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DevilDriver

Understanding Power Compression

14 posts in this topic

Power compression is a topic that is rarely discussed, but always important. When you hear someone call various theile/small parameters a

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To very briefly expand on a thought:

BL Compression is the least resolved issue. Cms compression has been something understood very well for quite some time; things like wide roll surrounds and various spider designs have made Cms compression a relatively solvable issue. BL compression is still a big problem. There are treatments out there that intend to resolve this issue (split coil, XBL^2, and LMT), but each has their own inherent issues. One thing often forget by those who are big fans of certain designs is that there is no free lunch in engineering. To name a couple, XBL^2 sacrifices BL and efficiency, split coil suffers from significant flux modulation and inductance issues, and LMT suffers from high Mms, high inductance, flux modulation, and generally poor transient response.

Speaker engineering is often about making the most appropriate compromise, rather than trying to avoid compromise at all; you'll find the second route very challenging. ;)

Edited by DevilDriver
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When power is applied to the voice coil, the metal becomes hotter, and resistance increases.

How is this measured? I know it happens. I am just curious. It seems to be logical to assume this increase in resistance would be linear to some degree. The measurement of 200deg C will double the resistance and result in a 3db loss in acoustical output is an great example. This also makes me wonder about different coil compositions and what implications said variable would have on not only to the rise itself but the equation used to measure and/or estimate the rate and amount of change.

Edit: I just went through the Pinned explaination of how to measure impedance rise. I posted too soon. :)

Edited by Chris
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One more quick question. What is "split coil" and what is its function?

Great read!

I am working on a detailed explanation of the different BL technologies and their respective advantages/disadvantages. I will try to get that up by next weekend.

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One more quick question. What is "split coil" and what is its function?

Great read!

I am working on a detailed explanation of the different BL technologies and their respective advantages/disadvantages. I will try to get that up by next weekend.

Awesome. I look forward to it. Thank you for taking your time to share this information with everyone.

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One more quick question. What is "split coil" and what is its function?

Great read!

I am working on a detailed explanation of the different BL technologies and their respective advantages/disadvantages. I will try to get that up by next weekend.

Awesome. I look forward to it. Thank you for taking your time to share this information with everyone.

No problem. Big thanks to you and those who reply. It makes things more gratifying and is also conducive to expanding on each topic.

Greatly appreciated guys!

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very nice read bro!

like chris mentioned, it's awesome to learn things in a hobby one loves, and in my case, provides my income as well.

also, how does one build a box around these things? i've heard of building a box twords a specific imedence rise, or one that controls it, so that you stay at or around the impedence your amplifiers crave. this is for competition purposes of course. i mean, is it just trial and error in playing with box volume? or can a decent program, like bb6p, actually forecast this with reliable accuracy?

wheeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee :slayer:

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To me the concerns over BL and CMS power compression are limited to high excursion (20mm+) woofers. Even then, to achieve such extreme throw most designs require a large box or lots of power - most of the time well over 500W - to approach Xmax. A typical 4" coil (pro audio) can see over 3db of power compression at less than 500W (pink noise - low crest factor) without exceeding 1/2 Xmax. "Car subs" which are long-throw dont use 4" coils, but do have much more magnet area and most likely exhibit the same levels of power compression. Now, when we look at midbass, midrange, and tweeters we are also much more concerned over thermal power compression as well as they usually dont reach Xmax very often.

BL and CMS linearity are much more important in limiting distortion. As was stated above, at any frequency, the coil is shuffling through the gap many, many times a second and non-linearities in BL and CMS show up as distortion products.

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I had never really heard of this topic until today via one of audioholic's posts. I did a google search and this article came up, but on s10forum.com. I thought to myself, wow, that's a pretty in depth topic for an s10 forum, but then I saw the author and did a quick search here. Awesome writeup as always, DD. =)

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