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Old 3rd April 2010, 05:08 PM   #1
sivrat is offline sivrat  South Africa
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Default Need some help with some bass

Hi guys,

I am busy building some speakers using a set of HIVI 6.8 and some old sony tweeters (till I can get something worth while) I am driving them through a chip amp (td2050).

I am tuning the port to 44 hz.

So far, they sound pretty good considering they are a mock up. The box is not sealed properly, nor is it padded.

However the bass response is not quite right. It seems a little low and requires as fair bit of EQ to get it up and then it seems to lack a bit of bottom end.

The port I am using is 50mm and 17.9mm long using the winISD calc.

Should I try a longer or shorter port?

I dont have any measuring equipment so I am using my ears at the moment.
Any advice?
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Old 4th April 2010, 10:52 AM   #2
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Interesting project. You don't mention the type of tweeter/impedance what is a big flaw, like so many other posters, when they ask questions. I assume that your woofer driver is this one
HiVi D6.8 6" Poly Bass/Midrange Shielded

There's this nice project with your driver and I assume you want to make one similar, what's your objections.
Totem Acoustic - Columns - Forest
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Old 4th April 2010, 12:52 PM   #3
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This driver HiVi D6.8 6" Poly Bass does not a very high SPL, more close to 82/83dB. With a different alignment you can get maybe more peaks, that's all, and have to adjust for living room. The ext. size is similar to the "Totem", with BR/Port on the same side as drivers, 38L/38Hz alignment. I did not check Xmax on this config. but should not be that bad.

You can use a L1 Air Core Coil (Erse type #EAC34-18-2000) on the woofer and a RLC circuit to smooth the woofer peak in parallel with L2 Laminated Core Coil (Erse type #ELC54-18-8500) and in place of C3 cap (3.70uF) you can use a (smaller only) 3.6uF cap that you can find.

This speaker X-over is using a Visaton (G 20 SC 8 OHM) tweeter with nominal impedance Z=8 Ohm (Rdc=4.8 Ohm). This his very important when changing your xover for your speakers because it all changes when using different drivers.
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Old 4th April 2010, 01:00 PM   #4
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Default 2-WAY X-over for HiVi D6.8 6in Poly Bass+Visaton G20SC-08

Woofer is at ~64cm from bottom of the baffle and tweeter at ~79cm, port at ~25cm all aligned in the middle of the front baffle. The drivers are also in phase from ~400Hz to 8000Hz, as you can see from graph#2, important for a good response and imaging (less nulls).

Last edited by Inductor; 4th April 2010 at 01:07 PM.
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Old 4th April 2010, 01:00 PM   #5
sivrat is offline sivrat  South Africa
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HI Inductor

The tweeter came out of a pair of old sony desktops.
they are 12ohm. They are used a simple cap for crossover and I have left them as is. I left out the info as the highs and mids all sound fine

I wired the pair in parrallel giving the a 4.8 ohm resistance. Low, I know, but for the levels I am playing the amp doesn't really seem to mind.

Also forgot to mention, the Box I am using is 14 liters.

Thanks for the response!

Travis
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Old 4th April 2010, 01:08 PM   #6
sivrat is offline sivrat  South Africa
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Utlimately, I want to bi-amp the system and use an active cross over, either via PC or build a linkwitz type... but that will come later

With regards to the bass response, I am guessing I got my port wrong. I am a complete beginner, so please forgive any holes in my logic, but the bass reflex should allow the driver to get a little further down into the bass freq's, which is what seems to be missing in my current config.


My main question really is how does having a port that is too long or too short affect the bass?
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Old 4th April 2010, 01:09 PM   #7
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Quote:
Originally Posted by sivrat View Post
HI Inductor

The tweeter came out of a pair of old sony desktops.
they are 12ohm. They are used a simple cap for crossover and I have left them as is. I left out the info as the highs and mids all sound fine

I wired the pair in parrallel giving the a 4.8 ohm resistance. Low, I know, but for the levels I am playing the amp doesn't really seem to mind.

Also forgot to mention, the Box I am using is 14 liters.

Thanks for the response!

Travis
That's all very important information that people usually don't bother writing. The box with 14L can change everything. I initially was trying to have a 1.order xover but it doesn't seem to work very well. I will look at it. Same X-over with 14L/47Hz
Attached Images
File Type: gif 14L-47Hz.gif (21.0 KB, 117 views)

Last edited by Inductor; 4th April 2010 at 01:17 PM.
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Old 4th April 2010, 01:12 PM   #8
sivrat is offline sivrat  South Africa
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let me have a look at the value of the cap being used on the tweeters and get back to you.

Thanks a bunch man, much appreciated!
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Old 4th April 2010, 01:16 PM   #9
sivrat is offline sivrat  South Africa
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The cap is 1.5 uf....
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Old 4th April 2010, 01:43 PM   #10
Loren42 is offline Loren42  United States
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I would ask that you actually measure the frequency response of the cabinet, but that is not a trivial request.

Still, simply listening to a speaker is not the best way to qualify the quality of a speaker. You need measurements to act as a reference for a path to improvement and to spot problems with the system.

Also, speaker placement in the room, baffle step diffraction, and room acoustics all play a big part on how the system sounds.
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