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Old 21st January 2006, 08:49 PM   #1
mikee55 is offline mikee55  United Kingdom
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Default Is this possible?

Hello All,Can I ask,has anyone done this?I have a pair of 3 way loudspeakers that use 12" woofers.Would it be possible to add a linkwitz transform circuit instead of any form of bass boost circuit? Or would the signal be ruined from an audiophile/quality point of view.After all it could accept a non low pass filtered signal and boosts low in the freqency range,not to effect mid.Therefore would the speaker system work?Probably not as well as a seperate sub,which every audiophiles main question is "what about the wife?".
Unfortunatly,my wife loves "her" speakers,and a sub is not allowed! EQing is acceptable....

Thanks.mikee55
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Old 21st January 2006, 11:13 PM   #2
Collo is offline Collo  Australia
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Provided the bass driver has excess excursion and power handling available, it should be possible.
The Linkwitz transform adds some group delay - WinISD pro lets you model this, and it doesn't look too bad (under 15msec).

regards
Collo
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Old 23rd January 2006, 05:25 AM   #3
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Mike, yes it can be done.

The question is should it be done!

SPL will be limited by excursion. Also, if it is not undersized, then simple bass boost will do.

If it is an active speaker then you can add on a LT circuit which you would have to custom-make, and include a power supply (or tap in to an existing one). If it is a passive speaker, then you need to be able to get in between the pre and power amps.

Have you considered some creative ways to get a sub into the room unobtrusively?
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Old 23rd January 2006, 08:48 AM   #4
mikee55 is offline mikee55  United Kingdom
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Default What are my options?

Hi mate,I'm limited to what I can do to hide a sub.I've considered a fair few ideas

inside sofa,"no"
tv stand,got LCD,"no"
IB ceiling,"WHAT! NO"

Have tried bass boost,but voices always seem to boom,especially Female radio/tv presenters,artist and actresses.Graphic EQ's aren't any better either.I'm not after explosions but depth can help movies and I do like underground Dance (Rave Oldskool Hardhouse).Although my room is appx 4m x 3m x 2m(h) there must be somthing I can do?(as long as she's happy)

Cheers Mikee55
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Old 23rd January 2006, 09:09 AM   #5
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The LTF should only be used with closed-box woofers. Are your boxes of this type ? I they are bass-reflex other tricks can be used.

Group delay is not a concern with LTF - if done properly. The contrary is true actually if you do it well.

Regards

Charles
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Old 23rd January 2006, 11:42 AM   #6
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Personally I think it's a fine idea if :
a) It's a sealed box (as phase_accurate mentioned).
b) The 12" woofer is of good quality
c) The electronics in the LT circuit is of good quality.
I assume you are inserting the LT circuit between pre and power amps.
Having said that, I wouldn't do it myself (bit of a purist) because you are adding another op-amp into the fullrange signal path.
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Old 23rd January 2006, 12:35 PM   #7
mikee55 is offline mikee55  United Kingdom
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Default They're sealed

Hi,They're 22.5" x 14 x10"(hwd-internal with no T/S parameters) sealed cabs.Sticker on back says response down to 45hz and 50w power.I know they might not be up to being LT'ed,but I did try an LT on one cab when I first discovered the circuit on Linkwitz's website.I didn't attempt to tune the circuit,I just used his values.The room filled up with bass on the end of my 100w (peak power) amp,and because I only made a mono circuit and didn't tune it properly (let alone play any music-I just tested that it worked),I don't know how well it sounded or whether it was better than a bass/treble control with respect to vocals.I played some Hardhouse and got a nice sounding bass and after 1 minute,disconnected it and stuck it in my car.Is it possible?
Thankyou.mikee55
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Old 24th January 2006, 07:27 AM   #8
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If you don't have driver parameters, how are you going to design it?

A LT is based on fs, VAS, Qts and Vb. If you only have Vb then its a case of pin the tail on the donkey!

Here's info on making one:
http://sound.westhost.com/project71.htm

A simple one band of parametric eq sounds like it might serve you better. You can tweak it for different music, and adjust til you like what you hear.

Each octave lower requires 4x displacement, hence moving the F3 down from 45 Hz to 20 Hz requires over 4x the excursion. This could reduce output by 24 dB or more!

Lets say your speaker can reach 100db peaks at the moment - quite respectable. Now add in the boost to lower the F3 down to 20 Hz and you now can only hit 76 dB where there is some deep bass. If you turn it up you might get drivers bottoming.

I'm curious: what bothers your partner about the ideas you've had, esp IB?

What about a triangular sub that fits in a corner painted the same colour as the walls to look it is part of the walls?
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Old 25th January 2006, 10:00 AM   #9
mikee55 is offline mikee55  United Kingdom
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Default Hello

Hi Paul Spencer,I was planning on measuring the parameters for the speakers.I don't normaly have the system playing loud with respect to my neighbour.How would a parametric help? Wouldn't this be similar to LT,trying to boost bass? Isn't this type of Eq meant to correct a lumpy response?Could you explain how I could use it,please.
Having big speakers in the lounge,is bad enough with not much room,an extra box would take up more room!,says the misses.
What if I replaced the mids with a small bass/mid say from Audax?Put a pipe from baffle to back,to create a box in a box.Use another amp to power the mid/bass and tweeter,then an active crossover on the bass driver,effectivly bi-amping.Perhaps a Class A emitter follower,from Rod's site for the Bass/mid and treble.And then try and sort the bottom end.

Cheers.Mike
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Old 25th January 2006, 10:14 AM   #10
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You don't need to know Fs or Vas or Qts, what matters is the in-box response. So you don't need to take anything apart just measure Fc and Qtc. This is slightly simplistic approach in that you can't model the excursion, but for a novice or a quick way, it's fine - just use your ears to see if it's loud enough or clean enough.

And the comment regarding group delay - the LT actually usually improves GD, if Qt is lowered (which it usually is).
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