FR Design Goal? Which is the "best" curve? - diyAudio
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Old 19th April 2013, 11:01 AM   #1
markusA is offline markusA  Sweden
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Default FR Design Goal? Which is the "best" curve?

I've been doing the modelling thing for a while now and there's alway one thing that never stops bugging me and that's the target curve of the simulations.

I'm doing a BR (2-way Bass Reflex) with a 15" mid-woofer.
It's possible to get insaine LF response if you tune it for an extended bass shelf.
It looks much neater with a B4 or Be4 style curve but I'm not sure what is the best compromise?

The standard model is equal to an anechoic chamber, we are obviously not sitting in one of those at home.
Add diffraction/baffle step and the curv looks very different, pretty awful really.
Add room gain and we're back in business again.
Percieved loudness isn't making things easier either, do we want equal'ish loudness (rising LF response) or flat FR?

A standard 1A electric bass guitarr has it's E-string at approximately 41Hz.
Some will have a B-string at 30Hz but I can't say for sure how common that is?
A kickdrum is usually tuned above 40Hz so I guess I'm wondering how much emphasis you should put on the bottom octave?
We have electronic/artificial instruments and there's always the pipe organ I guess?

So, keeping in mind box tuning, diffraction, room gain and the low bass beeing firmly in the modal region for the room, what is a good FR curve to aim for?
How low is it necessary to tune it?
How will a bass shelf "sound" compared to a smooth rolloff?

The devil is in the details...
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Last edited by markusA; 19th April 2013 at 01:26 PM.
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Old 19th April 2013, 01:19 PM   #2
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For organ dubstep you need the octave between 20 and 40, but for most other music it is really not required. Kickdrum is actually quite high, some 80 Hz from memory.
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Old 19th April 2013, 01:30 PM   #3
markusA is offline markusA  Sweden
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That's pretty much what I'm getting at, I'm not sure it's worth any extra hassle to extend the LF past 40Hz?
A 40Hz tune will be smaller and easier to build in every aspect.
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Old 19th April 2013, 02:12 PM   #4
6.283 is offline 6.283  Germany
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In short:

In the bass, it all depends on your room (modes).

In the mid/highs, it depends on your room (RT60) and the dispersion width of your speakers:

- If they exhibit "regular but uniform beaming", then the response can be flat.

- If they are wide dispersion, then they need a slightly falling response.

- If they are omni they need more tuning.

- And if you use a FR driver that beams quite strongly (like a 5" or bigger), you need a rising response. But in my opinion the sound of the latter really $uck$
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Old 19th April 2013, 02:23 PM   #5
markusA is offline markusA  Sweden
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1" Compression driver + SEOS-15 waveguide will handle the HF.
15" Mid-Woofer flush mounted.
900Hz'ish crossover frequency.


I'll be aiming for a 45 degree toe-in (crossing in front of listener) and a 15-20 degree off axis listening position.
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Old 19th April 2013, 02:32 PM   #6
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Hi 6.283,

I just had a look at your website, which I would like to recommend to others. Your analysis of what makes speakers disappear is right on the mark and fully coincides with my own experiments. It may see a bit ot, but on the other hand, Markus is going to build, and may find some inspiration from it.

The point is, it is not just about getting the FR straight; the way a loudspeaker radiates its sound, as well as the interference caused by the cabinet, are essential issues that will have to be adressed as well.

Edit: just see I cross posted, and the approach you take is a valid one in this respect.

Last edited by vacuphile; 19th April 2013 at 02:35 PM.
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Old 20th April 2013, 01:57 PM   #7
6.283 is offline 6.283  Germany
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Thanks, Vacuphile !

Yeah, there was another thread about the disappearing act

Invisible speakers: who has achieved, or experienced this?


MarkusA,

40Hz and a flat FR for the mids/highs sounds like the primary way to go with this driver set.
Such big horns radiate approx. +- 20 @ -3dB and sounds pressure drops fast under angle. So you have a lot direct sound and very little reflections. Thus, keep it straight.
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Old 20th April 2013, 03:11 PM   #8
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This also may be an "Equal Loudness" curve question? Playing loud I like FR flat. Low volume, I like an increase in bass and maybe treble.

How loud do you usually listen to your system?
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Old 20th April 2013, 03:30 PM   #9
Pano is offline Pano  United States
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A solid 40Hz can be quite satisfying. As mentioned, unless you're doing dubstep, it's plenty. Get a solid 40 and you'll be surprised how deep it sounds.

For the overall curve I like the classic B-K falling response. That is, the response falls to -6dB from ~400Hz up to 20KHz. You can shift the 400Hz knee to your liking, but the -6dB point at the top is a very good target.
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Old 20th April 2013, 07:11 PM   #10
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I shoot for the JBL target curve in room:
Official Classe SSP-800 thread.

I have my low corner at 33Hz in room and it works well enough. But I would not give up the ability to feel the kick to get lower in frequency.
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