Quantum 2 (and other Quantums?) Midbass Suckout

[Kencat]

I'm creating a new topic here because I think it deserves to be discussed separately. Two Q2 owners (first JP and now Me ) seem to have an issue with the Q2s sound in the midbass region. I have been listening to mine now for nearly a week, and something was bothering me. The extreme low bass is fantastic when the music has it. The highs are amazing. But, I was finding that the music was fatiquing, and that voice (especially male) was too high end oriented, lacking something. I started writing a reponse to my own post about getting the Q2s operational, but felt midstream that this should be it's own topic. I'll start with a quote from JP in the other thread.



If after a while you still find the speakers to be a bit lacking, try pulling them out some so that there's nothing in between them, as with any speaker, the Q2s like space. I too still recommend trying to flip the polarity on the midbass driver. I've discovered with my Tannoys that the "body" range of ~300-500Hz is very important to impart musicality and richness that real instruments have. Unfortunately, this is right smack in the middle of the midbass driver's range, so if the inverted phase is causing a sound suckout here, you will find the result uninvolving. If you don't like the change, well, it's only four screws and two slide on connectors to revert to the previous arrangement. Of course, wait a while first before trying this to be sure of what you like.

- JP

I think JP is right about this midbass suckout. I have been finding the sound to be very high-mid biased, to where male voices were just too high or strident almost. I was listening to an Elvis (the king) greatest hits CD last night, and found his lower range richness lacking.

I've playing with the equalizer on my old Winamp prog. This is a 10 band eq with 60, 170,310, 600, 1K, 3K 6K, 12K, 14K, 16K bands. I started 1st with trying to knock down the high end (6K to 16K) which helped somewhat but still didn't do it, voice was not right still.

I've currently got it set with a 10 db peak at 310 to 600 Hz tapering off on both ends to 0 dB at 60 and 3K. This now fills in the male voice lower end and makes the overall sound richer and fuller.

Now to figure out why this mid-bass suckout is occurring (I offer these points for more discussion and investigation):

(1) JP has found that switching the midbass coupler polarity to a "normal" condition (driver + to speaker terminal +) does the trick. This would mean that Infinity screwed up big time with this design. Is this likely? I have to (want to ?) believe something else is wrong. Reversing the polarity may be compensating for improper room acoustics ? same as messing with an equalizer - or something else.

(2) Room acoustics/speaker placement. The midbass reverse polarity and the straight-out-the- back porting of this driver must be playing hell with reflected sounds from the back wall. Suggestions to get rid of other nearby speakers and keeping space between the Q2's etc. etc. are all valid. Maybe the Q2s need a much larger room, with the speakers farther from the walls, or closer....who knows? I guess only experimentation can find that "just right" combination to allow the midbass to blossum as it was meant to. OR, has anyone already found it???

(3) Degraded crossover. The midbass 40 mF cap is an electrolytic. The two humongogiganto caps on the woofer are electrolytics. JP has identified the other caps to be metallized types which can also be off due to age. I don't know as I'm writing this, what the possible effect of the loss of capacitance values for the 3 electrolytics would be without further study, and maybe someone more knowledgeable could help after studying the schematics, but it may be that a hole is created at the woofer to midbass coupler crossover point of 200 Hz and the midbass to mid crossover point of 600 HZ. This seems to be the area of the problem.

(4) Open to other suggestions here - HELP :D

Does anyone know Arnie Nudell enough to try to contact him to find out "what the hell were you thinking?" when they created this wierd midbass driver arrangement :D ?

JP, I elect you. Wouldn't you like to go visit the Genesis facility????

Other Quantum owners may be experiencing the same thing. It would be nice to hear from you all about whether this is so, because if it isn't, it could lend some clues to the Q2 issue.

[bocoogto]

If the Q2's have this deficiency, the Q3's and other Quantums likely do, also. Mr. Watkins may have an opinion on this. He was quite vocal about the use of his woofer in the QLS-1 when I spoke with him a few years ago. He said the QLS-1 and Q2 have too much cabinet volume for the woofer design, making them prone to bottoming with high input levels. He said Infinity ignored his advice to reduce cabinet volume to that of the Q3 to avoid the problem. I had called him for advice on why my Q2 woofers bottom before the rest of the system is at maximum output.

Reduction of cabinet volume may help reduce the problem of bottoming woofers, but would also reduce very low frequency output.

Just thought you may be interested.

[Negotiableterms]

Gentlemen, I am no speaker guru, and you have me thoroughly confooozed.

Trying to think this through:

The midbass unit is crossed over to the midrange drivers on the top side and the woofer on the bottom. In the frequency interval where the crossover occurs, both drivers operate. If they aren't connected in the same phase, cancellation will occur and you'll have a drop out (to near-zero) in that range.

Could this be what's happening? To find out, you'd have to check the absolute phase of each driver. Don't ask me how ya do this. I rely on JP for all technical wizardry.

[Kencat]

Gentlemen, I am no speaker guru, and you have me thoroughly confooozed.

Trying to think this through:

The midbass unit is crossed over to the midrange drivers on the top side and the woofer on the bottom. In the frequency interval where the crossover occurs, both drivers operate. If they aren't connected in the same phase, cancellation will occur and you'll have a drop out (to near-zero) in that range.

Could this be what's happening? To find out, you'd have to check the absolute phase of each driver. Don't ask me how ya do this. I rely on JP for all technical wizardry.

NG, the other factor in the equation is that the crossover is a 6 dB/Octave type, meaning the overlap at the lower and upper crossover points is fairly substantial. The midbass coupler is also only working from 200 to 600 Hz. Infinity had some real magic thinking going on with this one.

Time to shutdown the computer. Major thunderstorm happening.

[Negotiableterms]

Infinity had some real magic thinking going on with this one.

Well, at least one can note that the magic thinking remained in place for a good number of years. The first midbass coupler was in the QLS, and the last midbass coupler was in the Kappa 9, I think, or maybe even later. 20 years?

[Charivari]

Interesting post, Ken. It definitely goes to show that it takes a lot of listening to a pair of speakers or any audio component for that matter to get a feel for its sound. Something that just cannot be had in an hour's visit at an audio store unless one is already very experienced in what to listen for.

Each of your points could be interacting to produce the result you're hearing.

2. The positioning could be causing some issues, especially if you're relying on the midbass to be reflected off of the wall. The furniture you have placed between the speakers and the spare speakers on either side could be blocking the reflection of this wave. If the sound you want is when the Q2s act a bit like a dipole, this can cause for a dead sound. Just ask anyone who's tried playing a pair of Magnepans sitting in the place where a door previously was ... doesn't sound as good as one'd expect, as experience taught me (though it was a fun experiment). To test for this, try moving the other speakers somewhere else and pull the Q2s out into the room.

Furthermore, reflections off of the side walls could be causing peaks and nulls. Being a mechanical wave, or rather a pressure phenomenon, you can mentally visualize soundwaves like ripples on a pond, just rather than being vertical changes of a surface, they're density changes. If the reflected sound wave coincides with that coming from the drivers thanks to the distant being a multiple of the soundwave length at specific frequencies and the harmonics, it could add the intensities together ruining the flat response. Should such work together to align a peak with a valley, then you'll have a null where you won't hear the signal or, more likely, hear that frequency and those right around it be greatly reduced in intensity. Should the peaks be in the midrange/upper midrange while the nulls hit a bit lower in the lower midrange and midbass region, it could produce a similar result to what you may be hearing. However, unless you have a really funky room, this wouldn't hit in just that broad swath of midbass and would be noticeable in several areas of the frequency response due to harmonics (a signal at twice the frequency of the main signal can still cause peaks and nulls when every other wave aligns with one of the lower freq). In this case, just moving the Q2s by a few inches to a foot or so should cause a very noticeable shift in frequency(ies) of the suckout and thus clue you in as to the cause.

3. Possible. If the midbass potentiometer is somehow still dirty despite your cleaning or is somehow damaged, it could result in a much lower signal passing from the midbass driver causing what you're hearing. You can measure this with an ohm meter quite easily If the wires are damaged (pinched, corroded, partially broken), then the resistance within could be sufficient to again cause a great reduction in output. This is again quite easy to test with an ohm meter, a good wire should measure no resistance at the X1 setting. As to the capacitor, if it was bad bad, then nothing would get through, period. If it were drifting off value, you wouldn't notice a suckout, but more of a fair intensity peak near one of the crossover frequencies where the driver has begun to overlap other drivers' responsibilities and likely a small hole elsewhere (but nothing so severe as to seem the suckout you're noticing). If it were just somewhat bad or otherwise degraded, then maybe a suckout could occur. However, in the midbass region, it's nowhere near as easy to hear an old cap as with treble and even midrange. It would pretty much either cause the driver not to work at all or cause a degradation in sound quality, but not really a severe suckout, afaik.

4. The Bose Fairies have cursed you. Or, maybe the previous owner of your place was an audio masochist and secretly installed hidden midbass traps inside the walls, ceiling, and floor to cause bad audio. More seriously, it could be an issue in the upstream components. Maybe your amp, preamp, source, or whatever else you're using connected to the Infinities has some issues going on. If you have a spare receiver floating around somewhere, you could hook it up to the Q2s and at low volume (to keep from killing the receiver), listen for that midbass issue. If you no longer hear it, then you'll have to figure out which electronic component is giving you grief. Or, you could try the same system on a different pair of speakers, though you won't be able to fully eliminate the Q2s from the blame.

Now, as to my favorite, I still believe #1 could be playing a major part in it. My Q2s sounded gawdawful with the midbass driver hooked up according to the schematic. As I said before, there was an uppermidrange/treble bias and no upper or midbass. When I connected my midbass drivers contrary to what the schematics dictated, though in agreement with how my very early Q2s were hooked-up (the Watkins and midbass drivers and crossover sections being about the only thing in them not hacked up [due to the midrange and treble pots becoming too dirty to use] and didn't even look touched), the sound was balanced and was as it should compared side-by-side to my Tannoys -- no slouches in their own right. This could be due to my rather funky room that is L-shaped with a jut into the bottom of the L and the inside being composed of a very flimsy wall that moves with the bass. My room also isn't particularly large as far as the Infinities are concerned and it could be that when I sit ~10' away, it isn't far enough for the midbass to behave appropriately when connected as the schematics dictate. Maybe with repositioning, my Q2s would behave differently. It's happened before -- after moving my speaks shortly after I measured that incredibly low bass and posted my results to AK, I've been unable to recreate it again or anything near. Yet, I do not believe this to be the case.

The four-way crossover is 1st order all the way through, which means that the drivers remain time-aligned and phase-aligned/coherent so long as they are physically aligned. Were this not true, speaker makers like Thiel would never have sold anything. At the wavelengths we're dealing with, there is no way that I can see for the midbass's output to suddenly switch polarity in a normal room ... unless the transmission line enclosure does something to it. (There's a possibility that I haven't sufficient knowledge to comment on.) Still, I think the midbass should be connected + to + and - to -, simple as that.

Is that to say that Infinity really screwed up? Maybe not. As I said, my early Q2s were connected the way I now have them, contrary to the schematic. It could very well be that the schematic is wrong, as I've commented elsewhere, but that the speakers were assembled correctly. Though yours, Ken, are connected according to the schematic. Perhaps the previous owner did open up your Q2s or paid a tech to do so to affect some repair, perhaps to replace the L-pads that corrode very quickly, and very badly. Then, using the schematics from Infinity, connected the midbass drivers opposite how they were. There is evidence that your pair has been tampered with in that the midbass wires were removed from their original hole and put through another, further back. It is an interesting thought. At any rate, I'm going to keep my Q2s "wrong" for now as they sound like balanced speakers should to my ears and it's not like these are the first good pair of speakers I've heard.

As to contacting Nudell, get ahold of him and arrange a time. I'll drop by and chat. Some of us PacNor'Westers are looking at arranging a Seattle area meet soon. Maybe we can get a factory tour and interview with Nudell at Genesis Loudspeakers in Seattle. :scratch2: Man, that'd be great.

- JP

[Charivari]

Gentlemen, I am no speaker guru, and you have me thoroughly confooozed.

Trying to think this through:

The midbass unit is crossed over to the midrange drivers on the top side and the woofer on the bottom. In the frequency interval where the crossover occurs, both drivers operate. If they aren't connected in the same phase, cancellation will occur and you'll have a drop out (to near-zero) in that range.

Could this be what's happening? To find out, you'd have to check the absolute phase of each driver. Don't ask me how ya do this. I rely on JP for all technical wizardry.
I've not had the official technical training of some on this forum, but I'll make some comments based on intuition coming from a brief lifetime of electronics experience, some scientific background, and personal observation. Basically, yep, you're correct. If the driver is inverted in phase to those drivers immediately above and/or below it and overlaps some, as is typical in all but the most esoteric of designs, then it'll do as you posted. At the crossover frequencies, much will be nulled ranging from slightly to fully depending upon how much the inverted phase driver is outputting compared to the in phase driver. However, the interaction is a bit more complex than that when one factors in harmonics in that the driver in question can wreak havoc way beyond it's own frequency limit when ever its null overlaps with another driver's peak. This happens at random, of course, but significantly so at even harmonics, or multiples of the frequency said driver covers. So, a driver putting out an out of phase signal, can cause noticeable cancellations at 800 Hz, 1600 Hz, and so forth where half is canceled at the first, 1/4 at the latter, and, well, I'm sure you get the picture.

Of course, this is very simplified assuming ideal drivers in free space without baffle, interdriver, intradriver, and room interactions that make it much more complex with bouncing waves all over the place. Meaning, perfect nulls won't happen nor perfect peaks nor perfect wave alignment, so "suck-out", reduced but still hearable, is observed rather than the "anti-noise" phenomenon or complete cancellation.

Blah, my brain isn't working too quickly tonight, so pardon the blaring errors and go for the gist.

- JP

[Kencat]

Well, yesterday was re-arrangement day. I removed the Mach 2s and placed the HPM-60s on top of the Q2s (not ideal, but I need them for the HT setup). Pulled the Q2's out to apprx 2 ft from the back wall and approx 2 ft from the side walls (This is actually what the owners manual says btw, for uncoloured sound. Moving closer to the walls enhances the bass).

The problem is essentially solved. Running everything in "flat" mode has the sound balanced nicely now. Elvis' voice is back :thmbsp:

Running the same piece of music on Winamp with the midbass enhanced equalizer settings is now unnatural and too much. Taking the equalizer out now sounds best.

As you may notice in the pic, I'm running the HK AVR-45 as pre-amp. Provides a more warm gentle sound compared to the Nikko Beta II, and has a wider soundstage with more reverberant high percussion. The Nikko seemed to chop off the "ring" of a cymbal or other high frequency percussion instrument. (I'm learning that I am not a Nikko person :scratch2: )

Also, I did not switch to the HK until after I confirmed that the re-arrangement did improve the mid-bass suckout with the Nikko. In case someone caught the potential dual factor change which would muddy the conclusions :D

So, more listening required to analyse my poor speakers to death. :music:

[Kencat]

Yesterday I swapped the wires on the midbass couplers to see what would happen. Things happened alright...but not for the good.

The drivers took over the sound. It was way too much. In fact it seemed that the whole mid to high end was gone. Also, instruments seemed out of sync with each other...symbals were occuring either before or after (can't tell which) the drum hit. Keyboard and electric guitar were dominated by a lower end drone. Overall the bass was muddier, the tightness was gone. I think the worst part though was the effect between the tweeters and the rest of the music (noting that in the original wiring both the mid-bass coupler and the tweeters are wired out of phase)


Some pieces of music were very unenjoyable if not absolutely irritating with sounds seeming dislocated. The overall sound became almost monaural, the imaging was very centered. Room filling spaciousness (soundstage) was much reduced. Once crisp and clear understandable vocals were now muffled.

I've put the wiring back to where it was. Ahhhh...much better :music:

This was a very interesting experiment for me. The difference was not subtle. Per my ears and in my room, I would say that the out of phase wiring per the Infinity schematics is intended. How it all works..... :dunno: ........only those boys from Infinity back in the 70's know for sure.

[wineslob]

Yesterday I swapped the wires on the midbass couplers to see what would happen. Things happened alright...but not for the good.

The drivers took over the sound. It was way too much. In fact it seemed that the whole mid to high end was gone. Also, instruments seemed out of sync with each other...symbals were occuring either before or after (can't tell which) the drum hit. Keyboard and electric guitar were dominated by a lower end drone. Overall the bass was muddier, the tightness was gone. I think the worst part though was the effect between the tweeters and the rest of the music (noting that in the original wiring both the mid-bass coupler and the tweeters are wired out of phase)


Some pieces of music were very unenjoyable if not absolutely irritating with sounds seeming dislocated. The overall sound became almost monaural, the imaging was very centered. Room filling spaciousness (soundstage) was much reduced. Once crisp and clear understandable vocals were now muffled.

I've put the wiring back to where it was. Ahhhh...much better :music:

This was a very interesting experiment for me. The difference was not subtle. Per my ears and in my room, I would say that the out of phase wiring per the Infinity schematics is intended. How it all works..... :dunno: ........only those boys from Infinity back in the 70's know for sure.


The culprit is the crossover design causing the driver in question to be out of phase if you were to hook it up the "regular" way ie: pos to pos neg to neg. Very common in 3-4 way crossovers.

[Kencat]

The culprit is the crossover design causing the driver in question to be out of phase if you were to hook it up the "regular" way ie: pos to pos neg to neg. Very common in 3-4 way crossovers.

Hey there wineslob,

do you know why this is? All the crossover points in the Q2 are done with 1st order cicuits. I thought there was no phase shifting with 1st order????
Sure would like to understand that concept.