Quad 11L - easy and free cure of midrange problems - diyAudio
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Old 17th February 2010, 05:48 AM   #1
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Smile Quad 11L - easy and free cure of midrange problems

Hi all

I've read the thread where people have tried improving the Quad 11L, especially in the midrange, where it does seem to have serious problems.

In a moment of sheer bordom, i decided to take a look at the problem.

I started by looking at the crossover and the wiring, in the hope i'd find something wrong here. a close look at the crossover feeding the bass unit showed it to be 12db design, and the tweeter was fed by an 18db type with a 1R5 resistor in series with the tweeter.

All farly conventional really, the values seemed reasonable, but the 20uf capacitor in the tweeter circuit did get the old grey matter working overtime.

It's been too many years since my days at college and speaker crossover theory is not something you use every day, but i felt that someone had missed something here.

back in the very early 70's when i was learning my trade, all calculations were worked out on paper, then "tweaked" using the best equipment there is: our ears! There were obvously basic rules concerning the different phase responses of different types of crossover.

The circuit feeding the Bass unit in the Quad 11L is what used to be called "12db Butterworth" type. Now this was a comonally used design as it's performance was well known.

One of the important things that had to be kept in mind was the phase response at the crossover frequency. In those days it was common for many two driver speaker designs to have both units fed by 12db filters. Because of this, the tweeter had to be wired "out of phase" with the bass unit to overcome the phase cancellaction at the crossover frequency.

When it came to designs that used 12db and 18db circuits, things were a little "fluffy" when it came to phase response. I remember my teacher saying that "in theory" the tweeter should be in phase with the bass unit, BUT it could also be wired out of phase. All to do with mathamatics, which have no place here. he stated it was best to listen to the speakers with the tweeters in and out of phase to see which "sounded " best. In theory there should be no difference, but......

So i did the simplest of mods to my 11L's. Luckily i had "bi-wired" mine to my amp, they do sound a little cleaner, even if your just using one stereo amp.

I swapped the leads on the tweeter leads on both speakers, and hey presto... clean midrange, depth and a more enjoyable sound. I then performed a very simple test using a speach program on BBC Radio Four as the source, and using just one speaker, listened with the tweeter wired one way then the other.

Standing away drom the speaker, one thing was immediatley noticed, with it wired "in phase" the voice seemed to eminate from inside the speaker, but when wired "out of phase" the voce came from "around" the speaker. It's hard to describe but it was more realistic, and it didn't show any of the normally expected side effects of being wired incorrectly (loss of presence, detail,hollow etc).

Having listened to the speakers this way for a few weeks now has been so enjoyable. Imaging is better, the intergration of the two drive units seems to be perfect, and the detail can be quite shocking at times.

So guys, give it a try. Give it a few days on stuff you know well, don't forget, you've listened to them the wrong way round for a long time!!!

Richard
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Old 17th February 2010, 11:55 AM   #2
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Best phasing is hard to predict by looking at a system. It is primarily a function of driver depth, crossover frequency and crossover order of the two sections. Assuming the Quad designers were at all competent (I assume they were) they would have picked the best relative polarities for their system. Reversing that connection will then add a wide and deep hole in the crossover region. The "voice coming from around the speaker" is indicative of the lesser forward energy from a misconnected speaker.

Here is a series of measurements that show how crossover order effects best phasing of a 2way system (AR4x)

Crossover mods for the AR4x - The Classic Speaker Pages Discussion Forums

Regards,
David
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Old 17th February 2010, 02:22 PM   #3
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Hi Dave

Thanks for the reply. I've read your piece on the AR4x, and i agree with your findings, the tweeter should be in phase with the bass unit if your using a 6db/12db combnation crossover.

The Quad 11L does have an issue with the midrange, often too forward, and when played loud it can get a little "honky". I would also expect Quad's engineers to be competant, but they are not the same company they once were. they have become rather distant, not wishing to answer even basic questions!

I'm in the electronics trade, and part of my training in the early 70's was speaker design. I know a lot has changed since then, especially attitudes towards design, sometimes to the detriment to what the speakers actually sound like.

I have done a lot of listening to the Quads, wired both ways, and i wouldn't say there was actually a dip around the crossover frequency, more a levelling off. Going back to normal wiring certainly makes the speaker much more "middy".

I'm using a much modified Marantz amp to drive them, and i'm comparng the Quads to my monitors in my home studio, they now share a very simlar midrange, something that used to really hack me off before. By the way, my monitors are Alesis M1 Mk2's (active), which are only slightly larger than the quads.

The improvements are better imaging, and as i said before, more detail etc.

It would be nice to hear from any owners out there who'd care to try this simple experiment

Last edited by oxforddickie; 17th February 2010 at 02:26 PM. Reason: Added and corrected
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Old 17th February 2010, 04:26 PM   #4
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Hi Richard,

Actually, the AR4x worked best with tweeter out of phase relative to the woofer for first and second order networks. That was the point, that it was hard to predict until you attempt a crossover point and order (slope) what the best connection will be.

I'm surprised your Quads are better when reverse connected, but not everybody shoots for modern Linkwitz Reilly (in phase through the crossover region) type targets. Sometimes you get stuck with 90 degrees between the sections, more or less, and the best connection becomes one of preference. That sounds like the case for your system.

Yeah, Quad isn't the company they used to be. I worked for KEF in the early 80's and we rubbed elbows with the lads in Huntingdon a lot, mostly Peter, Ross and Mike Albinson. Is there any UK presence now or is it just the Chinese side? Who did you design speakers for?

Regards,
David
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Old 17th February 2010, 08:18 PM   #5
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Hi Dave

Am listening to TV sound through them, and it sounds fine... to me at least, and i guess that's all that matters :-)

Although speaker design was a small part of the training at college, i stayed in the electronics repair industry in the end, although all things audio have remained No 1 to me. I even went into the Quad arena, and am back there now decoding them using software, for playback on modern day equipment.

Richard

Last edited by oxforddickie; 17th February 2010 at 08:20 PM.
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