Bagby Mandolin DIY Speaker Review

[Everett T]

Waveguides permit use of less expensive components with lower crossover points. Ribbon tweeters have a long and expensive history of spontaneous combustion under load, sacrificing many an unwary amplifier to their pitiless god, Voltar.

Here are some results from waveguides/ horn loading dome tweeters from John years ago.
http://www.zaphaudio.com/hornconversion.html

 

[RickS]

Nice build Rick,

interesting that the port tuning is higher than specified by the late Jeff Bagby. It’s supposed to be 38Hz, here we’re looking closer to 48Hz. That would create the bass bump.

I wonder whether the new NRX2 driver unit affected the bass tuning, or whether this wasintentional on your part? Some people do like a bit more mid-bass punch than flat.

And of course it depends on your room acoustics and speaker placement and listening preference what kind of bass response is more or less preferable.
But if one wanted flat bass response all it needs is a port slightly longer by a couple of inches.

the midwoofer’s resonance notch around 1.x kHz (“???”); well that’s likely inaudible due to masking by the tweeter, but I find it incredible how the NFS can resolve it at such high resolution.

also the crossover is specified at 1.8Khz; it’s surprising that the tweeter rolls off earlier than that and leaves a dip in the summed response around 3Khz. Jeff’s own speaker measurement doesn’t have that.

All in all, i think I’m nitpicking here; from the lens of an amateur DIY hobbyist.

As a consumer or potential builder with plenty of time on one’s hands, as a first build speaker I think this is an excellent showing- and remarkable for such a low priced speaker.

Look at that midrange distortion at 86dB from 300Hz up! At 55dB down- that is class leading!Literally off (below) the chart!!!

Thanks, and good catch on the port tuning, but cannot take credit or blame for it. Also, you are correct that the newer version of the woofer affects the tuning, but not all that much...

I built to the drawing and it has a 5 inch port and that tunes to 48 Hz. To get to 38 Hz, would require almost doubling the length to 9 inches. According to BassBox Pro sim, it also would have a worse port resonance around 700 Hz AND an f3 of 50 Hz. I talked to Meniscus about another design discrepancy (will post later), but Mark was out and he worked with Jeff. Will check on the tuning, but for now, it is according to the supplied drawing.

 

[RickS]

Anyone got a suggested price?

The bare-bones version doesn’t come with the port and other stuff, so you gotta choose the full package, then you have MDF costs. Can this be made out of a single 48x96 board (I believe so), and so keeping the options for everything at the default I am thinking of putting it at $380.

Would maybe round to $400 for the pair...

To do the 1 inch front baffle, you are going to need pricier sheet of MDF or an additional 1/4 inch sheet and glue as I did.

 

[MZKM]

Also, you are correct that the newer version of the woofer affects the tuning

Perhaps @amirm should update the title to “Bagby Madolin 2”, which is what Meniscus calls it.

 

[sarumbear]

I can never understand why a DIY speaker builder use an enclosure and driver layout as worst as it can be. Tweeter at the centre & a parallelepiped box with sharp corners. Olson explained 70 years ago that this is the worst possible shape for a speaker enclosure. Most manufacturers are ignorant or don't care but a DIY builder that is spending good money???

 

[RickS]

Thanks again @amirm and sympathize with the congestion as I have similar issues in May/June.

I will also say that am concerned these may not have been the best example of Jeff's work...

Here is what I can add for others who might be interested in building these speakers:

1. As usual, these are built to the design based on what is supplied with the kit. In this case, documentation was kind of skimpy and there were some misdirects. Along with the cabinet tuning discussed earlier, the lack of measurements to validate against affected getting optimal results. When building, I did search for some, but did not find any. As has already been noted, the drivers have been updated and the box tuning too. In this regard, I note the drawing is clearly labeled Mandolin 2. However, it is pretty clear that Jeff's document was not updated as it refers to the original woofer part number. Recently, I search for some other builds and found another discrepancy...
2. Despite the drawing, the other builds have the tweeter offset from the woofer. Upon finding this, I did check with Meniscus, but Mark was out and he worked with Jeff on these. If the tweeter was supposed to be offset, it calls into question what the measurement axis may have been and whether the offset was done to lower diffraction (vs front baffle bevels that were not in the design).
3. Lastly. normally would have beveled the port, but there was a bit of time lapse between when I built and shipped to Amir. Gluing in the port is one of my last steps and you can see I used some wood filler around it. Since had to wait for it to dry, forgot to round it over before I packaged up. Fortunately, does not appear to have had a negative effect.

Since I usually rely on Amir to review, I only gave these a cursory listen. Since he was unable to listen to them, will share my impression. While they seemed decent, I had high expectations. That said, I thought they sounded dull. In hindsight, seeing the off-axis high-end roll off, kind of makes sense now. EDIT: Felt I should add that the high-end rolloff could be eq'd as am doing with the DXT tweeter for Directiva.

Will see if Meniscus can add anything that would make me consider rebuilding, but even with the issues, did not score all that badly. Will update the thread when I know get Meniscus' clarification.

 

[Francis Vaughan]

I can never understand why a DIY speaker builder use an enclosure and driver layout as worst as it can be.

Indeed. I think the trouble is that in marketing kits there is a lot of pressure to make the effort of building the kit as simple as possible. They are marketed as a cost effective and simple way of getting a good speaker. People doing a full DIY effort may not be those in the market for a kit. Rather they are enthusiasts and will design their own. They will be inclined to put the effort into constructing a much more optimal cabinet.

I feel there is a missed opportunity to design and market a very high quality kit that a newby DIYer can build with a minimum set of hand tools. I occasionally toss about ideas for such a design. The work on open source waveguides over on https://www.somasonus.net is a really interesting start.

The thing about a minimal set of handtools is that with the right tools you can make anything. You don't need a workshop filled with very expensive power tools or a CNC router. With care you could make a furniture quality acoustically sensible cabinet with nothing more than a Japanese draw saw, a couple of chisels and sandpaper.

 

[ROOSKIE]

I plan to use the dimple again soon in a DIY active home speaker and I used to use the NE0 version of this tweeter on my car dash.
The directivity characteristics of the top are nice this way as less sound bounces around with all the car glass. Lots of car audio people like the various ring radiators and dimple domes for this reason. I really liked it and in near field/car audio it can handle very low crossover points (especially using active X-overs)
I had a couple pairs of Boston Acoustics speakers that used the NEO dimple dome as well. I really liked the tweeter there as well. (M25 and M350) It had a slightly darker sound sig which often works for me, but you could aim the speakers right at you and get the vibrancy back if needed. Everything sounded good on them. Same with the Polk lSIM703's which use a ring radiator. The Polk L200's are here now and I am about to try them. They also use a ring.

Anwyay Chane makes the L3, a speaker that uses a version of the SB dimple dome and Poly version of the 6.5" woofer. $390 each/ $780 a pair.
https://www.chanemusiccinema.com/chane-l3.html

This is a very close commercial design to the DIY effort, I wonder if anyone has expereinces with them?

*By the way the dimple tweeter does have a very slight waveguide. It is not a 180 degree face. Certainly not the same as an advanced larger one, but it is slightly guided*

 

[ROOSKIE]

Thanks, and good catch on the port tuning, but cannot take credit or blame for it. Also, you are correct that the newer version of the woofer affects the tuning, but not all that much...

I built to the drawing and it has a 5 inch port and that tunes to 48 Hz. To get to 38 Hz, would require almost doubling the length to 9 inches. According to BassBox Pro sim, it also would have a worse port resonance around 700 Hz AND an f3 of 50 Hz. I talked to Meniscus about another design discrepancy (will post later), but Mark was out and he worked with Jeff. Will check on the tuning, but for now, it is according to the supplied drawing.

So far my experiences with port tuning have mirrored Troels Gravesen
http://www.troelsgravesen.dk/vent_tuning.htm

Essentially all my ports are about 20% shorter in length then tuning programs will calculate even with good end correction.

It looks to me by eye balling the charts here like you likely have a tuning of 42-45hz with 5" port despite predictions of 48hz.

To get 38hz you likely just need to add about 1.5-2".
For anyone newer who wants to tweak tuning.
The Parts Express adjustable length ports are good for this and you can adjust/re adjust the length and listen/measure before finally gluing them fixed.
Also the cabinet filling will affect the tuning to some degree.

 

[hardisj]

Dip in woofer response at 1700Hz is cone/surround termination left untreated characteristic for sb17nrxc.

Bingo.

See this a lot in other drivers. From Scanspeak to Dyn to SB. But not Purifi.

 

[Dmitri]

Indeed. I think the trouble is that in marketing kits there is a lot of pressure to make the effort of building the kit as simple as possible. They are marketed as a cost effective and simple way of getting a good speaker. People doing a full DIY effort may not be those in the market for a kit. Rather they are enthusiasts and will design their own. They will be inclined to put the effort into constructing a much more optimal cabinet.

I feel there is a missed opportunity to design and market a very high quality kit that a newby DIYer can build with a minimum set of hand tools. I occasionally toss about ideas for such a design. The work on open source waveguides over on https://www.somasonus.net is a really interesting start.

The thing about a minimal set of handtools is that with the right tools you can make anything. You don't need a workshop filled with very expensive power tools or a CNC router. With care you could make a furniture quality acoustically sensible cabinet with nothing more than a Japanese draw saw, a couple of chisels and sandpaper.

Yes! Previous reviews have often brought up the reduced relative value of diy designs because of both the “added expense of personal time,” but also that DIY’rs would be hard pressed to create a speaker enclosure that would have the integrity of a commercially manufactured speaker. Perhaps this is true with complex designs, but if one is doing it for the joy of creating their own speaker system then the “time costs” hold little meaning, and building a box with more than adequate integrity is not rocket science nor does it require exotic tools. It’s a fun way to learn more about the process, and can be very rewarding experience.

 

[Jim Matthews]

https://www.eighteensound.it/en/resources/suggested-designs/

The reason loudspeaker boxes use squared edges is that they're easy to make, can be sold as flat packs and require no special tools for assembly.

 

[sarumbear]

The thing about a minimal set of handtools is that with the right tools you can make anything. You don't need a workshop filled with very expensive power tools or a CNC router. With care you could make a furniture quality acoustically sensible cabinet with nothing more than a Japanese draw saw, a couple of chisels and sandpaper.

Agree 100%. I’m no carpenter, but using some very basic tools I managed to build the prototype enclosure of Silver 5L. I do however had read Olsen and knew the shape I needed to create.

if your box is the wrong shape, you cannot get a smooth frequency response - full stop!

 

[sarumbear]

https://www.eighteensound.it/en/resources/suggested-designs/

The reason loudspeaker boxes use squared edges is that they're easy to make, can be sold as flat packs and require no special tools for assembly.

You are mistaken. Mass producing angled edged enclosure panels is no different to straight cornered ones.

I know from experience.

 

[tktran303]

I guess it depends on the designers intentions.

Having built, or commissioned to be built, almost half a dozen kits, I can say that a straight sided box IS much easier to build than a kit with fancy shapes or front baffle.
It all depends on the designers objectives.

For instance, if you use to offset tweeters and mount your 2.5 way design with the drivers horizontally, then you don’t get a symmetrical horizontal response.

tradeoffs, tradeoffs

 

[sarumbear]

Having built, or commissioned to be built, almost half a dozen kits, I can say that a straight sided box IS much easier to build than kit with fancy shapes.

the question is how much easier/cheaper? I have commissioned around 6000 pairs of Silver5L enclosures back in the 90s. The difference between straight corners and angled was less than 2% of the enclosure cost. We had three sources and their prices differ more than that!

when you are talking small numbers cost can be higher. But if a DIYer is building it why would the person cares about the cost? If a kit manufacturer is building it, as I said above price difference is negligible. Besides, they would have a USP that is worth way more than that small cost penalty.

 

[Zvu]

Bingo.

See this a lot in other drivers. From Scanspeak to Dyn to SB. But not Purifi.

If you look at the hard cone transducers, there won't be any resonance either. That's one of the reasons i like HC (hard coned ) drivers. Ordinary Dayton RS180 doesn't suffer from it but Satori MW16P does.

 

[RealityCheck18]

Very interesting,

OK, off-set the tweeter a bit and do a round over along the space baffle. Tune it to 38Hz--port resonance. Just spitballing here (don't light the torches yet!) I ponder if by throwing a passive radiator on the back (the kind CSS sells that are adjustable tuned from the front) would that solve the port resonance problem without causing too many other problems? Back in the day, I had a pair of 6.5" two-ways with an 8" passive radiator that worked very well--no chuffing noted

Besides the obvious cost of decent passive radiators, might be a better option for lower tuned, smaller enclosures? Don't throw rocks at me yet, return those black helicopters to base as it is a pondering. I've used passive radiators to save a lot of space with 20Hz tuned 12" subs with no chuffing issues so wonder if it would be a reasonable solution for smaller bookshelf speakers that attempt to create some form of bass response?

Very good results for that speaker, Jeff Bagby (RIP) was a practitioner of the dark art of crossover building.

 

[Zvu]

No dark art here. Just common sense, or at least it should be common.

These midwoofers don't deserve aditional investment in passive radiators. I've worked with them and while they are good value and hold their ground at high volumes, they lack transparency big time compared to other woofers in price range. I wouldn't know what to use them for now, and i was able to buy them at 34€/piece.

Erin measured them and they behaved very bad. If i was in US, i'd use Anarchy 7" woofers which cost exactly the same as SB17NRX2C.

https://www.diysoundgroup.com/speaker-parts/speaker-components/woofers/anarchy7-4ohm.html

 

[ROOSKIE]

I ponder if by throwing a passive radiator on the back (the kind CSS sells that are adjustable tuned from the front) would that solve the port resonance problem without causing too many other problems? Back in the day, I had a pair of 6.5" two-ways with an 8" passive radiator that worked very well--no chuffing noted

Port chuffing and port resonance are not at all the same thing.
Seems to be a common source of confusion and I am not completely sure why.
You can have resonce issues with a PR. Obviously no chuffing which is good.
Anyway a PR is often an option but it may not add much. Worth trying for the right DIY person.