THAM15 - a compact 15" tapped horn - Page 3 - diyAudio
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Old 21st January 2011, 05:28 AM   #21
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Thanks, positive feedback (or the oposite) from the brilliant minds here mean alot to me, you know the issues involved, you know what to expect, critics without knowhow does not bother me, but when you guys post a sugestion it goes straight to the drawingboard.

So there is now a MKIII and even a MKIV in the works outside dims and folding geometry are the same, it's just a matter of reflector positions, so there's nothing fancy going on there, but it will show the importance of .

The MKIII and MKIV are post build modifications, adding reflectors in the bottom path via the cutout, it is a four pice kit due to the bottom brace, where the MKIII is for the MKII post build, and the MKIV is for the original post build, are you with me on this ? (not very clear i know, I'll try to explain).

Jbell's sugestion very early on when William's proposal to use refelctors came up, was to add refelctors in the bottom path only, and William's sugestion was to use them in the upper path, both valid and very intresting ideas to be taken most seriously under consideration.

So, William's proposal is the base for the MKII, which is shown above, and JBell's is the base for the MKIV whick I will give a go in the near future since I use the original, the MKIII is a hybrid adding reflectors along the entire path of the horn.

The MKIII mod was sugested by Djim69 from the netherlands over at speakerplans.com, and he even posted a very nice picture to describe it :

Click the image to open in full size.

SlaitH, who built the MKII's shown above, later figured out that the MKIII modification perhaps could be fitted post build.

All of this, phew..., can now be arraganged as follows :

Original THAM15
Original THAM15 with relfectors in the upper path - MKII
Original THAM15 with relfectors in the upper and lower paths - MKIII (post build mod. of MKII)
Original THAM15 with relfectors in the lower path only - MKIV (post build mod. of the original)

The MKII and/or MKIII can be identified by the appature chamfer, this is not present on the original and the MKIV.

The only way to know for sure is to remove the driver and look inside, or (perhaps easier) ask the guy who built them
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Old 21st January 2011, 10:18 AM   #22
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Click the image to open in full size.

Perhaps this picture shows my thinking in a better way.

Detailed drawings reamins to be produced for the MKII, MKII and MKIV proposals.
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Old 21st January 2011, 10:53 AM   #23
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Wow to much input! It all looks like fun. Andy
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Old 21st January 2011, 03:07 PM   #24
epa is offline epa  Netherlands
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ive red somewhere(i think it was on this forum)that someone have tested a horn ,with curved reflectors ,straight reflectors and without reflectors.
the outcome was that the horn wihtout reflectors played loudest in the low end.
anyone
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Old 21st January 2011, 04:11 PM   #25
jbell is offline jbell  United States
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epa:

I can confirm in my dozens of TH cabinets, that adding reflectors is always a net minus. That doesn't mean that they aren't helpful. Usually they shave off the peaks and fill in the valley's so to speak, but at an overall loss of 'area under the curve' because the shaving of the peaks is more net minus than the filling in of the valleys is a net plus.

My best analogy is that segments of a folded TH are like piano strings... too many that are similar equal a note that sticks out too loud. If they are all different, then it's like playing a rich chord on a piano. A reflector changes the resonance of that segment of the horn, and a shallow reflector affects it completely different than a 45degree reflector. Some resonances are beneficial. (This is all just my opinion... who knows, I may be crazy....)

My suggestion for the fewest reflectors that will have the maximum positive impact on the martisson cabinet is shown in red.
Attached Images
File Type: jpg thamreflectors.JPG (23.1 KB, 1266 views)

Last edited by jbell; 21st January 2011 at 04:13 PM.
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Old 21st January 2011, 04:42 PM   #26
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Jim: I was thinking the same things. I did not see any shallow shallow reflector in his test lineup but seem to recall thay worked better than the 45 degree reflectors in some cases. I would realy like to see a 3015LF driver in your vershoin of the THAM15 box. Andy
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Old 21st January 2011, 06:41 PM   #27
Djim is offline Djim  Netherlands
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Martinsonn;

In my reflector suggestion (you named it: THAM MKIII) it was not just the reflectors in the first selection but together with… Anyways, I include a picture of my suggestion.

Click the image to open in full size.

My reflectors are based on one of the oldest theories in acoustics that no wall should have a parallel image. That’s why my reflectors always will ‘see’ (at least) one edge of the corner (grey line to make this visible). Also, I never try to make them perfect 45 degrees but more or less 30-40 degrees. This is also based on AES guidelines/papers.

I also agree with Jbell that the less reflectors the better since they will introduce new side effects in other areas. But if you want to use the Tham up to 250/300Hz you have to deal with the dip around 170/180Hz.



Last edited by Djim; 21st January 2011 at 06:59 PM.
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Old 21st January 2011, 07:46 PM   #28
Djim is offline Djim  Netherlands
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Sorry for the bad drawing (especialy last reflector section which comes way to much in the path) since I have no skills/software in this area... Just make every reflector about 15 - 20 degrees and start from the grey line. when two reflectors 'see' each other it always will be in a 30-40 degree angle or 60 - 80 degree angle...

Last edited by Djim; 21st January 2011 at 07:51 PM.
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Old 21st January 2011, 09:03 PM   #29
epa is offline epa  Netherlands
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Quote:
Originally Posted by jbell View Post
epa:

I can confirm in my dozens of TH cabinets, that adding reflectors is always a net minus. That doesn't mean that they aren't helpful. Usually they shave off the peaks and fill in the valley's so to speak, but at an overall loss of 'area under the curve' because the shaving of the peaks is more net minus than the filling in of the valleys is a net plus.

My best analogy is that segments of a folded TH are like piano strings... too many that are similar equal a note that sticks out too loud. If they are all different, then it's like playing a rich chord on a piano. A reflector changes the resonance of that segment of the horn, and a shallow reflector affects it completely different than a 45degree reflector. Some resonances are beneficial. (This is all just my opinion... who knows, I may be crazy....)

My suggestion for the fewest reflectors that will have the maximum positive impact on the martisson cabinet is shown in red.
intresting,so avoiding simular lengts first,and then if nessecary correct with non 45 degrees deflectors.
i gues the best way to go is bilding a test box with a removable side.
could one make them of some sort of stiff foam?
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Old 21st January 2011, 09:44 PM   #30
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Quote:
Originally Posted by epa View Post
intresting,so avoiding simular lengts first,and then if nessecary correct with non 45 degrees deflectors.
i gues the best way to go is bilding a test box with a removable side.
could one make them of some sort of stiff foam?
For a useful exercise, try working out what resonances might be set up with the parallel walls and the like in the tapped-horn, or at what frequencies those reflectors are actually going to be useful, then determining whether or not those frequences are actually going to be in or even near the tapped-horn's passband. I'll bet that you'll find that those frequencies are outside, perhaps even way outside, the tapped-horn's passband.

IMO good bracing is going to be a lot more useful in the tapped-horn than inserting reflectors or ensuring that no walls are parallel. With that in mind, don't skimp on bracing in the 1st or 3rd sections of the tapped-horn. If you do, the end result will be panel flex and increased distortion at the upper end of the tapped-horn's passband (my experience).
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