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How to get more boomy bass?
How to get more boomy bass?
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Old 7th November 2019, 02:09 PM   #1
Igla is offline Igla  Slovenia
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Join Date: Jun 2003
Location: Slovenia
Default How to get more boomy bass?


I have a specific problem I can't solve or find anything usefull on Google.
The thing is I built a floorstanding boombox for my daughter.
Internal volume of the box is 55 liters (about 1.94 cubic feet) and it has 2 bass reflex ports at the back with internal diameter of 72 milimeters (about 2.94 inches).
I only put polyester damping sheets (1/2 inch thick) on back and bottom panel. This gives me the bass response I like.
The drivers are about 40 years old and I don't have any data except impedance and rated power (two 8'' woofers 50W/4ohm ; two mids 30W/8ohm). Mid drivers go high enough to also serve as tweeters.
We can say I just placed ''two loudspeakers in one box''. The amp is Lepy amp and the source is bluetooth module.
I will attach the photo later but just imagine two mid drivers at the top of the box and two 8'' woofers below. One mid and one woofer on left channel and the second mid and woofer on right channel. Below is quick drawing of crossover.
I don't have any measuring equipment and no drivers data to simulate the response so all tuning was done only by ears.
I'm used to the sound of my system but this boombox sounds good; perhaps too good for a boombox and old cheap drivers. It has the sound I usually like: rounded and reasonable deep bass, slightly recessed mids and nice hights. I can sit there and just enjoy the music.

So; where is the problem?
Well; my daughter (as all teenagers I suppose) does not care about transient response and micro details in bass response. All she wants is boomy, fat and punchy bass so in her dictionary ''only big and fat bass is good bass''. As big as it gets.

I can increase bass with tone controls on the amp or I can lower the mids and hights with crossover to virtually increase the bass. I could also do baffle step filter to increase the bass response but I would like to start with the tuning of the box.
I would like to tune the box in that way I could get as much bass as I can with this setup. I tuned the bass reflex ports by ears I cut PVC pipes much longer then shorten them centimeter by centimeter and listened till I got the biggest bass I could.

Is there any other way to make this box to sound more boomy? If I understand correctly I would need to increase Q factor of the box/system. Correct?
How you do that?

Thanks for the answer;
Attached Images
File Type: jpg Crossover.jpg (87.8 KB, 387 views)
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Old 7th November 2019, 03:52 PM   #2
seedlings is offline seedlings  United States
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Given a 1.94 ft3 box with two 3” ports

ROUGH calculations
8” tunes to 43Hz
4” tunes to 55Hz
0.5” tunes to 80Hz

If you want more boominess, triple the box size for a modest 6dB boost near port frequency. There is no magic. Probably just max out the bass EQ, or swap drivers.
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Old 7th November 2019, 03:58 PM   #3
impuls60 is offline impuls60  Norway
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Are you running a stereo signal in a mono box? Giving them their own volume might help giving more bass. If you add more loose dampening material the effective volume would get larger which would be in line with Seedlings recommendation.

Last edited by impuls60; 7th November 2019 at 04:00 PM.
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Old 7th November 2019, 04:07 PM   #4
phase_accurate is offline phase_accurate
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Shorten the port lenght and it will get boomy. Just try with a simulator to see what I mean.


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Old 7th November 2019, 05:38 PM   #5
ILikeFoodz is online now ILikeFoodz  United States
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I always thought smaller box volume tended to result in higher Q/boomier bass? I know this is true for sealed at least. For ported I would imagine a higher port resonance qould also be needed, so one would shorten the port length. Am I missing something here?

If I'm correct, then filling in part of the box volume with something rigid like sand (don't actually do this, sand in the driver motor is a bad thing...) or sealing off part of the box and then shortening the port should give your "desired" result
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Old 7th November 2019, 05:48 PM   #6
Lojzek is offline Lojzek  Croatia
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Shortening ports is the way to achieve the goal. I would immediately pull out the vent and first give it a try the baffle thickness acting as a vent. Might be satisfyingly boomy saving you from further work.
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Old 7th November 2019, 06:07 PM   #7
picowallspeaker is offline picowallspeaker  Italy
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More power from the amplifier
What else?

It's like learning sex during the Victorian era: you get to the wedding night and there are many things to do that you never imagined.
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Old 7th November 2019, 06:21 PM   #8
fatmarley is offline fatmarley  England
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Block one of the ports to see how that sounds.
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Old 7th November 2019, 06:23 PM   #9
fatmarley is offline fatmarley  England
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Old 7th November 2019, 08:06 PM   #10
Igla is offline Igla  Slovenia
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Location: Slovenia
Thanks for the answers.
I have attached a photo of my boombox. The loudspeaker is half finished. I need to finish a small box to put in power supply, amp and bluetooth module. It will sit on the top of the boombox.
I run left mid driver and upper woofer on left channel of the amp and right mid driver and the woofer at the bottom on right channel of the amp. This was the easiest way to connect the drivers with the amplifier I have available at the moment Lepy amp:
Lepai V3S Mini Hi-Fi Stereo Digital Amplifier Amp mp3 | eBay
I have tried one of my TPA3116 amps but Lepai runs those drivers better.

I have done lots of experiments:
First I lined all internal walls with loudspeaker insulation (white polyester sheets about 2 centimeters thick). I had a feeling like the insulation was sucking bass energy. The bass was there but like it was stucked in the box and didn't came out.
Then I started to remove the insulation piece by piece.The best results I get if the insulation is only on the back wall and at the bottom. This sounds much better and it lets the bass go out of the box.
I tried removing both BR tubes but the bass became weak and small. Then I tried one port - 6 centimeters length gives the best bass. But the box gives bigger bass with 2 tubes. I played with the length of tubes and it seems that with length of 16 centimeters I get the most bass the box can give. I will try again and shorten both tubes during weekend inch by inch and listen.

It could be this is the limit with those woofers and I can't do anything else with the box and the only thing I can do is to crank up the bass potentiometer on the amp. Perhaps I could decrease the volume of the box to see the effect.

I could get better woofers but this suppose to be a cheap project with what I have available at the moment in my working room.
Those woofers are from old loudspeakers made by Ei Nis (a company from former Yugoslavia) - I have attached a photo I found on internet - about 20 liters closed boxes with mediocre sound and weak bass. I don't have and I can't find no parameters of those old woofers so I can't do simulations.
Attached Images
File Type: jpg boombox.jpg (235.9 KB, 253 views)
File Type: jpg Ei_Nis.jpg (50.3 KB, 252 views)

Last edited by Igla; 7th November 2019 at 08:11 PM.
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