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aubergine 3rd July 2008 05:33 PM

LS3/5A Subwoofer
Hello Gentlemen,

I've just come across two pairs of Spendor LS3/5A (and a Quad 405-2) that were sitting in a new house we've bought.

I've got a few ideas (split them up, etc) but all involve getting some bass reinforcement for these speakers to ease the load off the small woofers in them.
There are a few designs optimised for the LS3/5A.

The AB1 clones do not go low enough for my liking (I do pro sound and to me, there's nothing like tasty low bass).

There are Fried Model H subs which I can split into two and use one per speaker. if you've heard these, please comment. If you know where to get the right drive units near London, please comment.

There's the Satterbergs (f3 at 28hz), which seem to use 10" drive units in a sealed or reflex box. Plans and advice would be greatly appreciated.

I have a spare bandpass box loaded with the Void V18-1000 (5" VC, magnet the size of a dinner plate) that I could use to provide bass for the whole system, run with an active crossover.

I also have the option of purchasing a driver, fashioning a crossover and designing my own box. What drivers suit sub duty for these mini monitors and would a sealed box, transmission line or reflex suit this purpose best?

Oh, I have searched the forum and have found nothing completely suitable and just want some feedback, really.

Thanks for reading,

richie00boy 3rd July 2008 05:52 PM

The question really is are you trying to do a passive design to run off the same amp as the main speakers, or how adventurous do you feel with box building and assembling electronics?

SY 3rd July 2008 05:56 PM

Indeed. Passive subs just won't meld correctly. You want an active crossover and biamping, with a pretty low Q second order HPF at resonance to take care of the midbass bloat.

I wouldn't bother with old stuff like the Satterbergs. This one calls for a sealed box with a high-quality driver or a very well-damped TL.

aubergine 4th July 2008 03:19 PM

I've got a load of spare amps and enough active xovers to be getting on with, so that's fine. I've built a PA system before, so that'll be fine. Thoughts?

sreten 4th July 2008 03:56 PM


TBH I'd sell the (very valuable) LS3/5A's before
you blow them up with one of your PA amplifiers.

18" 98dB/W is not what is required to go with them ....


SY 4th July 2008 04:11 PM

I'd start by putting a broad -2dB notch centered at about 160Xz, then a Q = 0.4-0.5 second order high pass at 80-90 Hz for the LS3/5A. The sub will take a 4th order Linkwitz-Reilly low pass. There are a LOT of good 12" drivers out there intended for sealed boxes which should take you down nicely to 30Hz, unequalized.

Don't tempt fate and try to play them much louder, though; like Quad 57s, the LS3/5A just is not built for volume, top to bottom. So your sub doesn't have to go super loud at very low frequencies in order to keep up, and that's a good thing because you can now EQ a decent design down to 20 Hz or lower.

This is pretty close to a setup I ran some years ago with original Rogers. After years and years of not getting it right and giving up the subwoofer idea, I finally took off my anti-equalization hair-shirt, tried it again, and suddenly things worked much, much better. My subs were 30W54 in a transmission line, but these days I wouldn't bother getting that fancy.

jotom750 4th July 2008 04:29 PM

I also think you should have a go at selling them. I got 630
for my 15 ohm Rogers pair. They went to Japan !

This site may be of use:-

aubergine 5th July 2008 06:01 AM

Thanks SW. I won't be running my Rogers loud, just had a spare sub that's a bit overkill but would work. Your recommendation on how to run them is what I'll try on my Xover + EQ. Should be perfect for home listening.

Sreten, I'm running them of Quad 405-2s like my first post suggested ;) . Not all of us pro sound guys are idiotic enough to run all of our amps a millimetre before clip at 134+ dB, mmkay?

jotom, is where I found the AB1-lookalike plans. Thanks, though. Not selling these, the other half likes these much better than my floorstanders (No, I'm not a crazy man who sticks L Acoustics VDOSCs in their living room, complete with matching Labhorns).

philpoole 5th July 2008 07:02 AM

I managed to acquire my Dad's Chartwell LS3/5As and Volt subwoofer a year or so ago.
The sub was a passive kit from wilmslow maybe 15 years or so ago, and I gather he asked them to tailor its crossover to complement the monitors.

They sound awesome, and plenty of presence with the sub, but I tend to have the monitors upstairs alone for quieter listening, and the sub in with the home theatre. I prefer the LS3/5As without the sub.
It might have been because I was using a NOS DAC at the time, which can have a fairly overdone bass, but last time I heard them together, the bass did seem a bit overbearing. The EQ of the crossover in the LS35a is adjusted to give a perception of more bass, by reducing the HF response, amongst other things. I think this can make finding a subwoofer to go with it quite hard.
- Look at SY's post about a notch and an high pass for the monitors alone, as well as the usual crossover for the sub. Sums it up really.

Not everyone's cup of tea, but they're awesome little speakers.

aubergine 5th July 2008 02:12 PM

Thanks for your help everyone. I'll get cracking with a quality sealed box.

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