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Old 30th November 2007, 10:01 AM   #1
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Default Holdent - Goldwood 15 with B3N project?

Sorry for not contacting you personally about this, but I am still on a restricted account due to just signing up, plus I think others may benefit from this as well-

Did you ever get around to testing the B3N with a low end helper? I'm thinking about stepping over to the OB dark side and want to try a low budget setup using the B3N, probably with the Goldwood 215/8 that you mentioned, or maybe the Eminence Alpha 15 if I'm feeling rich. I feel that the Goldwood may match up with the B3N a bit better in terms of sensitivity, according to MJK's notes on sentivity of full range driver vs bass helper.

I would be going all passive with this design and would be doing it purely for experimentation, but may need some guidance on a decent Xover point and baffle size.


Thanks!!
Max C.
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Old 30th November 2007, 12:19 PM   #2
sreten is offline sreten  United Kingdom
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Hi,


Click the image to open in full size.

*Magnet weight: 20 oz. *Fs: 29 Hz *SPL: 87.8 dB 1W/1m *Vas: 12.95 cu. ft.
*Qms: 7.08 *Qes: 2.69 *Qts: 1.95 *Xmax: 3.5mm *Net weight: 5 lbs.

Goldwood GW-215/40/8 15" OEM Woofer 40 oz for $7 more.

Click the image to open in full size.

*Magnet weight: 40 oz. *Fs: 29 Hz *SPL: 90 dB 2.83V/1m *Vas: 9.69 cu. ft.
*Qms: 5.07 *Qes: 1.29 *Qts: 1.03 *Xmax: 3.5mm

Is better choice if you want to follow MJK's methodology.
Noting you can raise Qts somewhat with inductor series R.
Qts=2 seems to me too high for MJK's approach.

The B3S with Zaphs 8k filter should be workable.

/sreten.
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Old 30th November 2007, 12:39 PM   #3
Kensai is offline Kensai  United States
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Don't forget that inductors in your low pass will add resistance that will increase the drivers Qts, so if you were to use a nice low frequency xo point and use, say 20gauge Jantzen inductor(s) to achieve it, you will be adding 1-2 Ohms in series right there, which may be enough.

Kensai
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Old 1st December 2007, 08:44 PM   #4
holdent is offline holdent  Canada
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I'm still playing with the GW-215/8 with the Hi-Vi BN3. I love the sound of the B3N but not really happy with the GW-215/8.

The big limitation for me is the GW-215's power handling and tendency to sound "boomy" at higher volume levels. The GW-215 has an advertised Xmax of 3.5mm. I estimate that this Xmax can be exceeded around 28 Hz with only 4 watts of power. With the woofer mounted on a baffle that is 36x40 in, this corresponds to a simulated max SPL of around 95 dB over 40 Hz.

Now for the GW-215/40/8:
Unfortuantely Goldwood doesn't seem to provide the Sd and BL for any of its drivers so I had to estimate them for both drivers. I started by "guesstimating" that the driver's Sd was approx. 820 cm2. Using Martin's TS_Consistency_Vas sheet the BL for the GW-215/40/8 works out to a calculated 10.367 Newton/amp. Using these params in the same baffle above, the driver's Xmax is exceeded with 7 watts of power at freqs around 22 Hz corresponding to a max SPL of around 100 dB over 40 Hz. Fortunately the GW-215/40/8 is more sensitive must be padded down to work with the B3N. Note though, because this driver has a higher Qts, the F3 is higher than the GW-215's (a drawback).

So, I agree with Sreten - the Goldwood GW-215/40/8 is probably a better choice. However I also have the Eminence Alpha 15A and find its a much better driver. The Alpha is more sensitive, has a slightly higher Xmax, and can handle much greater power. It starts to exceed its Xmax at 9 watts near 34 Hz. This provides a max SPL around 105 dB over 40 Hz.

So you pay for what you get! The Alpha 15A is about double the price of a GW-215 but sounds far better than the GW-215. With the H-Vi B3N, the B3N starts to become the limiting factor.

I'd skip the Goldwood GW-215 (or GW-215/40/8) and spent the extra $50 for a pair of Alpha 15As.
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Old 1st December 2007, 10:34 PM   #5
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I think i'll do just that - get the Alphas. I'm impressed with Eminence so far, having built a fun set of speakers with the Beta-10CX coaxials.

Do you plan on running the B3N + Alpha combo passively? I'm pretty set on passive, but not sure what Xover point the B3N will be happy with, but Zaph says powerhandling is good over 200hz.

The Alpha probably needs to be padded ~6-10dB to mate well with the B3N, correct? I'd probably be using a 20"x38" baffle ala MJK's article as well....


Thanks,
Max C.
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Old 2nd December 2007, 05:24 PM   #6
holdent is offline holdent  Canada
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I am running the B3N/Alpha 15A combination passively. So far I've been using an Eminence PXB2:500 crossover (http://www.partsexpress.com/pe/showd...number=290-630 ) which is a 500 Hz, 18 dB/octave high pass, 12 dB/octave low pass (Butterworth) for 8 ohm drivers. The B3N has an Re of 6.5 ohms so the actual crossover frequency is higher (which likely helps flatten the frequency response for a Butterworth crossover).

The baffle I'm using is 30 x by 36 in. (It's actually a 18 in wide baffle with 6 in wings on either side). The Alpha is on the vertical center 20 in up. The B3N is placed assymetrically 30 in up and 2 in to the left (or right) of the centerline.

I use L-pads to pad down the Alphas right now. I prefer a slightly warmer sound so I'd suggest padding them down about 7 dB. I also used Zaph's notch filter for the B3S to help control the peak around 8 KHz (Sreten suggested this earlier). It uses a 4.3 uF capacitor, 0.08 mH inductor, and 30 ohm resistor all in parallel (see http://www.zaphaudio.com/audio-speaker18.html but ignore L1 and R2 components of this filter. They're for a BSC which is not needed here).

Good luck!
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Old 3rd December 2007, 02:56 PM   #7
sreten is offline sreten  United Kingdom
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Hi,

FWIW L padding the Alpha's will drastically affect Q alignment.

If the gist of MJK's article is followed, 500Hz low pass is too high.

If the outline of MJK's article is to be followed, include the offset
alignment of the crossover frequencies and near his crossover
values then the relative sensitivities of the drivers need to be
similar. In this context the GW-215/40/8 with a highish DCR
inductor will work better than the Alpha 15 with the B3S.

Also note that R5 should be reduced somewhat as the
loop impedance at 8Khz no longer includes R2, say 22 R ?

Quote:
Remove R2 and L1 completely, replace R5 with a 20 ohm.
If the Alpha only has slightly higher Xmax than the GW, this is
all that matters, power handling is not relevant. The Alpha
would give slightly higher maximum output. The GW because
of its lower sensitivity should handle more power than the
Alpha - this is expected due to overall lower senstivity.

The gist being the GW/B3S needs a lot more juice that the
Alpha/108 but does not go as loud. If does go somewhat
lower due to lower Fs this will be at the expense of maximum
loudness, which is limited due to the B3S sensitivity.

No-one should expect high power handling from OB's, e.g.
bi-amping at 300hz with 2x100w for the B3S. The B3S might
take it, hitting 104dB peaks, but the bass end will struggle.

This is simply due to the baffle loss. OB's do not just lose driver
efficiency at low frequencies, they lose effectively the same
amount of excursion capability, maximum levels are limited.
In other words maximum levels in the bass drop like a brick
(12dB/octave) from the frequency you hit excursion limiting,
the only way to reduce this frequency is reduce levels.

/sreten.
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Old 3rd December 2007, 10:07 PM   #8
holdent is offline holdent  Canada
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Sreten:
I suspected, but don't know how to calculate how the Lpad affects the total Q. I've never used a Lpad on a woofer before and tried to look it up in my copy of the Loudspeaker Design Cookbook (7th ed). All I found so far is that the Lpad will maintain a constant impedence for the network (unlike series resistance). I know that adding series resistance increases the Qes and hence the Qts. However an Lpad is a series resister and parallel resister (yes?) so how do you calculate the Qts change with the parallel resistor?

As well I re-read my comments about the crossover and realized I should have said more. I only used the Eminence one as a starting point because I already have it. I have the inductors and caps on order from PE suggested by Martin (I already a Fostex FE103E to play with as well). At louder levels the peak at 2KHz of the Alpha 15A is very obvious (and very annoying!).
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Old 4th December 2007, 10:15 AM   #9
sreten is offline sreten  United Kingdom
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Hi,

Looking back towards the amplifier the L-pad appears as a series
resistance of its two legs in parallel, e.g. an L-pad with 4R series
and 8R parallel giving 8R in with an 8R load gives 2.7R impedance.

Plug this into : http://www.mhsoft.nl/spk_calc.asp#newqts

/sreten.
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Old 5th December 2007, 11:23 PM   #10
holdent is offline holdent  Canada
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Sretan:
An L-pad looking back towards the amplifier should present a constant impendence - yes? (I'm not sure what you meant.)

Since I wanted a way to to actually model an L-pad on woofer in Martin King's MathCad worksheets for an OB I contacted him and asked how this could work. He very graciously modified the worksheet and sent it back to me. The surprising result was that an L-pad has very little affect on the Q(!). Using the worksheet I modeled the Alpha 15A in the baffle described previously (30 x 36 in with the Alpha centred horizontally, 20 in up from the bottom). The low pass used is still a 2nd order Butterworth at 500Hz and the L-pad set to -7dB. Here's the predicted response:

Click the image to open in full size.

The red curve is the response before adding the L-pad. The blue curve is with the L-pad set to -7 dB (the series resistor is calculated to be 3.265 ohms and parallel [or shunt] 4.763 ohms).

Don't ask me to explain what's happening -- if I could work this out myself I wouldn't have to contact Martin. Thanks to Martin for taking the time to do this! (His worksheets are great - see quarter-wave.com)
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