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-   -   Low frequency horns (http://www.diyaudio.com/forums/multi-way/137072-low-frequency-horns.html)

jamikl 22nd January 2009 08:13 AM

Low frequency horns
 
I recently got hold of 4 X Eminence Beta 15A and have been looking for ways to use them. I was a bit disappointed with most things I tried in the various modeling programs so last night I thought why not try them like the old altec A7s. Two speakers into a front loaded horn with a reflex cabinet looking after the back of the speakers. Usually there is a problem with simulations of these as the port and the horn interact and give pretty ragged looking response. I started out with enclosures of between 180 and 200 litres and a horn length between 32cm and 39 cm, 0.7, 0.8 and 1.5 expansions, 3200 to 3800 sq.cm mouth and 400 to 600sq cm. throat. The sealed, not ported boxes,.. showed almost even response from 50 hz to several hundred Hz. About 5 - 6 dB down at 40 hz. In the group delay time x Frequency never went over 400 and the xmax was ok up to about 100 watts at which the output was 122dB.

The questions are: As this is showing such a level response without a port how is it that the reactances, which are all over the place and dropping below a couple of hundred Hz, allow the sound output to be so even? Would it really work like this and
sound OK? Is Horn response not accurate if the diaphragm area is a lot larger, up to 4 : 1, than the throat area.

I would appreciate any comment from GM and others who know horns. Thanks,
jamikl

jamikl 23rd January 2009 01:01 AM

Trying again.
jamikl

gedlee 23rd January 2009 02:01 AM

Put the 4 15's in four boxs and spread them around the room. Forget about LF horns.

CLS 23rd January 2009 03:00 AM

How about 4 x BIB?:devilr:

And of course you may "spread them around the room" when all of those horns are built. :D

tinitus 23rd January 2009 03:16 AM

500-600 liter might be good if isobaric design

Closed it will go straight to 40hz

If you want more boom you could try a very big slot

With both drivers on front you need at least 1000liter
You may then benefit from doing a 2.5 way

Much depends on other drivers

jamikl 23rd January 2009 08:56 AM

Thanks for those replies although they don't address the questions. I am trying to understand why the horn as described above models so low and level. Ii has even output far below what the dimensions indicate. the group delay is lower than a lot of other simulations of various types and the speaker does not run out of xmax until considerably higher power levels and SPL levels than in all the other enclosures. This is in about 200l enclosure stuffed to 20cm on the Horn Response chart. This is with two speakers per enclosure. One speaker in a heavily stuffed 200 litre box with a stuffed port, aperiodic ?, works quite well too but nowhere near the SPL. If I can confirm that the horn may work as simulated it would be worth building.

The room, as in a lot of Australian homes, is not over large but very open plan. It is about 6m x 4m, completely open on one side to a 1.6 metre hallway which is open again to a 4m wide kitchen with only a breakfast bar between kitchen and hallway. The side of the room opposite the hallway is nearly all glass. Seems an ideal location for horns backed against the window wall and aimed along the long length to the far kitchen wall. I cannot modify the room(s) in any way as it is not my house.

I like to feel the emotion and the power in a piece of music. I listen to most types of music except post nineties pop, however there teen and early twenties people here also.

subs will be used as I like pipe organs.
jamikl

bjorno 23rd January 2009 01:07 PM

2 Attachment(s)
Quote:

The sealed, not ported boxes,.. showed almost even response from 50 hz to several hundred Hz. About 5 - 6 dB down at 40 hz.


Hi jamikl,

My req. Use a sealed box.

Have you tried to calculate your horn using this information? See picture 1(1)

1(1)

jamikl 24th January 2009 02:50 AM

Thanks for the reply bjorno. I do have the ML sheets which are based on leach's work but I am not trying to design a horn for 40 - 50 Hz but am trying to understand why a horn in a sealed, not vented box, and designed for a cutoff anywhere between 140Hz and 190 hz is, in Horn Response V20.10 is showing good response down to 50 Hz and whether it will actually work down to that frequency.

All radiation down to 50 Hz is passing through the horn and it is quite flat. Horn lengths are only bewteen 32cm and 38cm. As I understand it, that shouldn't work. If it does work it would be a great use for the Eminence Beta 15As that I Have.

This sealed box of 200 - 240 Litres contains 2 15As in parallel connected to a single horn as in the Altec voice of the theatre etc. The throat area is only about .33 of the total piston area of the two speakers. Would this cause problems with what is a relatively light paper cone?
jamikl

tinitus 24th January 2009 03:33 AM

1000liter closed, 40hz ;)

What you describe sound to me more like what they call scoop-bins, but a big one with 2 drivers :D

GM 24th January 2009 04:12 AM

First off, model it as a simple sealed cab and compare it to the same rear Vb horn. You should see the sealed cab's peaked response flattened/extended as well as its impedance peak shifted downward due to the restrictive throat and air mass plug in the horn. Since the horn is small, it's only really loading the BW above the driver's mass corner, hence the extended HF BW.

Not familiar with this driver, so don't have a clue as to whether it can handle 4+:1 CR at rated power, but it will probably be fine in a HIFI/HT app.

Bottom line, if the specs are accurate, it should perform ~ as predicted except for the effect the driver's break-up modes BW will have on it. Note that you'll have to calc the volume trapped under the horn throat and add this into the Vtc field along with Atc = S1 to get the most accurate sim.

GM


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