MJK’s Jordan JX92S OB with a Goldwood GW-1858 Woofer in an H Frame

[MJK]

If the specifications are real, I think it will work fine.

 

[MJK]

>>> So I think that you want the H frame poisnted right at the listening position. I think if you have them 3 to 4 feet out into the room you should do well with the bass freauencies.

Mine will be about 3 to 4 feet in front of the rear wall with a BIB behind each (but with about 2 feet of space in between). I look forward to playing with room placement. Fortunately, i have a dedicated listening room (that has been doubling as an exercise room lately).

Can the depth of the H frame can be made less deep? I am planning on using standard lumber which is 11.25 deep with the 15 inch drivers. Can i do this without losing too much bass?

Yes, the change in bass output will be small.

 

[InclinedPlane]

If you do not care about the efficiency of the Alpha 15A in an H frame, you might consider adding some weights to the cone. This will lower fs, raise Qts, and drop the SPL/W/m. I would try the Alpha 15A unmodified first, that should get you down to 30 Hz. Listen and then decide if you want to add weights.

Hold the phone! The motor on the Alpha15 is already too weak for its factory moving mass much like the woofers from Bob Carver's Amazing Loudspeaker. Adding mass is a nasty idea imo. Here's an excerpt from the Stereophile review:

The Q of the Amazing's bass alignment is around 1, considerably higher than the 0.5–0.7 range most designers opt for. Don't expect tight, well-defined bass from such a design. This, according to Bob, is just the sort of bass quality he likes—"a warm, rolling bass."

Warm rolling bass is nice. I liked it. This is what I got from my Alphas. But they don't kick and they don't 'snap'. They can't. That is why I gave them up. They don't do percussion justice. We are forever drooling over fullrange drivers with giant magnets. Why? They offer better rise time. The better the immediacy, the more realistic the presentation. Bass drivers need to be selected, imo, on the same premise. Otherwise they won't keep up; they just trail behind in a kind of 'bass backwater' . Due to the dipole design they can still be quite detailed but reproduce the recorded material inaccurately. Now I don't plan to keep my cheap Pyle PPA15s forever, but what a difference! They kick, they snap, and they keep up.

 

[valleyman]

For interest, a little sim of the Goldwood in an H frame, electrical LR4 @ 70Hz

 

[valleyman]

InclinedPlane, I think you may be right btw... It is possible that with my Alphas I thought they lacked bass in OB when really what they lacked was the ability to hit me in the chest with their bass notes. The quality is there and the low notes reverberate beautifully around the room which is what endeared me to them, but they dont have any "thump". Sometimes (especially with electronic music) I want to be knocked over. The Goldwoods have a slightly larger magnet.... maybe they will be a better compromise.

Maybe using an H frame with a second sealed/ported sub would be an interesting experiment. No idea how the two would interact though, but if you ended up with the best of both worlds it could be an enviable setup

 

[tinitus]

I thought they lacked bass in OB when really what they lacked was the ability to hit me in the chest with their bass notes.
....... but they dont have any "thump".

Isnt that the nature of OB dipole...and why some people love them fore that very reason
At some point you may even say the same about closed versus BR
I suspect that a closed box fore bass works better than a BR ditto in the terms of integrating with a dipole mid/tweet

SB Acoustic 12" goes pretty low in closed at around 90db and I would like to see someone try it with a fullrange driver

 

[valleyman]

I too love them for that very reason!

The quality is there and the low notes reverberate beautifully around the room which is what endeared me to them

I just wish they could have this quality but with some more punch

Maybe what I should really be looking for lower Qts drivers with plenty of Xmax and using EQ to compensate for the rollof exhibited by these drivers

Maybe a CSS SDX15 in OB with lots of EQ would fit the bill!

 

[tinitus]

Maybe what I should really be looking for lower Qts drivers with plenty of Xmax and using EQ to compensate for the rollof exhibited by these drivers

And you may need more woofers but not very "cost effective"

 

[kristleifur]

It is possible that with my Alphas I thought they lacked bass in OB when really what they lacked was the ability to hit me in the chest with their bass notes. The quality is there and the low notes reverberate beautifully around the room which is what endeared me to them, but they dont have any "thump".

Isnt that the nature of OB dipole...and why some people love them fore that very reason
At some point you may even say the same about closed versus BR

I have no OB experience, but I have heard a few different amps. Those Tripath amps that I have heard have put plenty of Thump! into previously flabby speakers, compared to Class-AB amps. I'm curious how much the amplifier can affect OB bass dynamics.

 

[Godzilla]

Valleyman, is that measurement for the 18 or 15 inch Goldwood?

If not the 15 inch could you run a sim on this please.

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=290-346

TIA,
Godzilla

 

[valleyman]

Hi Godzilla

That sim is for the 18. I can run one for the 15 no problem, but I can't find info on the BL anywhere. Goldwood don't seem to provide datasheets for their drivers...
I think it will sim pretty similarly to the 18", just with lower efficiency (and max SPL). That seems to be the tradeoff they have made with the smaller driver.

I'm fairly intrigued by the EQd lower Qts driver in an H frame idea now. I'm hoping a linkwitz transform can be used for this (is there anywhere better/cheaper than ESP for LT boards?).
Getting hold of an SDX15 in the UK is going to be a real problem, but Mad About Sound carries the Adire Tempest which I think will suit this application well. I'm hoping this sub can go in my reference system, so the extra money could be very well spent.

 

[valleyman]

Seems I was wrong... that last FR i posted was in fact for the 15" goldwood, not the 18"... Here in fact is the sim for the 18". Electrical LR4 @ 75Hz.

As I suspected, very similar but with more efficiency. It's not all that surprising though as the drivers have very similar parameters. (btw calculated BL for the 15" is around 10.65)

 

[holdent]

valleyman - I have also been frustrated that Goldwood doesn't provide enough T/S params to use Martin's worksheets. I tried emailing them earlier in the year to obtain both the BL and Sd params for the GW-215/8 without a reply. Unfortunately I don't have a woofer tester yet and can't get these figures for myself.

To sim this woofer I used a calculated BL of 6.167 which isn't close to the 10.65 which you came up with (so the sim I got wasn't anywhere near as good). Can you post how you came up with the BL? I used Martin's T_S_Consistency_Check_Vad worksheet; fed in the published Fs, Re, Qms, Qes, and Vas; and used an Sd guess of 820 cm2.

MJK (Martin) - I tried duplicating the 18" sims you ran and came up against the same Sd issue. I used a gues of Sd = 1130 cm2 - is this right?

 

[Godzilla]

Thanks Valleyman!

Does your sim show the efficiency of the driver is about 81db per watt? I am going to use a dedicated sub amp and want to make sure I have enough juice.

Thanks again for the sim!

Godzilla

 

[valleyman]

Hi holdent

I used Unibox to work out the Bl. I just double checked it and got the same result. Also double checked the sim for the 15" and it came out the same
The efficiency is only 81dB with the 15" so a reasonably powerful amp is probably needed

 

[holdent]

valleyman - Oops - I just realized that the woofer I sim'd is different than the one Godzilla linked to. I sim'd the GW-215/8; Godzilla linked to the GW-215/40/8.

The GW-215/40/8 is a better woofer for a H-frame. Once I entered the same params I got the same result.

Godzilla to answer your question, using the H-frame lenght of 11.25" you specified earlier I also got a sensitivity of 81 db/w.

 

[holdent]

Godzilla - to add to the previous post: you can use GW-215/40/8 and go to 200 Hz if necessary using a 120 Hz LR2 crossover (the rising response of the H-Frame is reduced by the xover). Above 200 Hz the response of this H-frame (again 11.25" in length) drops approx. 20 dB by 400 Hz.

Unfortunately this woofer in the H-frame is relatively insensitive and it has an advertised X-max of 3.5 mm. At 100 watts input this system has a sim'd output level of just over 100 dB and sim'd woofer displacement over 4 mm for all freqs below 45 Hz. Martin (MJK) has argued in many posts that, in practice, this is much less of a problem than it may look. In contrast, John Janowitz (of AESpeakers) disagrees with this. There has been a very interesting discussion of this over in the AudioCircle.com site in the Open Baffle Speakers area (see http://www.audiocircle.com/circles/index.php?topic=59619.20).

 

[Godzilla]

>>> Unfortunately this woofer in the H-frame is relatively insensitive and it has an advertised X-max of 3.5 mm.

The sims are excellent! But now i am wondering if the Goldwood or the Eminence Alpha 15 would be a better choice???

Can you sim the Alpha 15 please?

http://www.parts-express.com/pe/psh...407&FTR=alpha 15&CFID=295418&CFTOKEN=77564547

I did not realize how efficiency drops in an H frame and don't want to spend a lot of money on an additional amp to power them.

TIA!
Godzilla

 

[valleyman]

Here's the Alpha 15. Less extension, more efficiency than the goldwood 15".

So we seem to have:

Goldwood 15": Low efficiency, good extension
Alpha 15: better efficiency, less extension
Goldwood 18": best of both worlds

It's worth noting though that the goldwood 15" is quite a bit cheaper than the Alpha 15. Going for a straight OB tends to sacrifice extension for efficiency, so the Goldwood 15" in OB could end up looking like the Alpha 15 in H frame for less money and in a smaller package.
Sim on the way

 

[valleyman]

Seems I am off the mark here. I had thought after reading MJKs paper:
http://www.quarter-wave.com/OBs/U_and_H_Frames.pdf

that U and H frames gave greater bass extension but less efficiency than OBs due to the effective extra mass added by the air in the frames.

Here is a sim of the Goldwood 15 in an OB, same size as the H frame (17.5x17.5). Strangely enough it has less extension and less efficiency than the H frame.
Upon rereading Martin's article, I notice that the OB used is actually both wider and taller (20x40) than the U and H frames it is compared to which gives rise to the greater efficiency. Running the sims with this baffle show it to be around 83dB.

Martin, is there a reason you chose to compare such small U and H frames to such a large OB? I suppose you could argue the wings of the U and H frame contribute to their size but the comparison doesn't seem entirely fair