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Discussion in 'Amps and Cabs [BG]' started by TijlT, Jan 20, 2018.
1/(1/R1 +1/R2 etc) = R parallel.
Which is good enough for an amp that likes 4 ohms.
Now we're getting somewhere!
Or R1 X R2 / R1 + R2. Easier formula for two drivers that sometimes you can just do in your head bones.
I think that only work if you were born with 4, 8, or 16 fingers.
Or working with 10 ohm speakers. Which I happen to have a bunch of for some strange reason.
5.3 ohms is close enough to call it a nominal 4 ohms. What's important is the level match and power match.
And here I am!
Tomorrow I'll be able to test it out!
Although I have a question about the impedance at the bottom of this post.
From start to finish..
So I used for this a plug and play jack plate.
Because it did what I wanted and I didn't had to struggle with solder.
It also gives me the possibility to use the cab at 4ohm or 16ohm or 2 times 8ohm.
I installed the two BP102 8ohm's which gives me 4,2ohm which is perfect! But for the 16ohm input I get 17,8 and the 8's are 6,5. Now I wonder if the 16 and 8ohms inputs will work that way? Can an amp be used at 17,8ohm when 16 is ment?
The 2x8ohm isn't that important to me but interesting to know if things will start to melt when I use them.
Wait a minute, are you trying to run the 210's in series with the 115 for a 16 ohm load? If so, I would not recommend it. The electro-mechanical parameters will fight each other, series connections work MUCH better with identical drivers. The reason why parallel connection (or dual mono of you have a 2 channel amp) works best is because the low output impedance of the amp dominates the impedance equations.
Also, if the dual mono (8 ohm + 8 ohm) jacks are not FULLY isolated (including the sleeve terminal) from each other, you can destroy a bridged amp (including many class D amps that are internally bridged). This is an example of a feature that can get in the way of a safe product.
Okay! Then lets not do that!
btw it has now the 2 BP102 8ohm's in it. I'll test it out tomorrow and I might try it again with the two BP102 4ohm's in it instead. Unless there is a reason why I shouldn't try.
I would wire the two 8 ohm BP-102's in series, and then parallel those with the 8 ohm 15. I think that will get you the best natural matching of sensitivity. Eliminate all of the impedance switching connections from the jack plate, just one or two jacks wired together (parallel) with the tip going to the + of the 10" pair and the + of the 15" driver, the sleeve going to the - of the 10" pair and the - oft he 15" driver. There will of course be the series connection wire between the remaining + and - terminals of the 10" pair. This has the highest chance of getting close.
You COULD use the 4 ohm pair in series (in place of the 8 ohm pair) but I think that would make the 10's too prominent in the blend of the cabinet. You certainly wouldn't want to parallel the 10" pair in either case.
When you measure the resistance of a voice coil with an ohm meter, you will usually see something smaller than the rated nominal impedance. It seems to usually fall between 3/4 and 7/8 of the rating IME, but there is no hard and fast rule. The voice coil is not a resistor, but it has resistance. The nominal impedance (4 Ohm, 8 Ohm, 16 Ohm) is a specification by the manufacturer and refers to impedance (resistance of AC) and not resistance (resistance to AC or DC). I've seen 8 Ohm rated speakers measure as low as 5 Ohms. When you measure multiple speakers in series or parallel, or even worse series AND parallel, the error in reading seems to stack up to an even larger error. In other words, don't worry Go by the ratings and the math. Impedance varies with frequency and most of the time the amp is going to see something above the nominal. DC reading is the absolute minimum @ 0 Hz... in other words DC.
Or, take the high road, the easier route and just wire up as Andy said above
Was the 2nd BP102 easy to find there?
So I tried the cab yesterday with the 8ohm's and turned the Ashdown EVO III 500W amp at half the power. I can already say that the over-excursion problem is now fixed and delivers an impressive good sound! It now sounds like it should! Thank you!!!! I'll try the same tonight with the 4ohms.
But another question. You said "This has the most likelihood of sounding pretty good, and has a real world power handling of around 250-maybe even 300 watts "RMS". Just be sure you wire the series pair correctly, positive of one driver to the negative of the other." I don't get it. What do you mean with this? Or better, what does this mean when using the cab with the Ampeg SVT Classic 300W tube amp?
Series wiring is just as described...the positive of one speaker goes to the negative of the other. The remaining 2 terminals (one positive and one negative) are your speaker outputs.
Actually I was more talking about the watts I understand speaker wiring but thanks for the help!
The series wiring is necessary for power & sensitivity balance with the 15" driver.
Yes but the 250-300 watt? Or were you talking about the BP102's only?
Talking about the real world balance between the 10's and 15.
and total cab power handling if I am not mistaken.
Trying it with the 4 ohm ones would not raise power handling because the 15 would get overpowered before the tens.
Okay I need your help again guys.
I tested the cab with the 8ohm's in my rehearsal room which is quite a solid shed and it sounded great!
I tried it with the 4ohm to and that's indeed a no go! The over excursion was back. Less than before but very noticeable!
I placed the 8ohm back and then I decided the cab was fixed. Based on a test with the Ampeg SVT Classic with gain on 5 and master volume at 4,5. Quite loud!
Then I went try it in a studio where the room sounds perfect and now all of a sudden the 15" has over excursion!? I remember @agedhorse told me I could use the LF version of the Delta 15. Could this be the problem? The studio guy and me noticed the 15 sounds less 'good' when you hit the lowest sounding string of the bass guitar.
Also there is a constant humm in the 15!
To clarify, are you using the Delta 15a or the LF version?
If using the 15A, you will still be power limited on the 15 to about 150 watts but it will sound good up to that point. Also, the power handling falls pretty quickly below about 60Hz.
At this moment I'm still using the 15A. Not the LF version. Should I use the LF version?