DIY Sub Questions

[jason str]

8 minutes ago, CECAA850 said:

You can definitely hear them bottom out.

 

What design are you referring to ?

 

 

[CECAA850]

My dual driver table tuba.

[jason str]

Table Tuba has exposed drivers, if you wish to experiment see how the sound differs closing off the driver access door. Its harder to detect.

[derrickdj1]

A hpf(high pass filter) is employed in subwoofers to limit lower frequencies.  The role can be to limit undesirable frequencies or to protect the driver.  A sub box is tuned to a certain frequency determine by design, box size and driver specs.  No EQ should be done below the tuning.  Most music does not go below 35 Hz and a hpf can be employed at around 40 Hz to clean of the sound.  In the case of small sealed subwoofer, a hpf is not need.  The reason behind this is that the box acts as a quasi filter.  The build up of pressure inside the box at increasing volume will limit driver excursion but not protect the voice coil from thermal damage.

 

A vented subwoofer will unload, or act as if it is in free air below tuning.  In this case a hpf is used to protect the driver.  Also, at tuning, distortion starts to skyrocket, ealed, horn or vented.  Where as, sealed subs are more prone to thermal damage, vented subs are more prone to mechanical damage.  Any EQ boosting will alter the stress relationship between the drive and sub box and may cause problems sooner.

[jason str]

2 hours ago, derrickdj1 said:

A hpf(high pass filter) is employed in subwoofers to limit lower frequencies.  The role can be to limit undesirable frequencies or to protect the driver.  A sub box is tuned to a certain frequency determine by design, box size and driver specs.  No EQ should be done below the tuning.  Most music does not go below 35 Hz and a hpf can be employed at around 40 Hz to clean of the sound.  In the case of small sealed subwoofer, a hpf is not need.  The reason behind this is that the box acts as a quasi filter.  The build up of pressure inside the box at increasing volume will limit driver excursion but not protect the voice coil from thermal damage.

 

A vented subwoofer will unload, or act as if it is in free air below tuning.  In this case a hpf is used to protect the driver.  Also, at tuning, distortion starts to skyrocket, ealed, horn or vented.  Where as, sealed subs are more prone to thermal damage, vented subs are more prone to mechanical damage.  Any EQ boosting will alter the stress relationship between the drive and sub box and may cause problems sooner.

 

Too many variables are involved with sealed cabinets, small cabinet size helps but not eliminate over excursion issue especially if using heavy EQ for compensation of low frequencies.

 

Correct on the ported designs.

 

Horn designs have too many variables as well for a one rule fits all approach.

 

 

[derrickdj1]

It is a common practice to not use a hpf in small sealed subs.  As I stated in an earlier post the safest way to protect the driver is to determine the max voltage for excussion and use limiters, hpf and a reasonable person on the volume knob.  Clipping in the digital domain can change this and lead to driver damage.  The statements were correct.

[jason str]

45 minutes ago, derrickdj1 said:

It is a common practice to not use a hpf in small sealed subs.  As I stated in an earlier post the safest way to protect the driver is to determine the max voltage for excussion and use limiters, hpf and a reasonable person on the volume knob.  Clipping in the digital domain can change this and lead to driver damage.  The statements were correct.

 

Common practice for who ? Manufactures who design subwoofers absolutely use filters, or if passive let you know what max voltage and/or high pass filter setting to use.

[derrickdj1]

I thought we were talking about what we as consumers do in the home and not manufacturing.  Manufactures do use filters and DSP in their subs.  This prevents a lot of product from being damage since they can't assume their average customer is well versed on setting up their sub.  This discussion is on DIY subs.  A small sealed subwoofer does not need a hpf in the vast majority of cases.  Most of us that post regularly on the AVS DIY subwoofer forum don't use hpf with our sealed sub for HT.  In home theater, you want to maximize the LFE. With proper selection of sealed sub box and amp power, the sub should have a natural roll off of 12 db per octave (2nd order slope) which is enough to protect the driver.  Nothing is fool proof and in the wrong hand, pretty much any speaker or sub can be torn up.

[ACV92]

Man, apparently I have some more homework to do.  I feel inadequate....  I just wanted to plug the sub in, mess with a couple little knobs, and dance around my room spilling beer as I go because it sounds 'so good'!!  With that being said, I want to talk to average folks about audio like my uncle talks to me about photography and Ham radio.  I want to watch them physically glaze over as my mouth moves and feel good inside doing it.  When I mention Xmax and excursion intelligently and they think I'm talking dirty I'll know that I've been steadily climbing the mountain.  Alright, enough sarcasm.

 

I've dabbled since I was a teenager, built a few car systems, moved to home audio, but never knew enough to 'really' know what I was doing.  I've got some time before I dive into this little project so I feel that I should fill my down time with the some audio education.  I'm just looking for some good places to start.  What books/websites would you guys recommend that cover the spectrum of design, T/S parameters and their interactions/behaviors, crossovers, enclosures, etc.  I understand that experience is an exponential component within theoretical and empirical applications.  I have a little experience but need a better theoretical foundation to build on.  Your suggestions and analyses have been very helpful.  It is appreciated.

 

One other note, I feel a little dirty being on a Klipsch forum and I haven't mentioned Klipsch in my posts.  This sub setup will be with my KG 5.5's.  I know, not the most noteworthy of Klipsch's past and present offerings., but I've been happy with them.  I want to try the Crites tweeter diaphragms upgrade to see if brings the upper end to life a little more.  If I had the money, Palladium's and some Marantz Model 9's.  A more obtainable target for me are the RF-7's.  But, that's a ways off.  Sorry all, I'm rambling.  I need to go to bed....

 

Thanks again.

 

[DizRotus]

Geddes has a paper on multiple subs that I found useful.  I'll try to locate it attach it to a post when I'm on a proper computer, rather than this antique iPad.

[DizRotus]

I located the pdf on my computer, but it exceeds the forum's upload limit.  Go to the site below and click on "Papers."  

 

http://www.gedlee.com/

 

I'm not suggesting that Geddes is the last word, but it is, IMO, interesting and useful.

[jason str]

6 hours ago, derrickdj1 said:

I thought we were talking about what we as consumers do in the home and not manufacturing.  Manufactures do use filters and DSP in their subs.  This prevents a lot of product from being damage since that can't assume their average customer is well versed on setting up their sub.  This discussion is on DIY subs.  

 

Absolutely, it is on DIY subs but the manufactures know what they are doing as the normal DIY builder not so much. Why not go the extra step and make the normal DIY build as good or better than manufactures could.

 

A small sealed subwoofer does not need a hpf in the vast majority of cases.  Most of us that post regularly on the AVS DIY subwoofer forum don't use hpf with our sealed sub for HT.  In home theater, you want to maximize the LFE. With proper selection of sealed sub box and amp power, the sub should have a natural roll off of 12 db per octave (2nd order slope) which is enough to protect the driver.  Nothing is fool proof and in the wrong hand, pretty much any speaker or sub can be torn up.

A small sealed sub has rolloff as you mention but in order to use it for home theater you need to EQ the hell out of it to get it to perform unless its in the smallest sealed off room. Maximizing a small sealed cabinet for LFE is the wrong approach in the first place.

 

 

 

 

[RoboKlipsch]

Thanks for the replies I figured i didnt understand the design of horn subs.  Jason remember plate amps are used for ported subs too and they always need the hpf.  At pe they designed all their flat packs to not need hpfs but as u say...if used it makes for a very high output sub above the hp

[RoboKlipsch]

Jason all the major manufacturers that make sealed subs eq the heck out of them they just build in the eq instead of the diy guy adding it himself.  Ported certainly has more output and doesnt need eq but sealed is used for either space saving or to get the lowest frequencies a ported sub cant do with authority.  If horn length determines the low end of a horn its the same issue...when u want a flat response below 20 something has to be done and each alignment has limits.

[CECAA850]

2 minutes ago, RoboKlipsch said:

..when u want a flat response below 20 something has to be done and each alignment has limits.

Correct.  See Hoffmans iron law.

[RoboKlipsch]

51 minutes ago, CECAA850 said:

Correct.  See Hoffmans iron law.

LOL not sure why I never bothered to read your signature before but yes, you do appear to be a fan of Klipsch and I understand the mod status!  Am I reading correctly that the RF7 theater is all powered by separate amplifiers????  Please explain....

[CECAA850]

9 minutes ago, RoboKlipsch said:

Please explain....

I have 4 amps with a total of 8 channels of amplification.  I use 7 of the 8.

 

[CECAA850]

I also have a Behringer EP-2500 powering my IB sub.  It's not pictured and in another room.

[derrickdj1]

1 hour ago, CECAA850 said:

I have 4 amps with a total of 8 channels of amplification.  I use 7 of the 8.

 

Looking good there buddy!

[derrickdj1]

I have used sealed Chase subs, Epik, and the UM 18's in the past 5  or 6 years.  On the DIY Chase and UM 18 subs no hpf was used.  These were 4 or 4.5 cu ft. boxes.  EQ was used on all to elevate the 20 Hz. region.  At 20 Hz a gain +6 to +8 was used in the DSP.  This is a large boost and no hpf was used in these subs safely.  All these subs were played at Reference level without hesitation.  If the sub box, driver and amp selection are appropriate, the chance of driver damage is minimal.  Now, if someone want to raise their sub trim +10 and and turn the volume all the way, he may find trouble playing movies that loud.  Will the trouble be from over excursion in the sealed box, not likely.  The trouble will come from clipping the signal in the digital domain and lead to burning out the VC in the majority of cases.