Single sheet TH challenge - Page 127 - 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 3rd January 2012, 12:40 AM   #1261
djk is offline djk
diyAudio Member
 
djk's Avatar
 
Join Date: Feb 2001
Location: USA
"You say this like you have a different high SPL rig? Care to share? "

Just more of the same thing. The original build on the dual-15 PPSL was 24 boxes, and 26 of the horn-loaded 12s (one pair of which went with a pair of dual-18 PPSL). I've never run more than 8 of the dual-15 PPSL at any one job.
__________________
Candidates for the Darwin Award should not read this author.
  Reply With Quote
Old 3rd January 2012, 02:54 AM   #1262
diyAudio Member
 
Join Date: Dec 2009
Location: California
Quote:
Originally Posted by djk View Post
"Please correct me if this is wrong. "

The 6dB boost is a requirement of the 6th order design using a low Qts woofer, it is not needed per se for a PPSL design.

The PPSL principle may be applied using sealed, vented, dipole or horn configurations; the driver parameters selected according to the type of loading you wish to employ.
Hi djk,

Thank you for the clarification. I'll play with some different designs to see if I can get more realistically useable models.




Quote:
Originally Posted by djk View Post
"D&B and Dub music that can have constant waveforms below 40Hz. "

Does it really?
Depends on the track. There are tons of dubstep tracks that are very mid-range-y, but there are plenty that have a bit more energy down that low.

epa did some scans of a few dubstep tracks a while ago:
Scan session 1
Scan session 2
  Reply With Quote
Old 3rd January 2012, 09:24 AM   #1263
diyAudio Member
 
Join Date: Jun 2007
Hi Art,

Quote:
Originally Posted by weltersys View Post
The fact that in most respects Hornresp sims are very close to reality is proof that your theory is, for the most part, sound.
Just to clarify - it is not my theory :-). Hornresp simply uses the standard lumped-element loudspeaker model, similar to AkAbak.

Quote:
Originally Posted by weltersys View Post
From what I can see of the two William Cowan 60Hz tapped horns connected in parallel, the LF response has increased by about 2 dB compared to the upper response.
In theory, for two speakers connected in parallel compared to one speaker, the difference at high frequencies should be 3 dB and the difference at low frequencies should be 6 dB. When SPL levels are not normalised for comparison purposes, this is exactly what Hornresp shows for the William Cowan 60Hz tapped horn example - see attachment (6 dB difference at 40Hz, 3 dB difference at 400Hz).

Quote:
Originally Posted by weltersys View Post
The Hornresp sim for the SH15 shows the low corner dropping almost 10 Hz using four cabinets, a much larger spread.
In your example (four speakers compared to one speaker) the difference at high frequencies is 6 dB and the difference at low frequencies is 12 dB - as expected.

Quote:
Originally Posted by weltersys View Post
Looking at the LF response of one and two of a 2x10" tapped horn with a similar rolloff as the William Cowan horn, I see no difference, in other words, the 2 dB (or so) increase Hornresp predicts does not occur.
It just doesn't make any sense. With two speakers, the horn mouth area is effectively doubled, but the measurements suggest that there has been no change in LF acoustical loading due to the increased mouth "piston" size. I would have thought that there should be some change.

Quote:
Originally Posted by weltersys View Post
Do you have any real-world measurements that reflect the theoretical dropping of the LF corner in TH that Hornresp predicts?
Unfortunately I don't have any real-world measurements of anything :-). I am totally reliant on data provided by people such as yourself, to test the validity of the Hornresp models.

Kind regards,

David
Attached Images
File Type: png Compare.png (26.3 KB, 320 views)
__________________
www.hornresp.net
  Reply With Quote
Old 4th January 2012, 12:57 AM   #1264
diyAudio Member
 
Join Date: Jan 2008
Quote:
Originally Posted by David McBean View Post
Hi Art,
Just to clarify - it is not my theory :-). Hornresp simply uses the standard lumped-element loudspeaker model, similar to AkAbak.

In theory, for two speakers connected in parallel compared to one speaker, the difference at high frequencies should be 3 dB and the difference at low frequencies should be 6 dB.

With two speakers, the horn mouth area is effectively doubled, but the measurements suggest that there has been no change in LF acoustical loading due to the increased mouth "piston" size. I would have thought that there should be some change.

Unfortunately I don't have any real-world measurements of anything :-). I am totally reliant on data provided by people such as yourself, to test the validity of the Hornresp models.

Kind regards,

David
David,

After hearing and measuring the 6 dB increase across the frequency range down the center of left /right stacks, commonly referred to as "power alley", I was surprised to hear your model uses a reduced upper response.

To test that "lumped-element loudspeaker model theory", I did some testing using a pair of small horn loaded speakers today.
The small speakers each have a pair of Eminence 6" and APT tweeters on conical horns, the lows are ported.

The tests were done with the mic on axis 2 meters from the speakers, which were on stands elevating the acoustical center to 2 meters, approximating a full space reading.

Tests were done with the speakers together, and also at 2 meters on center spread between them. Speakers were "toed in" to point at the test mic.

In both cases, the average level difference between one and two was uniformly about 6 dB throughout the range of the speakers.

Above 5000 Hz, the gain (or loss) is erratic due to the wavelengths being so small and the speakers , being on unlevel ground were not exactly equidistant to the microphone, causing dips in response (AKA “comb filtering”, or cancellation).
Also of note, because the speakers used are not perfectly matched (as can be seen in the lower two “2x6spread” screen shot) summation is not exactly 6 dB, though quite close.

Real-world measurements of these horn loaded top cabinets and TH low cabinets indicate to me that some of the theory you base the Hornresp model on could perhaps use some adjustment to reality.

That said, most users of Hornresp work indoors, and room reflections make mincemeat of fine frequency response detail.

Most of my work is outdoors, where it is harder to hide a 2-3 dB problem.

Thanks again for sharing Hornresp.

Art
Attached Images
File Type: png 2x6spread.png (88.5 KB, 291 views)
File Type: png 2x6Together.png (92.4 KB, 285 views)
  Reply With Quote
Old 4th January 2012, 07:16 AM   #1265
diyAudio Member
 
Join Date: Jun 2007
Hi Art,

Quote:
Originally Posted by weltersys View Post
After hearing and measuring the 6 dB increase across the frequency range down the center of left /right stacks, commonly referred to as "power alley", I was surprised to hear your model uses a reduced upper response.
The Hornresp model doesn't use a 'reduced upper response' - it simply calculates the SPL by applying the following standard formulas and generally-accepted techniques (as documented in Leo Beranek's "Acoustics", for example).

Assuming:

c = 344 metres per second
rho = 1.205 kilograms per cubic metre
Pref = 2 * 10 ^ -5 newtons per square metre

W = acoustical output power in watts
A = spherical surface area in square metres through which the sound radiates

Then:

Sound intensity in watts per square metre I = W / A

Sound pressure in newtons per square metre P = (I * c * rho) ^ 0.5

SPL = 20 * Log10(P / Pref) decibels

CASE 1:

For a single speaker with an output of 1 acoustic watt at high frequencies, where the sound pressure is measured in free space at a distance of 2 metres:

W = 1
A = 4 * Pi * 2 ^ 2

SPL = 20 * Log10(((1 / (4 * Pi * 2 ^ 2) * 344 * 1.205) ^ 0.5) / (2 * 10 ^ -5))

SPL = 103.14 dB

CASE 2:

For two speakers each with an output of 1 acoustic watt at high frequencies, where the total sound pressure is measured in free space at a distance of 2 metres:

W = 1 + 1 = 2

SPL = 20 * Log10(((2 / (4 * Pi * 2 ^ 2) * 344 * 1.205) ^ 0.5) / (2 * 10 ^ -5))

SPL = 106.15 dB

Assuming constant directivity, the theoretical increase in far-field SPL at high frequencies for two speakers compared to one speaker is 3 dB not 6 dB. This is clearly documented in many authoritative reference texts, including the JBL Professional Sound System Design Reference Manual.

Quote:
Originally Posted by weltersys View Post
To test that "lumped-element loudspeaker model theory", I did some testing using a pair of small horn loaded speakers today.
Thanks for taking the time to conduct the tests, and for advising me of the results.

Quote:
Originally Posted by weltersys View Post
Real-world measurements of these horn loaded top cabinets and TH low cabinets indicate to me that some of the theory you base the Hornresp model on could perhaps use some adjustment to reality.
I cannot explain your latest measurements - they appear to be defying the laws of physics in that there is twice as much power coming out as is going in. I am reluctant to arbitrarily adjust the Hornresp results to fit your unique reality :-).

Kind regards,

David
__________________
www.hornresp.net
  Reply With Quote
Old 4th January 2012, 06:48 PM   #1266
diyAudio Member
 
Join Date: Jan 2008
Quote:
Originally Posted by David McBean View Post
Hi Art,
For two speakers each with an output of 1 acoustic watt at high frequencies, where the total sound pressure is measured in free space at a distance of 2 metres:
W = 1 + 1 = 2
SPL = 20 * Log10(((2 / (4 * Pi * 2 ^ 2) * 344 * 1.205) ^ 0.5) / (2 * 10 ^ -5))
SPL = 106.15 dB
Assuming constant directivity, the theoretical increase in far-field SPL at high frequencies for two speakers compared to one speaker is 3 dB not 6 dB. This is clearly documented in many authoritative reference texts, including the JBL Professional Sound System Design Reference Manual.

Thanks for taking the time to conduct the tests, and for advising me of the results.

I cannot explain your latest measurements - they appear to be defying the laws of physics in that there is twice as much power coming out as is going in. I am reluctant to arbitrarily adjust the Hornresp results to fit your unique reality :-).

Kind regards,

David
I searched through the JBL Professional Sound System Design Reference Manual and could find no clear documentation that the theoretical increase in far-field SPL at high frequencies for two speakers compared to one speaker is 3 dB not 6 dB.

But a two meter test on a horn speaker is not in the far field anyway.

Perhaps you are referring to figure 1-3 or Figure 2-7 in the JBL Professional’s Sound System Design Reference Manual ( 1999 edition), where two non-correlated noise sources added together sum to only a 3 dB gain .

However, when two coherent (in phase) sources are added, SPL rises by 6.02 dB.

from:
Total dB level adding of two incoherent uncorrelated sound source - combining decibels or SPL sound pressure level add signal noise levels - sengpielaudio Sengpiel Berlin

“Adding of two incoherent sound pressure levels or voltage levels:
Adding of two values of the same level give an increase of the total level of (+)3 dB.

Adding of two coherent sound pressure levels or voltage levels:
Adding of two values of the same level give an increase of the total level of (+)6 dB.
This is obtained by feeding two side-by-side loudspeakers with the same signal.”

At any rate, the results of my test do not defy any laws of physics, they merely demonstrate the predicted 6 dB increase that occurs when a second speaker equally powered is added with a phase coherent summation.

Phase coherent summation of two sources is harder to achieve the higher the frequency because of the progressively shorter wavelengths, indoor reflections and outdoor wind often do result in a net gain (or loss) of less than 6 dB for two coherent sources.

On February 16, 2005, I tested HF horns and small dome tweeters in a line array outdoors.
The results are below.

They are also consistent with the 6 dB increase in level addition of coherent sources, not some “unique reality”.

Anyone doing similar tests outdoors will get similar results .

Art
Attached Images
File Type: png 2:16:05HFtest.png (59.6 KB, 260 views)
File Type: png NonCoherent.png (7.1 KB, 256 views)
File Type: png Coherent.png (7.3 KB, 13 views)
  Reply With Quote
Old 5th January 2012, 06:04 AM   #1267
diyAudio Member
 
Join Date: Jun 2007
Hi Art,

Many thanks for this reference - I will study it closely.

Hornresp is predicting the power response of the two speakers, whereas your measurements are showing the pressure response. From a power perspective, can you see any flaw in the logic of my calculations?

Thanks for initiating this discussion, it is proving to be very interesting :-).

Kind regards,

David
__________________
www.hornresp.net
  Reply With Quote
Old 5th January 2012, 04:22 PM   #1268
diyAudio Member
 
Join Date: Jan 2008
Quote:
Originally Posted by David McBean View Post
Hi Art,

Many thanks for this reference - I will study it closely.

Hornresp is predicting the power response of the two speakers, whereas your measurements are showing the pressure response. From a power perspective, can you see any flaw in the logic of my calculations?

Thanks for initiating this discussion, it is proving to be very interesting :-).

Kind regards,

David
I have a hard time figuring out the logic of your calculations, the only flaw I can see is that they disagree wth actual testing, which is done in dB SPL.

Interestingly, testing indoors, where the sound feild is reverberant, (incoherent) results in a net three dB gain rather than 6 dB doubling a pair of speakers.

Hornresp correctly figures the LF gain as 6 dB (+3dB for doubling radiating surface, +3 dB for doubling power), I don’t understand the reason why the theory used would not allow the same to happen at high frequencies.

Perhaps you are using an omni model, when all horns have directionality?
Art
  Reply With Quote
Old 5th January 2012, 07:08 PM   #1269
AndrewT is offline AndrewT  Scotland
diyAudio Member
 
Join Date: Jul 2004
Location: Scottish Borders
Weltersys,
go back to the basic two drivers producing a common mono signal that are close coupled.
Look at the way the pair of drivers set up a beamed wavefront that consists of multiple interference patterns.
Now determine how frequency affects the way the beamed interference patterns spread out.

High frequencies produce a much narrower beam than Lower frequencies.

That's where we get our range of frequency limits when applying the coupled bass drivers. Within the limited frequency range the levels are increased by +6dB, due to +3dB from the doubled power input and +3dB from the doubled efficiency of air coupling to the doubled Sd.

As frequency rises we come outside that range of limiting frequencies and the extra efficiency of the doubled Sd is gradually lost and is replaced with the interference fringes that were mentioned by a few posters earlier in the thread.
__________________
regards Andrew T.
  Reply With Quote
Old 6th January 2012, 06:31 AM   #1270
diyAudio Member
 
Join Date: Jun 2007
Quote:
Originally Posted by weltersys View Post
I have a hard time figuring out the logic of your calculations, the only flaw I can see is that they disagree wth actual testing, which is done in dB SPL.
Hi Art,

I tried simulating two parallel speakers in AkAbak - the predicted system response is consistent with your test measurement results (+6dB across the entire frequency range).

It would seem there is something in the established theory that I am missing :-).

I can replicate your results by a simple change to one line of the Hornresp code, but I need to understand what is going on first (not sure how long it will take me). To cover all situations perhaps I should include a "coherent / non-coherent" option in the Multiple Speakers tool.

Thanks again for highlighting this issue - hopefully Hornresp will eventually be a better product as a result of your very valuable feedback.

Kind regards,

David
__________________
www.hornresp.net
  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
Here is a Challenge latala Solid State 41 12th May 2011 02:13 AM
Renovation Challenge ZirconiumZephyr Multi-Way 16 1st September 2009 09:38 AM
Design Challenge #1 kgillies Subwoofers 12 13th June 2007 04:20 PM
a challenge --or I need help lawrence99 Car Audio 0 9th March 2005 05:44 AM
The challenge ! thylantyr Solid State 51 24th July 2003 09:41 PM


New To Site? Need Help?

All times are GMT. The time now is 01:10 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