Any advantages of High Q or Low Q?

Hi;
I have made several ported speaker systems and am familiar with Thiele's alignment tables. I know the tradeoffs between higher and lower Qts in terms of Box volume and fb vs fs; ie. Qts higher than ~ 0.4 and Vb>Vas but f3<fs while lower Qts is the opposite. Is there anything more to picking a driver Qts to design a ported system than this (for instance transient response) that goes with Qts?
Systems I have made to date have had Qts of 0.38-0.57.
Currently I am looking to make a 2 Way ported system with a 6-6.5" woofer. I was considering Vifa NE180W-8, Dayton RS150 and SEAS H1217 all with Qts in the 0.39-0.47 range but read a review of the Silver Flute W17RC38-4 with a Qts of 0.24. Since it is outside of the range I have used to date I was curious the tradeoffs. $ and box size are not a consideration here, just want to know the technical tradeoffs
Thanks!
 
Hi;
I have made several ported speaker systems and am familiar with Thiele's alignment tables. I know the tradeoffs between higher and lower Qts in terms of Box volume and fb vs fs; ie. Qts higher than ~ 0.4 and Vb>Vas but f3<fs while lower Qts is the opposite. Is there anything more to picking a driver Qts to design a ported system than this (for instance transient response) that goes with Qts?
Systems I have made to date have had Qts of 0.38-0.57.
Currently I am looking to make a 2 Way ported system with a 6-6.5" woofer. I was considering Vifa NE180W-8, Dayton RS150 and SEAS H1217 all with Qts in the 0.39-0.47 range but read a review of the Silver Flute W17RC38-4 with a Qts of 0.24. Since it is outside of the range I have used to date I was curious the tradeoffs. $ and box size are not a consideration here, just want to know the technical tradeoffs
Thanks!

Don't forget that the manufacturer's "advertised specs" are only an average of the actual specs that they intend the driver to have in production. It's likely that any single driver of a given model will deviate from the advertised specs. When the driver is used in a vented box it is a good idea to measure the broken in driver before planning for any alignment because in general vented alignments are less tolerant of misalignment than closed box alignments. Given two of the same driver, the parameters may vary in an "opposite" fashion. You need to check the drivers in hand. There is no "better" or "worse" manufacturer in this regard, only drivers with wider or narrower distribution in the parameters. Always measure!

-Charlie
 
Thanks Charlie,
I certainly have experienced the range in manufacturing variation between two identical speakers in my most recent project. One speaker in the pair came out within a few % of the spec, the other was off by >25% (and yes - this was after break in). But still, back to my original question; even given that advertised specs are only an average - are there any other quantifiable sound characteristics that go with lower or higher Qts drivers (assuming that one measures the actual T-S parameters after break in and designs the box around those parameters) would you prefer a high or low Qts for some other reason?
thanks!
 

norman bates

Member
2003-11-25 2:28 am
if I remember, the Silver flutes spec were close to manufact........

Besides the motor acting as a brake, (meaning higher F3's), my buddy swears by .3 qts bass drivers (subs), but he likes 6th order (boosted at F9 ported at F9).

He also liked a 100db 12" guitar speaker (granted sealed it rolled at 200hz) but it was smooth and very detailed for a 12", excellent to cross at 1.2khz.

I believe in rigid, light cones, and strong magnets. More detail usually (not comparing kevlar versus paper, but qts vs qts), think some Lowthers. I think Qms has a lot to do with the high end detail also.

"Qms: Driver mechanical Q

Qms is the mechanical Q of the speaker and only takes the speaker's mechanical properties into consideration. It is a measurement of the control coming from the speaker's mechanical suspension, which is made up of the surround and spider."

A jbl 2206 doesn't sound as good as a 2204 probably due to the stiffer suspension that is needed to protect it when playing at greater than 200 watts for hours. A lower qms doesn't want to move as easily as a higher qms. The old 15s that were used in 2 ways (going up to 1khz nicely) had high qms numbers, and wanted HUGE boxes (like 10-20ft3 for ported).

I'm using the 4ohm 8" silver flute in my current project (qts = .23). They sound nice, especially for the $38 cost. Sort of a costco driver, not the cheapest nor the best, but a great value.

I've ran the 6.5" silver flute (8ohm shielded, qts = .31), but I should not have tried to push them up to 5khz (no dispersion). 2.5khz-3.5khz crossed would have been better. A very nice driver I recommend to all, now unobtanium.

So to me, I'd want a lower qts for the detail (strong magnet), but a higher qms for a suspension that won't rob detail in the high end ............ Oh yea, I'd like a shorting ring or copper cap to clean up distortion from 100hz up.

Not really a simple answer, huh ?

Nver2manybike, where was the review of the silver flute ?

Norman
 
Currently I am looking to make a 2 Way ported system with a 6-6.5" woofer. I was considering Vifa NE180W-8, Dayton RS150 and SEAS H1217 all with Qts in the 0.39-0.47 range

The Silver Flute W17RC38-4 is a great choice if you're on a budget. However, in terms of performance, it is not of the same class as the others. The Vifa NE and the Dayton RS excel in dynamics whereas the Seas is "ultra smooth". I can't tell from technical specs. My subjective observations are from listening test.

I'm not to sure whether the SF Qts is actually 0.24. My measurements of the 8 ohm version indicate 0.43

Regards
Mike
 
Hi Norman;
Thanks for your insights explaining some of the tradeoffs relating to Mechanical and Qts and other aspects of the sound output and design (other than Box size and f3). As for the "review" of the silver flute - it wasn't anything quantitative, just a customer comment on the Madisound website (was actually the review of the 5 1/2" unit that got my interest: The Madisound Speaker Store)
 
Hi Mike - thanks for your listening observations. Actually the 8 ohm driver is listed as having a slightly higher Qts (0.29 vs 0.24 for the 4 ohm unit). The impedance curves do give the impression of being rather low and broad compared to other drivers but of course that could be a matter of the scales on the plot - I have not plugged in the -6db points in a calculator or anything.
For a more level playing field compare - what do you think of the SEAS Excel 7" W18EX-002? It has a claimed Qts of 0.26 and is on sale right now at Madisound for $129.
 
For a more level playing field compare - what do you think of the SEAS Excel 7" W18EX-002? It has a claimed Qts of 0.26 and is on sale right now at Madisound for $129.

That's one sexy driver.

I've not tested this W18EX before. Looking at the TS and the FR plot, I don't know what to make of it. Maybe it's meant for horn loading.

The problem I find with low Qts (like 0.26) is the early bass roll-off. 75Hz for a 2-way is not my cup of tea. I prefer it to go down to 50Hz. It can be tuned lower in a BR if one doesn't mind compromising a bit of flatness.

On the flip side, drivers with Qts=0.26 exhibit excellent bass definition. Most of the time, to get it to sound right requires EQ in the bass.

The W18EX is compounded by a rising response, a slight peak at about 1kHz and lastly a severe cone breakup at 5kHz. To correct all the problems, the component cost for a passive crossover, Eq and others will likely cost more than the driver. That's something I want to avoid. I prefer to start off with a more friendly driver rather than fighting it along the way.

Using digital like miniDsp or EQ will defray the passive components cost. If that is the route you're on, you only have the drivers cost to content with.
 

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"would you prefer a high or low Qts for some other reason?"


I'll take a low Q in most occasions, assuming similar levels of complexity in the design and xover and no extreme output level requirements, assuming a similar cutoff frequency, because the low Q design will tend to have less phase shift near its cutoff and a little more extension. By using a lot of workarounds, I got a (15") bass driver with a Qts of 0.17 at 37 hz to work flat down to 50hz in a BR enclosure, with good extension down to about 32hz, to the extent it sounds closer to a closed box at low frequencies without a significant BR 'honk' while keeping about 100db/w/m sensitivity in 100 cu liters.
 
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You may want to check out the Dayton RS180s-8. This is the 7" shielded version. Great bass dynamics. Overall, a good performer and it's not too costly. Qts=0.38

I've been working with it for quite a while, in different incarnations. Latest is with a 1" horn compression driver.

Thanks Mike - yes, I like the RS series, I have the 8" version in a 3 way box, maybe the 7" version you point out would be better for a 2 way system than the 6" version I was thinking of. Cool horn driver :) I was actually thinking of pairing it with the Vifa XT25
 
I have a pair of the SF's on order, as for really cheap woofer, they are quite good. I have RS150's and if tamed, pretty good. A cost leader i it's class ( several steps above the SF) I really like the Seas reed paper woofers, but I keep thinking I want try the SB and Usher too.

Thank you for your comments. Was wondering what you meant by "tamed" when referring to the RS150? The cone breakup looks reasonably high for a driver of this size no? Is it the somewhat high Le or some other difficulty I can't see from the curves?
Thanks
 
Though I don't have the 6", I'm sure both the 6" and 7" will mate well with the XT25. The 7" will have more bass than the 6". If you're experiencing boomy bass in your room, I would go for a smaller woofer. It's also easier to get better vocals with a smaller woofer.

There are a lot of trade-offs in designing speakers. Knowing the environment/room and what you expect from your speakers will alleviate a lot of frustrations.
 
Thanks -
So what I net out from your info and Pete's is that I should stick with Qts around 0.38 give or take unless I really want to push for the better bass definition of a low Qts driver - but I will probably need equalization in that case and will also likely be giving up on f3. THANKS!

What I think Dickason is saying is that if you use a woofer with Qts > 0.4, then you can expect degraded transient/ frequency response, and the reverse. That is, Qts <0.4, then you can expect better performance. With vented systems, I don't think that it necessarily follows from what he said that transient/ frequency response improves as Qts is decreased. My guess would be that all of the alignments with Qts < 0.4 are about the same in regards to transient/ freq. response.

Regards,
Pete