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PostPosted: 16 Mar 2021, 19:44 
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Joined: 16 Mar 2021, 19:18
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Location: United States
Hi all - and I am happy to join this forum!

After 10 years of building a speaker, I threw myself back into deep water. I love full range speakers, especially from Fostex. Also, I wanted a bit of a more complex build so I decided to build a Ron Clarke Horn - the Austin A166, coupled with a Fostex FE 166NV.
I had to scramble a few different plans across forums, because I live in the US now and needed imperial scale + found an updated plan for the 166NV.

Why am I here: I am about 80% done and have put one of the speakers together (one side panel still open). And I noticed that the driver is not centered within the combustion chamber. I followed the plans, especially the original by Ron Clarke. So I was wondering if you think this looks all fine and okay, or if I messed up my front panel and the driver sits about an inch too low?

On another note, you may see that I combined two 3/4" plywoods for the front. I did that for more stiffness and to have a clean / no-gap front. To get air moving better behind the Fostex, I used a router to cut the edge of the inner panel, I hope you ca see that in the pictures as well. Do you think this is enough space for eir to move properly? All together, that whole section seems a bit tight to me, but maybe that is how it should be..

Last comment is, that I will add some carpet foam padding in the combustion chamber. I hear a really annoying tone in voices, when they are dominant in singing. So I think this might be from a reflection behind the driver and I hope to be able to mitigate that with some dampening material. Any thoughts on that are welcomed as well.

Thank you!!
Gabe


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PostPosted: 17 Mar 2021, 14:09 
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Joined: 16 Mar 2021, 19:18
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Location: United States
I said combustion and obviously meant compression - ha..


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PostPosted: 18 Mar 2021, 13:17 
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Joined: 03 Jun 2020, 11:06
Posts: 118
Location: France
Congratulations @Gabe634 : your work takes a nice start ! 8-)

It's not easy to assemble all those slanted joints... :|

A friend of mine, who worked extensively from scratch on the subject of a Wide-Band speaker coupled to a horn, told me that what took him the most of time in work and tests was the setting of the compression chamber : driver, volume, damping, coupling to the throat of the horn.

According to him, these parameters - and notably damping - first determine strongly the voicing / tone of the mid and mid-bass range of the system driver + horn, while the bass extension is mainly set by the size of the mouth.

He also told me that the FOSTEX speakers tend to have some kind of "nasal" tone on the voices, that must be corrected in a way or another. That's what he found - among other - on tests with a 7" FE166S project (below, at right), and finally preferred to have a 8" custom designed driver for another project (below, at left) :

Image

Image

I never ventured seriously in the horn territory, staying in the Bass-Reflex system with my 7" TRIANGLE T17FL2 (made in France, long discontinued now) :

Image

That said, I had to work quite carefully the internal damping :

Image

And also had to correct a +4/+5dB step in the loudspeaker response, starting at 1KHz and ending at 10KHz, which gave a very dynamical tone at the first glance, but tiring in the long run and finally somewhat artificial sounding. I used a simple Baffle Step Correction filter as a basis, and fine-tuned it by ear :

Image

The 1.2mH coil determines the cut-off frequency, the 8R2 resistor fixes the level, the 1.5µF allows to compensate the highs drop that often occurs on Wide-Band speakers, avoiding the use of a super-tweeter (which I have found to destroy all the interest of a WB speaker).

Image

Beside the careful damping work and tests that your compression chamber might require, maybe that kind of filter would also help ?.

-tbln.

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PostPosted: 18 Mar 2021, 15:38 
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Joined: 16 Mar 2021, 19:18
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Thanks a lot for your detailed answer! And wow - that horn looks crazy! Can't imagine the work that went into it..

Just a few things:
- I absolutely agree with keeping any tweeter out in a full range speaker project.
- Its good to hear that others have noticed similar issues with the mid / voice. I don't have equipment to measure it, but I can tell that something is off.
- A filter is an option. At this point I am very positive, that I have an issue with the compression chamber and the none existing dampening. Once I figured that out as best as possible, I might tinker around with some electronic components in a later stage. Right now I'd just mess it up even more :)

So that being said, I think the position of the driver (being significantly lower than the deepest part of the chamber) is a given at this point. Unless someone here built this or a similar horn and tells me I used a plan with off measurements, I guess I just have to go with it.

That leaves me with the following question:
I read about people using very thin dampening material behind the driver within the chamber. Thin as in carpet padding that is 2-4mm thick only. When I look at your pictures, you are using some really thick wool-like material. Are there any rule of thumbs or good introductory papers on what type of material and amount to use? Or is that pretty much up to me? I also read about people dampening the backside of the magnet of the driver, as it also provides a huge reflection area. Any material and amount suggestions are welcome! I would probably just order 2-3 different materials and test it out.


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PostPosted: 18 Mar 2021, 17:50 
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Joined: 16 Mar 2021, 19:18
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I think I am going to order one of those:
https://www.madisoundspeakerstore.com/a ... ning-yard/

And experiment with a double layer behind the driver and a single layer on the side + on the magnet.


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PostPosted: 19 Mar 2021, 01:15 
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Joined: 13 Jan 2018, 21:33
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Location: australia
Also something to consider is the amount of time to break in a new driver. I noticed some strange voicing of my Dayton audio ps180 full range drivers which took about six months to normalise. I estimate 150 hours or so of listening. I also went with a BSC but with proper placement could left out.

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PostPosted: 19 Mar 2021, 12:24 
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Joined: 16 Mar 2021, 19:18
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Location: United States
Thanks! That is a good point and something I noticed many times before. I might just have them run every day in the basement for a week to speed up the process / before I glue the last side panel on.

Once I get there I will also share more / better pictures of the full build. I found it hard to come around some good information about that specific horn, so maybe in the future someone will want that info.

Oh, another thing I did not mention: I have a very cheap and drastically underdimensioned Amp at the moment. Its a Dayton Audio DTA-2.1BT2, which I only use because I don't have a good amp available right now. I am interested in buying a Audiolab 6000A PLAY later on, but don't have the budget for it just yet. I expect that to have a huge impact as well.


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PostPosted: 19 Mar 2021, 12:38 
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Joined: 03 Jun 2020, 11:06
Posts: 118
Location: France
Yes, Woodo is right : I did not mentioned the break-in of the speaker that may attenuate the tonal signature of the Fostex... And the inspiration for my response correction filter also came from him (thanks again, Woodo - I would never thought about that tip !)

That said, if you do not have any damping material at all in your compression chamber, you musn't be surprised if unwanted resonances are present. As you guessed it : this is really the first point to work on, rather by ear trial and errors, which may be time consuming, but worth the expense in the end !

Well, about the damping material :

1 - my enclosure is a Bass-Reflex, so it has nothing to do with a compression chamber like yours or my friend's ones. The damping requirements are not the same - at least partly IMHO - because it also influences the coupling of the horn to the compression chamber, a problem that do not exist in Sealed or BR enclosures.

2 - the book from Vance Dickason (the Loudspeaker CookBook) has many interesting points on the effect of damping / stuffing a cab, being Sealed or Bass-Reflex, but nothing about Horns, unfortunately...

3 - being not in the "Horn trip" :D , I have no real recommendations for you... But you may be also advised if you search on the web information about transmission line speakers, TQWT or folded horns : many exists with Wide-Band speakers of all sizes. I even wonder if there's not already something on those subjects on the forum ? See DIYA projects, DIYA photo gallery...

4 - the damping material that I use here is house insulation cotton wool, in 50 and 100mm thick, with respective densities of 25kg/m3 and 18kg/m3. Cheap and very efficient to tame unwanted resonances.

-tbln.

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PostPosted: 28 Mar 2021, 08:53 
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Joined: 16 Mar 2021, 19:18
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Location: United States
Quick update: I managed to install the wool felt - started with a thin 1cm layer (will experiment with adding more) in the compression chamber. Huge difference! The really annoying pitch sounds are gone. Now it is more about the character of the driver, and the fact that I am only clamping one side panel down at the moment. So I will have them both run for 20hours or so, try to add more wool and eventually close the box of permanently.

Once that happens I will give a bigger update and share some more pictures.

One thing I can say is that they are very demanding when it comes to angle and room. I tried the living room first and it was a disaster. Now the entry area with carpet, couches and wide open space - much more depth and dynamic (as long as you are in the right angle to the speaker).


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