Unpleasant noises from my IB

[toecheese]

Compare that response to Mach 5s- I told them I considered taking a flight to Canada to get the speakers (would be the same cost as shipping them) and got offered... FREE BEER. That's customer service :-)

[canaris]

How much better are the Mach 5's than let's say then the Tempests..? I just converted my two Tempests sealed sonosubs to an IB....and I want more...and I am stuck between ordering two more Tempests or 4 Machs.....the Xmax on the T's is way more than the Machs...I wonder what better 4 T's or 4 Machs's?

[DrWho]

You really should be implementing a high pass filter on any subwoofer - especially IB's where the cone is essentially unloaded at the lowest of frequencies. Just pick a region where the measured output is already falling and then drop it off as fast as you can. You can't hear below 20Hz anyway, so all you're changing is the amount of visceral impact - but it's not going to be a huge change since there isn't output in the first place.

This will also work to remove a crap load of frequency intermodulation distortion (aka "doppler effect") and should work to really clean up the bass.

To be honest, there is no reason why Adire shouldn't be able to provide a recone kit. There should be nothing wrong with your magnet and basket structure. Voice coils are also very easy to replace. Just seems a bit odd - I thought it was acceptable industry standard to provide recone kits

[drf]

DrWho wrote:

To be honest, there is no reason why Adire shouldn't be able to provide a recone kit. There should be nothing wrong with your magnet and basket structure. Voice coils are also very easy to replace. Just seems a bit odd - I thought it was acceptable industry standard to provide recone kits

I was thinking this too, although I have no experience with adire so I didn't want to say anything. One of my suppliers had some clients who Blew a set of Wharfdales by overpowering them, because there was no real proof wharfdale sent out there tech and re-coned the drivers. It is as viable as replacement.

I don't know if it has been questioned before, however is an IB the best enclosure/system for adire subs? I have known of a few subs that just can't handle too large rear enclosure.

[Ayreonaut]

DrWho wrote:

You really should be implementing a high pass filter on any subwoofer - especially IB's where the cone is essentially unloaded at the lowest of frequencies. Just pick a region where the measured output is already falling and then drop it off as fast as you can. You can't hear below 20Hz anyway, so all you're changing is the amount of visceral impact - but it's not going to be a huge change since there isn't output in the first place.

IB subwoofer cones are "unloaded" at all frequencies. Excursion is the limiting factor. If you run out of excursion, you need more displacement. Many IBs generate clean output down into the single digits. The DC filters in most consumer electronics serve to high pass around 5 Hz, which works out very well. Drywall cracking infrasonics are where its at! Don't throw it away!

[Chrisbee]

Ayreonaut wrote:

IB subwoofer cones are "unloaded" at all frequencies. Excursion is the limiting factor. If you run out of excursion, you need more displacement. Many IBs generate clean output down into the single digits. The DC filters in most consumer electronics serve to high pass around 5 Hz, which works out very well. Drywall cracking infrasonics are where its at! Don't throw it away!

I was thinking the same thing.

I can get well over 90dB at 9 feet at 10Hz (RS SPL meter uncorrected) from my 4 x 15" IB with virtually no cone movement at all.

One day I'll double the number of drivers and finally get some real bass out of it!

I don't need a high pass filter. I just need more turbo boost!

[DrWho]

I should rephrase, below the resonant frequency of the system you no longer have mechanical damping - you're relying entirely upon the electrical damping inside the amp to control the cone excursion. And it gets worse when you consider the non-linear behavior of the air on the cone as the piston becomes smaller and smaller relative to the wavelengths being reproduced.

One of the analogies I've heard compares displacing X volume of water with a rod (~1 cm^2) and a frisbee (~20 cm^2). Though you have to move the rod 20x further for the same displacement, it's going to move much easier than the frisbee. (The analogy of course assumes that there is an appropriate baffle present). Though moving to more drivers increases the overall displacement, it also increases the area of the piston - making the displacement more effective.

Another factor that comes into play is the non-constant pressure in front of and behind the driver. When a low frequency sound is sent out into the room, some of that is going to bounce back and arrive in front of the driver (same thing happening in the rear too). The changing pressure seen by the driver is going to change how it behaves - if a large transient hits while there is a null in front of the driver, you're going to realize far larger excursions, yet measure the same SPL. That cool fan sub takes advantage of this effect by creating air pressure with the fan blades - and then only small excursions are needed for the same SPL. The opposite effect is that a lower pressure is going to cause over-excursion. I've been told that this same physical system is why passive radiators often need 4x the excursion of the active driver.

I'm by no means a driver expert, but I thought some of these ideas were rather interesting. I don't think it's a huge sacrifice to trade cracking walls for a system that doesn't blow itself apart

[Chrisbee]

Interesting points. Though I have some further thoughts.

An IB cone is not limited to the front surface only. The back of the cone usually "sees" a finite rear enclosure. A pressure wave returning to the front of cone from the listening room is likely to be matched by a pressure wave returning from the rear volume. Only if the IB uses the great outdoors will there be no returning wave to match that arriving at the front. The phase of the returning pressure waves is very unlikely to match cone movement.

How is this "problem" related only to the IB? A reflex system below system resonance suffers driver unloading. Would it too not also suffer from returning pressure waves? Wouldn't the reflex cone drive its own reflex port into an infrasonic rumble?

Wouldn't these returning pressure waves be much reduced in comparison with the originating pulse from the driver cone?

It might be possible to monitor an IB or reflex system driver using the voicecoils as a low impedance microphone. While another IB (or VLF-capable sub) at the other end of the room plays a suitable signal.

Meanwhile: In at least one real-life IB situation: If the driver being monitored was an AE IB15 then I doubt much would be found emanating from the driver terminals with such stiff suspension. My very leaky IB enclosure is subject to the prevailing SW winds but no cone movement has been detected by its formerly worried owner so far.

I don't think we need worry too much about returning pressure pulses from the IB affecting itself. The change in atmospheric pressure from a returning VLF transient is simply too small to have any detrimental effect on sound quality.

I believe The Thigpen Rotary Sub has yet to prove itself as silent as an IB when receiving no signal. Perhaps it needs a folded, tapered and heavily damped labyrinth of sufficient length to avoid unwanted pipe resonances?

[norpus]

toecheese wrote:

Okay, I am unhappy with Tempest. I was told they don't have a rebuild kit, but are more than willing to sell me new ones.

Considering it went out without warning (or maybe the sounds I'm hearing is the warning...) and that it can't be rebuilt.. why would I want to stick with them?

(well, maybe I shouldn't be so harsh on them- the answer was from a reseller and not the manufacturer, so I'm going to follow up that route- but I still need to buy some)

Toecheese, I use a pair of Tempest 15D8 on my rear IB. They make a good IB driver set IMO. 4 would definitely be better though and you'd have plenty of power with the EP2500 remaining. Did you overpower the first two at all? When stress testing, I have heard mine both clip (with a smaller Behringer A500) and bottom (with a 500watt AB plate amp) - neither distortion sounds good and is v easy to hear, but you need to be careful with only 2 drivers. Four would give you the headroom you might be craving

[canaris]

I have been using dual Tempests in sealed 5 cube boxes now for the last 3 years....only last week I converted them to IB...and am astonished at the difference. I am about to order 2 more simply because I want to crank it up there and right now ...kind of afraid to... for the money I find the Tempest an excellent woofer.

[DrWho]

Chrisbee wrote:

Interesting points. Though I have some further thoughts.

An IB cone is not limited to the front surface only. The back of the cone usually "sees" a finite rear enclosure. A pressure wave returning to the front of cone from the listening room is likely to be matched by a pressure wave returning from the rear volume. Only if the IB uses the great outdoors will there be no returning wave to match that arriving at the front. The phase of the returning pressure waves is very unlikely to match cone movement.

Unless the rear chamber and the front chamber are identical in shape, then the pressure waves are going to arrive at different times.

How is this "problem" related only to the IB? A reflex system below system resonance suffers driver unloading. Would it too not also suffer from returning pressure waves? Wouldn't the reflex cone drive its own reflex port into an infrasonic rumble?

It's not, but in a "small box" (relative to wavelength), you effectively see a static increase in pressure inside the cabinet that matches the movement of the cone. Below the system resonance, the leakiness of the port becomes the swamping issue.

Wouldn't these returning pressure waves be much reduced in comparison with the originating pulse from the driver cone?

It might be possible to monitor an IB or reflex system driver using the voicecoils as a low impedance microphone. While another IB (or VLF-capable sub) at the other end of the room plays a suitable signal.

Meanwhile: In at least one real-life IB situation: If the driver being monitored was an AE IB15 then I doubt much would be found emanating from the driver terminals with such stiff suspension. My very leaky IB enclosure is subject to the prevailing SW winds but no cone movement has been detected by its formerly worried owner so far.

I don't think we need worry too much about returning pressure pulses from the IB affecting itself. The change in atmospheric pressure from a returning VLF transient is simply too small to have any detrimental effect on sound quality.

I agree, the pressure in front of and behind the driver shouldn't move the cone around (in other words, that's not what I was saying). For a changing air impedance and a given voltage applied to the motor of the driver, you are going to realize different cone excursions and SPL. When the impedance of the air goes down, the acoustical damping on the cone is less as well as the SPL (the two are intimately related). But with an increase in impedance, the SPL goes up and the excursion goes down. In the modelling programs, the pressure infront of the driver is considered to be constant (normal air pressure in the room) and so the impedance is assumed constant. However, whenever the pressure in front of the driver goes down, the air impedance also goes down. It works in the other direction too, but a higher impedance isn't going to be the cause of a driver bottoming out

I believe The Thigpen Rotary Sub has yet to prove itself as silent as an IB when receiving no signal. Perhaps it needs a folded, tapered and heavily damped labyrinth of sufficient length to avoid unwanted pipe resonances?

lol - I was just referring to it in principle (increasing air pressure to increase the air impedance seen by the driver). Another equally effective approach is to use a horn - only they need to be insanely huge...

With an IB, you have no control over the impedance seen by the driver and it is certainly going to change with the dynamic response of the room. It is a nonlinear system making it very difficult to predict, but it happens. It just becomes a bigger issue with IB's because the cone excursion is an unstable system - compared to other designs where the cone excursion is better controlled (small sealed cabinets and vented systems above the port tuning)

Also, when cranking any type of system there are going to be peaks centered around the impedance peak of the system - usually the Fs of the driver. This is due to the heating of the voice coil adding a resistive component to the impedance response (reducing the output more at frequencies where the impedance is low). Peak excursion is generally going to happen around 15-20Hz, which isn't going to be very pleasant when the signal is riding along a huge 10Hz wave.

[Chrisbee]

Mike

Thanks for your interesting responses to my ramblings.

I am not sure at this point whether you "like" the IB subwoofer or not.

Given sufficient displacement an IB can run rings round anything else on the planet except perhaps a giant exponential horn. The IB is a clear winner domestically. Requiring very little effort or expense for remarkable extension, high SPLs and low distortion. A horn would have to be of industrial proportions to have any useful output at 10Hz. Yet a set of 4 rather modest 15" drivers set in a small cube in the wall or floor can manage 100dB at 10Hz with ease.

My own experiences of using an IB for enjoying organ music suggests that distortion is still very low at frequencies and SPLs that most box subs can only dream about. The huge organ pipes tiptoe effortlessly on jumbling icebergs of infrasonics. The clarity of timbre, leading edge, sustain and decay of these very low notes is phenomenal. The beating that occurs between the great pipes constantly changes pace and frequency. No other subwoofer could lay bare the near-infrasonic landscape of an organ piece so effortlessly and so graphically for so little effort or outlay.

It is never enough that a subwoofer reproduces very low frequency sounds loudly enough to be heard. It must do so with very low distortion to make the exercise worth the effort. The IB can do all this without needing to physically dominate the listening room.

[brucek]

DrWho wrote:

Also, when cranking any type of system there are going to be peaks centered around the impedance peak of the system - usually the Fs of the driver. This is due to the heating of the voice coil adding a resistive component to the impedance response (reducing the output more at frequencies where the impedance is low). Peak excursion is generally going to happen around 15-20Hz, which isn't going to be very pleasant when the signal is riding along a huge 10Hz wave.

I have to admit that you could fit my understanding of speaker and driver behaviour on the head of a pin, but something about this statement just doesn't ring true.

I would have to guess that that the wire used to wind voice coils would possess a neutral temperature coefficient such that its DCR would remain fairly constant over a large temperature range. Is not the concern of voice coil heating solely one of protection against warping or damage to the enamel shellac dielectric that protects the wire? Is a current that is less than damaging really going to change the DCR of a coil?

* It would seem to me that the DCR of the voice coil would be considered insignificant and overwhelmed at resonance (Fs) by the high frequency dependant AC impedance. At that frequency, is not the system inductive reactance and capacitive reactance equal and opposite to produce a minimum current condition, so as to result in a pure equivalent maximum impedance that is totally resistive? This AC resistance wouldn't be caused by the DCR of the coil or the small amount of change in DCR because of heating. The DCR for an 8 ohm driver would be a fairly constant ~6 ohms. At least that would be my take on it - or maybe I'm way off.

Do you have any references I might read to support your interesting statement?

brucek

[toecheese]

I've been suffering all this time with a single woofer waiting for Mach5 to get the high-excursion18s out. As of this date, the Mach5s are still not here- and considering that no one has actually seen- much less listened to them, I guess I'll have to pass. (Worried about other aspects too- like 'bottomless motor').

Meanwhile, the Tempests are cheaper now- $135 shipped. Everyone's advice seems to be that I should be driving 4 of them...

[mrogowski]

Well, I certainly hear you on the time-frame issue. My apologies for this. For those of you who are still on the fence with the IXL, They have arrived in Canada and are making their way here as I write this.

The Tempests have being around a long time and have proved themselves thrice over. I personally wouldn'd hesitate on getting them for HT.

Best of luck!

Mark

[toecheese]

Thanks, Mark. My neighbor is building his HT now and may be in the market for the 18.4s when they're available.