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Offline Simon Briggs  
#1 Posted : 11 August 2019 18:18:04(UTC)
Simon Briggs


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The musings and pains of a loudspeaker designer

Since I built my last big project, first completed in 1996 with several revisions followed and it was finalised in 2002.
This project was featured in the April 2002 issue of HiFi News & Record review magazine where the then editor Steve Harris enjoyed a thorough listen and the resulting article certainly courted some interest, some not entirely to my liking however and not unexpected.

2002 – 2017 resulted in about a dozen smaller systems, but none fulfilling, some were excellent including a miniature 6 litre design, which was well received by those who have heard it.

Shortly afterward I began looking at a successor,… marriage and a family intervened, but now that my lovely daughter is getting older, I have some additional time available so have recently revisited the project.

Now I have a gleaning as to what it will look like….

Sealed box bass, with….

Force cancellation loaded with dual horizontally opposed bass drivers (large!!) which loads into a much larger sealed chamber.

Separately decoupled sealed box upper bass / midrange and treble sections.

My last big design was 3 ½ way low tuned low group delay reflex, this one will be a straight forward all sealed three way system.

How big will it be? Not exactly sure yet, but similar in size to my last big build, with a somewhat bigger bass section.
Sensitivity? Well around 92-3 dB/w

Power handling? Not sure as I will not need to use much more than 200 wpc

Crossovers? Both passive and active systems will be used. 250 / 2700 Hz crossover points

Drivers? A high performance and dynamic full range used as an upper bass / mid unit,
Bass dual opposed 18" drivers of low resonance.

Treble a high performance high power dome tweeter

Influences? A couple of those are obvious together with lessons learned from my big 1996 project.
Here is a very, very rough sketch, drawn during a 30 minute leisure walk this morning.

So now what?

Much fun to follow…..

Simon


UserPostedImage

Edited by user 11 August 2019 18:21:37(UTC)  | Reason: Not specified

Offline Steveh100  
#2 Posted : 12 August 2019 09:01:04(UTC)
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Simon

None of my business really but I'd just say I always think bass impact and timing is compromised with side firing bass units

It's only subtle and timing may not be as important to you as it is to me...
Offline Simon Briggs  
#3 Posted : 12 August 2019 09:59:23(UTC)
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Originally Posted by: Steveh100 Go to Quoted Post
Simon

None of my business really but I'd just say I always think bass impact and timing is compromised with side firing bass units

It's only subtle and timing may not be as important to you as it is to me...


From my own experience, this depends upon several variables such as the crossover frequency / topology used again active or passive, driver layout, number of drivers and not least the bass alignment.

From my own research.......

Use a single side mount driver, apply a high(ish) crossover point and a reflex alignment, I agree, the timing may well be compromised. And in commercial systems I have investigated, to my ears, considerably.

Now use a Low Q sealed box alignment, pair of drivers mounted in force cancellation, good drivers, right crossover topology and keep the crossover point below about 300 Hz or so, get the design right and the system can give great result and reward the designer with great timing and dynamics, Naim NBL speaker exploited the best points (sealed box, 250Hz crossover 18dB/Oct) and it is great in these areas, ref MC review of such in HFN/RR

oh, and to my frustration I am extremely sensitive to rhythm and system timing errors!! Biggest bugbear of my life
BigGrin
Offline sandyk  
#4 Posted : 12 August 2019 10:59:04(UTC)
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Hi Simon

Many years ago I didn't believe that directionality mattered too much in the area normally covered by subwoofers,
until I converted both my DIY Class A Preamp and 15W/Ch. Power Amplifier to fully DC coupled.
Very low frequencies then had a "preciseness" about the sound , where it felt like I was being physically hit in the guts with some material
Perhaps it only matters so much where the power amplifier has a virtually full power response to almost D.C. ?

Kind Regards
Alex
thanks 1 user thanked sandyk for this useful post.
Simon Briggs on 12/08/2019(UTC)
Offline Simon Briggs  
#5 Posted : 12 August 2019 11:09:31(UTC)
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Originally Posted by: sandyk Go to Quoted Post


Hi Simon

Many years ago I didn't believe that directionality mattered too much in the area normally covered by subwoofers,
until I converted both my DIY Class A Preamp and 15W/Ch. Power Amplifier to fully DC coupled.
Very low frequencies then had a "preciseness" about the sound , where it felt like I was being physically hit in the guts with some material
Perhaps it only matters so much where the power amplifier has a virtually full power response to almost D.C. ?

Kind Regards
Alex


Now that is interesting, thanks Alex, something I need to investigate further
ATB
Simon
Offline Martin Colloms  
#6 Posted : 12 August 2019 18:12:15(UTC)
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Extended LF bandwidth is rarely encountered

It is what drove me to acquire the Magico S5II, with in-room 25Hz at fair power and low distortion.

Even so, the Devialet LF and group delay compensation for , gave a small but audible timing and phase improvement in the Devialet context.

I recently tried delay compensated Eclipse sub with the TD 510 series sub sat system, bandwidth to 17Hz in room, and it also convinced both for tune playing and for surprisingly good timing.

I will experiment further ..

Martin Colloms
Offline Simon Briggs  
#7 Posted : 12 August 2019 18:35:16(UTC)
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Originally Posted by: Martin Colloms Go to Quoted Post
Extended LF bandwidth is rarely encountered

It is what drove me to acquire the Magico S5II, with in-room 25Hz at fair power and low distortion.

Even so, the Devialet LF and group delay compensation for , gave a small but audible timing and phase improvement in the Devialet context.

I recently tried delay compensated Eclipse sub with the TD 510 series sub sat system, bandwidth to 17Hz in room, and it also convinced both for tune playing and for surprisingly good timing.

I will experiment further ..

Martin Colloms


Agreed Martin, this is what has lead me away from sub-sat systems

This is an interesting read for those not familiar with the Eclipse system

https://www.eclipse-td.c...ts/td725swmk2/index.html
Offline Simon Briggs  
#8 Posted : 15 August 2019 11:47:25(UTC)
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Progress will be slow on this project, not exactly a surprise as it, or something similar has been in gestation since about 2001 or so!!

Some of my friends here and elsewhere can sense the frustration I have with the length of time this has taken.

Now it seems good that at least that I have arrived at some form of core project idea I can build upon.

Constantly working on evolving ideas, a few odd bits I may post here, but one thing, the biggest part (problem) at the moment I will face will be funding the darn thing!!



Edit from 6 years ago!!

Originally Posted by: Simon Briggs Go to Quoted Post
Currently working on a classic three way influenced by the NS1000 but using an excellent 15" bass a special mid and various tweeters TBA
Like the NS1000 which will reach quite deep mine will reach a solid 25Hz in room perhaps better


This thread was interesting

http://forum.hificritic....g-sealed-box-bass-system

Edited by user 27 June 2020 11:18:40(UTC)  | Reason: Not specified

Offline Simon Briggs  
#9 Posted : 16 August 2019 16:33:18(UTC)
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Going to go with one mid range unit as I want to keep things simple. I will play with my Seas 8" FR unit to start with, but will consider others. They must have the best balance between power handling and midrange dynamics

This unit looks very promising as well
Offline Simon Briggs  
#10 Posted : 18 August 2019 12:18:59(UTC)
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Big speaker update 18/08/19
Currently working on the best way to mount the smaller internal midrange module within the main upper module. It will be decoupled from this and the main speaker as well
Offline Shadders  
#11 Posted : 19 August 2019 22:53:08(UTC)
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Originally Posted by: Simon Briggs Go to Quoted Post
Big speaker update 18/08/19
Currently working on the best way to mount the smaller internal midrange module within the main upper module. It will be decoupled from this and the main speaker as well

Hi,
The current issue of Elektor has an article on a sub-woofer design. It states "Time Corrected Woofer". It is a theoretical presentation - has formulas, and a computer program to download.

https://www.elektormagaz...gazine/elektor-110/51140

Detals of the design :
http://www.breem.nl/lsp/LoudspeakerSystem.htm

The article presents a sealed box design approach, uses a zobel network to remove the resonance such that the amplifier sees a near resistive load, and has a compensation filter in opamp form to boost the low frequency below the cut off frequency for a flat frequency response.

The program which can be downloaded for free, calculates the values for the zobel network, and the compensation filter. You will have to purchase the article (if possible) to understand the circuit and details on the operation of the program - if the website (breem.nl) does not explain this.

Regards,
Shadders.
Offline Simon Briggs  
#12 Posted : 20 August 2019 09:27:36(UTC)
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Thanks Shadders,
I will read this with interest
Regards,
Simon
Offline Simon Briggs  
#13 Posted : 20 August 2019 09:38:44(UTC)
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I am going to build the small mid-range enclosure which will use two drivers, an 8" Seas FR as the upper bass/mid and the tweeter in a waveguide and one that has a waveguide already.

I will whip up a passive crossover to listen to them on demountable baffles, which means that I can listen to different drivers as and when.

Tweeters I will be listening to will be a Seas DXT and the Audax 34mm dome in a separate waveguide. The Seas Fr unit will be my first experiment and then later the Seas built Jantzen JA-8008 HMQ
Offline Shadders  
#14 Posted : 20 August 2019 15:56:19(UTC)
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Originally Posted by: Simon Briggs Go to Quoted Post
I am going to build the small mid-range enclosure which will use two drivers, an 8" Seas FR as the upper bass/mid and the tweeter in a waveguide and one that has a waveguide already.

I will whip up a passive crossover to listen to them on demountable baffles, which means that I can listen to different drivers as and when.

Tweeters I will be listening to will be a Seas DXT and the Audax 34mm dome in a separate waveguide. The Seas Fr unit will be my first experiment and then later the Seas built Jantzen JA-8008 HMQ

Hi,
Are you sure you want to use an 8inch driver for the mid range frequencies ?. What is the polar radiation diagram for this unit at the upper frequencies you want to use ?

I selected a 6inch bass/mid range unit which will be used upto 2.5kHz. This unit will be reasonably directional and drops 3dB at 30degrees off axis at 2.5kHz. Will the 8inch driver drop a lot more ?

I checked the Jantzen website and it does not provide off axis SPL.

Regards,
Shadders.
Offline Simon Briggs  
#15 Posted : 20 August 2019 17:05:26(UTC)
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Originally Posted by: Shadders Go to Quoted Post
Originally Posted by: Simon Briggs Go to Quoted Post
I am going to build the small mid-range enclosure which will use two drivers, an 8" Seas FR as the upper bass/mid and the tweeter in a waveguide and one that has a waveguide already.

I will whip up a passive crossover to listen to them on demountable baffles, which means that I can listen to different drivers as and when.

Tweeters I will be listening to will be a Seas DXT and the Audax 34mm dome in a separate waveguide. The Seas Fr unit will be my first experiment and then later the Seas built Jantzen JA-8008 HMQ

Hi,
Are you sure you want to use an 8inch driver for the mid range frequencies ?. What is the polar radiation diagram for this unit at the upper frequencies you want to use ?

I selected a 6inch bass/mid range unit which will be used upto 2.5kHz. This unit will be reasonably directional and drops 3dB at 30degrees off axis at 2.5kHz. Will the 8inch driver drop a lot more ?

I checked the Jantzen website and it does not provide off axis SPL.

Regards,
Shadders.


Yes I have considered this carefully and the 8 inch is absolutely fine for what I want to do. My favourite 6 1/2" Seas unit is no longer made so looked elsewhere, I was lucky with the 8" Full range unit which had the clarity and dynamics I was after.

It does drop off somewhat more off axis than the 6 inch units I have in stock, and have been testing a range of units that I have available, but have selected the 8 inch unit simply on superior sonic grounds, it is that good.

The Jantzen is much the same and is excellent. Likely that the Seas FR unit will be good enough and could be an excellent match with the Seas DXT.

I no doubt will have much frustrating fun playing with them.
I do not need the off axis performance and have used the 8 inch seas FR unit successfully in another system with an Audax tweeter and it was excellent.

This is not a commercial speaker and the listening room will not have to accommodate more than two listeners at any one time. Unlikely I will be anywhere near 20 degrees off axis let alone 30.

Edited by user 20 August 2019 17:06:30(UTC)  | Reason: Not specified

Offline Shadders  
#16 Posted : 20 August 2019 18:18:26(UTC)
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Originally Posted by: Simon Briggs Go to Quoted Post


Yes I have considered this carefully and the 8 inch is absolutely fine for what I want to do. My favourite 6 1/2" Seas unit is no longer made so looked elsewhere, I was lucky with the 8" Full range unit which had the clarity and dynamics I was after.

It does drop off somewhat more off axis than the 6 inch units I have in stock, and have been testing a range of units that I have available, but have selected the 8 inch unit simply on superior sonic grounds, it is that good.

The Jantzen is much the same and is excellent. Likely that the Seas FR unit will be good enough and could be an excellent match with the Seas DXT.

I no doubt will have much frustrating fun playing with them.
I do not need the off axis performance and have used the 8 inch seas FR unit successfully in another system with an Audax tweeter and it was excellent.

This is not a commercial speaker and the listening room will not have to accommodate more than two listeners at any one time. Unlikely I will be anywhere near 20 degrees off axis let alone 30.

Hi,
Below is a website where the person has tested various drivers and produced plots for the distortion etc. The Seas DXT is listed - is it the one you are referring to ?

http://www.audioexcite.com/?page_id=178

The range of drivers tested is predominantly SB Acoustics, or Scanspeak. Else, you could check out :

https://www.audioxpress..../categories/vc-testbench

Regards,
Shadders.
Offline Simon Briggs  
#17 Posted : 20 August 2019 18:22:25(UTC)
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Thanks will check the site out
Offline Pete_w  
#18 Posted : 20 August 2019 19:59:04(UTC)
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Originally Posted by: Simon Briggs Go to Quoted Post
Unlikely I will be anywhere near 20 degrees off axis let alone 30.[/size]


Non-speaker-designer here, going off topic. Interesting. Some authors (Keith Howard, notably, over the years) seem to worry a lot about off-axis radiation and seem to think you want plenty of it so that you get a broad frequency spectrum in the reflections that you get back off the sidewalls. Personally, having lived with Martin Logans for 10 years, I'm with you in the school of "the bast sidewall is no sidewall at all" - you're happily embracing narrowing dispersion, whereas my 'Logans avoid it in the first place, having very restricted directivity....

Pete
Offline Simon Briggs  
#19 Posted : 21 August 2019 12:38:13(UTC)
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Originally Posted by: Shadders Go to Quoted Post

Hi,
The Seas DXT is listed - is it the one you are referring to ?


Yes An interesting tweeter for the money, however the top Scan tweeters are very good
Offline Simon Briggs  
#20 Posted : 21 August 2019 12:39:32(UTC)
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Originally Posted by: Pete_w Go to Quoted Post
Originally Posted by: Simon Briggs Go to Quoted Post
Unlikely I will be anywhere near 20 degrees off axis let alone 30.


Non-speaker-designer here, going off topic. Interesting. Some authors (Keith Howard, notably, over the years) seem to worry a lot about off-axis radiation and seem to think you want plenty of it so that you get a broad frequency spectrum in the reflections that you get back off the sidewalls. Personally, having lived with Martin Logans for 10 years, I'm with you in the school of "the bast sidewall is no sidewall at all" - you're happily embracing narrowing dispersion, whereas my 'Logans avoid it in the first place, having very restricted directivity....

Pete


Agreed, Pete
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