DCAudioDIY.com

DC Area Audio DIYer's Community
It is currently August 17th, 2018, 12:42 pm

All times are UTC - 5 hours [ DST ]




Post new topic Reply to topic  [ 87 posts ]  Go to page Previous  1 ... 4, 5, 6, 7, 8, 9  Next
Author Message
PostPosted: November 20th, 2017, 1:40 pm 
Offline

Joined: February 28th, 2013, 3:31 pm
Posts: 869
SoundMods wrote:
Cogito wrote:
Tom,

I am confused because, the spread sheet you gave me hows the resonance frequency going down as the volume of the sealed box increases. I am equating the resonance frequency with bass response. Chris's modeling shows there is not particular correlation between volume an f3.

Which is more relevant for determining bass response, resonance frequency fs or f3?

BTW, I found references online that xmax 7mm in each direction or 14mm total.



I felt the need to jump in here. The simple answer to your question is both.

The lowest woofer resonance you can obtain is the free-air resonance. That's with the woofer sitting on a counter out in the open. Box loading raises the measurable system resonance. The bigger the box the lower the speaker resonance. Since any of the practical box sizes do not represent a true infinite baffle you will be limited by the box size. Linear excursion peak-to-peak is the other limiting factor. Woofers as a generic group are designed to "pump" air with long travel of the cone. Or -- you can use bigger woofers. Electrovoice made a 30-inch diameter woofer that could do 20-hz in the box. WOW!

F sub s would be the speaker resonance in the box and F sub 3 is the response that is 3-db lower than the over-all average from that frequency and higher. Or where the roll-off is considered to start and considered the low frequency response limit of the speaker.

I hope this helps.


RIght on except for one point. Fs is free air resonance and Fb is resonance in whatever enclosure into which you place the driver.


Top
 Profile  
 
PostPosted: November 20th, 2017, 3:33 pm 
Offline
User avatar

Joined: July 24th, 2015, 4:17 pm
Posts: 656
Location: Parkville, Maryland
tomp wrote:
SoundMods wrote:
Cogito wrote:
Tom,

I am confused because, the spread sheet you gave me hows the resonance frequency going down as the volume of the sealed box increases. I am equating the resonance frequency with bass response. Chris's modeling shows there is not particular correlation between volume an f3.

Which is more relevant for determining bass response, resonance frequency fs or f3?

BTW, I found references online that xmax 7mm in each direction or 14mm total.



I felt the need to jump in here. The simple answer to your question is both.

The lowest woofer resonance you can obtain is the free-air resonance. That's with the woofer sitting on a counter out in the open. Box loading raises the measurable system resonance. The bigger the box the lower the speaker resonance. Since any of the practical box sizes do not represent a true infinite baffle you will be limited by the box size. Linear excursion peak-to-peak is the other limiting factor. Woofers as a generic group are designed to "pump" air with long travel of the cone. Or -- you can use bigger woofers. Electrovoice made a 30-inch diameter woofer that could do 20-hz in the box. WOW!

F sub s would be the speaker resonance in the box and F sub 3 is the response that is 3-db lower than the over-all average from that frequency and higher. Or where the roll-off is considered to start and considered the low frequency response limit of the speaker.

I hope this helps.


RIght on except for one point. Fs is free air resonance and Fb is resonance in whatever enclosure into which you place the driver.



My bad.

_________________
Walt


Top
 Profile  
 
PostPosted: November 20th, 2017, 5:29 pm 
Offline

Joined: October 21st, 2013, 6:53 pm
Posts: 259
BTW, I found references online that xmax 7mm in each direction or 14mm total.[/quote]

I needed that!


Top
 Profile  
 
PostPosted: November 20th, 2017, 5:54 pm 
Offline

Joined: October 21st, 2013, 6:53 pm
Posts: 259
Hey sashi,

At this point you need to go out and buy some speakerbuilding books. Loudspeaker Design Cookbook by Vance Dickason is pretty good to have.

I cant' tell you very much more, because at some point you need to be driven by an uncontrollable urge to seek out this information yourself.

The one thing I can tell you is that speakerbuilding is pretty easy. You just have to get started!

The hard part, The part you can't speed up or abbreviate, is collecting a library of experiences. It takes specific experiences to understand specific principles, and in most cases you just have to wait until it happens.

That doesn't mean you don't do anything in the meantime. You need to start designing and building stuff, and asking questions, even if you don't really know what you are doing!

If you don't have the tools, get the tools. The primary things you need are a contractors table saw so you can cut parallel lines, and a router so you can cut round holes.

If you can't make that commitment, then maybe you can find somebody that is passionate enough about your ideas that they will help you pull them off, but it's always better if you do it yourself!

Chris


Top
 Profile  
 
PostPosted: November 20th, 2017, 6:05 pm 
Offline

Joined: July 17th, 2016, 6:24 am
Posts: 417
Thanks Tom and Walt.

The box calculations based on T/s parameters seem to be an approximation under some "assumed" conditions. By that I mean, there doesn't seem to be any allowance for
1. Input power
2. Strength of the magnet
3. damping of the enclosure
4. Geometry of the enclosure

_________________
Shashi


Top
 Profile  
 
PostPosted: November 20th, 2017, 6:14 pm 
Offline
Site Admin
User avatar

Joined: February 28th, 2013, 10:38 am
Posts: 912
Cogito wrote:
Thanks Tom and Walt.

The box calculations based on T/s parameters seem to be an approximation under some "assumed" conditions. By that I mean, there doesn't seem to be any allowance for
1. Input power

Not relevant. Performance should be independent of power until you run out of linear excursion or the voice coil gets hot enough to create power compression.

Cogito wrote:
2. Strength of the magnet

T/S parameters depend on, among other things, magnet strength, so that's already in there.

Hi-Fi Loudspeakers and Enclosures by Cohen is also a good reference...

Roscoe


Top
 Profile  
 
PostPosted: November 20th, 2017, 6:19 pm 
Offline

Joined: July 8th, 2016, 4:34 pm
Posts: 207
Lots of books -

https://www.parts-express.com/cat/refer ... ucation/74

https://smile.amazon.com/s/ref=nb_sb_no ... r+building

probably some even in your local library.


Top
 Profile  
 
PostPosted: November 20th, 2017, 6:40 pm 
Offline

Joined: October 21st, 2013, 6:53 pm
Posts: 259
Roscoe Primrose wrote:
Cogito wrote:
Thanks Tom and Walt.

The box calculations based on T/s parameters seem to be an approximation under some "assumed" conditions. By that I mean, there doesn't seem to be any allowance for
1. Input power

Bassbox says you can put 100 watts in there and not exceed Xmax. I don't know if you know what 100 watts is, but 100 watts is a lot of power!


Top
 Profile  
 
PostPosted: November 20th, 2017, 7:34 pm 
Offline

Joined: October 21st, 2013, 6:53 pm
Posts: 259
So, I'm not sure about what the engineers say about this:

My information defines fc as the box resonance, and f3 as the low end rolloff.

From this I would assume that if fc is above f3, it is a competing signal with the bandwidth of information the driver is supposed to be faithfully reproducing in a flat manner, hence detrimental to the performance of the system.


However, if fc is belowb f3, the resonance is producing gain in a place where you are losing gain from the natural rolloff of the system, and therefore might be beneficial in extending the low end response of the system altogether.

Chris


Top
 Profile  
 
PostPosted: November 20th, 2017, 7:42 pm 
Offline

Joined: February 28th, 2013, 3:31 pm
Posts: 869
chris1973 wrote:
BTW, I found references online that xmax 7mm in each direction or 14mm total.


I needed that![/quote]

The definition of Xmax is the linear travel in one direction not both. It is also the distance of the direction where the linear travel is the lowest. If you have 5mm in one direction and 4mm in the other the correct value is 4mm. The limit can be a loss of suspension compliance or a loss of motor strength. Sometimes the limit in one direction is compliance and the other direction motor strength. Some manufacturers cheat and specify both directions or even total excursion even if not linear to make the drivers look better. If a driver has an Xmax of 7mm in each direction the correct spec for comparison is 7mm not 14mm.


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 87 posts ]  Go to page Previous  1 ... 4, 5, 6, 7, 8, 9  Next

All times are UTC - 5 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 6 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group