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Old 1st March 2006, 03:25 PM   #1
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Default Do I need a Crossover??

Hi Guys,
I have a Philips LX700 digital surround reciever. Being not so happy with the bass , I've decided to build a Sub of my own.
The current sub (50W RMS) is a 6" Flat cone driver with a woox passive radiator. It also has a rear Bass Port (why?? when u have a passive radiator?)

I'm thinking of a 12" Active Sub.

I am not really sure of the crosssover frequency of the existing sub. The reciever has a Sub line out.
If i'm building a new sub, Should I have a crossover or a low pass filter? (if yes, how would i measure the cut off freq?)
Or is this taken care of by the reciever when i take the output from the Sub line out?
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Old 1st March 2006, 04:26 PM   #2
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The active sub you build will have a plate amp. The plate amp usually has a variable XO and variable gain built in for ease of tuning. The sub output from your receiver may or may not be filtered but either way it doesn't matter as this is looked after inside the plate amp.

Ported passive radiator?
Never heard of it.
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Old 1st March 2006, 04:38 PM   #3
sreten is offline sreten  United Kingdom
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Default Re: Do I need a Crossover??

Quote:
Originally posted by Arunkumar14_th

The current sub (50W RMS) is a 6" Flat cone driver with a woox passive radiator. It also has a rear Bass Port (why?? when u have a passive radiator?)
Hmm......

perhaps you should provide more details as something sounds
seriously wrong, you might be able to improve your current sub.

e.g. fit a decent quality driver.

/sreten.
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Old 1st March 2006, 05:06 PM   #4
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Find the user manual for your receiver, then you will know if it has a crossover / bass management or whatever. If it does then it gives you more options.

What power output/response are you aiming for?

My 15"/250l sonosub is still waiting for 'proper' power, it has even just been downgraded from 2x80W to 2x30W! but that's still enough for my normal movie use.
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Old 1st March 2006, 06:20 PM   #5
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Default Re: Re: Do I need a Crossover??

Quote:
Originally posted by sreten

Hmm......

perhaps you should provide more details as something sounds
seriously wrong, you might be able to improve your current sub.
/sreten.
Well, I used to have the setup in a small room, The sub placed just below my computer table & It used to sound just gr8.
Now that i've moved to a larger room, The same placement was not satisfactory. I tried placing the sub in a corner, The bass response increased but it still lacks clarity. (My room size is 13x20 ft)

Well, I dont know what philips had in mind while designing this sub, but this is a rear ported system and also has a passive radiator. Rear port is causing a lot of problem as I cannot place it near the walls. Also the port makes a lot of noise at around 25Hz.
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Old 1st March 2006, 06:48 PM   #6
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Default Re: Re: Re: Do I need a Crossover??

Quote:
Originally posted by Arunkumar14_th
The current sub (50W RMS) is a 6" Flat cone driver with a woox passive radiator. It also has a rear Bass Port (why?? when u have a passive radiator?)...
...Well, I dont know what philips had in mind while designing this sub, but this is a rear ported system and also has a passive radiator. Rear port is causing a lot of problem as I cannot place it near the walls. Also the port makes a lot of noise at around 25Hz.
Certain that the extra device is passive and not second active driver? That is agreeably wierd if it has passive + port. It could be an interesting alignment to fool with - passive radiator with suspension + free port could be used to control Helmholtz bandwidth / system Q... Passive elements may decouple and increase system order... Curious.

If port "chuffs" at low freq / high SPL, it is too small diameter for tuning frequency. Making it bigger (also means much longer at given tuning frequency) can solve or reduce the problem. This should also allow near-wall placement. Most of my 4th order cabinets (actually being ~QB3 in general) have had port facing rear or down and no artifacts. Larger tube basically reduces velocity amplitude, all other things being equal.

*edit:*
Also, try breaking / rounding / filletting port edges. Could be exciting tube modes with entrance effects if hard edges.

Enjoy!
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Old 1st March 2006, 10:22 PM   #7
simon5 is offline simon5  Canada
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It could be a 6th order bandpass, they use a passive for one and a port for the other. Special stuff.
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Old 2nd March 2006, 10:39 AM   #8
sreten is offline sreten  United Kingdom
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Default Re: Re: Re: Do I need a Crossover??

Quote:
Originally posted by Arunkumar14_th

Well, I dont know what philips had in mind while designing this sub,
but this is a rear ported system and also has a passive radiator.
Hi,

a description of the air spaces in the subwoofer, and the placement
of the driver, passive radiator and port in relation to the air spaces
in the subwoofer would help.

e.g. are there 2 airspaces.
The driver is between the aispaces.
The PR connects one air space to the outside world.
The port connects the other airspace to the outside world.

The above describes a 6th order bandpass, normal reflex
(4th order) high pass for bass roll off, + 2 order low pass
for mid rolloff.

/sreten.
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Old 2nd March 2006, 02:52 PM   #9
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Yep. Makes sense that way. I figured it would have been mentioned that the woofer and passive radiator were not in the same "baffle".

I would say a partial answer to the original question is that a crossover is only needed so that the woofer/dedicated amp doesn't heat up more than necessary or produce mid+ artifacts (if this sub remains in use).
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Old 2nd March 2006, 06:13 PM   #10
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Guys, Coming back to the XO,

What would be the best solution? as am not sure what type of amp i get in Bangalore, India.

It may or may not be an amp with a XO.
But, even if this has a XO, i really dont know the lower cut off for my satellites.

I dont have good resources here in Bangalore. Especially for Amps & Drivers.

Thinking of improving my sub or adding a Passive one to my existing amp removing the current sub.

I really dont know how a Bolton would do, as the T/S for these are not publised.

I really think that a 8 incher with a very good sealed box would solve my issue. 50W RMS of my existing reciever is ok for 8" woofer I assume..
I really do not need all the power, but good & clean bass.

any suggestions?....
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