Bgw amp plus eq for free!

[Riley Casey]

That really fundamental difference between a speaker as sound producer, that is part of a musical instrument and a speaker as reproducer, a PA speaker, studio monitor or hifi speaker. Very different animals. Best bass amp I ever owned in the early 1970s was an Ampeg B15 with a small sealed enclosure with a D130 guitar speaker and tube amp. I've never heard a bass amp since that sounded as good since then. Not an amp I'd ever want to play a track thru tho.

From Alden (mathematician)/D'Appolito in Advanced Speaker SystemsAn example of the Musicians' exception with regards to a sealed box having a pretty low Qtc for utmost transients

[BMWCCA]

That really fundamental difference between a speaker as sound producer, that is part of a musical instrument and a speaker as reproducer, a PA speaker, studio monitor or hifi speaker. Very different animals. Best bass amp I ever owned in the early 1970s was an Ampeg B15 with a small sealed enclosure with a D130 guitar speaker and tube amp. I've never heard a bass amp since that sounded as good since then. Not an amp I'd ever want to play a track thru tho.

When I was a kid, I played my Gibson EB-0 bass through my stereo which had JBL 030s with D130s in them. Mostly because I had nothing else at home that worked better. I was very careful with the D130s which are still with me today. Unless you changed it, did the B15 really have a d130, or maybe a D140 or at the very least a 130A, not the D130 with the aluminum voice coil? I never thought of the D130 as robust enough for a bass amp. If I'm wrong, I have a spare D130 I could try!

[RMC]

Hi Riley,

Thanks for the comment.

In my view many people have been looking at this short-sighted i.e. sealed box providing good transients and no one else. I happen to think there's probably a substitute to the sealed cab and its penalties (excursion, efficiency, distortion).

Where i'm going both MI and SR drivers are welcome, IF they meet some very simple spec(s).

I'm in the process of writing this down for a post, should come soon.

Richard

[Ian Mackenzie]

Hi Richard,

The thing is sealed enclosures back in the 50’s and 60’s were large infinite baffle systems with one, two or four 12 inch drivers. Bozak were into the style of system.

But AR changed the notion of a sealed box loudspeaker with a much smaller and far less efficient acoustic suspension system. These book shelf system became popular with NY apartment dwellers.

If you compared a Bozak system to an AR3 the Bozak would sound like a much larger loudspeaker (which it is) because of the cone area and efficiency.

Today passive radiators are becoming more popular in premium near field monitors by Focal and Bear Foot. I recall EV had a passive radiator system called the Interface A. The Celestion Ditton 66 was a passive twelve inch passive radiator design in the 60’s and 70’s with bass extension down to the first octave.

I have no experience with guitar enclosures but the often feature quad ten inch drivers.

[RMC]

Hi Ian,

Many people think that Edgar Villchur (and Henry Kloss) at AR invented the Acoustic Suspension speaker. Not the case though. The patent on this belongs to scientist Harry Olson who was Director of RCA Labs. Moreover the patent for the passive radiator also belongs to Harry Olson.

Villchur and others must have had a licence or permission from Olson to use and market these technologies.

In any case i think i found a way to bypass or so the need for a sealed box in many situations. My following post explains.

Richard

[RMC]

A POSSIBLE SUBSTITUTE FOR THE CLOSED BOX...

After writing about resistive/restricted vents i've been thinking is there an alternative to the sealed box that mitigates its higher excursion, lower efficiency and increased distortion. An option that would allow lesser penalties than involved with the Acoustic Suspension enclosure, while being "transients friendly".

What if we could achieve this type of response curve OR SO but this time with driver Qts in a vented cab instead of a determined box Qtc in a sealed type. Being vented means higher efficiency, plus there's a port helping LF reproduction, less cone excursion and lower distortion. I'm not pretending this would be perfect or 100% equivalent, but my impression is that it could be similar waters. Getting there differently!

I think a vented cab with a pretty low Qts woofer might provide a worthy alternative to the closed box transient response. At what level of similitude exactly i can't say but i'm confident it would work at least in part. I've already seen here guys using e.g. E140 in a cab that will roll-off the bass with a drooping curve and seemed happy with it.

MI drivers are often gifted with a pretty low Qts number, i've prior said its not an accident that is true, the reason for these quite low Qts drivers is exactly their improved transient response, that musicians know and love. Good thing these aren't the only woofers having a low Qts, a number of Sound Reinforcement drivers have it too.

I listed just a few examples in the 15" popular size, MI: K140, E130, E140, SR: 2205H, 2220H, 2227H. What these have in common is a pretty low driver Qts, not intended for VLF duty, only "general purpose" bass. Their Qts is between 0.17 and 0.21, and have a reasonable Vas number to keep cab size in the medium range (say 3-4 cu.ft., box tuning to determine). No need for multiple woofers to get decent efficiency.

Low Qtc sealed cabs and low Qts drivers in vented cabs lead to a similar result LF response wise, that is a somewhat gentle but extended rolloff. Driver bandwidth required by user may come into play, if you need some more frequency extention you'd go for an MI version and if you don't need that then going for a SR version, while both drivers remain low Qts animals.

After dicussing each type of vented LF alignment and their transient performance, Dickason (The Loudspeaker Design Cookbook) mentions that higher Qts drivers have less than spectacular transient capability, then also adds "the degraded transient performance of this alignment family using high Qts drivers." (P.46). The impulse response shown by Eargle for a couple of higher Qts driver alignments only confirms Dickason here. Pretty clear to me.

Quite low Fs drivers, say in the 20's hz, often with massive cone and foam surround are not necessarily good candidates for this application since they're designed mostly for VLF reproduction, not for utmost transients.

I'm on the fence with some drivers e.g. E145 due to Vas 430 liters (middle value between Giskard 428 L and Win ISD calculated 432 L) , that Vas number seems somewhat high to get a mid size box, plus Qts may be about borderline for a low Qts driver designation. But it may still work here, though others seem like no brainers.

My 3 cents, lol

Richard

[Ian Mackenzie]

How about a transmission line?

PMC over in the UK has they say perfected a modern transmission line. A number of leading recording studios have taken them on board.

Their approach to stuffing the line is apparently somewhat different.

[RMC]

Obviously transmission line hasn't passed JBL testing, they don't appear to have retained that enclosure principle, and i can't remember any major manufacturer having made these. Not my type of gear, nor familiar with the PMC.

IMF was known for TL making, but apart from them ?

As far as i understand it this is rather low efficiency stuff so not really the kind of substitute i had in mind for the closed box. The TL's lossy aspect appears to come from absorption by the amount of damping material used.

The deeper bass impression would be caused by the even softer LF roll-off than a sealed box.

[Mr. Widget]

Obviously transmission line hasn't passed JBL testing...

Or perhaps it hasn't made financial sense. Most TL enclosures are fairly complex and on the larger and heavier side. Large, heavy, and complex all equate to costly.

Throwing an 8" - 12" driver in a 1 to 2 cu ft box with a cardboard tube is much more cost effective.


Widget

[RMC]

Thanks Widget.

Down to earth common sense and economics prevail.

When the Transmission Line was named i completely forgot about the transient aspect of the TL speaker, so here it is.

Supposedly superior to the sealed box.

Well, Dickason doesn't appear to be convinced about that...

(Vance Dickason, The Loudspeaker Design Cookbook, 5th ed, P.74)

Richard

[Ian Mackenzie]

Hi Richard,

I don’t think JBL felt a transmission line suited their mainstream philosophy.

I do know that Lor Kramer ( former senior associate at JBL and Disney Entertainment) who l met at Greg Timbers home said that a Bessel bass reflex alignment was something JBL was proud of. That as a practical application was implemented by Greg Timbers in some of the consumer statement systems.

The thing is that some of these larger companies don’t talk publicly about their product secrets and therefore don’t patent them. An electronic feedback servo is another way of improving on a conventional dynamic loudspeaker. That’s been around for over 40 years. Philips were the first use it in a domestic consumer loudspeaker.

FYI Vance Dickason’s diy loudspeaker cookbook isn’t an up to date or widely recognised reference in consumer or professional loudspeaker engineering. No these days. There are vastly improved measurement systems and design software applications available these days. That was when he was cutting his teeth on the subject of loudspeaker. Vance spends most of his time these days profiling loudspeaker drivers in the Voice Publication.

FYI PMC have been manufacturing studio monitors for over 30 years and are widely used through USA studios

https://pmc-speakers.com/30-years-making-music

A link on the PMC transmission line

https://pmc-speakers.com/technology/atl

[Ian Mackenzie]

Anther consideration that subjectively clouds bass reflex and sealed enclosure comparisons is the listening environment.

Many laypersons are oblivious to the difference in the low frequency response of a bass reflex loudspeaker (lower f3 and high pass 18/24 db slope) and a sealed enclosure (higher f3 and high pass 12 db slope).

On paper in free space the bass reflex system looks superior.

The impact of these different systems can be measured in a real room where the system is mounted on a floor or near a wall floor junction.

The effect is a hump in the bass reflex low frequency response in the 40-100 hertz region. This accounts for the subjectivity boomy bass associated with the bass reflex system. The additional low frequency output further excites a room’s natural modal resonances. The ringing of these un damped low frequency resonances modes subjectively clouds the loudspeaker performance.

This can be modelled and measured in REW. LF Room correction can then be applied. I believe this to be a superior approach to evaluation of the differences in low frequency systems.

On the other hand the sealed system with the same enclosure placement delivers a far smoother bass response. This is well recognised by loudspeaker engineers. So they tune the port for a smoother in room response than a maximally flat response tuning. Unfortunately diy loudspeaker builders with a limited understanding of the big picture miss this important step in the development of their diy design.

The point is that a maximally flat bass reflex tuning will sound boomy unless specific low frequency EQ is applied such as a Dirac.

[RMC]

I've known PMC for a while, been getting periodically in my e-mail offers from a local PMC dealer for years. However their use of Transmission Line was unknown, and doesn't really change things. Each manufacturer tries to differentiate its offer from others with some sort of technology, whether for bass, mid or highs. ATC and JBL monitors, for example, do it too. Nonetheless they all claim to have reached the summit!

I do have gear (not speakers) using Bessel filters, these are said to provide better phase response.

The pretention that Dickason's Loudspeaker Cookbook isn't up to date nor a widely recognised reference reflects your own opinion, while he's at the 7th edition! I don't see any other having lasted that long and been updated 6 times! Besides you haven't mentioned a single better reference than Dickason, nor other software than REW.

If we assume, for a moment only, the book being outdated it wouldn't be the only text not up to date. Take for example Kramer/Timbers you mention, this time regarding their 1983 2245H JBL subwoofer article. This is much older than Dickason's but still never been updated. And certainly not for a lack of more recent 18" woofers since a number of others were released e.g. 2241, 2242, 2258, 2269, etc. They had many opportunities to update and didn't. (I left aside e.g. 2240, 2243 due to their low Qts and excursion capability not great for subwoofer duty).

Why JBL would avoid protecting some worthy stuff or secrets is beyond common sense, when they have trade marked "Aquaplas", also got a patent on the slipstream vent tube, a simple piece of plastic when you think of it. An unprotected invention or secret is pretty much worthless financially since it can be copied. When Nortel went under water, their patents sold at auction for around $5 Bilion if my memory is correct. No protection, no money.

Acoustics consultants specialising in rooms, large and small, studios, concert halls, etc. have existed and been busy way before REW was born. The laws of physics and acoustics haven't changed with REW, and they remain the same for everyone. REW is a tool, a freeware application, not a reference or a professional acoustical consultant.

For sure computers calculate and illustrate much faster than humans, but the knowledge and acoustical science don't come from REW, it originated from experts in the field (e.g. Beranek, Olson, Toole, etc.). So REW's certainly faster/cheaper might be the "revolution", but not necessarily better or more accurate than a professional's work.

It appears you don't own Dickason's book, preferring to rely on freeware. Your choice. The pic attached shows what Eargle (Loudspeaker Handbook, 2nd ed., P.129) thinks of Dickason's work. That was at Dickason's 4th ed. or so, which was further updated at least three more times since. Looks like the comment made was unjustified...

I'm out.

[Ian Mackenzie]

Hi Richard,

I don’t unfortunately understand your post.

My apologies but am getting old and my mind wonders if something doesn’t make sense to me. I loose my spot and l get confused.

Back to my point things have moved along quite a bit since the Cookbook was first published. Yes it is an interesting read. But it’s not an engineering design tool in which you can make discoveries with. A lot of that was trial and error with prototyping back in the day. I recall you don’t believe in prototypes? That’s bad if your using the Cookbook.

In a commercial situation it means concepts took a long time to get to market. I own several editions of the Cookbook and have corresponded with the author.

The Cookbook is based on loudspeaker theory and modelling in Enclosure Shop software by the LinearX company of which l own a copy. To understand the significance of this you need to research the advanced transducer models created in Enclosure Shop. I recommend you read the link below to join the dots.

How you decide to interpret this link and espouse your own views is up to you. The reader(s) of this thread can equally form their own view’s.

https://www.audioheritage.org/vbulle...0&d=1485552966

Today there far more advanced software(s) used to design and predict actual transducer designs from the ground up for any desired any enclosure loading.

Peter Larsen pioneer of these advanced software problems worked with JBL (with Greg Timbers) in the 1990’s. Peter’s wife sent me an amusing pic of Greg with a wig on at a work party. It was hilarious.

https://loudsoft.com/news/

These commercial software packages are only available to the trade and start at US$10,000 per module. They generally require an engineering degree to understand and use competently. The hardware interface is equally expensive. The Klippel Test and Measurement system is also used which costs upwards of US$100,000.00

Transducer engineers who use these advanced software packages hold the key to any finished commercial loudspeaker system design through to prototype testing and commercialisation. In practice most OEM transducer manufacturers customise specific transducers to the end use application of the OEM client. So for example a transmission line loudspeaker system has a transducer designed and manufactured for that specific enclosure and the overall system requirements. Those design details are proprietary knowledge. This applies equally to any other system loading.

Some OEM driver manufacturers have diy a range of loudspeaker drivers for purchase by diy enthusiasts. Most of the currently available JBL replacement drivers are designed and engineered to the requirements of specific JBL loudspeaker loudspeaker systems such as Pro Arrays or SR applications. They are not general purpose hifi woofers with a suitable LF response for a diy enthusiast to tinker with. It’s unfortunate but that’s how it is. Some diy enthusiasts don’t accept this and we leave it to them.

If you do a search someone from the EU a while back took offence to not being served up a current JBL driver specification to meet his expectations. It was quite distressing!

Btw back in the day JBL used damping resisters in the network on the woofer transducer to modify the transducer behaviours in a particular system (bass reflex). Its intuitive to check this out in the current JBL product support link which lists numerous system tech data sheets dating back to legacy systems.

Back to the diy audio thing feel free to hypothesis on your ideas.

[Ian Mackenzie]

If anyone wants to obtain the benefits of both a sealed and a bass reflex enclosure the answer is deceptively simple.

You simply build an enclosure with two separate chambers. One chamber is sealed and they other is the bass reflex. By using a seperate woofer in each isolated chamber the loadings function separately but the outputs sum.

Below is a link to a review of such a loudspeaker system which l have owned for over ten years. Yes really.

The design works quite well. I won't post my subjective opinion other than its low frequency performance is impressive for a dual 6 1/2 inch woofer system. The woofers are high quality Scan Speak units.

There are some measurements included link which you will find quite interesting.

http://www.legendspeakers.com.au/Bac...zHifiMay09.PDF

So it would seem I beat you to finding the answer in just one short post Of course I don't claim to be the inventor.

http://www.legendspeakers.com.au/Bac...zHifiMay09.PDF

This system is the work of an Australian loudspeaker designer Dr Rod Crawford who formerly worked as the lead loudspeaker engineer at Linn Sondek in the 1990's and then formed his own business after moving back to Australia.