Accidentialy got great bass from tiny speaker, how to scale?

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My all time dream is to build a portable speaker, which will be tiny, but have a great bass and overall sound, just like B&O's Beoplay A2 and others. I've tried many designs, but so far, had no luck, but couple days ago, I was playing with some components and have built a speaker, which has mega impressive deep bass - comparable to bass of much larger and heavier systems (of course not so loud, but still deep). It consists of 80mm speaker, which was removed from an old plasma tv - it was included in it's chamber, with tiny port on the side. The speaker is glued hermetically to short piece of carton tube, at another end of which, I've glued 80mm passive radiator from Logicool speakers (Japanese sub-brand of Logitech). It had decent sound for it's size - the bass level was on par with good quality bluetooth speakers of the same dimensions. Just for curiosity, I've attached remaining carton tube to the passive radiator side of the speaker and miracle happened - I've got very well defined, nicely articulated and deep bass. It is so great and deep, that when people come to my room and see this speaker on the table, they immediately start seeking subwoofer - they can't believe this speaker has that deep bass. I've created an non-scale drawing to better illustrate what I've designed. As I have understood, I've "designed" bandpass system with passive radiator. For the curiosity, I've tried attaching that longer tube to front of the speaker - no results, sound like drain pipe. Gluing tube together and moving passive radiator to the end - there was some bass, but way less than with shown config.

And now I have two questions:

1. I've managed to fry the speaker, by applying too much power to it. While I do have another one (from another channel of that tv), I would like to get some replacement, so that nice bass effect was due to characteristics of that speaker, or more likely to be enclosure design benefits?

2. Is it possible to shorten that long length part, but to still maintain the bass deepness? I want to make it portable, and at that length, it looks more like MANPADs, not the speaker :)

Thanks in advance!


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I would reckon that resonances in the 500mm long tube are emphasising certain lower frequencies to give a result which is subjectively pleasing to you.

Experimenting with that length may be worthwhile, but you may have already accidently hit on the sweet spot.

The enclosure and the speaker are obviously working together symbiotically, so changing either will change the audible result.

Happy experimenting!
There is an easiest solution. Download any tone generator for PC (I have one called SinGen), and inject the output of the PC audio card to the speaker via a suitable amp. From very high frequency, start to increase it until the output (audible) of the speaker becomes humped. This is where the speaker/tube is resonating. You may also put some particles of sand in the cone, and look which frequency the particles brinks with more amplitude (Height of the jumps).
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Do you have an iPad or an iPhone? Then it would be an easy task. For LF, you do not need anechoic. You can do nearfield measurement - place both the speaker and the phone on the floor, play some pink noise and use a slow spectrum analyzer on the iphone. There are free and paid programs. I think Sonic Tools was free.
What you have build looks like a TML with forechamber but with a passive radiator instead of the chamber. This most likely gives you an TML without the usual TML Problems like midrange resonances but will result in a high group delay.

For the response, I might be able to simulate it the day after tomorrow (Workstation is currently occupied with another workload and the setup takes time) an then we should be able to get a better look.
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