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Old 21st April 2013, 12:08 AM   #11
markusA is offline markusA  Sweden
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Sounds like a flat'ish response with a very slight downward slope as the frequency increases is the preferred way to go? 10dB drop over 2 decades looking at the graphs from the "The Subjective and Objective Evaluation of Room Correction Products" by Sean Olive.
Half of that below 1kHz.

Tailoring the response like in the article will probably require a dsp but it would seem making the speakers a little hot in the low end and slightly rolled off hf responce wouldn't be a cardinal sin.
40Hz will have to be good enough, that's what I have today with my ML-TQWT.
I'll take your word for it.

My usual daily listening is pretty low, low enough to keep a conversation going without to much of a problem.
When I really listen I probably average 90dB or so.

I'm very partial to a fleshed out LF and a rolled off casual HF.
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Old 21st April 2013, 01:33 PM   #12
6.283 is offline 6.283  Germany
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Both, the speakers for the B&K target curve and the speakers used by Olive had a wider dispersion than what are you going to build. So for them a slight roll off is indicated. A 1" in a 15" pasta bowl will have very narrow dispersion, so it should stay flatter.
If you roll off the highs it does not sound awful. Just find the slope that you like. But I also would compare it to flat.
No DSP required imho. Use a passive down-shelve.
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Old 21st April 2013, 01:57 PM   #13
Pano is offline Pano  United States
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Agree - do compare it to flat. The speakers and the room do make a difference. I use the B&K curve, I think the other would sound too heavy in my room. Your ears and brain don't work exactly like a microphone and chart, so you have to do some judgment by ear.

But either of those targets will give you good subjective results.
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Old 21st April 2013, 04:30 PM   #14
markusA is offline markusA  Sweden
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Well, I doubt there is any such thing as a perfect first trial crossover. It does however appear to affect the response quite a bit.

My latest efforts have been focused on trying to achieve a flat response without the aid of BSC or room contribution. I'm thinking the room gain should make the bottom a little more "full" as long as the baffle step doesn't cause a dip.
It's proving to be a challenge and F3 appears to end up at roughly 50Hz.
Adding a "typical" room gain will llower F3 to 40Hz.

I'll include a screen dump of the last example. I'm using the B&C 15TBX100.
LP crossover and baffle step included, no bsc and no room gain.
80L (20% fill) BR tuned at 50Hz.
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File Type: jpg FR.jpg (71.7 KB, 204 views)
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Old 21st April 2013, 09:29 PM   #15
gedlee is offline gedlee  United States
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Originally Posted by markusA View Post
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...
Given the fact that the end response of any "tuning, diffraction, room gain" will be completely dominated by the room, and that no two rooms are the same, what difference does any of this matter?

If you EQ the modal region - which is the only way to get good LF response - then the free field response of source does not matter at all. Just use several closed box subs, an electronic crossover with EQ and be done with it. Just tune the system the way you want it with the electronics.

Its so much easier that way.

All this talk of sub tuning is such a waste of time.
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Old 22nd April 2013, 08:58 AM   #16
markusA is offline markusA  Sweden
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Earl, you are one of my greatest sources of inspiration for this project and one of few who I percieve as really knowing what he's talking about. I very much appreciate your input and from what I've read earlier it sounds like a slightly unorthodox but successful way of solving the issue.

If I had limited time and plenty of resources I would probably just go ahead and do it like that. However, unfortunately my situation is very much the other way around. I have plenty of time and very limited resources.

Once I'm done building the speakers it will probably take me at least 2-3 years to save up enough cash to get a dsp (or electronic crossover) and a couple of cheap subs.
I wish things could be different but some matters are simply out of my control.

So, being unable to implement that solution in stage one, I have to build the speakers as stand alone units with no low end reinforcement from any sub. I'm very much aware that this is not the optimal way of doing things but I try to make the best I can with what I do have.

Any tips regarding target response, cabinet design, crossovers and EQ's are greatly appreciated but I simply can't afford a solution including any additional subs at the moment.
I could perhaps scrounge up the cash for a simple dsp build within a reasonable time frame but the subs will have to wait.

That's why I started this question regarding an extended bass shelf vs. flat response and what a desirable target response actually looks like..
A dsp could flatten the response after the fact since the tuning is lower with an EBS.
If I tune it higher for a flat response the dsp can't do all that much for the LF extension due to the physical limitations from the ported design.

A closed box with a Linkwitz transform would bring the low end extension but limit the peak output in a significant way and require a lot more power from the amp.
The Bass Reflex cabinet appears to be the best compromise although far from perfect.
I guess I'm just trying to find the best compromise and the best bang for the buck.
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Old 22nd April 2013, 12:50 PM   #17
gedlee is offline gedlee  United States
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Fair enough. You did not make clear that you were limited in budget. I still think that the HP characteristics of the woofer tuning are not really that important once one gets the speakers in the room. The thing is that the tuning of the system on paper will not mean a thing once the speakers interact with the room modes. But some DSP is still likely to yield a better LF in-room response than without it. I would still use a closed box and EQ the system in-situ (only at the LFs) with say a miniDSP based on some in-room measurements. Don't EQ anything above about 150 Hz though as you are only likely to make things worse rather than better.

There should be, as discussed, some falloff of the power response with frequency. I shoot for typically a -3 dB per decade drop in the listening axis response after about 1 kHz. But this depends very much on the speaker and if it is constant directivity or not. A true CD speaker up to 10 kHz and beyond needs a lot more axial response drop than a speaker with a beaming response.
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Old 22nd April 2013, 04:35 PM   #18
Pano is offline Pano  United States
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Quote:
Originally Posted by gedlee View Post
A true CD speaker up to 10 kHz and beyond needs a lot more axial response drop than a speaker with a beaming response.
That has been my observation, too.
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Old 22nd April 2013, 05:15 PM   #19
badman is offline badman  United States
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Quote:
Originally Posted by gedlee View Post
A true CD speaker up to 10 kHz and beyond needs a lot more axial response drop than a speaker with a beaming response.
Quote:
Originally Posted by Pano View Post
That has been my observation, too.
And mine. A flat axial CD 2 way a la geddes sounds very bright since it lacks the pattern narrowing of "normal" speakers.
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Old 22nd April 2013, 08:03 PM   #20
markusA is offline markusA  Sweden
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Good solid advice here, thanks for getting me to reevaluate the closed box option and speaking plainly regarding the FR.
I'll have to do some more modelling but it doesn't look half bad.
My pair of 15TBX100 will be shipped tomorrow, I'm as giddy as a schoolboy.
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