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Old 14th July 2012, 12:16 AM   #1
diyAudio Member
 
Join Date: Jun 2012
Location: Appalachia, in the middle of nowhere.
Default Many sub questions

Hi everyone, my first post.
But I have been lurking for a few months.
I am a born again audiophile. I was really into my stereo between 10 and 25 years ago but lost interest, this is obvious by me still using my BSR - RTA Equalizer from the '80's.(Remember DAK?) Oh.. and a DBX-120A...Doh
.
Now I am building it up again.
So, I have 2 - 3.1 ft.^3 cabinets with Pyle (of crap) 15's in them now but I want to change them to a pair of 12's.
I bought some Infinity 1262w's (I know, should have got lab 12's or something) but I am going to use them for now.
I have done many simulations with:
Subwoofer Design Toolbox
A J Vented designer 2.0
WinISD
I am just learning Hornresponse V29.10 and struggling with Akabak (major learning curve)
.
My first question, if I choose to go BR, the port will only fit in one direction (up-down) without using an elbow.
I was thinking of running the ports out the bottom and sitting the speakers up off the floor. Is this a good idea at all?
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If so, how far do I need to elevate the speakers?

.
I bought 3 -4" port kits from PE with the flanged bell, so I could use the tube and coupler from the third kit to make the ports a few inches longer than the 17" that the kits come with.(Sub toolbox and AJ vented seem to want about 22" (~21 Hz Fb)).
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I still have my 30 year old copy of Radio Schmucks "Building Speaker Enclosures" and saw a picture of a box vented through the bottom with the standoffs holding up the speaker forming a sort of horn shape starting at the port and expanding at 30 degrees included angle to the front of the speaker. I would use 2 X 4's standing up 3-1/2"
This would fit into my set up well, but would it work well at all?
.
Last question, if I did go BR, what frequency would I need on the high pass filter to prevent over excursion of the speaker?
I assume right at Fb W/24dB per octave, but what do I know.
.
It has relatively long Xmax at 13 mm (+- 6.5) but if I am using Hornresp. correctly it will hit Xmax even at 100W at something near 80 Hz., although I am not sure that I am using Hornrsp. correctly and A J Vented says it hits Xmax at ~ 22 Hz @ 300 watts.
.
Anyway,
I have a Cerwin Vega CV-900 to drive the subs and a Dynaco 80 to drive the mids/tweeters.
I am crossing over with the DBX-120A (120 Hz) right now but may get a DCX2496 so I can do it right. I might even Bi-amp in that case as I also have an old Opamp labs SM-100 servo amp and another set of 2 ft.^3 boxes with 12's in them.
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The mid/ tweeter box is ~0.9 ft.^3 and each contains 4, 5-1/4" MCM 15-1595 speakers (they called them "Bullfrog Monitor replacement's" way back then")
Also it has 5 el-cheapo Peizo tweeters in each channel.
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Obviously I will be building all new speaker boxes in the future (maybe even a PPSL) but I need to get by with what I have right now for the time being.
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I also just bought a Behringer DEQ 2496 with the recommended microphone.
I replaced my 30 year old Peavy mixer with a NOS Tascam M106 (yea EBAY) and also bought a Yamaha MV-802 mixer (no EQ at all) so I can handle all of the inputs I need which are:
Satellite TV
DVD player
Ipod
MC-303 groovebox
Korg Poly 61M synth
Ensonic ESQ-1 synth
All of which are stereo so require 2 channels each.
.
So Hello, hope I bombarded you with enough info to answer my questions.
I look forward to participating on this forum.
Oh, I am a lab tech at a heat engine research lab and also a machinist (Tool&die).
I presently set up test cells and instrument Stirling cycle heat engines, using Labview to collect data.
I also perform all the tests and make many of the modifications on the hardware in our fairly complete machine shop.
I guess you could say I am "handy"

well, Thank you in advance

ShadyDave

PS I may not be back to my computer until Monday, so be patient.
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Old 14th July 2012, 04:32 PM   #2
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Join Date: Jan 2008
Quote:
Originally Posted by Shadydave View Post
I was thinking of running the ports out the bottom and sitting the speakers up off the floor. Is this a good idea at all?
.
If so, how far do I need to elevate the speakers?

.

I still have my 30 year old copy of Radio Schmucks "Building Speaker Enclosures" and saw a picture of a box vented through the bottom with the standoffs holding up the speaker forming a sort of horn shape starting at the port and expanding at 30 degrees included angle to the front of the speaker. I would use 2 X 4's standing up 3-1/2"
This would fit into my set up well, but would it work well at all?
.
Last question, if I did go BR, what frequency would I need on the high pass filter to prevent over excursion of the speaker?
I assume right at Fb W/24dB per octave, but what do I know.
.
It has relatively long Xmax at 13 mm (+- 6.5) but if I am using Hornresp. correctly it will hit Xmax even at 100W at something near 80 Hz., although I am not sure that I am using Hornrsp. correctly and A J Vented says it hits Xmax at ~ 22 Hz @ 300 watts.

ShadyDave
Dave,
Downfiring ports work well, if too close to the floor the floor boundary will become part of the port, lowering Fb.

Special port shapes can be effective, but generally require testing to see if the Fb is as planned as they don't fit the typical circular duct most programs model.

A 24 dB per octave high pass filters should be a few Hz lower than the Fb.

Xmax is a one way figure, an Xmax of 13 mm is 26mm peak to peak.

Fb can be verified by putting a white dot on the cone and doing a frequency sweep, excursion will be at minimum at Fb.

Art
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Old 14th July 2012, 09:26 PM   #3
tvrgeek is offline tvrgeek  United States
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Elbows are not totally evil. Also, a flared port can be a tad shorter.
Linkwitz also has a spreadsheet that helped with understanding x-max.

I will tell you this, anywhere near half that the distortion goes through the roof.

How do those drivers model in a low Q sealed box? I find the room gain compensates just about right for sealed boxes. ( I run a pair of Peerless 12's in 60L sealed boxes). You don't want a sub that models flat down to whatever silly low number, like 20, in a room. You actually want it to roll off much earlier. Sealed rolls off at half the slope. Just about right to get the end result in balance.
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Old 15th July 2012, 03:17 PM   #4
diyAudio Member
 
Join Date: Jun 2012
Location: Appalachia, in the middle of nowhere.
Default Discovered yet another good sim program

Thank you for the replies.

Quote:
Originally Posted by tvrgeek
How do those drivers model in a low Q sealed box? I find the room gain compensates just about right for sealed boxes. ( I run a pair of Peerless 12's in 60L sealed boxes). You don't want a sub that models flat down to whatever silly low number, like 20, in a room. You actually want it to roll off much earlier. Sealed rolls off at half the slope. Just about right to get the end result in balance.
I have been doing all my modeling at work during lunchtime, as I have no internet connection at home.
I finally took my thumb drive home with all my speaker specs and sim programs, and I found another program on my thumb drive that I have not used yet.
Woofer Box Model and Circuit designer 4.5
I like it as I can put the crossovers and even an LR filter in it, and it is very intuitive to learn (I am very partial to .xls simulations because I have written so many myself).
.
I spent many hours with that yesterday and I have decided to go with a sealed box.
There seems to be much better control of cone excursion and I have read that SQ is much better with a sealed box, unless you have a very good BR design. Also I found that 2 sim programs tell me I need a 6" diameter port.
.
What would you consider a "Low Q" sealed box value?
My box volume gives a Qtc of 0.669
.
At 300 Wrms and with just a 22 Hz 4 pole high-pass filter and a 100 Hz (LR) low pass I can get 100 dB @ 25Hz without exceeding Xmax and peak output of 110 dB @ 70 Hz per speaker. So I guess 103 dB and 113 dB with the pair.
But is this at 1 Meter?
I may find out when I do the room response file.
No decent help file for Woofer Box and Circuit Model
.
I still need to input the room parameters, I am sure that I will get significant gain from them.
.
This is good enough for now, and is only temporary.
Seems I've got the bug and will have to build some good speaker cabs W/good drivers.
.
Quote:
Originally Posted by weltersys
Xmax is a one way figure, an Xmax of 13 mm is 26mm peak to peak.
Does this mean that I should input 26 mm as Xmax?
.
Well I did some research and found:
AJ Sealed (and Ported) designer V2.0 the Xmax is input as amplitude, not peak to peak.
.
I found a reference on DIY Audio and Video dot com that says Winisd wants amplitude in the DriverEditor file.
Quote "Maximum peak linear excursion".
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I have not figured out what AKAbak wants, but I have a long way to go before I will be competent with that program.
It reminds me of PSpice and I assume it is a powerful tool.
.
I can not find out what Woofer Box Model and Circuit designer 4.5 wants (Peak or Pk. to Pk) No help file
.
I have one other question for anyone who uses simulations.
When I input speaker diameter, should that be based on the radiating area?
I am assuming that I do not input 30.5 cm for a 12" speaker.
The radiating area on the 1262W converts to a diameter of 26.0 cm.

I thank all for your help.

Dave
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Old 15th July 2012, 03:33 PM   #5
bjorno is offline bjorno  Sweden
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Quote:
Originally Posted by Shadydave View Post
..The radiating area on the 1262W converts to a diameter of 26.0 cm..
Hi,

The Radiation Area(Sd) or the Radiation Diameter are correct to use in simulation programs.

b
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Old 16th July 2012, 09:59 AM   #6
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Quote:
Originally Posted by Shadydave View Post
.
At 300 Wrms and with just a 22 Hz 4 pole high-pass filter and a 100 Hz (LR) low pass I can get 100 dB @ 25Hz without exceeding Xmax and peak output of 110 dB @ 70 Hz per speaker. So I guess 103 dB and 113 dB with the pair.
But is this at 1 Meter?
I may find out when I do the room response file.
No decent help file for Woofer Box and Circuit Model
.
I still need to input the room parameters, I am sure that I will get significant gain from them.
.
I wouldn't count on the peak SPL rating you've given: while they will mechanically put out 110dB at 70Hz, if any lower frequencies were present, you'd hear the sound of different parts of the speaker bouncing off each other.

If you take the high pass to 40Hz (sufficient for probably 90% of music), you'll gain significant SPL capability at the expense of some bass extension. This is something you could experiment with to find the balance that's right for you.

Room gain and wall/corner loading will provide considerable boost to the LF: winISD models a speaker in half-space (ie, in a field). IIRC, you gain 3dB by putting the speaker up against a wall (quarter space), and another 3dB by putting the speaker in a corner (eighth space).
The above figures rely on the walls being perfectly rigid, so that all the LF energy is directed into the room.

Put simply, room gain is complicated business and several members here have used many subwoofers placed strategically around the room to iron out the room's effects on the low stuff. Most of us make do with the more pedestrian approach of repeatedly moving the sub around the room until the best sound is found.

Chris
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Old 16th July 2012, 06:21 PM   #7
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Quote:
Originally Posted by Shadydave View Post

Does this mean that I should input 26 mm as Xmax?

Dave
If your speaker is listed for 26 mm Xmax, use 26, if it is listed as 13 mm Xmax, use 13.

As I mentioned previously, Fb can be verified by putting a white dot on the cone and doing a frequency sweep, excursion will be at minimum at Fb in a ported box, it increases rapidly above and below Fb.
When you measure excursion by eye using a ruler you will be reading peak to peak, so divide that figure by 2 to see how close you are to Xmax.

A speaker in a sealed box just steadily increases in excursion, dropping in output as frequency decreases.
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Old 17th July 2012, 03:19 PM   #8
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Default Reflective room

I did not realize how much gain you can get from the Room response.
I made a room model with the "Baffle Edge Diffraction & Room Response Reinforcement" model that goes along with the Woofer Box and Circuit Designer.
It shows 8.3 dB gain at 70 Hz and 10.7 dB gain at 30 Hz.
.
I need to get a good model going on winISD as I would think it is a more accurate model.
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I also know that I am going to have to invest in some corner absorbers and a few wall mounted absorbers as the room is 16' X 22' with 12" concrete block walls.
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I just received the Behringer DCX 2496 and plan on playing around with filtering quite a bit, including LR highpass filters.
.
Thanks for all the help, I will update as I run into problems and also try to figure out how to post a few pictures.

Dave
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Old 17th July 2012, 04:12 PM   #9
tb46 is offline tb46  United States
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Hi Shadydave,

Give Hornresp a try: Hornresp

It has a nice help file, and is extremely versatile. I'll attach a quick example of a bass reflex using the Infinity 1262W:

Regards,
Attached Images
File Type: jpg Infinity_1262W_BR_Input.jpg (37.1 KB, 163 views)
File Type: jpg Infinity_1262W_BR_SPL.jpg (27.5 KB, 161 views)
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Old 18th July 2012, 10:31 PM   #10
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Default Hrsp file

tb46,
Thanks for that example.
I had almost the same simulation, but I did not know how to put ports into the sim.
My sim. had Fr and Tal, so only a sealed box.
When I saw your example and it had the port area and length, I spent some time in the menus until I figured out how to change that.
And then, I was getting weird results until I found where you set the port at the same plane as the driver.
Now it looks like your file, and results.
A few of my numbers were a little different, and I already have cabinets, so the volume is fixed.
This file shows the existing cabinet volume minus the speaker (4.1 L) and the port volume for a 24 Hz port..
This is the input file.

Click the image to open in full size.

And the output.

Click the image to open in full size.


At 24.0 Volts (~300 Watts) it gives me 100 dB at 25 Hz, and 112 or 113 dB between 70 and 100 Hz.
That agrees well with the "Woofer Box and Circuit Designer" program.

Anyway, thanks

Dave
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