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Old 19th January 2012, 10:23 AM   #1
mertol is offline mertol  Turkey
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Default Need Advice : Adding bass to my existing DIY 2 way active speakers

Hi All;

I have already finished my 2 way active passive line level XO using monitor. After changing the tweeter from westra to something decent I am %90 happy with it. Excellent imaging, a lot of micro detail however very little bass at all.

The bass I have used is 4.5 inch with an fs of 70hz in a sub 20 liter sealed cabin. So needless to say it's not going anything below 100hz at all.

(I will add the pictures ones I am home)

I now want to add active bass enclosures to the mix. As I have used passive line level XO (and I am very happy with it) there is no way to use a bandpass (insertion loss is way too much) on the current mid bass. And as I do want all of the internal amplifiers to be the same (for serviceability and all will have the same gain) each bass unit will be driven by a stereo LM1875T amplifier board.

My target is to have a decent bass between 35-120hz in 40-60 liter sealed cabin with the LM1875T's at moderate listening levels.

Here are my questions :

1) Should I use a single large driver (12 inch or more) or should I better use a 2x10 incher per channel.

2) If I use a single driver, is it possible to BTL the output of LM1875T ? Does it worth it?

3) If I use 2x drivers, considering that I use passive line level low pass filter , should I use independent filters for each driver+amplifier pair , or can I just share the output of single filter? Will anything change
including output level?

4) My current setup is

--------High Pass-----> Amplifier---->Tweeter
Source ----X
--------Low Pass------> Amplifier---->Mdi/Bass

If I put a third filter, running in parallel, an other low pass, will it couse decrease in sound output? My amplifiers impedance is very high...

5) If I use 2x drivers each with it's own independent amplifier channel, how much DB's will I gain? 3 or 6 (range is 35-120hz)

very best regards
Mertol
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Old 19th January 2012, 10:30 AM   #2
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Is adding a line-level Linkwitz Transform filter an option? This greatly increases your flexibility in design and allows you to achieve very deep bass.
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Old 19th January 2012, 10:38 AM   #3
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I would go towards much more power from the amplifier
and surely steeper curve to cut the low freq , which necessarily brings to active crossovering .
The drivers could be also 6-8 " ,and their major characteristics would be :
stiff construction , high excursion , high b*l product ; stiff construction is
related to the power they'll have to sustain and how they can bear high temperature .
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Old 19th January 2012, 11:18 AM   #4
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IMO, two satellites using 4.5" drivers + large subs will not sound right.
Bass will play apart.
Better to go three way, using your 4.5" as mid and find a woofer (not sub) playing until 300 hz or so.
Better blending, authority in the midbass, clearer sound, more dynamics..
Then, active XO. Mini DSP?

Last edited by bobodioulasso; 19th January 2012 at 11:26 AM.
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Old 19th January 2012, 11:27 PM   #5
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by mertol View Post
As I have used passive line level XO (and I am very happy with it) there is no
way to use a bandpass (insertion loss is way too much) on the current mid bass.
Mertol
Hi,

Not true, insert a small series capacitor related to amplifier input
impedance or replace the input coupling cap with the same value.

You should have done the same for the tweeter. Only low pass
requires some insertion loss, if you are talking first order PLLXO.

rgds, sreten.
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Old 20th January 2012, 09:41 AM   #6
mertol is offline mertol  Turkey
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Quote:
Originally Posted by a_tewinkel View Post
Is adding a line-level Linkwitz Transform filter an option? This greatly increases your flexibility in design and allows you to achieve very deep bass.
I have it on the 2 way monitor (with a bypass switch and a pot to adjust amount) While it adds some bass, not as much as I want. It's obvious that the 4.5 incher in a sealed cabined has it's limits.
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Old 20th January 2012, 09:46 AM   #7
mertol is offline mertol  Turkey
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Quote:
Originally Posted by bobodioulasso View Post
IMO, two satellites using 4.5" drivers + large subs will not sound right.
Bass will play apart.
Better to go three way, using your 4.5" as mid and find a woofer (not sub) playing until 300 hz or so.
Better blending, authority in the midbass, clearer sound, more dynamics..
Then, active XO. Mini DSP?
Actualy it's going to be a 3 way and 100-120hz first order passive line level XO should let it blend OK. I don't want to use an active XO , as so far I am quite happy with the passive line level XO.

What are the good 10 inchers (I prefer to keep the price reasonably low, say below 30-40 use per driver) that can do good in a sealed box?
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Old 20th January 2012, 10:20 AM   #8
AndrewT is offline AndrewT  Scotland
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Hi,
the existing sealed box speaker will have a 2pole LF roll-off. The Q could be anywhere.

If you add a 2pole Q=0.7071 active filter to coincide with the speaker F-3dB you will get a close approximation to half of an LR crossover.

Now add on your bass only speaker and feed it with a 4pole Q=0.5 filtered signal. You have an LR crossover.

Next.
If you use one 8ohms speaker driver then use one chipamp.
If you decide to use two 8ohms speaker drivers, then use two chipamps. Each 8ohms driver having it's own dedicated single chipamp amplifier.
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Old 20th January 2012, 11:30 AM   #9
mertol is offline mertol  Turkey
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Quote:
Originally Posted by AndrewT View Post
Hi,
the existing sealed box speaker will have a 2pole LF roll-off. The Q could be anywhere.

If you add a 2pole Q=0.7071 active filter to coincide with the speaker F-3dB you will get a close approximation to half of an LR crossover.

Now add on your bass only speaker and feed it with a 4pole Q=0.5 filtered signal. You have an LR crossover.

Next.
If you use one 8ohms speaker driver then use one chipamp.
If you decide to use two 8ohms speaker drivers, then use two chipamps. Each 8ohms driver having it's own dedicated single chipamp amplifier.
Thanks a lot.
The following question could be very stupid. Assuming that I will use 2x drivers connected to two chip amps:

Is it ok to use one filter and divide the output to two inputs of the amps , or should I divide the input and apply two identical filters and feed each amp from it's own filter. (As I am using PLLXO, filters don't cost time and money. )

PS: I know that roll of characteristics of the sealed two-way is not an ideal pattern and blending will not be 'perfect' but what I am looking for is not a all flat output but coherent, not boomy, fast bass with controllable roll of below 35hz...
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Old 20th January 2012, 11:36 AM   #10
AndrewT is offline AndrewT  Scotland
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use one filter with a low output impedance.
That one filter is capable of driving many high input impedance loads.
i.e. no problem, two amps on one filter.

Remember I said a close approximation to half an LR crossover.
Once you have this up and running you can then decide if you want to make the satellite roll-off to more closely approach an LR Q=0.5 roll-off.
You can measure the Q and F-3dB of the satellite after you have learned how to do that.
Then you can alter the Qbox or apply a Linkwitz transform to give a pretty accurate LR crossover.
But, get the simple option running and have a listen.
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