# Question for the technically minded..

Discussion in 'Amps and Cabs [BG]' started by david_l_perry, Sep 15, 2003.

1. ### david_l_perry

Feb 3, 2003
Chorley, Preston UK
Horn Impedance
Question for the technical minded guys...
why does the Impedance of a high frequency Horn in a bass cab not effect the overall resistance of the cab..?

ie a 2x10 4ohm cab (2 8ohm 10" drivers) have the same 8ohm horn as an 8ohm 4x10 cab and the same 8ohm horn as a 4ohm 6x10..?

Any takers ?

2. ### pbdCommercial User

Jul 17, 2003
Metro Detroit
owner Procables N Sound
When multiple drivers are used in one cabinet they often will be wired series/parallel. 4 8 ohm speakers could equal 8 ohms by tying each pair together in series (making 16 ohm) then tying the two pairs in parallel bringing it back to 8 ohm. using this math you can figure the wiring that must be going on.

3. ### Eric Moesle

Sep 21, 2001
Columbus OH
Why did you ask this same question in two differently named threads???

4. ### fretlessrock

Aug 8, 2002
Connecticut
High freq horns are typically fed by the output side of a crossover network and the crossover does not necessarily show the impedance of the drivers on the output side. So, you can have a complex network on the output side and the crossover network can still show the source a normal impedance.

It is similar to the way that you have to calculate the power distribution of a network of speakers based on impedance. You will have a variable impedance and power distribution at the input as you sweep frequency across it and power is applied to various drivers.

That is one reason why crossovers need to be designed based on the actual parts in use, hopefully with the aid of a network analyzer, and not just by throwing a few inductors and caps together because it worked for someone else's design.

5. ### Joris

You're not making even the least bit of sense to me as a professional engineer and long time speaker builder. Where did you get all this nonsense?

6. ### McHack

Jul 29, 2003
Central Ohio!
Perhaps he meant Impotence,, as opposed to Impedence.?

7. ### BillyB_from_LZ

Sep 7, 2000
Chicago
Come on Joris, tell us how you really feel?

A woofer's impedance at high frequencies is quite a bit higher than its nominal impedance (example 8 ohms).

If a horn's nominal impedance is say 8 ohms at 5 Khz, then it will be the lowest impedance unit in the cab at that frequency (and would then have the greatest influence on the cabinet's impedance in the upper ranges). I've never seen a horn's impedance curve to know if they are in the 8/16 ohm range at high frequencies.

Most of an amp's power output goes to produce low frequencies though and the load on the amp at highter frequencies is less critical.

8. ### pbdCommercial User

Jul 17, 2003
Metro Detroit
owner Procables N Sound
I'm with you fretlessrock. it sounds like your saying your crossover should match your speakers spec's for the best optimal sound. When checking impedance of a cabinet you will pick up the crossover as well as/instead of the individual speakers so this will not give you an accurate reading.

9. ### fretlessrock

Aug 8, 2002
Connecticut
Hi Joris, your classy and informative response was incredibly helpful to all. Thanks for spending so much time on clearing up the confusion.

I stand by my assertion that the impedance seen at the input to a crossover is not the same as the impedance seen if those drivers were paralleled without a crossover.

The power delivered to the various components is also not governed by impedance ratio but by the crossover points.

Maybe I'm wrong. Please feel free to use your lifelong experience as an engineer to tell us how and we will all be better off.

Pete

10. ### Mark Reccord

What I said in the other thread:

At low frequencies the amp only "sees" the impedance of the woofer because the components in the crossover make the horn seem like an open circuit in parallel with the woofer. Actually it appears as an impedance that increases as frequency increases away from the crossover point. At high frequencies the opposite happens. And in between it's a combination of both and the math gets very complex. The impedance quoted in specs is the nominal impedance averaged over the frequency range of the cab.

11. ### Joris

Mark nails it on the head.

Now wait a minute. My response was indeed not helpful at all to the thread, but only served to inform you of the fact that you described a pretty simple electronic building block in a too elaborate and messy way. Most of the information you supplied was over the head of the original poster (from what I gathered), and even if this was not the case, your post wasn't the least bit clear on what you meant, because half of it is wrong. And I did all that to prevent half-true information from spreading. And yes, that makes me right. No matter how you twist it.

These impedances DO get in the way, even if they are not constants. Woofers do tend to increase their imp. at higher frequencies, but not nearly enough to keep the total imp. at a safe value. A tweeter has its nominal imp. at high frequencies, and a low impedance at low frequencies. Even lower than woofers. It'll fuse without a crossover.

If I'm not mistaken, a reduced load impedance of an amp at higher frequencies could lead to oscillations and destroy the tweeter.

12. ### throbbinnut

Don't a lot of cabs use those horrid Piezo tweeters which are basically akin to a capacitor? This would mean it had a large impedance at low frequencies and a lower impedance at high frequencies. Some of those advertise that they don't need a crossover.

Since I can't stand tweeters on a bass cabinet, I'm not intimately familiar with them so I could be wrong.

Chris

13. ### david_l_perry

Feb 3, 2003
Chorley, Preston UK
Cheers Mark, Joris
Informative and very usefull replies

Solves the mystery

Dave

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