Re-coned Advents sound "tubby", what's the fix??

[justw]

I have been lurking in this group for years but now need some advice and help. I have recently aquired a pair of early Large Advents. This is my third pair of these so I am no stranger to the sound. Anyway, The woofers had been replaced with totally unsuitable drivers. Soooo, I bought a couple of original woofers that the masonite ring was removed from, a 12" cone and a new spider, and presumably a new voice coil, had been very well installed. After mounting in the cabinets with appropriate ammounts of grey, monkey s*#t, sealant I proceeded to burn them in as they don't appear to have had much use. Overall the FrankenVents sound close to the same as my Advent/1's and my newer Large Advents but, the bass is a little "tubby" and the midrange is noticeably lower. If I turn up the midrange control on my Marantz receiver two clicks the midrange sound fine but the bass is still "tubby". Obviously the tubbiness is due to the altered cone of the woofer. Is there a simple fix for tubby bass? Like more or less fiber fill or a series resistor? I am not too keen about making changes to the crossover but I suppose a little tweaking couldn't hurt. The midrange may be due to crossover differences between the early model and Newer model. As the bottom units of a stacked pair they work fine but I would be happier if the "sound" more closely matched my others. Thanks in advance for any guidance.

[Guest daveshel]

I don't know what 'tubby' sounds like but if you don't have a good seal on the woofer you will lose your bottom octave and the next octave up will be accentuated. I guess I would call that 'boomy.'

[Doug G.]

It's the 12" cones. You must have original woofers (or ones exactly like them) for your Advents to have the bass that was designed into them. If you put bigger coned woofers into them, the Q is actually raised and the bass drops off sooner. There will also be a mid-bass hump that you hear as "tubby".

You can't just take any woofer and plop it into any speaker and expect it to sound the same. This is true of any well designed speaker, not just the Advents.

Don't mess around. Get two original Advent woofers. They're not that difficult to find. Don't alter the electronics trying to get a sound you won't be able to capture anyway.

Doug

[justw]

daveshel - Yes, I suppose "boomy" could apply too. Nope, no air leaks.

Doug - Thanks. Yes I know the sound will be altered. But was hoping that the differences could be minimized by some simple means. No, I am not keen to modify the crossover but if I could add a parallel resistor here or remove some fiberfill to reduce the mid-bass hump I would probably be satisfied with the sound. That being said, how does one lower the Q of a speaker enclosure? Is that what tuned ports are for?

[dynaco_dan]

>daveshel - Yes, I suppose "boomy" could apply too.

>Nope, no air leaks.

>

>Doug - Thanks. Yes I know the sound will be altered. But was

>hoping that the differences could be minimized by some simple

>means. No, I am not keen to modify the crossover but if I

>could add a parallel resistor here or remove some fiberfill to

>reduce the mid-bass hump I would probably be satisfied with

>the sound. That being said, how does one lower the Q of a

>speaker enclosure? Is that what tuned ports are for?

>

Hi Justw;

Doug hit the nail right on the head.

Go out and buy two woofers off of ebay.

Myself, I prefer the original woofers with the masonite ring.

If need be, re-foam them.

Maybe it will cost you $50.00 for this project.

Good luck.

[Doug G.]

justw,

A bigger cone requires a bigger cabinet. The reason the Q is raised with the larger cone in the same volume is because the larger cone area compresses more air within the enclosure and thus, there is more resistance to the movement of the cone. This raises the resonant frequency of the system and the bass response drops off rapidly below this frequncy.

You would have to have a cabinet that results in the same cone movement resistance with the 12" cone as with the 10" cone in the Advent speaker. If this condition were met, I would expect an even lower bass response given the larger cone area.

I don't know what the exact dimensions of the enclosure would have to be but I know there are formulas for calculating this.

I hope this has been clear and I hope you are able to get your Advents sounding as they should. It is still amazing that the kind of low bass response present in these speakers is possible with a cabinet this size.

Vern is correct that it wouldn't cost too much to get the proper woofers into your Advents.

Doug

[justw]

Makes sense. I have reconed my other two pairs but for several reasons thought this might be doable. The woofer I installed has a larger cone but not quite as resillient as originals were. Also in the orginals though the cones were 10" the masonite ring extended to the 12" frame and had to have some flex to it as well. Therefore, my replacement though not as flexible has more surface area. Which, seems to me, should compensate some.

Note: I am by no means a speaker expert but have been an electronic technician in various fields for about 30 years.

Update:

I had inadvertantly connected the woofer wires reverse so the phase relationship to the tweeter was 180° off. Once corrected male voices smoothed out considerably. I also elevated them a few inches off the floor to immitate the setup of my other speakers on spikes. Oddly the midbass hump is not as perceptable now when I A/B with my Large Advents. A quick, though not completely accurate, check with my RS SPL meter and a tone generator show that the Original Large Advents are within 5dB to about 25Hz and the Frankenvent starts rolling off about 50Hz but still audible down to maybe 30Hz and the midbass bump is maybe 5dB around 90Hz.

I think i am going to "live" with these a while either beside or on top of my stacked pair and next time I have the urge to pull the woofers I will remove half the fiberglass. Since Q is inversely proportional to resistance then if I reduce friction inside the cabinet I will lower the Q.

Note to purists: Any mods to these will be reverseable and not destructive! The main reason I bought this third pair was to have some spare parts for my stacked pair that I wouldn't trade for any speaker ('cept maybe a mint pair of Dalquist DQ10's...).

[justw]

I was in babble mode last night. So, before any one catches my mistatement, what I meant to type was:

I think i am going to "live" with these a while

either beside or on top of my stacked pair and next time I

have the urge to pull the woofers I will remove half the

fiberglass. Since Q is proportional to resistance

if I reduce the resistance inside the cabinet be removing some of the fiberglass, I will lower the Q. Maybe switching to foam like my newer Advents have is worth a try?

[Doug G.]

What you say makes sense, assuming the fill adds quite a bit of resistance.

Also, if you are going to use these in a triple set-up, the bass response shouldn't be as critical as the other two pair provide plenty of it. Just so you don't end up with that annoying mid-bass boom.

Let us know how it works. Do we really have to wait until the next time you happen to remove the woofers? :^)

What kind of surrounds do the 12" woofers have?

Doug

[justw]

>Also, if you are going to use these in a triple set-up, the

>bass response shouldn't be as critical as the other two pair

>provide plenty of it. Just so you don't end up with that

>annoying mid-bass boom.

Exactly my thinking.

>

>Let us know how it works. Do we really have to wait until the

>next time you happen to remove the woofers? :^)

>

Unless I can the stuff out through the tweeter hole! I don't feel like messing with that sealing stuff again. I used that grey reubbery stuff, I call it Monkey S*&t.

>What kind of surrounds do the 12" woofers have?

Cloth, that is why I think they should closely approximate the Masonite ring woofers.

>

>Doug

[justw]

Well after living with my Frankenvents, and some emarassment with someone here asking "what freakin kind of woofers are those?" I swapped them out with a pair of non-masonite ring woofers I finally got around to refoaming. I decided the only way to get rid of the midbass hump would be to install a port, yechhhh, or a passive radiator on the rear. Not wishing to deface an otherwise very nice pair of U3 Large Advents I replaced them. They are breaking in now but already are nice. Amazing how a frigged up bass response can alter your perception of the mid and high frequencies. These 12" Frankenvent woofers have got to be good for something though. Someday I need to calculate the TS parameters to find the cabinet volume they would work in. Anyone care to offer a guess? Assuming all else equal but the cone displacement and area increased to 12". Anyways consider this pair restored. Now about that fourth pair.....

[Guest GranPa]

With the new cones, if you had a 5db hump at 90Hz, the cabinet is too

small for them. More damping material, or a better quality damping

material would help lower the Qtc somewhat without butchering the cabs.

Quality damping material should make the cabinet "act" 20% bigger.

[dynaco_dan]

>I have been lurking in this group for years but now need some

>advice and help. I have recently aquired a pair of early Large

>Advents. This is my third pair of these so I am no stranger to

>the sound. Anyway, The woofers had been replaced with totally

>unsuitable drivers. Soooo, I bought a couple of original

>woofers that the masonite ring was removed from, a 12"

>cone and a new spider, and presumably a new voice coil, had

>been very well installed. After mounting in the cabinets with

>appropriate ammounts of grey, monkey s*#t, sealant I proceeded

>to burn them in as they don't appear to have had much use.

>Overall the FrankenVents sound close to the same as my

>Advent/1's and my newer Large Advents but, the bass is a

>little "tubby" and the midrange is noticeably lower.

>If I turn up the midrange control on my Marantz receiver two

>clicks the midrange sound fine but the bass is still

>"tubby". Obviously the tubbiness is due to the

>altered cone of the woofer. Is there a simple fix for tubby

>bass? Like more or less fiber fill or a series resistor? I am

>not too keen about making changes to the crossover but I

>suppose a little tweaking couldn't hurt. The midrange may be

>due to crossover differences between the early model and Newer

>model. As the bottom units of a stacked pair they work fine

>but I would be happier if the "sound" more closely

>matched my others. Thanks in advance for any guidance.

Hi there;

I see this is almost one year old, so I assume the situation has settled down by now.

I see new cone and spyder.

The replacement units would be critical for similar spec's.

Was the cabinet insulation/foam reduced or increased in quantity?

Normally putty wasn't used for sealing but it is not a bad idea to use it for both drivers.

You can't just pluck x # number of pounds fibreglas out of the cabinets and replace it with x # pounds synthetic fillers.