Speaker distortion and Volume

[Luckie]

I use a 1972 Road 440 head w/ a 218 cab.
But around 7 on the volume knob the speakers distort, albeit in a musical way.
Some folks want that driven sound, but for a lot of the work I do I need a cleaner tone with more volume.
What's causing that problem, and how can I solve it/control it?
I don't think the amp is causing the problem, as I just had it checked out and had the transistors biased. But the amp may be voiced to distort this way, I don't know.
So my question is, can my cab not handle the power? Or is my amp voiced this way? Would adding an extension cabinet dissipate the power and reduce distortion?

I understand that these are very rig-specific questions, so if theres info you need from me about my setup, just ask.
I'll try to record the sound I'm talking about next time I get to rehearsal.
And of course, no pic no rig.

[Luckie]

Anybody?

[Kenner]

Dude...have you tried a different cabinet?

[Arjank]

Originally Posted by Luckie

Anybody?

Can you see/hear if both woofers make this distorted sound?
Do the woofers move far in and out when distortion occurs? Or do they just slightly move.
Have you tried another amp on the 218? or another cab on the amp?

[playerunk]

from what you are saying it seems that you have reached the xmax of the drivers (the distance it can travel without distorting) and that's that.. Adding more power wont do any good.. only more speakers.

[billfitzmaurice]

Either your amp is running out of headroom or your speakers are running out of excursion or both. A second cab would make a big difference, if the amp can handle the impedance load, but I'd make sure it's not the amp before doubling the size of the speaker cartage.
BTW, your speaker cab looks terribly undersized for two eighteens, unless it's two feet or more deep.

[Luckie]

Originally Posted by Arjank

Can you see/hear if both woofers make this distorted sound?
Do the woofers move far in and out when distortion occurs? Or do they just slightly move.
Have you tried another amp on the 218? or another cab on the amp?

They both make that sound.
They extend pretty far, you can see them moving.
I've never had another amp to run it into, or another cab to use.

[christw]

Got any local music shops that you can A/B your amp and cab in?

[Arjank]

Originally Posted by Luckie

They both make that sound.
They extend pretty far, you can see them moving.
I've never had another amp to run it into, or another cab to use.

It can be the amp or the speakers.
If the amp starts to distort it also loses "control" over the speakers which will make them move in and out erratically.
Or, if the voice coil of the woofers start to leave the air gap, distortion will rise (excursion higher then xmax).

What is the power rating of the amp?

[Luckie]

Originally Posted by billfitzmaurice

Either your amp is running out of headroom or your speakers are running out of excursion or both. A second cab would make a big difference, if the amp can handle the impedance load, but I'd make sure it's not the amp before doubling the size of the speaker cartage.
BTW, your speaker cab looks terribly undersized for two eighteens, unless it's two feet or more deep.

The amp is designed to run an 8 ohm extension with the 218, and I already have the stock 118 cab to do so.
Actual cab depth is 19 inches, how does that affect the speakers in this case?

Originally Posted by Arjank

What is the power rating of the amp?

375 watts RMS

Originally Posted by christw

Got any local music shops that you can A/B your amp and cab in?

I sure do, but hauling a 218 isn't the easiest thing to do.
Looks like I'll have to though, to diagnose the problem.

[Arjank]

Originally Posted by Luckie

The amp is designed to run an 8 ohm extension with the 218, and I already have the stock 118 cab to do so.
Actual cab depth is 19 inches, how does that affect the speakers in this case?

If the cabinet was closed it would not be so much of a problem. Since it's a ported design the cabinet looks undersized for these 18's. But we do not have any Thiele Small parameters of these 18's so we can not really tell if it's a design fault.
I don't think that this is the root cause of your problem.

[billfitzmaurice]

Originally Posted by Luckie

The amp is designed to run an 8 ohm extension with the 218, and I already have the stock 118 cab to do so.
Actual cab depth is 19 inches, how does that affect the speakers in this case?

A cab that's too small for the drivers chokes off low end response. I can't say how large your cab should be without knowing what drivers it uses. It's hard to imagine a good 2x18 not being loud enough, but if the drivers are vintage 1972 that explains a lot.

[Arjank]

Originally Posted by Luckie

375 watts RMS

This is (possibly)enough power to bring two older 18's (which we think are in a faulty enclosure) to their knees.
A good designed ported cabinet could decrease cone excursion (read, increase mechanical power handling)

[BassmanPaul]

Originally Posted by Luckie

The amp is designed to run an 8 ohm extension with the 218, and I already have the stock 118 cab to do so.
Actual cab depth is 19 inches, how does that affect the speakers in this case

375 watts RMS

I sure do, but hauling a 218 isn't the easiest thing to do.
Looks like I'll have to though, to diagnose the problem.

How about renting an amp for the weekend?? Shouldn't cost too much and give you plenty of time to suss out your problem.

[Luckie]

Originally Posted by billfitzmaurice

A cab that's too small for the drivers chokes off low end response. I can't say how large your cab should be without knowing what drivers it uses. It's hard to imagine a good 2x18 not being loud enough, but if the drivers are vintage 1972 that explains a lot.

They're EV built 18's, if that helps.
Would it be possible to find new speakers that would have better handling and match the enclosure?

I read somewhere that this rig was very carefully designed with regards to cab size, power, etc. Was their science insufficient to properly design this?

[Luckie]

Originally Posted by BassmanPaul

How about renting an amp for the weekend?? Shouldn't cost too much and give you plenty of time to suss out your problem.

It may not cost much, but it's still money I don't have.
I both love and hate this rig, it sounds incredible for rock music and lower levels are super clean, but its a b**** to transport and it gets dirty at stage volumes.
I'd love to sell it off and buy something better suited, but who's buying 218 cabs these days?

[billfitzmaurice]

Originally Posted by Luckie

They're EV built 18's, if that helps.

What vintage? If 1972 it's probably displacement limited to 100 watts or less before farting out.

I read somewhere that this rig was very carefully designed with regards to cab size, power, etc. Was their science insufficient to properly design this?

In 1972 the science of vented enclosures was in its infancy.

[Luckie]

Originally Posted by billfitzmaurice

What vintage? If 1972 it's probably displacement limited to 100 watts or less before farting out.

In 1972 the science of vented enclosures was in its infancy.

The cab could be as late as 1975, speakers are original.
I'll open it up later to see if there are any ratings on em.

I see.

[billfitzmaurice]

Originally Posted by Luckie

The cab could be as late as 1975, speakers are original.
I'll open it up later to see if there are any ratings on em.

I see.

Drivers do not have their displacement printed on them. The EV of that period, the SRO18, didn't even list excursion on the engineering data sheet, though it did specify a 100 watt voice coil. The DL18X of the mid 80s required 7 cubic feet of net cabinet size per driver for best results.

[JimmyM]

it's a 218 cab from the 70's, back when they didn't really put out any serious volume like now. it's to be expected.