Hi guys,
I'm hooked on tapped horns after the success of my 6 foot monster. I now want to build a horn with an 8" driver and reasonable size. I came up with this design. It's outer size is only 28x19x10.25 inches. Very easy build with all right angle cuts except where the driver board meets the outer panel.
I haven't picked out a driver yet. I don't plan to go beyond 50 watts rms. I hope to get strong output in the 45Hz and above with some extension down to 40Hz. This leads me to some questions:
How does the increasing volume from throat to mouth affect performance? I see horn designs here with very small increasing volume and other with much.
Is there a way to estimate minimum frequency response before roll-off from length of horn path? The path of this horn is about 84".
Thanks, John
I'm hooked on tapped horns after the success of my 6 foot monster. I now want to build a horn with an 8" driver and reasonable size. I came up with this design. It's outer size is only 28x19x10.25 inches. Very easy build with all right angle cuts except where the driver board meets the outer panel.
I haven't picked out a driver yet. I don't plan to go beyond 50 watts rms. I hope to get strong output in the 45Hz and above with some extension down to 40Hz. This leads me to some questions:
How does the increasing volume from throat to mouth affect performance? I see horn designs here with very small increasing volume and other with much.
Is there a way to estimate minimum frequency response before roll-off from length of horn path? The path of this horn is about 84".
Thanks, John
An externally hosted image should be here but it was not working when we last tested it.
The "quarter wave" resonance should be about 50 Hz, but I expect you'll get reasonable output (with higher excursion) quite a bit below that.
The throat area looks like a good match for Eminence Alpha8 or Beta8 drivers.
Like Andrew suggested, try it in HornResp and see what happens.
How did you arrive at 50 Hz resonance? Did you use HR? I agree, that HR is important to check design, but just looking for a quick way to estimate box resonance.
It might get closer to 40 Hz if it behaves according to theory.
84 inches = 213 cm = 2.13 m
344 m/s / (4*2.13) = 40.3 Hz for the theoretical minimum 1/4 wavelength resonance of this cabinet based on theory alone.
I typically start with the driver, not the cabinet sketch, but your approach is equally valid.
84 inches = 213 cm = 2.13 m
344 m/s / (4*2.13) = 40.3 Hz for the theoretical minimum 1/4 wavelength resonance of this cabinet based on theory alone.
I typically start with the driver, not the cabinet sketch, but your approach is equally valid.
I used an old home-made spreadsheet that's really for front loaded horns. Minimum cone velocity was at about 50Hz. I assume resonance will be about the same in a tapped horn?
Resonance in a horn is never at exactly a quarter wavelength due to the flare and acoustic impedance at the mouth.
I'm interested to see what you get out of HornResp. So far I've been too lazy to learn to use it.
If I was building a horn I would though.Cheers - Godfrey
Some rough calculations for horns...
Ideal throat size for a given driver (for best impedance match, efficiency etc):
St = 415*Re*((Sc/BL)^2)*(Qts/Qes)
where: St is throat area in square meters
and Sc is effective cone area in square meters
Usable frequency range for a given driver on a horn:
Fminimum = Fs*Qts
Fmaximum = 2*Fs/Qts
The above is for high-efficiency horns.
YMMV, especially with "tapped horns".
Ideal throat size for a given driver (for best impedance match, efficiency etc):
St = 415*Re*((Sc/BL)^2)*(Qts/Qes)
where: St is throat area in square meters
and Sc is effective cone area in square meters
Usable frequency range for a given driver on a horn:
Fminimum = Fs*Qts
Fmaximum = 2*Fs/Qts
The above is for high-efficiency horns.
YMMV, especially with "tapped horns".
Search for hornresp tutorials, they're out there (I know - I wrote one of em...)
As far as the length, sure, horn theory allows us to make predictions. Some driver/horn combinations will get closer than others. I doubt that you could convince a driver to play significantly lower than the 1/4 wavelength resonance, pretty sure that physics is on my side with that prediction. Many driver/horn combinations won't quite get that far.
Hmm...
Tried out HR. Response drops off fast below about 60Hz. Works better as a FLH, with a rear chamber of about 20L - Decent output down to 40Hz.
Then again I'm a total noob at HR and TH so maybe I'm doing something wrong.
60Hz seems kind of high, but I don't know. I'm afraid, being a noob with HR, me lousing up the HR data and botching a design with potential.
Anyway, I reworked the design for a longer path. The box comes out a bit larger at 33x20x10 O.D., but the path length is 24" longer. Even widening the box to 12" and using a 10" driver, the box is still pretty small.
I measured the path from the very back of the throat (where the 1.5" dimension is) to the edge of the lumber at the mouth (if that is the correct way).
An externally hosted image should be here but it was not working when we last tested it.
You're definitely going to be best served if you pick a driver first and then build a box around that driver. Tapped horns are very driver specific.
I built a smallish tapped horn for an MCM 55-2421 that measures 29.25"x27.5"x9" externally that also holds a Foster 115w plate amp. This one is tuned to 28Hz and puts out over 110db down to that frequency. It's a great combination that cost me less than $100 including wood and hardware.
I built a smallish tapped horn for an MCM 55-2421 that measures 29.25"x27.5"x9" externally that also holds a Foster 115w plate amp. This one is tuned to 28Hz and puts out over 110db down to that frequency. It's a great combination that cost me less than $100 including wood and hardware.
Hi. I just read your review of the subwoofer on mcm. Wish I knew about this little driver a while ago. Do you have plans for the box you have built that you could possibly upload, or email me? thanks either way.
Hi tsloms,johnr66,
Agree, That’s the easy way when using HR but at first and of most importance, input for a system design could incorporate a cabinet size restriction, thus the driver choice is not the primary task to take into consideration.
Here is a picture I draw some times ago but hesitated to post as I could be overflowed with postings telling me this isn’t the way to design TH: s as when the right decisions to be made is way different and can already be found in other postings here at DiyAudio.
See the method picture here below.
I don’t claim my proposed method is the optimal way to fit unknown drivers parameter-wise into a ready built box, but this is the way I prefer to do. Note: I don’t promise to post new information in a hurry as you know I’m a very slow replier.
There could be days, even weeks before I post again.
What do you think?
On topic comments about my picture are welcome.b
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Hi BjornoWhat do you think?
Regarding the equations at the bottom of your picture:
In the first formula for Stopt, I think the Sd term should be squared so the formula becomes:
Stopt = 406 x Re x Sd^2 / Bl^2
Then it is similar to my formula in post 8.
Your second formula looks right, though. I didn't check the math, but tried a few examples and the results look correct, with Vas in cubic meters and Stopt in square meters.
Regards - Godfrey
Hi Godfrey,
Thank you for finding the Sd error, of course it should be Sd^2. Yes, the Vas is in m^3 and Stopt in m^2.
b
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Here is my first foray into building tapped horns. It uses the MCM 55-2421 8" driver and the 115W Foster plate amp from Jack Hidley. This entire build cost less than $100 including wood and hardware.
It has external dimensions of about 29.25"x27.5"x8.5". I actually built this sub about 2 months ago and have been enjoying its clean sound in my living room since then. It is tuned to 28Hz and will provide 110db down to this frequency.
Here are my new arrivals. For $25 each I had to get a few extras.
I hung these in my basement and drove all 6 of them with a single 115w amp to break them in. These were broken in at 30Hz for 48 hours.
These parameters were slightly different than my originals but have been adjusted slightly due to folding which changed them a bit.
The schematic. It was kept at 3.5 cubic feet before folding.
The SPL response at 2.83v input. Nearly 95db down to 28Hz.
Phase response
Group Delay
Impulse Response
Max SPL--Over 110db down to 28Hz
Driver Displacement--According to HR it is slightly over Xmax but the amp rolls off at about 28Hz as well which should help to protect the driver.
Here is the drawing in AutoCAD which makes it very easy to fold the horn. In this drawing the amp will fit at an angle in the upper left of the pic. The driver will sit directly next to it.
The enclosure is nearly completed at this point. It took a mere 3 hours to assemble once all of the pieces had been cut. The 1/2" plywood that I used is some inexpensive stuff from Lowes that was slightly warped that they marked down to $7 a sheet just to get them out of the way for them. I used the PL premium and a brad nailer which made assembly very easy. Highly recommended!!!
I really didn't want to stick an amp in my entertainment center so I built the amp into the box. I know that BFM strongly frowns on this but the amp is plugged into the same outlet as my receiver as well so no ground loop issues here. I also wanted to make the enclosure as slim as possible so I made it 8.5" wide internally. This required me to mill down the amp to fit. Good bye warranty!!
Here is a pic showing the driver and amp installed in the box. Note that airflow from the enclosure will also help to cool the amp, not that it gets very warm anyways. It's a very tidy slim package.
This is the completely assembled enclosure. To this day I have not finished the enclosure. A buddy of mine wanted to buy this one but hasn't picked it up yet. He wants to finish it himself.
Here is the home so far of this tapped horn. For scale that is a 50" Samsung Plasma next to it and my latest project, my 64" tall TLAH's. Sitting back in the corner like they are and aimed towards the corner they really don't use up any extra floorspace. If I do end up keeping this sub I may paint it to match the walls to better help it blend in.
With a total outlay of less than $100 I have been extremely pleased with this overall package. Although they don't hit the lowest notes they sound amazing with movies and just incredible with music. Clean and loud explain it well. Keep in mind that this replaces my Onkyo 5100 HTIB sub with its 10" "sub" and 290 peak watt amp. For hardcore movie watching I still rely on my 4 sealed IXL18's in my basement.
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