Electrical Impedance Max? |
Post Reply |
Author | ||
KaphaSound
Registered User Joined: 22 July 2020 Status: Offline Points: 102 |
Post Options
Thanks(0)
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.
|
||
toastyghost
The 10,000 Points Club Joined: 09 January 2007 Location: Manchester Status: Offline Points: 10920 |
Post Options
Thanks(0)
|
|
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. |
||
DMorison
Old Croc Joined: 14 March 2007 Location: Aberdeen Status: Offline Points: 1647 |
Post Options
Thanks(0)
|
|
Sorry to call you out, but, slight brain fart here no?
|
||
toastyghost
The 10,000 Points Club Joined: 09 January 2007 Location: Manchester Status: Offline Points: 10920 |
Post Options
Thanks(0)
|
|
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... |
||
fatfreddiescat
Young Croc Joined: 15 October 2010 Location: N.E.Wales Status: Offline Points: 1081 |
Post Options
Thanks(0)
|
|
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. |
||
KaphaSound
Registered User Joined: 22 July 2020 Status: Offline Points: 102 |
Post Options
Thanks(0)
|
|
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 |
||
snowflake
Old Croc Joined: 29 December 2004 Location: Bristol Status: Offline Points: 3118 |
Post Options
Thanks(0)
|
|
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.
|
||
fatfreddiescat
Young Croc Joined: 15 October 2010 Location: N.E.Wales Status: Offline Points: 1081 |
Post Options
Thanks(0)
|
|
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. |
||
toastyghost
The 10,000 Points Club Joined: 09 January 2007 Location: Manchester Status: Offline Points: 10920 |
Post Options
Thanks(0)
|
|
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. |
||
Post Reply | |
Tweet |
Forum Jump | Forum Permissions You cannot post new topics in this forum You cannot reply to topics in this forum You cannot delete your posts in this forum You cannot edit your posts in this forum You cannot create polls in this forum You cannot vote in polls in this forum |