Originally Posted by goneten
It is all very well adding mass to lower Fs, but it also reduces efficiency. So you still need to add more power to get the same SPL as before you added the mass.
You've paraphrased my previous post pretty well! ;-)
More power = more heat = more chance for thermal compression whether you like it or not.
You must have flunked the thermodynamics part of your engineering program. [-), More heat doesn't necessarily mean higher temperatures. If that were true, power plant cooling towers would all glow like the sun. In reality they don't even get hot enough to boil water. It is all about how well the heat can be dissipated. A high efficiency speaker or a tweeter with low mass has fewer opportunities to dissipate heat. Thermal compression in the real world is more of a problem for tweeters than woofers, for that reason. Maybe you've never held the cone/voice coil assembly for a high efficiency woofer and compared it to what you find in low efficiency woofers. Because I have friends who rebuild speakers as a business, I have.
I know what it means and I never said Hoffman was related to equalisation, thermal compression or excursion.
Really? Your erroneous statements keep telling a different story.
It stands to reason that if you apply EQ boost that will cause woofer excursion to increase.
A good example of a half-truth. Of course boosting bass causes more excursion of a woofer cone, but you have to consider what the excursion of the cone was before you equalized it. The reason they equalize most small woofers to obtain flat response is because without the eq, the bass response would be falling off. Response falling off means excursion falling off. There is a target for excursion versus frequency versus SPL for a given diaphragm area that all direct radiator speakers regardless of box size or efficiency have to follow. To reiterate - it is possible to achieve this target a number of different ways. But, in the end the same target must be met regardless of how the speaker is built internally.
The port gives you a back door, but the port sacrifices bass extension in order to do its job. Bandpass speakers also sacrifice response extension, this time at high frequencies, in order to provide their other advantages. The law of conservation of energy is very rigid but their are situations where you trade off what you don't care about to get what you do care about.
All things being equal between two identical woofers, one in a large box and one in a small box the amount of power will differ to reach a given SPL and more EQ is needed in the smaller box.
Wrong, and this may surprise you. It is possible to have a woofer that would give flat response in a small box without eq. If you put the same driver into a large box, then it will not have flat response. You then have to equalize it to get flat response out of it in the big box. It will also be a poor performer from the standpoint of efficiency in the large box. So, the claim that the smaller box always
requires more equalization is false. I repeat, you can put a high mass speaker into a small box and obtain flat response without equalization. The origional Sunfire subwoofers were early examples of this approach, but I don't know if they went far enough to have truly flat response without equalization. They made some relatively new steps in that direction.
Based on our exchanges you give me the impression that you don't think a small box is without compromise and I don't agree with that at all.
All speakers are a big ball of compromises. I'll bet that you have not built or helped build as many large box speakers as I have. My first serous subwoofer used a Earthquake (and by this I mean one that was actually used for that circa 70s movie) subwoofer My driver was rebuilt, so I don't know the precise parameters of the original driver. At any rate its measured T/S parameters said put it into an 18 cubic foot vented box (the size of a fridge) and it will be flat down to 20 Hz. Independent measurements in opens paces say that is what happened. It was very efficient and blew me out of my living room (for my needs) with a 15 wpc power amp. I also have years of experience with a close friend who is into whole-house subwoofers. His current system has 5 Ficar 18 inchers, each with a 1250 wpc power amp driving it. It too is very efficient but he uses it to do things like 120 SPL at 10 Hz which is someplace I never went with my 18 cubic foot monster. At any rate, I have woked hands on with voicing it and tuning it so I know what sort of eq it needs.
Actually, what I find funny is that our exchanges began because you have a problem with my signature.
Wrong again. You chose something that has multiple reasonable meanings. You apparently don't want to take responsibility for your own choices and you aren't totally aware of the details of engineering subwoofers.
I think it's pretty obvious that displacement is the name of the game when discussing very low frequencies, but you don't seem to grasp that for some reason.
You must have reading comprehension problems because I've repeatedly said that large volume displacement is required for low frequency, high SPL response in this exchange of posts.
I've repeatedly pointed out that there is a fixed connection between displacement and LF response and SPL. You've been arguing that this is modified by the size of the box and that simply isn't true. If you don't get this by now then I should stop trying to talk to you because of your rather obvious learning-challenged status. ;-)
No matter, you are welcome to dissect every line of text if it makes you feel better.
You got a lot to learn kid, starting with reading comprehension. I guess that is why you didn't learn how subwoofers actually work from your previous readings. A little hands-on construction would help you, as well.