X12 come out at 4.6 Ohms so the safest tap for the amp is 4R but I doubt it would mind being on 8R in any case, low is the way to go with valves.

You could indeed just put an L pad in the tens circuit (leave them in series. VERY verboten for hi fi but gitists are weird!)

Dave.

This is the first I've heard about an L-pad. I did a little research and looks like I'll have to do a bit more but this sounds like the correct path. I did make a mistake earlier. The 10's are parallel. They end up being 8ohm together and in series with the 8ohm 15" the cab is 16" then split with the 16ohm 4x12 cab the whole set up ends up being 8ohm. Sorry for the mistake, I'm on nightshift, it's 7am and my brain isn't working properly right now.

Would I be able to make a L-pad or T-pad out of resistors since I don't really need it to be variable? If so, what watt rating would you recommend?

Thanks a lot for your input. The combination of these cabs have taken a few years to to get this far. The tone is wonderful but this volume imbalance seems to be the last hiccup.

-Richard
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Re: Balancing Speaker Cab levels

Postby Sam Spoons » Tue May 07, 2019 3:27 pm

It might be worth putting the 10s in series and in parallel with the 15" in that cab, that should increase the distribution of power to the 15 and reduce it to the 10s. Dave? does that sound right?
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Re: Balancing Speaker Cab levels

Postby ef37a » Tue May 07, 2019 4:25 pm

Sam Spoons wrote:It might be worth putting the 10s in series and in parallel with the 15" in that cab, that should increase the distribution of power to the 15 and reduce it to the 10s. Dave? does that sound right?

Yes, that would be an easy first step Sam. Putting drivers in series can have an effect on the frequency response but I doubt it will be a factor for a rock cab! Series also buggers the damping factor but valve guitar amps don't have much anyway.

Yes, you could make up a resistive attenuator. You only need two resistors but it could be a lot of faffing about to get the power sharing spot on. I would bring the speaker conns outside the cab so you can play with the values more easily. Actually, if it does not already have one a dual jack plate would be handy. Wire the 15 to one jack and the 10s to the other for now and once you get it sorted wire the jacks in parallel then the cab can be easily slaved to another.

Will do you sum sums.
Ok, first off, use these resistors: https://uk.rs-online.com/web/p/products ... lsrc=aw.ds
I don't trust other types. They need to be mounted on a heat sink (sqr ft of Ally? See data sheet) in order to dissipate their rated maximum but for music signals you can scale that back a bit but remember! A smaller sink means it will all get hotter!

Start with 10R 100W in series with the tens wired in parallel. If that does not produce enough attenuation you can put resistors across the speakers. These do not need to be of such high power but nothing below 10 watts. As I said, bit of a faff getting the balance right so I would lash the thing up on a heatsink with terminal "chock blocks" Five amps are enough but bigger makes fiddling easier (or is that coz I am getting bloody old?)

Once you have the levels right you can tidy it all up and mount it in the cab but be aware of the heat, don't want to melt any insulation.
I don't know how you play or the genre but be aware that a 120W valve amp can put out over 200W if driven into hard distortion.

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Re: Balancing Speaker Cab levels

Postby BigRedX » Tue May 07, 2019 6:35 pm

You haven't considered cab design and how that will impact on the efficiency of the speakers contained within. Or cab placement for that matter. If the 2 x 10 cab is closer to the OPs ears then the 1 x 15 when the rig is set up then it is going to sound louder.

Also if this is a live rig unless each cab is individually mic'd up and put through the PA by a sandman who is sympathetic to the band's needs then the OP is completely wasting his time.
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Re: Balancing Speaker Cab levels

Postby Sam Spoons » Tue May 07, 2019 9:08 pm

BigRedX wrote:You haven't considered cab design and how that will impact on the efficiency of the speakers contained within. Or cab placement for that matter. If the 2 x 10 cab is closer to the OPs ears then the 1 x 15 when the rig is set up then it is going to sound louder.

The 10's and the 15 are in one cab

Also if this is a live rig unless each cab is individually mic'd up and put through the PA by a sandman who is sympathetic to the band's needs then the OP is completely wasting his time.

This is true and if you are miked up you probably don't need a 120 watt valve stack anyway, but we're not sure exactly what the OP is trying to achieve.
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Re: Balancing Speaker Cab levels

Postby BigRedX » Wed May 08, 2019 8:18 am

Sam Spoons wrote:
BigRedX wrote:You haven't considered cab design and how that will impact on the efficiency of the speakers contained within. Or cab placement for that matter. If the 2 x 10 cab is closer to the OPs ears then the 1 x 15 when the rig is set up then it is going to sound louder.

The 10's and the 15 are in one cab

Also if this is a live rig unless each cab is individually mic'd up and put through the PA by a sandman who is sympathetic to the band's needs then the OP is completely wasting his time.

This is true and if you are miked up you probably don't need a 120 watt valve stack anyway, but we're not sure exactly what the OP is trying to achieve.

I see. I mis-read about about the speakers being inside the same cab. We still don't know what the internal construction of the cab is. If this is a commercial design I would't be surprised to find that the 2 x10 and 1 x 15 sections are in separate compartments. First off I'd turn the cab upside down so that the 1 x15 driver is at the top and see if that sounds better.

If the OP had answered my first post we all might have a better idea of what this rig is for and what he is trying to achieve. IMO mixing driver sizes without using crossovers is a bad idea. As I said before it leads to inconsistencies in the sound depending on where you are stood. This arrangement of cabs might sound fine (not withstanding the 2 x10 component being too loud) from the OPs perspective as the player, but audience members are going to get a completely different tonal picture.

I stand by my original advice that the OP is best off ditching all his current cabs and replacing them with 1 more cabs that produce the sound he wants and are all the same in design all have the same drivers inside.
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Re: Balancing Speaker Cab levels

Postby ef37a » Wed May 08, 2019 8:39 am

It would seem Red, that the OP has been playing around for some time with this cab and has hit upon a speaker combination he likes?

In fact this is pretty much how it was done in the early days of amp development and still is to an extent*. Ever wondered why the top of a 4X12 exactly matches the footprint of a 100W head? They certainly did not tailor the amp sleeve to the cab!

There are plenty of guitarist mixing speaker types in cabs. Sometimes an exercise in futility because one speaker type will be so much more sensitive than another that it drowns it out, or one speaker has a pronounced "honk" (V30s, e.g. are very "middy") and a more restrained drive unit is again lost in the mix.
Basically there are no rules and precious little science but do try to get impedances about right, + or - 50% and power sharing correct.

*Sometimes the amp designer is given a speaker and told "make that sound good, all we can spend on a speaker."

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Re: Balancing Speaker Cab levels

Postby Sam Spoons » Wed May 08, 2019 9:19 am

Wot Dave sez, but to add I have never seen an electric guitar cab with a crossover (or a tweeter BTW) but mixing speaker sizes, while not common, is far from unheard of.
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Re: Balancing Speaker Cab levels

Postby ef37a » Wed May 08, 2019 9:35 am

Sam Spoons wrote:Wot Dave sez, but to add I have never seen an electric guitar cab with a crossover (or a tweeter BTW) but mixing speaker sizes, while not common, is far from unheard of.

"Hartke" bass cab Sam had a central tweeter but I remember thinking at the time....

WTF??!!

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Re: Balancing Speaker Cab levels

Postby BigRedX » Wed May 08, 2019 9:41 am

Mixing speaker cone sizes without using a crossover between might not be uncommon, but it is not good practice and more importantly for the OP will not give consistent results for all listening positions.

I'm assuming this is for a live rig, and the OP is obviously interested in getting the right sound. However by mixing cab designs and speaker cone sizes he will not be giving his audience the same sonic experience. Once he has sorted out the imbalance with the 2 x10 option of the rig he might well have the perfect sound where he is stood on stage, but very few of the audience will hear what he is hearing, and surely it is just as important that the audience get the right sound too?

Also if the PA is in anyway important at getting that guitar sound FoH then each different sized speaker will need to be mic'd up. If you are playing large arenas in a big name band, then it will probably happen. For the average <500 capacity venue, you'll get one mic on the "best" sounding or most conveniently located cab and that will be that.
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Re: Balancing Speaker Cab levels

Postby Sam Spoons » Wed May 08, 2019 9:47 am

Yes, mostly true but I have never seen a guitar speaker with a crossover. The differences in frequency response between 10", 12" and 15" guitar speakers are relatively small with a huge overlap so all a crossover would do is remove and top end from the 15" and any low end from the 10"s which would be pretty much self defeating.

ef37a wrote:
Sam Spoons wrote:Wot Dave sez, but to add I have never seen an electric guitar cab with a crossover (or a tweeter BTW) but mixing speaker sizes, while not common, is far from unheard of.

"Hartke" bass cab Sam had a central tweeter but I remember thinking at the time....

WTF??!!

Dave.

Yeah, quite common in bass cabs (definitely a plus for slap bass styles), My Ashdown 2 x 10 and #2 son's Warwick combo both have tweeters, as do most acoustic guitar amps. Still never seen one in an electric guitar cab though.
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Re: Balancing Speaker Cab levels

Postby ef37a » Wed May 08, 2019 9:55 am

I see Sam, I agree, no tweeter for a sixer cab,

But a crossover for the tens? At what frequency? They are probably ok for 70Hz and up and a crossover at say 100Hz is going to need some big mother inductors and the non-polarized caps won't be cheap.

A crossover also, of itself does nothing to balance levels. In a perfect world both speaker would be 3dB(?) down at Xover f and then the response levels out again. Yes some crossovers have tweeter attenuating resistors but they will be picked for a specific set of drivers.

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