Hornresp - Page 179 - diyAudio
Go Back   Home > Forums > Loudspeakers > Subwoofers

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 1st April 2011, 03:55 PM   #1781
diyAudio Member
 
Join Date: Jan 2008
Quote:
Originally Posted by David McBean View Post
Quote:
Hi Art,

The multiple speaker (green) trace does however pass through the -1dB point at a lower frequency than the single speaker (white) trace.

Kind regards,

David
Yes, it does pass through the -1dB point at a lower frequency than the single speaker.
Just as it does with two of the cabinets, in the same exact position, with one powered and the other shorted out, as is shown in post 1776.

The trace passing through the -1 dB point is due to the approximately one dB forward gain afforded by the larger frontal area of the two cabinets.
When that extra gain is taken into account, there is no change at all in the LF corner frequency of the two TH compared to one.

I had forgot that important little detail when I posted the chart in #1771.

Also note that no LF "bump" prior to the cut off frequency occurs as it does in the William Cowan 60 hertz tapped horn Hornresp simulation.

Art Welter
  Reply With Quote
Old 1st April 2011, 04:22 PM   #1782
diyAudio Member
 
Join Date: Jan 2008
Quote:
Originally Posted by NEO Dan View Post
Hi Art,
On your keystone TH design the mouth is a relatively small portion of the face of the box, and although the distance between them is not great I don't really think they are tightly coupled.
You don't seem to be thinking in terms of wavelength.
The wavelength of 35 Hz is about 32 feet long, 1/4 wavelength is 8 feet. The center to center distance between the mouth openings is only 26.5 inches, just over 2 feet.

The two cabinets have almost exactly 6 dB of gain when placed together and powered by the same voltage, if they were not actually "closely coupled", the gain would be less and the frequency response would be different.

The Keystone design mouth to frontal area ratio is a bit higher (smaller mouth compared to frontal area) than a DSL TH-115 or TH-118, or similar designs.

The DSL TH-115, with over 50% of the frontal area used by the mouth, also has no change in the LF corner when used in multiples.

The Keystone is similar in mouth to frontal area as the more usual tall single fold TH like the William Cowan 60 hertz tapped horn Hornresp simulation that David McBean chose to use as an example.

Art Welter
  Reply With Quote
Old 1st April 2011, 05:51 PM   #1783
AndrewT is online now AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
What limits the low end of the frequency response of a conventional horn loaded driver?

Horn length, Horn taper, Horn Mouth area.

The most difficult to get really low is Mouth area. This results in many conventional horns being truncated to reduce actual Mouth Area and as a side effect make the total volume much smaller than the full size horn.

Take a conventional horn loaded driver and ensure it has a taper to give 30Hz and a length to give 20Hz and a mouth to give 30Hz. Now truncate it because that horn was far too big for "my room".
The taper LF limit remains at 30Hz, halving the length of the horn increases the LF length controlled frequency to 40Hz and the reduced mouth area probably about 25% to 33% of the 30Hz horn will increase the LF frequency by about 1 octave, i.e. about 60Hz.

Now take two of those truncated conventional horns and stack them. The mouth area has doubled and the Mouth frequency moves down half an octave.
The doubled up truncated horn gains +3dB from the doubled power fed to the combination. It also gains +3dB @ ~ 60Hz due to the doubled driver horn area (moves twice as much air).
But at 45Hz the pair have gained a lot more than that +6db. That effect cannot be obtained with a pair of Tapped Horns. A Tapped Horn is not a Truncated Horn, it is a different animal.
__________________
regards Andrew T.
  Reply With Quote
Old 1st April 2011, 06:26 PM   #1784
diyAudio Member
 
Join Date: May 2007
Quote:
I've done data outputs for rectangular horns where one pair of sides are the conical expansion onto which the curved sides are laid . The last data column there represents the length from throat to mouth measured along the wood of the conical pieces, ie. it is the axis measurement expanded by 1/cos(theta) where 'theta' is the half-angle
This wasn´t my question to David. I asked about the up and downside. About straight sides this is totally uninteresting as it is only a question of stretch-factor. Besides that, the tractrix made by Edgar using this technique is as long from the ideal as can be. Made with straight sides a radial horn would be far better. Have made a spreadsheet.

Last edited by revintage; 1st April 2011 at 06:30 PM.
  Reply With Quote
Old 1st April 2011, 09:13 PM   #1785
NEO Dan is offline NEO Dan  United States
diyAudio Member
 
NEO Dan's Avatar
 
Join Date: Jun 2008
Location: N.E. Ohio
Quote:
Originally Posted by weltersys View Post
You don't seem to be thinking in terms of wavelength.
The wavelength of 35 Hz is about 32 feet long, 1/4 wavelength is 8 feet. The center to center distance between the mouth openings is only 26.5 inches, just over 2 feet.

The two cabinets have almost exactly 6 dB of gain when placed together and powered by the same voltage, if they were not actually "closely coupled", the gain would be less and the frequency response would be different.

The Keystone design mouth to frontal area ratio is a bit higher (smaller mouth compared to frontal area) than a DSL TH-115 or TH-118, or similar designs.

The DSL TH-115, with over 50% of the frontal area used by the mouth, also has no change in the LF corner when used in multiples.

The Keystone is similar in mouth to frontal area as the more usual tall single fold TH like the William Cowan 60 hertz tapped horn Hornresp simulation that David McBean chose to use as an example.

Art Welter
Hi Art,
You might use the system design function to come up with the aggregate mouth area needed to support 35Hz, then divide that across the intended number of bins per stack.
And hope that being within the prefered portion of a wavelength at the high cutoff gives you tight coupling.


Quote:
Originally Posted by revintage View Post
This wasn´t my question to David. I asked about the up and downside. About straight sides this is totally uninteresting as it is only a question of stretch-factor. Besides that, the tractrix made by Edgar using this technique is as long from the ideal as can be. Made with straight sides a radial horn would be far better. Have made a spreadsheet.
Hi Lars,
It sounds like you are already have it figured out now? The method I would use in a spreadsheet would be to do a Hornresp export of the area in 1cm increments and then divide that by the width or height of your planned expansion to derive the unknown dimension.
__________________
Regards,
Dan
  Reply With Quote
Old 2nd April 2011, 05:45 AM   #1786
diyAudio Member
 
Join Date: Jun 2007
Quote:
Originally Posted by revintage View Post
About Export. when printing out horn data I guess "Side length" is for cutting a template for a square horn. In other words it is width with stretch factor added.

If I have understood everything right there will be no problem when doing a square horn but if it is for rectangular there are no data for top/ bottom. Anything you can add?
Hi Lars,

You understand correctly :-).

Template lengths for the left and right sides of a square or rectangular horn are exported when the Width Flare is specified as Con or Exp, but not when the Width Flare is specified as Uni.

Template lengths for the top and bottom sides of a square or rectangular horn are not exported.

Kind regards,

David
__________________
www.hornresp.net
  Reply With Quote
Old 2nd April 2011, 05:59 AM   #1787
diyAudio Member
 
Join Date: Jun 2007
Quote:
Originally Posted by tb46 View Post
When you model a tapped horn with 4 drivers by multiplying the cross-sections of a single driver TH by four, Hornresp gives you the same SPL response that you get from using the multiple speakers output on the single version of that tapped horn (provided you make the approriate adjustments in Eg).
Hi Oliver,

Your comment above prompted me to do some further validation tests.

The SPL response of two William Cowan 60 hertz tapped horns connected in parallel and radiating into 2 x Pi half-space was compared against the results for a single similar system radiating into 1 x Pi quarter-space, and also against the results for a single similar system with two drivers connected in parallel and the cross-sectional areas doubled, radiating into 2 x Pi space. Eg was set to 2.83 volts and Rg set to 0 ohms in all three cases.

The SPL predictions are identical for the three different configurations. This would suggest to me that there can’t be too much wrong with Hornresp tapped horn multiple speakers model :-).

Kind regards,

David
__________________
www.hornresp.net
  Reply With Quote
Old 3rd April 2011, 01:18 AM   #1788
diyAudio Member
 
Join Date: Nov 2007
I tried comparing the results of my vent length equation (see The Subwoofer DIY Page - Port Calculations) against HornResp's predictions by simming a 80 litre volume that's being tuned to various frequencies with a 140cm^2 vent.

This first table shows the predicted lengths using my vent calculation:

20 Hz - 121.5 cm
30 Hz - 48.6 cm
40 Hz - 23.4 cm
50 Hz - 11.2 cm
60 Hz - 4.8 cm
70 Hz - 0.9 cm


This second table shows the lengths predicted by HornResp

20 Hz - 118.0 cm
30 Hz - 51.6 cm
40 Hz - 27.0 cm
50 Hz - 15.0 cm
60 Hz - 8.8 cm
70 Hz - 5.2 cm


It looks like HornResp is predicting longer vents are required to achieve the same Fb (except for 20 Hz). The difference between the lengths seems to vary from 4.3 cm down to 3.0 cm @ 30 Hz, suggesting that the end-correction factor that HornResp is not only slightly different, but also somewhat frequency-dependent.

Curiously enough, if my equation is predicting vent lengths that are longer than required (see vent tuning that suggests the calculated lengths might be just under 20% too long), that means that the vent lengths predicted by HornResp might even more inaccurate...
  Reply With Quote
Old 3rd April 2011, 05:36 AM   #1789
diyAudio Member
 
Join Date: May 2007
Hi Dan and David,
What I want to is data templates for the curved sides laid out flat. This is what JMLLC calls "planar cut of petals". No problems to use that flare though.
  Reply With Quote
Old 3rd April 2011, 06:24 AM   #1790
diyAudio Member
 
Join Date: Jun 2007
Quote:
Originally Posted by Brian Steele View Post
I tried comparing the results of my vent length equation (see The Subwoofer DIY Page - Port Calculations) against HornResp's predictions by simming a 80 litre volume that's being tuned to various frequencies with a 140cm^2 vent.
Hi Brian,

You obviously used a release of Hornresp older than Version 28.00 when doing your comparisons :-).

Kind regards,

David
Attached Images
File Type: png Helmholtz.png (21.6 KB, 127 views)
__________________
www.hornresp.net

Last edited by David McBean; 3rd April 2011 at 06:28 AM.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Hornresp Class FlipC Subwoofers 8 3rd November 2008 06:23 PM
Some questions about hornresp brsanko Full Range 4 18th October 2008 09:36 PM
Hornresp help / JX150 316a Multi-Way 0 11th February 2004 03:56 PM


New To Site? Need Help?

All times are GMT. The time now is 10:27 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2