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Old 28th December 2014, 09:28 AM   #1
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Default Bass section design

I was given excellent advise here before, so here is another attempt at breaking down my design into smaller pieces.

I'm looking into designing a 3-way system, plus two existing 12" sealed subs I have. I'll leave the midrange and treble for another thread, but wanted to get input about the bass section. This bass section will be directly driven by a class-D amp, probably a Wyred4Sound 250 W per channel (crossover upstream from the amp).

I envision a box (per side), thinking a sealed box to match the subwoofers, and a separate unit housing midrange and tweeter sitting on top of it. The subwoofers will take the bass below 80Hz, so that eliminates the need for very low bass from the boxes under design.

But how big should the drivers be, and how many should I use per side? My room is 15x15x8 feet.

A driver under consideration is this ScanSpeak Classic 8" The Madisound Speaker Store
It seems to have nice frequency and impedance behavior up to about 800Hz. Maybe think about a XO frequency around 500-600Hz?
How do I figure out if I need two of these, or just one will do?

How about using four 6" woofers instead of two 8"? Both would approximate an added 100 square inches of cone surface...or three 7"?

I probably have a million more questions about this, but I guess these are the basics to get started.

Thank you!
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Old 28th December 2014, 10:58 AM   #2
AndrewT is offline AndrewT  Scotland
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Are you designing a 4way speaker system?

Which section are you asking about in this Thread?
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regards Andrew T.
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Old 28th December 2014, 11:19 AM   #3
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And how are you thinking of crossing over at 80Hz? (active, passive, natural rolloff?) Do you have any gain control on the subs?

Ralf
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Old 28th December 2014, 11:24 AM   #4
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Default Together ...

Quote:
Originally Posted by LewinskiH01 View Post
I was given excellent advise here before, so here is another attempt at breaking down my design into smaller pieces.

I'm looking into designing a 3-way system, plus two existing 12" sealed subs I have. I'll leave the midrange and treble for another thread, but wanted to get input about the bass section. This bass section will be directly driven by a class-D amp, probably a Wyred4Sound 250 W per channel (crossover upstream from the amp).

I envision a box (per side), thinking a sealed box to match the subwoofers, and a separate unit housing midrange and tweeter sitting on top of it. The subwoofers will take the bass below 80Hz, so that eliminates the need for very low bass from the boxes under design.

But how big should the drivers be, and how many should I use per side? My room is 15x15x8 feet.

A driver under consideration is this ScanSpeak Classic 8" The Madisound Speaker Store
It seems to have nice frequency and impedance behavior up to about 800Hz. Maybe think about a XO frequency around 500-600Hz?
How do I figure out if I need two of these, or just one will do?

How about using four 6" woofers instead of two 8"? Both would approximate an added 100 square inches of cone surface...or three 7"?

I probably have a million more questions about this, but I guess these are the basics to get started.

Thank you!
... not Separately. Extra c/o region contraindicated.

You should be able to find MR drivers that can be operated cleanly over a one decade frequency band (80-800+ Hz) and exhibit a dispersion pattern that matches that of the HF. driver in the c/o overlap region. I prefer MTM arrangements when the drivers are properly voiced. The use of multiple drivers provides a symmetrical radiation pattern with respect to the tweeter axis and mitigates displacement limitation on system output imposed by a single MR driver. Note: Volume Displacement [VD] = [SD]*[Xmax] is the parameter of interest here. Recomment use of a sealed, well damped, enclosure for these. SWAG on driver size: 6"-10".

Regards,

WHG
Regards,

Last edited by whgeiger; 28th December 2014 at 11:30 AM.
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Old 28th December 2014, 11:53 AM   #5
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Quote:
Originally Posted by AndrewT View Post
Are you designing a 4way speaker system?

Which section are you asking about in this Thread?
Yes: treble, midrange, bass, subass...whatever we call below 80Hz. I'm asking about the bass, so from about 80 to the crossover into midrange.
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Old 28th December 2014, 11:56 AM   #6
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Quote:
Originally Posted by giralfino View Post
And how are you thinking of crossing over at 80Hz? (active, passive, natural rolloff?) Do you have any gain control on the subs?

Ralf
All crossovers are to be active. My only source is a computer, and the plan is to use Acourate for room correction, driver linearization, and digital crossovers, and feed an 8-channel DAC that will in turn directly drive an amp driving speaker drivers directly. The subs have gain control, and the DAC will also have trim available.
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Old 28th December 2014, 12:03 PM   #7
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Quote:
Originally Posted by whgeiger View Post
... not Separately. Extra c/o region contraindicated.

You should be able to find MR drivers that can be operated cleanly over a one decade frequency band (80-800+ Hz) and exhibit a dispersion pattern that matches that of the HF. driver in the c/o overlap region. I prefer MTM arrangements when the drivers are properly voiced. The use of multiple drivers provides a symmetrical radiation pattern with respect to the tweeter axis and mitigates displacement limitation on system output imposed by a single MR driver. Note: Volume Displacement [VD] = [SD]*[Xmax] is the parameter of interest here. Recomment use of a sealed, well damped, enclosure for these. SWAG on driver size: 6"-10".

Regards,

WHG
Regards,
Ok, I need assistance understanding this post. I guess from my newbeeness.

What do you mean by "extra c/o region contraindicated"? Might you be suggesting to do without the bass drivers, and just have subwoofers, mids/bass drivers, and tweeter?

How should I connect the VD formula to the room size? What is SD and Xmax?

Sorry for sending questions back!
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Old 28th December 2014, 12:20 PM   #8
AndrewT is offline AndrewT  Scotland
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the mid and upper bass driver will need a band pass filter.
Since you propose 80Hz to 800Hz (a bit over 3octaves) you need a well behaved driver that can operate without distortion creating resonances over that whole range. Finding that will not be easy.

Using 80Hz avoids the need for enormous Xmax and also avoids the need for large EQ to "flatten" the bass response.
I suggest you look at drivers that give a near Butterworth roll off using a sealed box, at your 80Hz. i.e. aim for a Q=1/sqrt(2)

Then once you have candidates, look at what SPL each can achieve at 80Hz and select a short list that meet your F-3dB and SPL targets.
After that it probably comes down to price.
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Last edited by AndrewT; 28th December 2014 at 12:22 PM.
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Old 28th December 2014, 12:47 PM   #9
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Quote:
Originally Posted by AndrewT View Post
the mid and upper bass driver will need a band pass filter.
Since you propose 80Hz to 800Hz (a bit over 3octaves) you need a well behaved driver that can operate without distortion creating resonances over that whole range. Finding that will not be easy.

Using 80Hz avoids the need for enormous Xmax and also avoids the need for large EQ to "flatten" the bass response.
I suggest you look at drivers that give a near Butterworth roll off using a sealed box, at your 80Hz. i.e. aim for a Q=1/sqrt(2)

Then once you have candidates, look at what SPL each can achieve at 80Hz and select a short list that meet your F-3dB and SPL targets.
After that it probably comes down to price.
Trying to follow.

Q=0.707...but which Q? Looking at this driver I linked to above The Madisound Speaker Store
It list mechanical, electrical, and total Q. Assuming you mean Total Q, this one driver has Q=0.31.
Looking at various 6 & 7" woofers from ScanSpeak and Seas, their Total Qs are around 0.3-0.45...far from 0.707.
What will I gain with "drivers that give a near Butterworth roll off using a sealed box, at your 80Hz"?

BTW, my comment about using that driver between 80 and 800 Hz was from my [admittedly] basic interpretation of the graphs on that website. Maybe I'm reading it wrong? Is that driver recommendable for that range? If not, why? Then I learn.

Thank you for helping! Sorry about the basic questions.
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Old 28th December 2014, 01:05 PM   #10
Scott L is offline Scott L  United States
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Default 80-800 Hz is no easy feat

This is the mid-bass to lower mid range area. You will want to be able to move some air. By the way, SD=cone area. Xmax is the linear travel excursion of the voice coil in the gap.
Following my own rule-of-thumb, it is desirable to maintain linear response one octave above and below the crossover points. Between 80-800 is also the area where one encounters baffle step. Therefor, I would use two drivers to cover this range, with, an option being one driver of slightly different design, because,
which ever driver is used up to 800Hz should maintain some linear response up to 1600, which is usually where cone break up starts.
Since you are using sealed subs below 80Hz, which is actually a fine idea, I would stay with a sealed enclosure for your mid-bass driver(s) as well.
If you go with two drivers per side to cover this range, I'd include a partition within the enclosure so each driver sees it's own air space. Target the Q value to be real close to a .707 value for best results. If it was me, I'd use 2 each at 8inch drivers per side. Now the search for drivers begins. To me, this is always the fun part. Budget is of concern here. Good luck with your project. Research, and more research highly recommended.
****p.s. Look up what a 1.5 way means for your "bass section"********
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