Speaker Cabinet design: Interpreting Thiele-Small data, using sofware, and tuning

[Justin Thomas]

I would expect the lab technicians to know, understand, and work within their gear's design parameters. Musicians? You give us way too much credit. "Well, that tube plugged in to that socket, so, what's the problem again?"

Certain product lines should be manufactured with an understanding that they will be subjected to a lot of misuse and a certain amount of abuse. Hand tools, guitar amps... of course, said contingency planning comes at a price, which practically no one is willing to pay. Just my way of thinking.

Anyway, should we get back to the actual point of the thread now?

Justin

[The Dude]

I sort of understand what you're saying, but I'm not sure I agree- and I'm not trying to pick a fight.

I know it's not real world, but someone who uses gear for a living or even a "consistent hobbyist" should be expected to know better. It's not unreasonable to expect them to read the user manual for something they make a living with (even though I'm sure many don't).

e.g. - I didn't change or check my oil for 50,000 miles and my car blew up. What a poorly designed POS.

As to the original topic: Many have hinted very judiciously. I'll just say it. TSP is mostly useless data for building a guitar cabinet. A bass guitar cabinet where low frequency is important, yes. The specs are valuable for speaker comparison. Flame on.

[Justin Thomas]

No fight picked! I understand your expectations, and I share them. Maybe I'm letting the worst of the worst guide my build philosophies, because I can't afford to fend off the lawyers when Mr. Dumbis blows up his amp... you are probably also dealing with some higher-caliber folks... I usually get the "this is my first amp..."

Hey, I blew up MY share of quality stuff, and I read the manuals. Basic human instinct: "what's the worst that can happen?"

All in good fun.

Justin

[bob p]

As an aside, I don't see this as a problem with Class D amps any more so than solid state amps of any other class. Misuse of any product outside it's design specs is a user problem- not a design problem.

I see Class D amps failing when they get abused with silly loads. That they are more sensitive to load Z doesn't mean they have a design flaw, the problem is with users not understanding the equipment. Maybe the users are smarter where you are, but around here they don't worry too much about Z matching and they tend to burn up a lot of gear.

"It worked fine at rehearsal but it died when I dimed it into extra cabs at the gig."

[bob p]

I'll be gigging this weekend with a stock Bugera v22 (badge removed, lol!) and a Weber attenuator with a mic on it. I get no complaints and I can lift it (sometimes, lol).

That V22 is a heavy little amp for what it is. A large part of it's weight is the damned MDF cabinet. If the amp were any heavier, like a 2x12 30 watter, I'd consider separating the chassis into a separate cab, and rebuilding a cab out of lighter material. I really hate the weight factor that MDF adds to an amp. Which reminds me -- How's your rehab going? Do you still have a weight restriction?

[J M Fahey]

Oh, you can make a new way lighter cabinet out of 15 mm plywood.
No need to Tolex it, add corner caps, nothing fancy.
Just slightly round edges and corners with a rubber disk sander and paint it with marine grade varnish.
Will look nice and stand a lot of abuse.

[olddawg]

That V22 is a heavy little amp for what it is. A large part of it's weight is the damned MDF cabinet. If the amp were any heavier, like a 2x12 30 watter, I'd consider separating the chassis into a separate cab, and rebuilding a cab out of lighter material. I really hate the weight factor that MDF adds to an amp. Which reminds me -- How's your rehab going? Do you still have a weight restriction?

Thanks for asking. Yeah I have restrictions. I'm not supposed to lift over 15lbs for a year. Mostly because of the meds. I go to Cardio Rehab 3 times a week too. Yeah that V22 IS heavy for what it is. There was a guy that was making Baltic birch ply replacement cabs for them that cost more than the amp! Lol! Go figure. Luckily my band wanted me back bad enough to load my gear. I'm very lucky. Seems that after 3 stents and the whole ordeal I only lost 5% heart function. I'm still on the "normal" bell curve even. Low normal but still!

[Enzo]

My cardiologist told me not to lift anything heavy, so now I have to sit down to pee.



Stay out of the hospital dawg, the cardio food sucks.

[The Dude]

My cardiologist told me not to lift anything heavy, so now I have to sit down to pee.......

[olddawg]

My cardiologist told me not to lift anything heavy, so now I have to sit down to pee.



Stay out of the hospital dawg, the cardio food sucks.

They had my BP so low with the wrong meds that I was passing out on the toilet for a couple of weeks. But yeah my whole diet and lifestyle has changed. People don't get why I no longer do shots. You hang in there Enzo. Your knowledge and advice is golden.

[Enzo]

Oh I hear you, you have my sincere best wishes. I was on a bunch of meds for various things, and a bunch of them had the side effect of lowering BP. Trouble is they almost made it go away. I remember at one point it was like 53/44. Standing up was a three step process: stand up bowed, then torso to 45 degrees, then stand erect. Otherwise I'd faint. I remember having to lie over the counter at work sometimes when walking about. Re did my med array and BP is now reasonable. I don't know if you do oxygen, but I had to tow a bottle of that around for quite a while too. Now I use a concentrator and only now and then while sleeping now.

Do the rehab, get better.

[Gingertube]

Cautions:
As stated above, with ported enclosures, the mechanical damping of the speakers disappears at and below the port tuning frequency. That is not too much of an issue with high damping factor, down to very low frequencies, of a SS Amp but is an issue for low damping factor tube amps. So loose tune only, broad (in frequency) small peak.

When you have the option always wire 2 speakers in parallel rather than series, that way they aid in electrically damping their companion.

Cheers,
Ian

[Malcolm Irving]

...
When you have the option always wire 2 speakers in parallel rather than series, that way they aid in electrically damping their companion. ...

Two 8 ohm speakers in parallel would certainly have better damping than two 8 ohm speakers in series.
But comparing two 4 ohm speakers in series, against two 16 ohm speakers in parallel? I think the damping would be the same.

EDIT: the more I think about this - the less confident I am about either of these statements! But I'll leave them there to see if it sparks any discussion.
To really get to the bottom of damping, we need to look at the total X/R ratio of the circuit, as seen by an oscillating back e.m.f. at each speaker. We could assume that the conditions at each speaker are the same (i.e. the same oscillating e.m.f. is present at each speaker). It gets complicated because the reactance of the speaker (at low frequency near the resonance) is a mechanical effect rather than an electrical one.

[Mike Sulzer]

Two 8 ohm speakers in parallel would certainly have better damping than two 8 ohm speakers in series.
But comparing two 4 ohm speakers in series, against two 16 ohm speakers in parallel? I think the damping would be the same.

EDIT: the more I think about this - the less confident I am about either of these statements! But I'll leave them there to see if it sparks any discussion.
To really get to the bottom of damping, we need to look at the total X/R ratio of the circuit, as seen by an oscillating back e.m.f. at each speaker. We could assume that the conditions at each speaker are the same (i.e. the same oscillating e.m.f. is present at each speaker).

Assume identical speakers boxed the same way, or if in the same box, it is designed so that each sees the same air load with both operating as if in the single cabinet.

Two 8 ohm speakers in parallel driven from the 4 ohm tap of a tube amp output transformer damp in a certain way. Two 8 ohm speakers connected in series connected to the 16 ohm tap damp in the same way because the voltage across and the current through each speaker is the same in both cases.

If you use an SS amp with a very low output impedance, the speaker resistance is the electrical limit on the damping. (It is a significant factor with tubes, too) One speaker sees a voltage source; two in parallel see a voltage source. The combination in series sees the voltage source. Make the voltage from the amp twice as high, and each speaker sees the same voltage across it and current through it as if it were used alone with the original voltage. Thus the same thing is happening and the damping is the same.

[Gingertube]

Parallel Connection:
Looking away from each of the parallel connected speakers you see the output impedance of the amp in parallel with the other speakers impedance.

Series Connection:
Looking away from each of the speakers you see the output impedance of the amp in series with the other speaker impedance.

I haven't been convinced to change my mind.
Cheers,
Ian