GoodSoundClub - Romy the Cat's Audio Site

In the Forum: Horn-Loaded Speakers
In the Thread: Jessie Dazzle Project

Post Subject: Upper-bass as a system's fulcrum: Part IPosted by jessie.dazzle on: 3/8/2010

First off, I forgot to mention an interesting observation: Before running the sweeps (previous post), since the drivers in the upper-bass horns are new, I decided to verify/optimize rear chamber volume (they are easily adjustable)... I wasn't expecting to have to move the piston much, but in fact I did move it quite a lot, and was surprised at how much this movement affected the output of lower frequencies. Prior to this, with the 16 Ohm versions, I had only adjusted rear chamber volume with filters (coils) in place, and for whatever reason, the effect was less pronounced.

Romy wrote:

"...It looks the acoustically the default location of your horns is not the best in your room... Still, you alternative wall position might not be the best in the room and you might have even better location..."

Yes, and for the moment, there is no possibility to optimize placement; the entire system, along with the first completed mid-bass horn have had to be pushed to one side of the main room, in order to leave space for the construction of the second mid-bass horn.

"...If you implement let say 450Hz filter and add 2-3dB of the upperbass out[put], then you virtually increase the output of your upperbass in the frequencies that you are looking for..."

Yes, I follow.

"...Be advised that you will have a LOT of problems to do it as it is very hard to low-pass this driver with speaker-level crossover as the coil the crossover will talk with inductance of the driver and combined coil will be much lower. You would need to use a coil 3-4 times larger then what calculation would suggest but this overly large coil would talk too much with your MF channel. Multi-amping will kill the problem and the crossover in the amp will not be seeing the driver inductance. Using the speaker level crossover you need to use larger coil..."

I run the lower-mid horn (S2 into 180Hz tractrix) down to 400Hz, so I'd like to low-pass the upper-bass at that point. A 2.50mH coil (which would, according to calculations, low-pass the driver at 510Hz) has almost no effect; 4.50mH starts to make an audible difference, but the driver is still playing a lot of mid-range. I have larger coils on hand, but have not yet tried them.

"...So, you roll off the upperbass sooner then the channel would like you to do and boost 2-3 dB of the channel’s gain. You might not have those 2-3dB driving the thing from a single amp. To get 3dB more you will need to go to another tap but it would make the output tube to be loaded harder at the frequency of given channel and might make the sound too slow... Also, do not forget that you use first order filets and change of the loading for a given channel will very much affect loading for other channels..."

What really surprised me was how good everything sounded with no filter on the upper-bass horns, and all drivers connected to the same (8 Ohm) tap; sure I'm getting too much mid-range from the upper-bass horn, but its not as destructive as I would have predicted.

"...So, what you need to do if you need more gain but do not have it? You need to drop the level of your other associated channels. It would not be a good idea to do it for bass channels as adding resistors would affect damping. However for HF channel adding resistors (dividers or juts single resistors) would be fine. Find a non-inductive resistor (very important) of a few watts and use it with your MF driver, driving it for a few dB down and matching your yellow reference line. Do the same with tweeter and fundamental channel and your will have proper upperbass balance for your system..."

Yes, finding the proper level of attenuation should be fairly simple; as previously discussed, I could use the L-Pads already in place (currently bypassed) on all MF and HF drivers to establish the correct level, then build the corresponding resistive voltage dividers.

"...I do not know what kind bass you use but add the LB channel to the mix (still using the NEW yellow line as reference)..."

Two 16 cubic ft concrete enclosures; each housing a single McCauley 6174 (18" paper cone; rubber suspension), driven by a pair of M1.1s.

"...Then you would need to do a very important thing- to fine tune what would be your Yellow Reference Line (YRL). At this point your YRL is purely arbitrary but you need to bind it to you room. Here are some techniques that you might find useful. Shut down your fundamental channel (still ONLY for one left or right channel) and use ONLY MF and Midbass [upper-bass?] to get the sound that you feel is right. It shell be a proper balance between the violins/violas and cello section in complex (very important) music. I usually use Vienna or Berlin Philharmonic only for reference balance; use what performance you fine is right for you. After you set up your MF and Midbass [MF and upper-bass ?] and feel that you have attenuated MF good enough to have proper balance then add bass [assuming you mean mid or lower-bass] channel. If your MF/Midbass [MF/upper-bass?] balance is correct then running your bass [mid and lower-bass?] channel a few dBs lower then YRL or higher YRL shall NOT make you to wish to change the MF/Midbass [MF/upper-bass?] balance..."

Though I don't know if the "[corrections]" I added are what you intended to write, reading it this way make sense to me.

"...Do the same with tweeter [tweeter and MF I assume] , and then with tweeter and bass [tweeter and upper-bass I assume]..."

"...After you do feel confident about your MF/Midbass [MF/upper-bass?] balance than begin to inject your Fundamental Channel. Start it from 15dB down and begin to add it (check the phase) very slow until you begin to recognize the very first sighs of it auditable contribution..."

I have tried using the 180Hz horn as you use your 250Hz horn; that is to say, to play attenuated lower-MF; I've also tried addressing MF via two channels, each contributing equally in terms of amplitude. The jury is still out as to which will be the final configuration, but I have to say that I can't fully justify attenuating the 180Hz horn when it gives such life to cello and larger wind instruments, both brass and wood.

Also, as one might expect, the high location of this horn running without attenuation affects overall depiction of space. My ears tell me that there is potential to exploite this, turning it to an advantage, provided the listener is able to sit at least 10 feet away.

This issue will get the time it deserves once construction of the mid-bass horns is complete, and I'm able to move the system back to its original place in the room, at which point I will do exactly as you describe.

Can you confirm that in the following two paragraphs, in place of "mid-bass" you meant to write UPPER-BASS, so that it would read as follows (my apologies if this was not your intent)?

"...The result of all of it shall be your confidence that your MF/UPPER-BASS balance is proper for the given location of your UPPER-BASS channel in the room. A pair of UPPER-BASS Channels shall be loading the room with thick and “crowded” sound, acting as a virtual pedal point for your MF. The channel shall also to unload it from the room with proper speed but not faster than it has to. You need to have some music that has the “cello crash” and you need to make sure that your room will be “dramatically” loaded but not over-loaded and will very “gracefully” release the load. Ironically, if everything is done poorly [properly?] then the “drama” and the “grace” will not fluctuate from volume too much.

When you reach the point where you feel you somewhere near the proper MF/UPPER-BASS balance you need to think about your sound not as it a playback but as you are conducting a live orchestra and it is your responsibility to shape the balance in a way you feel it need to be. If you feel that your best MF/UPPER-BASS balance would be different at different recordings then you do not have proper MF/UPPER-BASS balance yet. The MF/UPPER-BASS balance of your system shall be more accurate than any random orchestral balance out there. Then your playback system becomes a reference against which all orchestral and recording deviations will be measuring. You personally shall have absolute confidence and supreme believe in your MF/UPPER-BASS balance. If you go in future for multi-amping then do not forget regularly check the outputs your amps (tubes are not stable) to make sure that your MF/UPPER-BASS balance still hold a reference level..."

It is entirely possible that I end up multi-amping the system further than is already the case (a second pair of amps currently drives lower-bass); if not going for full DSET, I could imagine driving mid-bass and upper-bass from a dedicated pair of amps.

Once the mid-bass horns are done, I'll move the system, get it sounding a good I'm able, then post a composite of sweeps showing curves for all channels in a single frame.

Thanks much,

jd*

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