top spec nearfield monitor with extended LF response - diyAudio
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Old 16th May 2012, 04:01 PM   #1
legezer is offline legezer  United Kingdom
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Default top spec nearfield monitor with extended LF response

I am looking to build a set of nearfields. I have some knowledge of acoustics (I have measured and treated several rooms, including building tuned Helmhotz panels for one) but only a little knowledge of speaker design. As a little knowledge can be a terrible thing I will be getting Wilmslow audio to do the specifics of the design.
My room is only 12' (3 m 66cm) x 8' 3" (2m 50cm)
currently I have a good amount of broadband absorbtion and diffusion, but I am here long term, so I am going to build tuned panels soonish.
speakers are either side of my workstation mounted vertically on stands, 2ft(60cm) from the back wall and 1ft(30 cm) from the side walls. so the tweeters are 4'4" apart and thats the distance from ear to tweeter when I'm in mixing position.

I know I want all my drivers in vertical alignment, I do not want duplicate drivers and I do not want a separate sub

I do not require great volume at all but need the bass still to be there at low volumes

I am leaning towards a 3 way design using up to a 3" ATC dome to cover the vocal range in a tried and tested combination with a great soft dome tweeter.

But I really want to get the bass extension down to 30something hz +-2db. The best speaker I have heard for really delivering subs clearly from a small box to a close listening position (and it was in a small very well treated room) was the PMC AML1, which is a tiny transmission line apparently a scaled down version of that in the LB1. But I haven't been able to find any designs for small transmission lines.

I could afford the box to be significantly bigger than the AML, and If it were possible to avoid a port or TL it seems to me desireable (I'm into simplicity wherever possible)- I had been under the impression that it wouldn't be possible to get the bass response I am after with a sealed box, but the guzauski-swist GS-3a claims +-2db down to 28hz from 2 cubic foot sealed enclosure. I haven't been able to find any info on the 12" Dayton aluminium driver it uses, but must it sacrifice sensitivity for this response as the system is driven by 4k of amps!
The GS-3a is right at the cusp of what I could fit in size-wise at 24"(60cm) high by 14.4" (37cm) by 15.5" (40cm)deep (in its vertical alignment) but a 12" might be overdoing it a bit for the room, so- finally getting to specific questions-

is there a 10" driver that I could put into a correspondingly smaller sealed enclosure and still get down smoothly into the 30s? or would a 12" be the way to go(remembering I do not need to go very loud, and I'd rather not have to run a massive amp)

do you have any materials/techniques/designs on how to as near as possible eliminate resonances in a sealed enclosure?

are there any issues with treating the construction as 2 separate boxes tailored to the drivers they house ? any tips for how then to unify them as 1 unit while keeping them as de-coupled as possible…
any other advice/links/anything that can help me succeed in this quest.

many thanks in advance

Last edited by legezer; 16th May 2012 at 11:13 PM.
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Old 16th May 2012, 04:56 PM   #2
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Hi, I have experience with the 3" ATC dome. It will need to crossover at about 1KHz with the bass. Therefore you will need an agile bass driver which to a certain extent conflicts with deep bass. You should not rule out a small powered sub operating from 50Hz down.

From the size of your room wide dispersion dome may not be the best option even if it is a low distortion driver. Remember it is only low distortion over its pass band which is narrow. You will need more room treatment to defeat the wide dispersion hence creating a self defeating exercise. Study the JBL 4312M. Vertical alignment will mean you will need to sit further away for proper integration.
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Old 16th May 2012, 05:07 PM   #3
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The task you are about to undertake is quite difficult for a novice. You will need to do much research.
DIY Loudspeaker Projects Troels Gravesen
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Old 16th May 2012, 06:13 PM   #4
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From everything I read about the ATC 3" dome it works best when crossed in at 380Hz.
This is what ATC themselves do and they should know their own driver rather well.


The Barefoot Sound Micromain 35 does 39-20 000Hz +- 1.5dB out of a 19L box.
Might be worth a look just for inspirations sake if nothing else.
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Old 16th May 2012, 09:12 PM   #5
legezer is offline legezer  United Kingdom
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Quote:
Originally Posted by Charles Darwin View Post
From everything I read about the ATC 3" dome it works best when crossed in at 380Hz.
This is what ATC themselves do and they should know their own driver rather well.
The Barefoot Sound Micromain 35 does 39-20 000Hz +- 1.5dB out of a 19L box.
Might be worth a look just for inspirations sake if nothing else.
Thanks for the info! yes I was thinking it would be in the 300s somewhere. I haven't heard the barefoot stuff, but I am very much inclined towards keeping it simple and having 2 or 3 drivers pointing at me in alignment.
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Old 16th May 2012, 09:23 PM   #6
legezer is offline legezer  United Kingdom
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Quote:
Originally Posted by spladski View Post
The task you are about to undertake is quite difficult for a novice. You will need to do much research.
DIY Loudspeaker Projects Troels Gravesen
Thanks for the info!
I have been looking on here, but the smaller TL designs don't seem to have the LF extension, and they don't seem to have any infinate baffle designs. I am definitely not taking this lightly. I have a friend who designs (and I mean really develops) PA speakers, and he could model it for me, but he's not gonna know much about the drivers or designs for small enclosures
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Old 16th May 2012, 09:46 PM   #7
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Crossover frequency for the ATC 3" depends on implementation. 380Hz is OK with 4th order filters. This is what ATC use with active crossovers.
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Old 16th May 2012, 10:00 PM   #8
legezer is offline legezer  United Kingdom
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Quote:
Originally Posted by spladski View Post
From the size of your room wide dispersion dome may not be the best option even if it is a low distortion driver. Remember it is only low distortion over its pass band which is narrow. You will need more room treatment to defeat the wide dispersion hence creating a self defeating exercise. Study the JBL 4312M. Vertical alignment will mean you will need to sit further away for proper integration.
thanks this could be very useful advice. I did say up to a 3" as I did think there may be reasons why smaller could be more suitable, and here's one.

re your last point maybe this is an argument for going 2-way? many of the speakers that would excel at this distance (pmc AML1 or 2, Meyer HD1) are 2-way.
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Old 16th May 2012, 10:12 PM   #9
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You haven't stated which is your preference. Active or passive. TL designs do not automatically confer more bass. It is a volume related thing. Read Stereophile review of small TL from PMC.
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Old 16th May 2012, 11:06 PM   #10
legezer is offline legezer  United Kingdom
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Quote:
Originally Posted by spladski View Post
You haven't stated which is your preference. Active or passive. TL designs do not automatically confer more bass. It is a volume related thing. Read Stereophile review of small TL from PMC.
Passive. I'd like to be able to continue using my Quad 405mk2 but realise I may have to match something more powerful (even though I don't need high levels)
depending on the design.
I want to keep the crossover as simple as possible so I can spend the money on quality components rather than lots of them, so I need to select drivers that naturally complement each other

Thanks, I will have a look at that article. I'm leaning towards a sealed box but don't know all the variables for getting the optimum performance 'down there'. At some point I will take the idea to wilmslow...but the more knowledge I can get before that point the better.
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