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Multi-Way Conventional loudspeakers with crossovers

BR simulation vs experimental results.
BR simulation vs experimental results.
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Old 9th June 2019, 09:18 AM   #11
oon_the_kid is offline oon_the_kid  Malaysia
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Quote:
Originally Posted by diyuser2010 View Post
At an 80dB midband level around 1khz, you need the bass at 60 hz to be 100 dB, or 20dB louder to be perceived at the same level. For highest efficiency, tune at Fs or higher. Not to say that one can't tune below that, though you are in the compliance controlled region ( not mass controlled ) and if the suspension is tight, you may not get near what the simulation says.
Thanks for your lengthy reply. Really appreciate it. Yup, I did have a high pass filter at about 40Hz to reduce power below port tuning.

This makes sense, I am not familiar on the basis is the model and assumptions. But tunign below Fs is probably not what a lot of people will do and the inacuracy of the model might be the cause of deviation.

I am also most concern about the drop at port tuning, as if the port not working at all.

I will try to measure while barricading the area so the the port energy only points front and see if it makes any difference.

OOn
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Old 9th June 2019, 11:27 AM   #12
bentoronto is offline bentoronto  Canada
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BR simulation vs experimental results.
Seems to me the agreement of sim and mic are quite good. A whole lot better than I'd expect.

On the other hand, the only measurement that counts in the end is made at your listening chair. Domestic room acoustic influences will overwhelm the little variations in up-close mic measurements. So then you need to introduce DSP to fix things since it would only be random luck if the bumps in the sim were helpful or harmful to the room response.

The smart future methodology will be to assess the room first and then do a sim that recognizes drivers, boxes, and rooms in the mix.

B.
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Last edited by bentoronto; 9th June 2019 at 11:34 AM.
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Old 9th June 2019, 11:54 AM   #13
Michael Chua is offline Michael Chua  United States
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Quote:
Originally Posted by oon_the_kid View Post

The speaker driver is a Faitalpro 4Fe32

The freq response by Omnimic measurement shows a 12db drop from 150Hz to 50Hz.
Your port tuning is too low (left plot-black trace). Tuning to 80Hz will give you a F3 of 83Hz (center plot)

Or better still, change it to a Sealed Box (right plot F3=142Hz) and cross over to a woofer for bass.
Attached Images
File Type: gif Faitalpro 4Fe32.gif (40.0 KB, 194 views)
File Type: gif Faitalpro 4Fe32_PORTED_FB80Hz.gif (39.8 KB, 195 views)
File Type: gif Faitalpro 4Fe32_SEALED.gif (39.3 KB, 195 views)
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Old 10th June 2019, 01:30 AM   #14
oon_the_kid is offline oon_the_kid  Malaysia
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Hi Michael,

Thanks for the simulation, i didn't mention earlier that i tried another box at 80 Hz and it sounds better and sims better.

Simulation based on the worksheet i have and your differs by a about 2db at 60 Hz. But iwill still be happy if i had a result that was anything close to what you were getting.

I wanted more bass extension, and one way of achieving it is by dropping the port frequency and giving it a small 3-6 db boost by dsp. If had the based on your simulation, i would add a 4 db boost electronically at 60Hz, i would achieve a frequency response of -3db at 60Hz. Would have been more than adequate for me.

However kn my case it was 12db down at 50 Hz and 18db down at 60Hz. That is not realistic to correct electronically.

Even at my other box where i tuned it to 80Hz, it was down at -6db at 70Hz but there was a big dip at 80Hz port tuning frequency.

I can't quite undertand the cause of the dip. Although for the simulation to be off might be because of as what another poster has mentioned, that port tuning below Fs is quite inaccurate..

Oon

It seems as if the port is not doing its job. I stuffed the box with acoustastuff lightly. Could that be the source of the problem? Maybe i should use a absorbent material that is only on the walls.

Oon
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Old 10th June 2019, 03:13 AM   #15
johnsurnamerobinson is offline johnsurnamerobinson
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Stuffing the enclosure on a bass reflex will radicaly affect the Q same as resistitive ports.Not many sim prograns can accurately model stuffing.I take it what you are trying to design is a 6th order br ?.
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Old 20th June 2019, 10:31 PM   #16
oon_the_kid is offline oon_the_kid  Malaysia
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Hi,

Not really. I am not tuning to any specigic allignment or order. What i am ttying to donis to achieve freq response as low as possible with the sid of a DSP. Theorectically if i have a 60Hz port tuning and gave a 4-6 db boost at 60 Hz and a steep rolloff at 50 Hz i can achieve a freq response if 60Hz.

So the key differece here is designing with a DSP in mind rather than purely passive ststem.

Oon
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Old 21st June 2019, 01:18 AM   #17
bentoronto is offline bentoronto  Canada
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BR simulation vs experimental results.
Quote:
Originally Posted by oon_the_kid View Post
So the key differece here is designing with a DSP in mind rather than purely passive ststem.
That is very smart.

In addition to FR per se, a great DSP like the fabulous Behringer DCX2496 can also introduce protection limiting (with several parameters awaiting your choice) and extra-low-sonic HP filtering. And all available to be modified in seconds (once you learn how to use the device).

There are certain very obvious issues that others will recite to you like cone excursion max, power needs, etc. But more germane to your question is type of box.

As with motional feedback, boxes can be well-behaved and natural for DSP or MFB or they can be otherwise. Easy to tell because the "cooperative" models are also the leaders in sound quality (sealed, OB, labyrinth) and others (BR, tapped "horn", short true horn, TL on a bad day....) are not.

BR plus DSP is like having two independent brains running the speaker. Think about it.

B.
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Last edited by bentoronto; 21st June 2019 at 01:21 AM.
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Old 21st June 2019, 04:36 AM   #18
johnsurnamerobinson is offline johnsurnamerobinson
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What you are describing IS in effect a sixth order system> The proceedure is normaly to design a normal reflex max flat response system THEN down tune it by 1/2 octave and then provide a bass boost at this NEW frequency with an active high pass filter with Q=2.
This gives a steeper roll off below the new LOWER system resonance.Allowing deeper bass from a given size box/driver. There are some downsides to this approach. Some of these disadvatages might possibly be negated somewhat by DSP as phase shift and transient response can be much better with DSP than analogue filters.Anyway it works!!
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Old 21st June 2019, 05:27 AM   #19
oon_the_kid is offline oon_the_kid  Malaysia
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Quote:
Originally Posted by johnsurnamerobinson View Post
What you are describing IS in effect a sixth order system> The proceedure is normaly to design a normal reflex max flat response system THEN down tune it by 1/2 octave and then provide a bass boost at this NEW frequency with an active high pass filter with Q=2.
This gives a steeper roll off below the new LOWER system resonance.Allowing deeper bass from a given size box/driver. There are some downsides to this approach. Some of these disadvatages might possibly be negated somewhat by DSP as phase shift and transient response can be much better with DSP than analogue filters.Anyway it works!!
Aha, I see now. Okay. Thanks for letting me know what it is officially called.

Incidentally do you have some reading material on this. Would very much like to read up about it. The internet seems to give me the double ported version....

Oon

Last edited by oon_the_kid; 21st June 2019 at 05:34 AM.
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Old 21st June 2019, 08:41 PM   #20
johnsurnamerobinson is offline johnsurnamerobinson
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Yes most refs to 6th order are for multi chambered multi port subs this is different,There was a construction article in ww some years ago. Try starting a thread on diy audio asking for a practical design,the guys here are great.When I did it I simply retuned a pair of tannoys by lengthing the port (with a cardboard tube)and building the filter from op amps,To be connected between pre and power amp.(tape loop on an integrated amp or between cd player and amp.I will have a look on the web for you and report back. If you do start a thread do make sure you dont ask about 6th order subs!!!!
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