Best Full range 15" driver - Beyma 15WR400 2x15

[5StringPocket]

Shorten the port by an inch.

Hmm, my software handle for adjusting port length is tuning frequency but this isn't about tuning.
Using the frequency graph of my Fb 50.2, 4" port model to find the effective F0 and F3 points for the lower half bandwidth seems to give a damping ratio of 0.659.
Increasing Fb to 53.4 Hz shortens the port to 3". Using the same graphical method to find the effective F0 and F3 points gives a damping ratio of 0.701 which is critically damped. This should provide an optimum transient response. Pretty cool, thanks.

 

[agedhorse]

IMO, it will sound better. It wouldn't hurt to shorten it another 1/2" either.

 

[3rdcurve]

Sunuva gun. You build and I’ll buy!

 

[5StringPocket]

Sunuva gun. You build and I’ll buy!

DIY projects take way too much time and effort to build and sell unless you're done with it and need to make room for a new project. Shipping is also so expensive it really kills any desire to build something you don't think you'll keep. DIY posts with design objectives, component choices, software models, construction drawings, build photos, some simple audio measurements, and at least a subjective evaluation of tone should give someone enough information to decide if they want to take the plunge given the downside. A good audio demo is like gold but not practical for most DIY folks. I'd love to have Nate Navarro or MDBass do a pro demo on my rig. One can dream...

Here are a few of my personal observations which guide my thinking when I get curious about a build. Comments and discussion with known experts in the field and being willing to learn and test these ideas also helps.
- First, it's a bass guitar cab not a PA cab so design criteria are different. It seems that FOH often rolls off bass guitar under 50 Hz in order to slot the bass right above the kick drum in the mix.
- Bass guitar notes are not sine waves, but consist of a fundamental and a series of overtones. Most of the energy in a note is pretty evenly split between the fundamental and 1st overtone. The low B or low E fundamental is not as important as that 1st overtone in putting out a solid bass tone. Too much fundamental causes rumble which turns to mud.
- The interesting challenge is to select the right drivers and optimize tradeoffs in the enclosure design to get the performance and sound you want. Practical bass cabs for gigging need to be well constructed, solidly braced, properly tuned, and fall within reasonable size and weight limits. Many players have to move their own gear and these days often don't want a single box to weigh more than 50 or 60 lbs. If under 40 lbs then go modular.
- When selecting a driver, the T/S parameters and frequency response drive the design and define its limits. Decent modelling software should show you what your power vs frequency looks like and when you can expect to reach Xmax as frequency drops.
- For a ported enclosure, a driver with Qts between 0.30 - 0.35 seems to be optimum. Adjusting enclosure volume, port cross section, and port length are handles to optimize the power handling and frequency response curve. Graphical inspection is useful to dial it in. An oversized box will give a big low end but power handling suffers and it may lack focus. An undersized box may not have enough low end or have an exaggerated hump around 120 Hz that sounds boomy. One thing that has been pointed out to me is that giving up some deep bass below 50 Hz in exchange for more power in that critical 50 - 100 range gives a more solid and defined bass response.

 

[5StringPocket]

I find it irritating when trying to do comparisons, that driver manufacturers sometimes use different methods to derive Xmax. This is a key variable in determining the excursion-limited low frequency limit. For comparisons to be meaningful you really need apples-to-apples in a common software simulator.
@Arjank made the observation in a different thread that some manufacturers use a Klippel estimation for Xmax, which can be be somewhat generous, while others use the physical measurement Xmax = (Winding length - gap depth) / 2.
The Beyma 15WR400 lists an Xmax of 6.3 mm, but with a 16 mm winding and an 8 mm gap the physical Xmax based on overhang is only 4.0 mm. Respectable, but only 63.5% of the claimed Xmax so perhaps they use the Klippel estimate?
Products - Beyma - Professional Speaker Manufacturer since 1969

The Celestion Pulse15 has a 17.5 mm winding and an 8 mm gap for a physical Xmax based on overhang of 4.75 mm, which is given on the spec sheet. With this criteria, the Celestion seems to have a throw about 19% longer than the Beyma.
https://www.parts-express.com/pedocs/specs/294-2466--pulse-15-spec-sheet.pdf

From this, it would seem reasonable to either reduce the Beyma Xmax to 4.0 mm or increase the Celestion Xmax to 7.5 mm (6.3 * 1.19) when doing a comparative model of these drivers in a software simulator like Boxsim or Eminence Designer. I've built a cabinet with the Beyma 15WR400 and it is a beast with real low-end fortitude. I've also been curious about the Celestion Pulse15 but dismissed it because of its lower sensitivity and Xmax. When I adjust Xmax to use the same method for both, the Celestion compares more favorably than expected while costing $100 less and lighter by 2.6 lbs. Both drivers have a good frequency response for bass guitar but I think would be voiced a bit differently. The biggest differences I see are in the lower Qts (0.3 vs 0.43) and higher magnet strength BL (19.2 vs 15.06) for the Beyma. I'm wondering if it would be best to stick with the Beyma or try the Celestion in a 3.0 cu-ft 2-way ported enclosure?

Here is a Boxsim MaxSPL plot for the Pulse 15 in a 3 cu-ft enclosure using frequency and impedance plot data and a Tractrix horn high-passed at 3110 Hz. Not too shabby.

 

[HaphAsSard]

The Beyma 15WR400 lists an Xmax of 6.3 mm, but with a 16 mm winding and an 8 mm gap the physical Xmax based on overhang is only 4.0 mm. Respectable, but only 63.5% of the claimed Xmax so perhaps they use the Klippel estimate?
Products - Beyma - Professional Speaker Manufacturer since 1969

Beyma states their method clearly, if not very loudly, in the spec sheet (page 1, footnote 4):

"The Xmax is calculated as (Lvc - Hag)/2 + (Hag/3,5), where Lvc is the voice coil length and Hag is the air gap height."

^ [Emphasis added. The comma in "3,5" is of course to be read as a dot (the use of the comma and the period for ease of reading large figures and for decimal separation is reversed - compared to English - in many languages.]

 

[5StringPocket]

Beyma states their method clearly, if not very loudly, in the spec sheet (page 1, footnote 4):

"The Xmax is calculated as (Lvc - Hag)/2 + (Hag/3,5), where Lvc is the voice coil length and Hag is the air gap height."

^ [Emphasis added. The comma in "3,5" is of course to be read as a dot (the use of the comma and the period for ease of reading large figures and for decimal separation is reversed - compared to English - in many languages.]

Thanks, guess I didn’t read all the fine print. Using this for the Celestion then gives an Xmax = (17.5 - 8.0) / 2 + (8.0 / 3.5) = 7.0 mm for the Pulse15. This should at least put the two drivers on equal footing for model evaluation.

This may be conjecture but here goes...
Both drivers have 3" diameter voice coils and similar gap height, so if motor strength vs moving mass (F=ma) is considered, is a higher ratio capable of accelerating the cone faster (more perceived punch)?
Beyma 15WR400: BL/Mms = 19.1 / 91.0 = 0.211
Celestion Pulse15: BL/Mms = 15.06 / 83.3 = 0.181
The Beyma has a higher BL/Mms, more gain in the 120-200Hz range, and more middle mids.

 

[3rdcurve]

The 2x15 build I did with the Pulse 15s had lowend for days….they actually would make decent subs. However, at the time my only head was a BB800 and I didn’t have enough EQ capability to bring the low mids and high mids in line with where I wanted them. P with flats - fabulous. Anything else lacked definition for me. That said, with a head that has multiband/parametric EQ, and maybe a decent HF horn they are a great driver and a bargain price.

 

[5StringPocket]

I've adjusted both models to use an Eminence F151M-8 HF driver, which I have on hand, mated to a Faital STH100 Tractrix horn. The high-pass is a 3rd order Butterworth at 3110 Hz with a 100-watt Eminence L-pad for level adjustment. Phase alignment looks pretty good for both Celestion and Beyma drivers but leaning toward Beyma as still the better choice.

 

[6thplanet]

Used with a tweeter, the Beyma would be a better choice as it's FR is smoother. By itself, the Celestion might be better with its peaky 2K bump. All personal preference of course.

 

[5StringPocket]

Used with a tweeter, the Beyma would be a better choice as it's FR is smoother. By itself, the Celestion might be better with its peaky 2K bump. All personal preference of course.

I agree that the Beyma would be better in a 2-way with a quality HF horn and its more forward mids would be another plus. Definitely articulate (not a “slow” 15) but has plenty of low end.

 

[Arjank]

I find it irritating when trying to do comparisons, that driver manufacturers sometimes use different methods to derive Xmax. This is a key variable in determining the excursion-limited low frequency limit. For comparisons to be meaningful you really need apples-to-apples in a common software simulator.

Yes that's indeed annoying, the least each manufacturer could do is provide the voice-coil length and air gap depth. This still doesn't give you accurate numbers to compare though. Even if all manufacturers would use Klippel won't change that except if they would provide all Klippel measurements. That way you could identify which part of the system (driver) is exceeding the 10% distortion limit and what type of distortion. Distortion caused by non-linearities of the suspension will sound different from those caused by the an asymmetrical motor or caused by the drop of the magnetic flux.

 

[6thplanet]

I agree that the Beyma would be better in a 2-way with a quality HF horn and its more forward mids would be another plus. Definitely articulate (not a “slow” 15) but has plenty of low end.

I see the Pulse as having more forward mids, hence my statement. From the FR graphs, the Beyma has a 4db peak at 2K, the Pulse has almost a 10dB peak. Both rolling off approximately the same, but the Pulse still showing break up at 3K, the Beyma showing a bit more control during roll off. I don't see what smoothing each it using, so kinda hard to guess.

 

[Arjank]

The Beyma probably has a more thicc cone compared to the Pulse 15 (91gr mmd vs 55gr, same VC diameter). The heavier paper cone is less prone to these resonance peaks.

 

[5StringPocket]

The Beyma probably has a more thick cone compared to the Pulse 15 (91gr mmd vs 55gr, same VC diameter). The heavier paper cone is less prone to these resonance peaks.

I was looking at Mms, since Beyma doesn't list Mmd but agree with your observation. It's surprizing how what looks like a relatively simple system has so many interacting variables which affect the end result.

Mms (g) - mass of the suspension system (including acoustic load). This is the mass of the cone, coil and other moving parts of a driver, including the acoustic load imposed by the air in contact with the driver cone.
Mmd (g) mass of the suspension system (without the acoustic load).

 

[Arjank]

I was looking at Mms, since Beyma doesn't list Mmd but agree with your observation. It's surprizing how what looks like a relatively simple system has so many interacting variables which affect the end result.

Mms (g) - mass of the suspension system (including acoustic load). This is the mass of the cone, coil and other moving parts of a driver, including the acoustic load imposed by the air in contact with the driver cone.
Mmd (g) mass of the suspension system (without the acoustic load).

I did make a mistake, I wrote down the mmd instead of the mms for the Pulse 15 so it's 91 vs 83.3 grams. The difference is not that big and therefore those peaks are not due to the cone mass. It's probably more of a dustcap issue (size and material).

 

[agedhorse]

Determining Xmax is not always easy because some motors more abruptly lose control and some more gradually lose control depending on more than just the VC height and measured gap depth.

This is the one advantage of Klippel testing, combined with experience. It’s performance based data rather than physical data.

 

[5StringPocket]

Well, I'm at the end of my DIY journey. I've learned a lot and have some nice sounding cabs which have incorporated concepts and improvements picked up along the way. This Beyma 15WR400_HF100 cab should use up most of the spare parts I have on hand along with the triangular center braces and custom 3rd order high pass I made for this build. I had to modify the dimensions slightly so that all the 1/2" ply needed could be cut from one 4 ft x 4 ft piece but kept internal volume at 3 cu-ft. Here is the updated construction drawing.

 

[5StringPocket]

All sides, baffle, bracing, and ports have been made with cutouts, mounting holes drilled and anchors in place. Here are pics of the baffle with 15" driver and HF horn mounted to check the fit and an exploded view of the enclosure sides with bracing in place.

 

[6thplanet]

Looks like a solid build!