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Old 12th September 2005, 02:01 AM   #1
JinMTVT is offline JinMTVT  Canada
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Default Aiming for SQ in a sub ...

I would like to start a thread about something we don't quite talk about that often in the sub section ...

and that is SOUND QUALITY

everyone wants a flat FR down to 10hz
( wich noone never gets neway )

and everyone is looking for 100+db output at sub 40hz!!
( well some do get way more than that with recent projects! ;p )

But what about sound quality in the 0-100hz range???

What should we be expecting in that range of the audio?

Does our earing mechanism enable us to get distortion at this low level ? what is the threshold we are looking for here in distortion?
are there based scintific numbers under wich there is no point in trying to improve quality in sub bass ?

Then, enclosure/design ...
Is the W-OBaffle still the champ in SQ design ?
if not, what is then ?
what are compromises when looking into SQ ..
i'd say that since it's always a balance of everything, we have to let go some SPL and FR to get better SQ right ?

Drivers distortion, is there material ? cause i don't see graphs often when looking at 15+ subs on websites
it's like everybody is almost ignorin the SQ of the drivers when used for sub-bass

what is the best crossover frequency for the sub bass ?
2 way?
3 way ?

i'd say that using a 3-way system , the sub can be let to operate only the seriusly low hz ( 50-70 and lower.. )
but what about using large 15-18" up to 200hz ?
300hz ?

neway, i started this trend cause i want to talk more about SQ in bass....something that we don't mention often

so please add to this thread with your ideas and knowledge about how to get the best possible SQ and it's compromises in low bass
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Old 12th September 2005, 03:43 AM   #2
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A few Pluses
Flat BL curve
Large/No enclosure
Linear suspension
The golden rule of DIY:
Build nice, or build twice!
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Old 12th September 2005, 05:26 AM   #3
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My current take on this at the moment is that it's better to use a sub down low and cross to some woofers above that point, with some decent SD but more modest excursion and more top end.

My feeling is that a good point to cross is around 40 Hz - use subs below that to get brute force excursion and pressurise the room in monopole vented subs - mono with sufficient displacement to get the output. Then above this point cross to some woofers with a low distortion motor and a flat response up to 1khz, but crossed over to mids at say 200 Hz. I think the critical bass for fidelity is actually higher than most subs can handle with finesse - 40 - 200 Hz. There are some that believe that "fast bass" is a matter of getting a good integration of upper bass up into the lower midrange. I believe that the ear is more sensitive above 40 Hz.

So my current take:

1. brute force monopoles up to 40 Hz
2. multiple driver dipole / U frame woofers up to 200 Hz
3. crossing to your preferred mid and tweeter arrangement

I'm considering doing this as my next speaker upgrade, putting my MTMs in open baffle, adding a pair of 10" Peerless CSX per side then my current AV12 subs.

I've tried crossing my AV12s up as high as 80 Hz with a 4LR active xo, but wasn't happy with the result when it comes to acoustic double bass.
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Old 12th September 2005, 02:04 PM   #4
JinMTVT is offline JinMTVT  Canada
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so Paul,
what you are pointing is at more than 40hz quality starts becoming the priority again, and we need to make different arrangement for this to happen.

But a 4 way systems begins to lack the simple attitude though, and is usually twice harder to setup correclty( crossover, number os outputs... ) than a standard 3 way setup nah ?

what do you think about using 18" and more sized subs?
using a fe of them ?
do you believe that the usable freq range of subs goes down on par with their diameter?

if we use the sub higher, doesn't it permit to use a mid woofer that extends usually greater in the upper range?

just a thought.. i know that you have played with subs extensivly so
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Old 12th September 2005, 04:13 PM   #5
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My impression of the criteria that leads to the best SQ is the word 'flat':

Flat Bl curve
Flat FR curve
Flat GD curve
Flat Phase curve
Flat THD and IMD curves

Of course, it's impossible to acheive, but keeping those in mind helps in choosing the driver, the amp, the EQ, the box (or IB), the LP filter, etc., etc.


It's a very interesting idea. Velo has tried with the 1812 and claims to have found a nightmare crossing the 2 drivers. Seems to possibly be a source of bad measurement results in the latest AVTalk tests (where it looks as though the x-over is at 63ish Hz). Still, I personally think it can work very well. Let us know how it's going if you decide to persue it.

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Old 12th September 2005, 04:58 PM   #6
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Flatness of the distortion graphs is rather meaningless. Low distortion is much more important.
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Old 12th September 2005, 05:41 PM   #7
simon5 is offline simon5  Canada
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It depends 454Casull.

For example, if you measure the Soundblaster Audigy 4 Pro (which is a very solid soundcard in SQ)...

IMD = 0.0021% which is excellent but...
IMD (15 kHz) = 0.0210% which is less good...

You can get a soundcard like the M-Audio Revolution 7.1 which is probably higher IMD rating but flat across the range because there's no resampling.

I agree with you that most of the time, lower distortion is better.
DIYaudio for President !
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Old 12th September 2005, 06:52 PM   #8
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How about a bandpass enclosure, the low bandwidth will attenuate the harmonics so the distortion will be lower.
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Old 12th September 2005, 07:04 PM   #9
JinMTVT is offline JinMTVT  Canada
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what about the linkwitx thing OB enclosure?
is it one of the best way to get less distortion ?
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Old 13th September 2005, 01:47 AM   #10
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"Flatness of the distortion graphs is rather meaningless. Low distortion is much more important."


Have you ever seen a THD or an IMD graph of a subwoofer before?

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