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In the Forum: Horn-Loaded Speakers
In the Thread: Jessie Dazzle Project
Post Subject: Responses to Romy Paul & RonniePosted by jessie.dazzle on: 8/5/2007
Thanks Romy, Paul, and Ronnie for the comments and encouragement :
Here are some responses :
1) Rubber gaskets :
Maybe it is not so important to have an “air-tight” seal (???). The rubber gaskets are there to seal the cover to the rear chamber. Ronnie, that’s a really great idea, it would however require machined parts.
2) Rear chamber volume :
The idea is to start with a rear chamber that is tuned for 35-40Hz (so larger than I may need) I could then reduce the volume to tune the chamber for higher frequencies. The chamber in the CAD model corresponds to the quoted Fs of the driver. (40Hz)... However, I need to verify this Fs specification by measurement, as the AK151 is a pre-T/S driver, and I seem to remember that the Fs quoted were estimated.
3) Strength of small end of Mid-Bass :
Yes I would agree... It would be easier to make if it were more cylindrical... However, I am trying to keep the weight for this part under 400 lbs.
I use a lot of long hemp fiber mixed in with hard modeling plaster, which I dose for maximum of strength, meaning I mix it very hard. I have had to destroy some failed attempts, and it requires use of heavy sledgehammer. I have a couple images showing this construction technique (180Hz horn) which I will send in a separate post (looks like this site now makes it possible to include images via the Mac browser... If I am not successful I will post them from a PC sometime during the week)
4) Material & construction options for the large end of the Mid-Bass horn :
Yes at one point my design was similar to what Romy suggests, but in my thoughts the tensioning straps served more as general structural members... I need to think about it with resonance-tuning in mind.
The material for the segments is still not completely decided... Current options are as follows :
A) Laser-cut steel ribs with expanded metal or mesh (exactly as Paul suggested), followed by a laminate of synthetic plaster and woven fabric (this synthetic plaster is the stuff the dentists use).
Pros : Can do it myself Cons : Heavy
B) A laminate of wood in 1/8th inch thick veneer sandwiching cork sheet. Ribs would be cut from thick wood. This would impose a design that is not round but octagonal. It would require the making of a forming tool (no big deal).
Pros : Can do it myself Cons : Octagonal horn section
C) Give the CAD data to my friend who has a prototype fabrication company, and pay for a milled mould so that he can then make the segments from a composite lamination of fiberglass+epoxy resin. I could also have the small end of the horn made by the same people (this approach would theoretically allow me make a few more 45Hz horns if anyone else wanted a pair).
Pros : Could sit back and wait for delivery Cons : Expensive
5) Frame conception :
Frame is very adjustable. All horns except the Upper-Bass (which has only axial adjustment) are vertically and axially adjustable on sliding blocks. A small modification would allow tilting them down (or up), but for the moment it is not in the plan. The horn supports are independent of the main frame, meaning the horns can be placed in any order desired; different supports can be added later. I will pick up the pre-cut metal for the frames tomorrow (a surprising 88 linear meters).
6) Location of Upper-Bass horn relative to floor :
The Upper-Bass horn is as low as I can get it without touching the floor.
7) Location of power amps :
Yes, the power amps sit within the frame, on their own sliding support between the Upper-Bass and Upper-Mid horns. For the moment I am using a pair of ML2s from 60Hz and above. (below 60Hz I use other amps with a pair of Lower-Bass enclosures). I will use the ML2s to get the horns dialed in... Once satisfied, I will take on the building of dedicated amplification... I was originally thinking 5ch Melqs... But am very much following your single-stage project. In any case, the frames can be adapted to hold dedicated amps.
8) Extension of frame to support 45Hz Mid-Bass horns :
Yes, it would require that the two frames be tied together.... There would also be a need to fix the tops of the extensions to the building. I am still working on this.
9) Potential problems with near-field listening :
I prefer a near-field set up; which is good, because I am forced to use a near-field setup.
When you (Romy) say :
“...the output of a lower midrange horn would be too prevailing”...
Do you mean the output from the 180Hz Lower-Mid will be coming from a point that is too high (or did you mean to say the 45Hz Mid-Bass horn)? Would tilting down the 180Hz horn help this (I understand it would restrict listening to one point)?
To answer Paul’s question :
“...So, where can you put this monster where you can still get far enough away to listen to it?...”
Though I like near-field listening, with the 45Hz horn in the picture, I would probably prefer having a bit more space than is currently the case. However, once the horns are done, for various reasons, I am considering moving... In which case I would find a place with proper space for the horns.
10) Integration of Injection Channel :
The frame provides the space to slide in an Injection Channel. I am however trying to avoid this. I would like to get tone from the drivers in the horns... I have recently received a few pairs of 8-inch drivers... Playing them in free-air, one German-made pair stands out. I have not yet tried them in the horns (the Upper-Bass horns are still not dry), but comparing them in free air to the Fane 8Ms, running full range with an identical signal, they are significantly more sensitive and seem to sound a bit warmer. I will post my findings when the horns are completely dry.
11) Axial adjustability of Lower-Mid horn.
The support has a 35cm range of axial adjustment.
12) Did you think already about the selection of the drivers and crossover points?
Here is what I currently have in place :
High-Frequency : Electrovoice T350 :
From : 16500Hz
To : Open
Upper Mid-Range : Vitavox S2 > 400Hz Tractrix :
From : 3200Hz
To : Open
Lower Mid-Range : Vitavox S2 > 180Hz Tractrix :
From : 790Hz
To : 3200Hz
Upper Bass : Driver still under consideration > 115Hz Tractrix :
From : 240Hz
To : 770Hz
Mid Bass : Vitavox AK151 > 45Hz Tractrix :
From : 60Hz (need parts)
To : 240Hz
Lower Bass : McCauley 6174 in 15 cu ft Sealed :
From : 15Hz
To : 60Hz
Crossovers horns (60Hz and up) : 1st order passive. No attenuation.
14) Replacement of Lower-Mid horn (180Hz) by Injection Channel :
I really appreciate the result of the 180Hz horn with the S2... Particularly in terms of "texture". It is responsible for such an important range... I would not expect this result from a direct radiating driver.
15) “Default” targeted vertical listening position :
It is the center of the Mid-Range horn (the 400Hz horn). This is one reason the Upper-Bass horn is not larger.
16) Location of rear wheel :
Yes moving this wheel further rearward would add a measure of stability. The current location of the rear wheel is based on a design that is made to come apart and fit in the elevator... The rear wheel is mounted to the vertical mast, which is on a (fore and aft) sliding support. What you see behind the vertical mast are the ends of the horizontal base rails. I may have to rethink this.
Once again, thanks for the all the terriffic input.
I will now try to post a couple images...
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