Need some help with some bass

[sivrat]

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?

 

[Inductor]

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

 

[Inductor]

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.

 

[Inductor]

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).

 

[sivrat]

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

 

[sivrat]

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?

 

[Inductor]

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

 

[sivrat]

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!

 

[sivrat]

The cap is 1.5 uf....

 

[Loren42]

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.

 

[Inductor]

Same 14L/47Hz with different X-over with 1.order on tweeter (I'm using the Visaton tweeter). You can use the RLC (in parallel with the woofer) or not, but because this woofer is nasty, if you don't, you will have a peak of ~4dB@1kHz. Use a 15R power resistor, a L2 Laminated Core Coil type 8.5mH (type Erse #ELC54-18-8500) and a C3 cap=3.60uF for the RLC
Have fun Travis.

 

[sivrat]

Thanks man, I will have a look at this and see what I can understand 🙂

Thanks a lot.

Travis

 

[Inductor]

If your tweeter has a good response under 2KHz, you can test a cap (C1+C2=16.8uF) of 18uF or bigger instead, on the woofer X-over arm. You should make mention of your front baffle dimensions also, and location of your drivers and port in same baffle. Note that final dimensions of baffle will be exterior (interior Liters+port/drivers volume+wood thickness=exterior volume/dimensions).

 

[Inductor]

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.

Hey Loren, how is your JBL now, did you change the room or the alignment of your speaker system? I've been reading your posts.🙂

If sound/listening is bad (and),
Measurement is bad (with everything else ok),
Then speakers are bad (a little or a lot, and you have to change something).

 

[Inductor]

sivrat sent me a PM saying he's using:
HiVi D6.8 Bass-Midrange with tweeter SEAS H0737-08 19TFF 1 and needs a xover. (1.order/passive).

First I would not do that because of issues with phase on the tweeter. (nasty inversions of phase/nulls through the xover band with a 1.order on tweeter and a second order on the mid-woofer). So for a 2.order xover (passive), I would start with/from this (safer) simulation with the appropriate Lpad R1/R2 atten.(-7,5 dB) on the tweeter.

 

[wintermute]

Hi Sirvat, even though you say the cabinet is only a mockup, do try to make sure it is sealed properly!! Mick (prickears) had a problem with his BR box with a dip (from memory) around 80Hz which showed up using an SPL meter. It turned out it was a leak that was causing it, after sealing it up properly the problem went away!

Unless your mockup reflects the true final then you are possibly waisting your time chasing problems which may not be there if the box is built properly in the first place 🙂

Tony.

 

[sivrat]

Inductor - thanks man, I will track down some parts for the XO. I tried to model it in winsid pro, but couldn't get the T/S parameters into the program without it throwing errors.

Wintermute - the box has been rebuilt. I needed to re-cut the front baffle for the new tweeter, so I decided to re-do the boxes with 16mm MDF. Will post the new dimensions. Having it non sealed is just to gain access without having to remove the drivers.

I am rushing things a bit as my wife and I are on red alert for the birth of my daughter 🙂 trying to get through all the projects that require a lot of noise, time and money.

Thanks again for the responses, will keep you all posted.