I need to say that with all huge advantages I have in my room with my midbass horns there is something that lost. I lost a great impulse response that I use to have on my old room with my direct radiating bass array covering up to 70Hz. I did not measure the Impulse response then and I did not measure it in the new room but I know how it sounds without any measurements.

The said truth is that as lower bass horn is the more ugly it reacts to short burst of signal. The legato expressions the properly midbass horns handle with untouchable grace. The short and ultra short expression the bass horns tend to possess “longer” then it needed.

If we are taking about 100Hz or even about 80Hz horns then the effect is more or less negligible but with midbass horns of 35-65Hz it is quite tot able. I do not believe in bass lower horns as I told before and I do not want even to look discuss their performance.

I do not have a solution of how to deal with it. Partially I mask the effect using the direct radiating bass channel. What I discover is that mitigation of volume greatly helps to minimize the effect. The key is to let the legato expression to be played by midbass horn at reference volume but the staccato expression to be played at lower volume. Dropping 1-2db at high-speed expression helps a horn to maintain the right auditable pulse response. Of cause I do not do it in real time there is no ways to do it. I set my midbass horn to sound properly all around but it is not perfect setting from impulse response perspective but rather a very well-groomed optimization of compromises.

 Here is what I would like to propose to deal with the problem. In my view to drive a midbass horn and to mediate the problem I described a special type of amplification need to be invented. It is sort of a compressor but the compressor that acts differently for fast and long signals. The long signal it bypassed but the short bursts it slightly attenuate. It is very important that it shall not act as a dynamic compressor and shall not react based upon volume of signal but rather duration of signal. Something similar to what Ed Methner did in his Bidat 20 years ago. In Bidat he had basically two types of processing – one of them used for conversion of short signal another for long signals. So, if to have something like this on analog level then it would be possible to deal with the limitation that I describe.

There is absolutely no thinking about it out there but I very much assure you that ALL with no exception bass horn suffer from this problem. I do not insist that my idea of Horn Timing Compressor will work, it rather patch the problem if such a devise were made. Still I feel that the notion of midbass horn under-performance at short signals has to be made known. I

I think that the ultimate solution would be not the Horn Timing Compressor but rather asymmetrical amplification.   The midbass horns dodo fine attack of the short notes but they all delay with decay. If to make an amp that would shorten decay of the fast notes then it would be a phenomenal solution. How to make an amp with “intelligent” decay that would be variable and self-moderated by a duration of notes I do not know yet, but this is what I am thinking about lately.

Romy the Cat wrote:

The midbass horns dodo fine attack of the short notes but they all delay with decay. If to make an amp that would shorten decay of the fast notes then it would be a phenomenal solution.

haralanov wrote:

Your midbass horns have delay with decay, because there are a lot of internal reflections (acoustic resonances) that takes some time to settle down below the treshold of hearing. It can not be compensated by "special type of amplification"... These resonances could be controlled only mechanically by making some kind of "acoustic diode" that absorbs the energy of the sound that is reflected back to the neck of the horn. Something like this…. The drawing is very rough, but it allows you to get the idea. The blue spray illustrates the damping material.

Brilliant thinking, haralanov.  I like the idea of  acoustic diode, even if  do not know if it would be affective s we do not know the true reasons why fast notes have issue with bass horns, You feel that it is due to settling down the internal reflections but I am not sure if it is the reason. It very much might be the re-entry reflections. With the mouth of this size the horn become a very sensitive microphone… I can give another few reasons why the effect might exist. They are all hypotheses and there is no conformation what is the true reasons. You need to understand that all horn knowledge that we have and all horn theory that we visualize exist only for static applications and no one deal with transients processing by horns.

Last night I called to Bruce Edgar and asked him if anybody in past dealt with the notion. He pretty much confirm that no one look into it seriously. If Edgar does not know it then no one does, that is for sure. Bruce pointed me out to any interesting scientific thing that I did not know – the group velocity. The applied idea is the propagation of groups of short pulses across the horn would follow different principles then one long pulse.  I think I need to drive pulses and squares across my bass horn and to see what is going on.

I like the idea of acoustic diodes but it might be not so simple and we might need some sort of acoustic semiconductor as the presses that make the short notes to sound different then long notes might be not as linear as internal reflections are. I do not have answers now and I need to consult with more people about it.

I've sort of been wondering if you might bring this up; it is exactly the concern I had when briefly listening to my one completed 40Hz horn. In my case, there was no other mid-bass channel to use for comparison; still this characteristic was apparent.

Such is the price one pays for having bass horns one can truly bring home to mother! There will always be those nights when what we really want is a confidently nasty little red-head...

I have not ruled out taking on a mistress in the form of some sort of direct radiating setup (like your bass line arrays) running in roughly the same frequency range as the 40Hs horns. I don't know that it is a realistic means of addressing the issue and successfully integrating such a relationship usually proves to be very taxing.

jessie.dazzle wrote:

Romy wrote: "...The legato expressions the properly midbass horns handle with untouchable grace. The short and ultra short expression the bass horns tend to possess “longer” then it needed..." I've sort of been wondering if you might bring this up; it is exactly the concern I had when briefly listening to my one completed 40Hz horn. In my case, there was no other mid-bass channel to use for comparison; still this characteristic was apparent. Such is the price one pays for having bass horns one can truly bring home to mother! There will always be those nights when what we really want is a confidently nasty little red-head... I have not ruled out taking on a mistress in the form of some sort of direct radiating setup (like your bass line arrays) running in roughly the same frequency range as the 40Hs horns. I don't know that it is a realistic means of addressing the issue and successfully integrating such a relationship usually proves to be very taxing.

Jessie, you might consider my response extremely strange but I very confident that I very much correct in my suspicion. My suspicion is that you are incorrect and we are talking about very different things. My comment was about very minor satellites, about a nuance character, not about the dominating quality. The effect I experience is very minor and I absolutely assure that no one who heard my playback ever noticed the thing in the direction I described.  The effect exists but at the degree that serves purely semi-theoretical purpose and it is WAY below the level that any motivation to change anything would appear. 

What you describe it feels like much stronger effect. Knowing that you was listening your midbass horn only briefly and as a uncompleted prototypes I absolutely assure you that what you hear was not what I am taking about but the effect of improperly integrated midbass.

You shall not hear the sound of ONLY midbass horn as in your case it is very narrow band devise and it has to be supplemented with channels the serve the overtones. Also, the integration of the 40 Hz horns are long and creative process – you will not be able to do over a few days of briefly listening. This site well documents the efforts and time I went over. It took 3 months until I was able to get the level, application and filtration that work.  The horn people who visited me did not believe that the horns where it is but it took a very deliberate tuning that sometime is not so orthodox and straight forward. You did not go over it and I feel that your comments are a bit premature.

Make a good direct radiating midbass channel. Make your playback to sound well with it. Then engage your midbass horn and make your playback to sound with the midbass horn identical to the direct radiating midbass channel. Then, ONLY THEN, comment about the differences between your midbass horn and direct radiator. I think you do a methodological de-service to yourself making concussions about uncompleted random midbass that were played with some kind of random playback that was not tuned to play with horn midbass.

I think we will return to this conversation but if you will be at the same boat as I am then you would agree that the subject is more has to do not with the actual sound but with some sort of sonic finesse.  For whatever it worth it shall motivate to built an alternative midbass channels, not that you are not free to do it…

Ok, I will share with you some ideas that I have in my head how to deal with horn decay asymmetry. They are in a way the further development of the Haralanov’s idea of acoustic diode – the brilliant concept from my point of view.

Before I will go into explanations I need to again to insist that what I am talking about, the decay asymmetry is not the same as too long decay of improperly integrated horn. The whole idea is that horn shall operate in the way that you shall not be able to be bother with whatever decay it has. I absolutely inset that my midbass horn made to sound properly and no one listening my installation would admit that the decay is relatively longer then attack. In fact as I type this post I have a local audio guy in my room who is here for many hours and I will just for fan question him if he feel the too long decay from anywhere in my room. I absolutely convinced that he will not confirm that he hear anything destructive.

The answer is that I am not just a guy who cut wood, solder tubes and connect wire but I am creating Sound and the longer decay that I was impaling about has factored in the total configuration and calibration of my installation. Still as the person who dealt with all little idiosyncrasies of my playback tuning I do admit that I observed the decay asymmetry in midbass horn.

So, the conversation is more theoretical or rather conceptual but I very much might not be so as if a good solution is found then it might open doors for something else.

The Haralanov idea of acoustic diode is powerful but a bit incorrect. We do not need a diode but we need some kind semi-diode that would be fully transparent in one direction and to be semi-transparent in other. Why so? From all that I know about horns there is nothing in them that would cause the asymmetrical decay. Sure, horns by nature are band-pass resonators with own ringing but the square wave ringing might be easily moderated by driver damping. So, where the asymmetry of decal might come from? The most probably it comes, as I proposed above from the fact that horn mouth acts as very sensitive microphone that pick up re-entry of bass from the room. Since horn condense the re-entered sound it might create a contra-pressure to driver (that I think is negligible for midbass horn) and the most important it create the “wondering re-entered bass”. For sure it is hugely delayed only God knows exactly how it affect Sound but a large even ¼ size 40 horn are large with a lot of room for re-entered bass to wonder around.

Now, let to put the Haralanov idea of acoustic semi-diode is use. Pretend we drive a signal from generator across the horn, read it with microphone in the listening position and output to scope. Very soon we will be able to recognize what would be distortions difference between transient signals and slow signal. We do not care about any distortions that are there and cares ONLY about delta between sustain waves and pulses. We can easy to extract the amplitude and the bandwidth of that delta. Let pretend that it will be let say extra 2dB at 70Hz-100Hz for 40Hz horn for a given room. Now we do something kinky. We have ULF channels that are sitting on opposite side in time-aligned position to midbass. The ULF channels sue 20Hz lowpass sharp filter. So, what we do it taking with another filter 2dB at 70Hz-100Hz from the main signal and inject them to ULF channels in opposite phase but after the ULD own lowpass filter. So, now we have the ULF channels that serve double purpose – pump the ULF as main duty and to cancel the midbass “wondering re-entered bass” by injecting the opposite phase error.

If you feel that it is not bold enough then let take the concept further.  Pretend we have at the mouth of the midbass horn a small mono-poll driver, shooting insider of the horn (toward to the throat) the back-phase of the asymmetrical decay error.  I named this little speaker Re-Entry Corrector.  This Re-Entry Corrector would not need any calibration – just slide the Re-Entry Corrector filtration and level (it would be perfect to use a digital crossover) and tune the back-phase inspection until a sustain wave and transient wave would have the same passing across the horn for a given room.

This is a very different thinking about the midbass horn. Many other options are available. We can put a pressure sensor in back chamber or a microphone at listening position and from that extrapolate and predict the need from re-entry. Do not forget that we do not do “room correction”. All that we are trying to do is just to slightly touch one very narrow zone of spectra that might come boomy from bass re-entry. I think it very much might be 1-2 db at very marrow width.

What I described are not the blueprint what to do but juts the inspiration how the things might be done.

unicon wrote:

Bass FRQ have enough power to vibrate horn mouth and constructional area nearby them.  use a chip contact Mic in your horn mouth n monitor how does it vibrate Remember the time I insisted for having access to your midbass horn driver screws ? I left a threat also with graphs showing how loosening to tightening the screws can change the impulse response ...

From: John Hasquin
Sent: Wednesday, June 15, 2011
To: Bessnow, Roman
Subject: Re: Meow

"I think your decay is prolonged because the larger room is providing acoustical pressure feedback into your 45Hz lower bass horn. This feedback is modulating your horn and creating artificial decay that is not supposed to be there. This is almost like echo, but not exactly. Like you said, the large mouth acts as sensitive microphone now. The smaller room you had was not able to provide enough acoustical pressure feedback at a frequency that affected your tractrix midbass horns. Also the tractrix midbass horn’s smaller mouth and smaller woofer would be less sensitive to this effect. The larger room’s feedback frequency is much lower so it affects the lower bass horn with its large mouth instead of the tractrix midbass horns. The larger room volume also boosts the acoustical gain of this feedback just like a larger box boosts the efficiency of high sensitivity woofers. I don’t see room modifications being possible or practical. The room is what it is. The only ways I can think of trying to control this problem is with amplification change or woofer change. It might be interesting to try a transconductance or current amplifier. Something like the Pass Labs F1 amplifier. The reason for this is the transconductance amplifier is a current control amplifier so it sends current to the voice coil in relation to the music signal. In other words it is always controlling voice coil current and if an outside acoustical force tries to modulate the cone the current in the voice coil acts as an electronic brake to prevent the cone from being moved. The higher output impedance of the transconductance amplifier also serves as a load for any energy created in the voice coil by cone modulation. Most amplifiers are voltage controlled and have low output impedance. This low impedance cannot provide any load for the modulated energy to be dissipated so the cone continues to move and exaggerates decay. Some people believe you want a low impedance to serve as an electric brake for the woofer cone, this is not true. In order to provide cone braking, the energy in the voice coil needs a load to dissipate into. This is why unused speakers sitting in a room will act as a sound trap. The below thread shows that the tapped horn acted as a better bass trap when the speaker leads were left open instead of shorted together.

   http://www.diyaudio.com/forums/subwoofers/182464-th-bass-trap.html