Speakerplans.com Homepage
Forum Home Forum Home > General > Newbie Discussion
  New Posts New Posts RSS Feed - Electrical Impedance Max?
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

Electrical Impedance Max?

 Post Reply Post Reply
Author
Message
KaphaSound View Drop Down
Registered User
Registered User


Joined: 22 July 2020
Status: Offline
Points: 102
Post Options Post Options   Thanks (0) Thanks(0)   Quote KaphaSound Quote  Post ReplyReply Direct Link To This Post Topic: Electrical Impedance Max?
    Posted: 17 November 2021 at 1:36pm
Is there a problem with too much electrical impedance? From what I understand the higher the impedance the greater the efficiency, but according to hornresp the current design I’m planning is topping out at around 90 ohms or so which seems fairly high relative to some other hornresp plots I’ve seen.
Back to Top
toastyghost View Drop Down
The 10,000 Points Club
The 10,000 Points Club
Avatar

Joined: 09 January 2007
Location: Manchester
Status: Offline
Points: 10920
Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 17 November 2021 at 6:23pm
Speaking generally, the higher the value for electrical impedance, the less current is drawn for a given applied voltage. Whether that is related to efficient output depends on the corresponding sound power output at the same frequency.

Large, relatively narrow peaks of electrical impedance versus frequency are normal and will indicate the resonant frequencies of the driver and enclosure. For example, you’ll observe a peak at the port tuning frequency for a reflex or ported enclosure.

What type of enclosure are you trying to model? That sort of value suggests that you’ve made a typo somewhere if it’s the nominal or average value across the frequency range of interest.
Back to Top
DMorison View Drop Down
Old Croc
Old Croc


Joined: 14 March 2007
Location: Aberdeen
Status: Offline
Points: 1647
Post Options Post Options   Thanks (0) Thanks(0)   Quote DMorison Quote  Post ReplyReply Direct Link To This Post Posted: 17 November 2021 at 8:23pm
Originally posted by toastyghost toastyghost wrote:


Large, relatively narrow peaks of electrical impedance versus frequency are normal and will indicate the resonant frequencies of the driver and enclosure. For example, you’ll observe a peak at either side of the port tuning frequency for a reflex or ported enclosure.

Sorry to call you out, but, slight brain fart here no?
Back to Top
toastyghost View Drop Down
The 10,000 Points Club
The 10,000 Points Club
Avatar

Joined: 09 January 2007
Location: Manchester
Status: Offline
Points: 10920
Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 17 November 2021 at 11:02pm
Originally posted by DMorison DMorison wrote:

Originally posted by toastyghost toastyghost wrote:


Large, relatively narrow peaks of electrical impedance versus frequency are normal and will indicate the resonant frequencies of the driver and enclosure. For example, you’ll observe a peak at either side of the port tuning frequency for a reflex or ported enclosure.


Sorry to call you out, but, slight brain fart here no?


Well caught, thanks! Too many days of poor sleep on the trot the peaks are however the resonant frequency for the transducer alone, or the sealed enclosure, which is apparently where my brain went but my fingers didn't follow...
Back to Top
fatfreddiescat View Drop Down
Young Croc
Young Croc
Avatar

Joined: 15 October 2010
Location: N.E.Wales
Status: Offline
Points: 1081
Post Options Post Options   Thanks (0) Thanks(0)   Quote fatfreddiescat Quote  Post ReplyReply Direct Link To This Post Posted: 18 November 2021 at 9:16am
The max impednce is not an issue to be concerned with, just means less current will flow and therefore less power is dissipated by the VC. 
In hornresponse you can look at the phase angle of the impedance graph which can be of concern for linear class amplifiers ( class A, AB, B, G, H).
For a phase angle of 90 deg, no power will be dissipated by the load but all the power will be dissipated by the output transistors of the linear amplifier, loudspeakers don't ever present a 90 deg reactive load but it is worth looking at the phase angles, as this can give you an indication of how tough a load it will be and whether your amps are going to be behaving like space heaters.
Class D on the otherhand can have a trick up it's sleeve whereby instead of dumping the power accross the output transistors it is largely returned to the power supply capacitors so works out to be far more efficient and doesn't cook the amplifier.




Back to Top
KaphaSound View Drop Down
Registered User
Registered User


Joined: 22 July 2020
Status: Offline
Points: 102
Post Options Post Options   Thanks (0) Thanks(0)   Quote KaphaSound Quote  Post ReplyReply Direct Link To This Post Posted: 18 November 2021 at 9:53am
Thanks for the quick replies! It’s a fairly simple FLH design and only the highest narrow peak hits about 86ohms so not nominal, I’ve just seen folks ask for the electrical impedance plot on other designs and was curious what info you can really extract from the plot or really if there’s anything that would distinctly look off i.e peaks that are too high.

Edited by KaphaSound - 18 November 2021 at 9:55am
Back to Top
snowflake View Drop Down
Old Croc
Old Croc


Joined: 29 December 2004
Location: Bristol
Status: Offline
Points: 3118
Post Options Post Options   Thanks (0) Thanks(0)   Quote snowflake Quote  Post ReplyReply Direct Link To This Post Posted: 18 November 2021 at 10:40am
for a FLH with a given nominal impedance the conditions for maximum efficiency and maximum sensitivity are different. Have a look at the Marshall Leach paper.
Back to Top
fatfreddiescat View Drop Down
Young Croc
Young Croc
Avatar

Joined: 15 October 2010
Location: N.E.Wales
Status: Offline
Points: 1081
Post Options Post Options   Thanks (0) Thanks(0)   Quote fatfreddiescat Quote  Post ReplyReply Direct Link To This Post Posted: 18 November 2021 at 11:33am
A single impedance peak of 90 Ohm's shouldn't be a problem for any decent amplifier, can be more of a challenge if using 6th order bandpass where there are three distinct peaks and the usable bandwith is almost entirely centered on the area where the impedance is rapidly changing. 
When I changed from using 6th order bandpass to ported horns with some Fane 15XB's many years ago, the amps ran a lot cooler.
For a horn system I wouldn't lose any sleep over it.
Back to Top
toastyghost View Drop Down
The 10,000 Points Club
The 10,000 Points Club
Avatar

Joined: 09 January 2007
Location: Manchester
Status: Offline
Points: 10920
Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 18 November 2021 at 6:15pm
A narrow peak of a high value is fine; you’ll find that this is where the predicted values in the model might not be as ‘extreme’ in reality - Hornresp is using a model based on an axisymmetric, circular horn of infinitely rigid material, for example, which I assume isn’t what you’ll build…

That’s an important factor to consider when folding and building the predicted horn. Check the ‘advanced center line method’ for a good rule of thumb to follow when doing that. If you can’t use CAD tools, a pencil, paper, scissors, and string can be useful for that!

With a front-loaded horn, one thing to watch for is where the impedance minima falls between the resonant peaks. If designed for maximum efficiency and a suitable high pass filter is used, FLH designs are typically thermally limited way before excursion becomes an issue - getting heat out of the rear chamber or away from the throat may be a problem, especially if the chamber is small or the horn length is short.

Since a relatively broad region of low impedance will require much more current, and therefore heat buildup, it could be an issue if this region sits across the frequencies making up the dominant note or fundamental of the music’s bass. There are ways to mitigate this in the design, but they all come with their own compromises and limitations.
Back to Top
 Post Reply Post Reply

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.06
Copyright ©2001-2023 Web Wiz Ltd.

This page was generated in 0.125 seconds.