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Author Topic: Can F3 be lowered too far when coupling subs  (Read 2913 times)

Brian Elstro

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Can F3 be lowered too far when coupling subs
« on: February 12, 2009, 06:31:58 pm »

Ok, two scenarios that I would like to run past everyone..... keep in mind that all these 'specs' are hypothetical. Bear with me if you can!

Say I have built a 'perfect' small 80hz horn, mouth circumference and flare rate are all perfect (I wish.... but I digress). The driver I am using specs out at Fs-40hz, or 42hz dependant upon the selection I make (there are two drivers capable of being used in this design, one I designed the horn around, the other has very similar specs but requres a larger Vb... which can be achieved with either filling the cab or venting).... I prefer to not vent or port and keep the sealed rear chamber because it helps the motor structure maintain control. I am building 8 of them for either two clusters of four, or center clustered in 8. The plan is to use in groups of four in small venues and 8 in larger. Now on to my issue.

#1- I get to load in, see that I will be able to corner load two per side. When I do the F3 of the two cabs lowers and thus allows my little 80hz horns to get down and dirty into the ~40hz range.

#2- I'm doing a festival, outdoors, and will be center clustering subs, allowing all 8 to couple, my F3 now is lowered to ~30hz, and running beautifully.

My question- when you place a driver in a horn, the Fs lowers (the only figures I can remember finding was ~20%.... arrgh). When you couple horns the F3 lowers. If the F3 of a cabinet gets below the Fs of the driver, the cab unloads and there goes your driver, at least in a bandpass or similar alignment. Horns, IMO, are not much different especially when we talk of smaller horns. Or are they? It seems to make sense to me, but I cant seem to find any information on making sure you dont lower the F3 of the cab below the Fs of the driver. I also know how to estimate how low the F3 will go for individual cabinets, but how low will the Fs drop in the horn?
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Art Welter

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Re: Can F3 be lowered too far when coupling subs
« Reply #1 on: February 12, 2009, 10:33:40 pm »

Brian,

What is the question?
A properly designed horn drops at about 12 dB per octave below F3.
A bandpass or bass reflex drops at 24 dB per octave below F3.
Below the horn F3 the cabinet will behave like an infinite baffle.
As you add small bass horns together, the F3 will lower quite a bit more than with a bass reflex cabinet.
You would want to high pass four units together higher than 8 units together.
Until you actually build the real deal, “perfection” is worth the paper it’s printed on.

Art Welter
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Brian Elstro

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Re: Can F3 be lowered too far when coupling subs
« Reply #2 on: February 13, 2009, 10:09:21 am »

"As you add small bass horns together, the F3 will lower quite a bit more than with a bass reflex cabinet."

.... exactly my point, but I already knew this....

When using multiple cabinets together, will (or can) F3 be lowered below the Fs of the speaker? When you lower the F3 below the Fs in an IB cab, you will unload the driver, and typically blow it (especially at high power). The same for horns (or at least it is by my understanding). Or can this phenomenon even happen due to the fact that individual cabinet specs will take over?
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Art Welter

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Re: Can F3 be lowered too far when coupling subs
« Reply #3 on: February 13, 2009, 03:36:14 pm »

Brian,

The answers depend on the speaker. Check X limit to get an idea, if it is way more than X max you are probably heading the right direction for survivability in a small horn.

Some speakers have suspensions and cones that can be driven to bejezus below FS and survive. I owned one and a half tons of EV 150X, FS 35 HZ, never ripped any in straight horns only 45” deep, with 30 HZ HP filters.

Prior to that, had over fifty EVM 15B, FS 43 HZ, in straight horns only 30” deep, never tore any of them either, using 30HZ  24 DB per octave HP filters.
Those 2x15” cabinets were used alone or in arrays of as many as 16.

Well, once we tore up eight 15B of  with an aux fed sub foot pedal “accident” that resulted in highly compressed sub frequencies generated by a harmonizer two octaves down from a whammy bar guitar (probably a fair amount of 20 HZ) clipping a Crest 8001 into them. Opened up the back of the cabinet and could see a lot of daylight through where the cones had been. That set up may not have had a HP filter, oops. Expecting a bit much from a 60-80 HZ horn.

On the other hand EV 15L  (also 43 HZ FS), would tear up in monitor use every once in a while with less power behind them.

Art Welter
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Brian Elstro

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Re: Can F3 be lowered too far when coupling subs
« Reply #4 on: February 17, 2009, 12:23:40 pm »

Art, saying X limit is the same as X mech in my book, correct? If so, then I think I'm going in the correct direction with my thinking. I know that Xmech is usually 15% or so higher than Xmaxx, but there is usually very little published information, and is making me question my methods. Thanks for your help!
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Johan Diettrich

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Re: Can F3 be lowered too far when coupling subs
« Reply #5 on: February 17, 2009, 12:44:49 pm »

Xmax is often quite more then 15% more. Dependant on how you calculate Xmax around Xlim = Xmech = 2 x Xmax. Most manufactures in Europe do state Xmech amongst the other parameters in their files.

Diettrich
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Art Welter

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Re: Can F3 be lowered too far when coupling subs
« Reply #6 on: February 18, 2009, 05:22:13 pm »

Brian,

There is no way to derive X mech or X limit from X max. Those limits are set by the way the speaker is designed and manufactured. You need to get the specs from the manufacture.

Also determine whether the measurements are one way or peak to peak, which varies from company to company, and prediction programs also.

Or measure them yourself with a sine wave generator into an amp, a white dot on the cone, and a ruler. Run a low tone, like 15 HZ, turn up the amp till the cone clacks, measure.

You can also do this by hand, pushing the cone back and forth to the "end stops".

In the case of the EVX-150A, X max is 6.4 MM (.25”), yet the displacement limit is rated at 39.4 mm (1.55”) peak to peak.
With enough power, you literally can drive the coil out of the gap, but not damage it. Won’t sound very clean, but no tears, and probably no clacking either, though I have not done an excursion test, but never heard one bottom out in all the time I owned them.

Art Welter
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